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Abstract

To provide a sheet containing styrene resin with excellent impact resistance. [Solution] A sheet comprising a first biaxially oriented layer, an adhesive layer provided on the first biaxially oriented layer, and a second biaxially oriented layer provided on the adhesive layer, wherein the first and second biaxially oriented layers are biaxially oriented layers of styrene resin.

Description

[Technical Field]

[0001] The present disclosure relates to a sheet. [Background Art]

[0002] Sheets made of styrenic resin are widely used in fields such as packaging containers. Studies have been ongoing to improve the impact resistance of styrenic resin sheets. For example, Patent Document 1 discloses a styrenic resin composition containing a specific styrenic resin and specific fine particles, in order to solve the problem of providing a molded article formed of a styrenic resin composition excellent in impact strength. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 07-323474 [Summary of Invention] [Problem to be Solved by the Invention]

[0004] Resin materials are lightweight and have transparency, so their use as alternatives to glass materials for displays of electronic devices, building materials, automobiles and the like has also been studied. In order to accommodate such expansion of applications, demands for improved impact resistance for sheets containing styrenic resin have been increasing. Therefore, an object of one aspect of the present disclosure is to provide a sheet containing a styrenic resin that is excellent in impact resistance. [Means for Solving the Problem]

[0005] The inventors of the present invention have found that a sheet having excellent impact resistance can be obtained by laminating a plurality of biaxially stretched layers containing a styrenic resin via an adhesive layer. The present disclosure provides the following [1] to [3] in some aspects. [1] A sheet comprising a first biaxially oriented layer, an adhesive layer provided on the first biaxially oriented layer, and a second biaxially oriented layer provided on the adhesive layer, wherein the first biaxially oriented layer and the second biaxially oriented layer are biaxially oriented layers of styrene resin. [2] The sheet according to [1], wherein the difference between the refractive index of the biaxially oriented layer of the styrene resin and the refractive index of the adhesive layer is 0.08 or less. [3] The sheet according to [1] or [2], wherein the styrene resin comprises styrene monomer units and (meth)acrylic acid ester monomer units. [Effects of the Invention]

[0006] According to one aspect of this disclosure, a sheet containing a styrene-based resin with excellent impact resistance is provided. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the sheet. [Modes for carrying out the invention]

[0008] The embodiments of this disclosure are described in detail below. This disclosure is not limited to the embodiments described below.

[0009] Figure 1 is a schematic cross-sectional view showing one embodiment of the sheet. The sheet (laminated sheet) 1 shown in Figure 1 comprises a first biaxially oriented layer 11, an adhesive layer 12 provided on the first biaxially oriented layer 11, and a second biaxially oriented layer 13 provided on the adhesive layer 12. The first biaxially oriented layer 11 and the second biaxially oriented layer 13 are biaxially oriented layers of styrene resin.

[0010] The styrene-based resin contained in the biaxially stretched layer of the styrene-based resin is a polymer mainly containing styrene-based monomer units as monomer units. The styrene-based monomer may be styrene (unsubstituted styrene) or substituted styrene. Unsubstituted styrene refers to styrene that does not have substituents (styrene that does not have functional groups other than one vinyl group). Substituted styrene refers to styrene in which at least one of the hydrogen atoms on the benzene ring and the hydrogen atoms constituting the vinyl group is substituted with substituents such as alkyl groups and halogen groups.

[0011] Examples of substituted styrenes include alkylstyrene, halogenated styrene, nitrostyrene, acetylstyrene, and methoxystyrene.

[0012] Alkylstyrene may be, for example, an alkylstyrene having one, two, or three alkyl groups. Examples of alkylstyrene having one alkyl group include α-alkylstyrene such as α-methylstyrene, o-alkylstyrene such as o-methylstyrene and o-ethylstyrene, m-alkylstyrene such as m-methylstyrene and m-ethylstyrene, and p-alkylstyrene such as p-methylstyrene, p-ethylstyrene and p-tert-butylstyrene.

[0013] Examples of alkylstyrenes having two alkyl groups include 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, and 4,α-dimethylstyrene (1-methyl-4-isopropenylbenzene). An example of alkylstyrene having three alkyl groups is 2,4,6-trimethylstyrene.

[0014] Examples of halogenated styrenes include fluorostyrene, chlorostyrene, dichlorostyrene, bromostyrene, dibromostyrene, and iodostyrene.

[0015] The styrene monomers described above may each be derived from chemical recycling. For example, styrene derived from chemical recycling can be obtained by thermally decomposing a polymer containing styrene as a monomer unit.

[0016] Furthermore, the styrene monomers described above may each be independently derived from biomass. In this specification, "biomass-derived" means at least one of the following: actually containing biomass-derived carbon, and being assigned biomass-derived characteristics by the mass balance method. Here, the mass balance method refers to "a method in which, in the processing and distribution process from raw materials to products, when a raw material with certain characteristics (e.g., biomass-derived raw material) is mixed with a raw material that does not have those characteristics (e.g., petroleum-derived raw material), the characteristics of a portion of the product are assigned according to the amount of raw material with those characteristics input" ("Roadmap for the Introduction of Bioplastics" (Ministry of the Environment, Ministry of Economy, Trade and Industry, Ministry of Agriculture, Forestry and Fisheries, Ministry of Education, Culture, Sports, Science and Technology, established January 2021)).

[0017] According to the mass balance method, biomass-derived characteristics can be assigned to individual products, regardless of the actual biomass content in each product, within a range corresponding to the amount of biomass-derived raw materials used. Certification systems are used to ensure the reliability of the assignment of biomass-derived characteristics. Styrene monomers may be certified by any of the certification systems as styrene monomers to which biomass-derived characteristics have been assigned according to the mass balance method. Examples of certification systems include international certification systems such as ISCC PLUS, ISCC EU, RSB Global Advanced Products, and REDcert.

[0018] The styrene monomer may contain one or more of the above-mentioned styrene monomers. The styrene monomer preferably contains at least one of styrene and α-methylstyrene, and more preferably contains styrene. The styrene monomer may also contain styrene monomers derived from chemical recycling, or may consist only of styrene monomers derived from chemical recycling. The styrene monomer may also contain styrene monomers derived from biomass, or may consist only of styrene monomers derived from biomass. The styrene monomer may consist only of styrene monomers that are neither derived from chemical recycling nor biomass, or may contain styrene monomers that are neither derived from chemical recycling nor biomass, and at least one of styrene monomers derived from chemical recycling and styrene monomers derived from biomass.

[0019] Styrene resins may contain only styrene monomer units as monomer units, or they may contain monomer units other than styrene monomer units. The content of styrene monomer units may be 3% by mass or more, 5% by mass or more, 8% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 23% by mass or more, based on the total mass of the styrene resin, and may be 100% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 45% by mass or less. If the styrene resin contains styrene units, the content of styrene units may be within the above numerical range as the content of styrene monomer units.

[0020] The styrene resin may further contain unsaturated carboxylic acid ester monomer units. An example of an unsaturated carboxylic acid ester monomer is a (meth)acrylic acid ester monomer. An example of a (meth)acrylic acid ester monomer is an alkyl (meth)acrylate. In an alkyl (meth)acrylate, the number of carbon atoms in the alkyl group (alkyl group other than the (meth)acryloyl group) may be 1 or more, and may be 20 or less, 16 or less, 14 or less, 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, or 4 or less.

[0021] Examples of alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and the like. The unsaturated carboxylic acid ester monomer may include one or more of these monomers. From the viewpoint of further improving the transparency of the sheet 1, the styrenic resin may contain a (meth)acrylate monomer unit, and in particular, may contain a methyl (meth)acrylate unit.

[0022] From the viewpoint of further improving the transparency of the sheet 1, the content of the unsaturated carboxylic acid ester monomer unit may be 10% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, or 70% by mass or more, based on the total mass of the styrenic resin. From the viewpoint of further improving the impact resistance of the sheet 1, the content may be less than 100% by mass, 98% by mass or less, 96% by mass or less, or 95% by mass or less based on the total mass of the styrenic resin. When the styrenic resin contains a methyl (meth)acrylate unit, the content of the methyl (meth)acrylate unit may fall within the numerical range described above for the content of the unsaturated carboxylic acid ester monomer unit.

[0023] The styrenic resin may or may not further contain monomer units other than the styrenic monomer and the unsaturated carboxylic acid ester monomer. Examples of other monomers include vinyl cyanide monomers, unsaturated carboxylic acid monomers, carboxylic anhydride monomers, vinyl carboxylate monomers, and the like.

[0024] Examples of vinyl cyanide monomers include (meth)acrylonitrile and cyano(meth)acrylate. Examples of unsaturated carboxylic acid monomers include (meth)acrylic acid, fumaric acid, maleic acid, and itaconic acid. An example of a carboxylic anhydride monomer is maleic anhydride. An example of a vinyl carboxylate monomer is vinyl acetate.

[0025] The content of vinyl cyanide monomer units, unsaturated carboxylic acid monomer units, carboxylic anhydride monomer units, and vinyl carboxylate monomer units may be 0% by mass or more, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less, based on the total mass of the styrene resin.

[0026] Styrene resins do not need to contain butadiene units as monomer units, nor do they need to contain diene monomer units (for example, conjugated diene units such as butadiene units, isoprene units, and chloroprene units). Here, "styrene resin does not contain a certain monomer unit" means that the styrene resin does not contain that monomer unit at all, or that it contains it only as an unavoidable impurity.

[0027] The styrene-based resin may be, for example, a polymer of styrene monomers, or a copolymer of styrene monomers and (meth)acrylic acid ester monomers.

[0028] A polymer of styrene monomers is a polymer that mainly contains only one or more types of styrene monomer units as monomer units. A polymer of styrene monomers is preferably a homopolymer of one type of styrene monomer, and more preferably a homopolymer of styrene.

[0029] In polymers of styrene monomers, the content of monomer units other than styrene monomer units may be 15% by mass or less, 10% by mass or less, 8% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the total mass of the polymer of styrene monomers.

[0030] A copolymer of a styrene monomer and a (meth)acrylic acid ester monomer is a copolymer that mainly contains only one or more styrene monomer units and one or more (meth)acrylic acid ester monomer units as monomer units. Preferably, the copolymer of a styrene monomer and a (meth)acrylic acid ester monomer is a copolymer of one styrene monomer and one (meth)acrylic acid ester monomer, and more preferably, a copolymer of styrene and methyl (meth)acrylate.

[0031] In a copolymer of a styrene monomer and a (meth)acrylic acid ester monomer, the content of monomer units other than styrene monomer units and (meth)acrylic acid ester monomer units may be 10% by mass or less, 8% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the total mass of the copolymer of the styrene monomer and the (meth)acrylic acid ester monomer.

[0032] The styrene resin may be a styrene resin modified with rubber (hereinafter also referred to as "rubber-modified styrene resin") or a styrene resin that is not modified with rubber (hereinafter also referred to as "non-rubber-modified styrene resin"). A rubber-modified styrene resin is one in which particles of a rubbery polymer are dispersed in a matrix of a styrene polymer. An example of a rubber-modified styrene resin is a diene-based rubber-modified styrene resin containing a rubbery diene copolymer. A diene-based rubber-modified styrene resin can be obtained, for example, by dissolving a rubbery diene polymer in a styrene monomer or a mixture of a styrene monomer and another monomer (for example, an unsaturated carboxylic acid ester monomer) and polymerizing (preferably by graft polymerization). From the viewpoint of excellent transparency, the styrene resin is preferably a non-rubber-modified styrene resin.

[0033] The weight-average molecular weight (Mw) of styrene resins may be 30,000 or more, 40,000 or more, or 50,000 or more, and may be 300,000 or less, 280,000 or less, 260,000 or less, 240,000 or less, 220,000 or less, 200,000 or less, 180,000 or less, 160,000 or less, 140,000 or less, 120,000 or less, or 100,000 or less. The Mw of styrene resins refers to the value determined by the following method.

[0034] In this specification, Mw refers to the value calculated by GPC (gel permeation chromatography) on a polystyrene basis. Specifically, it refers to the value measured under the following conditions. Device: Manufactured by Shodex Corporation, Product name: "Shodex SYSTEM-21" Column: PLgel MIXED-B Measurement temperature: 40℃ Solvent: tetrahydrofuran Flow rate: 1.0mL / min Detection method: RI Sample concentration: 0.2% by mass Injection volume: 100μL Calibration curve: Using standard polystyrene (manufactured by Polymer Laboratories), the relationship between elution time and elution amount is converted to molecular weight to determine various average molecular weights.

[0035] The melt flow rate (MFR) of styrene resins may be 0.3 g / 10 min or higher, 0.5 g / 10 min or higher, 0.7 g / 10 min or higher, 1 g / 10 min or higher, 1.3 g / 10 min or higher, 1.6 g / 10 min or higher, 2 g / 10 min or higher, 2.4 g / 10 min or higher, 2.8 g / 10 min or higher, 3.2 g / 10 min or higher, or 3.6 g / 10 min or higher, and may be 20 g / 10 min or lower, 15 g / 10 min or lower, 10 g / 10 min or lower, 8 g / 10 min or lower, or 6 g / 10 min or lower. The MFR of styrene resins refers to the value measured in accordance with JIS K 7210-1:2014 under conditions of 200°C and a load of 5 kg.

[0036] In this specification, "biaxially oriented styrene resin layer" refers to a layer formed by biaxially oriented a resin composition whose main component is a styrene resin. The styrene resin content in the biaxially oriented layer may be 80% or more by mass, 83% or more by mass, 86% or more by mass, 88% or more by mass, 90% or more by mass, 92% or more by mass, 94% or more by mass, 95% or more by mass, 96% or more by mass, 97% or more by mass, 98% or more by mass, or 99% or more by mass, based on the total mass of the biaxially oriented layer. The biaxially oriented layer may consist solely of styrene resin.

[0037] Examples of other components that may be included in the biaxially stretched layer of styrene resin, besides the styrene resin itself, include antioxidants, gelling inhibitors (e.g., polyoxyethylene alkyl ether (POE)), ultraviolet absorbers, light stabilizers, lubricants, plasticizers, colorants, antistatic agents, flame retardants, compatibilizers, mold release agents, antifogging agents, softeners, fluidity modifiers, leveling agents, defoamers, foaming agents, thickeners, surfactants, light-shielding agents, matting agents, mineral oil, reinforcing fibers such as glass fibers, carbon fibers and aramid fibers, and fillers such as talc, silica, mica, and calcium carbonate.

[0038] For example, if the biaxially oriented layer of styrene resin contains a diene-rubber modified styrene resin, the biaxially oriented layer of styrene resin may contain a rubbery diene polymer (diene-rubber component (hereinafter also simply referred to as "rubber component"). The content of the rubber component in the biaxially oriented layer of styrene resin may be 0% by mass or more, based on the total mass of the biaxially oriented layer of styrene resin, and may be 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.6% by mass or less, 0.3% by mass or less, or 0.1% by mass or less, from the viewpoint of having better transparency of sheet 1.

[0039] The rubber content of a biaxially stretched styrene resin can be measured by dissolving 0.25 g of a biaxially stretched styrene resin in 50 ml of chloroform, adding iodine monochloride to react with the double bonds in the rubber component, then adding potassium iodide to convert the remaining iodine monochloride into iodine, and finally back-titrating with sodium thiosulfate (iodine monochloride method). The analytical method is described, for example, in "(3) Rubber Content" on page 659 of "New Edition Polymer Analysis Handbook," edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, Kinokuniya Shoten (1995 edition), and can be measured using this method.

[0040] The refractive index of the biaxially oriented layer of the styrene resin may be 1.35 or higher, 1.42 or higher, 1.48 or higher, or 1.51 or higher, and may be 1.7 or lower, 1.62 or lower, 1.58 or lower, or 1.55 or lower. In this specification, the refractive index refers to the value obtained by the critical angle method under the conditions of a sample temperature of 23°C and a measurement wavelength of 589 nm. The composition and refractive index of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 in sheet 1 may be the same as those of each other.

[0041] The stretch ratios in the MD (Machine Direction; sheet flow direction) and TD (Transverse Direction; direction perpendicular to the sheet flow direction) of the biaxially stretched layer of styrene resin may be 1.2 times or more, 1.5 times or more, 1.8 times or more, or 2.0 times or more, and may be 5.0 times or less, 4.0 times or less, 3.5 times or less, or 3.0 times or less, respectively. The stretch ratios of MD and TD may be the same or different.

[0042] When the MD stretching ratio of a biaxially oriented layer of styrene resin is m and the TD stretching ratio is n, the surface magnification ratio, expressed as m × n, may be 1.4 times or more, 2 times or more, 3 times or more, or 4 times or more, and may be 25 times or less, 16 times or less, 13 times or less, or 10 times or less.

[0043] In this specification, the stretch ratio refers to the percentage change in the biaxially stretched layer of a test specimen before and after heating, specifically as follows: Stretch ratio = Y / Z (unit: [times]) This refers to the value calculated by the following formula. In this formula, Y represents the length [mm] of the straight line drawn on the MD or TD of the biaxially oriented layer before heating, and Z represents the length [mm] of the straight line after the test piece has been left to shrink for 60 minutes in an oven at a temperature 30°C higher than the Vicat softening point of the biaxially oriented layer, as measured in accordance with JIS K7206. Drawing a straight line on the MD yields the stretch ratio of the MD, and drawing a straight line on the TD yields the stretch ratio of the TD.

[0044] The thickness of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 may be 0.01 mm or more, 0.03 mm or more, 0.05 mm or more, or 0.06 mm or more, and may be 1.0 mm or less, 0.8 mm or less, 0.6 mm or less, 0.4 mm or less, or 0.2 mm or less. In sheet 1, the thicknesses of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 are the same, but in another embodiment, the thicknesses of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 may be different.

[0045] The ratio of the sum of the thicknesses of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 to the sum of the thicknesses of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13 (sum of the thicknesses of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 / sum of the thicknesses of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13) may be 50% or more, 60% or more, or 70% or more, and may be 99% or less, 97% or less, or 95% or less.

[0046] The adhesive layer 12 is composed of an adhesive. As the adhesive, any adhesive capable of bonding styrene resins together can be used as appropriate. Examples of adhesives include ethylene thiol adhesives, acrylic adhesives, epoxy adhesives, silicone adhesives, vinyl alcohol adhesives, polyurethane adhesives, polyester adhesives, polyether adhesives, phenolic adhesives, polyimide adhesives, and rubber adhesives such as SBR, SIS, and SBS. The adhesive layer 12 may contain one or more of the above-mentioned adhesives.

[0047] The refractive index of the adhesive layer 12 may be 1.35 or higher, 1.42 or higher, 1.48 or higher, or 1.50 or higher, and may be 1.7 or lower, 1.62 or lower, 1.58 or lower, or 1.55 or lower. The refractive index of the adhesive layer can be adjusted by adjusting the type of main component constituting the adhesive and by adjusting the content of the refractive index adjusting agent (for example, nanoparticles of metal oxides such as zirconia).

[0048] The refractive index of the biaxially oriented layer of styrene resin and the refractive index of the adhesive layer 12 may be the same. The refractive index of the biaxially oriented layer of styrene resin may be smaller or larger than the refractive index of the adhesive layer 12. The difference between the refractive index of the biaxially oriented layer of styrene resin and the refractive index of the adhesive layer 12 may be 0.00 or more, and from the viewpoint of having better transparency of sheet 1, it may be 0.80 or less, 0.50 or less, 0.30 or less, 0.20 or less, 0.10 or less, 0.08 or less, 0.06 or less, 0.04 or less, or 0.02 or less.

[0049] The thickness of the adhesive layer 12 may be 0.001 mm or more, 0.005 mm or more, 0.01 mm or more, or 0.02 mm or more, and may be 0.1 mm or less, 0.08 mm or less, or 0.06 mm or less.

[0050] The ratio of the thickness of the adhesive layer 12 to the sum of the thicknesses of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13 (thickness of adhesive layer 12 / sum of the thicknesses of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13) may be 1% or more, 3% or more, or 5% or more, and may be 50% or less, 40% or less, or 30% or less.

[0051] In sheet 1, the main surface areas of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13 are all equal. In another embodiment, these areas may differ from each other. For example, the main surface area of ​​the adhesive layer 12 may be smaller than the main surface areas of the first biaxially oriented layer 11 and the second biaxially oriented layer 13.

[0052] The thickness of sheet 1 may be 0.1 mm or more, 0.2 mm or more, or 0.3 mm or more, and may be 10 mm or less, 7 mm or less, 5 mm or less, or 3 mm or less.

[0053] Sheet 1 consists of a first biaxially oriented layer 11, an adhesive layer 12, and a second biaxially oriented layer 13. The composition of the sheet is not limited to this, and it may further include other layers. The sheet may include biaxially oriented layers other than the first biaxially oriented layer 11 and the second biaxially oriented layer 13, and may include adhesive layers other than the adhesive layer 12.

[0054] The sheet may, for example, comprise a first biaxially oriented layer, a first adhesive layer provided on the first biaxially oriented layer, a second biaxially oriented layer provided on the first adhesive layer, a second adhesive layer provided on the second biaxially oriented layer, and a third biaxially oriented layer provided on the second adhesive layer. Hereinafter, this sheet will also be referred to as a "5-layer sheet." The 5-layer sheet may further comprise a third adhesive layer provided on the third biaxially oriented layer and a fourth biaxially oriented layer provided on the third adhesive layer. Hereinafter, the 5-layer sheet in this case will also be referred to as a "7-layer sheet." In the 5-layer sheet, at least three biaxially oriented layers are laminated via adhesive layers, and if the 5-layer sheet is a 7-layer sheet, at least four biaxially oriented layers are laminated via adhesive layers; however, the number of biaxially oriented layers (and adhesive layers) is not limited to these. In a five-layer sheet, five or more biaxially oriented layers may be laminated via an adhesive layer. Although not described in detail here, a five-layer sheet may also be a 15-layer sheet in which eight biaxially oriented layers are laminated via an adhesive layer, or a 17-layer sheet in which nine biaxially oriented layers are laminated via an adhesive layer, and so on.

[0055] In the five-layer sheet, the first biaxially oriented layer and the second biaxially oriented layer are biaxially oriented layers of the styrene-based resin described above. The details of the first biaxially oriented layer and the second biaxially oriented layer in the sheet may be the same as those described above for the first biaxially oriented layer 11 and the second biaxially oriented layer 13, respectively. The details of the first adhesive layer may be the same as those described above for the adhesive layer 12.

[0056] Furthermore, the details of the biaxially oriented layers in the five-layer sheet, other than the first and second biaxially oriented layers, may be independently the same as those described above for the first biaxially oriented layer 11 and the second biaxially oriented layer 13. More specifically, the third and fourth biaxially oriented layers may be independently the biaxially oriented layers of the styrene-based resin described above. The details of the third and fourth biaxially oriented layers may be independently the same as those described above for the first biaxially oriented layer 11 and the second biaxially oriented layer 13. The details of the adhesive layers in the five-layer sheet, other than the first adhesive layer, may be independently the same as those described above for the adhesive layer 12. More specifically, the details of the second and third adhesive layers may be independently the same as those described above for the adhesive layer 12.

[0057] In a five-layer sheet, the composition and refractive index of the first biaxially oriented layer, the second biaxially oriented layer, and the third biaxially oriented layer may all be the same. Similarly, in a seven-layer sheet, the composition and refractive index of the first biaxially oriented layer, the second biaxially oriented layer, the third biaxially oriented layer, and the fourth biaxially oriented layer may all be the same. In a five-layer sheet, the composition and refractive index of all biaxially oriented layers may all be the same.

[0058] In a five-layer sheet, the thickness and main surface area of ​​the first, second, and third biaxially oriented layers may all be the same, or they may be different. In a seven-layer sheet, the thickness and main surface area of ​​the first, second, third, and fourth biaxially oriented layers may all be the same, or they may be different. In a five-layer sheet, the thickness and main surface area of ​​all biaxially oriented layers may all be the same.

[0059] In a five-layer sheet, the ratio of the sum of the thicknesses of the first biaxially oriented layer, the second biaxially oriented layer, and the third biaxially oriented layer to the sum of the thicknesses of the first biaxially oriented layer, the first adhesive layer, the second biaxially oriented layer, and the third biaxially oriented layer may be within the range described above, as the ratio of the sum of the thicknesses of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 to the sum of the thicknesses of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13 in sheet 1. In a seven-layer sheet, the ratio of the total thickness of the first biaxially oriented layer, the first adhesive layer, the second biaxially oriented layer, the second adhesive layer, the third biaxially oriented layer, the third adhesive layer, and the fourth biaxially oriented layer to the total thickness of the first biaxially oriented layer, the second biaxially oriented layer, the third adhesive layer, and the fourth biaxially oriented layer may be within the range described above, as the ratio of the total thickness of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 to the total thickness of the first biaxially oriented layer 11, the adhesive layer 12, and the second biaxially oriented layer 13 in sheet 1. The ratio of the total thickness of all biaxially oriented layers in a five-layer sheet to the total thickness of all biaxially oriented layers and all adhesive layers may be within the range described above, as the ratio of the total thickness of the first biaxially oriented layer 11 and the second biaxially oriented layer 13 to the total thickness of the first biaxially oriented layer 11, adhesive layer 12, and second biaxially oriented layer 13 in sheet 1.

[0060] In a five-layer sheet, the composition and refractive index of the first adhesive layer and the second adhesive layer may be the same or different. In a seven-layer sheet, the composition and refractive index of the first adhesive layer, the second adhesive layer, and the third adhesive layer may all be the same or different. If the sheet comprises multiple adhesive layers, the composition and refractive index of the multiple adhesive layers may all be the same or different.

[0061] In a five-layer sheet, the difference between the refractive index of the first adhesive layer and the refractive index of the second adhesive layer may be 0.00 or greater, and may be 0.80 or less, 0.50 or less, 0.30 or less, 0.20 or less, 0.10 or less, 0.08 or less, 0.06 or less, 0.04 or less, 0.02 or less, or 0.01 or less.

[0062] In a 7-layer sheet, the difference between the maximum and minimum refractive indices of the first, second, and third adhesive layers may be within the range described above as the difference between the refractive index of the first adhesive layer and the refractive index of the second adhesive layer in a 5-layer sheet. If the sheet comprises multiple adhesive layers, the difference between the maximum and minimum refractive indices of the multiple adhesive layers may be within the range described above as the difference between the refractive index of the first adhesive layer and the refractive index of the second adhesive layer in a 5-layer sheet.

[0063] In the 5-layer and 7-layer sheets, the refractive index of the biaxially oriented styrene resin layer may be the same as the refractive index of the first adhesive layer, the second adhesive layer, and the third adhesive layer. In the sheet, the refractive index of the biaxially oriented styrene resin layer may be smaller or larger than the refractive index of the first adhesive layer, the second adhesive layer, and the third adhesive layer. The difference between the refractive index of the biaxially oriented styrene resin layer and the refractive index of the first adhesive layer, the difference between the refractive index of the biaxially oriented styrene resin layer and the refractive index of the second adhesive layer, and the difference between the refractive index of the biaxially oriented styrene resin layer and the refractive index of the third adhesive layer may each be independently within the range described above as the difference between the refractive index of the biaxially oriented styrene resin layer and the refractive index of the adhesive layer 12 in sheet 1.

[0064] In a five-layer sheet, the thickness and main surface area of ​​the first adhesive layer and the second adhesive layer may be the same or different. In a seven-layer sheet, the thickness and main surface area of ​​the first adhesive layer, the second adhesive layer, and the third adhesive layer may all be the same or different. If the sheet has multiple adhesive layers, the thickness and main surface area of ​​all multiple adhesive layers may be the same or different.

[0065] In a five-layer sheet, the ratio of the combined thickness of the first adhesive layer and the second adhesive layer to the combined thickness of the first biaxially oriented layer, the first adhesive layer, the second biaxially oriented layer, the second adhesive layer, and the third biaxially oriented layer may be within the range described above as the ratio of the thickness of adhesive layer 12 to the combined thickness of the first biaxially oriented layer 11, adhesive layer 12, and second biaxially oriented layer 13 in sheet 1. In a seven-layer sheet, the ratio of the combined thickness of the first adhesive layer, the second adhesive layer, the second adhesive layer, the third biaxially oriented layer, the third adhesive layer, and the fourth biaxially oriented layer may be within the range described above as the ratio of the thickness of adhesive layer 12 to the combined thickness of the first biaxially oriented layer 11, adhesive layer 12, and second biaxially oriented layer 13 in sheet 1. The ratio of the total thickness of all adhesive layers to the total thickness of all biaxially oriented layers and all adhesive layers in a five-layer sheet may be within the range described above as the ratio of the thickness of adhesive layer 12 to the total thickness of the first biaxially oriented layer 11, adhesive layer 12, and second biaxially oriented layer 13 in sheet 1.

[0066] The sheet described above can be manufactured, for example, by a method including the steps of producing multiple biaxially oriented layers (a first biaxially oriented layer, a second biaxially oriented layer, and, if necessary, a third biaxially oriented layer and a fourth biaxially oriented layer, etc.) and laminating the multiple biaxially oriented layers via an adhesive. In the step of producing multiple biaxially oriented layers, for example, first, a styrene-based resin and other components used as needed are mixed and extruded from a die (especially a T-die) by an extruder under known conditions to obtain an unstretched sheet. Next, the unstretched sheet is stretched sequentially or simultaneously in the biaxial direction to obtain a biaxially oriented sheet. Multiple biaxially oriented layers can be produced by cutting the obtained biaxially oriented sheet to a predetermined size. Alternatively, multiple biaxially oriented layers can be produced by repeating the operation up to obtaining a biaxially oriented sheet multiple times.

[0067] In the process of laminating multiple biaxially oriented layers via an adhesive, first, an adhesive is applied to the surface of one prepared biaxially oriented layer (the first biaxially oriented layer). Next, another biaxially oriented layer (the second biaxially oriented layer) is placed on top of the adhesive-coated surface of the first biaxially oriented layer, and the adhesive is cured. After that, adhesive is applied to the exposed surface of the stacked biaxially oriented layer, and yet another biaxially oriented layer is placed on top of it, and the adhesive is cured. This process is repeated as needed. This results in a sheet in which multiple biaxially oriented layers are laminated via an adhesive layer.

[0068] The sheet may consist of a laminate in which biaxially oriented layers and adhesive layers are alternately laminated, as in Sheet 1, and may also include parts other than the laminate. The sheet may further comprise other layers other than the biaxially oriented layers and adhesive layers described above.

[0069] Other layers may, for example, be surface layers that constitute one surface of the sheet. Examples of surface layers include layers containing one or more selected from known release agents, antifogging agents, and antistatic agents. Such surface layers can be produced, for example, by coating the surface of the laminate with a coating agent containing one or more selected from known release agents, antifogging agents, and antistatic agents. The method of coating the laminate with the coating agent is not particularly limited and may be a method using a roll coater, knife coater, gravure roll coater, etc., or it may be spraying, dipping, etc.

[0070] Other functional layers can also be used as surface layers. Examples of other functional layers include layers having at least one function selected from penetration prevention, heat shielding, scratch prevention, low refractive index, high refractive index, antifouling, antistatic, anti-glare, transparent conductivity, and electromagnetic wave shielding. These surface layers do not necessarily have to be stretched independently. Adhesives may be used to attach the surface layers to the laminate.

[0071] In one embodiment, the sheet may comprise a laminate (A) comprising a first biaxially oriented layer (A), an adhesive layer (A) provided on the first biaxially oriented layer, and a second biaxially oriented layer (A) provided on the adhesive layer (A); and a laminate (B) provided on the laminate (A) and comprising a first biaxially oriented layer (B), an adhesive layer (B) provided on the first biaxially oriented layer (B), and a second biaxially oriented layer (B) provided on the adhesive layer (B). The details of laminates (A) and (B) may be as described above as details of sheet 1. As the intermediate layer, for example, the functional layer described above can be used.

[0072] The sheet described above can be used in sheet form or plate form (i.e., in its as-manufactured state), or it can be used after being molded into a desired shape by vacuum forming, pressure forming, hot plate forming, etc. The sheet can be used as a glass substitute material, for example, as a display component such as display panels for electronic devices, a film component such as protective film, a glass substitute component for building materials such as window glass, windows and roofs for automobiles and other transportation equipment, daylighting glass, lighting equipment, mirrors, etc., an interior and exterior component for buildings, automobiles, and transportation equipment, aquarium material, exterior material for greenhouses and plant factories, electronic equipment component, container, agricultural and industrial component, optical equipment component, lens, filter, road light-transmitting board, sign, indicator component, medical equipment component, stationery, etc. [Examples]

[0073] The present disclosure will be described in more detail below based on the examples. However, the present disclosure is not limited to these examples.

[0074] [Sheet manufacturing] (Comparative Example 1) The apparatus was constructed by connecting a fully mixed continuous reactor with a volume of approximately 20 L equipped with a stirring blade, a tower-type plug-flow continuous reactor with a volume of approximately 11 L, and a flash-type defoliation tank equipped with a preheater in series. A solution consisting of 66.0 parts by mass of methyl methacrylate, 22.0 parts by mass of styrene, and 12.0 parts by mass of ethylbenzene was mixed with 0.0073 parts by mass of t-butyl peroxyisopropyl monocarbonate and 0.32 parts by mass of n-dodecyl mercaptan to prepare the raw material solution. This raw material solution was supplied at a rate of 3.9 kg per hour to the fully mixed continuous reactor maintained at a temperature of 125°C to allow the polymerization reaction to proceed. The conversion rate at the outlet of the fully mixed continuous reactor was controlled to 55-58%. The resulting polymerization solution was supplied to the tower-type plug-flow continuous reactor, which was adjusted to have a gradient from 125°C to 144°C in the direction of flow, and the polymerization reaction was further allowed to proceed. The conversion rate at the outlet of the tower-type plug-flow continuous reactor was controlled to 75-78%.

[0075] The polymerization solution exiting the tower-type plug-flow continuous reactor was introduced into a flash-type defoliation tank under reduced pressure of 1.3 kPa while being preheated to 230°C, and unreacted monomers were removed at a tank temperature of 235°C. The resulting composition was extracted at 232°C using a gear pump and extruded into strands to produce pelletized methyl methacrylate-styrene copolymer (A-1). Copolymer (A-1) contained 75% by mass of methyl methacrylate (MMA) units and 25% by mass of styrene (St) units, based on the total mass of copolymer (A-1). The Mw of copolymer (A-1) was 70,000, and the MFR was 4 g / 10 min.

[0076] The obtained pelletized copolymer (A-1) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.0 mm (the sheet of Comparative Example 1).

[0077] (Comparative Example 2) A pelletized copolymer (A-1) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.5 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / second, a stretching ratio of 2.1 times in the MD direction, and a stretching ratio of 2.1 times in the TD direction to obtain a biaxially oriented sheet with a thickness of 0.4 mm (a sheet of Comparative Example 2 consisting of one biaxially oriented layer).

[0078] (Example 1) A pelletized copolymer (A-1) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.0 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / second, and a stretching ratio of 2.5 times in both the MD and TD directions to obtain a biaxially oriented sheet (thickness: 0.18 mm). The obtained biaxially oriented sheet was cut out to prepare two biaxially oriented layers measuring 40 cm x 40 cm. An adhesive (Denka Co., Ltd., EN-thiol-based adhesive "Hardrock OP-1840-05") was applied to the entire surface of one of the obtained biaxially oriented layers to a thickness of 0.04 mm using a bar coater, and the other biaxially oriented layer was placed on top of the applied adhesive. Subsequently, the adhesive was cured by ultraviolet irradiation to obtain a sheet (sheet of Example 1) in which two biaxially stretched layers were laminated with the adhesive layer in between. The thickness of the sheet of Example 1 was 0.4 mm.

[0079] (Example 2) Copolymer (A-1) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.0 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / sec, and a stretching ratio of 3.3 times in both the MD and TD directions to obtain a biaxially oriented sheet (thickness: 0.07 mm). The obtained biaxially oriented sheet was cut out to prepare four biaxially oriented layers measuring 40 cm x 40 cm. Adhesive (Hardrock OP-1840-05, an ene-thiol-based adhesive manufactured by Denka Co., Ltd.) was applied to the entire surface of one of the obtained biaxially oriented layers to a thickness of 0.04 mm using a bar coater, and another biaxially oriented layer was placed on top of the applied adhesive. The adhesive was then cured by ultraviolet irradiation. Furthermore, the adhesive was applied to a thickness of 0.04 mm using a bar coater so as to cover the entire surface of the stacked biaxially oriented layers. Another layer of biaxially oriented material was then placed on top of the applied adhesive, and the adhesive was cured by ultraviolet irradiation. This process was repeated twice to obtain a sheet (sheet of Example 2) in which four biaxially oriented layers were laminated with the adhesive layer in between. The thickness of the sheet of Example 2 was 0.4 mm.

[0080] (Example 3) Copolymer (A-1) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.0 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / sec, and a stretching ratio of 2.25 times in both the MD and TD directions to obtain a biaxially oriented sheet (thickness: 0.22 mm). The obtained biaxially oriented sheet was cut out to prepare four biaxially oriented layers measuring 40 cm x 40 cm. Adhesive (Denka Co., Ltd., EN-thiol-based adhesive "Hardrock OP-1840-05") was applied to the entire surface of one of the obtained biaxially oriented layers to a thickness of 0.04 mm using a bar coater, and another biaxially oriented layer was placed on top of the applied adhesive. The adhesive was then cured by ultraviolet irradiation. Furthermore, the adhesive was applied to a thickness of 0.04 mm using a bar coater so as to cover the entire surface of the stacked biaxially oriented layers. Another biaxially oriented layer was then placed on top of the applied adhesive, and the adhesive was cured by ultraviolet irradiation. This process was repeated twice to obtain a sheet (sheet of Example 3) in which four biaxially oriented layers were laminated with the adhesive layer in between. The thickness of the sheet of Example 3 was 1.0 mm.

[0081] (Example 4) A sheet (sheet of Example 4) was obtained in the same manner as in Example 3, except that an acrylic adhesive (Hardlock UVX-7000, manufactured by Denka Co., Ltd.) was used as the adhesive. The thickness of the sheet of Example 4 was 1.0 mm.

[0082] (Example 5) Except for using an ene-thiol-based adhesive (Denka Co., Ltd., "Hardlock OP-1840-05") and a zirconia nanoparticle dispersion (Nippon Shokubai Co., Ltd., "Zircostar ZP-153") mixed in a mass ratio of 1:4 as the adhesive, changing the thickness of the adhesive applied using a bar coater to 0.27 mm in all cases, and applying the adhesive and then drying it before adding another biaxially stretched layer, the procedure was the same as in Example 3 to obtain the sheet (sheet of Example 5). The thickness of the sheet of Example 5 was 1.0 mm, and the thickness of each adhesive layer in the sheet of Example 5 was 0.04 mm.

[0083] (Example 6) A pelletized methyl methacrylate-styrene copolymer (A-2) was prepared in the same manner as in Comparative Example 1, except that the methyl methacrylate content in the raw material solution was 52.8 parts by mass and the styrene content was 35.2 parts by mass. Copolymer (A-2) contained 60% by mass of methyl methacrylate units and 40% by mass of styrene units based on the total mass of copolymer (A-2). The Mw of copolymer (A-2) was 180,000 and the MFR was 1 g / 10 min. A sheet (sheet of Example 6) was obtained in the same manner as in Example 3, except that copolymer (A-2) was used instead of copolymer (A-1).

[0084] (Comparative Example 3) Polystyrene (manufactured by Toyo Styrene Co., Ltd., Toyo Styrofoam GP, product name: HRM12) was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.5 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / second, a stretching ratio of 2.1 times in the MD direction, and a stretching ratio of 2.1 times in the TD direction to obtain a biaxially oriented sheet with a thickness of 0.4 mm (a sheet of Comparative Example 3 consisting of one biaxially oriented layer).

[0085] (Example 7) Polystyrene similar to that used in Comparative Example 3 was melt-kneaded at 230°C and 70 rpm using a single-screw extruder with a screw diameter of 40 mm, and extruded through a T-die to obtain an unstretched sheet with a thickness of 1.0 mm. The obtained unstretched sheet was sequentially stretched using a biaxial stretcher at a stretching temperature of 135°C, a stretching speed of 30 mm / second, and a stretching ratio of 2.25 times in both the MD and TD directions to obtain a biaxially oriented sheet (thickness: 0.22 mm). The obtained biaxially oriented sheet was cut out to prepare four biaxially oriented layers measuring 40 cm x 40 cm. Adhesive (Hardrock OP-1840-05, an ene-thiol-based adhesive manufactured by Denka Co., Ltd.) was applied to the entire surface of one of the obtained biaxially oriented layers to a thickness of 0.04 mm using a bar coater, and another biaxially oriented layer was placed on top of the applied adhesive. The adhesive was then cured by ultraviolet irradiation. Furthermore, the adhesive was applied to a thickness of 0.04 mm using a bar coater to cover the entire surface of the stacked biaxially oriented layers. Another biaxially oriented layer was then placed on top of the applied adhesive, and the adhesive was cured by ultraviolet irradiation. This process was repeated twice to obtain a sheet (sheet of Example 7) in which four biaxially oriented layers were laminated with the adhesive layer in between. The thickness of the sheet of Example 7 was 1.0 mm.

[0086] [Physical properties and evaluation] (Refractive index) Using an Abbe refractometer (DR-M2, manufactured by Atago Co., Ltd.), the refractive indices of the biaxially oriented layer and adhesive layer in each example and comparative example were determined under the conditions of a sample temperature of 23°C and a measurement wavelength of 589 nm. The results are shown in Tables 1 and 2. The refractive index of the adhesive layer was measured using a sample prepared by curing the adhesive by ultraviolet irradiation.

[0087] (Impact resistance) Each example and comparative example sheet was cut to 90 mm x 55 mm to prepare measurement samples. Using a film impact tester (Yasuda Seiki Seisakusho Co., Ltd., No. 181-L), the impact strength (pendulum impact hole punching strength) of each measurement sample was measured according to ASTM D3420 at 23°C and 50% RH. The results are shown in Tables 1 and 2. A higher impact strength value indicates superior impact resistance.

[0088] (transparency) In accordance with JIS K7136:2000, the haze of each example and comparative example sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.). The results are shown in Tables 1 and 2. A smaller haze value indicates better transparency.

[0089] [Table 1]

[0090] [Table 2] [Explanation of symbols]

[0091] 1...Sheet, 11...First biaxially oriented layer, 12...Adhesive layer, 13...Second biaxially oriented layer.

Claims

1. It comprises a first biaxially oriented layer, an adhesive layer provided on the first biaxially oriented layer, and a second biaxially oriented layer provided on the adhesive layer, A sheet in which the first biaxially oriented layer and the second biaxially oriented layer are biaxially oriented layers of styrene resin.

2. The sheet according to claim 1, wherein the difference between the refractive index of the biaxially oriented layer of the styrene-based resin and the refractive index of the adhesive layer is 0.08 or less.

3. The sheet according to claim 1 or 2, wherein the styrene resin comprises styrene monomer units and (meth)acrylic acid ester monomer units.

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