JP2006168088A - Multilayered sheet and diffusion sheet comprising it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered sheet excellent in dimensional stability and light diffusibility and used in a molded product for a screen lens or a diffusion sheet. <P>SOLUTION: The multilayered sheet has a multilayered constitution wherein the intermediate layer (b) of the multilayered sheet comprises a resin composition containing a polymer based on a styrenic monomer unit and a specific unmelted compound, and surface layers (a) and (c) comprise a styrenic resin composition containing a polymer based on a styrenic monomer unit, the specific unmelted compound and a specific light-resistant agent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilayer sheet and a diffusion plate comprising the same. More specifically, the present invention relates to a multilayer sheet excellent in light diffusibility, dimensional stability, and light resistance used for a transmissive screen of a screen of a projection television or the like and a liquid crystal TV, and a diffusion plate made of the same.

  A screen lens such as a transmission screen is widely used to administer an image of a projection television and realize a target display. The screen lens is generally configured by combining lens molded bodies such as a lenticular lens and a Fresnel lens so that the observer can observe a bright image and have a wide viewing angle. The light projecting material used for these screen lenses has been widely used methacrylic resin, which is excellent in transparency, light resistance, scratch resistance, etc., and has excellent molding processability. It has been carried out by extrusion molding, cast molding, injection molding and the like.

  Since the methacrylic resin used as a base material for such a screen lens molded article has a high water absorption rate, the dimensional change of the screen lens molded article occurs, the screen warps or floats, and the optical properties are impaired. There has been a problem that the screen lens is detached from the frame. Further, there has been a problem that the screen lens is deformed when the temperature at the time of transportation or the use environment temperature is high.

In order to solve these problems, Patent Document 1 discloses an aromatic vinyl monomer, a (meth) acrylic acid ester monomer, a polyfunctional unsaturated monomer mixture and a styrene-diene copolymer. A method for obtaining a Fresnel lens by dissolving and polymerizing is disclosed. However, this technique is insufficient to obtain a molded article for a screen lens having excellent light diffusibility.
In addition, since the methacrylic resin used as the base material of the diffusion plate of the liquid crystal TV has a high water absorption, the dimensional change of the diffusion plate molding occurs, the warping of the diffusion plate occurs, and the optical characteristics are impaired. It was. Further, when the image or lamp light is projected for a long time, the color used is deteriorated due to deterioration of the resin used for the screen lens or the diffusion plate, and the image is discolored.

Japanese Patent Laid-Open No. 5-341101

  The subject of this invention is providing the multilayer sheet | seat used as a molded object for screen lenses which was excellent in dimensional stability and light resistance, and was excellent in light diffusivity, and a diffusion plate.

  As a result of diligent studies to solve the above problems, the present inventors made a resin composition containing a polymer mainly composed of a styrene monomer unit and an unmelted compound as an intermediate layer of a multilayer sheet, By using a polymer composed mainly of monomer units and a styrenic resin composition containing a specific unmelted compound and a specific light-resistant agent as the surface layer and the back layer, it has excellent dimensional stability and light resistance. The present inventors have found a multilayer sheet excellent in light diffusibility and a diffusion plate comprising the same, and have reached the present invention.

That is, the present invention provides (1) a multilayer sheet (a) having a multilayer structure (a: surface layer, b: intermediate layer, c: back layer) comprising the following components, and c) a styrene resin composition comprising the following component (A). Product b) Resin composition comprising the following component (B): Component (A): 90 to 100% by mass of styrene monomer units and vinyl compound monomer units 0 to 10 copolymerizable with styrene monomer units 1 to 10 parts by mass of an unmelted compound having a refractive index difference of 0.005 or less and an average particle diameter of 5 to 15 μm and a hindered amine compound of 0.1% by mass with respect to 100 parts by mass of a styrene polymer composed of mass%. Styrenic resin composition (B) component comprising 1-2 parts by mass and 0.1-2 parts by mass of a benzotriazole-based compound: 90-100% by mass of styrene monomer units and styrene monomer units Vinyl compound copolymerizable with 1 to 10 parts by mass of an unmelted compound having a refractive index difference of 0.05 to 0.15 and an average particle diameter of 2 to 10 μm with respect to 100 parts by mass of a styrene polymer composed of 0 to 10% by mass of body units (2) The multilayer sheet has a thickness of a), c): 0.005 to 0.5 mm, and b): 1 to 7 mm. (3) The multilayer sheet is (3) a multilayer sheet. (1) or (2) multilayer sheet obtained by extruding a), b), and c), and (4) a crosslinked polymer mainly composed of styrene as the unmelted compound used in component (A). The multilayer sheet according to any one of (1) to (3), wherein the unmelted compound used in the component (5) and (B) is a crosslinked polymer mainly composed of methyl methacrylate (1) The multilayer sheet according to any one of to (3), or any one of (6) (1) to (5). It is a diffusion plate consisting of a multilayer sheet.

  Industrial Applicability According to the present invention, an unprecedented multilayer sheet excellent in light diffusibility and a diffusion plate comprising the same can be provided very advantageously in the industry. Since the multilayer sheet of the present invention is excellent in light diffusibility, dimensional stability, and light resistance, it can be suitably used for optical applications such as Fresnel lenses, lenticular lenses, and diffusion plates.

Hereinafter, the present invention will be described in detail.
Examples of the styrenic monomer used in the present invention include styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, and the like, and styrene is preferable.

  Examples of the vinyl compound monomer copolymerizable with the styrenic monomer unit in the present invention include methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, and 2-ethylhexyl acrylate. , (Meth) acrylic acid ester monomers such as octyl acrylate, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, methacrylic acid, acrylic acid, maleic anhydride, maleic acid, itaconic acid, itaconic anhydride And unsaturated carboxylic acid monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and other maleimide monomers. These may be used alone or in combination of two or more.

The styrene polymer used in the surface layer a), the intermediate layer b), and the back layer c) of the present invention is 90 to 100% by mass of a styrene monomer unit and vinyl copolymerizable with the styrene monomer unit. It is 0-10 mass% of compound monomer units, Preferably it is 100 mass% of styrene-type monomer units. When the styrene monomer unit is less than 90% by mass, the multilayer sheet may be deformed due to moisture absorption.

The unmelted compound used for the surface layer a) and the back layer c) of the present invention is a compound having a melting point or softening point at 200 ° C. or higher in an atmosphere of 101.3 kPa (1 atm). When the melting point and softening point are less than 200 ° C., the compound is easily melted at the time of melt-kneading with a styrene-based polymer, or at the time of forming a sheet of a styrene-based resin composition or at the time of injection molding, and can retain excellent optical properties. Can not.

The unmelted compound has a refractive index difference within 0.005 with respect to the styrenic polymer used for the surface layer a) and the back layer c). When the refractive index difference exceeds 0.005, the total light transmittance is lowered and the light diffusibility is lowered.

The unmelted compound has an average particle size of 1 to 15 μm, preferably 2 to 14 μm. When the average particle diameter is less than 1 μm, the haze and diffusivity are reduced and the light diffusibility is lowered, and when it exceeds 15 μm, the total light transmittance is lowered and the light diffusibility is lowered. The average particle size of the unmelted compound was measured using a Coulter Multisizer (manufactured by Beckman Coulter).

Moreover, an unmelted compound is 1-10 mass parts containing with respect to 100 mass parts of styrene-type polymers used for surface layer a) and back layer c), Preferably it is 2-8 mass parts. When the content of the unmelted compound is less than 1 part by mass, the haze and diffusivity are reduced and the light diffusibility is lowered. When the content exceeds 10 parts by mass, the total light transmittance is lowered and the light diffusibility is lowered.

The unmelted compound used for the surface layer a) and the back layer c) is preferably a crosslinked copolymer mainly composed of styrene. For example, styrene cross-linked beads can be used.

The styrene resin composition used for the surface layer a) and the back layer c) of the present invention is 0.1 to 2 parts by mass of a hindered amine compound, preferably 0.2 to 100 parts by mass of the styrene polymer. 1.8 parts by mass. It is 0.1-2 mass parts of benzotriazole type compounds with respect to 100 mass parts of styrene polymers, Preferably it is 0.2-1.8 mass parts.
When the amount of the hindered amine compound or the benzotriazole compound is less than 0.1 parts by mass, the light resistance is lowered, and when it exceeds 2 parts by mass, the resulting multilayer sheet is not preferable because of high yellowness.
The styrenic resin compositions used for the surface layer a) and the back layer c) need not be the same and may be different.

Examples of the hindered amine compound include decanoic acid bis (2,2,6,6-tetramethyl-1 (octyloxy) -4-piperidinyl) ester, 1,1-dimethylethyl hydroperoxide, bis (1,2,2, 6,6-pentamethyl-4-piperidyl) [[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] butyl malonate, bis (1,2,2,6,6- Pentamethyl-4-piperidyl) sebacate, methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate and the like Can be used.

Examples of the benzotriazole compounds include 2- (2H-benzotriazol-2-yl) -p-cresol, 2- (2H-benzotriazol-2-yl) -4-6-bis (1-methyl-1-phenyl) Ethyl) phenol, 2- [5-chloro (2H) -benzotriazol-2-yl] -4-methyl] -6- (tert-butyl) phenol, 2,4-di-tert-butyl-6- (5 -Chlorobenzotriazol-2-yl) phenol, 2- (2H-benzotriazol-2-yl) -4,6-di-tert-pentylphenol or the like can be used alone or in combination.

The unmelted compound used in the intermediate layer b) of the present invention is a compound having a melting point or softening point at 200 ° C. or higher in an atmosphere of 101.3 kPa (1 atm). When the melting point and softening point are less than 200 ° C., the compound is easily melted at the time of melt-kneading with a styrene-based polymer, or at the time of forming a sheet of a styrene-based resin composition or at the time of injection molding, and can retain excellent optical properties. Can not.

The unmelted compound has a refractive index difference of 0.05 to 0.15, preferably 0.06 to 0.14 with respect to the styrenic polymer used in the intermediate layer b). If the difference in refractive index is less than 0.05, the haze and diffusivity become small and the light diffusibility decreases, and if it exceeds 0.15, the total light transmittance decreases and the light diffusivity decreases.

The average particle size of the unmelted compound is 2 to 10 μm, preferably 3 to 8 μm.
When the average particle diameter is less than 2 μm, the haze and diffusivity are reduced and the light diffusibility is lowered, and when it exceeds 10 μm, the total light transmittance is lowered and the light diffusibility is lowered. The average particle size of the unmelted compound was measured using a Coulter Multisizer (manufactured by Beckman Coulter).

Moreover, content of an unmelted compound is 1-10 mass parts with respect to 100 mass parts of styrenic polymers used for the intermediate | middle layer b), Preferably it is 2-8 mass parts. When the content of the unmelted compound is less than 1 part by mass, the haze and diffusivity are reduced and the light diffusibility is lowered. When the content exceeds 10 parts by mass, the total light transmittance is lowered and the light diffusibility is lowered.

The unmelted compound used in the intermediate layer b) is preferably a crosslinked copolymer mainly composed of methyl methacrylate. For example, polymethylmethacrylate crosslinked beads (hereinafter referred to as “PMMA crosslinked beads”) and the like can be mentioned.

  Although there is no restriction | limiting in particular in the manufacturing method of the styrene-type polymer of this invention, The block polymerization method, suspension polymerization method, solution polymerization method, and emulsion polymerization method can be employ | adopted suitably.

  There is no restriction | limiting in particular in the mixing | blending method of an unmelted compound, The method of mix | blending by the method of mix | blending with the method of mix | blending with the styrenic polymer etc. before the superposition | polymerization of a styrene-type polymer, the superposition | polymerization, etc. are mentioned.

  Although there is no particular limitation on the method of mixing the unmelted material with the styrene polymer, for example, after premixing with a known mixing device such as a Henschel mixer or a tumbler mixer, a single screw extruder or a twin screw extruder, etc. Uniform mixing can be achieved by melt-kneading using an extruder.

Alternatively, a high-concentration mixture of unmelted compounds may be prepared by the above-described method, and the high-concentration mixture and the styrene polymer may be dry blended at the time of sheet forming.

  An additive can be mix | blended with the styrene-type resin composition used for the surface layer a) and back layer c) of this invention, and the resin composition used for the intermediate | middle layer b) as needed. For example, a plasticizer, a lubricant, silicone oil or the like can be blended in order to improve fluidity and releasability. Moreover, an antistatic agent can be mix | blended for dust prevention of a molded article. Moreover, in order to provide heat resistance, a heat stabilizer can be mix | blended. In addition, colorants such as fluorescent whitening materials can be blended.

The thickness of the multilayer sheet of the present invention is 0.005 to 0.5 mm for the surface layer a) and the back layer c), and 1 to 7 mm for the intermediate layer b). If the surface layer a) and the back layer c) are less than 0.005 mm, the multilayer sheet may be discolored by light irradiation, and if it exceeds 0.5 mm, the multilayer sheet may be deformed by moisture absorption. Also, if the intermediate layer b) is less than 1 mm or exceeds 7 mm, excellent light diffusibility cannot be obtained.
It should be noted that the thicknesses of the surface layer a) and the back layer c) are not necessarily the same and may be different.

In the multilayer sheet of the present invention, the front layer a), the intermediate layer b), and the back layer c) were separately manufactured while extruding the intermediate layer b). The surface layer a), the intermediate layer b), and the back layer c) may be simultaneously extruded. The latter method is economically advantageous and also advantageous in terms of quality that it is easy to prevent scratches and foreign matter from being mixed on the sheet surface during lamination.

The diffusing plate of the present invention is a member that is used in, for example, a liquid crystal display (LCD) or the like and scatters and diffuses light from a backlight to make the entire screen uniform brightness.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. In addition, both the part and% in an Example were represented on the basis of mass.

Production of styrenic polymer (A) A first complete mixing tank having a volume of about 5 liters and a second complete mixing tank of about 15 liters connected in series, and further a first devolatilization tank and a second devolatilization tank equipped with a preheater. Two volatilization tanks were connected in series. With respect to 100 parts by mass of styrene, 15 parts by mass of ethylbenzene, 0.01 parts by mass of t-butylperoxyisopropyl monocarbonate, and 0.2 parts by mass of 2,4-diphenyl-4-methyl-1-pentene were mixed with a raw material solution. did. This raw material solution was supplied to the first complete mixing tank controlled at 135 ° C. at 6.0 kg / hour. The conversion rate at the outlet of the first complete mixing tank was 28% by mass. Next, it extracted continuously from the 1st complete mixing tank, and supplied to the 2nd complete mixing tank controlled to 135 degreeC. The conversion rate at the second complete mixing vessel outlet was 63% by mass. Next, it extracted continuously from the 2nd complete mixing tank, heated with the preheater, and introduce | transduced into the 1st devolatilization tank controlled to 67 kPa and 160 degreeC. Furthermore, it extracted continuously from the 1st devolatilization tank, heated with the preheater, and introduce | transduced into the 2nd devolatilization tank controlled to 1.3 kPa and 230 degreeC, and the monomer was removed. This was extruded and cut into strands to obtain pellet-shaped styrenic polymer A-1.

The styrene polymer A- was prepared in the same manner as the styrene polymer A-1, except that a monomer solution comprising 80% by mass of styrene and 20% by mass of methyl methacrylate (hereinafter referred to as “MMA”) was used. 2 was obtained.

Table 1 shows the composition of the resulting styrenic polymer.

Polyorganosiloxane cross-linked beads (B)
As the polyorganosiloxane crosslinked beads, Tospearl 2000B manufactured by Toshiba Silicone Co., Ltd. having an average particle diameter of 6 μm and a refractive index of 1.420 was used. Table 2 shows the average particle diameter and refractive index.

MMA-nBA copolymer crosslinked beads (C)
In an autoclave equipped with a stirrer, 20 parts of methyl methacrylate, 80 parts of n-butyl acrylate, 5 parts of divinylbenzene as a crosslinking agent, 0.2 part of benzoyl peroxide as a polymerization initiator, and sodium dodecylbenzenesulfonate as a suspension stabilizer 001 parts, 0.5 part of tribasic calcium phosphate and 200 parts of pure water were charged and polymerized at 95 ° C. for 6 hours and further at 130 ° C. for 2 hours. After completion of the reaction, washing, dehydration, and drying were performed to obtain bead-shaped crosslinked beads (C). The average particle diameter of the crosslinked beads (C) was 4 μm, and the refractive index was 1.460.

Styrene cross-linked beads (D)
In an autoclave equipped with a stirrer, 100 parts of styrene, 5 parts of divinylbenzene as a crosslinking agent, 0.2 part of benzoyl peroxide as a polymerization initiator, 0.001 part of sodium dodecylbenzenesulfonate and 0.5 calcium triphosphate as a suspension stabilizer And 200 parts of pure water were charged and polymerized at 95 ° C. for 6 hours and further at a temperature of 130 ° C. for 2 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain bead-shaped crosslinked beads D-1. The average particle diameter of the crosslinked beads was 8 μm, and the refractive index was 1.595. A bead-shaped crosslinked bead D-2 having an average particle diameter of 3 μm and a refractive index of 1.595 was obtained by the same production method as D-1, except that 1.0 part of tricalcium phosphate was used. Further, a bead-shaped crosslinked bead D-3 having an average particle diameter of 13 μm and a refractive index of 1.595 was obtained by the same production method as D-1, except that 0.2 part of tricalcium phosphate was used. Further, bead-like crosslinked beads D-4 having an average particle diameter of 18 μm and a refractive index of 1.595 were obtained by the same production method as D-1, except that 0.1 part of tribasic calcium phosphate was used.

PMMA cross-linked beads (E)
100 parts of methyl methacrylate in an autoclave with a stirrer, 5 parts of divinylbenzene as a crosslinking agent, 0.2 part of benzoyl peroxide as a polymerization initiator, 0.001 part of sodium dodecylbenzenesulfonate as a suspension stabilizer and 0 calcium triphosphate 0.5 part and 200 parts of pure water were charged, and polymerization was carried out at a temperature of 95 ° C. for 6 hours and further at a temperature of 130 ° C. for 2 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain PMMA crosslinked beads E-1 which are bead-shaped crosslinked beads. The average particle diameter of the crosslinked beads was 8 μm, and the refractive index was 1.494. A bead-like PMMA crosslinked bead E-2 having an average particle diameter of 1 μm and a refractive index of 1.494 was obtained by the same production method as E-1, except that 1.5 parts of tribasic calcium phosphate was used. Further, bead-like PMMA crosslinked beads E-3 having an average particle diameter of 3 μm and a refractive index of 1.494 were obtained by the same production method as E-1, except that 1.0 part of tricalcium phosphate was used. Furthermore, bead-like PMMA crosslinked beads E-4 having an average particle diameter of 13 μm and a refractive index of 1.494 were obtained by the same production method as E-1, except that 0.2 part of tricalcium phosphate was used.

Styrene polymers A-1 to A-2 and crosslinked beads B, C, D-1 to D-4, E-1 to E-4, and bis (2,2,6,6-tetra) as hindered amine compounds Methyl-4-piperidyl) sebacate and 2- (2H-benzotriazol-2-yl) -4,6-di-tert-pentylphenol as a benzotriazole-based compound were mixed in the mixing ratios shown in Tables 2 and 3. In a single-screw extruder with a diameter of 40 mm, the mixture was kneaded at a temperature of 240 ° C. and a screw rotation speed of 100 rpm, and pelletized to obtain pellets of styrene resin compositions 1 to 23.
The styrene resin compositions 1 to 12 in Table 2 correspond to the styrene resin compositions in the surface layer a) and the back layer c), and the styrene resin compositions 12 to 23 in Table 3 correspond to the intermediate layer b. ).

Examples 1-9, Comparative Examples 1-18
Using each of the styrenic resin compositions 1 to 23, a multilayer sheet having each configuration was prepared using a T-die type multilayer extruder. The multi-layer extruder is composed of one 65 mmφ full flight screw single screw extruder for the main intermediate layer b), two 30 mmφ full flight screw single screw extruders for the surface layer a) and the back layer c). A test extruder in which each molten resin was joined and multilayered by a feed block was used. Each cylinder temperature in sheeting was operated and molded at 230 ° C.
The optical characteristics, light resistance, and water absorption warpage data of the obtained multilayer sheet are shown in Tables 4-6.
In addition, the resin 1 in Tables 4 to 6 refers to the styrene resin composition 1. Hereinafter, the resin 2 to the resin 23 refer to the styrene resin composition 2 to the styrene resin composition 23.
As for the optical characteristics for using the multilayer sheet for the diffusion plate, it is necessary to exhibit excellent light diffusibility that the haze is 99% or more, the total light transmittance is 60% or more, and the diffusivity is 20% or more. It is.

The measuring method of each physical property value is as follows.
(1) Total light transmittance, haze: Measured according to ASTM D-1003 using a Nippon Denshoku Industries HAZE meter (NDH-2000).
(2) spreading factor: using Nippon Denshoku Industries Co., Ltd. goniophotometer (GC5000L), acceptance angle light transmittance _{I 0} of 0 °, measured receiving angle 70 ° light transmittance _{I 70,} the following equation Calculated.
Diffusion rate (%) = (I ₇₀ / I ₀ ) × 100
(3) Refractive index: About an unmelted compound, it measured in the atmosphere of wavelength 589nm and 23 degreeC with the Abbe refractometer. Moreover, about the styrene-type polymer, it measured at the temperature of 25 degreeC using the potassium iodide saturated aqueous solution as a contact liquid using the digital refractometer (ATAGO RX-2000).
(4) Light resistance: A color difference ΔE after 400 Hr irradiation was measured using a xenon weather meter manufactured by Toyo Seiki Seisakusho, Atlas CI65A. Using a color difference meter (Σ-80) manufactured by Nippon Denshoku Co., Ltd., L, a, and b were measured, and the color difference ΔE for light resistance evaluation was determined by the following equation.
ΔE = ((L−L ′) ² + (aa ′) ² + (b−b ′) ² ) ^1/2
However, L, a, b are hues before light resistance evaluation, and L ′, a ′, b ′ are hues after light resistance evaluation (after 400 Hr irradiation). The color difference ΔE was 1 or less.
(5) Hygroscopicity: The obtained multilayer sheet was cut into a size of 300 mm × 300 mm, and the amount of deformation after standing for 7 days in an atmosphere of 50 ° C. and 80% humidity was measured on a scale. The hygroscopicity was good when the deformation was 0.2 mm or less.
(6) Yellowness: L, a, and b were measured using a color difference meter (Σ-80) manufactured by Nippon Denshoku Co., Ltd., and the b value was shown as a measure of yellowness. The b value was 1 or less.
(7) Resin composition of styrenic polymer: A styrene-based polymer is dissolved in deuterated chloroform to prepare a 2% solution, and FT-NMR (FX-90Q type, manufactured by JEOL Ltd.) is used as measurement data. ¹³ measured and calculated from the peak areas of styrene and methyl methacrylate.

  It can be suitably used for optical applications such as a full-lens lens, a lenticular lens, and a diffusion plate.

Claims (6)

A multilayer sheet having a multilayer structure (a: surface layer, b: intermediate layer, c: back layer) comprising the following components.
a), c) Styrenic resin composition comprising the following component (A).
b) A resin composition comprising the following component (B).
(A) Component: To 100 parts by mass of a styrene polymer comprising 90 to 100% by mass of a styrene monomer unit and 0 to 10% by mass of a vinyl compound monomer unit copolymerizable with the styrene monomer unit 1 to 10 parts by mass of an unmelted compound having a refractive index difference of 0.005 or less and an average particle diameter of 5 to 15 μm, 0.1 to 2 parts by mass of a hindered amine compound, and 0.02 of a benzotriazole compound. A styrene-based resin composition containing 1 to 2 parts by mass.
Component (B): To 100 parts by mass of a styrene polymer comprising 90 to 100% by mass of a styrene monomer unit and 0 to 10% by mass of a vinyl compound monomer unit copolymerizable with the styrene monomer unit. A resin composition comprising 1 to 10 parts by mass of an unmelted compound having a refractive index difference of 0.05 to 0.15 and an average particle diameter of 2 to 10 μm. The multilayer sheet according to claim 1, wherein the thickness of the multilayer sheet is a), c): 0.005 to 0.5 mm, and b): 1 to 7 mm. The multilayer sheet according to claim 1 or 2, wherein the multilayer sheet is obtained by extruding a), b) and c). The multilayer sheet according to any one of claims 1 to 3, wherein the unmelted compound used for the component (A) is a crosslinked polymer mainly composed of styrene. The multilayer sheet according to any one of claims 1 to 3, wherein the unmelted compound used for the component (B) is a crosslinked polymer mainly composed of methyl methacrylate.   A diffusion plate comprising the multilayer sheet according to claim 1.