JP2011075888A - Light diffusion sheet, method for manufacturing light diffusion sheet and light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet having high light diffusion and high light transmission. <P>SOLUTION: The light diffusion sheet contains polypropylene resin, having density of 30-100 kg/m<SP>3</SP>, and number of bubbles per cm<SP>2</SP>of sheet face of 1×10<SP>6</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light diffusion sheet, a method for manufacturing a light diffusion sheet, and a light emitting device.

  Conventionally, this type of light diffusion sheet has been used as, for example, an illumination cover, a light diffusion plate of a display, or the like.

  As such a light diffusion sheet, for example, rod-shaped bubbles are dispersed, and the axial direction of the rod-shaped bubbles is parallel to the sheet surface and directed in one direction (for example, Patent Documents). 1) or using a resin as a base material, including bubbles having an expansion ratio of 1.5 or less and an average particle diameter of 0.5 to 50 μm, a total light transmittance of 40 to 80%, and a parallel light transmittance A light diffusion plate (for example, Patent Document 2) of 6.5% or less is known.

JP 2004-079522 A JP 2006-276838 A

  By the way, when the light diffusion sheet is used as, for example, a cover of an indoor lighting fixture, high light diffusibility is required to irradiate the entire room, and light from a light source can be emitted from the viewpoint of energy efficiency. As long as it can be irradiated indoors, a high light transmittance is required.

  However, in recent years when conventional light diffusing sheets are required to have higher light diffusibility and higher light transmittance, it is possible to sufficiently satisfy such demands. Can not.

  In view of the above problems, an object of the present invention is to provide a light diffusion sheet having high light diffusibility and high light transmittance.

The present invention provides a light diffusing sheet characterized in that it contains a polypropylene resin, has a density of 30 to 100 kg / m ³ , and has a number of bubbles of 1 × 10 ⁶ or more per 1 cm ^{2 of} the sheet surface. .

In the present invention, a light diffusion sheet is produced using a polypropylene resin, having a density of 30 to 100 kg / m ³ and a number of bubbles per 1 cm ^{2 of} the sheet surface of 1 × 10 ⁶ or more. In the method for producing a light diffusion sheet.

  Furthermore, this invention exists in the light-emitting device provided with the said light-diffusion sheet and a light source.

  ADVANTAGE OF THE INVENTION According to this invention, the light-diffusion sheet and light-emitting device which have high light diffusibility and high light transmittance can be provided.

1 is a schematic cross-sectional view of an annular die according to an embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

The light diffusion sheet of the present invention has a density of 30 to 100 kg / m ³ , preferably 30 to 90 kg / m ³ , more preferably 35 to 80 kg / m ³ .
The light diffusing sheet of the present invention has an advantage that it is easy to produce because the density is 30 kg / m ³ or more.
Moreover, the light diffusion sheet of the present invention has an advantage that it is lightweight and has high flexibility when the density is 100 kg / m ³ or less. Further, the light diffusion sheet of the present invention is advantageous in that it can be easily installed with respect to various light sources by being lightweight and having high flexibility.

Further, in the light diffusion sheet of the present invention, the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁶ or more. The light diffusing sheet of the present invention has an advantage that it has high light diffusibility and high light transmittance because the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁶ or more.
The surface of the sheet means a surface perpendicular to the thickness direction, and also means a surface irradiated with light from a light source.
The light diffusion sheet of the present invention preferably has 2 × 10 ⁶ to 2 × 10 ⁷ bubbles per cm ^{2 of} the sheet surface. The light diffusion sheet of the present invention has a number of bubbles of 2 × 10 ⁶ or more per 1 cm ^{2 of} the sheet surface, so that the illuminance from the light emitting device is increased when the light diffusion sheet of the present invention is attached to the light emitting device. There is an advantage that it becomes more uniform. In addition, the light diffusion sheet of the present invention has an advantage that a decrease in illuminance from the light emitting device can be suppressed because the number of bubbles per 1 cm ^{2 of} the sheet surface is 2 × 10 ⁷ or less.

The “number of bubbles per 1 cm ^{2 of the} sheet surface” can be determined by the method described in Examples.

Furthermore, when the light diffusion sheet of the present invention is attached to a light box, the average luminance measured by a two-dimensional color luminance meter is preferably 1300 cd / m ² or more, more preferably 1500 cd / m ² or more. When the light diffusion sheet of the present invention is attached to a light box, the measured value of average luminance by a two-dimensional color luminance meter is 1300 cd / m ² or more, so that necessary illuminance can be ensured.
The “average luminance by a two-dimensional color luminance meter when attached to a light box” can be obtained by the method described in the examples.

  The light diffusion sheet of the present invention has a total light transmittance of preferably 20% or more, more preferably 25% or more. Since the light diffusion sheet of the present invention has a total light transmittance of 20% or more, there is an advantage that the illuminance from the light emitting device is further increased when the light diffusion sheet of the present invention is attached to the light emitting device. .

Furthermore, the light diffusion sheet of the present invention preferably has a bubble cross section exposed on at least one side of the sheet surface, and more preferably a bubble cross section exposed on both sides of the sheet surface. The light diffusing sheet of the present invention is such that, when the light diffusing sheet of the present invention is attached to the light emitting device, the light irradiated to the sheet surface from the light source when the bubble cross section is exposed on at least one surface of the sheet surface. Can be prevented from being reflected, so that there is an advantage that the illuminance is further increased, and there is also an advantage that light can be diffused efficiently.
The sheet surface means a surface perpendicular to the thickness direction.

  The light diffusion sheet of the present invention has a thickness of preferably 0.3 to 1.5 mm, more preferably 0.5 to 1.5 mm. The light diffusion sheet of the present invention has an advantage that the light diffusibility is high because the thickness is 0.3 mm or more, and further has an advantage that the strength of the sheet itself is high. Further, the light diffusion sheet of the present invention has an advantage that the total light transmittance and the light transmittance are high because the thickness is 1.5 mm or less.

Furthermore, the light diffusion sheet of the present invention contains a polypropylene resin.
The polypropylene resin preferably has a melt flow rate of 0.2 to 5 g / 10 min, more preferably 0.2 to 4 g / 10 min, and even more preferably 0.3 to 3.5 g / 10 min. is there. The polypropylene resin has an advantage that the load on the extruder is suppressed and the productivity is improved in the process of producing the light diffusing sheet because the melt flow rate is 0.2 g / 10 min or more, and the foaming agent There is an advantage that the quality of the foamed material that can easily flow the polypropylene resin composition smoothly through the mold can be improved. In addition, since the polypropylene resin has a melt flow rate of 5 g / 10 min or less, in the process of producing a light diffusion sheet, it becomes easier to hold pressure in the mold, and foamability is increased, resulting in foaming. There is an advantage that the density of the body is prevented from becoming too high.
Specific examples of the polypropylene resin include homopropylene and copolymers of propylene and other olefins.
The copolymer of propylene and another olefin may be either a random copolymer or a block copolymer, but a block copolymer is preferred because of excellent heat resistance.
Examples of other olefins copolymerized with propylene include, in addition to ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, and the like. An α-olefin having 4 to 10 carbon atoms.
Of these, homopolypropylene having excellent foamability and heat resistance and block copolymer polypropylene are preferable, and homopolypropylene having excellent heat resistance is more preferable.
Moreover, as a polypropylene resin used by this invention, since a foamability is excellent, it is preferable to use a high melt tension polypropylene resin. Examples of the high melt tension polypropylene-based resin include high melt tension polypropylene (HMS-PP) having free end long chain branching in the molecular structure by electron beam cross-linking and the like, and a high molecular weight component to increase the melt tension. There are things that have been raised. Commercially available products can be used as the high melt tension polypropylene, and specific examples of the commercially available products include trade name “New Train SH9000” manufactured by Nippon Polypro Co., Ltd. and trade name “DaployWB135HMS” manufactured by Borealis.
The polypropylene resin may be a single type of resin, or two or more types may be appropriately combined and mixed.
The polypropylene resin preferably contains a propylene monomer unit in an amount of 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more.

The light diffusion sheet of the present invention preferably contains a thermoplastic elastomer.
Examples of the thermoplastic elastomer include a polyolefin-based thermoplastic elastomer and a styrene-based thermoplastic elastomer.
The styrenic thermoplastic elastomer comprises a styrene monomer unit, preferably 70% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less.
In the present invention, the thermoplastic elastomer is particularly preferably a polyolefin-based thermoplastic elastomer from the viewpoint of excellent compatibility with a polypropylene resin as a base resin.

Examples of the polyolefin-based thermoplastic elastomer include, for example, a polymerization type elastomer which is produced directly in a polymerization reaction vessel by polymerizing a monomer serving as a hard segment and a monomer serving as a soft segment; a Banbury mixer or a biaxial Blend type elastomer produced by physically dispersing polyolefin resin that becomes hard segment and rubber component that becomes soft segment using kneader such as extruder; kneading such as Banbury mixer and twin screw extruder When the polyolefin resin that becomes the hard segment and the rubber component that becomes the soft segment are physically dispersed using a machine, the rubber is completely or partially crosslinked in the polyolefin resin matrix by adding a crosslinking agent. Obtained by dispersing, Crosslinking elastomer and the like.
In the present invention, the olefinic thermoplastic elastomer is produced by physically dispersing a hard segment and a rubber component to be a soft segment from the viewpoint of easy recycling of the manufactured light diffusion sheet. Non-crosslinked elastomers are preferred.

The non-crosslinked elastomer may be a single type or a mixture of two or more types.
In the present invention, by extruding and foaming a mixture of the non-crosslinked elastomer and the polypropylene resin, there is an advantage that it is easy to produce with an extruder similar to the case of extrusion foam molding with a polypropylene resin alone. Furthermore, there is an advantage that the risk of foaming failure due to the crosslinked rubber is suppressed as compared with the non-crosslinked elastomer.

  The light diffusion sheet of the present invention is configured as described above. Next, a method for manufacturing the light diffusion sheet of the present invention for manufacturing the light diffusion sheet of the present invention will be described.

The light diffusing sheet manufacturing method of the present invention uses a polypropylene resin, has a density of 30 to 100 kg / m ³ , and diffuses light so that the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁶ or more. Manufacture sheets.

  Below, the manufacturing method of the light-diffusion sheet of this embodiment is demonstrated.

  The method for producing a light diffusing sheet according to the present embodiment includes a foam nucleating agent-containing resin composition obtained by melt-kneading a thermoplastic resin composition comprising the polypropylene resin and a thermoplastic elastomer and a cell nucleating agent in an extruder. Get.

  Examples of the extruder include a single-screw extruder, a twin-screw extruder, and a tandem extruder. In the present embodiment, a tandem type extruder is preferably used from the viewpoint of easy adjustment of the extrusion conditions.

The cell nucleating agent promotes the generation of cell nuclei when foaming the resin composition, and has an effect on the refinement and uniformity of the cells.
Examples of the bubble nucleating agent include inorganic compounds, organic compounds, inert gases, and the like. Examples of the inorganic compound include talc, mica, silica, diatomaceous earth, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, and potassium sulfate. , Barium sulfate, sodium bicarbonate, glass beads and the like. Examples of the organic compound include polytetrafluoroethylene, azodicarbonamide, a mixture of sodium hydrogen carbonate and citric acid, and the like. Nitrogen etc. are mentioned as said inert gas. Among the bubble nucleating agents, talc is preferable as the inorganic compound, and polytetrafluoroethylene is preferable as the organic compound. As the cell nucleating agent, one kind may be used alone, or two or more kinds may be used.
The amount of the cell nucleating agent is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 8 parts by weight with respect to 100 parts by weight of the thermoplastic resin composition before mixing the cell nucleating agent. It is.
In the light diffusing sheet manufacturing method of the present embodiment, the cell nucleating agent may be mixed with the thermoplastic resin composition in its own form, or in a form contained in a masterbatch with the thermoplastic resin composition. You may mix.
In the method for producing a light diffusing sheet of the present embodiment, the bubble nucleating agent may be mixed with the thermoplastic resin composition and then supplied to the extruder, or the bubble nucleating agent and the thermoplastic resin may be supplied. You may supply to an extruder, without mixing with a composition.
The base resin of the masterbatch is not particularly limited as long as it has good compatibility with the thermoplastic resin composition. For example, homopolypropylene, block polypropylene, random polypropylene, low density polyethylene, high A density polyethylene etc. can be used conveniently.

The manufacturing method of the light diffusing sheet of this embodiment may use various additives usually used for foam molding as an optional component.
Examples of the additive include a weather resistance stabilizer, a light stabilizer, a pigment, a dye, a flame retardant, a crystal nucleating agent, a plasticizer, a lubricant, a surfactant, a dispersant, an ultraviolet absorber, an antioxidant, and a filler. , Reinforcing agents, antistatic agents and the like. Among these, the surfactant improves the slip property and the anti-blocking property. Moreover, a dispersing agent improves the dispersibility of an inorganic filler. Examples of the dispersant include higher fatty acids, higher fatty acid esters, higher fatty acid amides, and the like.
The addition amount of the additive can be appropriately set as long as it does not impair the effects of the present invention. For example, the addition amount used for foam molding of a normal thermoplastic resin can be employed.
The additive is contained in the masterbatch from the viewpoint of easy handling, and from the viewpoint of suppressing the possibility of production environment contamination due to powder scattering when the additive is in powder form. It is preferable to use in.

  In addition, the light diffusing sheet manufacturing method of the present embodiment is obtained by mixing and kneading the cell nucleating agent-containing resin composition and the foaming agent with an extruder to obtain a foaming agent-containing resin composition, and using an extrusion foaming method. The foaming agent-containing resin composition is foamed by a mold attached to the extruder and a foam is obtained.

In the present embodiment, carbon dioxide is preferably used as the foaming agent.
Further, in the present embodiment, from the viewpoint that the foam bubbles can be formed more finely than when other foaming agents are used, as the carbon dioxide, supercritical carbon dioxide, subcritical carbon dioxide. Or liquefied carbon dioxide is preferably used.
In this embodiment, the amount of the foaming agent is appropriately adjusted according to the density of the foam to be formed (that is, the density of the light diffusion sheet to be formed).
The amount of the foaming agent is preferably 1 to 12 parts by weight, more preferably 2 to 10 parts by weight, and even more preferably 3 to 8 parts by weight with respect to 100 parts by weight of the thermoplastic resin composition. is there. In this embodiment, since the amount of the foaming agent is 1 part by weight or more with respect to 100 parts by weight of the thermoplastic resin composition, the density of the foam can be kept low. There is an advantage that lightness and flexibility are improved. Further, in this embodiment, when the amount of the foaming agent is 12 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin composition, foaming occurs in the mold, and foam breakage occurs. There is an advantage that it is suppressed that a large void is generated in the foam.

As the mold, an annular die as shown in FIG. 1, that is, a bubble generating part 2 formed by constricting a resin flow path, and a foam for growing the generated bubbles and smoothing the foam surface An annular die having the molding part 1 is preferably used. In the present embodiment, by using the annular die as the mold, it is possible to suppress the generation of corrugation in the bubble generation unit 2 by an appropriate slip resistance in the foam molding unit 1, and the surface is smooth. A foam can be obtained.
The bubble generating part 2 is a narrow resin flow path (foaming agent-containing resin composition flow path part 3) formed by the annular die-out side mold 5 and the annular die-in side mold 4 and the foam molding part. This is the part where the interval between the channels following 1 is the smallest.
Moreover, it is preferable that the mold surface of the foam molded part 1 has a satin-like shape that has been subjected to blasting and then plated in order to prevent high-temperature resin from adhering and to have appropriate slip resistance. . The surface roughness (Ra) of the satin is preferably 0.4a to 3.2a, more preferably 0.5a to 2.0a.
The corrugate is a large number of ridges and valleys formed by undulation of the foam from the annular die to absorb the circumferential linear expansion due to the deposition expansion.

In the light diffusing sheet manufacturing method of the present embodiment, when extrusion foaming is performed, the resin discharge speed V in the bubble generation unit 2 is preferably 50 to 300 kg / (cm ² · hr), more preferably 70 to 250 kg / h. (Cm ² · hr), more preferably 100 to 200 kg / (cm ² · hr). Moreover, in the manufacturing method of the light-diffusion sheet of this embodiment, when extrusion-foaming, the resin pressure immediately before an annular die becomes like this. Preferably it is 7 Mpa or more, More preferably, it is 8-30 Mpa. The production method of the light diffusing sheet of this embodiment has the advantage that the foaming property of the foaming agent-containing resin composition can be improved by extrusion foaming under these conditions, and further, the foam of the foam obtained is removed. There is also an advantage that the strength of the film of the bubbles can be further increased while being miniaturized. In the present embodiment, these conditions improve the processability when processing the obtained foam, and there is an advantage that, for example, slicing processing for exposing the cell cross section can be easily performed.

The light diffusing sheet manufacturing method of the present embodiment has an advantage that bubbles can be easily miniaturized when the discharge speed V is 50 kg / (cm ² · hr) or more. There is also an advantage that it is easy to reduce the density of the film.
Further, in the method of manufacturing the light diffusion sheet according to the present embodiment, when the discharge speed V is 300 kg / (cm ² · hr) or less, the resin generates heat in the bubble generation unit 2 of the mold, and the bubble breaks. This has the advantage that the foam density can be reduced, and the corrugated corrugation is less likely to occur, the bubble diameter is uniform, and the foam surface is more smooth. There is also.
The discharge speed V is appropriately adjusted according to the cross-sectional area of the bubble generating portion 2 of the annular die and the extrusion discharge amount.
In the manufacturing method of the light diffusing sheet of this embodiment, as a method for adjusting the cross-sectional area of the bubble generating unit 2, the length (in the case of a flat mold) of the bubble generating unit 2 of the mold or the aperture (of the annular die) And a method of changing the interval (in the case of a flat die or an annular die) between the bubble generating portions 2 of the die.

Furthermore, in the method of manufacturing the light diffusion sheet according to the present embodiment, when the resin pressure immediately before the annular die is 7 MPa or more, bubbles start to be generated in the portion before the bubble generating portion 2 of the annular die. There is an advantage that a good foam can be obtained. In addition, the light diffusing sheet manufacturing method of the present embodiment has the advantage that the load on the extruder can be suppressed because the resin pressure immediately before the annular die is 30 MPa or less, and the foaming agent There is also an advantage that it is possible to suppress the possibility that the foaming agent is difficult to press-in due to the pressure when the slag is injected becomes too high.
The resin pressure immediately before the annular die is appropriately adjusted according to the molten resin viscosity, the extrusion discharge amount, and the cross-sectional area of the bubble generating portion 2 of the annular die.
The molten resin viscosity is appropriately adjusted depending on the viscosity of the resin composition in the extruder, the amount of foaming agent added, and the molten resin temperature.
In this specification, the molten resin temperature is a temperature measured by a thermocouple attached in a direct contact with the molten resin in a straight pipe mold for measuring the resin pressure immediately before the annular die. means.
The molten resin temperature is preferably in the range of about 10 ° C. to 20 ° C. higher than the melting point of the polypropylene resin used in this embodiment, from the viewpoint of improving foamability. In the manufacturing method of the light diffusing sheet of this embodiment, when the molten resin temperature is 10 ° C. or higher, crystallization of polypropylene is difficult to occur, the viscosity increase is moderated, and the extrusion conditions are easily stabilized. There is an advantage that the load can be suppressed. Moreover, the manufacturing method of the light-diffusion sheet of this embodiment suppresses a possibility that foam breakage may occur without the speed of solidification of the resin after foaming catching up with the foaming speed when the molten resin temperature is 20 ° C. or lower. There is an advantage that the density of the foam can be lowered.

Moreover, the manufacturing method of the light-diffusion sheet of this embodiment cuts the said foam with a cutter etc., obtains a foam sheet, and removes the skin of this foam sheet by slicing, and obtains a slice foam sheet.
In the method for producing a light diffusing sheet of this embodiment, the cell cross section of the sheet can be exposed by removing the skin of the foamed sheet by slicing.
As the slicing machine used in the slicing process, a known machine such as a type in which a blade rotates can be used.

In the light diffusing sheet manufacturing method of the present embodiment, one sliced foam sheet may be used as a light diffusing sheet, or a plurality of sliced foam sheets may be used as a light diffusing sheet.
In the manufacturing method of the light diffusing sheet of this embodiment, when a plurality of sliced foam sheets are stacked, the number of sheets is preferably 4 or less from the viewpoint of improving light transmittance.

Next, the light emitting device of the present invention will be described.
The light emitting device of the present invention is a light emitting device comprising the light diffusion sheet and the light source of the present invention.
Examples of the light source include an LED, a fluorescent lamp, a light bulb, and the like.

  The light diffusing sheet of the present invention, the method for producing the light diffusing sheet of the present embodiment, and the light emitting device of the present invention have the above-mentioned advantages due to the above configuration. The manufacturing method of a diffusion sheet is not limited to the said structure, A design change is possible suitably.

  For example, the light diffusing sheet manufacturing method of the present embodiment uses a cell nucleating agent-containing resin composition, but the light diffusing sheet manufacturing method of the present invention may be an embodiment that does not use a cell nucleating agent. In that case, a thermoplastic resin composition and a foaming agent may be mixed and kneaded to obtain a foaming agent-containing resin composition.

  Next, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1
First, a tandem extruder in which a second extruder having a diameter of 75 mm was connected to the tip of a first extruder having a diameter of 65 mm was prepared.
Next, polypropylene resin (Nippon Polypro, New Strain SH9000 MFR (melt flow rate): 0.3 g / 10 min) 60 wt% and thermoplastic elastomer (Mitsubishi Chemical Thermorun Z101N MFR: 14 g / min) 40 wt% % Master batch (Talpet 70P manufactured by Nippon Talc Co., Ltd.) containing 100% by weight of a thermoplastic resin composition (resin composition density: 892 kg / m ³ ) and 70% by weight of talc having an average particle size of 12 μm as a cell nucleating agent. ) 10 parts by weight were supplied to the first extruder and melt kneaded to obtain a cell nucleating agent-containing resin composition.
Then, with respect to 100 parts by weight of the thermoplastic resin composition, 4.2 parts by weight of carbon dioxide in a supercritical state as a foaming agent is pressed into a first extruder, The foaming agent-containing resin composition was obtained by uniformly mixing and kneading the foaming agent.
Next, an annular die of a mold attached to the tip of the second extruder (the diameter φ of the bubble generation part of the mold: 35 mm, the interval between the bubble generation parts of the mold: 0.25 mm, the outlet of the foam molding part From the diameter of the part φ: 70 mm), the discharge amount is 30 kg / hr (discharge speed V = 109 kg / c (m ² · hr)), the resin temperature is 175 ° C., and the resin pressure is 9.8 MPa just before the ring die. The foaming agent-containing resin composition was extruded and foamed, and a foam on a cylinder was formed in a foam forming part of an annular die.
Then, the foam was cooled and molded by applying the foam onto the cooled mandrel and blowing air from the air ring to the outer surface portion of the foam.
Next, the cooled cylindrical foam was cut by a cutter at one point on the mandrel to obtain a foam sheet.
Next, the obtained foamed sheet is sliced with a splitting machine (“AB-320D” manufactured by Fortuner) to remove the skin portion on both sides, and the slice with the bubble cross section exposed on both sides having a thickness of 1.0 mm A foam sheet was obtained.
Then, various tests (density, total light transmittance, haze value, average cell diameter, sheet thickness, melt flow rate, average luminance (B), and luminance between light sources are described below for the sliced foam sheet as a light diffusion sheet. Difference (ΔB)).
Note that the average luminance (B) and the difference in luminance between light sources (ΔB) are adjusted so that the extrusion direction during foam molding is parallel to the longitudinal direction of the fluorescent lamp of the light box. It was installed in a box and measured.

(Example 2)
The slice foam sheet was produced in the same manner as in Example 1.
A slice foam sheet as a light diffusing sheet is installed in the light box so that the extrusion direction at the time of forming the foam and the longitudinal direction of the fluorescent lamp of the light box are perpendicular to each other. Various tests were carried out in the same manner as in Example 1 except that the inter-brightness brightness difference (ΔB) was measured.

(Example 3)
The amount of the master batch with respect to 100 parts by weight of the thermoplastic resin composition was 8 parts by weight, the amount of carbon dioxide with respect to 100 parts by weight of the thermoplastic resin composition was 4.3 parts by weight, The light diffusion sheet was the same as in Example 1 except that the resin temperature at that time was 174 ° C., the resin pressure immediately before the annular die was 11.6 MPa, and the thickness of the slice foam sheet was 0.5 mm. In addition, various tests were performed in the same manner as in Example 1.

Example 4
Instead of the masterbatch, polytetrafluoroethylene was used as a cell nucleating agent, and the amount of the polytetrafluoroethylene relative to 100 parts by weight of the thermoplastic resin composition was 1 part by weight, and 100 parts by weight of the thermoplastic resin composition The amount of carbon dioxide relative to the part was 4.6 parts by weight, the resin temperature during extrusion foaming was 176 ° C., the resin pressure immediately before the annular die was 10.8 MPa, and the thickness of the sliced foam sheet was 0 A light diffusion sheet was prepared in the same manner as in Example 1 except that the thickness was 5 mm, and various tests were performed in the same manner as in Example 1.

(Example 5)
Except that the foamed sheet obtained in Example 1 was sliced with a splitting machine to remove the skin part of one side, and a sliced foamed sheet with a foam cross section exposed on one side with a thickness of 0.5 mm was obtained. A light diffusing sheet was prepared in the same manner as in Example 1, and various tests were performed in the same manner as in Example 1.

(Example 6)
A light diffusing sheet was prepared in the same manner as in Example 1 except that the light diffusing sheet of Example 5 was installed so that the surface with the skin where the bubble cross section was not exposed was on the light source side. Various tests were conducted in the same manner as above.

(Example 7)
As a thermoplastic resin composition, polypropylene resin (E111G, manufactured by Prime Polymer Co., Ltd.) (MFR: 0.5 g / 10 min) 50% by weight and polypropylene resin (PL500A, manufactured by Sun Allomer Co., Ltd.) (MFR: 3.5 g / 10 min) ) 10% by weight and 40% by weight of thermoplastic elastomer (R110E, manufactured by Prime Polymer Co., Ltd.) (MFR: 1.5 g / 10 min) were used, and carbon dioxide with respect to 100 parts by weight of the thermoplastic resin composition. Light diffusion sheet as in Example 1, except that the amount of carbon was 4.3 parts by weight, the resin temperature during extrusion foaming was 178 ° C., and the resin pressure immediately before the annular die was 11.1 MPa. In addition, various tests were carried out in the same manner as in Example 1.

(Example 8)
The foam sheet obtained in Example 1 was sliced with a splitting machine to remove the skin portion on one side to obtain three sliced foam sheets with a bubble cross section exposed on one side having a thickness of 0.5 mm. The three sliced foamed sheets are overlapped to form a 1.5 mm light diffusion sheet so that the extrusion direction during molding is the same, and the extrusion direction during foam molding and the length of the fluorescent lamp of the light box The light diffusing sheet was installed in the light box so that the direction was perpendicular, and the light diffusing sheet was the same as in Example 1 except that the average luminance (B) and the difference in luminance between light sources (ΔB) were measured. In addition, various tests were carried out in the same manner as in Example 1.

(Comparative Example 1)
A light diffusion sheet was prepared in the same manner as in Example 1 except that the amount of the masterbatch was set to 2 parts by weight with respect to 100 parts by weight of the thermoplastic resin composition, and various tests were performed in the same manner as in Example 1. did.

(Comparative Example 2)
As the foam sheet, PP foam sheet (product name: Neoflatboard NF5-120-200B) manufactured by Sekisui Plastics Co., Ltd. was used, and the skin part on both sides was removed by slicing the foam sheet with a splitting machine. A light diffusing sheet was prepared in the same manner as in Example 1 except that a sliced foam sheet having a bubble cross section exposed on both sides having a thickness of 1.5 mm was prepared, and various tests were performed in the same manner as in Example 1. did.

  The foam sheets and light diffusion sheets of Examples and Comparative Examples were subjected to the following tests.

(density)
The density was measured based on the method described in JIS K 7222-1999.
Specifically, a test piece of 10 cm ³ or more (100 cm ³ or more in the case of semi-hard and soft-hard materials) is cut from the foamed sheet so as not to change the original cell structure of the sample, and its mass is measured. The density was calculated by the following formula.
Density (kg / m ³ ) = Test piece mass (g) / Test piece volume (cm ³ ) × 10 ³

(Total light transmittance and haze value)
The total light transmittance and haze value were measured according to the method described in JIS K 7361.
Specifically, three 50 × 50 mm test pieces were cut out from the foamed sheet, and the test pieces were used in a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) to measure the total light transmittance and haze value. did. What averaged the measured value of the light transmittance and haze value of three test pieces was made into the light transmittance and haze value of a foam sheet.

(Average bubble diameter)
The average cell diameter was measured according to the test method of ASTM D2842-69.
Specifically, the foamed sheet is cut along the MD direction (extrusion direction) and the TD direction (direction orthogonal to the extrusion direction), and the center part of each cut surface is a scanning electron microscope (S-3000N, Hitachi, Ltd.). ) And enlarged.
Next, the photographed image was printed on A4 paper, and one straight line having a length of 60 mm was drawn on the image. In addition, about the cut surface cut | disconnected in MD direction, the straight line was drawn in parallel with MD direction, and about the cut surface cut | disconnected in TD direction, the straight line was drawn in parallel with TD direction.
The magnification of the electron microscope was adjusted so that 10 to 20 bubbles were present on the straight line.
The average chord length (t) of the bubbles was calculated from the number of bubbles present on the straight line by the following formula, and the average chord length (t) was defined as the average bubble diameter in each direction (MD direction, TD direction).
Average chord length (t) = 60 / (number of bubbles × photo magnification)
When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. Also, if some of the bubbles are in point contact with a straight line, this bubble is included in the number of bubbles, and if both ends of the straight line are located in the bubble without penetrating the bubbles Includes the bubbles in which both ends of the straight line are located in the number of bubbles.
Then, as shown in Equation, the arithmetic mean value of the cell diameters of the obtained MD direction cell diameter (D _MD) and TD direction (D _TD) was defined as the average cell diameter of the foamed sheet.
Average bubble diameter = (D _MD + D _TD ) / 2

(Bubble density)
The cell density (cells / cm ³ ) is the density (ρ: kg / m ³ ) when the thermoplastic resin composition is measured in an unfoamed state based on the average cell diameter (C: mm) and JIS K7112-1999. ) And the apparent density (D: kg / m ³ ) of the foamed sheet measured based on JIS K7222-1999.
Bubble density (pieces / cm ³ ) = (ρ / D−1) / {(4/3) × π × (C / 10/2) ³ }

(Thickness of slice foam sheet and light diffusion sheet)
The thickness of the slice foam sheet and the light diffusion sheet was measured with a thickness gauge manufactured by Mitutoyo Corporation.
Specifically, the average value of the thickness measured using a thickness gauge at a point where the sheet width is divided into 12 equal parts in the TD direction of the sheet every 10 m in the MD direction of the sliced foam sheet (at two ends when less than 10 m). It was set as the thickness of the slice foam sheet. The total thickness of the laminated slice sheets (in the case where the light diffusion sheet is not laminated) is the thickness of the light diffusion sheet.

(Number of bubbles per 1 cm ^{2 of} sheet surface)
Regarding the light diffusion sheet, the number of bubbles per 1 cm ^{2 of} the sheet surface (number) was calculated from the bubble density (number / cm ³ ) and the thickness (cm) of the light diffusion sheet.
Number of bubbles per 1 cm ² surface of the sheet (number) = cell density (number / cm ³ ) × thickness (cm)

(Melt flow rate of polypropylene resin)
The melt flow rate of the polypropylene resin was measured at a test temperature of 230 ° C. and a test load of 21.18 N in accordance with JIS K7210: 1999 method B.
When a single polypropylene resin is used, the melt flow rate of the polypropylene resin of the present invention means the melt flow rate measured by the above method.
Also, when using a mixture of two or more types of polypropylene resins, the melt flow rate of each individual species is measured by the measurement method described above, and calculated from the respective melt flow rate values as follows: Means. Here, when the polypropylene resin is a mixture of n types of polypropylene resins, the melt flow rate of the mixture is calculated by the following equation.
Melt flow rate of the mixture (g / 10 min) = (MFR ₁ ) ^C1 × (MFR ₂ ) ^C2 ×... × (MFR _n ) ^Cn
Here, the melt flow rate of the polypropylene resin 1 is MFR ₁ , the melt flow rate of the polypropylene resin 2 is MFR ₂ ,..., And the melt flow rate of the polypropylene resin n is MFR _n. The content ratio of 1 is C1, the content ratio of the polypropylene resin 2 is C2, and the content ratio of the polypropylene resin n is Cn. Further, the content ratio of the polypropylene resin n is obtained by dividing the weight of the polypropylene resin n by the weight of the entire polypropylene resin.

(Average luminance (B))
The average luminance (B) was measured under the following conditions using a light box (NEW5000 inverter, manufactured by Fuji Film Imaging) and a two-dimensional color luminance meter (CA2000, manufactured by Konica Minolta).
First, the milky white light diffusion plate on the upper surface of the light box was removed and placed on a flat surface, and the lens position of the CCD camera of the two-dimensional color luminance meter was set 50 cm above the upper surface of the light box. At this time, the light box and the CCD camera were set so that their central axes coincide.
Before starting the measurement, turn on the light box for about 1 hour in advance, and fix the light diffusion sheet so that it does not sag on the top surface of the light box (distance about 20 mm from the top of the fluorescent lamp) after the illuminance stabilizes. Then, the average luminance in the light-emitting surface of the light box was measured with a two-dimensional color luminance meter.

(Brightness difference between light sources (ΔB))
Simultaneously with the measurement of the average brightness, the brightness difference between the light sources of the two fluorescent lamp tubes in the light box was measured. That is, the light emitting surface is divided into 50 sections in the center of the light box and in the direction perpendicular to the longitudinal direction of the fluorescent lamp, and the luminance on a 4 mm rectangular surface is measured with a spot. And the difference between the minimum luminance generated between fluorescent lamps is the luminance difference between the light sources. This luminance difference between light sources was used as an index of light diffusion performance.

  The results of the above test are shown in Table 2. Further, in order to compare those having the same “thickness”, those having a thickness of 0.1 cm are summarized in Table 3, and those having a thickness of about 0.15 cm are summarized in Table 4. The comprehensive evaluations in Tables 2 to 4 are based on the criteria in Table 1.

As shown in Table 3, Examples 1 and 2, which are within the scope of the present invention, have the same thickness, but the number of bubbles in the sheet per cm ² is smaller and the density is within the scope of the present invention. Compared with the large comparative example 1, it was shown that the average luminance is high, that is, the light transmittance is high.
In addition, as shown in Table 4, Example 8, which is within the scope of the present invention, is comparable to Comparative Example 2 in which the number of bubbles in a sheet per 1 cm ² is smaller than within the scope of the present invention although the thickness is comparable. Thus, it was shown that the average luminance is high and the luminance difference between the light sources is low, that is, the light transmittance is high and the light diffusibility is high.

  1: foam forming part, 2: bubble generating part, 3: foaming agent-containing resin composition flow path part, 4: ring die-in side mold, 5: ring die-out side mold

Claims (7)

A light diffusing sheet comprising a polypropylene resin, having a density of 30 to 100 kg / m ³ , and having 1 × 10 ⁶ or more bubbles per 1 cm ^{2 of} the sheet surface. The light diffusion sheet according to claim 1, wherein when attached to the light box, a measured value of average luminance by a two-dimensional color luminance meter is 1300 cd / m ² or more.   The light diffusion sheet according to claim 1 or 2, wherein a cross section of the bubble is exposed on at least one surface of the sheet surface.   The light diffusion sheet according to any one of claims 1 to 3, further comprising a thermoplastic elastomer.   The light diffusion sheet according to any one of claims 1 to 4, wherein the light diffusion sheet is produced using carbon dioxide as a foaming agent. A light diffusion sheet comprising a polypropylene resin, having a density of 30 to 100 kg / m ³ and producing a light diffusion sheet so that the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁶ or more. Sheet manufacturing method.   The light-emitting device provided with the light-diffusion sheet and light source of any one of Claims 1-5.

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