JPH103811A - Translucent and diffusible sheet for light source protecting cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize the light source energy, to uniformize the brightness of a light diffusing surface, to prevent the generation of transparence of a light source image, and to improve the balance of transmittance and diffusibility of light by containing cross-linked polymer particles so as to satisfy the predetermined expression. SOLUTION: In a sheet formed by containing cross-linked polymer particles, of which shape and refraction factor and control of distribution of particle diameter can be controlled, in the transparent resin, a lamp image measurement value is obtained so as to satisfy a special relation between the measured lamp image measurement value and the total light beam transmittance, which is simultaneously measured. Namely, the cross-linked polymer particles, which are mainly composed of the transparent resin and which are formed into circles or ellipses at the time of projecting onto a two-dimensional flat surface and which simultaneously satisfy the predetermined expressions 0.1<=H<=1.0, 0.1<=Dd <=20, and 0.02<=|Nm -Nd |<=0.1 are mixed, contained. Relation between the lamp image measurement value (LR) of the sheet and the total light beam transmittance (TT), which is measured in accordance with JIS K-7105, is obtained so as to satisfy a specified expression LR<=0.6+(50-TT)×0.002. Transmittance and diffusibility of light is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover sheet for protecting an exposed light source, and more particularly to a cover sheet capable of efficiently utilizing the energy of the light source, having no image of the light source, and having an excellent balance between light transmission and diffusion. And a light transmitting / diffusing sheet for a light source protective cover.

[0002]

2. Description of the Related Art An example of the use of a light source protective cover for sufficiently transmitting light from a light source to supply light source energy and at the same time uniformly diffuse the light source to prevent the light source from directly contacting the eyes of an observer is used. And facility lighting covers, various displays, display signs, and the like. Conventionally, in order to obtain these members, it has been generally performed to disperse fine particles having different refractive indices in a transparent resin so as to have a light diffusing property.

For example, Japanese Patent Application Laid-Open No. 2-194058 discloses a light diffusing resin in which fine particles of a silicone resin having a specific average particle diameter are dispersed in a transparent resin.
JP-A-3-207743 discloses a resin molded product in which a methacrylic resin and a specific amount of polymethylsilsesquioxane having a specific average particle size are blended.
JP-A-7-100985 discloses a laminated resin plate comprising two types of resin layers in which a transparent resin is mixed with a specific amount of a light diffusing agent having a specific average particle size. JP 7
JP-A-214684 discloses a resin plate in which two types of light diffusing agents having a specific average particle diameter and a specific refractive index are mixed in a specific amount to a methacrylic resin.

[0004]

Problems to be Solved by the Invention
No. 8 and JP-A-3-207743, the light-diffusing resin or resin molded article is visually evaluated for the see-through state when installed on the front surface of the fluorescent lamp. Since it is a qualitative evaluation method based on judgment, it cannot be said that an optimal member as a light source protective cover sheet has been obtained. Further, the optimum refractive index range of the fine particles to be dispersed in the transparent resin has not been studied, and from this point of view, it cannot be said that the sheet is the optimum member for the light source protective cover sheet. JP-A-7-
The resin plate described in Japanese Patent Application Laid-Open No. 100985 and Japanese Patent Application Laid-Open No. 7-214684 has not been evaluated for the transparent state of a light source image. Further, the shape of the light diffusing agent has not been studied, and it cannot be said that the light diffusing agent is an optimal member for a light source protective cover sheet. That is, it is difficult to say that the materials disclosed in the above four publications are suitable for light source protection cover applications.

In particular, recently, light sources with high luminance and low power consumption have appeared, and there is a need for a light source protective cover material having a higher commercial value.

SUMMARY OF THE INVENTION It is an object of the present invention to control the relationship between light transmittance and light-transmitting characteristics of a light source image based on a quantitative evaluation method suitable for a light source protective cover, so that the energy of the light source can be used effectively. It is an object of the present invention to provide a light source protective cover sheet having a light-diffusing surface with a uniform brightness and a light-transmitting / diffusing property in which a light source image cannot be seen through.

[0007]

According to a first aspect of the present invention, a transparent resin is mainly used, the shape when projected on a two-dimensional plane is a circle or an ellipse, and the following formulas (II) to (IV) are simultaneously satisfied. A sheet containing satisfactory crosslinked polymer particles, and the lamp image measurement value (LR) of the sheet and JIS K-710
The relationship with the total light transmittance (TT) measured according to 5 is
A light transmitting / diffusing sheet for a light source protective cover, characterized by satisfying the following formula (I).

LR ≧ 0.6 + (50−TT) × 0.002 (I) 0.1 ≦ H ≦ 1.0 (II) 0.1 ≦ D _d ≦ 20 (III) 0 .02 ≦ | N _m −N _d | ≦ 0.1 (IV) (in the above formula, H is a flatness determined from an image of crosslinked polymer particles projected on a two-dimensional plane, and N _m is a transparent resin. , N _d represents the refractive index of the crosslinked polymer particles, and D _d represents the weight average particle size (μm) of the crosslinked polymer particles.) In the second embodiment of the present invention, 100 parts by weight of the transparent resin is used. A surface layer (A) containing 0.1 to 40 parts by weight of the crosslinked polymer particles, and 0 to 10 parts by weight of the same or different crosslinked polymer particles as the above crosslinked polymer particles based on 100 parts by weight of the transparent resin. And the content of the crosslinked polymer particles in the surface layer (A) is the same as that of the base layer (B).
In a two-layer sheet more than the content of the crosslinked polymer particles in,
And the lamp image measurement value (LR) of the sheet and JIS
-Total light transmittance (TT) measured according to K-7105
Is a light transmitting / diffusing sheet for a light source protective cover, characterized by satisfying the following formula (I).

LR ≧ 0.6 + (50−TT) × 0.002 (I) In the second invention, both surfaces of the base material layer (B) are sandwiched between the surface layers (A). The configuration is preferably applied.

In the present invention, a methacrylic resin is preferably used as the transparent resin.

The present inventor has found that the uniformity of the brightness of the light diffusion surface of the light source protective cover sheet and the transparency of the light source image can be quantitatively evaluated as a "lamp image measured value", and based on the evaluation method. The present invention was completed by developing a sheet that satisfies a specific relationship between the measured value of the lamp image and the total light transmittance.

FIG. 1 shows an outline of a measurement arrangement of lamp image measurement values. In the figure, 11 is a fluorescent tube, 12 is a light source protective cover sheet, and 13 is a luminance meter. In other words, the "lamp image measurement value LR" is a value obtained by giving a specific distance to the front surface of an illumination light source provided with two fluorescent tubes 11 having a specific tube diameter and power consumption in parallel at a specific distance. The light source protective cover sheet 12 is installed, and the luminance distribution within a specific range on the surface of the sheet is measured by the luminance meter 13, and is defined as the ratio between the obtained maximum luminance value _Lmax and minimum luminance value _Lmin. And is derived by the following equation (V).

LR = L _min / L _max (V) The closer this value is to 1, the more uniform the brightness of the light diffusing surface and the judgment is made that the sheet is a light source protective cover sheet in which the image of the light source cannot be seen through. it can.

Using the above method, the present inventor obtains a lamp image measurement value for a sheet containing a crosslinked polymer particle whose shape, refractive index and particle size distribution can be controlled in a transparent resin, and obtains the measured value. It was found that a specific relationship was established between the measured lamp image value and the total light transmittance measured at the same time, and that a material suitable for the relationship was very preferable as a light source protective cover sheet. .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the expression "mainly composed of a transparent resin" means that 50% by weight or more of the transparent resin is contained. Further, the transparent resin used in the present invention,
Haze measured according to JIS K-7105 is 10%
It is defined as a substance that: Specifically, methacrylic resin, polycarbonate resin, polystyrene resin, styrene-methyl methacrylate copolymer resin, styrene-
Butadiene copolymer resin, polyvinyl chloride resin and the like. A methacrylic resin is particularly preferably employed as the transparent resin.

The methacrylic resin that can be used in the present invention includes a resin mainly composed of methyl methacrylate, such as a homopolymer of methyl methacrylate, and one or more of methyl methacrylate and copolymerizable with methyl methacrylate. , A heat-resistant acrylic resin, a low-hygroscopic acrylic resin, and the like. These may be used alone or may be blended. Further, as a monomer copolymerizable with methyl methacrylate, methyl methacrylate and methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, acrylonitrile, acrylic acid, methacrylic acid, vinyl pyridine, vinyl morpholine, vinyl pyridone tetrahydro Furfuryl acrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylacrylamide, 2-hydroxyacrylate, ethylene glycol monoacrylate, glycerin monoacrylate, maleic anhydride, styrene, and α-methylstyrene are exemplified. In order to maintain transparency and simultaneously provide impact resistance, an impact-resistant acrylic resin is used, and its rubber elastic body is disclosed in JP-A-53-55854 and JP-A-55-55854.
Nos. 94917 and 61-32346. Briefly, it is a multi-stage polymer produced by a multi-stage sequential polymerization method in which an elastic layer and an inelastic layer are alternately formed around an acrylic polymer core material.

The crosslinked polymer particles used in the present invention include those which are insoluble in the monomers and precursors which form the transparent resin or which are insoluble at the melting point of the transparent resin. It can be produced using a method such as a polymerization method, a microsuspension polymerization method, an emulsion polymerization method, and a dispersion polymerization method. The crosslinked polymer particles can be controlled in shape, particle size distribution, and refractive index depending on the production method and the type of the monomer used as a raw material.
The balance of diffusivity can be adjusted.

Next, formulas (II) to (IV) shown above will be described.

The shape of the crosslinked polymer particles used in the present invention shows a circle or an ellipse when projected on a two-dimensional plane, that is, by observing the crosslinked polymer particles with a general optical microscope or electron microscope. It is necessary that the resulting image be circular or elliptical. When the shape of the particles projected on a two-dimensional plane is circular or elliptical, light can be diffused in a transparent resin in a three-dimensionally uniform direction. Further, it is necessary to satisfy the following equation (2) when observing an image obtained in the same manner to obtain an oblateness H by image processing.

0.1 ≦ H ≦ 1.0 (II) Preferably, 0.5 ≦ H ≦ 1.0.

The oblateness is obtained from the radius a of the longer main shaft 21 and the radius b of the shorter main shaft 22 in the observed image of the particles schematically shown in FIG. 2 by the following equation (VI). Can be

Next H = b / a ...... (VI ), crosslinked polymer particles used in the present invention, it is necessary that the weight average particle diameter D _d satisfy the following formula (III).

0.1 ≦ D _d ≦ 20 (III) The particle size distribution of the crosslinked polymer particles can be measured by a known light-transmitting sedimentation particle size distribution measuring method or the like. The particle size can be determined. When the weight average particle size does not fall within the range of 0.1 μm or more and 20 μm or less, the particles can be used by classifying the particles so as to fall within the above range. The weight average particle size of the crosslinked polymer particles is 0.
When it is in the range of 1 μm or more and 20 μm or less, refraction and reflection of visible light are effectively generated at the interface between the transparent resin and the particles, and high light diffusivity can be provided.

Further, it is preferable that particles having various particle sizes are uniform within a specific range without being mixed. Specifically, the half width of a peak structure appearing as a particle size distribution is 10%.
When the particle size is not more than μm, the light scattering intensity by individual particles becomes uniform, and uniform optical characteristics can be obtained.

The refractive index N _d of the crosslinked polymer particles used in the present invention must satisfy the following formula (IV) in absolute value of the difference from the refractive index N _m of the transparent resin to be dispersed. is there.

0.02 ≦ | N _m −N _d | ≦ 0.1 (IV) The refractive index of the crosslinked polymer particles is measured by a liquid immersion method or the like using a liquid having a known refractive index. Can be. The refractive index of the transparent resin can be measured by a general “Abbe refractometer”. When the absolute value of the difference between the refractive indices of the crosslinked polymer particles and the transparent resin is in the range of 0.02 or more and 0.1 or less, the light amount loss when light passes through the inside of the particles dispersed in the transparent resin is small. In addition, it is possible to prevent the light transmittance from being extremely reduced.

Further, in the present invention, the absolute value of the difference between the refractive index N _d of the crosslinked polymer particles and the refractive index N _m of the transparent resin |
N _m -N _d | a, the ratio of the weight average particle diameter D _d of the cross-linked polymer particles, to satisfy the following formula (VII), becomes uniform light scattering angle by the individual particles, such isotropic It is particularly preferable because optical characteristics can be obtained.

0.005 ≦ | N _m −N _d | / D _d ≦ 0.03 (VII) Specific examples of the crosslinked polymer particles used in the present invention include:
Particles such as a crosslinked styrene polymer, a crosslinked acrylic polymer, a crosslinked styrene-acrylic copolymer, a crosslinked styrene-butadiene copolymer, a crosslinked siloxane polymer, a crosslinked urethane polymer, and the like. They can be used alone or in combination of two or more.

The structure of the light source protective cover sheet in the present invention may be a single layer structure or a multilayer structure as long as the transparent resin contains the above-mentioned crosslinked polymer particles. More preferably, it has a three-layer structure. The preferred range of the amount of the crosslinked polymer particles used varies depending on the structure of the light source protective cover sheet. That is, in the case of a single-layer structure,
For 100 parts by weight of the transparent resin, the crosslinked polymer particles 0.1
It is preferably in the range of 40 to 40 parts by weight. In this case, it is preferable that the transparent resin is contained in an amount of 60% by weight or more.

On the other hand, the light source protective cover sheet
In the case of a layer or a three-layer structure, the surface layer (A) in which the crosslinked polymer particles are in the range of 0.1 to 40 parts by weight with respect to 100 parts by weight of the transparent resin, and the crosslinked weight with respect to 100 parts by weight of the transparent resin. The crosslinked polymer particles in the base material layer (B), wherein the coalesced particles comprise the base material layer (B) in the range of 0 to 10 parts by weight, and the content of the crosslinked polymer particles in the surface layer (A) is in the base material layer (B). Must be greater than the content of The surface layer (A) is made of a transparent resin of 60.
The base material layer (B) preferably contains 70% by weight or more of the transparent resin. In the case of a two-layer structure, the surface layer (A) is preferably installed and used on the side where light from a light source is emitted, that is, on the side observed as a light source protective cover, and is preferably used. In this case, a structure in which both surfaces of the base material layer (B) are sandwiched between surface layers (A) is preferable.

The light source protective cover sheet of the present invention preferably has a total thickness of 0.1 to 10 mm, more preferably 0.5 to 5 mm, for both a single layer and a multilayer. If a two-layer or three-layer structure, the ratio / t _B / t _A thickness t _B of the thickness t _A and the base layer of the surface layer (A) (B) is preferably in the range of 1 to 1000.

In the present invention, in the case of a two-layer or three-layer structure, the transparent resin and the crosslinked polymer particles of each layer may be the same or different as long as they satisfy the above conditions. Is the same type as the surface layer (A)
This is preferable because the adhesion between the substrate and the base layer (B) is improved. Further, by changing the content of the crosslinked polymer particles in each layer or changing the thickness of each layer, the optical characteristics of the light source protective cover can be controlled.

The method for producing the light source protective cover sheet according to the present invention is preferably a method capable of uniformly dispersing the crosslinked polymer particles in a transparent resin, for example, a polymerizable monomer or a partially polymerized polymerizable polymer. One or more resin compositions obtained by dispersing the particles in a syrup of a monomer and polymerizing, or by mixing, melt-kneading and extruding the particles in a pre-polymerized transparent resin, and the like. Can be obtained by various molding methods.

In order to obtain a smooth sheet, a corrugated sheet, or a prism sheet, an extruded sheet forming method using a T-die is given as an example. The sheet can be subjected to secondary processing by a method such as vacuum forming, pressure forming, stampable forming, and used as a light source protective cover. Further, the light source protective cover sheet of the present invention can be obtained by a method such as profile extrusion molding, blow molding, injection molding, and compression molding using an annular die.

In order to obtain a sheet having a multilayer structure, a coextrusion molding method in which two or more resin compositions are simultaneously melted and extruded,
A method of laminating one of the two types of resin compositions while extruding one of them in a single layer, a method of pressing and thermocompression bonding after preforming the two types of resin compositions, a method of continuously overlapping and bonding , Vacuum forming, laminating at the time of pressure forming, and the like.

The light source protective cover sheet of the present invention contains other components such as an inorganic pigment, a dye, a reinforcing agent, a filler, a release agent, and a charging agent as long as the optical properties and other physical properties are not impaired. Including an inhibitor, a heat stabilizer, an antioxidant, a nucleating agent, a light stabilizer, an ultraviolet absorber, a plasticizer, and the like in any process of manufacturing, such as a kneading process at the time of raw material manufacture and a molding process of a light source cover. Can be.

In the measurement of the lamp image measurement value, a commercially available fluorescent tube according to JIS C-7601 can be used. Specifically, a straight pipe type, a pipe diameter of 1525 mm, and a power consumption of 18 W are used. The two fluorescent tubes are arranged in parallel so that the center-to-center distance is 120 mm, the sheet is placed 30 mm (preferably 10 mm) apart from the surface of the fluorescent tube, and the length on the surface of the molded body is 20 mm by a luminance meter. , A luminance distribution in a range of 200 mm in width is measured, and a ratio between a maximum luminance value and a minimum luminance value is derived to obtain a measured lamp image value.

The measurement of the total light transmittance is based on JIS K
The measurement can be performed using a commercially available measuring instrument according to the -7105 method.

Using the sheet for the light source protective cover manufactured as described above, the measured value of the lamp image (LR) and JIS
-Total light transmittance (TT) measured according to K-7105
The present invention is achieved when the relationship with the following formula (I) is satisfied.

LR ≧ 0.6 + (50−TT) × 0.002 (I)

[0041]

The present invention will be specifically described below with reference to examples and comparative examples. The evaluation and test methods used in each of the examples and comparative examples are as follows.

(1) Observation of Shape of Crosslinked Polymer Particles: About 0.01 g of crosslinked polymer particles were sampled, carbon-deposited, and 3,000 times with a scanning electron microscope (“S-530” manufactured by Hitachi, Ltd.). Observe the shape at a magnification of. In the obtained circle or ellipse image, the radius of the two main axes is measured, and the oblateness H is obtained.

(2) Measurement of particle size distribution of crosslinked polymer particles:
The crosslinked polymer particles are dispersed in an aqueous solution of a surfactant by ultrasonic waves, and a centrifugal automatic particle size distribution measuring device (“C” manufactured by Horiba, Ltd.)
The particle size distribution is measured by a light transmission type sedimentation particle size distribution measuring method using "APA-700 type"). From the obtained particle size distribution, a weight average particle size _Dd is determined.

(3) Measurement of refractive index of cross-linked polymer particles: The cross-linked polymer particles are immersed in a liquid having a known refractive index, and measured using an Abbe refractometer (“Type 3” manufactured by Atago Co., Ltd.).

(4) Measurement of lamp image measurement value: straight tube type N-color fluorescent tube (trade name “Paluk FL20SS-EX-
N ", manufactured by Matsushita Electric Works, Ltd., with a center-to-center distance of 120 mm
And a sheet test piece is placed at a distance of 15 mm from the surface of the fluorescent tube. 1 from the test piece
at a distance of m from the luminance meter (“CA-
1000 ") is fixed, and the luminance distribution of an area enclosed by 25 mm in length and 180 mm in width on the surface of the test piece is measured, and a lamp image measurement value is derived from the obtained maximum luminance value and minimum luminance value.

(5) Measurement of total light transmittance: JIS K-
The total light transmittance of the sheet test piece is measured using a haze meter (“1001-DP type” manufactured by Nippon Denshoku Industries Co., Ltd.) according to 7105.

The materials used in each of the Examples and Comparative Examples were prepared as follows.

Preparation of crosslinked polymer particles: A raw material silane having three hydrolyzable functional groups and one methyl group on a silicon atom is subjected to a hydrolysis reaction, followed by a condensation reaction to form fine particles, and a silicone having a crosslinked structure. A polymer particle is obtained. Furthermore, the particles are classified so that the weight average particle diameter falls within a range of 0.1 to 20 μm by a method combining a sedimentation classification method using a difference in sedimentation speed of particles and a centrifugal classification method using centrifugal force. Thus, crosslinked polymer particles (C) having a particle size distribution having a half width of 2 μm are obtained.

Further, commercially available crosslinked polystyrene particles (trade name “Techpolymer SBX”, manufactured by Sekisui Chemical Co., Ltd.) were classified in the same manner as the above crosslinked polymer particles (C), and the half width of the particle size distribution was 8 μm. The crosslinked polymer particles (D) are obtained.

Using these particles (C) and (D), the above evaluations (1) to (3) are performed, and the results shown in Table 1 are obtained.

Adjustment of light source protective cover material: transparent resin,
The above crosslinked polymer particles (C) or (D), and other components as required, were blended at the concentrations shown in Table 2, blended with a Henschel mixer, and then heated to a resin temperature of 250 ° C with a vented 40 mmφ single screw extruder. To obtain a raw material used for the surface layer (A). Using the same method, the transparent resin and other components are blended at the concentrations shown in Table 2 and pelletized to obtain a raw material used for the base material layer (B).

Examples 1 and 2 A methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Kogyo Co., Ltd.), the crosslinked polymer particles (C) or (D), and a raw material for a surface layer (A) composed of talc, A first extruder using a methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Kogyo Co., Ltd.), the crosslinked polymer particles (C) or (D), and a raw material for a base layer (B) composed of calcium carbonate. (Screw diameter 50 mmφ, L / D = 32, single axis), second extruder (screw diameter 25 mmφ, L / D = 32, single axis), a multi-manifold die, and a unit including three polishing rolls. An extruded sheet was formed to form a three-layer sheet having a width of 300 mm. The obtained sheet showed a configuration in which the surface layer (A) was laminated on both surfaces of the base material layer (B). The thickness of each resin layer was adjusted by the discharge amount balance of two extruders. The thickness of the entire sheet was adjusted to 2.0 mm by polishing roll clearance. The sheets (4) and (5) were evaluated using the sheet as a test piece. The results are shown in Table 3 and FIG. FIG. 3 is a diagram showing the relationship between the measured value of the lamp image and the total light transmittance.

The lamp image value (LR) is 0.62 to
0.63, and the total light transmittance (TT) was as high as 55 to 56%, which was very preferable because the following formula (I) was satisfied.

LR ≧ 0.6 + (50−TT) × 0.002 (I) Therefore, almost no image of the fluorescent tube as the light source is recognized, and the light from the light source is sufficiently transmitted and bright, and Uniformly diffused light was obtained.

Examples 3 and 4 Raw materials for a surface layer (A) composed of methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Kogyo Co., Ltd.) and the above-mentioned crosslinked polymer particles (C) or (D), and a methacrylic resin ( The same as in Examples 1 and 2, using the trade name "Del Powder 70H" (manufactured by Asahi Kasei Corporation), the above-mentioned crosslinked polymer particles (C) or (D), and raw materials for the base layer (B) composed of barium sulfate. To obtain a two-layer sheet. The obtained sheet had a configuration in which the expression layer (A) was laminated on one surface of the base material layer (B). The sheets (4) and (5) were evaluated using the sheet as a test piece. The results are shown in Table 3 and FIG.

The lamp image value (LR) is 0.60
0.61, the total light transmittance (TT) was 57%, which satisfied the above formula (I), no image of the fluorescent tube was recognized, and the light was uniformly diffused as in Examples 1 and 2. Light was obtained.

Examples 5 to 6 Example 1 was repeated except that the raw material for the base material layer (B) was not used.
In the same manner as in Examples 1 to 2, a single-layer sheet consisting only of the raw material for the surface layer (A) was obtained. The sheets (4) and (5) were evaluated using the sheet as a test piece. The results are shown in Table 3 and FIG.

The lamp image value (LR) is 0.62 to
0.63, the total light transmittance (TT) is 57 to 58%, which satisfies the above expression (1), no image of the fluorescent tube is recognized, and light is sufficiently transmitted as in Examples 1 to 4. At the same time, it was confirmed that they were uniformly dispersed.

Comparative Examples 1-2 A methacrylic resin (trade name "Del Powder 70H", manufactured by Asahi Kasei Kogyo Co., Ltd.) and a raw material for the surface layer (A) composed of talc
A three-layer sheet was obtained in the same manner as in Examples 1 and 2, using a methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Corporation) and a raw material for the base layer (B) composed of calcium carbonate. The obtained sheet had a configuration in which the surface layer (A) was laminated on both surfaces of the base layer (B), and the thickness ratio of the surface layer (A) to the base layer (B) was different. The sheets (4) and (5) were evaluated using the sheet as a test piece. The results are shown in Table 3 and FIG.

The lamp image value (LR) is 0.56 to
0.57, the total light transmittance (TT) was 60 to 61%, which did not satisfy the above formula (I). Therefore, the image of the fluorescent tube as the light source was visually confirmed, and it was found that the amount of transmitted light was obtained in the same manner as in Examples 1 to 6, but the light diffusion was inferior.

Comparative Example 3 The same method as in Comparative Examples 1 and 2 was used except that a methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Kogyo Co., Ltd.) and a raw material for the surface layer (A) composed of titanium dioxide were used. ,
A three-layer sheet was obtained. The obtained sheet had a configuration in which the surface layer (A) was laminated on both surfaces of the base material layer (B). The sheets (4) and (5) were evaluated using the sheet as a test piece.
The results are shown in Table 3 and FIG.

The lamp image value (LR) was 0.63, and the total light transmittance (TT) was 30%, which did not satisfy the above formula (I). Although the image of the fluorescent tube was not confirmed, the light transmittance was poor. However, the light source energy cannot be used effectively.

Comparative Example 4 The same method as in Examples 5 to 6 was used except that a methacrylic resin (trade name “Del Powder 70H”, manufactured by Asahi Kasei Corporation) and a raw material for the surface layer (A) composed of amorphous silica were used. hand,
A single-layer sheet consisting only of the raw material for the surface layer (A) was obtained. The sheets (4) and (5) were evaluated using the sheet as a test piece. The results are shown in Table 3 and FIG.

The lamp image value (LR) is 0.45 and the total light transmittance (TT) is 70%, which does not satisfy the above formula (I). However, the light diffusion property was inferior to the high light transmission property.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

The light transmitting / diffusing sheet for the light source protection cover of the present invention effectively utilizes the energy of the light source, and the light diffusion surface has a uniform brightness so that the light source image cannot be seen through. Very useful as a cover material.

[Brief description of the drawings]

FIG. 1 is a schematic view of a device for measuring a lamp image measurement value of a light transmitting / diffusing sheet for a light source protective cover of the present invention.

FIG. 2 is a diagram schematically showing an observed image of crosslinked polymer particles used in the present invention.

FIG. 3 is a graph showing a relationship between a measured value of a lamp image and a total light transmittance in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Fluorescent tube 12 Sheet for light source protection cover 13 Luminometer 21 Long main axis in particle image 22 Short main axis in particle image

Claims (4)

[Claims] 1. A method according to claim 1, wherein the main component is a transparent resin, and the shape when projected on a two-dimensional plane is a circle or an ellipse.
A sheet containing crosslinked polymer particles that simultaneously satisfies (IV), and a lamp image measurement value (LR) of the sheet
A light transmitting / diffusing sheet for a light source protective cover, wherein a relationship between the light transmittance and the total light transmittance (TT) measured according to JIS K-7105 satisfies the following formula (I). LR ≧ 0.6 + (50−TT) × 0.002 (I) 0.1 ≦ H ≦ 1.0 (II) 0.1 ≦ D _d ≦ 20 (III) 0.02 ≦ | N _m −N _d | ≦ 0.1 (IV) (where H is the oblateness determined from an image obtained by projecting the crosslinked polymer particles on a two-dimensional plane, N _m is the refractive index of the transparent resin, N
_d is the refractive index of the crosslinked polymer particles, D _d represents a weight average particle size of the crosslinked polymer particles ([mu] m). ) 2. A crosslinked polymer particle having a circular or elliptical shape when projected on a two-dimensional plane and simultaneously satisfying the following formulas (II) to (IV) is defined as 0 based on 100 parts by weight of the transparent resin. A surface layer (A) containing 1 to 40 parts by weight, and a base layer containing 0 to 10 parts by weight of the same or different crosslinked polymer particles satisfying the conditions of the above crosslinked polymer particles with respect to 100 parts by weight of the transparent resin. (B), wherein the content of the crosslinked polymer particles in the surface layer (A) is larger than the content of the crosslinked polymer particles in the base material layer (B). Sheet Lamp Image Measurement (LR) and JIS K-7
105. A light-transmitting / diffusing sheet for a light source protective cover, wherein the relationship with the total light transmittance (TT) measured according to Formula (105) satisfies the following formula (I). LR ≧ 0.6 + (50−TT) × 0.002 (I) 0.1 ≦ H ≦ 1.0 (II) 0.1 ≦ D _d ≦ 20 (III) 0.02 ≦ | N _m −N _d | ≦ 0.1 (IV) 3. The light transmitting / diffusing property for a light source protective cover according to claim 2, wherein the sheet is a three-layer sheet having a configuration in which both surfaces of a base material layer (B) are sandwiched between surface layers (A). Sheet. 4. The light transmitting / diffusing sheet for a light source protective cover according to claim 1, wherein the transparent resin is a methacrylic resin.