JPWO2008010552A1 - Styrenic resin composition and molded body - Google Patents

Abstract

To provide a light diffusion sheet having excellent dimensional stability, light resistance, optical characteristics, and antistatic properties. A resin composition containing a copolymer containing 50 to 100% by mass of a styrene monomer unit and 50 to 0% by mass of a (meth) acrylic acid monomer unit as a main component and a specific unmelted compound is used as an intermediate layer. A copolymer mainly composed of 20 to 50% by mass of a styrene monomer unit and 80 to 50% by mass of a (meth) acrylic acid ester monomer unit, a specific unmelted compound and a specific light resistance agent A multilayer sheet excellent in dimensional stability, light resistance, light diffusibility, and antistatic properties, comprising a resin composition containing a surface layer and a back layer.

Description

  The present invention relates to a multilayer sheet excellent in light diffusibility, dimensional stability, light resistance, and antistatic properties. In particular, the present invention relates to a light diffusing sheet used as a light diffusing plate for a transmissive screen of a screen such as a projection television or a liquid crystal television.

  A screen lens such as a transmission screen used for a projection television projects an image on the screen and displays the image. Since this screen lens is desired to be bright and have a wide viewing angle for an observer, the screen lens is generally configured by combining lens moldings such as a lenticular lens and a Fresnel lens. For these lens molded bodies, methacrylic resins having excellent transparency, light resistance, scratch resistance, molding processability, etc. are widely used. These molded bodies are produced by press molding, extrusion molding, cast molding, injection molding, etc. Generally molded.

  Since the methacrylic resin used for such screen lenses has a high water absorption rate, the dimensional change of the molded body for the screen lens occurs, the screen warps and floats, the optical properties are impaired, and the screen is removed from the frame. There was a problem that the lens dropped out. 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 a mixture of an aromatic vinyl monomer, a (meth) acrylic acid ester monomer, and a polyfunctional unsaturated monomer with a styrene-diene copolymer. A method is disclosed in which a polymer is dissolved and polymerized to obtain a Fresnel lens. However, this technique is insufficient to obtain a molded article for a screen lens having excellent light diffusibility.
In addition, methacrylic resin used as a base material for light diffusion plates of liquid crystal televisions also has a high water absorption rate, resulting in a change in dimensions of the light diffusion plate molding, warping of the light diffusion plate, and a loss of optical properties. Had. Further, when the image or lamp light is irradiated for a long time, there is a problem that discoloration occurs due to deterioration of the resin used for the screen lens and the light diffusion plate, and the image discolors.

Japanese Patent Laid-Open No. 5-341101

  An object of the present invention is to provide a multilayer sheet excellent in dimensional stability, light resistance, light diffusibility, and antistatic property, particularly a multilayer sheet used as a light diffusion sheet such as a molded article for a screen lens or a molded article for a light diffusion plate. Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors contain a copolymer mainly composed of a styrene monomer unit and a (meth) acrylic acid ester monomer unit and a specific unmelted compound. Containing a styrene-based monomer unit and a (meth) acrylic acid ester-based monomer unit as a main component, a specific unmelted compound, and a specific light-proofing agent It has been found that a multilayer sheet excellent in dimensional stability, light resistance, light diffusibility, and antistatic properties can be obtained by using the resin composition to be used as a surface layer and a back layer, and the present invention has been achieved.

That is, the present invention has the following gist.
(1) A light diffusing sheet having a multilayer structure, wherein the surface layer a and the back layer c are composed of the following component (A), and the intermediate layer b is composed of the component (B).
(A) Component: With respect to 100 parts by mass of a styrene copolymer comprising 20 to 50% by mass of a styrene monomer unit and 80 to 50% by mass of a (meth) acrylate monomer unit, the styrene type 1 to 10 parts by mass of an unmelted compound having a refractive index difference with the copolymer 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 benzotriazole A styrenic resin composition comprising 0.1 to 2 parts by mass of a compound and 0.1 to 3 parts by mass of an amine surfactant.
Component (B): Styrenic monomer with respect to 100 parts by mass of styrene copolymer comprising 50 to 100% by mass of styrene monomer units and 50 to 0% by mass of (meth) acrylate monomer units. A styrene-based resin composition comprising 1 to 10 parts by mass of an unmelted compound having a refractive index difference with a copolymer of 0.05 to 0.15 and an average particle diameter of 2 to 10 μm.
(2) In the above (1), the unmelted compound contained in the component (A) is a cross-linked copolymer containing a styrene monomer and a (meth) acrylate monomer as monomer units. The multilayer sheet as described.
(3) The multilayer as described in (1) or (2) above, wherein the unmelted compound contained in the component (B) is a crosslinked polymer containing a (meth) acrylic acid ester monomer as a monomer unit. Sheet.
(4) The multilayer sheet according to any one of (1) to (3), wherein the hindered amine compound is bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate.
(5) Any of the above (1) to (4), wherein the benzotriazole-based compound is 2- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol A multilayer sheet according to any one of the above.
(6) The multilayer sheet according to any one of (1) to (5), wherein the amine surfactant is N-hydroxyethyl-N- (2-hydroxyalkyl) amine.
(7) The above component further contains 0.0005 to 0.5 parts by mass of a benzoxazole compound in 100 parts by mass of the styrene copolymer in at least one of the component (A) and the component (B). The multilayer sheet according to any one of (1) to (6).
(8) The multilayer sheet according to (7), wherein the benzoxazole-based compound is 2,5-thiophenediyl (5-t-butyl-1,3-benzoxazole).
(9) The multilayer according to any one of (1) to (8), wherein the thickness of the surface layer a and the back layer c is 0.005 to 0.5 mm, and the thickness of the intermediate layer b is 1 to 7 mm. Sheet.
(10) The multilayer sheet according to any one of (1) to (9), which is obtained by simultaneously extruding the surface layer a, the intermediate layer b, and the back layer c.
(11) A light diffusion sheet using the multilayer sheet according to any one of (1) to (10) above.

  The light diffusing sheet obtained in the present invention is excellent in optical properties, dimensional stability, light resistance, and antistatic properties, and thus can be suitably used for optical display applications.

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 (meth) acrylic acid ester monomer in the present invention include methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, and the like. Is mentioned. These may be used alone or in combination of two or more. Methyl methacrylate, ethyl acrylate or n-butyl acrylate, or a mixture thereof is preferable.

  The styrene copolymer in the component (A) used for the surface layer and the back layer of the present invention is a styrene monomer unit of 20 to 50% by mass, preferably 35 to 50% by mass, and (meth) acrylic acid. It is composed of 80 to 50% by mass, preferably 65 to 50% by mass of an ester monomer unit. When the styrenic monomer unit is less than 20% by mass, the resulting light diffusion sheet may warp due to moisture absorption, and when it exceeds 50% by mass, the light resistance may be lowered and discoloration may occur due to light irradiation.

  The styrene copolymer in the component (B) used for the intermediate layer of the present invention is a styrene monomer unit of 50 to 100% by mass, preferably 70 to 100% by mass, and a (meth) acrylic acid ester. It consists of 50 to 0% by mass of monomer units, preferably 30 to 0% by mass. If the styrene monomer unit is less than 50% by mass, it may be deformed by moisture absorption.

  The styrene copolymer in the component (B) used for the intermediate layer of the present invention is not only a styrene monomer and a (meth) acrylic acid ester monomer, but also a vinyl monomer copolymerizable with these. The monomer may be copolymerized, and the amount is preferably 10 parts by mass or less with respect to 100 parts by mass of the total amount of the styrene monomer and the (meth) acrylic acid ester monomer. Examples of the copolymerizable vinyl monomer include vinyl cyanide monomers such as acrylonitrile and methacrylonitrile; methacrylic acid, acrylic acid, maleic anhydride, maleic acid, itaconic acid, itaconic anhydride, and the like. Unsaturated carboxylic acid monomers; maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide and the like. These may be used alone or in combination of two or more.

The unmelted compound in component (A) is preferably a compound having a melting point or softening point at 200 ° C. or higher under an atmosphere of 1 atm. When the melting point and the softening point are less than 200 ° C., the compound is likely to melt at the time of melt-kneading with the styrene-based copolymer, or at the time of forming a sheet of the styrene-based resin composition, and may not retain excellent optical properties. is there. The refractive index difference between the styrene copolymer and the unmelted compound in the component (A) is within 0.005, preferably within 0.003. When the refractive index difference exceeds 0.005, the total light transmittance and the light diffusivity are lowered. Moreover, the average particle diameter of an unmelted compound is 1-15 micrometers, Preferably it is 5-14 micrometers. 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. The average particle size of the unmelted compound is a value obtained by measurement using a Coulter Multisizer (manufactured by Beckman Coulter, Inc.). The measurement is performed by a laser diffraction light scattering method, water is used as a solvent, a sample is dispersed for 1 minute using an output of 200 W using a homogenizer, and the concentration of PIDS (Polarization Intensity Differential Scattering) is adjusted to 45 to 55%. The water refractive index was measured as 1.33, and the average particle diameter was calculated from the volume distribution.
It is necessary that the unmelted compound is contained in an amount of 1 to 10 parts by weight, preferably 2 to 9 parts by weight with respect to 100 parts by weight of the styrene copolymer in the component (A). When the content of the unmelted compound is less than 1 part by mass, the haze and diffusivity become small and the light diffusibility decreases, and when it exceeds 10 parts by mass, the total light transmittance tends to decrease. The unmelted compound in the component (A) is not particularly limited, but a crosslinked copolymer containing a styrene monomer and a (meth) acrylate monomer as monomer units is preferable.
Examples of the styrenic monomer include styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, and the like, and styrene is preferable. Examples of the (meth) acrylic acid ester monomer include methyl methacrylate, ethyl methacrylate, and methyl acrylate, and methyl methacrylate is preferable.

In the component (A), 0.1 to 2 parts by mass of a hindered amine compound, preferably 0.2 to 1.2 parts by mass and 0.1 to 0.1 parts by mass of a benzotriazole compound with respect to 100 parts by mass of a styrene copolymer. It is necessary to contain 2 parts by mass, preferably 0.2 to 1.2 parts by mass.
When the hindered amine compound and the benzotriazole compound are each less than 0.1 parts by mass, the light resistance is lowered. When the hindered amine compound and the benzotriazole compound are more than 2 parts by mass, the yellowness of the obtained light diffusion sheet tends to increase.
The hindered amine compound is an amine-based light stability improver, for example, decanoic acid bis (2,2,6,6-tetramethyl-1 (octyloxy) -4-piperidinyl) ester, 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, etc. There is. These may be used alone or in combination of two or more.
The benzotriazole-based compound is an ultraviolet absorber, for example, 2- (2H-benzotriazol-2-yl) -p-cresol, 2- (2H-benzotriazol-2-yl) -4-6. -Bis (1-methyl-1-phenylethyl) phenol, 2- [5-chloro (2H) -benzotriazol-2-yl] -4-methyl] -6- (t-butyl) phenol, 2,4- Di-t-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- (2H-benzotriazol-2-yl) -4,6-di-t-pentylphenol, 2- (2H- And benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol. These may be used alone or in combination of two or more.

In the present invention, the component (A) contains 0.01 to 3 parts by mass, preferably 0.1 to 2.5 parts by mass of an amine surfactant, based on 100 parts by mass of the styrene copolymer. It is necessary to contain. When the amount of the amine surfactant is less than 0.01 parts by mass, the antistatic property may not be sufficient. When the amount exceeds 3 parts by mass, the resulting resin composition or molded article may be discolored.
Examples of amine surfactants include alkyl diethanol amine, polyoxyethylene alkyl amine, alkyl diethanol amide, polyoxyethylene alkyl amide, N-hydroxyethyl-N- (2-hydroxyalkyl) amine, and the like. You may use independently and may use 2 or more types together.

In the present invention, at least one of the component (A) and the component (B) is preferably 0.0005 to 0.5 parts by mass of a benzoxazole-based compound that is a colorant and a so-called fluorescent brightening agent. More preferably, the content is 0.0008 to 0.2 parts by mass. When the content of the benzoxazole-based compound in at least one component is 0.0005 parts by mass or more, the yellowness of the resulting multilayer sheet is reduced as compared with less than 0.0005 parts by mass, and the appearance is improved. As a result, the total light transmittance of the resulting multilayer sheet tends to increase, which is preferable. The amount of 0.5 parts by mass or less is preferable because the light resistance of the resulting multilayer sheet is improved as compared with the case of exceeding 0.5 parts by mass.
Examples of the benzoxazole compounds include 2,5-thiophenediyl (5-t-butyl-1,3-benzoxazole, 2,5-thiophenediyl (5-t-butyl-1,3-benzoxa). Examples thereof include a mixture of 10% sol and 90% dicyclohexylphthalate, 4,4′-bis (benzoxazol-2-yl) stilbene, and these may be used alone or in combination.

The unmelted compound used for the component (B) is preferably a compound having a melting point or softening point at 200 ° C. or higher under an atmosphere of 1 atm. When the melting point and softening point are less than 200 ° C, the unmelted compound is easily melted at the time of melt kneading with the styrene copolymer or at the time of forming a sheet of the styrene resin composition, and excellent optical properties cannot be maintained. There is. Moreover, the refractive index difference of the styrene-type copolymer and unmelted compound in (B) component is 0.05-0.15, Preferably it is 0.07-0.13. When the difference in refractive index is less than 0.05, the haze and diffusivity of the obtained light diffusion sheet are reduced and the light diffusibility is lowered, and when it exceeds 0.15, the total light transmittance and the light diffusivity are lowered. The average particle diameter of the unmelted compound is 2 to 10 μm, preferably 3 to 9 μm. When the average particle size of the unmelted compound is less than 2 μm, the haze of the obtained light diffusion sheet is reduced and the light diffusibility is lowered, and when it exceeds 10 μm, the total light transmittance is lowered. The average particle size of the unmelted compound is a value obtained by measurement using a Coulter Multisizer (manufactured by Beckman Coulter, Inc.). The measurement is performed by a laser diffraction light scattering method, water is used as a solvent, a sample is dispersed for 1 minute using an output of 200 W using a homogenizer, and the concentration of PIDS (Polarization Intensity Differential Scattering) is adjusted to 45 to 55%. The water refractive index was measured as 1.33, and the average particle diameter was calculated from the volume distribution.
Moreover, it is necessary for an unmelted compound to contain 1-10 mass parts with respect to 100 mass parts of styrene-type copolymers in (B) component, Preferably it is 2-9 mass parts. When the content of the unmelted compound is less than 1 part by mass, the haze of the obtained light diffusion sheet is reduced and the light diffusibility is lowered. When the content exceeds 10 parts by mass, the total light transmittance is lowered. Although it does not specifically limit as an unmelted compound in (B) component, The crosslinked copolymer which has a (meth) acrylic acid ester monomer as a main component is preferable. Examples of the (meth) acrylic acid ester monomer include methyl methacrylate, ethyl methacrylate, and methyl acrylate, and methyl methacrylate is preferable.

  There are no particular restrictions on the method for producing the styrene copolymer in component (A) and the styrene copolymer in component (B), but bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization are used. It can be suitably employed.

  (A) There is no restriction | limiting in particular in the mixing | blending method of each raw material of a component and (B) component, The method of mix | blending immediately before superposition | polymerization before superposition | polymerization of each styrene-type copolymer, superposition | polymerization, and the separated styrene-type copolymer, The method of mix | blending by melt mixing etc. is mentioned.

Even when each styrene copolymer is pelletized and then melted and mixed with an unmelted compound, the mixing method is not particularly limited. For example, premixing is performed using a known mixing device such as a Henschel mixer or a tumbler mixer. Then, it can mix uniformly by performing melt kneading using an extruder such as a single screw extruder or a twin screw extruder.
In addition, a high-concentration mixture in which an unmelted compound is mixed at a high concentration with a styrene-based copolymer is prepared, and this high-concentration mixture and the styrene-based copolymer are dry-blended at the time of manufacturing the light diffusing sheet. You may use for the raw material what the content of the compound becomes a regular density | concentration.

  Additives can be blended into the styrene copolymer in the component (A) and the styrene copolymer in the component (B) as necessary. For example, a plasticizer, a lubricant, silicone oil or the like can be blended in order to improve fluidity and releasability. Moreover, in order to provide further thermal stability, a thermal stabilizer can be mix | blended. In addition, a coloring agent can also be mix | blended.

  The light diffusion sheet of the present invention has a multilayer structure, and the thickness of each layer is 0.005 to 0.5 mm, preferably 0.03 to 0.2 mm, for the surface layer a and the back layer c composed of the component (A). The intermediate layer b composed of the component (B) is preferably 1 to 7 mm, more preferably 1.2 to 2.5 mm. If the surface layer a and the back layer c are less than 0.005 mm, the obtained light diffusion sheet may be discolored by light irradiation, and if it exceeds 0.5 mm, it may be deformed by moisture absorption. Further, if the intermediate layer b is less than 1 mm or exceeds 7 mm, excellent optical characteristics may not be obtained.

  The light diffusing sheet may be a sheet obtained by extruding the surface layer a, the intermediate layer b and the back layer c separately by heat fusion or the like, or a T-die or multi-manifold die using a feed block. 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.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not construed as being limited to these examples.

Method for Producing Styrene Copolymer The tank used for the production is a first devolatilization tank in which a first complete mixing tank having a volume of about 5 L and a second complete mixing tank of about 15 L are connected in series, and a preheater is further attached. And two second devolatilization tanks were connected in series.
Further, 15 parts by mass of ethylbenzene, 0.01 parts by mass of t-butylperoxyisopropyl monocarbonate, 2,4-diphenyl- with respect to 100 parts by mass of a monomer solution composed of 10% by mass of styrene and 90% by mass of methyl methacrylate. 4-Methyl-1-pentene (0.2 parts by mass) was mixed to prepare a raw material solution. 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%. 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 a pellet-shaped styrene copolymer (A-1).

  Except having used the monomer solution comprised by styrene 40 mass% and methyl methacrylate 60 mass%, it implemented similarly to (A-1) and obtained the styrene-type copolymer (A-2).

  Except having used the monomer solution comprised by 80 mass% of styrene and 20 mass% of methyl methacrylate, it implemented similarly to (A-1) and obtained the styrene-type copolymer (A-3).

  Styrene copolymer (A-4) was obtained in the same manner as (A-1) except that a monomer solution composed of 100% by mass of styrene and 0% by mass of methyl methacrylate was used.

Polyorganosiloxane cross-linked beads which are unmelted compounds (B)
As an unmelted compound, polyorganosiloxane cross-linked beads (average particle size 6 μm, refractive index 1.420, Toshiba Silicone Tospearl 2000B) were used.

Production method of unmelted MMA-nBA copolymer crosslinked beads (C) 20 parts by mass of methyl methacrylate, 80 parts by mass of n-butyl acrylate, 5 parts by mass of divinylbenzene as a crosslinking agent, and polymerization initiator as an autoclave with a stirrer , 0.2 parts by weight of benzoyl peroxide, 0.001 part by weight of sodium dodecylbenzenesulfonate and 0.5 parts by weight of calcium triphosphate and 200 parts by weight of pure water as a suspension stabilizer were charged at a temperature of 95 ° C. for 6 hours. Further, polymerization was performed at a temperature of 130 ° C. for 2 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain crosslinked beads (C). The average particle size of the crosslinked beads (C) of the unmelted compound was 4 μm, and the refractive index was 1.460.

Production Method of Unmelted Styrene-MMA Crosslinked Beads (D) 40 parts by mass of styrene, 60 parts by mass of methyl methacrylate, 5 parts by mass of divinylbenzene as a crosslinking agent, and benzoyl peroxide 0 as a polymerization initiator .2 parts by mass, as a suspension stabilizer, 0.001 part by mass of sodium dodecylbenzenesulfonate, 0.5 part by mass of tricalcium phosphate, and 200 parts by mass of pure water were charged at 95 ° C. for 6 hours, and further 130 ° C. For 2 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain crosslinked beads (D-1). The average particle size of (D-1) was 8 μm, and the refractive index was 1.535.
A crosslinked bead (D-2) having an average particle diameter of 3 μm and a refractive index of 1.535 was obtained by the same production method as (D-1) except that 1.0 part by mass of tricalcium phosphate was used.
Further, a crosslinked bead (D-3) having an average particle diameter of 13 μm and a refractive index of 1.535 was obtained by the same production method as (D-1) except that 0.2 part by mass of tricalcium phosphate was used.
Furthermore, a crosslinked bead (D-4) having an average particle diameter of 18 μm and a refractive index of 1.535 was obtained by the same production method as (D-1) except that 0.1 part by mass of tricalcium phosphate was used.

Production method of unmelted PMMA crosslinked beads (E) 100 parts by mass of methyl methacrylate in an autoclave equipped with a stirrer, 5 parts by mass of divinylbenzene as a crosslinking agent, 0.2 parts by mass of benzoyl peroxide as a polymerization initiator, suspension As a stabilizer, 0.001 part by mass of sodium dodecylbenzenesulfonate, 0.5 part by mass of tribasic calcium phosphate and 200 parts by mass of pure water were charged, and polymerization was performed 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 crosslinked beads (E-1). (E-1) had an average particle diameter of 8 μm and a refractive index of 1.494.
A 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 by mass of tricalcium phosphate was used.
Further, a crosslinked bead (E-3) having an average particle diameter of 3 μm and a refractive index of 1.494 was obtained by the same production method as (E-1) except that 1.0 part by mass of tricalcium phosphate was used.
Furthermore, a crosslinked bead (E-4) having an average particle diameter of 13 μm and a refractive index of 1.494 was obtained by the same production method as (E-1) except that 0.2 part by mass of tricalcium phosphate was used.

Colorant (F)
As a colorant, fluorescent whitening agent 2,5-thiophenediyl (5-t-butyl-1,3-benzoxazole) (Ubitex OB manufactured by Ciba Specialty Chemicals) (F-1), resin colorant Mitsubishi Chemical resin Dial Resin BLUE J (F-2) was used.

  Styrene copolymers (A-1) to (A-4), crosslinked beads B and C, (D-1) to (D-4), (E-1) to (E-4), hindered amine compounds Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate as a benzotriazole compound, 2- (2H-benzotriazol-2-yl) -4,6-di-t-pentylphenol, amine N-hydroxyethyl-N- (2-hydroxyalkyl) amine as a system surfactant and (F-1) and (F-2) as colorants were mixed in the mixing ratios shown in Tables 2 and 3. The obtained mixture was kneaded at a temperature of 240 ° C. and a screw rotation speed of 100 rpm in a 40 mm diameter single screw extruder, pelletized, and pellets of the styrenic resin compositions 1 to 36 shown in Tables 2 and 3 Got.

Examples 1-13, Comparative Examples 1-26
Using the styrenic resin compositions 1 to 36, a light diffusion sheet having a three-layer structure shown in Tables 4 to 8 was prepared using a T-die type multilayer extruder having a feed block. The multi-layer extruder is composed of a single 65mmφ full flight screw single screw extruder for the intermediate layer and a single 30mmφ full flight screw single screw extruder for the front and back layers. A test extruder that was joined and multilayered was used. Each cylinder for sheeting was operated and molded at 230 ° C.
The optical properties, light resistance, water absorption warpage and antistatic properties of the obtained light diffusion sheet were evaluated, and the data are shown in Tables 4-8.
When the haze is 99% or more, the total light transmittance is 65% or more, the diffusivity is 17% or more, the b value indicating yellowness is less than 1, and the light resistance is less than 1, the color difference ΔE value can be judged as good optical characteristics. . Further, it is necessary that the water absorption warpage is less than 1 mm for exhibiting excellent dimensional stability, and the surface specific resistance value is 10 ¹² Ω or less for exhibiting excellent antistatic properties.

Each measuring method of the obtained light diffusion sheet 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) Light resistance: A color difference ΔE after 400 Hr irradiation was measured using a xenon weatherometer and Atlas CI65A manufactured by Toyo Seiki Seisakusho.
(4) Dimensional stability (water absorption warpage): A light diffusion sheet cut to a size of 180 mm × 180 mm is left in an atmosphere of 50 ° C. and 80% humidity for 7 days, and the amount of deformation at the four corners before and after being left is measured with calipers. The average value was taken as the value of water absorption warpage, and this value was taken as a measure of dimensional stability.
(5) Yellowness and color difference: L, a and b were measured using a color difference meter (Σ-80) manufactured by Nippon Denshoku Industries Co., Ltd., and b value was shown as a measure of yellowness. The color difference ΔE in the light resistance evaluation was determined by the following formula.
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).
(6) Antistatic property: Surface specific resistance value of a molded body which was conditioned for 24 hours at a temperature of 23 ° C. and a humidity of 50% RH in accordance with JIS K-6911, a surface specific resistance measuring machine manufactured by KAWAGUCHI (R503) This value was used as a measure of antistatic properties.

Evaluations other than the light diffusion sheet were performed as follows.
(7) 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 copolymer, 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).
(8) Resin composition of styrene-based copolymer: FT-NMR (FX-90Q type manufactured by JEOL Ltd.) is used as a measurement material by dissolving styrene-based copolymer in deuterated chloroform to prepare a 2% solution. 13C and calculated from the peak areas of styrene and methyl methacrylate.

The multilayer sheet of the present invention is excellent in dimensional stability, light resistance, light diffusibility, and antistatic properties, and is particularly useful as a transmissive screen for screens such as projection televisions and a light diffusion plate for liquid crystal televisions.

The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2006-196541 filed on July 19, 2006 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (11)

A multilayered light diffusing sheet, wherein the surface layer a and the back layer c are composed of the following component (A), and the intermediate layer b is composed of the component (B).
(A) Component: With respect to 100 parts by mass of a styrene copolymer comprising 20 to 50% by mass of a styrene monomer unit and 80 to 50% by mass of a (meth) acrylate monomer unit, the styrene type 1 to 10 parts by mass of an unmelted compound having a refractive index difference with the copolymer 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 benzotriazole A styrenic resin composition comprising 0.1 to 2 parts by mass of a compound and 0.1 to 3 parts by mass of an amine surfactant.
Component (B): Styrenic monomer with respect to 100 parts by mass of styrene copolymer comprising 50 to 100% by mass of styrene monomer units and 50 to 0% by mass of (meth) acrylate monomer units. A styrene-based resin composition comprising 1 to 10 parts by mass of an unmelted compound having a refractive index difference with a copolymer 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 unmelted compound contained in component (A) is a cross-linked copolymer containing a styrene monomer and a (meth) acrylic acid ester monomer as monomer units. .   The multilayer sheet according to claim 1 or 2, wherein the unmelted compound contained in the component (B) is a crosslinked polymer containing a (meth) acrylic acid ester monomer as a monomer unit.   The multilayer sheet according to any one of claims 1 to 3, wherein the hindered amine compound is bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate.   The benzotriazole-based compound is 2- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol. Multi-layer sheet.   The multilayer sheet according to any one of claims 1 to 5, wherein the amine surfactant is N-hydroxyethyl-N- (2-hydroxyalkyl) amine.   At least one of (A) component and (B) component contains 0.0005-0.5 mass part of benzoxazole type compounds further with respect to 100 mass parts of styrene copolymers. The multilayer sheet according to any one of 6.   The multilayer sheet according to claim 7, wherein the benzoxazole-based compound is 2,5-thiophenediyl (5-t-butyl-1,3-benzoxazole).   The multilayer sheet according to any one of claims 1 to 8, wherein the thickness of the surface layer a and the back layer c is 0.005 to 0.5 mm, and the thickness of the intermediate layer b is 1 to 7 mm.   The multilayer sheet as described in any one of Claims 1-9 obtained by extruding the surface layer a, the intermediate | middle layer b, and the back layer c simultaneously.   The light-diffusion sheet using the multilayer sheet as described in any one of Claims 1-10.