Multilayer molded products, light diffusers

Abstract

The present invention provides a multilayer molded product that exhibits excellent heat resistance, brightness, chromaticity, and diffusivity even when light diffusing agents and quantum dots are added to the multilayer molded product. [Solution] According to the present invention, a multilayer molded article is provided comprising an A1 layer, an A2 layer, and a B layer, wherein the A1 layer is provided on one surface of the B layer directly or via another layer, and the A2 layer is provided on the other surface of the B layer directly or via another layer, the A1 layer and the A2 layer are each composed of a resin composition A, and the B layer is composed of a resin composition B, the resin composition A contains a styrene polymer A, the styrene polymer A has 50 to 97% by mass of styrene monomer units, 3 to 15% by mass of (meth)acrylic acid units, and 0 to 35% by mass of (meth)acrylic acid ester units, and the resin composition B contains a styrene polymer B, the styrene polymer B has 88 to 100% by mass of styrene monomer units, 0 to 2% by mass of (meth)acrylic acid units, and 0 to 10% by mass of (meth)acrylic acid ester units.

Description

Technical Field

[0001] The present invention relates to a multilayer molded product and a light diffusing plate.

Background Art

[0002] A light diffusing plate is used in a display device such as a liquid crystal display. For example, as disclosed in Patent Document 1, a light diffusing plate made of a multilayer molded product using a styrene-based polymer is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in order to improve functions, additives such as quantum dots have been added to multilayer molded products in addition to light diffusing agents. Even when such addition is performed, a multilayer molded product having a resin composition and a layer combination excellent in heat resistance, luminance, chromaticity, and diffusion rate has been demanded.

[0005] The present invention has been made in view of such problems, and provides a multilayer molded product excellent in heat resistance, luminance, chromaticity, and diffusion rate even when a light diffusing agent and quantum dots are added to the multilayer molded product.

Means for Solving the Problems

[0006] According to the present invention, the following inventions are provided. [1] A multilayer molded article comprising an A1 layer, an A2 layer, and a B layer, wherein the A1 layer is provided on one side of the B layer directly or via another layer, and the A2 layer is provided on the other side of the B layer directly or via another layer, the A1 layer and the A2 layer are each composed of resin composition A, and the B layer is composed of resin composition B, the resin composition A contains styrene polymer A, the styrene polymer A has 50 to 97% by mass of styrene monomer units, 3 to 15% by mass of (meth)acrylic acid units, and 0 to 35% by mass of (meth)acrylic acid ester units, and the resin composition B contains styrene polymer B, the styrene polymer B has 88 to 100% by mass of styrene monomer units, 0 to 2% by mass of (meth)acrylic acid units, and 0 to 10% by mass of (meth)acrylic acid ester units. [2] A multilayer molded article according to [1], further comprising a C1 layer and a C2 layer, wherein the C1 layer is directly provided on one side of the B layer, the C2 layer is directly provided on the other side of the B layer, the A1 layer is directly provided on the opposite side of the C1 layer from the side on which the B layer is provided, and the A2 layer is directly provided on the opposite side of the C2 layer from the side on which the B layer is provided, and the C1 layer and the C2 layer are each composed of a resin composition C, the resin composition C includes a styrene polymer C, the styrene polymer C comprises 35 to 70% by mass of styrene monomer units and 30 to 65% by mass of (meth)acrylic acid ester units. [3] The resin composition B comprises quantum dots, as described in [1] or [2]. [4] A multilayer molded article according to any one of [1] to [3], wherein at least one of the resin composition A and the resin composition B contains a light diffusing agent. [5] The resin composition A comprises 0.1 to 25% by mass of a light diffusing agent based on 100% by mass of the resin composition A, as described in any one of [1] to [4]. [6] The resin composition B comprises 0.01 to 10% by mass of quantum dots with respect to 100% by mass of the resin composition B, as described in any one of [1] to [5]. [7] The resin composition B comprises 0.1 to 25% by mass of a light diffusing agent and 0.01 to 10% by mass of quantum dots, as described in any one of [1] to [6]. A light-diffusing plate comprising a multilayer molded product as described in any one of [8][1] to [7]. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows the laminated structure of a multilayer molded product with two types and three layers according to one embodiment of the present invention. [Figure 2] Figure 2 shows the laminated structure of a 3-type, 5-layer multilayer molded product according to one embodiment of the present invention. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature can stand alone as an independent invention.

[0009] 1.Multilayer molded product 1-1. First Embodiment The multilayer molded article 1 according to the first embodiment of the present invention comprises an A1 layer, an A2 layer, and a B layer. The multilayer molded article 1 may also include layers other than the A1 layer, the A2 layer, and the B layer.

[0010] Layer A1 is provided on one side of layer B either directly or via another layer, and layer A1 is provided on the other side of layer B either directly or via another layer. Furthermore, other layers may be provided outside layers A1 and A2. The other layers are not limited as long as they do not impair the effects of the present invention, and may be resin layers, barrier layers, etc. The barrier layer is, for example, a layer having a barrier function against oxygen and water vapor, and is a metal vapor-deposited film, a metal oxide film, a silicon oxide film, an oxidizride film, a nitride film, a metal foil, or a laminate of these films, or a laminate of these films with a resin film (e.g., polyethylene terephthalate, polyvinyl alcohol, polyethylene vinyl alcohol, etc.).

[0011] In one example, as shown in Figure 1, layer 11 (layer A1) may be directly provided on one side of layer 20 (layer B), and layer 12 (layer A2) may be directly provided on the other side of layer 20 (layer B).

[0012] Layers A1 and A2 are each composed of resin composition A. Resin composition A contains styrene polymer A.

[0013] Styrene polymer A contains 50 to 97% by mass of styrene monomer units, preferably 70 to 92% by mass, relative to 100% by mass of monomer units contained in styrene polymer A. Styrene polymer A also contains 3 to 15% by mass of (meth)acrylic acid units, preferably 8 to 14% by mass, relative to 100% by mass of monomer units contained in styrene polymer A. Styrene polymer A also contains 0 to 35% by mass of (meth)acrylic acid ester units, preferably 0 to 20% by mass, relative to 100% by mass of monomer units contained in styrene polymer A. By setting the values ​​within these ranges, even when light diffusing agents and quantum dots are added to multilayer molded products, excellent heat resistance, brightness, chromaticity, and diffusivity are achieved.

[0014] The content of styrene monomer units in styrene polymer A is specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, and 97% by mass, and may be within the range of any two of the values ​​exemplified here. Furthermore, the content of (meth)acrylic acid units in styrene polymer A is specifically, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15% by mass, and may be within the range of any two of the values ​​exemplified here. Furthermore, the content of (meth)acrylic acid ester units in styrene polymer A is specifically, for example, 0, 5, 10, 15, 20, 25, 30, and 35% by mass, and may be within the range of any two of the values ​​exemplified here.

[0015] As the resin composition A constituting the A1 layer and the A2 layer, resin composition A1 and resin composition A2 can be used respectively. The components of resin composition A1 and resin composition A2 may be the same as or different from each other. When they are the same, the manufacturing process and equipment can be simplified compared to the case where they are different, and cost reduction etc. can be expected. On the other hand, when they are different, the characteristics required for each layer can be adjusted individually. For example, in the layer closer to the light source, a styrene-based polymer A with a higher content of (meth)acrylic acid units may be used.

[0016] The B layer is composed of a resin composition B. The resin composition B contains a styrene-based polymer B.

[0017] The styrene-based polymer B has 88 to 100% by mass, preferably 97 to 100% by mass, of styrene-based monomer units with respect to 100% by mass of the monomer units contained in the styrene-based polymer B. Also, the styrene-based polymer B has 0 to 2% by mass of (meth)acrylic acid units with respect to 100% by mass of the monomer units contained in the styrene-based polymer B. Further, the styrene-based polymer B has 0 to 10% by mass of (meth)acrylic acid ester units with respect to 100% by mass of the monomer units contained in the styrene-based polymer B. The styrene-based polymer B particularly preferably has 100% by mass of styrene-based monomer units with respect to 100% by mass of the monomer units contained in the styrene-based polymer B. By setting such a range, even when a light diffusing agent and quantum dots are added to the multilayer molded product, it is excellent in heat resistance, luminance, chromaticity, and diffusion rate.

[0018] The content of styrenic monomer units in the styrenic polymer B is specifically, for example, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100% by mass, and it may also be within the range between any two of the values exemplified herein. Further, the content of (meth)acrylic acid units in the styrenic polymer B is specifically, for example, 0, 0.5, 1, 1.5, 2% by mass, and it may also be within the range between any two of the values exemplified herein. Further, the content of (meth)acrylate units in the styrenic polymer B is specifically, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and it may also be within the range between any two of the values exemplified herein.

[0019] Note that the B layer may be composed of two or more layers each constituted by the resin composition B, but preferably the B layer is composed of only one layer. The two or more layers constituting the B layer may have the same or different components of the composition constituting each layer as long as they are within the range of the above resin composition B.

[0020] Next, each monomer unit of the styrenic polymer A and the styrenic polymer B will be described. The styrenic monomer unit is a structural unit derived from the styrenic monomer used in the polymerization of the styrenic polymer. The styrenic monomer is styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, p-t-butylstyrene, etc., alone or as a mixture of two or more, and preferably styrene.

[0021] Further, the (meth)acrylic acid unit is a structural unit derived from the (meth)acrylic acid used in the polymerization of the styrenic polymer. The (meth)acrylic acid is acrylic acid, methacrylic acid, etc., and methacrylic acid is preferred.

[0022] Furthermore, the (meth)acrylic acid ester unit is a constituent unit derived from the (meth)acrylic acid ester used in the polymerization of the styrene-based polymer. The (meth)acrylic acid ester is an acrylic acid ester, a methacrylic acid ester, etc., with methacrylic acid ester being preferred. The (meth)acrylic acid ester is, for example, an alkyl (meth)acrylic acid ester. The number of carbon atoms in the alkyl group of the alkyl ester is, for example, 1 to 30, preferably 1 to 10, and more preferably 1 to 5. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, isomiristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, etc. Methyl methacrylate is particularly preferred among (meth)acrylic acid esters.

[0023] Styrene polymers A and B may have constituent units derived from styrene monomers and monomers copolymerizable with (meth)acrylic acid (and even (meth)acrylic acid esters), to the extent that they do not impair the effects of the present invention. The monomer units used in styrene polymers A and B can be independently selected from the above monomer units, but they may also be the same as each other.

[0024] At least one of resin composition A and resin composition B preferably contains a light-diffusing agent. In one example, resin composition A contains a light-diffusing agent and resin composition B does not. In another example, resin composition B contains a light-diffusing agent and resin composition A does not. In yet another example, both resin composition A and resin composition B contain a light-diffusing agent.

[0025] The light diffusing agent can be any particles that have a refractive index different from that of styrene polymer A or styrene polymer B and have the effect of diffusing incident light. The light diffusing agent may be organic or inorganic particles. Examples of organic particles include styrene polymer particles, acrylic polymer particles, and siloxane polymer particles. Examples of inorganic particles include glass beads, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium dioxide particles, and talc. In particular, it is preferable that the light diffusing agent is at least one selected from the group consisting of styrene polymer particles, acrylic polymer particles, and siloxane polymer particles. The average particle diameter of the light diffusing agent (C) is preferably 1 to 20 μm. If the average particle diameter of the light diffusing agent (C) is less than 1 μm, the hue may deteriorate, and if it exceeds 20 μm, the light diffusing effect may not be sufficient. The light diffusing agents contained in resin composition A and resin composition B may be the same or different.

[0026] Resin composition B preferably contains quantum dots. In one example, resin composition B contains quantum dots, while resin composition A does not.

[0027] Quantum dots are light-emitting particles that emit light when exposed to light from a light source, and are also known as fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals. Resin composition B may contain two or more types of quantum dots.

[0028] Quantum dots can be various types of quantum dots, including known quantum dots, but inorganic particles are an example. The inorganic particles constituting the quantum dots may be particles with a core-shell structure. In particles with a core-shell structure, the composition of the inorganic compound constituting the shell is different from the composition of the inorganic compound constituting the core. Particles with a core-shell structure may have two or more shell layers. Furthermore, quantum dots are nanoparticles having a particle size of several nanometers to several tens of nanometers (for example, the particle size of the inorganic particles is 1 to 20 nm).

[0029] Examples of inorganic compounds that constitute the inorganic particles that make up quantum dots include CdS, CdSe, CdTe, CdTeSeS, ZnS, ZnSe, ZnSeS, ZnTe, ZnTeS, InP, PbSe, PbS, AgInS2, CuInS2, CsPbCl3, CsPb(Cl / Br)3, CsPbBr3, CsPb(Br / I)3, etc. Examples of core and shell combinations (core / shell) include CdSe / ZnS, InP / ZnS, CulnS2 / ZnS, PbSe / ZnS, PbS / ZnS, PbSe / PbS, CdSe / CdS, CdTe / CdS, CdTe / ZnS, etc. From the viewpoint of toxicity, the inorganic compounds that make up the inorganic particles (quantum dots) preferably do not contain Cd.

[0030] Furthermore, organic ligands may be arranged on the surface of the quantum dots. Examples of organic ligands include amine ligands, thiol ligands, fatty acid ligands, phosphine ligands, and phosphine oxide ligands.

[0031] Resin composition A may contain polymers (resin components) other than styrene polymer A, as long as the effects of the present invention are not impaired. However, when the total amount of polymers contained in resin composition A is taken as 100% by mass, it preferably contains 90 to 100% by mass of styrene polymer A, more preferably 95 to 100% by mass, and even more preferably (substantially) 100% by mass. The content of styrene polymer A, when the total amount of polymers contained in resin composition A is taken as 100% by mass, is specifically, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, or 100% by mass, and may be within the range of any two of the values ​​exemplified here.

[0032] Resin composition B may contain polymers other than styrene polymer B (resin components) as long as it does not impair the effects of the present invention. However, when the total amount of polymers contained in resin composition B is taken as 100% by mass, it preferably contains 95 to 100% by mass of styrene polymer B, more preferably 99 to 100% by mass, and even more preferably (substantially) contains 100% by mass. The content of styrene polymer B, when the total amount of polymers contained in resin composition B is taken as 100% by mass, is specifically, for example, 95, 96, 97, 98, 99, 99.5, or 100% by mass, and may be within the range of any two of the values ​​exemplified here.

[0033] Resin composition A preferably contains 0.1 to 25% by mass of a light diffusing agent, more preferably 0.5 to 10% by mass, based on 100% by mass of resin composition A. Sufficient light diffusing properties and brightness can be obtained within this range. Specifically, the content of the light diffusing agent in resin composition A is, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, and 25% by mass, and may be within the range of any two of the values ​​exemplified here.

[0034] Resin composition B preferably contains 0.1 to 25% by mass of a light diffusing agent, more preferably 0.5 to 10% by mass, based on 100% by mass of resin composition B. Sufficient light diffusing and brightness can be obtained within this range. Specifically, the content of the light diffusing agent in resin composition B is, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25% by mass, and may be within the range of any two of the values ​​exemplified here.

[0035] Resin composition B preferably contains 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, of quantum dots based on 100% by mass of resin composition B. Sufficient brightness and chromaticity can be obtained within this range. Specifically, the quantum dot content in resin composition B may be, for example, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within the range of any two of the values ​​exemplified here. Note that if two or more types of quantum dots are used (for example, when green quantum dots and red quantum dots are used in combination), the quantum dot content refers to the total amount of those dots.

[0036] Resin composition B preferably contains 0.01 to 10% by mass of green quantum dots per 100% by mass of resin composition B. Specifically, the content of green quantum dots in resin composition B may be, for example, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within the range of any two of the values ​​exemplified here. Here, green quantum dots can be, for example, core / shell type quantum dots with adjusted core particle size (e.g., CdSe, CdTe, CuInS2, etc.), or perovskite-type quantum dots with adjusted particle size and halide composition (e.g., CsPbBr3, etc.).

[0037] Resin composition B preferably contains 0.01 to 10% by mass of red quantum dots per 100% by mass of resin composition B. Specifically, the content of red quantum dots in resin composition B may be, for example, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10, and may be within the range of any two of the values ​​exemplified here. Here, red quantum dots can be, for example, core / shell type quantum dots with adjusted core particle size (e.g., CdSe, CdTe, CuInS2, etc.), or perovskite-type quantum dots with adjusted particle size and halide composition (e.g., CsPb(Br / I)3, etc.).

[0038] Resin composition A and resin composition B may each contain other additives such as flame retardants, lubricants, processing aids, antiblocking agents, antistatic agents, antifogging agents, antioxidants, softeners, plasticizers, inorganic reinforcing agents, crosslinking agents, pigments, dyes, etc., to the extent that they do not impair the effects of the present invention.

[0039] 1-2. Second Embodiment The multilayer molded article 2 according to the second embodiment of the present invention comprises an A1 layer, an A2 layer, a B layer, a C1 layer, and a C2 layer. The following description will focus on the differences from the first embodiment, and the description of the A1 layer, A2 layer, and B layer, which are common to both the first embodiment and the second embodiment, will be omitted.

[0040] As shown in Figure 2, layer 31 (layer C1) is directly provided on one side of layer 20 (layer B), and layer 32 (layer C2) is directly provided on the other side of layer 20 (layer B). Layer 11 (layer A1) is directly provided on the opposite side of layer 31 (layer C1) from the side where layer 20 (layer B) is provided. Layer 12 (layer A2) is directly provided on the opposite side of layer 32 (layer C2) from the side where layer 20 (layer B) is provided. In addition, other layers may be provided on the outside of layers A1 and A2.

[0041] The C1 and C2 layers are each composed of resin composition C. Resin composition C contains a styrene polymer C.

[0042] The styrene-based polymer C contains 35 to 70% by mass of styrene-based monomer units relative to 100% by mass of monomer units contained in the styrene-based polymer C. Furthermore, the styrene-based polymer C contains 30 to 65% by mass of (meth)acrylic acid ester units relative to 100% by mass of monomer units contained in the styrene-based polymer C. By setting the copolymer contained in resin composition C, which constitutes layers C1 and C2, the heat resistance, brightness, chromaticity, and diffusivity of the multilayer molded product are not impaired, and interlayer adhesion is also excellent.

[0043] The content of styrene monomer units in styrene polymer C is specifically, for example, 35, 40, 45, 50, 55, 60, 65, and 70% by mass, and may be within the range of any two of the values ​​exemplified here. Furthermore, the content of (meth)acrylic acid ester units in styrene polymer C is specifically, for example, 30, 35, 40, 45, 50, 55, 60, and 65% by mass, and may be within the range of any two of the values ​​exemplified here.

[0044] Next, the monomer units of the styrene polymer C will be described. The styrene monomer units are constituent units derived from the styrene monomers used in the polymerization of the styrene polymer. The styrene monomers are styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, pt-butylstyrene, etc., either alone or in mixtures of two or more, and styrene is preferred.

[0045] Furthermore, the (meth)acrylic acid ester unit is a constituent unit derived from the (meth)acrylic acid ester used in the polymerization of the styrene-based polymer. The (meth)acrylic acid ester is an acrylic acid ester, a methacrylic acid ester, etc., with methacrylic acid ester being preferred. The (meth)acrylic acid ester is, for example, an alkyl (meth)acrylic acid ester. The number of carbon atoms in the alkyl group of the alkyl ester is, for example, 1 to 30, preferably 1 to 10, and more preferably 1 to 5. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, isomiristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, etc. Methyl methacrylate is particularly preferred among (meth)acrylic acid esters.

[0046] Styrene polymers A and B may have constituent units derived from styrene monomers and monomers copolymerizable with (meth)acrylic acid esters, to the extent that they do not impair the characteristics of the present invention. The monomer units used in styrene polymer C can be selected independently from the monomer units used in styrene polymers A or B, but they may also be the same as those used in styrene polymers A and B.

[0047] Resin composition C may contain polymers other than styrene polymer C (resin components) as long as it does not impair the effects of the present invention. However, when the polymers contained in resin composition C are taken as 100% by mass, it preferably contains 90 to 100% by mass of styrene polymer C, more preferably 95 to 100% by mass, and even more preferably (substantially) contains 100% by mass. The content of styrene polymer C, when the polymers contained in resin composition A are taken as 100% by mass, is specifically, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, and 100% by mass, and may be within the range of any two of the values ​​exemplified here.

[0048] Resin composition C may contain other additives such as flame retardants, lubricants, processing aids, antiblocking agents, antistatic agents, antifogging agents, antioxidants, softeners, plasticizers, inorganic reinforcing agents, crosslinking agents, pigments, dyes, etc., to the extent that they do not impair the effects of the present invention.

[0049] 1-3. Light Diffuser An embodiment of the present invention is a light-diffusing plate comprising a multilayer molded product of the first or second embodiment described above.

[0050] The light diffuser may have a laminated ultraviolet absorbing layer containing an ultraviolet absorber or light stabilizer. The light diffuser may also have an antistatic layer. The antistatic layer can be provided, for example, by applying an antistatic agent to the surface of the light diffuser. The application of the antistatic agent suppresses the adhesion of dust and other particles due to static electricity after the light diffuser is installed in the backlight device, allowing it to be used for a long period without a decrease in brightness.

[0051] The light diffuser may have fine irregularities such as embossing formed on one or both sides of it. Furthermore, the light diffuser may have semicircular, elliptical, or prism-shaped lens forms formed on one or both sides of it.

[0052] 2. Manufacturing method of multilayer molded product (light diffuser plate) Resin composition A can be manufactured by adding necessary additives (light diffusers, other additives) to styrene polymer A. If resin composition A contains additives, some or all of the additives (type or amount) may be added during the polymerization of styrene polymer A. Alternatively, some or all of the additives (type or amount) may be dry blended and melt-kneaded in an extruder. Alternatively, some or all of the additives (type or amount) may be melt-kneaded together with a small amount of styrene polymer A (or another resin component) to create a pelletized masterbatch, and then the styrene polymer A and the masterbatch may be dry-blended and melt-kneaded. Similarly, resin compositions B and C can be manufactured by similarly adding necessary additives (light diffusers, quantum dots, other additives).

[0053] Polymerization methods for styrene polymers (styrene polymer A, styrene polymer B, styrene polymer C, etc.) include known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferable. Examples of solvents that can be used include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

[0054] During the polymerization of styrene-based polymers, polymerization initiators, chain transfer agents, crosslinking agents, and other polymerization aids can be used as needed. Radical polymerization initiators are preferred as polymerization initiators, and known and commonly used ones include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane; hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide; alkyl peroxides such as t-butylperoxyacetate and t-amylperoxyisononanoate; and t-butylcumylperoxide, di-t-butylperoxide, dicumylperoxide, and di-t-hexylperoxide. Examples of peroxy esters include dialkyl peroxides such as t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyethertetrakis(t-butyl peroxycarbonate), N,N'-azobis(cyclohexane-1-carbonitride), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile], and one or more of these can be used in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, and terpinolene.

[0055] In the case of continuous polymerization, styrene-based polymers can be produced by a method comprising a polymerization step, a defoliation step, and a granulation step.

[0056] First, in the polymerization process, known fully mixed stirring tanks or tower reactors are used to control the polymerization reaction by adjusting the polymerization temperature and other factors to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

[0057] The polymerization solution containing the polymer that has exited the polymerization process is transferred to the defoliation process, where unreacted monomers and polymerization solvent are removed. The defoliation process consists of a vacuum defoliation tank with a heater or a defoliation extruder with a vent. The molten polymer that has exited the defoliation process is transferred to the granulation process. In the granulation process, the molten resin is extruded in strand form from a porous die and processed into pellets using a cold-cut method, an air-hot-cut method, or an underwater-hot-cut method.

[0058] Multilayer molded products (light diffusing plates) can be manufactured by molding and laminating resin compositions (resin composition A, resin composition B, resin composition C, and other resin compositions) using various methods such as extrusion molding and injection molding, but are preferably manufactured by extrusion molding.

[0059] Examples of extrusion molding include a method in which a resin composition is melt-kneaded using a single-screw or twin-screw extruder, continuously extruded through a T-die, and then cooled and solidified using a cooling roll unit. The extrusion molding is preferably co-extrusion molding, which involves lamination by co-extrusion. For example, when molding the multilayer molded product 1 shown in Figure 1, resin composition A and resin composition B are melt-kneaded separately and then continuously co-extruded through a T-die to form two types and three layers. Similarly, when molding the multilayer molded product 2 shown in Figure 2, resin composition A, resin composition B, and resin composition C are melt-kneaded separately and then continuously co-extruded through a T-die to form three types and five layers.

[0060] When forming an uneven surface on the surface of a light diffuser, a transfer mold can be provided on the surface of a cooling roll, and any desired uneven shape can be formed by changing the shape of the transfer mold. Furthermore, when laminating a surface layer on both sides or one side of the light diffuser, methods such as co-extrusion, bonding, heat bonding, solvent bonding, casting, and surface coating can be employed. [Examples]

[0061] The present invention will be described in more detail below with reference to examples. These examples are illustrative and do not limit the scope of the present invention. In the table, St, MAA, and MMA refer to styrene, methacrylic acid, and methyl methacrylate (or monomer units derived therefrom), respectively.

[0062] [Production of styrene copolymers P-1 to P-12] A polymerization process was constructed by connecting the first and second reactors, which are fully mixed stirred tanks, and the third reactor, which is a plug-flow type reactor with a static mixer, in series, and styrene resin was produced under the conditions shown in Table 1. The capacities of each reactor were 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition listed in Table 1, and the raw material solution was continuously supplied to the first reactor (P-11 and P-12 are the second reactor) at the flow rate shown in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor (P-11 and P-12 are the second reactor) to the concentration shown in Table 1 (mass-based concentration relative to the total amount of raw material styrene, methacrylic acid, and methyl methacrylate), and then uniformly mixed. The polyoxyethylene lauryl ether and polymerization initiator listed in Table 1 are as follows. Polyoxyethylene lauryl ether: Emulgen 109P manufactured by Kao Corporation was used. Polymerization initiator-1:1,1-di(t-butylperoxy)cyclohexane (Perhexa C, manufactured by NOF Corporation) was used. Polymerization initiator-2: 2,2-di(4,4-t-butylperoxycyclohexyl)propane (Pertetra A, manufactured by NOF Corporation) was used. In the third reactor, a temperature gradient was created along the direction of the flow, and the temperature was adjusted so that it reached the levels shown in Table 1 at the intermediate and outlet sections. Next, the polymer-containing solution continuously extracted from the third reactor was introduced into a vacuum defloration tank with a preheater, consisting of two stages in series. The preheater temperature was adjusted to the resin temperature shown in Table 1, and the pressure was adjusted to the pressure shown in Table 1 to separate the unreacted styrene, methacrylic acid, methyl methacrylate, and ethylbenzene. The resulting mixture was then extruded in strand form through a porous die, and the strands were cooled and cut using a cold-cut method to form pellets.

[0063] [Table 1]

[0064] [Examples 1-10, Comparative Examples 1-8] <Preparation of resin composition A> Styrene polymer A and a light diffusing agent (Tospar 130, manufactured by Momentive Performance Materials) were mixed in the proportions shown in Table 2 or Table 3. The mixture was then kneaded at a temperature of 230°C in a 26 mm diameter twin-screw extruder to form pellets of resin composition A.

[0065] <Preparation of resin composition B> A hexane dispersion of a styrene polymer and perovskite-based green quantum dots (CsPbBr3) and a hexane dispersion of perovskite-based red quantum dots (CsPb(Br / I)3) were mixed in the proportions shown in Table 2 or Table 3, and the dispersion was applied to the styrene polymer. Subsequently, the hexane dispersion was evaporated to obtain a styrene polymer with quantum dots coated on its surface. The styrene polymer coated with the quantum dots obtained above and a light diffusing agent (Tospar 130, manufactured by Momentive Performance Materials) were mixed in the proportions shown in Table 2 or Table 3. The mixture was then kneaded in a 26 mm diameter twin-screw extruder at a temperature of 230°C to form pellets of resin composition B.

[0066] <Resin composition C> Resin composition C used styrene copolymer pellets as shown in Table 2 or Table 3.

[0067] <Manufacturing of multilayer sheets (multilayer molded products)> Multilayer sheets of each composition were created using resin compositions A to C in a T-die type multilayer extruder. The multilayer extruder used was a test extruder consisting of one 30mmφ full-flight screw single-screw extruder for layers A1 and A2, one 65mmφ full-flight screw single-screw extruder for layer B, and one 30mmφ full-flight screw single-screw extruder for layers C1 and C2, where the molten resins of each layer were combined in a feed block for multilayer formation. The cylinder temperature for each layer during sheet formation was 230°C, and the thickness of each layer was molded to be 0.4mm for layers A1 and A2, 1.0mm for layer B, and 0.1mm for layers C1 and C2. If layers C1 and C2 were not included, the thicknesses were molded to be 0.4mm for layers A1 and A2 and 1.2mm for layer B.

[0068] [Evaluation of multilayer sheets (multilayer molded products)] The evaluation methods and criteria for each evaluation item are explained below. The results are shown in Tables 2 and 3.

[0069] <Heat resistance> Multilayer molded products were cut to 80 mm in the MD direction and 10 mm in the TD direction, and the load deflection temperature was measured with the two layers stacked. The measurement conditions were based on JIS K-7191, with a heating rate of 120°C / hr, a bending stress of 0.45 MPa, and a support distance of 64 mm. The results were then evaluated according to the following criteria. A: Load deflection temperature is 95°C or higher B: Load deflection temperature is 90°C or higher, but less than 95°C. C: Load deflection temperature is 85°C or higher, but less than 90°C. D: Load deflection temperature is less than 85°C

[0070] <Brightness / Chromaticity> Multilayer molded products were cut to 300 mm in the MD direction (Machine Direction: sheet feeding direction) and 200 mm in the TD direction (Transverse Direction: direction perpendicular to the MD direction). These were then mounted as light diffusers in a 20-inch direct-lit backlight device equipped with blue LEDs, and the luminance and chromaticity were measured using a Topcon Techno House colorimeter (BM-7A) with the blue LEDs illuminated. The products were then evaluated according to the following criteria. (brightness) A: Brightness is 5000 cd / m² 2 That's all. B: Brightness is 4500 cd / m² 2 More than 5000cd / m 2 less than C: Brightness of 4000 cd / m² 2 More than 4500cd / m 2 less than D: Brightness is 4000 cd / m² 2 less than (chromaticity) A: Both the x and y chromaticity coordinates are between 0.32 and 0.34 B: Either the x-chromaticity coordinate or the y-chromaticity coordinate is 0.30 or greater, and less than 0.32. C: Either the x-chromaticity coordinate or the y-chromaticity coordinate is 0.28 or greater, but less than 0.30. D: Either the x-chromaticity coordinate or the y-chromaticity coordinate is less than 0.28.

[0071] <Diffusion rate> The multilayer molded product was cut to 50mm x 50mm, and the light transmittance I0 at a receiving angle of 0° and I at a receiving angle of 70° were measured using a variable angle photometer (GC5000L) manufactured by Nippon Denshoku Industries Co., Ltd. 70 The following was calculated by measuring and using the following formula. Diffusion rate (%) = (I 70 / I0)×100 The evaluation was then conducted according to the following criteria. A: Diffusion rate of 25% or more B: Diffusion rate of 22% or more, but less than 24% C: Diffusion rate of 19% or more, less than 22% D: Diffusion rate less than 19%

[0072] <Interlayer adhesion> Ten test specimens were prepared by cutting multilayer molded products to 100mm x 100mm, and a heat cycle test was conducted. The test conditions consisted of standing at -20°C for 30 minutes, followed by standing at 70°C for 30 minutes, with one cycle being performed for 100 cycles. The results were then evaluated according to the following criteria. A: Zero test specimens showed delamination. B: 1 to 4 test specimens in which delamination was confirmed. C: 5 to 7 test specimens in which delamination was confirmed. D: Eight or more test specimens in which delamination was confirmed.

[0073] [Table 2]

[0074] [Table 3] [Explanation of Symbols]

[0075] 1,2:Multilayer molded product 11:A1 layer 12:A2 layer 20 :B layer 31:C1 layer 32:C2 layer

Claims

1. It comprises layer A1, layer A2, and layer B, The A1 layer is provided on one side of the B layer directly or via another layer, and the A2 layer is provided on the other side of the B layer directly or via another layer. The A1 layer and the A2 layer are each composed of resin composition A. The aforementioned layer B is composed of resin composition B, The resin composition A comprises a styrene polymer A, The styrene polymer A is 50 to 97% by mass of styrene monomer units, (Meth)acrylic acid units 3 to 15% by mass, It contains 0 to 35% by mass of (meth)acrylic acid ester units, The aforementioned resin composition B includes a styrene polymer B, The styrene polymer B is 88 to 100% by mass of styrene monomer units, (Meth)acrylic acid units 0-2% by mass, (Meth)acrylic acid ester units 0 to 10% by mass, Multilayer molded product.

2. It further includes a C1 layer and a C2 layer, The C1 layer is provided directly on one side of the B layer, and the C2 layer is provided directly on the other side of the B layer. The A1 layer is provided directly on the opposite side of the C1 layer from the side on which the B layer is provided. The A2 layer is provided directly on the opposite side of the C2 layer from the side on which the B layer is provided. The C1 layer and the C2 layer are each composed of resin composition C. The resin composition C comprises a styrene polymer C, The styrene-based polymer C is 35-70% by mass of styrene monomer units, (Meth)acrylic acid ester units comprising 30 to 65% by mass, A multilayer molded article according to claim 1.

3. The resin composition B comprises quantum dots, as described in claim 1.

4. The multilayer molded article according to claim 1, wherein at least one of the resin composition A and the resin composition B contains a light diffusing agent.

5. The multilayer molded article according to claim 1, wherein the resin composition A contains 0.1 to 25% by mass of a light diffusing agent based on 100% by mass of the resin composition A.

6. The multilayer molded article according to claim 1, wherein the resin composition B contains 0.01 to 10% by mass of quantum dots based on 100% by mass of the resin composition B.

7. The multilayer molded article according to claim 1, wherein the resin composition B comprises 0.1 to 25% by mass of a light diffusing agent and 0.01 to 10% by mass of quantum dots, based on 100% by mass of the resin composition B.

8. A light-diffusing plate comprising a multilayer molded product according to any one of claims 1 to 7.

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