JP2000503417A - Bidirectional retroreflective sheet - Google Patents

Abstract

(57) [Abstract] The zones of the cube corner element array are oriented in the direction of about 90 degrees so as to provide just two major planes exhibiting improved retroreflective performance for light incident on the sheet at large illumination angles. Disclosed are cube corner retroreflective sheet structures that are arranged alternately. According to one embodiment, the sheet includes a body layer having a modulus of less than 7 × 10 ⁸ Pascal and a cube corner element formed from a material having a modulus of greater than 16 × 10 ⁸ Pascal. . According to a second embodiment, the sheet is bonded to the major surface of the overlay film having two major surfaces and containing the first polymer material and the overlay film having the least amount of broken lands. A plurality of substantially independent cube corner elements.

Description

Description: FIELD OF THE INVENTION The present invention relates to retroreflective products. More particularly, the present invention relates to a cube corner retroreflective sheeting comprising alternating cube corner arrays of orientations such that the principal planes of illumination angles are substantially perpendicular to one another. BACKGROUND OF THE INVENTION Retroreflective sheets have the ability to return light incident on the major surface of the sheet to the original light source direction. This unique capability has led to the widespread use of retroreflective sheets in a wide variety of applications requiring enhanced attractiveness associated with markings for vehicle and human safety purposes. Typical examples where retroreflective sheets are used are to place these sheets on road signs, safety cones and barricades, especially in poor lighting conditions, for example when driving at night or when rough At the time of the weather, it is possible to increase the attractiveness. In such applications, the sheet can typically be adhered to a relatively flat, hard surface, thus making the sheet relatively inflexible. In addition, signage applications are characterized by a relatively predictable standardized display geometry. There are essentially two types of retroreflective sheets: beaded sheets and cube corner sheets. Beaded sheets utilize a number of independent glass or ceramic microspheres to retroreflect incident light. From an optical point of view, the bead-type sheet exhibits strong rotational symmetry characteristics and irradiation angle characteristics because the beads have symmetry. However, beaded sheets tend to exhibit relatively low brightness when compared to cube corner sheets. In addition, beaded sheets typically exhibit relatively good flexibility because the beads are independent of one another. Cube corner sheets typically utilize an array of interconnected rigid cube corner elements to retroreflect light incident on a major surface of the sheet. The underlying cube corner elements, which are now well known in the retroreflective art, take a generally tetrahedral structure with three substantially perpendicular sides, each of which has a single reference point. (Ie, a vertex) and at the base triangle opposite the vertex. The axis of symmetry (ie, the optical axis) of the cube corner element is the axis that extends through the cube apex and divides the interior space of the cube corner element into three. In a conventional cube corner element having an equilateral triangle base, the optical axis of the cube corner element is perpendicular to the plane containing the base triangle. In use, light incident on the bottom surface of the cube-corner element is reflected from each of the three side surfaces and returned to the light source again. Retroreflective sheets generally include a structured surface that includes at least one array of cube corner elements to enhance the visibility of the object. When compared to the beaded sheet, the cube corner sheet exhibits a relatively large luminance with respect to light incident at a relatively low irradiation angle (for example, light that is almost perpendicularly incident). However, cube corner retroreflective sheets also exhibit relatively poor illumination angle and rotational symmetry properties. Further, cube corner retroreflective sheets are typically harder than beaded sheets. This is because all cube corner elements are interconnected. The optical elements of the cube-corner retroreflective sheet can be designed to exhibit optimal performance in a particular direction. To make this possible, the cube corner elements of the retroreflective sheeting may be formed such that their optical axes are inclined with respect to an axis perpendicular to the bottom surface of the sheet. For example, U.S. Pat. No. 4,588,258 to Hoopman (the '258 patent) discloses a tilted inclined pair forming an opposed matching pair.
A retroreflective sheet using an optical element including a cube corner element is disclosed. The sheet disclosed in the '258 patent has improved at large illumination angles
Principal plane showing retroreflective performance (defined as the x-plane in the '258 patent)
And a dependent plane exhibiting improved retroreflective performance at large illumination angles ('258 patent).
Are defined as the y-plane). When used, in '258 patent
It is therefore recommended that the orientation of the manufactured sheet be set so that the principal plane (eg, x-plane) exhibiting improved retroreflective performance coincides with the estimated entrance plane. For this reason,
The sheet according to the '258 patent has one preferred orientation. In many applications where attractiveness is required, it is possible to take advantage of a retroreflective sheeting with two principal planes that exhibits improved retroreflective performance at relatively large illumination angles. For example, some applications for signs can take advantage of these advantages. This is because the second major plane, which exhibits improved retroreflective performance at large illumination angles, provides a second preferred direction for placing the sheet on the road sign. If a second preferred direction is provided, efficiency should be increased and waste generated in the labeling process should be reduced. A second application that can take advantage of a retroreflective sheeting with two principal planes that exhibits improved retroreflective performance at large illumination angles is in the field of markings that provide attractiveness to vehicles, especially in trucks. This is the field of marking that provides attractiveness. Many of the accidents caused by trucks are side impacts caused by poor lighting conditions. This is because an accident is inevitable because an approaching vehicle cannot detect a truck crossing the traveling direction early. Research has shown that the right number of side collisions can be significantly reduced if the truck is properly marked to provide eye-catching. For example, see Finster, Schmidt-Clausen, Optimum Identification of Trucks for Real Traffic Situations, Report on Research Project 1.9103 of the Federal Highways Agency, April, 1992. The United States has introduced rules on retroreflective eye-catching systems for commercial vehicles. Other countries are considering cooperation through UN / ECE to regulate the marking of entire long and heavy vehicle contours. Marking the entire contour of a commercial vehicle (eg, marking the entire perimeter of the side and / or rear of the vehicle) allows an observer to know the dimensions of the entire vehicle. However, in order to apply markings over the entire contour, the retroreflective sheeting is arranged both horizontally (e.g., along the bottom and / or top surface of the vehicle) and vertically (e.g., along the sides of the vehicle). There is a need to. It would be desirable to provide a single retroreflective sheeting that exhibits equally good performance in either direction so that it can be placed in either the vertical or horizontal direction. The optics of the sheet must provide strong retroreflective performance in two orthogonal planes. From a physical point of view, in applications that add attractiveness to the truck, seats may be placed on the sides of vehicles that may include wavy surfaces and / or protruding rivets, or that may be made from flexible tarpaulins. Need to glue. Thus, the sheet must be able to match a rough or flexible substrate surface. SUMMARY OF THE INVENTION Briefly stated, the present invention provides a retroreflective sheet designed to exhibit optimal retroreflective performance for large illumination angles in two orthogonal directions. A retroreflective sheeting in accordance with the principles of the present invention includes a bottom surface and a structured surface opposite the bottom surface. The structured surface defines a plurality of zones of the cube corner retroreflective element. Such zones include at least one first zone that includes an array of optically opposed cube corner elements, and a second zone that includes an array of optically opposed cube corner elements. The optical axes of the opposing cube corner elements of the first zone are tilted to define a first major plane exhibiting improved retroreflective performance at large illumination angles, and further, the opposing cubes of the second zone. The optic axis of the corner element is tilted to define a second major plane (but perpendicular to the first major plane) that exhibits improved retroreflective performance at large illumination angles. Advantageously, a retroreflective sheet made in accordance with the principles of the present invention, in either the first plane or the second plane, has substantially the same response to light incident on the sheet at various angles of illumination. It exhibits such retroreflective performance. In a preferred embodiment of the sheet according to the invention, the arrangement of the cube corner elements of the first zone is such that the first major plane exhibiting improved retroreflective performance is substantially perpendicular to the edge of the sheet. And the array of cube corner elements in the second zone is oriented such that the second major plane exhibiting improved retroreflective performance is substantially parallel to the same edge of the sheet. Have been. Even more preferably, the retroreflective sheeting of the present invention has a plurality of alternating zones of cube corner element arrays, of which approximately half of the zones exhibit improved retroreflective performance. The major planes are oriented perpendicular to the longitudinal edges of the sheet and the remaining zones exhibit improved retroreflective performance with their major planes parallel to the longitudinal edges of the sheet. It is aimed at becoming. The retroreflective sheeting according to this embodiment is very well applicable when used in any of two orthogonal directions. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing a structured surface of one embodiment of a retroreflective sheeting in accordance with the principles of the present invention. FIG. 2 is an isoluminance curve diagram showing the retroreflective performance of a sample of a retroreflective sheet manufactured according to the prior art. FIG. 3 is an isoluminance curve diagram showing the retroreflective performance of a sample of the retroreflective sheet manufactured according to the present invention. FIG. 4 is a cross-sectional view of one embodiment of a retroreflective sheeting in accordance with the principles of the present invention. FIG. 5 is a cross-sectional view of a second embodiment of a retroreflective sheeting according to the principles of the present invention. These figures (but not FIGS. 2 and 3) are idealized and are not drawn to scale, and are merely for illustration and are not limiting. It is not something to be done. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS In describing preferred embodiments of the present invention, certain terms are used to provide a clear description. However, it is to be understood that the invention is not limited to the terms selected in this way, and that the terms selected in this way include all technical terms having similar meanings. According to the present invention, there is provided a cube corner retroreflective sheeting 10 exhibiting improved retroreflective performance for large illumination angles in just two principal planes. Further, the sheet exhibits substantially similar retroreflective performance at various illumination angles in either of the two major planes. Thus, in use, rather than tilting in a single preferred direction, as is common in many retroreflective sheets, it may be tilted in any of the two preferred directions. To make such an optical element, the structured surface of the sheet includes at least two zones of an array of cube corner elements. Each zone includes an array of optically opposed cube corner retroreflective elements, the optic axes of which are tilted to define a major plane that exhibits improved retroreflective performance at large illumination angles. ing. The optical axis of the cube corner retroreflective element of the first zone is tilted in a first plane, and the optical axis of the cube corner element of the second zone is tilted in a second plane. By arranging the array on the sheet such that the first plane is perpendicular to the second plane, two principal planes exhibiting improved retroreflective performance can be set. FIG. 1 shows an enlarged view of a portion of the structured surface of a retroreflective sheeting in accordance with the principles of the present invention. Referring to FIG. 1, the structured surface includes a plurality of alternating zones having an array of cube corner elements 12. As shown, the cube corner elements 12 are arranged in an array on one side of the sheet as optically opposed alignment pairs. Each cube corner element 12 takes the form of a three-sided prism having three exposed planes 22. The dihedral angle formed by the cube corner element plane 22 is typically the same for each cube corner element in the array, and is approximately 90 °. However, as is well known, this angle can be slightly offset from 90 °. See, for example, U.S. Patent No. 4,775,219 to Appledorn et al. In addition, although U.S. Pat.No. 4,588,258, which is incorporated herein by reference, discloses a preferred cube corner geometry, there is no substantial change in cube corner geometry. If the retroreflective profiles are considered to be substantially the same, they are considered to be within the scope of the present invention. Single principal plane showing improved retroreflective performance at large illumination angles by tilting opposing cube corner elements at an angle relative to the axis perpendicular to the reference plane of the sheet, and improved at large illumination angles And a single dependent plane exhibiting the determined retroreflective performance. In the structural surface of the sheet 10, a plurality of zones in a cube-corner array arranged at about 90 degrees alternately appear. Thus, sheet 10 is characterized by a first zone 6 containing an array of cube corner elements arranged in a first orientation on the sheet and a cube corner element arranged in a second orientation on the sheet. A first principal plane comprising a second zone 8 and exhibiting improved retroreflection performance at large illumination angles; and exhibiting improved retroreflection performance at large illumination angles, perpendicular to the first principal plane. And a second principal plane. In the embodiment shown in FIG. 1, the first zone 6 extends substantially parallel to the longitudinal edge of the sheet 10. The first zone 6 includes an array of cube corner elements 12 formed by three intersecting sets, including two dependent groove sets 26,28 and one main groove set 30. Each cube corner element 12 in the array is formed with its optical axis inclined in a plane perpendicular to the main groove 30. Thus, the cube corner arrangement in the first zone 6 presents an improved principal plane of retroreflective performance extending perpendicular to the main groove 30 and perpendicular to the longitudinal edge of the sheet 10. In the disclosed embodiment, each cube corner element is tilted at an angle of about 8.15 degrees with respect to an axis perpendicular to the bottom surface of the cube corner element, defining an included angle of the bottom triangle of 55.5, 55.5, and 69 degrees. . Further, the height of the cube corner elements is about 88.9 microns. The second zone 8 extends substantially parallel to the first zone 6 along the longitudinal direction of the sheet and has cube corner elements 12 that are substantially equivalent to the arrangement arranged in the first zone 6. Where the array in the second zone is oriented at 90 degrees to the array in the first zone 6. Generally, the advantages of the present invention are obtained by tilting opposing cube corner elements at an angle of about 7 degrees to about 15 degrees. See U.S. Patent No. 4,588,288. It will be appreciated that the specific geometries described in this paragraph relate to preferred embodiments of the present invention. It will be appreciated by those skilled in the optical arts that changes in the angle of tilt and changes in cube size may be made in accordance with the invention. If there is no substantial change in the cube geometry and the optical results are considered to be substantially the same, they should be considered within the scope of the present invention. FIG. 2 shows the retroreflection characteristics of a retroreflective sheet using an optical element according to the invention disclosed in U.S. Pat. No. 4,588,258 (the '258 patent). The optical element disclosed in the '258 patent has a single principal plane (represented by a plane extending in the direction of the two largest lobes of the isoluminance curve) exhibiting improved retroreflective performance at large illumination angles ) And a dependent plane (represented by a plane extending in the direction of the two shorter lobes of the isoluminance curve) exhibiting improved retroreflective performance at large illumination angles. Thus, in use, sheet products according to the optical elements of the '258 patent have a single preferred orientation. The present invention eliminates these limitations by providing two planes that exhibit improved retroreflective performance at large illumination angles. FIG. 3 is an isoluminance curve graph showing the retroreflective performance of the bidirectional sheet according to the embodiment disclosed in FIG. The measurement of the retroreflective brightness was obtained from a sample of the sheet according to FIG. A detailed description of the retroreflection test geometry and measurement angles can be found in ASTM E-808-93b, Standard Practice for Describbng Retroreflection. By reference, the contents are incorporated herein. As the measured values, values at an observation angle fixed at 0.33 degrees and a display angle (presentaion angle) fixed at 90 degrees were adopted. The irradiation angle was varied between 0 and 80 degrees, and the sheet was rotated so that the azimuth angle was in the range of 360 degrees. On the graph of FIG. 3, the illumination angles are represented by concentric circles, while the azimuths are represented by numerical values extending radially around the graph. The concentric isoluminance curve represents the relative amount of retroreflection of retroreflected light. The maximum amount of retroreflection is represented by the middle point of the graph, and the concentric isoluminance curve indicates that the amount of retroreflection decreases by 5% with respect to this maximum value. However, the unit of measurement is candela / lux / meter ^Two It is. Referring to FIG. 3, the retroreflective sheeting according to the present invention exhibits just four extended lobes exhibiting improved retroreflective performance at large illumination angles. These four lobes appear at 90 degree intervals starting at 0 degree azimuth (eg, 0 degrees, 90 degrees, 180 degrees, and 270 degrees). These four lobes define two major planes that exhibit improved retroreflective performance at large illumination angles. That is, the first plane extends through the plane of the sheet in the direction of 0-180 degrees, and the second plane extends through the sheet in the direction of 90-270 degrees. In addition, the sheet exhibits substantially similar retroreflective performance at different illumination angles in these two planes. For example, the retroreflection amount of the retroreflection light is about 5% of the maximum retroreflection amount at any of the azimuth angles of 0 degree, 90 degrees, 180 degrees, and 270 degrees at the irradiation angle of 60 degrees. Similarly, the amount of retroreflection of retroreflected light is approximately 30 percent of the maximum retroreflection at any azimuth angle of 0, 90, 180, or 270 degrees at an illumination angle of 40 degrees. The maximum retroreflected value of the retroreflected light of the test sample is 891.47 candela / lux / m ^Two Met. Therefore, the amount of retroreflection of the retroreflected light is approximately 267 candela / lux / m at an illumination angle of 40 degrees in any of these four planes. ^Two And about 45 candela / lux / m at an illumination angle of 60 degrees in any of these four planes. ^Two Met. The retroreflective performance of the sheet according to the present invention is considered to be substantially superior to the conventional retroreflective sheet at these four azimuthal angles at large illumination angles. Therefore, in use, the sheet can exhibit optimum retroreflective performance regardless of which of two different directions the sheet is oriented. Referring to FIG. 1, in a preferred embodiment of the sheet according to the invention, the zones of the cube-corner element are arranged alternately. Generally, an observer at a distance greater than about 100 meters from the sheet produces substantially uniformly shining light retroreflected from the sheet in response to light incident on the sheet at a relatively large angle of illumination. It is desirable to sense. Tests have shown that a zone approximately 3 mm to 25 mm wide meets this requirement. In a preferred embodiment, the zones are about 8 millimeters wide and extend along the length of the sheet. However, those skilled in the art will recognize that the zones may be shaped other than the longitudinally extending zones disclosed in FIG. Sheets according to the present invention can be manufactured using conventional methods well known in the art of cube corner retroreflective sheets. Briefly, according to one method, a structured surface mold is made using a precision machine tool, such as a diamond cutting tool. First, a master mold having a positive image of the structured surface is manufactured. First, a machinable support (typically aluminum or copper) is cut using a tool having an included angle of about 86.8 degrees to form a first set of grooves. Next, the second groove set is formed by rotating the support at about 55.5 degrees and using a tool having an included angle of about 61.8 degrees. Finally, the third groove set is formed by rotating the support about 124.5 degrees and cutting with a tool having an included angle of about 61.8 degrees. This method produces a master mold having a positive image of the cube corner surface with the interior angles of the triangles at the base of the cube corner element being about 55.5, 55.5, and 69 degrees. Next, a master-type replica is manufactured using a conventional replica method such as electroforming. Subsequently, the master-type replica is sliced using a precision cutting tool to produce a thin strip. Thereafter, the strips are rearranged to create a mold having a negative image corresponding to the structured surface shown in FIG. Next, a retroreflective sheet may be manufactured using this mold, or another mold may be manufactured through a replica manufacturing process. FIG. 4 is a cross-sectional view of one embodiment of a retroreflective sheeting in accordance with the principles of the present invention. The embodiment shown in FIG. 4 is specifically designed to provide the flexible retroreflective sheeting disclosed in US Pat. No. 5,450,235. The contents of this patent are incorporated herein by reference. The practice of the present invention provides a cube corner retroreflective sheet that retains good dimensional stability and a large retroreflective coefficient under conditions of large curvature. FIG. 4 shows an example of a cube corner retroreflective sheeting according to the present invention that includes a number of cube corner elements 12 and a support or body portion 14. The body portion 14 may include a land layer 16 and a body layer 18. The body layer typically serves to protect the sheet from the elements and / or impart mechanical integrity to the sheet. In a preferred embodiment, body layer 18 is the outermost layer on the front side of sheet 10. The land layer 16 is distinguished from the body layer 18 by being a layer disposed immediately adjacent to the bottom surface of the cube corner element, but in this specification, the term “land layer” refers to such a layer. Shall mean. The cube corner element 12 protrudes from a first or back surface 20 of the body portion 14. 16 × 10 for cube corner element 12 ⁸ It contains a light transmissive polymer material with a modulus greater than Pascal, and the body layer 18 contains 7 × 10 ⁸ Light transmissive polymer materials having a modulus of elasticity less than Pascal are included. Light enters the cube corner sheet 10 via the reference plane 21. Next, as indicated by arrow 23, the light passes through body portion 14, strikes plane 22 of cube corner element 12, and returns in the direction of incidence. In a preferred configuration, cube corner elements 12 and land layer 16 are made from similar or the same type of polymer to minimize the thickness of land layer 16. The thickness of the land layer 16 is typically between about 0 and 150 micrometers, preferably between about 1 and 100 micrometers. The thickness of the body layer 18 is typically between about 20 micrometers and 1,000 micrometers, preferably between about 50 micrometers and 250 micrometers. It is preferable to minimize the thickness of the land layer, but it is preferable that the sheet 10 have some land layer 16 to provide a flat interface between the run underlayer 16 and the body layer 18 . The height of the cube corner elements 12 is typically between about 20 micrometers and 500 micrometers, more typically between about 60 micrometers and 180 micrometers. Although the embodiment of the invention shown in FIG. 1 has a single body layer 18, it is within the scope of the invention to provide more than one body layer 18 in the body portion 14. By arranging a regular reflection coating layer (not shown) such as a metal coating layer on the back surface of the cube corner element 12, retroreflection by regular reflection can be promoted. The metal coating layer can be provided by well-known techniques such as vapor deposition or chemical deposition of a metal (eg, aluminum, silver, or nickel). Providing a primer layer on the back of the cube corner element may promote adhesion of the metal coating layer. In addition to or instead of the metal coating layer, a sealing film may be bonded to the back surface of the cube corner element. See, for example, U.S. Patent Nos. 4,025,159 and 5,117,304. The sealing film provides retroreflectivity according to the principle of total internal reflection by retaining the air interface on the back of the cube corner element. Also, a backing layer and / or an adhesive layer can be disposed on the backside of the cube corner element to enable the cube corner retroreflective sheet 10 to be secured to the support. The polymer material contained in the cube corner elements and body portion of the retroreflective sheeting of the present invention is light transmissive. This means that at a given wavelength, the polymer can transmit at least 70 percent of the intensity of the incident light. More preferably, the polymers used in the retroreflective sheeting of the present invention have a light transmission of greater than 80 percent, more preferably greater than 90 percent. The polymer material utilized for the cube corner elements preferably has hardness and stiffness. The polymer material may be a thermoplastic or a crosslinkable resin. The elastic modulus of these polymers is 18 × 10 ⁸ Larger than Pascal, more preferably 20 × 10 ⁸ Greater than Pascal. When a thermoplastic polymer is used in the cube corner element, the glass transition temperature is typically greater than 80 ° C and the softening temperature is typically greater than 150 ° C. Generally, the thermoplastic polymer used in the cube-corner layer is amorphous or semi-crystalline, and the linear shrinkage of the polymer is preferably less than 1 percent. Specific examples of thermoplastic polymers that can be used in the cube corner element include acrylic polymers such as poly (methyl methacrylate); polycarbonates; cellulose compounds such as cellulose acetate, cellulose (acetate / co-butyrate), and cellulose nitrate. Epoxy compounds; polyesters such as poly (butylene terephthalate) and poly (ethylene terephthalate); fluoropolymers such as poly (chlorofluoroethylene) and poly (vinylidene fluorolide); poly (caprolactam), poly (aminocaproic acid), poly (aminocaproic acid) Polyamides such as hexamethylenediamine-co-adipic acid), poly (amide-co-imide) and poly (ester-co-imide); polyolefins such as poly (ether imide); poly (methylpentene): poly (phenylene ether) ); Poly (phenylenesul) ); Poly (styrene), and poly (styrene) copolymers such as poly (styrene-co-acrylonitrile) and poly (styrene-co-acrylonitrile-co-butadiene); polysulfone; Polymers (ie, polymers containing small amounts (less than 10 weight percent) of silicone); fluorine-modified polymers such as perfluoropoly (ethylene terephthalate); and blends of poly (ester) and poly (carbonate), fluoropolymer and acrylic Mixtures of the above polymers, such as blends of system-based polymers. Other suitable materials for making cube corner elements are reactive resin systems that can be cross-linked via a free radical polymerization mechanism upon exposure to actinic radiation (e.g., electron beam, ultraviolet light, or visible light). . In addition, these materials may be polymerized by a thermal means by adding a thermal initiator such as benzoyl peroxide. Further, a resin that can be cationically polymerized by radiation may be used. Suitable reactive resins for forming cube corner elements may be a blend of a photoinitiator and at least one compound having an acrylate group. Preferably, the resin blend contains a bifunctional or polyfunctional compound that when irradiated ensures the formation of a crosslinked polymer network. Specific examples of resins polymerizable by a free radical mechanism include resins based on acrylic compounds derived from epoxy compounds, polyesters, polyethers, and urethanes; ethylenically unsaturated compounds; at least one acrylate side group Aminoplast derivatives having at least one acrylate side group; epoxy resins other than acrylated epoxy compounds; and mixtures and combinations thereof. As used herein, the term acrylate includes both acrylates and methacrylates. U.S. Pat.No. 4,576,850 to Martens, the entire disclosure of which is incorporated herein by reference, provides examples of cross-linkable resins that can be used in the cube corner elements of the present invention. It has been disclosed. Ethylenically unsaturated resins include both monomeric and polymeric compounds containing atoms of carbon, hydrogen, and oxygen, and, optionally, nitrogen, sulfur, and halogen. Oxygen or nitrogen atoms or both atoms are generally included in the ether, ester, urethane, amide, and urea groups. The ethylenically unsaturated compound preferably has a molecular weight of less than about 4,000, and preferably contains a compound containing aliphatic monohydroxy or aliphatic polyhydroxy groups and acrylic acid, methacrylic acid, itaconic acid, crotonic acid, Esters obtained by reaction with unsaturated carboxylic acids such as isocrotonic acid and maleic acid. Some examples of the compound having an acryl group or a methacryl group are listed below. The compounds listed are by way of illustration and not limitation. (1) Monofunctional compound: ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-hexyl acrylate, n-octyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, N, N-dimethylacrylamide; (2) bifunctional compound: 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentane glycol diacrylate, ethylene glycol diacrylate, triethylene glycol diacrylate, And tetraethylene glycol diacrylate; (3) polyfunctional compounds: trimethylolpropane triacrylate, glycerol triacrylate, pentaerythritol triacrylate, pentaerythrate Litol tetraacrylate, and tris (2-acryloyloxyethyl) isocyanurate. Some representative examples of other ethylenically unsaturated compounds and resins include: styrene; divinylbenzene; vinyltoluene; N-vinylpyrrolidone; N-vinylcaprolactam; Esters such as diallyl phthalate and diallyl adipate; and amides of carboxylic acids such as N, N-diallyl adipamide. Specific examples of photopolymerization initiators that can be blended with acrylic compounds include the following compounds: benzyl, methyl o-benzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and other benzophenone / tertiary amines , Acetophenone (e.g., 2,2-diethoxyacetophenone), benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, (1- (4-isopropylphenyl ) -2-Hydroxy-2-methylpropan-1-one, 2-benzyl-2-N, N-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 2,4,6-trimethylbenzoyldiphenyl Examples include phosphine oxide and 2-methyl-1-4- (methylthio) phenyl-2-morpholino-1-propanone. These compounds may be used alone or in combination.Cationically polymerizable materials include, but are not limited to, materials containing an epoxy functional group and a vinyl ether functional group. These systems are photoinitiated by onium salt initiators such as triarylsulfonium and diaryliodonium salts. Preferred polymers for cube corner elements include poly (carbonate), poly (carbonate) Methyl methacrylate), poly (ethylene terephthalate), and cross-linked acrylates (eg, polyfunctional acrylate or epoxy compounds, and acrylated urethanes blended with mono- and polyfunctional monomers). These polymers are preferred for the following reasons: One or more of thermal stability, environmental stability, transparency, excellent release from a tool or mold, and acceptability for a reflective coating layer. The polymer material used may be the same as the polymer utilized in the cube corner element, except that the thickness of the land layer must be minimized. Flattening results in a better interface between the cube corner element and the body layer, and cavities and / or interface roughness between the cube corner element and the land layer are eliminated. As a result, when light is retroreflected, the retroreflective sheet can exhibit optimal brightness. By providing a good interface, the spread of light due to refraction is prevented. In most cases, the land layers are integrated with the cube corner elements. "Integral" means that the land layers and cube corner elements are formed from a single polymer material, and does not mean that two different polymer layers are substantially combined into one. Absent. The polymer utilized in the cube corner elements and land layers may have a different refractive index than the body layer. While the land layer is desirably made from a polymer similar to the polymer of the cube corner elements, the land layer may also be made from a softer polymer such as that used in the body layer. The body layer includes a low modulus polymer to facilitate folding, curling, bending, or alignment. The elastic modulus is preferably 5 × 10 ⁸ Less than Pascal, more preferably 3 × 10 ⁸ Less than Pascal. Generally, the body layer polymer has a glass transition temperature of less than 50 ° C. With this polymer, the polymer material preferably maintains physical integrity at the temperatures applied to the cube corner elements. The polymer desirably has a Vicat softening temperature above 50 ° C. The linear shrinkage of the polymer is desirably less than 1 percent. Preferred polymer materials used in the body layer are resistant to degradation by UV light. As a result, the retroreflective sheet can be used for a long time in outdoor use. Specific examples of polymers that can be used in the body layer include the following polymers: Fluorinated polymers: poly (chlorotrifluoroethylene) [eg, St. Minnesota. Kel-F800 available from Paul's 3M ^TM Poly (tetrafluoroethylene-co-hexafluoropropylene) [eg Exac FEP available from Norton on Performance, Brampton, Mass.] ^TM Poly (tetrafluoroethylene-co-perfluoro (alkyl) vinyl ether) [for example, Exac PEA, also available from Norton Performance; ^TM Poly (vinylidene fluoride-co-hexafluoropropylene) [eg Kynar Flex-2800 available from Pennwalt Corporation of Philadelphia, PA] ^TM Ethylene copolymers of ionomers: poly (ethylene-co-methacrylic acid) containing sodium or zinc ions [see, for example, E.I. of Wilmington, Del.] Surlyn-8920 available from duPont Nemours ^TM And Surlyn-9910 ^TM Low-density polyethylenes: low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, etc .; plasticized vinyl halide polymers: plasticized poly (vinyl chloride), etc .; polyethylene copolymers: acid-functional polymers [for example, poly (Ethylene-co-acrylic acid), poly (ethylene-co-methacrylic acid), poly (ethylene-co-maleic acid), and poly (ethylene-co-fumaric acid)), acrylic-functional polymers (e.g., poly ( Ethylene-co-alkyl acrylate) wherein the alkyl group is a methyl group, an ethyl group, a propyl group, a butyl group, etc. _Three (CH _Two ) _n -Groups where n is 0-12], poly (ethylene-co-vinyl acetate) and the like; aliphatic and aromatic polyurethanes derived from the following monomers (1) to (3): (1) diisocyanate (e.g., dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexyl diisocyanate, diphenylmethane diisocyanate, and a combination of these diisocyanates), (2) polyol (e.g., poly Pentylene adipate glycol, polytetramethylene ether glycol, polyethylene glycol, polycaprolactone diol, poly-1,2-butylene oxide glycol, and combinations of these diols), and (3) a chain transfer agent (e.g., butanediol or hexane) Geo . Commercially available urethane polymers include PN-03 or 3429 from Morton International, Inc. of Seabrook, NH. Also, combinations of the above polymers may be utilized in the body layer of the body portion. Preferred polymers for the body layer include ethylene copolymers comprising units containing esters of carboxyl groups or carboxylic acids (e.g., poly (ethylene-co-acrylic acid), poly (ethylene-co-methacrylic acid), Poly (ethylene-co-vinyl acetate)]; ethylene copolymers of ionomers; plasticized poly (vinyl chloride); and aliphatic urethanes. These polymers are preferred for one or more of the following reasons: good mechanical properties, good adhesion to the land layer, transparency, and environmental stability. Polycarbonate cube corner elements and / or polycarbonate land layers and polyethylene copolymers (eg, poly (ethylene-co- (meth-2) acrylic acid), poly (ethylene-co-vinyl acetate), or poly (ethylene-co-acrylate)) In embodiments that include a body layer containing, the interfacial adhesion between the body layer and the land layer or cube corner element can be improved by placing a thin tie layer (not shown) between them. it can. After bonding the tie layer to the body layer, the body layer can be laminated to the land layer or cube corner element. The tie layer can be joined as a thin coating layer. For example, an organic solvent solution of an aliphatic polyurethane [e.g., Permutane, available from Permuthane Company of Peabody, Mass.] ^TM U26-248 and KJ. Seabrook, NH. Q-thane available from Quinn and Co., Inc. ^TM QC-4820]; aqueous dispersions of aliphatic polyurethanes [for example, NeoRez available from ICI Resins US of Wilmington, Mass.] ^TM R-940, R-9409, R-960, R-962, R-967, and R-972]; aqueous dispersions of acrylic polymers [for example, NeoCryl available from ICI Resins US, Wilmington, Mass.] ^TM A-601, A-612, A-614, A-621, and A-6092]; or an aqueous dispersion of an aliphatic urethane copolymer [e.g., Neo Pac available from ICI Resins US of Wilmington, Mass.] ^TM R-9000]. Alternatively, the adhesion of the tie layer to the body layer can be further improved using an electrical discharge method such as corona treatment or plasma treatment. Add colorants, UV absorbers, light stabilizers, radical scavengers or antioxidants, processing aids (eg, antiblocking agents, release agents, lubricants, etc.), and other additives to the body part or cube corner element It may be added. The particular colorant selected will of course depend on the desired color of the sheet. The colorant is typically added in an amount from about 0.01 weight percent to 0.5 weight percent. The UV absorber is added in an amount from about 0.5 weight percent to 2.0 weight percent. UV absorbers include, for example, derivatives of benzotriazole [eg Tinuvin available from Ciba-Geigy Corporation of Ardsley, NY] ^TM 327, 328, 900, 1130, Tin uvin-P ^TM Chemical derivatives of benzophenone [for example, Uvinul available from BASF Corporation of Clifton, NJ ^TM -M40, 480, D-50; Syntase available from Neville-Synthese Organics, Inc., Pittsburgh, PA. ^TM 230, 800, 1200], or a chemical derivative of diphenyl acrylate [eg Uvinul, also available from BASF Corporation of Clifton, NJ ^TM -N35, 539]. Light stabilizers that can be used include hindered amines, and are typically used in an amount of about 0.5 weight percent to 2.0 weight percent. Hindered amine light stabilizers include, for example, Tinuvin available from Ciba-Geigy Corp., Ardsley, NY. ^TM -14 4,292,622,770, and Chimassorb ^TM -944. Radical scavengers or antioxidants are typically used in amounts of about 0.01 to 0.5 weight percent. Suitable antioxidants include Irganox available from Ciba-Geigy Corp., Ardsley, NY. ^TM -1010, 1076, 1035, or MD-1024, or Irgafos ^TM Hindered phenolic resins such as -168. It is also possible to improve the processability of the resin by adding small amounts of other processing aids, typically 1% by weight or less of the polymer resin. Useful processing aids include fatty acid esters or amides available from Glyco Inc., Norwalk, Conn .; metal stearates available from Henkel Corp., Hoboken, NJ; or Hoechst Celanese Corporation, Somervil le, NJ Wax E available from ^TM Is mentioned. The cube corner retroreflective sheeting according to the embodiment shown in FIG. ⁸ Forming a structured surface comprising a plurality of zones of an array of cube corner elements according to FIG. 1 from a light transmissive material having an elastic modulus greater than Pascal; ⁸ Attaching a body layer comprising a light transmissive material having a modulus of elasticity less than Pascal to the plurality of cube corner element arrays. Steps (a) and (b) can be performed according to various known (or later devised) methods for making cube corner sheets. See, for example, U.S. Patent Nos. 3,689,346, 3,811,983, 4,332,847, and 4,601,861. However, it is assumed that the cube corner element is formed using a polymer having a high elastic modulus, and the body layer is formed using a polymer having a low elastic modulus. The body layer may be attached directly to the bottom of the cube corner element or may be attached to the cube corner element by a land layer. As described above, the land layer is preferably made of a material having a minimal thickness and preferably a high modulus. FIG. 5 is a schematic cross-sectional view of an embodiment of the present invention made in accordance with the principles of the invention disclosed in [US patent application Ser. No. 08 / 472,444]. The disclosure of that patent application is incorporated herein by reference. Also, the embodiment shown in FIG. 5 is designed to be a highly flexible retroreflective sheeting suitable for matching a wavy surface and / or a flexible surface. Briefly summarized, a microstructured composite sheet (eg, a retroreflective composite cube corner sheet) according to the embodiment disclosed in FIG. 5 includes (a) a plurality of substantially independent microstructure elements 98; A two-dimensional array (eg, an array of cube corner elements), and (b) an overlay film 99 having two major faces. However, this arrangement is bonded to the first major surface of the overlay film and has zero to a minimum amount of land layer, as shown below. The embodiment shown in FIG. 5 also shows the sealing film 97 fused with a portion of the base layer 99. As shown below, the cube corner element array includes a relatively rigid first polymer material, and the overlay film includes a relatively flexible polymer material. The microstructured elements are preferably cured in situ on the overlay film, and the material of the cube corner elements and the material of the overlay film preferably form an interpenetrating network. Briefly summarized, the retroreflective sheeting according to the embodiment shown in FIG. 5 is manufactured by a method including the following steps. (a) providing a tool comprising a molding surface having a plurality of suitable cavity openings for forming a desired microstructural element (eg, a cube corner element of a retroreflective article); A predetermined amount of a suitable flowable and curable resin composition for forming a microstructure element (e.g., a retroreflective cube corner element) on a molding surface (however, the resin preferably shrinks upon curing). Contacting the resin composition with a first major surface of an overlay film having first and second major surfaces; and (d) extending over the cavity and the tool. Minimizing the excess resin composition, preferably uniformly; subsequently, (e) curing the resin composition to form microstructure elements (e.g., cube corners) bonded to the overlay film. (F) removing the sheet from the tool; (g) applying mechanical stress to the sheet to separate substantially independent microstructural elements from surrounding microstructures. The step of breaking apart from the structural elements (provided that these elements are connected by lands). The resin composition and the overlay film are preferably in the following state. That is, when the resin composition contacts the overlay film, the resin composition penetrates the overlay film, and consequently, after the primary curing treatment, interpenetration between the material of the microstructured element and the material of the overlay film. A network structure is formed. The resin composition and the overlay film are preferably in the following state. That is, when the resin composition contacts the overlay film, the resin composition penetrates the overlay film and consequently, after the primary curing treatment, interpenetration between the cube corner element material and the overlay film material. A network structure is formed. Various techniques and methods have been developed for manufacturing cube corner retroreflective products. Any suitable technique for forming the desired arrangement of cube corner elements, for example, pin tying techniques, direct machining techniques, replica techniques, etc. , A tool having a molding surface having a plurality of cavities. Requirements for tools include that the cavities do not undesirably deform during manufacture of the composite product and that the array of cube corner elements can be separated from the tool after curing. Specific examples of known supports useful in forming tools for making replicas of cube corner elements include materials that can be directly machined. Such materials are preferably machined clean without forming burrs, exhibit low ductility and low graininess, and retain the correct dimensions after forming the grooves. Various machinable plastics (including both thermoset and thermoplastic materials) are known, such as acrylic compounds, and machinable metals such as aluminum, brass, copper, and nickel. ing. It is often desirable to use an initially generated replica or a subsequently generated replica of a machined or shaped surface (ie, a member on which the cube corner sheet of the present invention is formed) as a tool. Depending on the nature of the tool and resin composition used, the cured arrangement may be easily peelable from the tool, but may require a release layer to achieve the desired peeling properties. In some cases. Specific examples of release layer materials include induced surface oxide layers, intermediate thin metal coating layers, chemical silver plating layers, and combinations of various materials or coating layers. If desired, suitable agents can be added to the resin composition to obtain the desired peeling properties. As mentioned above, the tool can be made from a polymer, metal, composite, or ceramic material. In some embodiments, curing of the resin will be performed by irradiating through a tool. In such a case, the tool must have sufficient transparency so that the radiation can be irradiated through the resin. Specific examples of materials for making the tools utilized in such embodiments include polyolefins and polycarbonates. However, metal tools are typically preferred. This is because metal tools can have the desired shape, yet provide excellent optical surfaces and maximize the retroreflective performance of a given cube corner element configuration. Fluid resin is supplied to the molding surface of the tool. The requirements that the resin should have include, as the case may be, the resin flowing into the cavity of the molding surface by reduced pressure, pressure, or mechanical means. It is preferred to supply the resin in an amount sufficient to at least substantially fill the cavity. A critical factor in practicing the present invention is the selection of an appropriate polymer material for the cube corner element array and the overlay film. Typically, the array of cube corner elements preferably includes a thermosetting or strongly crosslinkable material, and the overlay film preferably includes a thermoplastic material. The excellent chemical and mechanical properties of thermoset materials result in cube corner elements that are optimized to maintain the desired retroreflectivity. In selecting the polymer component of the composite retroreflective material of the present invention, it is essential to select a polymer material that is compatible with the cube corner elements and the overlay film. In a preferred embodiment of compatibility, the material of the resin composition is capable of penetrating the overlay film, and then, when cured in situ, after curing, the material of the cube corner element and the material of the overlay film. Forming an interpenetrating network between them. A surprising aspect of the present invention is that the formation of an interpenetrating network between the cube-corner element and the overlay film in this way results in effective optical performance. By adhering a predetermined amount of the resin composition to the surface of the overlay film, screening of the specific resin composition and the overlay film can be easily performed. Priola, A., Gozzelino, G., and Ferrero, F., Proceedings of the XIII International Conference in Organic Coatings Science and Technology, Athens, Greece, July 7-11, 1987, pp. 308-18 discloses a test of a watch glass suitable for this purpose. A decisive criterion in selecting these components is the relative modulus for each component. As used herein, the term "modulus" refers to the initial grip separation distance of 12.5 centimeters, sample width of 2.5 centimeters, and grip separation speed of 2.5 centimeters per ASTM 882.75b, according to static load method A. Mean modulus of elasticity measured in minutes (1 inch / minute). As described above in connection with the basic principles that govern the optical properties of cube corner elements, even a small distortion in the geometry of the cube corner elements substantially degrades the optical properties of the cube corner elements. there's a possibility that. Therefore, a material having a high elastic modulus is preferable as a material used for the cube corner element. In this way, resistance to distortion is enhanced. The overlay film of the composite retroreflective material of the present invention is preferably a slightly lower modulus polymer material. During manufacture of the overlay film / cube corner array composite, each cube corner element is bonded to the overlay film. During curing of the cube corner element components, each cube corner element may undergo some shrinkage, depending on the composition of the cube corner element material. If the modulus of the overlay film is too high, the cube corner element may be subjected to torsional stress if the cube corner element shrinks during curing. If this stress is large enough, the cube corner elements may be distorted and optical performance may be degraded. If the modulus of the overlay film is sufficiently lower than the modulus of the cube corner element material, such deformation stresses can cause unwanted degradation of optical properties, even if the overlay film deforms with the shrinkage of the cube corner elements. Does not participate in the cube corner element. Also, the difference between the modulus of elasticity of the cube corner element and the overlay film depends on the dimensions of the cube corner element, but need not be so large. When the height of the cube corner element is low, the difference in modulus between the cube corner element and the overlay film need not be so large. Because when the cube corner elements become smaller, the shrinkage during curing does not increase so much when measured in absolute dimensional units, and the overlay film interacts with the cube corner elements, causing them to grow as large as the larger cube corner elements. This is because torsional stress and deformation stress do not occur. Generally, the difference in elastic modulus between the overlay film and the cube corner element is 1.0-1.5 × 10 ⁷ It can be said that it needs to be about Pascal or more. As the height of the cube corner elements decreases, it is possible to make this difference in elastic modulus closer to the lower limit of the range just described. However, it should be noted that there is a practical lower limit on the modulus of the cube corner element material. A predetermined level (typically about 2.0 to 2.5 x 10 for cube corner elements having a height of about 175 microns (7 mils). ⁸ Below the Pascal level, or less for smaller cube corner elements), the cube corner elements become too soft and do not exhibit sufficient mechanical stiffness to provide adequate fracture when stressed. Will not wake up. Cube corner elements are preferably about 25 x 10 ⁸ It has an elastic modulus higher than Pascal. If such breakage does not occur, decoupling of each cube corner element, which is essential for imparting the sheet's flexibility under stress and excellent optical properties, cannot be performed reliably. In addition to considering the relative modulus of the cube corner elements and the overlay film, there is a requirement that the modulus of the overlay film be relatively small. This requirement is indispensable for imparting a desired size of super-flexibility to the obtained composite retroreflective sheet. As described above, an array of cube corner elements is formed using a minimal amount of lands. If the amount of lands can be minimized, rupture of the lands will occur due to stretching of the overlay film or other suitable elastic deformation. This rupture can be caused by applying an elastic stress to the composite after the overlay film / cube corner array composite is made, or by simply removing the composite sheet from the manufacturing equipment. In this case, manufacturing efficiency is considerably improved. That is, the processing after casting which is important for breaking the more lands and obtaining the same effect becomes unnecessary, and the manufacturing cost is reduced. The thickness of the cured land (i.e., the thickness of the cube corner array material opposite the plane defined by the bottom of the cube corner elements) is preferably less than 10 percent of the height of the cube corner elements, more preferably Less than 1 percent. Sheets with thicker lands typically have less decoupling of each cube corner element, resulting in a less flexible product, or most of the bottom of the cube corner element Since it becomes difficult to decouple the material of the portion without damaging the portion, the retroreflective performance of the obtained sealing is reduced. On the other hand, if the lands are too thin, the optical performance of the sheet will degrade because the cracks will tend to spread across the bottom of the cube corner elements, rather than between each cube corner element where decoupling of the cube corner elements is desired. . Land thickness can be adjusted by adjusting the amount of flowable resin composition supplied to the tool, removing excess resin composition (e.g., using a doctor blade), and applying pressure to the overlay film. Squeezing out the composition, and the like. Preferably, the resin composition shrinks when cured. Preferably, the resin composition shrinks at least 5 volume percent upon curing, more preferably 5-20 volume percent upon curing. By using a resin composition of this type according to the present invention, it is easier to form a cube corner arrangement with a minimum or zero land thickness, thus obtaining the desired high flexibility. Do you get it. For example, a resin composition that shrinks upon curing will tend to penetrate into the cube corner cavities and, if supplied to the tool in an appropriate amount, will land only adjacent cavities in a narrow area, thus adjacent cube rotors There is a tendency that lands connecting only elements in narrow portions remain. This narrow portion is easily broken and each cube corner element is decoupled, as described below. The sheets of the present invention can, in theory, be formed with essentially no lands connecting adjacent cube corner elements, but in a typical mass production configuration, the height of the cube corner elements A minimum amount of land having a thickness of up to 10 percent of the land, preferably a land having a thickness of the order of 1 to 5 percent is formed. The resin selected for use in the array of cube corner elements preferably results in a product that exhibits high efficiency retroreflectivity and sufficient durability and weatherability. Specific examples of suitable polymers include acrylic compounds, polycarbonates, polyesters, polyethylenes, polyurethanes, and cellulose acetate butyrate polymers. Typically, poly (carbonate), poly (methyl methacrylate), polyethylene terephthalate, aliphatic polyurethane, and cross-linked acrylates (e.g., monofunctional or polyfunctional blended with monofunctional and polyfunctional monomers) Preferred are polymers such as hydrophobic acrylates or acrylated epoxy compounds, acrylated polyesters, and acrylated urethanes). These polymers are typically preferred for the following reasons: high thermal stability, environmental stability, transparency, excellent release from tools or moulds, and for receiving a reflective coating layer. One or more of high acceptability. Another example of a suitable material for forming an array of cube corner elements is a reaction that is crosslinkable via a free radical polymerization mechanism upon exposure to actinic radiation (e.g., electron beam, ultraviolet light, or visible light). Resin-based resin. In addition, these materials may be polymerized by a thermal means by adding a thermal initiator such as benzoyl peroxide. Further, a resin that can be cationically polymerized by radiation may be used. Suitable reactive resins for forming an array of cube corner elements may be a blend of a photoinitiator and at least one compound having an acrylate group. Preferably, the resin blend contains a mono-, di-, or multi-functional compound that, when irradiated, ensures the formation of a cross-linked polymer network. Specific examples of resins that can be polymerized by a free radical mechanism include resins based on acrylic compounds derived from epoxy compounds, polyesters, polyethers, and urethanes; ethylenically unsaturated compounds; at least one acrylate side group. Aminoplast derivatives having at least one acrylate side group; epoxy resins other than acrylated epoxy compounds; and mixtures and combinations thereof. As used herein, the term acrylate includes both acrylates and methacrylates. U.S. Pat. No. 4,576,850 (Martens) discloses examples of crosslinked resins that can be used in the arrangement of cube corner elements of the present invention. Ethylenically unsaturated resins include both monomeric and polymeric compounds containing carbon, hydrogen, and oxygen atoms, with the present invention optionally including nitrogen, sulfur, and halogen. It may be. Oxygen or nitrogen atoms or both atoms are generally included in the ether, ester, urethane, amide, and urea groups. The ethylenically unsaturated compound preferably has a molecular weight of less than about 4,000, and preferably contains compounds containing aliphatic monohydroxy groups, aliphatic polyhydroxy groups, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, Esters obtained by reaction with unsaturated carboxylic acids such as isocrotonic acid and maleic acid. These materials are typically readily available as commercial products and can be easily crosslinked. Some examples of suitable compounds having an acryl or methacryl group for use in the present invention are listed below. (1) Monofunctional compounds: ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, bornyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxy Ethyl acrylate and N, N-dimethylacrylamide; (2) Bifunctional compounds: 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentane glycol diacrylate, ethylene glycol diacrylate, triethylene Glycol diacrylate, tetraethylene glycol diacrylate, and diethylene glycol diacrylate; and (3) polyfunctional compounds: trimethylolpropane triacrylate, glycer Lumpur triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and tris (2-acryloyloxyethyl) isocyanurate. Monofunctional compounds typically tend to provide faster penetration of the overlay film material, while bifunctional and polyfunctional compounds typically provide an interface between the cube corner elements and the overlay film. It tends to provide more crosslinked and stronger bonds. Some representative examples of other ethylenically unsaturated compounds and resins include styrene; divinylbenzene; vinyltoluene; N-vinylformamide; N-vinylpyrrolidone; N-vinylcaprolactam; Esters, and polymethallyl esters (eg, diallyl phthalate and diallyl adipate); and amides of carboxylic acids (eg, N, N-diallyl adipamide). Specific examples of photopolymerization initiators that can be blended with the acrylic compound in the cube corner arrangement of the present invention include the following compounds: benzyl, methyl o-benzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl. Benzophenone / tertiary amine such as ether, acetophenone (eg, 2,2-diethoxyacetophenone), benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one , (1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-benzyl-2-N, N-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-methyl-1-4 (methylthio), phenyl-2-morpholine 1-propanone, bis (2,6-dimethoxybenzoyl) (2,4,4-trimethylpentyl) phosphine oxide, etc. These compounds may be used alone or in combination. Cationic polymerizable materials include, but are not limited to, materials containing an epoxy function and a vinyl ether function.These systems include triarylsulfonium and diaryliodonium salts. The photopolymerization is initiated by an onium salt initiator Preferably, the overlay film 99 used in the method of the present invention comprises an ionomer ethylene copolymer, a plasticized vinyl halide polymer, an acid functional polyethylene copolymer, an aliphatic polyurethane, an aromatic polyurethane, From the group consisting of aromatic polyurethanes, other light-transmitting elastomers, and combinations thereof The polymer material chosen is such a material that typically imparts the desired durability and flexibility to the resulting retroreflective sheeting while providing the desired favorable penetration of the cube corner elements by the resin composition. The overlay film 99 is preferably provided with a low overlay film 99 to facilitate folding, curling, bending, alignment, or stretching of the resulting retroreflective composite. Elastic modulus (e.g., about 13 × 10 ⁸ (Less than Pascal). Generally, the overlay film includes a polymer having a glass transition temperature of less than 50 ° C. When this polymer is used, the resulting overlay film preferably retains physical integrity under conditions to which the composite retroreflective sheet is exposed when the sheet is formed. The polymer desirably has a Vicat softening temperature above 50 ° C. Although the linear shrinkage of the polymer is desirably less than 1 percent, the use of certain combinations of polymer materials for the cube corner elements and the overlay will allow for greater shrinkage of the overlay material. Preferred polymer materials used in the overlay are resistant to degradation by UV light. As a result, the retroreflective sheet can be used for a long time in outdoor use. The overlay film must be light transmissive, and preferably is substantially light transmissive. For example, when the resin composition is applied, it becomes transparent or becomes transparent only under manufacturing conditions (e.g., only in response to curl conditions used to form an array of cube corner elements). Matte finished films are useful in the present invention. The overlay 99 film can be either a single-layer component or a multilayer component, as desired. In the case of multi-layer components, the layer to which the array of cube corner elements is bonded must have the properties described as being useful herein in connection with such bonding, and Other layers that do not come into contact must have the required properties to impart the desired properties to the resulting composite retroreflective sheeting. The overlay film 99 must have sufficient extensibility to effect decoupling of the cube corner elements, as described herein. The overlay film, as the case may be, may have rubber elasticity (i.e., after stretching, tends to show at least some recovery), or after stretching, does not tend to show substantial recovery. There may be. Specific examples of polymers that can be used in the overlay film in the present invention include the following polymers: (1) fluorinated polymer: poly (chlorotrifluoroethylene) [see, eg, St. Minnesota. KEL-F800 brand compound available from Paul's Minnesota Mining and Manufacturing]; poly (tetrafluoroethylene-co-hexafluoropropylene) [eg, EXACFEP brand compound available from Norton Performance of Brampton, Mass.]; Poly (tetrafluoroethylene-co-perfluoro (alkyl) vinyl ether) [eg, an EXAC PEA brand compound also available from Norton Performance]; poly (vinylidene fluoride-co-hexafluoropropylene) [eg, pencil KYNAR FLEX X-2800 brand compound available from Pennwalt Corporation of Philadelphia, Veneer; and (2) ionomer ethylene copolymer: poly (ethylene-co-methacrylic acid) containing sodium or zinc ions [eg, Delaware W EI of ilmington. SURLYN-8920 brand and SURLYN-9910 brand compounds available from duPont Nemours], etc .; (3) Low density polyethylenes: low density polyethylene, linear low density polyethylene, very low density polyethylene, etc .; (5) Polyethylene copolymer: acid-functional polymer [for example, poly (ethylene-co-acrylic acid), poly (ethylene-co-methacrylic acid), poly (ethylene- co-maleic acid), and poly (ethylene-co-fumaric acid)), an acrylic functional polymer (e.g., poly (ethylene-co-alkyl acrylate), wherein the alkyl group is a methyl group, an ethyl group, a propyl group, Butyl group etc., ie CH _Three (CH _Two ) _n A group {where n is 0 to 12}, poly (ethylene-co-vinyl acetate) and the like; (6) aliphatic and aromatic derived from the following monomers (1) to (3) Polyurethane: (1) diisocyanate [for example, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexyl diisocyanate, diphenylmethane diisocyanate, and a combination of these diisocyanates], (2) polyol [ For example, polypentylene adipate glycol, polytetramethylene ether glycol, polycaprolactone diol, poly-1,2-butylene oxide glycol, and combinations of these diols), and (3) a chain transfer agent (e.g., butanediol and hexane) Diol]. Commercially available urethane polymers include PN-03 or 3429 from Morton International Inc. of Seabrook, NH. Also, combinations of the above polymers may be utilized in the overlay film. Preferred polymers for the overlay film include ethylene copolymers comprising units containing carboxyl groups or esters of carboxylic acids (e.g., poly (ethylene-co-acrylic acid), poly (ethylene-co-methacrylic acid), Poly (ethylene-co-vinyl acetate)]; ethylene copolymers of ionomers; plasticized poly (vinyl chloride); and aliphatic urethanes. These polymers are preferred for one or more of the following reasons: favorable mechanical properties, good adhesion to the cube corner layer, transparency, and environmental stability. Requires colorants, ultraviolet (“UV”) absorbers, light stabilizers, radical scavengers or antioxidants, processing aids (eg, antiblocking agents, release agents, lubricants, etc.), and other additives Accordingly, it may be added to one or both of the retroreflective layer and the overlay film. The resin composition and the overlay film 99 are preferably in the following state. That is, when the resin composition contacts the overlay film, the resin composition penetrates the overlay film 99, and consequently, after the primary curing treatment, the material between the cube corner element material and the overlay film 99 material An interpenetrating network is formed. Also, if necessary, the polymer material of the retroreflective sheeting may include substances (e.g., flame retardants) that optimize the overall properties of the resulting sheet and the article to which the sheet is applied. . If necessary, coat the side of the cube corner element opposite the overlay film 99 with a reflective material known in the art of cube corner retroreflective products, such as aluminum, silver, or dielectric. May be. The layer of reflective material must not interfere with the decoupling of the cube corner elements. That is, the layers of reflective material are preferably easily separated at the edges of adjacent cube corner elements. Typically, such coating layers are thin, so that the coating layers do not exhibit significant tensile strength. The reflective material may cover all or only a portion of the cube corner elements in the array, as desired. If desired, different reflective materials may be used in combination at different portions of the array, or no reflective material may be used. Typically, the composite retroreflective sheeting further desirably includes a sealing layer 97 bonded to the retroreflective layer on the side facing the overlay film, as disclosed in U.S. Pat. No. 4,025,159. Preferably, sealing layer 97 includes a thermoplastic material. Specific examples include ionomer ethylene copolymers, plasticized vinyl halide polymers, acid functional polyethylene copolymers, aliphatic polyurethanes, aromatic polyurethanes, and combinations thereof. Optionally used in certain applications, this sealing layer has a significant effect in protecting the cube corner elements of the composite material from environmental effects, while creating the index difference required for total internal reflection. A sealed air layer, which is essential for the operation, can be kept around the cube corner elements. The decoupling of the cube corner elements provided by the present invention results in the sealing layer 97 having at least a portion thereof between the independent cube corner elements, typically in a pattern of sealing areas or sealing legs. As such, it can be directly adhered to the overlay film, thereby forming a cell containing a plurality of retroreflective cube corner elements. Specific examples of sealing techniques include high frequency welding, heat conductive sealing, ultrasonic welding, and reactive components (eg, a sealing material that bonds to the overlay film). The choice of sealing technique will depend in large part on the properties of the sealing layer and the overlay film. If the sealing layer 97 is bonded to a composite retroreflective material for coloring, improving optical properties, or protecting against environmental factors, the composition and physical properties of each component layer may vary significantly for either purpose. You need to pay attention. The composition of each component layer must be compatible with the method used to fuse the sealing layer to the composition. Preferably, the sealing layer 97 includes a thermoplastic material. Such materials are suitable for fusing utilizing relatively simple and commonly available thermal techniques. A common method utilized in the art to seal a thermoplastic layer to a retroreflective cube corner material uses a thermal embossing technique. The use of this technique results in the shape of a "chained connection" pattern of sealing zones formed by a plurality of individual cube corner elements forming a sealed pocket. Looking closely at the legs or "joints" of the thermally sealed area, the thermoplastic cube corner elements result in significant distortion of the cube corner elements in the fusion zone as a result of applying the thermal fusion method You can see that. This type of thermal distortion of the sealing leg typically extends far beyond the actual sealing zone due to the effects of heat conduction. With a significant number of individual cube corner elements in such a distribution in the material, the optical properties of the overall sheet can be significantly poorer than an unsealed sheet. For example, it may exhibit 30% to 40% degradation. Radio frequency ("RF") welding is an alternative technique to thermal fusion. In RF welding, fusion is performed by converting high frequency energy into thermal motion in the presence of polymer polar groups and heating the polymer with the thermal motion. The composite retroreflective sheet of the present invention can be attached to a desired support by various methods (including a method using mechanical means and an adhesive). If an adhesive is used, it is preferable to apply the adhesive only to a portion of the backside of the sheet to minimize degradation of retroreflective brightness, or preferably, use a sealing layer to cover the surface of the cube corner element. Is kept clean so that efficient retroreflection is performed. According to the above description, a retroreflective sheeting comprising a structured surface with zones of an array of cube corner elements arranged in alternating directions, and with improved retroreflective performance at large illumination angles A sheet having just two planes has been disclosed. While numerous embodiments of the invention have been illustrated and described, it can be assumed that the same results can be achieved without substantial modification, and that the particular embodiments and steps described above can be substituted. Those skilled in the art of retroreflective optical elements will appreciate. This application is intended to cover any such adaptations or variations of the present invention. Accordingly, it is intended that the invention be limited only by the appended claims and the equivalents thereof.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, L U, MC, NL, PT, SE), OA (BF, BJ, CF) , CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (KE, LS, MW, SD, S Z, UG), UA (AM, AZ, BY, KG, KZ, MD , RU, TJ, TM), AL, AM, AT, AU, AZ , BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, G E, HU, IL, IS, JP, KE, KG, KP, KR , KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, P L, PT, RO, RU, SD, SE, SG, SI, SK , TJ, TM, TR, TT, UA, UG, UZ, VN (72) Inventors Frey, Sheryl M.             United States, Minnesota 55133-3427,             St. Paul, Post Office Bo             Box 33427 (72) Inventor Keriher, John C.             United States, Minnesota 55133-3427,             St. Paul, Post Office Bo             Box 33427 (72) Inventor Rush, James E.             United States, Minnesota 55133-3427,             St. Paul, Post Office Bo             Box 33427 (72) Inventors Smith, Kenneth L.             United States, Minnesota 55133-3427,             St. Paul, Post Office Bo             Box 33427 (72) Inventors Schusch, Theodore Jay.             United States, Minnesota 55133-3427,             St. Paul, Post Office Bo             Box 33427

Claims (1)

[Claims] 1. A retroreflective sheeting comprising a support having a reference surface and a structured surface facing the reference surface, wherein the structured surface exhibits improved retroreflective performance at large illumination angles. A first zone including an array of cube corner elements whose optical axes are tilted to define a first principal plane, and a second principal plane exhibiting improved retroreflective performance at large illumination angles. A second zone comprising an array of cube corner elements having an optical axis inclined at a second zone, wherein the second plane is perpendicular to the first plane; Further, the retroreflective sheet has substantially the same retroreflective performance on the first plane and the second plane with respect to light incident on the sheet over an irradiation angle range. Present, said Retroreflective sheet. 2. 2. The retroreflective sheeting of claim 1, wherein the orientation of the array of cube corner elements in the first zone is oriented such that the first plane is disposed substantially perpendicular to a first edge of the sheet. . 3. The retroreflective sheeting of claim 1, wherein the first zone extends substantially parallel to a longitudinal edge of the sheet. 4. 2. The retroreflective sheeting of claim 1, wherein the orientation of the array of cube corner elements in the second zone is oriented such that the second plane is disposed substantially parallel to a first edge of the sheet. . 5. The retroreflective sheet according to claim 5, wherein the second zone extends substantially parallel to the first zone. 6. The retroreflective sheet of claim 1, wherein the width of the first zone is between about 3 millimeters and 25 millimeters. 7. The retroreflective sheet according to claim 1, wherein the width of the second zone is about 3 to 25 millimeters. 8. The retroreflective sheet according to claim 1, wherein the cube corner element includes a material having a refractive index of 1.46 to 1.60, and an optical axis of the opposing cube corner element is inclined by 7 to 15 degrees from a position perpendicular to the reference plane. . 9. The retroreflective sheet according to claim 1, wherein the cube corner element includes a material having a refractive index of about 1.5, and an optical axis of the opposing cube corner element is inclined by 8 to 9.736 degrees from a position perpendicular to the reference plane. 10. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, at least 16 candelas / lux / m for light incident on the surface of the sheet at an illumination angle of about 60 degrees in the first plane. When the sheet has a retroreflection coefficient of ² and is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, the light incident on the surface of the sheet at an irradiation angle of about 60 degrees in the plane is exhibits at least 16 coefficient of retroreflection of candelas / lux / m ^2, the retroreflective sheet of claim 1, wherein. 11. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, at least about 30 candela / lux / lux for light incident on the surface of the sheet at an illumination angle of about 60 degrees in the first plane. exhibit retroreflection coefficient m ^2, and the sheet is, when measured at an observation angle of 0.33 degrees, and the display angle of 90 degrees, with respect to light incident on the surface of the sheet with the irradiation angle of about 60 degrees in the plan exhibits at least coefficient of retroreflection of about 30 candelas / lux / m ² Te, retroreflective sheet of claim 1, wherein. 12. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, at least about 90 candela / lux / lux for light incident on the surface of the sheet at an illumination angle of about 40 degrees in the first plane. exhibit retroreflection coefficient m ^2, and the sheet is, when measured at an observation angle of 0.33 degrees, and the display angle of 90 degrees, with respect to light incident on the surface of the sheet with the irradiation angle of about 40 degrees in the plan exhibits at least coefficient of retroreflection of about 90 candelas / lux / m ² Te, retroreflective sheet of claim 1, wherein. 13. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, at least about 150 candela / lux / lux for light incident on the surface of the sheet at an illumination angle of about 40 degrees in the first plane. exhibit retroreflection coefficient m ^2, and the sheet is, when measured at an observation angle of 0.33 degrees, and the display angle of 90 degrees, with respect to light incident on the surface of the sheet with the irradiation angle of about 40 degrees in the plan exhibits at least coefficient of retroreflection of about 150 candelas / lux / m ² Te, retroreflective sheet of claim 1, wherein. 14． The retroreflective sheet according to claim 1, wherein a part of the structured surface is coated with a specular reflective material. 15. The retroreflective sheet according to claim 1, further comprising a sealant disposed adjacent to the structured surface. 16. 16. The retroreflective sheeting of claim 15, wherein the sealant is coupled to the support by a cross-linked network defining a plurality of cells having a retroreflective element hermetically sealed therein. 17． 16. The retroreflective sheeting of claim 15, wherein the sealant maintains an air interface with the structured surface, such that the cube corner elements undergo retroreflection according to the principle of total internal reflection. 18. The support has a body portion including a body layer containing a light-transmitting polymer material having an elastic modulus of less than 7 × 10 ⁸ Pascal, and the cube corner element has a shape of 16 × 10 ⁸ Pascal. The retroreflective sheet of claim 1, comprising a light transmissive polymer material having a modulus of elasticity greater than. 19. The body portion includes a land layer, the land layer having a thickness between 0 micrometers and 150 micrometers, and including a light transmissive polymer material having a modulus greater than 16 × 10 ⁸ Pascal; The retroreflective sheet according to claim 1. 20. The retroreflective sheet according to claim 1, wherein the land layer has a thickness of 1 micrometer to 100 micrometers. 21. The retroreflective sheet according to claim 1, wherein the cube corner element and the land layer include a polymer having a modulus of elasticity greater than 18 × 10 ⁸ Pascal. 22. The retroreflective sheeting of claim 1, wherein said body layer has a thickness of about 20 micrometers to 1,000 micrometers. 23. The retroreflective sheet according to claim 1, wherein the body layer has a thickness of 50 micrometers to 250 micrometers. 24. The retroreflective sheeting of claim 1, wherein the cube corner elements have a height of about 60 micrometers to 180 micrometers. 25. The cube corner element retroreflective sheet of claim 1 further comprising a polymeric material having a modulus of elasticity of greater than 18 × 10 ⁸ pascals. 26. The cube corner article, the retroreflective sheet of claim 1, further comprising an optically transparent polymeric material having a modulus of elasticity of greater than 20 × 10 ⁸ pascals. 27. The retroreflective sheet according to claim 1, wherein the cube corner element contains poly (carbonate), poly (methyl methacrylate), poly (ethylene terephthalate), or crosslinked acrylate. 28. The retroreflective sheet according to claim 1, wherein the body portion includes a land layer containing the same polymer material as the cube corner element. 29. 2. The retroreflective sheet according to claim 1, wherein the body layer contains a light transmitting polymer material having an elastic modulus of less than 5 × 10 ⁸ Pascal. 30. The support comprises an overlay film, the overlay film contains a first polymer material, and has two major surfaces; and the cube corner element contains a second polymer material; 2. The retroreflective sheeting of claim 1, wherein the retroreflective sheet is joined to the first major surface of the overlay film by broken lands, and wherein the cube corner elements are substantially independent. 31. 31. The retroreflective sheeting of claim 30, wherein the material of the microstructure element and the material of the overlay film form an interpenetrating network. 32. 31. The retroreflective sheeting of claim 30, wherein the lands have a thickness that is less than about 10 percent of the average height of the microstructure elements of the array. 33. 31. The retroreflective sheeting of claim 30, wherein the lands have a thickness that is less than about 1 percent of the average height of the microstructure elements of the array. 34. 31. The retroreflective sheeting of claim 30, further comprising a sealing layer adhered to the overlay film via openings between individual microstructured elements. 35. 31. The retroreflective sheet of claim 30, further comprising a reflective layer on the cube corner element. 36. 31. The retroreflective of claim 30, further comprising a sealing film adhered to the sides of the cube corner elements of the sheet in an interconnected network to form cells having the cube corner elements encapsulated therein. Sheet. 37. 31. A product comprising the sheet of claim 30 bonded so that the sealing film functions as a bonding layer. 38. A product to which the sheet according to claim 30 is attached. 39. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, a maximum retroreflectivity of 5 for light incident on the surface of the sheet at an illumination angle of about 60 degrees in the first plane. Percent retroreflectivity, and when the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, for light incident on the surface of the sheet at an illumination angle of about 60 degrees in the plane. The retroreflective sheet according to claim 1, which exhibits a retroreflectivity of 5% of the maximum retroreflectivity. 40. When the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, a maximum retroreflectivity of 30% for light incident on the surface of the sheet at an illumination angle of about 40 degrees in the first plane. Percent retroreflectivity, and when the sheet is measured at an observation angle of 0.33 degrees and a viewing angle of 90 degrees, for light incident on the surface of the sheet at an illumination angle of about 40 degrees in the plane. The retroreflective sheet according to claim 1, which exhibits a retroreflectivity of 30% of the maximum retroreflectivity.