JP6039168B2 - Protective sheet, method for producing protective sheet and polarizing plate - Google Patents

Description

  The present invention relates to a protective sheet and a polarizing plate.

  In recent years, liquid crystal display devices are widely used as an alternative to CRTs because they are thin, lightweight, and consume less power. Specifically, liquid crystal display devices are widely used from small items such as calculators and watches to large items such as automobile meters, PC monitors, and televisions.

  A liquid crystal display element incorporated in a liquid crystal display device includes a liquid crystal cell and a pair of polarizing plates disposed on both surfaces of the liquid crystal cell. This polarizing plate includes a sheet-like polarizer and a pair of protective sheets disposed on both sides of the polarizer. The protective sheet is a sheet for protecting the structure of the polarizer, and is generally made of triacetyl cellulose (hereinafter referred to as “TAC”) having a small birefringence and excellent transparency. Is formed.

However, this TAC has insufficient moisture and heat resistance, and when a polarizing plate using TAC as a polarizer protective film is used at high temperature or high humidity, there is a disadvantage that the performance of the polarizing plate such as the degree of polarization and the hue deteriorates. . In addition, TAC produces a phase difference with respect to obliquely incident light. Such a phase difference significantly affects viewing angle characteristics as the size of liquid crystal displays increases in recent years.
Therefore, the use of a heat-resistant acrylic resin as an alternative to TAC has been studied.

  Specifically, a protection sheet having a sea-island structure having a matrix phase containing a heat-resistant acrylic resin as a main polymer and a dispersed phase containing an acrylic rubber as a main polymer has been studied (for example, JP 2010-70646 A). No. publication).

  However, the protective sheet of the above-mentioned JP 2010-70646 has a relatively large average particle diameter of 0.05 to 0.35 μm of the acrylic rubber in the dispersed phase, and thus the transparency of the protective sheet cannot be sufficiently ensured. Have the problem.

JP 2010-70646 A

  The present invention has been made in view of these disadvantages, and an object of the present invention is to provide a protective sheet that is rich in heat resistance and flexibility, and that is highly transparent, and a polarizing plate having the protective sheet. And

The invention made to solve the above problems is
A sea-island structure protective sheet having a matrix phase containing a heat-resistant acrylic resin as a main polymer and a dispersed phase containing an acrylic rubber as a main polymer,
The refractive index difference between the matrix phase and the dispersed phase is 0.01 or less,
An average particle size of the dispersed phase is 1 nm or more and less than 50 nm.

  Since the matrix phase includes a heat-resistant acrylic resin as a main polymer and the dispersed phase includes an acrylic rubber as a main polymer, the protective sheet has high heat resistance and flexibility, and includes a matrix phase and a dispersed phase. The refractive index difference is 0.01 or less, and the average particle size of the dispersed phase is 1 nm or more and less than 50 nm, so that the transparency is high. In particular, since the average particle diameter of the dispersion layer is less than 50 nm, extremely high transparency can be obtained. That is, in theory, particles smaller than half of the wavelength of visible light do not adversely affect the transparency, but in reality, they appear cloudy due to the influence of visible light on the short wavelength side, but as described above, it is less than 50 nm. If so, extremely high transparency can be obtained without being affected by visible light on the end wavelength side.

  Moreover, in the said protective sheet, it is preferable that content of a dispersed phase is 5 to 40 mass%. Since it is more than the said lower limit, required flexibility can fully be exhibited, and since it is below the said upper limit, required transparency can fully be exhibited.

  Furthermore, in the said protection sheet, it is preferable that the retardation value of a plane direction is 0 nm or more and 15 nm or less, and the retardation value of a thickness direction is -15 nm or more and 0 nm or less. As a result, the transmitted light that has passed through the protective sheet is less likely to cause a phase difference. For this reason, even if it is used as a protective sheet for a sheet having a polarizing function, such as a polarizing plate, this polarizing function is not hindered. Have

  Moreover, in the said protection sheet, it is preferable that the total light transmittance of heat resistant acrylic resin is 90% or more, and sufficient transparency is obtained by this. Moreover, it is preferable that Vicat softening point is 105 degreeC or more and 140 degrees C or less. By being above the lower limit, for example, sufficient heat resistance can be exhibited when used as a protective sheet for a polarizing plate, and by being below the upper limit, the heat resistant acrylic resin can be melted during the production of the protective sheet. It has the advantage of being easy to manufacture and easy to manufacture.

  The heat-resistant acrylic resin preferably has a ring structure in the main chain. Thereby, the said protection sheet has an effect that heat resistance is higher.

  Moreover, in the said protective sheet, it is preferable that the mat | matte process is given to the single side | surface or both surfaces. Thereby, it has the advantage that it is easy to stick the surface which gave this mat process to another member via an adhesive agent. For example, the polarizing plate can be formed by firmly bonding the protective sheet to the polarizer by adhering the matted surface to the polarizer using a water-based adhesive.

  In addition, the protective sheet preferably includes a hard coat layer laminated on one side, and the hard coat layer can enhance the scratch resistance. Moreover, it is preferable that this hard-coat layer is formed by apply | coating an acrylic coating material, and can ensure the transparency of a sheet | seat by this.

  The present invention also includes a polarizing plate including a sheet-like polarizer and a pair of protective sheets laminated on both surfaces of the polarizer via an adhesive layer.

  As described above, the protective sheet of the present invention has an effect of being excellent in heat resistance and flexibility and having high transparency.

It is a schematic sectional drawing of the protection sheet which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the liquid crystal display element using the protection sheet of FIG. It is a schematic sectional drawing of the polarizing plate using the protective sheet which concerns on other embodiment of this invention.

  Hereinafter, a protective sheet according to an embodiment of the present invention will be described with reference to the drawings as appropriate.

  The protective sheet of this embodiment has a matrix phase containing a heat-resistant acrylic resin as a main polymer and a dispersed phase containing an acrylic rubber as a main polymer. In the protective sheet, the dispersed phase is dispersed in the matrix phase to form a sea-island structure. Hereinafter, each phase will be described.

<Matrix phase>
The matrix phase contains a heat resistant acrylic resin as a main polymer. The heat-resistant acrylic resin means a polymer containing acrylic monomers such as acrylic acid and methacrylic acid, and derivatives thereof as monomer components. Examples of the heat-resistant acrylic resin include methacrylic acid alkyl esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, acrylic acid What polymerized the 1 type or multiple types of acrylic monomer chosen from acrylic acid alkylesters, such as 2-ethylhexyl, is mentioned. This heat-resistant acrylic resin includes those obtained by copolymerizing an acrylic monomer and other monomer components. In the case of such copolymerization, the content (copolymerization ratio) of other monomer components is preferably 60% by mass or less, and preferably 50% by mass with respect to all monomer components constituting the heat-resistant acrylic resin. The following is more preferable, and 40% by mass or less is more preferable.

  The heat-resistant acrylic resin is preferably a polymer containing methyl methacrylate as a monomer component. When the heat resistant acrylic resin contains methyl methacrylate as a monomer component, the compatibility of the obtained heat resistant acrylic resin is improved. Examples of the polymer containing methyl methacrylate as a monomer component include a homopolymer of methyl methacrylate, a copolymer of methyl methacrylate and another monomer, and the like. Examples of other monomers copolymerizable with methyl methacrylate include methacrylic acid alkyl esters other than methyl methacrylate; acrylic acid alkyl esters, α-hydroxymethyl acrylic acid alkyl esters; styrene; o-methyl styrene. Alkyl-substituted styrene such as p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-alkyl-substituted styrene such as α-methylstyrene, α-methyl-p-methylstyrene, etc. Aromatic vinyl compounds; unsaturated nitriles such as acrylonitrile and methacrylonitrile; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; acrylic acid and methacrylic acid Unsaturated carbo such as maleic acid Mention may be made of the acids and the like. These other monomers include α-hydroxymethylacrylic acid alkyl esters, styrene, alkyl-substituted styrene, α-alkyl-substituted styrene, unsaturated, from the viewpoint of improving the flexibility and heat resistance of the resulting protective sheet. Carboxylic acids are preferable, α-hydroxymethyl acrylic acid alkyl esters, styrene, α-alkyl-substituted styrene, and unsaturated carboxylic acids are more preferable. Among them, α-hydroxymethyl methyl acrylate, styrene, α-methyl styrene, methacrylic acid are preferable. Acid is more preferred. As another monomer, when α-hydroxymethyl acrylic acid alkyl ester is used and copolymerized with methyl methacrylate, a lactone ring partially containing the polymer main chain is obtained by performing a dehydration reaction. Therefore, the heat resistance of the resulting heat-resistant acrylic resin is particularly improved. These monomers can be used alone or in combination. In such a copolymer of methyl methacrylate and another monomer, the content of other monomer components is preferably 50% by mass or less with respect to methyl methacrylate.

  As the other monomer copolymerizable with methyl methacrylate described above, alkyl acrylates are preferable. By using alkyl acrylates as other monomers, the heat resistant temperature of the resulting heat resistant acrylic resin is improved, and the fluidity during molding is increased. In such a copolymer of methyl methacrylate and an alkyl acrylate, the content of the alkyl acrylate monomer component is 0% relative to the total monomer component from the viewpoint of improving heat resistance. 1 mass% or more and 15 mass% or less are preferable, 0.2 mass% or more and 14 mass% or less are more preferable, and 1 mass% or more and 12 mass% or less are more preferable.

  As the alkyl acrylates, methyl acrylate and ethyl acrylate are preferably copolymerized in a small amount with methyl methacrylate, because the effect of improving the fluidity at the time of molding described above can be remarkably obtained.

  As the heat-resistant acrylic resin, isotactic polymethacrylic acid ester or syndiotactic polymethacrylic acid ester can also be used. In addition, as the heat-resistant acrylic resin, a commercially available product may be used as it is, or it can be produced from a commercially available product that becomes a precursor.

  As a method for producing the above heat-resistant acrylic resin, a conventionally known method can be employed. For example, a polymerization method such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, anion polymerization, etc. can be employed. It is. Bulk polymerization and solution polymerization without using a suspending agent or an emulsifier are preferred, and this can reduce the mixing of fine foreign substances. In the case of solution polymerization, an aromatic hydrocarbon solvent such as toluene can be used. In the case of bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation. Examples of the polymerization initiator used in the polymerization reaction include azo compounds such as azobisisobutyronitrile; organic peroxides such as benzoyl peroxide, lauroyl peroxide, and t-butylperoxy-2-ethylhexanoate. An oxide or the like can be used.

  In addition, when polymerization is performed under a temperature condition of 90 ° C. or higher, solution polymerization is generally employed. Among polymerization initiators soluble in organic solvents, those having a 10-hour half-life temperature of 80 ° C. or higher are used. It is preferable to use it. As such a polymerization initiator, specifically, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5- Examples include di (benzoylperoxy) hexane, 1,1-azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile, and the like. As the usage-amount of these polymerization initiators with respect to the said polymerization reaction, 0.005-5 mass parts is preferable with respect to 100 mass parts of all the monomers used for superposition | polymerization.

  In the polymerization reaction, a molecular weight regulator can be used as necessary. As this molecular weight regulator, those generally used in radical polymerization can be adopted. Specifically, for example, a mercaptan compound such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate can be used. These molecular weight regulators are preferably added in a concentration range such that the molecular weight of the heat-resistant acrylic resin is in a desired range.

  In addition, as a manufacturing method of heat resistant acrylic resin, it is possible to use the method described, for example in Japanese Patent Publication No.63-1964. In addition, as a heat-resistant acrylic resin, a ternary or higher copolymer is obtained by copolymerizing a methacrylic acid alkyl ester and / or an acrylic acid alkyl ester and one or more other monomers. You can also.

  In the above ternary or higher copolymer, other monomer components copolymerized with the alkyl methacrylate and / or the alkyl alkyl ester include, for example, styrene, α-methylstyrene, o-methylstyrene, p- Aromatic vinyl compounds such as methylstyrene, o-ethylstyrene, p-ethylstyrene and pt-butylstyrene; Unsaturated nitriles such as acrylonitrile, methacrylonitrile and ethacrylonitrile; N-methylmaleimide, N- Maleimides such as ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide; (meth) acrylamides such as acrylamide, methacrylamide, N-methylacrylamide, butoxymethylacrylamide, N-propylmethacrylamide; maleic anhydride, italy anhydride Unsaturated carboxylic acid anhydrides such as acid; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, α-substituted methacrylic acid and maleic acid; methyl (meth) acrylate, ( (Meth) ethyl acrylate, (meth) acrylate n-propyl, (meth) acrylate n-butyl, (meth) acrylate t-butyl, (meth) acrylate n-hexyl, (meth) acrylate cyclohexyl, ( Chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2,3,4,5,6 (meth) acrylic acid -Unsaturated carboxylic acid alkyl esters such as pentahydroxyhexyl and 2,3,4,5-tetrahydroxypentyl (meth) acrylate It is possible to adopt the kind and the like.

  As the resin constituting the matrix phase, in addition to the heat-resistant acrylic resin as the main polymer, an acrylic resin that is not a heat-resistant acrylic resin (hereinafter also referred to as “acrylic resin (a)”) may be used. Good. In this case, in the matrix phase, the respective contents of the heat-resistant acrylic resin and the acrylic resin (a) are the mass ratio of the acrylic resin (a) to the heat-resistant acrylic resin (acrylic resin (a) / heat resistance). (Acrylic resin) is preferably 0.1 / 99.9 or more and 50/50 or less. By adjusting the mass ratio of the acrylic resin (a) and the heat-resistant acrylic resin, it is possible to adjust the photoelastic coefficient and glass transition temperature (Tg) of the protective sheet obtained. The mass ratio is preferably from 0.1 / 99.9 to 40/60, more preferably from 0.1 / 99.9 to 35/65.

  The weight average molecular weight (Mw) in terms of polymethyl methacrylate (PMMA) by gel permeation chromatography (GPC) of the heat-resistant acrylic resin is preferably 10,000 or more and 400,000 or less, and preferably 40,000 or more and 300,000 or less. It is more preferable that it is 70,000 or more and 200,000 or less. By making Mw of the said heat resistant acrylic resin into the said range, while the intensity | strength of the protective sheet obtained improves, the workability and fluidity | liquidity of protective sheet shaping | molding improve. The molecular weight distribution (Mw / Mn) is preferably 1.8 or more and 3.0 or less, more preferably 1.8 or more and 2.7 or less, and further preferably 1.8 or more and 2.5 or less.

  The heat-resistant acrylic resin may be a mixture of two or more heat-resistant acrylic resins having different monomer component compositions, molecular weights, and the like. In this case, the weight average molecular weight means the average value.

  The Vicat softening temperature of the heat-resistant acrylic resin is preferably 105 ° C or higher and 140 ° C or lower, more preferably 110 ° C or higher, and further preferably 120 ° C or higher. The glass transition temperature (Tg) of the heat-resistant acrylic resin is preferably 110 ° C. or higher, more preferably 115 ° C. or higher, and further preferably 120 ° C. or higher. The melt index (ASTM D1238; I condition) of the heat-resistant acrylic resin is preferably 10 g / 10 min or less, more preferably 6 g / 10 min or less, and more preferably 3 g / 10 min or less from the viewpoint of the strength of the protective sheet obtained. Further preferred.

  When the heat-resistant acrylic resin is a heat-resistant acrylic resin not containing an aromatic vinyl monomer as a monomer component (hereinafter also referred to as “heat-resistant acrylic resin (1)”), the heat-resistant acrylic It is preferable that it is 40 mass% or more with respect to all the monomer components which comprise heat-resistant acrylic resin (1) as a content rate of the acrylic monomer component in a system resin (1). Examples of the acrylic resin (1) include methacrylic acid esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, and acrylic acid. What polymerized 1 or more types of monomers chosen from acrylic acid esters, such as 2-ethylhexyl, can be used.

  The weight average molecular weight of the acrylic resin (1) is preferably from 50,000 to 200,000, and more preferably from 70,000 to 150,000. By making this weight average molecular weight into the above range, the obtained protective sheet is excellent in strength and excellent in molding processability and fluidity at the time of forming the protective sheet.

  Furthermore, as a heat-resistant acrylic resin constituting the matrix phase, a heat-resistant acrylic resin containing an aromatic vinyl monomer as a monomer component and the above aromatic vinyl monomer as a monomer component are included. In the case of using together with a non-acrylic resin (1), it is also possible to use another acrylic resin together. In this case, the content of the other acrylic resin is preferably 20 parts by mass or less and more preferably 10 parts by mass or less with respect to 100 parts by mass of the total resin constituting the matrix phase. The content of the heat-resistant acrylic resin (1) is preferably 0.1 part by mass or more and 50 parts by mass or less, and 0.1 part by mass or more and 40 parts by mass with respect to 100 parts by mass of the total resin constituting the matrix phase. The following is more preferable, and 0.1 to 35 parts by mass is particularly preferable. Furthermore, the content of the heat-resistant acrylic resin is preferably 50 parts by mass or more and 99.9 parts by mass or less, and 60 parts by mass or more and 99.9 parts by mass or less with respect to 100 parts by mass of the total resin constituting the matrix phase. Is more preferably 65 parts by mass or more and 99.9 parts by mass or less. By making content of the heat resistant acrylic resin in a matrix phase into the said range, the heat resistance of the protective sheet obtained can be improved. Moreover, the heat resistance of the said protection sheet can be made high by using the heat resistant acrylic resin which has a ring structure in a principal chain.

<Dispersed phase>
The dispersed phase includes acrylic rubber as a main polymer. This acrylic rubber means rubber containing acrylic monomers such as acrylic acid and methacrylic acid, and derivatives thereof as monomer components. The acrylic rubber may be composed of only acrylic monomers, or may be composed of acrylic monomers and other monomers. Examples of the acrylic monomer include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, allyl methacrylate, methyl acrylate, ethyl acrylate, i-propyl acrylate, and n-butyl acrylate. Examples of other monomers include aromatics such as styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 2,4-diethylstyrene, 4-butoxystyrene, and N, N-dimethylaminostyrene. Vinyl compounds; α, β-ethylenically unsaturated nitrile compounds such as acrylonitrile, methacrylonitrile and vinylidene cyanide; Vinyl ester compounds such as vinyl acetate and vinyl propionate; Vinyl ether compounds such as ethyl vinyl ether, cetyl vinyl ether and hydroxybutyl vinyl ether Etc. These other monomers can be used alone or in admixture of two or more.

  The acrylic rubber may be crosslinked using a crosslinking agent. Examples of the crosslinking agent include sulfur; organic peroxides such as 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, di-tert-butylperoxydiisopropylbenzene; tetramethylthiuram monosulfide, tetramethylthiuram disulfide, etc. Organic sulfur compounds; oxime compounds such as p-quinonedioxime and p, p′-dibenzoylquinonedioxime; and polyamines such as hexamethylenediamine carbamate. When a crosslinking agent is used, a vulcanization accelerator such as diphenyl guanidine, zinc dimethyldithiocarbamate, 2-mercaptobenzothiazole, dibenzothiazyl sulfide may be used as necessary.

  The average particle size of the dispersed phase is 1 nm or more and less than 50 nm, preferably 2 nm or more and less than 50 nm, and more preferably 3 nm or more and less than 50 nm. There exists a possibility that the flexibility of a protective sheet may fall that the average particle diameter of a dispersed phase is less than the said minimum. Conversely, if the average particle diameter exceeds the above upper limit, the transparency of the protective sheet may be deteriorated.

  In the protective sheet, the content of the dispersed phase is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 35% by mass, and more preferably 20% by mass to 30% by mass with respect to the protective sheet. The following is more preferable. There exists a possibility that the flexibility of a protective sheet may fall that content of a dispersed phase is less than the said minimum. Conversely, if the content of the dispersed phase exceeds the above upper limit, the transparency of the protective sheet may be deteriorated.

  As this dispersed phase, one having a multilayer structure can be adopted. This multi-layer structure includes, for example, a two-layer structure composed of a core-shell structure, a three-layer structure composed of a central hard layer, a soft layer, and an outermost hard layer, and an intermediate hard layer between the soft layer and the outermost hard layer. It is possible to adopt a four-layer structure or the like further having layers.

  As the two-layer structure, for example, a core-shell structure composed of a core layer made of a rubber-like polymer and a shell layer made of an acrylic resin-based glassy polymer can be used. The rubbery polymer used for the core layer is not particularly limited as long as it is rubbery at room temperature. For example, a rubbery polymer containing butadiene as a main component (for example, butadiene homopolymer, butadiene-aromatic). Group vinyl copolymer, etc.) and rubbery polymers (eg, butyl acrylate-styrene copolymer, 2-ethylhexyl acrylate-styrene copolymer, etc.) mainly composed of alkyl acrylate. . In addition, it is preferable to employ | adopt a butadiene-styrene copolymer, and intensity | strength, productivity, and transparency can be improved by this. The glassy polymer used for the shell layer is not particularly limited as long as it is a glassy acrylic polymer at room temperature. For example, a methyl methacrylate homopolymer, a methyl methacrylate-methyl acrylate copolymer, or the like is used. be able to.

  In addition, examples of the dispersed phase having a multilayer structure of three or more layers include those in which a soft layer made of a rubbery polymer and a hard layer made of a glassy polymer are laminated in three or more layers. As the rubbery polymer used for the soft layer and the glassy polymer used for the hard layer, those described for the rubber particles having the two-layer structure can be used.

  As long as the effect of the present invention is not impaired, other polymers can be mixed in addition to the heat-resistant acrylic resin constituting the matrix phase and the acrylic rubber constituting the dispersed phase. Examples of other polymers include polyolefin resins such as polyethylene and polypropylene; polyamide resins; polyphenylene sulfide resins; polyether ether ketone resins; polyesters, polysulfones, polyphenylene oxides, polyimides, polyether imides, polyacetals, and the like. Plastic resins; and thermosetting resins such as phenol resins, melamine resins, silicone resins, and epoxy resins. Other polymers can be used singly or in combination. In addition, it is preferable that content of another polymer shall be 20 mass parts or less with respect to 100 mass parts of matrix phases.

<Ultraviolet absorber>
The protective sheet contains an ultraviolet absorber in the matrix phase. When the protective sheet contains an ultraviolet absorber in the matrix, the protective sheet is less likely to yellow. Moreover, when the said protective sheet is laminated | stacked on both surfaces of a sheet-like polarizer and a polarizing plate is formed, the ultraviolet-ray transmission to a polarizer can be suppressed. Moreover, it is preferable that this ultraviolet absorber is further contained in the dispersed phase. By further including an ultraviolet absorber in the dispersion layer, the dispersion uniformity of the ultraviolet absorber in the protective sheet is improved, and the protective sheet is laminated on both sides of the sheet-like polarizer to form a polarizing plate. When formed, ultraviolet transmission to the polarizer can be further suppressed.

  As the ultraviolet absorber, a benzotriazole compound can be used. In addition, a benzophenone compound, a benzoate compound, a triazine compound, a hindered amine compound, an oxalic acid anilide compound, a formamidine compound, a hydroxybenzoate It can be suitably selected from a system compound, a nickel system compound and the like. These can be used alone or in combination of two or more. Moreover, as an ultraviolet absorber, in order to prevent deterioration of a polarizing plate, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and has little absorption of visible light having a wavelength of 400 nm or more for effective use of visible light. Preferably there is.

  As the ultraviolet absorber, among the compounds listed above, the benzotriazole compounds, benzophenone compounds, benzoate compounds, and triazine compounds are highly transparent and excellent in preventing the deterioration of the polarizing plate. Therefore, it is preferable. In particular, it is more preferable to employ an ultraviolet absorber made of a benzotriazole-based compound that is less colored and highly transparent.

  Specific examples of the benzotriazole compound include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl). ) Phenyl] benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) ) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'-di) -Tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2,2 '-Methylene-bis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol], methyl-3- [3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol condensate, 2- (2-hydroxyphenyl) benzotriazole copolymer, 2- (2′-hydroxy-4′-octyl) Oxyphenyl) -2H-benzotriazole, 2- (2H-benzotriazol-2-yl) -4-methyl-6- (3,4,5,6-tetrahydrophtalimidylmethyl) phenol, 2,2 ′ -Methylenebis (4-tert-butyl-6-2H-benzotriazolylphenol), 2,2'-methylenebis (4-te Such as t- octyl -6-2H- benzotriazolylphenol) can be mentioned. As a commercial item, a brand name "KEMISORB279" (made by Chemipro), a brand name "TINUVIN360" (made by BASF Japan) is mentioned.

  Specific examples of the benzophenone compounds include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-n-octoxy. Benzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 2,2'-dihydroxy-4 -Methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone and 2-hydroxy-4-methoxy-2'-carboxybenzophenone Can do. As a commercial item, brand name "KEMISORB12", "brand name KEMISORB111" (all made by Chemipro), brand name "CHIMASSORB81" (made by BASF Japan) are mentioned.

  As said benzotriazole type compound and benzophenone type compound, it is preferable that the mass reduction | decrease in 300 degreeC and a heating for 20 minutes is 10% or less. The mass loss upon heating at 300 ° C. for 20 minutes is preferably 9% or less, more preferably 8% or less, still more preferably 6% or less, and particularly preferably 5% or less. When the mass reduction in heating at 300 ° C. for 20 minutes exceeds the above upper limit, there is a possibility that sufficient ultraviolet absorbing ability cannot be exhibited. The ultraviolet absorber having a mass loss of 10% or less upon heating at 300 ° C. for 20 minutes is preferably 2,2′-methylenebis [6- (2H-benzotriazol-2-yl) -4- (1, 1,3,3-tetramethylbutyl) phenol]. As a commercial item, brand name "KEMISORB12", brand name "KEMISORB111" (all made by Chemipro), brand name "CHIMASORB81" (made by BASF Japan), etc. are mentioned.

  As the triazine compound, for example, a compound having a 1,3,5-triazine ring can be preferably used. Specific examples include 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol. As a commercial item, a brand name "TINUVIN1577" (made by BASF Japan) is mentioned, for example.

Examples of the hindered amine compound include 4-hydroxy-2,2,6,6-tetramethylpiberidine, 1-allyl-4-hydroxy-2,2,6,6-tetramethylpiberidine, 1-benzyl. -4-hydroxy-2,2,6,6-tetramethylpiberidine, 1- (4-tert-butyl-2-butenyl) -4-hydroxy-2,2,6,6-tetramethylpiberidine 4-stearoyloxy-2,2,6,6-tetramethylpiberidine, 4-methacryloyloxy-1,2,2,6,6-pentamethylpiberidine, 1-benzyl-2,2,6 , 6-Tetramethyl-4-piberidylmalate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis (1,2,2,6,6-pentamethyl-4-piberidyl) Saxine Bis (2,2,6,6-tetramethyl-4-piberidyl) adipate, bis (2,2,6,6-tetramethyl-4-piberidyl) sebacate, bis (2,2,6,6-tetra Methyl-4-piperidyl) fumarate, bis (1,2,3,6-tetramethyl-2,6-diethyl-4-piberidyl) sebacate, bis (1-allyl-2,2,6,6-tetramethynol-4) -Piperidyl) phthalate, bis (1,2,2,6,6-pentamethyl-4-piberidyl) sebacate, 1,1 '-(1,2-ethanediyl) bis (3,3,5,5-tetramethylpipe Radinone), 2-methyl-2- (2,2,6,6-tetramethyl-4-piperidyl) imino-N- (2,2,6,6-tetramethyl-4-piperidyl) propionamide, 2 -Methyl-2- ( , 2,2,6,6-pentamethyl-4-piperidyl) imino-N- (1,2,2,6,6-pentamethyl-4-piperidyl) propionamide, 1-propargyl-4-β-cyanoethyloxy- 2,2,6,6-tetramethylpiperidine, 1-acetyl-2,2,6,6-tetramethyl-4-piperidyl-acetate, trimellitic acid-tris (2,2,6,6-tetramethyl- 4-piperidyl) ester, 1-acryloyl-4-benzyloxy-2,2,6,6-tetramethylpiperidine, bis (1,2,2,6,6-pentamethyl-4-piperidyl) dibutylmalonate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) dibenzylmalonate, bis (1,2,3,6-tetramethyl-2,6-diethyl-4-piperidyl ) Dibenzyl-malonate, bis (1,2,2,6,6-pentamethyl-4-piberidyl) -2- (3,5-di-tert-butyl-4-hydroxybenzyl) -2-n-butylmalonate Bis (2,2,6,6-tetramethyl-4-piperidyl) -1,5-dioxaspiro [5.5] undecane-3,3-dicarboxylate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) -1,5-dioxaspiro [5.5] undecane-3,3-dicarboxylate, bis (1-acetylbre 2,2,6,6-tetramethyl-4-piperidyl) -1 , 5-Dioxaspiro [5.5] undecane-3,3-dicarboxylate, 1,3-bis [2,2 ′-[bis (2,2,6,6-tetramethyl-4-piperidyl) -1 , 3-Dioxasic Rohexane-5,5-dicarboxylate]], bis (2,2,6,6-tetramethyl-4-piperidyl) -2- [1-methylethyl] -1,3-dioxacyclohexane-5,5 -Dicarboxylate]], 1,2-bis [2,2 '-[bis (2,2,6,6-tetramethyl-4-piperidyl) -2-methyl-1,3-dioxacyclohexane-5 , 5-dicarboxylate]], bis (2,2,6,6-tetramethyl-4-piperidyl) -2- [2- (3,5-di-tert-butyl-4-hydroxyphenyl)] ethyl -2-methyl-1,3-dioxacyclohexane-5,5-dicarboxylate, bis (2,6,6-tetramethyl-4-piperidyl) -1,5-dioxaspiro [5.11] heptadecane-3 , 3-Dicarboxylate Hexane-1 ′, 6′-bis-4-carbamoyloxy-1-n-butyl-2,2,6,6-tetramethylpiperidine), toluene-2 ′, 4′-bis (4-carbamoyloxy) -1-n-butyl-2,2,6,6-tetramethylpiperidine), dimethyl-bis (2,2,6,6-tetramethylpiperidine-4-oxy) -silane, phenyl-tris (2,2 , 6,6-tetramethylpiperidine-4-oxy) -silane, tris (1-propyl-2,2,6,6-tetramethyl-4-piperidyl) -phosphite, tris (1-propyl-2,2 , 6,6-tetramethyl-4-piperidyl) -phosphate, phenyl- [bis (1,2,2,6,6-pentamethyl-4-piperidyl)]-phosphonate, tetrakis (2,2,6,6- Tetrame Til-4-piperidyl) 1,2,3,4-butanetetracarboxylate, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, Tetrakis (2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butanetetracarbonamide, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) 1, 2,3,4-butanetetracarbonamide, 2-dibutylamino-4,6-bis (9-aza-3-ethyl-8,8,10,10-tetramethyl-1,5-dioxaspiro [5.5 ] -3-Undecylmethoxy) -s-triazine, 2-dibutylamino-4,6-bis (9-aza-3-ethyl-8,8,9,10,10-pentamethyl-1,5-dioxaspiro 5.5] -3-undecylmethoxy) -s-triazine, tetrakis (9-aza-3-ethyl-8,8,10,10-tetramethyl-1,5-dioxaspiro [5.5] -3- Undecylmethyl) -1,2,3,4-butanetetracarboxylate, tetrakis (9-aza-3-ethyl-8,8,9,10,10-pentamethyl-1,5-dioxaspiro [5.5] -3-undecylmethyl) -1,2,3,4-butanetetracarboxylate, tridecyltris (2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butanetetra Carboxylate, tridecyl tris (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, di (tridecinol) bis (2,2,6 6-tetramethyl-4-piberidyl) 1,2,3,4-butanetetracarboxylate, di (tridecyl) bis (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3 , 4-butanetetracarboxylate, 2,2,4,4-tetramethyl-7-oxa-3,20-diazadispiro [5,1,11,2] heneicosan-21-one, 3,9-bis [1 , 1-dimethyl-2- {tris (2,2,6,6-tetramethyl-4-piperidyloxycarbonyl) butylcarboyloxy} ethyl] -2,4,8,10-tetraoxaspiro [5.5 ] Undecane, 3,9-bis [1,1-dimethyl-2- {tris (1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyl) butylcarboeroxy} ethyl] -2,4 , 8,10-tetraoxaspiro [5.5] undecane, poly (2,2,6,6-tetramethyl-4-piperidyl acrylate), poly (1,2,2,6,6-pentamethyl-4- Piperidyl acrylate), poly (2,2,6,6-tetramethyl-4-piperidyl methacrylate), poly (1,2,2,6,6-pentamethyl-4-piperidyl methacrylate), poly [[bis (2, 2,6,6-tetramethyl-4-piperidyl) itaconate] [vinyl butyl ether]], poly [[bis (1,2,2,6,6-pentamethyl-4-piperidyl) itaconate] [vinyl butyl ether]], Poly [[bis (2,2,6,6-tetramethyl-4-piperidyl) itaconate] [vinyl octyl ether]], poly [[bis (1,2,2, , 6-pentamethyl-4-piperidyl) itaconate] [vinyl octyl ether]], dimethyl succinate-2- (4-hydroxy-2,2,6,6-tetramethylpiperidyl) ethanol condensate, poly [hexamethylene [ (2,2,6,6-tetramethyl-4-piperidyl) imino]], poly [ethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2, 6,6-tetramethylene-4-piperidyl) imino]], poly [[1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] Hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino]], poly [[6- (diethylimino) -1,3,5-triazine-2,4-dii ] [(2,2,6,6-tetramethyl-4-piberidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piberidyl) imino]], poly [[6-[( 2-ethylhexyl) imino] -1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6 6-tetramethyl-4-piperidyl) imino]], poly [[6-[(1,1,3,3-tetramethylbutyl) imino] -1,3,5-triazine-2,4-diyl] [ (2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino]], poly [[6- (cyclohexylimino) -1,3,5-triazine-2,4-dii L] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino]], poly [[6-morpholino -1,3,5-triazine-2,4-diinol] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4 -Piperidyl) imino]], poly [[6- (butoxyimino) -1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] Hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino]], poly [[6-[(1,1,3,3-tetramethylbutyl) oxy] -1,3,5 -Triazine-2,4-diyl] [(2,2,6,6- Tramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piberidyl) imino]], poly [oxy [6-[(1-piperidyl) -1,3,5- Triazine-2,4-diyloxy-1,2-ethanediyl] [(2,2,6,6-tetramethyl-3-oxo-1,4-piperidyl) -1,2-ethanediyl]] [(3,3 , 5,5-tetramethyl-2-oxo-1,4-piberidyl) -1,2-ethanediyl]], poly [oxy [6-[(1,1,3,3-tetramethylbutyl) imino]- 1,3,5-triazine-2,4-diyloxy-1,2-ethanediyl] [(2,2,6,6-tetramethyl-3-oxo-1,4-piperidyl) -1,2-ethanediyl] [(3,3,5,5-tetramethyl 2-oxo-1,4-piperidyl) -1,2-ethanediyl]], poly [[6-[(ethylacetyl) imino] -1,3,5-triazine-2,4-diyl] [(2, 2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piberidyl) imino]], poly [[6-[(2,2,6 , 6-Tetramethyl-4-piberidyl) butylimino] -1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [( 2,2,6,6-tetramethyl-4-piperidyl) imino]], 1,6,11-tris [{4,6-bis (N-butyl-N- (2,2,6,6-tetra Methyl-4-piperidyl) amino) -1,3,5-triazine-2 -Yl} amino] undecane, 1,6,11-tris [{4,6-bis (N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -1, 3,5-triazin-2-yl} amino] undecane, 1,6,11-tris [{4,6-
Bis (N-octyl-N- (2,2,6,6-tetramethyl-4-piperidyl) amino) -1,3,5-triazin-2-yl} amino] undecane, 1,6,11-tris [{4,6-bis (N-octyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -1,3,5-triazin-2-yl} amino] undecane, Polymethyl-propyl-3-oxy [1 (2,2,6,6-tetramethyl) piperidyl] siloxane, 1,1 ', 1 "-[1,3,5-triazine-2,4,6-triyl- Tris [(cyclohexylimino) -2,1-ethanediyl]]-tris [3,3,5,5-tetramethylpiperazin-2-one], 1,1,1-tris [polyoxypropylene- {4,6 -Bis (N-butyl-N- (2,2, , 6-tetramethyl-4-piperidyl) amino) -1,3,5-triazin-2-yl} aminoethermethyl] propane, 1,1,1-tris [polyoxyethylene- {4,6-bis ( N-butyl-N- (2,2,6,6-tetramethyl-4-piperidyl) amino) -1,3,5-triazin-2-yl} aminoethermethyl] propane, 1,1,1-tris [Polyoxyethylene- {4,6-bis (N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -1,3,5-triazin-2-yl} Aminoethermethyl] propane, 1,1,1-tris [polyoxypropylene- {4,6-bis (N-butyl-N- (2,2,6,6-tetramethyl-4-piperidyl) amino)- 1,3,5-triazine-2 -Yl} aminoethermethyl] provan, 1,1,1-tris [polyoxypropylene- {4,6-bis (N-butyl-N- (1,2,2,6,6-pentamethyl-4-piberidyl) ) Amino) -1,3,5-triazin-2-yl} aminoethermethyl] propane, 1,5,8,12-tetrakis [4,6-bis (N- (2,2,6,6-tetra) Methyl-4-piperidyl) -butylamino) -1,3,5-triazin-2-yl] -1,5,8,12-tetraazadodecane, 1,5,8,12-tetrakis [4,6- Bis (N- (1,2,2,6,6-pentamethyl-4-piperidyl) -butylamino) -1,3,5-triazin-2-yl] -1,5,8,12-tetraazadodecane Etc.

  Examples of the oxalic acid anilide compound include N, N′-diethyloxalic acid-bis-anilide, 2-ethoxy-2′-ethyl oxalic acid-bis-anilide, and 2-ethoxy-5. -Tert-butyl-2'-ethyloxalic acid-bis-anilide and 2-ethoxy-5-tert-butyl-2'-ethyl-4'-tert-butyloxalic acid-bis-anilide It is done. As a commercial item, brand name "TINUVIN312" and brand name "TINUVIN315" (made by BASF Japan) are mentioned.

  Examples of the formamidine ultraviolet absorber include N- (4-ethoxycarbonylphenyl) -N′-methyl-N′-phenylformamidine, N- (4-ethoxycarbonylphenyl) -N′-ethyl-N. Examples include '-phenylformamidine, N- (4-ethoxycarbonylphenyl) -N'-ethoxyl-N'-phenylformamidine and N- (4-ethoxycarbonylphenyl) -N', N'-diphenylformamidine. It is done.

  Examples of the triazine compound as the ultraviolet absorber include 2- [4,6-di (2,4-xylyl) -1,3,5-triazin-2-yl] -5-octyloxyphenol, 2- (4 , 6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol and the like. As the component (c) component hydroxybenzoate light stabilizer, 2,4-di-tert-butylphenyl-3 ′, 5′-di-tert-butyl-4′-hydroxybenzoate, 2,6-di-tert -Butylphenyl-3 ', 5'-di-tert-butyl-4'-hydroxybenzoate, n-hexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate and n-octadecyl-3,5-di -Tert-butyl-4-hydroxybenzoate and the like can be used.

  As the ultraviolet absorber, a compound having both a phenolic hydroxyl group and a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms is preferably used. Since the phenolic hydroxyl group of the ultraviolet absorber has a high polarity, it has a high affinity for the heat-resistant acrylic resin having an ester group with a high polarity. Since the branched alkyl group or linear alkoxy group of the ultraviolet absorber contains a carbon chain having a low polarity and an appropriate length, it has an affinity for an acrylic rubber that easily interacts with the carbon chain. high. Therefore, the ultraviolet absorber is likely to be present at the interface between the heat-resistant acrylic resin and the acrylic rubber. Therefore, the ultraviolet absorbent is uniformly dispersed in the matrix of the protective sheet. As a result, the protective sheet can exhibit an excellent ultraviolet absorbing ability.

  The ultraviolet absorber has a melting point of preferably 110 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 130 ° C. or higher. When the melting point of the UV absorber is less than the above lower limit, there is little volatilization when heated and melted for processing, precipitation and aggregation of the UV absorber at a molding outlet such as an extrusion outlet is difficult to occur, and contamination during sheet molding Is less likely to occur and does not hinder the transparency of the sheet.

  As content of the said ultraviolet absorber, 0.5 mass% or more and 10 mass% or less are preferable with respect to a matrix phase, 1 mass% or more and 9 mass% or less are more preferable, and 2 mass% or more and 8 mass% or less are further. preferable. There exists a possibility that the protective sheet obtained may not fully absorb an ultraviolet-ray as content of an ultraviolet absorber is less than the said minimum. Moreover, when content of a ultraviolet absorber exceeds the said upper limit, there exists a possibility that the heat resistance of a protective sheet may fall.

<Fine particles>
The protective sheet contains fine particles in the matrix phase. As the material of the fine particles, silicon dioxide is preferably used. In addition, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, silicic acid. It is also possible to use inorganic materials such as magnesium and calcium phosphate and organic materials such as cross-linked polymers. In addition, it is preferable to employ silicon dioxide as the material of the fine particles because the haze of the protective sheet can be reduced. Moreover, it is preferable from the viewpoint of reducing the haze of the protective sheet that the fine particles whose surface is treated with an organic substance is used as the material of silicon dioxide. Examples of the organic substance used for the surface treatment include halosilanes, alkoxysilanes, silazane, and siloxane. Examples of commercially available products include “Sirohovic” (manufactured by Fuji Silysia Chemical), “Aerosil 200V” (manufactured by Nippon Aerosil Co., Ltd.), and “Aerosil R972V” (manufactured by Nippon Aerosil Co., Ltd.). These can be used alone or in combination.

  The fine particles preferably have an average particle size of 0.005 μm to 2 μm, and more preferably 0.05 μm to 1 μm. The fine particles are arranged so as to protrude from the surface of the protective sheet, and the maximum protruding height of the fine particles is preferably 0.01 μm or more and 0.1 μm, and is 0.02 μm or more and 0.05 μm or less. Is more preferable. The fine particles are provided so as to protrude from the surface as described above by stretching (finely stretching) the sheet when forming the protective sheet.

  The content of the fine particles is preferably 0.005% by mass or more and 1% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, and more preferably 0.1% by mass or more and 0% by mass with respect to the protective sheet. .3% by mass or less is particularly preferable.

  The fine particles may be contained not only in the matrix phase but also in the dispersed phase. The fine particles to be contained in the dispersed phase can be the same material, maximum protrusion height and blending amount as those of the fine particles contained in the matrix phase.

<Protective sheet>
The protective sheet is formed by, for example, extrusion molding a mixture of a heat-resistant acrylic resin that forms a matrix phase and an acrylic rubber that forms a dispersed phase. Here, the protective sheet is formed into a sheet by being slightly stretched after extrusion. This stretching is preferably uniaxial stretching. Moreover, the draw ratio by this fine drawing is 1% or more and 5% or less. In order to realize the stretch ratio, for example, the extrusion is performed in a state where the tensile speed for pulling the cooled and formed sheet is 0.3% higher than the extrusion speed at which the molten material is extruded during the extrusion. As described above, fine stretching after extrusion makes it easy to dispose the fine particles in a state of protruding from the surface of the protective sheet, thereby improving the slipperiness of the protective sheet. Moreover, since it is fine extending | stretching, transparency of a protection sheet is maintainable.

  The thickness of the protective sheet is preferably 15 μm or more and 400 μm or less, more preferably 20 μm or more and 300 μm or less, further preferably 40 μm or more and 200 μm or less, and particularly preferably 40 μm or more and 150 μm or less. By setting the thickness of the protective sheet within the above range, the protective sheet can be provided with sufficient toughness, and the protective sheet can be easily wound.

  The thickness of the polarizing plate produced by bonding with a polarizer using the protective sheet is preferably from 150 μm to 800 μm, more preferably from 180 μm to 700 μm, and even more preferably from 200 μm to 600 μm. By setting the thickness of the polarizing plate in the above range, the handleability can be improved such that sufficient toughness can be imparted to the polarizing plate and the polarizing plate can be easily wound.

In the protective sheet, the planar retardation value (Re) is preferably 0 nm or more and 15 nm or less. Moreover, it is preferable that the retardation value (Rth) of the thickness direction is -15 nm or more and 0 nm or less. Here, the retardation value (Re) in the planar direction and the retardation value (Rth) in the thickness direction are defined by equations (a) and (b), respectively.
Re1 = (nx1-ny1) × d [nm] (a)
Rth1 = {(nx1 + ny1) / 2−nz1} × d [nm] (b)
Here, nx1 is the main refractive index in the planar direction of the protective sheet. ny1 is a refractive index in a direction orthogonal to nx1. nz1 is the main refractive index in the thickness direction of the protective sheet. d is the thickness of the protective sheet.

<Polarizing plate>
The protective sheet can be used as a polarizing plate protective sheet. Specifically, as shown in FIG. 1, a polarizing plate can be constituted by a pair of the protective sheets 1 and a plate-like polarizer 2 interposed between the pair of protective sheets 1. The protective sheet 1 and the polarizer 2 can be attached with an adhesive (not shown) such as aqueous glue.

<Liquid crystal display element>
The polarizing plate provided with the protective sheet 1 can be used in a liquid crystal display device. Specifically, as shown in FIG. 2, a liquid crystal display element can be configured from a liquid crystal panel and a pair of the polarizing plates attached to both surfaces of the liquid crystal panel 3. The polarizing plate and the liquid crystal panel 3 can be attached by an adhesive 4 such as an ultraviolet effect adhesive.

<Other embodiments>
In addition, this invention is not limited to the said embodiment, A various design change is possible, and it is also possible to give a mat process to the single side | surface or both surfaces of the said protection sheet. Thereby, the effect that it becomes easy to stick the surface which gave the mat | matte process to another member via an adhesive agent etc. is exhibited. In the polarizing plate of FIG. 3, the mat layer 5 is formed on one side of each of the pair of protective sheets 1. And the polarizer 2 is arrange | positioned between the mat layers 5 of this pair of protective sheets 1, and the mat layer 5 and the polarizer 2 are stuck by the water-system adhesive (illustration omitted). The mat layer 5 can be formed using a mat agent. Specifically, the mat layer 5 can be formed by applying a coating liquid containing a mat agent to one surface of the protective sheet 1. As the matting agent, organic or inorganic fine particles can be used. For example, silica, talc, calcium carbonate, precipitated barium sulfate, alumina, acidic clay, clay, magnesium carbonate, carbon black, tin oxide, titanium White, urea powder resin, etc. can be used.

  Moreover, as shown in FIG. 3, it is also possible to employ | adopt the structure by which the hard-coat layer 6 was laminated | stacked on the single side | surface of the said protection sheet. In the polarizing plate of FIG. 3, in one of the pair of protective sheets 1, the hard coat layer 6 is laminated on the surface of the protective sheet 1 that does not face the polarizer 2. Thereby, the abrasion resistance of the protective sheet 1 can be improved. The hard coat layer 6 is formed by applying an acrylic paint. Thereby, the transparency of the hard coat layer 6 is also ensured, and the transparency of the protective sheet 1 can be maintained.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

<Manufacture of heat-resistant acrylic resin>
[Synthesis Example 1]
(Heat resistant acrylic resin (A-1):
(Synthesis of methyl methacrylate-styrene-methacrylic acid-main chain 6-membered ring lactone)
As monomers, 35 parts by weight of methyl methacrylate, 25 parts by weight of styrene, 15 parts by weight of methyl α-hydroxymethyl acrylate and 8 parts by weight of methacrylic acid, 20 parts by weight of metaxylene, as a polymerization initiator, A liquid mixture composed of 50 mass ppm of “Perhexa C” (1,1-di (tert-butylperoxy) cyclohexane) manufactured by NOF Corporation and 1500 mass ppm of n-octyl mercaptan as a molecular weight regulator was prepared. This mixed solution was continuously supplied to a jacketed complete mixing reactor having an internal volume of 3 L at a feed rate of 1.5 L / hr, and a polymerization reaction was performed at a temperature of 125 ° C. By continuously supplying the polymerization reaction solution discharged from the reactor to a high-temperature degasser having a residence time of 2 hours set at a temperature of 260 ° C., hydroxymethyl groups and methoxy bonded to the polymer main chain A main chain 6-membered ring lactone was formed by a dehydration reaction from a carbonyl group, and unreacted substances were removed. Then, the heat resistant acrylic resin (A-1) was obtained by processing. This heat-resistant acrylic resin (A-1) was analyzed by neutralization titration, IR spectrum, and ¹³ C-NMR. As a result, a methyl methacrylate-derived structural unit, a styrene-derived structural unit, a main chain 6-membered ring lactone Each content rate of a containing structural unit and the methacrylic acid origin structural unit was 45 mass%, 30 mass%, 18 mass%, and 7 mass%. Moreover, the melt flow rate value (ASTM-D1238; 230 degreeC, 3.8 kg load) of a heat resistant acrylic resin (A-1) is 1.1 g / 10min, and a glass transition temperature (Tg) is 135 degreeC. And the refractive index was 1.528.

[Synthesis Example 2]
(Heat-resistant acrylic resin (A-2):
(Synthesis of methyl methacrylate-α-methylstyrene-methacrylic acid-main chain 6-membered ring lactone)
As monomers, 48 parts by weight of methyl methacrylate, 6 parts by weight of α-methylstyrene, 8 parts by weight of methyl α-hydroxymethyl acrylate and 5 parts by weight of methacrylic acid, 40 parts by weight of tert-butanol as polymerization reaction solvent, polymerization A liquid mixture consisting of 500 mass ppm of 1,1-di (tert-butylperoxy) -3,3,5-trimethylcyclohexane as an initiator and 200 mass ppm of n-octyl mercaptan as a molecular weight regulator was prepared. . This mixed solution was continuously supplied to a jacketed complete mixing reactor having an internal volume of 3 L at a feed rate of 1.5 L / hr, and a polymerization reaction was performed at a temperature of 125 ° C. By continuously supplying the polymerization reaction liquid discharged from the reactor to a high-temperature degassing apparatus having a residence time of 2 hours set at a temperature of 260 ° C., a main chain 6-membered lactone formation reaction and an unreacted product Was removed. Then, the heat resistant acrylic resin (A-2) was obtained by processing. This heat resistant acrylic resin (A-2) was analyzed by neutralization titration, IR spectrum, and ¹³ C-NMR. As a result, a structural unit derived from methyl methacrylate, a structural unit derived from α-methylstyrene, a main chain 6 Each content rate of a member ring lactone containing structural unit and a methacrylic acid origin structural unit was 80 mass%, 11 mass%, 6 mass%, and 3 mass%. Moreover, the melt flow rate value (ASTM-D1238; 230 degreeC, 3.8 kg load) of a heat resistant acrylic resin (A-2) is 1.5 g / 10min, and a glass transition temperature (Tg) is 132 degreeC. And the refractive index was 1.504.

<Manufacture of acrylic rubber>
[Synthesis Example 3]
(Three-layer acrylic rubber fine particles)
Charge 300 parts by mass of ion-exchanged water into a reaction vessel equipped with a stirrer, raise the temperature to 70 ° C. while purging with nitrogen, and then add 0.3 parts by mass of sodium dihexylsulfosuccinate and 0.3 parts by mass of potassium persulfate. did. Subsequently, as a monomer, a mixture consisting of 23 parts by mass of methyl methacrylate, 2 parts by mass of n-acrylic acid-n-butyl and 0.03 parts by mass of allyl methacrylate was added and held for 1 hour to carry out the polymerization reaction. Completed. Next, as a monomer, a mixture comprising 22 parts by mass of n-butyl acrylate, 28 parts by mass of styrene, and 1.0 part by mass of allyl methacrylate was added over 2 hours, and then the reaction was completed by maintaining for 2 hours. I let you. Furthermore, a monomer mixture consisting of 22 parts by mass of methyl methacrylate and 3 parts by mass of n-butyl acrylate as a monomer and 0.05 part by mass of n-octyl mercaptan as a molecular weight regulator was added over 1 hour. Thereafter, the reaction was completed by holding for 1 hour. The obtained latex was salted out using sodium sulfate as a salting-out agent, and then dehydrated, washed with water, dehydrated, and dried to obtain an acrylic rubber (B-1) as a powder. The resulting acrylic rubber fine particles (B-1) had a particle size of 45 nm and a refractive index of 1.519.

[Synthesis Example 4]
(Synthesis of two-layer acrylic rubber particles)
After charging 300 parts by mass of ion-exchanged water into a reaction vessel equipped with a stirrer and raising the temperature to 70 ° C. while replacing with nitrogen, 0.3 parts by mass of sodium dihexylsulfosuccinate and 0.3 parts by mass of potassium persulfate were added. Prepared. Subsequently, as a monomer, a mixture composed of 24 parts by mass of n-butyl acrylate, 28 parts by mass of styrene, and 2.0 parts by mass of allyl methacrylate was added over 2 hours, and then the reaction was maintained for 2 hours. Was completed. Next, after adding 45 parts by mass of methyl methacrylate and 3 parts by mass of n-butyl acrylate as a monomer and 0.05 parts by mass of n-octyl mercaptan as a molecular weight regulator, over 1 hour, The reaction was completed by holding for 1 hour. The obtained latex was salted out using sodium sulfate as a salting-out agent, and then dehydrated, washed with water, dehydrated and dried to obtain a two-layer acrylic rubber fine particle (B-2) as a powder. The resulting acrylic rubber fine particles (B-2) had a particle size of 49 nm and a refractive index of 1.518.

<Manufacture of protective sheet>
[Example 1]
45 parts by mass of the heat-resistant acrylic resin (A-1) obtained in the above synthesis example, 15 parts by mass of (A-2), 20 parts by mass of acrylic rubber fine particles (B-1), and (B-2 Example 1) After dry blending with 20 parts by mass, extrusion was performed using a T-die mounting extruder while adjusting the screw speed, the resin temperature in the cylinder of the extruder, and the temperature of the T die. A protective sheet was obtained. The protective sheet of Example 1 had a surface roughness Ra of 0.04 to 0.05 μm and a haze value of 0.8%. The surface roughness is an arithmetic average roughness measured according to JIS-B-0601-2001 and having a cutoff value λc of 2.5 mm and an evaluation length of 12.5 mm.

[Examples 2 and 3]
In Example 1, the protective sheets of Examples 2 and 3 were obtained in the same manner as in Example 1 except that the types and compounding ratios of the heat-resistant acrylic resin and acrylic rubber were as described in Table 1 below. It was. The protective sheet of Example 2 had a surface roughness Ra of 0.03 to 0.04 μm and a haze value of 0.7%. In addition, the protective sheet of Example 3 had a surface roughness Ra of 0.01 to 0.02 μm and a haze value of 0.6%.

[Comparative Examples 1-3]
In Example 1, an acrylic rubber (b-1) having a primary average particle size of 0.5 μm or more is used as the acrylic rubber, and the kind and blending amount of the heat-resistant acrylic resin, and the acrylic rubber (b A protective sheet of Comparative Examples 1 to 3 was obtained in the same manner as in Example 1 except that the blending amount of -1) was as described in Table 1 below. The protective sheet of Comparative Example 1 had a surface roughness Ra of 3.5 μm and a haze value of 8.5%. Moreover, the protective sheet of Comparative Example 2 had a surface roughness Ra of 2.5 μm and a haze value of 6.5%. Furthermore, the surface roughness (Ra) of the protective sheet of Comparative Example 3 was 1.5 μm, and its haze value was 5.2%.

<Evaluation>
The following evaluation was performed about the manufactured protection sheet. The evaluation results are shown in Table 1 below.

<Total light transmittance, haze>
It measured using the Suga Test Instruments Co., Ltd. double beam system haze computer (HZ-2).

<Refractive index difference>
Regarding the acrylic rubber sample, the medium having a refractive index of 1.59 and 1.49, respectively, was mixed with the resin sample while changing the ratio, and the point at which the cloudiness disappeared was defined as the refractive index (23 ° C., 550 nm). . And the difference with the refractive index with the heat-resistant acrylic resin (A-1, A-2) press-molded separately measured with the laser refractometer was computed.

<Resin viscosity (MI value)>
In a heated cylindrical container, a certain amount of synthetic resin was heated and pressurized at a predetermined temperature, and the amount of resin extruded per 10 minutes from the opening provided at the bottom of the container was measured. The test machine used was an extrusion plastometer defined by JIS K6760, and the measurement method was in accordance with JIS K7210.

(Discussion)
As shown in Table 1 above, the protective sheets of Examples 1 to 3 had a very low haze value and high transparency without being clouded as compared with the sheets of Comparative Examples 1 to 3.

  Since the protective sheet of the present invention is rich in heat resistance and flexibility and has high transparency, it can be used, for example, as a light guide plate protective sheet.

DESCRIPTION OF SYMBOLS 1 Protective sheet 2 Polarizer 3 Adhesive 4 Liquid crystal panel 5 Matt processed layer 6 Hard coat layer

Claims (8)

Ri Do different composition and weight average molecular weight of the monomer component as a main polymer, one of the heat-resistant acrylic resin of styrene-derived structural unit and a lactone structure, the other heat-resistant acrylic resin α- methylstyrene-derived structural unit and a lactone the weight average molecular weight having the structure (Mw) matrix containing 10,000 or more 400,000 or less and a molecular weight distribution (Mw / Mn) of a mixture of two or more heat-resistant acrylic resin Ru der 1.8 to 2.5 A sea-island structure protective sheet having a phase and a dispersed phase containing acrylic rubber as a main polymer,
The refractive index difference between the matrix phase and the dispersed phase is 0.01 or less,
An average particle size of the dispersed phase is 1 nm or more and less than 50 nm.   The protective sheet according to claim 1, wherein the content of the dispersed phase is 5% by mass or more and 40% by mass or less.   The protective sheet according to claim 1 or 2, wherein the retardation value in the planar direction is 0 nm or more and 15 nm or less, and the retardation value in the thickness direction is -15 nm or more and 0 nm or less.   4. The protective sheet according to claim 1, wherein the heat-resistant acrylic resin has a total light transmittance of 90% or more and a Vicat softening point of 105 ° C. or more and 140 ° C. or less.   The protective sheet according to any one of claims 1 to 4, wherein the heat-resistant acrylic resin has a ring structure in the main chain.   The protective sheet according to any one of claims 1 to 5, wherein mat processing is performed on one side or both sides. It is a protection sheet given in any 1 paragraph of Claims 1-6, Comprising: It is a manufacturing method of a protection sheet provided with the hard-coat layer laminated on one side,
A method for producing a protective sheet, wherein the hard coat layer is formed by applying an acrylic paint. A sheet-like polarizer,
A polarizing plate provided with a pair of protective sheet of any one of Claims 1-6 laminated | stacked through the adhesive bond layer on both surfaces of this polarizer.

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