TWI462832B - Protective sheet and polarizer - Google Patents

Description

Protective sheet and polarizing plate

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

In recent years, liquid crystal display devices have been widely used in place of CRTs because they are thin, light, and consume little power. Specifically, liquid crystal display devices are widely used from small items such as computers and clocks to large-scale articles such as automobile measuring instruments, PC screens, and televisions.

The liquid crystal display element incorporated in the liquid crystal display device has a liquid crystal cell and a polarizing plate disposed on one of the two sides of the liquid crystal cell. The polarizing plate includes a sheet-shaped polarizing element and a protective sheet disposed on one of two sides of the polarizing element. The protective sheet is a sheet for protecting the structure of the polarizing element, and is generally formed of triacetyl cellulose (hereinafter referred to as "TAC") having a small birefringence and excellent transparency.

However, the heat and humidity resistance of the TAC is not sufficient. When a polarizing plate using TAC as a protective film for a polarizing element is used under high temperature or high humidity, the performance of the polarizing plate such as a degree of polarization and a color tone is deteriorated. And TAC produces a phase difference for incident light in an oblique direction. In recent years, as the size of liquid crystal displays has been increasing, this phase difference has significantly affected the viewing angle characteristics. Therefore, it has been studied to use a heat-resistant acrylic resin instead of TAC.

Specifically, a protective sheet having a sea-shell 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, refer to Japanese Patent Laid-Open No. 2010-70646 Bulletin). Further, it has been studied that the matrix phase contains an ultraviolet absorber (for example, refer to JP-A-2010-70646).

Various studies have been made in the above-mentioned Japanese Patent Laid-Open Publication No. 2010-70646. However, when a heat-resistant acrylic resin is used as a substitute for TAC, it is necessary to sufficiently improve heat resistance, ultraviolet absorbing ability, and flexibility of the protective sheet.

Patent Document 1: JP-A-2010-70646

The present invention has been made in view of such disadvantages, and an object thereof is to provide a protective sheet having high heat resistance, high ultraviolet absorbing ability, and high flexibility, and a polarizing plate having the protective sheet.

In order to solve the above problems, the present invention is a protective sheet which 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 matrix phase The ultraviolet absorber contains a compound having 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.

The protective sheet has a sea-shell 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, so that the protective sheet has high heat resistance and high flexibility. The effect. Further, since the matrix phase contains an ultraviolet absorber, the protective sheet has an effect of being difficult to yellow, and the ultraviolet absorber of the protective sheet contains a phenolic hydroxyl group and a branched alkyl group or carbon number of 4 to 12 carbon atoms. a linear alkoxy group of 4 to 12. Since the phenolic hydroxyl group of the above ultraviolet absorbent has a high polarity, it has a high affinity for the above heat resistant acrylic resin having a relatively high polar ester group. Since the branched alkyl group or the linear alkoxy group of the above ultraviolet absorber has a low polarity and a carbon chain of an appropriate length, it has a high affinity for an acrylic rubber which easily interacts with the carbon chain. Therefore, the above ultraviolet absorber is likely to exist at the interface between the heat resistant acrylic resin and the acrylic rubber. Therefore, in the matrix of the protective sheet, the above ultraviolet absorbent is uniformly dispersed. As a result, the protective sheet can exhibit excellent ultraviolet absorbing ability.

The above dispersed phase preferably contains the above ultraviolet absorbent. The dispersed phase is improved in dispersion uniformity of the ultraviolet absorber in the protective sheet by containing the ultraviolet absorber. Therefore, when the protective sheet is formed in the two-layer layer of the sheet-shaped polarizing element to form a polarizing plate, the ultraviolet light penetration of the polarizing element can be further suppressed.

The content of the ultraviolet absorber in the matrix phase or the dispersed phase is preferably 0.5% by mass or more and 10% by mass or less. When the content of the ultraviolet absorber is less than 0.5% by mass, the protective sheet may not sufficiently absorb ultraviolet rays, and if the content of the ultraviolet absorber exceeds 10% by mass, the heat resistance of the protective sheet may be lowered. However, when the content of the ultraviolet absorber is 0.5% by mass or more and 10% by mass or less, the protective sheet can sufficiently absorb ultraviolet rays and maintain a state of high heat resistance.

The content of the dispersed phase is preferably 5% by mass or more and 40% by mass or less. When the content is 5% by mass or more, the flexibility of the protective sheet can be further improved. When the content is 40% by mass or less, the transparency of the protective sheet can be maintained.

In the protective sheet, the retardation value in the planar direction is preferably 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. As a result, the transmitted light that penetrates the protective sheet is less likely to cause a phase difference. Therefore, even if a protective sheet having a polarizing function such as a polarizing plate is used, there is an advantage that the polarizing function is not hindered.

The heat resistant acrylic resin preferably has a ring structure in the main chain. Thereby, the protective sheet can have an effect of higher heat resistance.

Preferably, the protective sheet is subjected to mat processing on one side or both sides. Thereby, it is possible to exhibit an effect that the surface on which the matte finish is applied is easily attached to another member via the adhesive. For example, the surface on which the matte finish is applied is followed by one surface of the sheet-shaped polarizing element by an aqueous adhesive, whereby the protective sheet can be firmly attached to the polarizing element to produce a polarizing plate.

Preferably, the protective sheet is provided with a hard coat layer in a single area layer. The scratch resistance of the protective sheet can be improved by the hard coat layer. Further, the hard coat layer is preferably formed by applying an acrylic paint. Thereby, the transparency of the protective sheet can be maintained.

Furthermore, the present invention also includes a polarizing plate including a sheet-shaped polarizing element and a protective layer laminated on one of both sides of the polarizing element by an adhesive.

As described above, the protective sheet of the present invention has high heat resistance, high ultraviolet absorbing ability, and high flexibility.

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

The protective sheet of the present 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. Thereby, the protective sheet has an effect of high heat resistance and high flexibility.

<matrix phase>

The matrix phase contains a heat-resistant acrylic resin as a main polymer. The heat-resistant acrylic resin means a polymer containing an acrylic monomer such as acrylic acid, methacrylic acid or a derivative thereof as a monomer component. Examples of the heat-resistant acrylic resin include alkyl methacrylates such as cyclohexyl methacrylate, tertiary butylcyclohexyl methacrylate, and methyl methacrylate; methyl acrylate and ethyl acrylate; One type or a plurality of types of acrylic monomers such as butyl acrylate, isopropyl acrylate or 2-ethylhexyl acrylate are polymerized. The heat-resistant acrylic resin also includes a copolymer of an acrylic monomer and another monomer component. In the case of such a copolymerization, the content ratio (copolymerization ratio) of the other monomer component is preferably 60% by mass or less, more preferably 50% by mass or less, more preferably 50% by mass or less, based on the total monomer component constituting the heat-resistant acrylic resin. It is preferably 40% by mass or less.

The heat resistant acrylic resin is preferably a polymer containing methyl methacrylate as a monomer component. By containing a heat-resistant acrylic resin containing methyl methacrylate as a monomer component, the compatibility of the obtained heat-resistant acrylic resin can be 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. Other monomers copolymerizable with methyl methacrylate, for example, alkyl methacrylates other than methyl methacrylate; alkyl acrylates; alkyl α-hydroxymethyl acrylates; styrene, ortho Alkyl-substituted styrene such as styrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α- An aromatic vinyl compound such as styrene substituted with an α-alkyl group such as methyl-p-methylstyrene; an unsaturated nitrile such as acrylonitrile or methacrylonitrile; and N-phenyl maleimide , non-cycloheximide such as N-cyclohexylmaleimide; unsaturated carboxylic anhydride such as maleic anhydride; acrylic acid, methacrylic acid, maleic acid, etc. Saturated carboxylic acids and the like. These other monomers are preferably α-hydroxymethyl acrylates, styrene, alkyl-substituted styrenes, and the like from the viewpoint of improving the flexibility and heat resistance of the protective sheet obtained. Α-alkyl substituted styrene, unsaturated carboxylic acid, more preferably α-hydroxymethyl methacrylate, styrene, α-alkyl substituted styrene, unsaturated carboxylic acid, of which, more preferably It is α-hydroxymethyl methacrylate, styrene, α-methyl styrene, methacrylic acid. When α-hydroxymethyl methacrylate is used as another monomer to copolymerize with methyl methacrylate, the dehydration reaction is further carried out, and since a lactone ring containing a part of the polymer main chain is formed, the result is particularly obtained. The heat resistance of the heat-resistant acrylic resin is improved. These monomers may be used singly or in combination of plural kinds. In the copolymer of such methyl methacrylate and another monomer, the content of the other monomer component is preferably 50% by mass or less based on the methyl methacrylate.

The other monomer copolymerizable with methyl methacrylate described above is preferably an alkyl acrylate. By using an alkyl acrylate as the other monomer, the heat resistance temperature of the obtained heat-resistant acrylic resin can be improved, and the fluidity at the time of molding processing can be increased. In the copolymer of methyl methacrylate and alkyl acrylate, the content of the alkyl acrylate monomer component is preferably 0.1 mass with respect to the total monomer component from the viewpoint of improving heat resistance. %% or more and 15% by mass or less, more preferably 0.2% by mass or more and 14% by mass or less, still more preferably 1% by mass or more and 12% by mass or less.

The alkyl acrylates described above are preferably obtained by copolymerizing a small amount of methyl acrylate and ethyl acrylate with methyl methacrylate in a small amount, since the fluidity at the time of the forming process can be remarkably improved.

The above heat-resistant acrylic resin may also be an isotactic polymethacrylate or a syndiotactic polymethacrylate. Further, the heat-resistant acrylic resin may be produced by directly using a commercially available product or a commercial product which is a precursor.

A method of producing the above-mentioned heat-resistant acrylic resin can be carried out by a conventionally known method, and for example, a polymerization method such as casting polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, or anionic polymerization can be employed. It is preferred to use bulk polymerization or solution polymerization without using a suspending agent or an emulsifier, whereby the incorporation of minute foreign matter can be reduced. Further, in the case of solution polymerization, an aromatic hydrocarbon solvent such as toluene can be used. Further, in the case of bulk polymerization, polymerization can be initiated by irradiation of free radicals or ionizing radiation generated by heating. Further, as the polymerization initiator used for the polymerization reaction, for example, an azo compound such as azobisisobutyronitrile, benzamidine peroxide, lauric acid peroxide, or tertiary butyl peroxy-2-hexanoate may be used. Organic peroxides, etc.

Further, when the polymerization is carried out at a temperature of 90 ° C or higher, generally, solution polymerization is used, but it is preferably used in a polymerization initiator which is soluble in an organic solvent, and a 10-hour half-life temperature of 80 ° C or higher is used. Specific examples of such a polymerization initiator include 1,1-bis(tri-butyl peroxy)-3,3,5-trimethylcyclohexane, cyclohexane peroxide, and 2, 5-Dimethyl-2,5-bis(benzoylperoxy)hexane, 1,1-azohexanecarbonitrile, 2-(aminoformamidine) Azo (carbamoylazo) isobutyronitrile and the like. The amount of the polymerization initiator used in the above polymerization reaction is preferably 0.005 to 5 parts by mass based on 100 parts by mass of the total monomers used for the polymerization.

In the polymerization reaction, a molecular weight modifier can be used as needed. As the molecular weight modifier, those generally used in radical polymerization can be used. Specifically, for example, a thiol compound such as butanol, octyl mercaptan, dodecyl mercaptan or 2-ethylhexyl acetate can be used. These molecular weight modifiers are preferably added in a concentration range in which the molecular weight of the heat-resistant acrylic resin is within a desired range.

In the method for producing a heat-resistant acrylic resin, for example, a method described in JP-A-63-1964 or the like can be used. Further, the heat-resistant acrylic resin can be obtained by copolymerizing an alkyl methacrylate and/or an alkyl acrylate with one or more other monomers to form a copolymer of three or more.

Among the above-mentioned copolymers of more than 3 yuan, other monomer components copolymerized with alkyl methacrylate and/or alkyl acrylate may, for example, be styrene, α-methylstyrene, o-methylstyrene, ortho. Aromatic vinyl compounds such as styrene, o-ethyl styrene, p-ethyl styrene and p-terphenyl styrene; unsaturated nitriles such as acrylonitrile, methacrylonitrile and ethacrylonitrile; N- Methyl maleimide, N-ethyl maleimide, N-cyclohexyl maleimide, N-phenyl maleimide, etc. Amines; acrylamide, methacrylamide, N-methyl acrylamide, butoxymethylacrylamide, N-propyl methacrylamide, etc. Non-saturated carboxylic anhydrides such as maleic anhydride, itaconic acid anhydride; acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, α-substituted methacrylic acid, maleic acid Unsaturated carboxylic acids such as acid; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (methyl) propyl N-butyl acrylate, butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloro (meth) acrylate Ethyl ester, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate and (meth)acrylic acid An unsaturated alkyl carboxylate such as 2,3,4,5-tetrahydroxypentyl ester or the like.

In addition to the heat-resistant acrylic resin as the main polymer, an acrylic resin which is not a heat-resistant acrylic resin (hereinafter also referred to as "acrylic resin (a)") may be further used as the resin constituting the matrix phase. . In this case, the content of each of the heat-resistant acrylic resin and the acrylic resin (a) in the matrix phase is preferably a mass ratio of the acrylic resin (a) to the heat-resistant acrylic resin (acrylic resin (a) ) / heat resistant acrylic resin) is 0.1/99.9 or more and 50/50 or less. The photoelastic coefficient and the glass transition temperature (Tg) of the obtained protective sheet can be adjusted by adjusting the mass ratio of the acrylic resin (a) to the heat-resistant acrylic resin. The above quality is preferably 0.1/99.9 or more and 40/60 or less, more preferably 0.1/99.9 or more and 35/65 or less.

The heat-resistant acrylic resin preferably has a weight average molecular weight (Mw) in terms of polymethyl methacrylate (PMMA) of a gel permeation chromatography (GPC), preferably 10,000 or more and 400,000 or less, more preferably 4 More than 10,000 to 300,000, and even more preferably 70,000 to 200,000. By setting the Mw of the heat-resistant acrylic resin to the above range, the strength of the obtained protective sheet can be improved, and the workability and fluidity of the protective sheet can be improved. Further, 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, still more preferably 1.8 or more and 2.5 or less.

The heat-resistant acrylic resin may be a mixture of two or more kinds of heat-resistant acrylic resins having different monomer compositions and molecular weights. At this time, the above weight average molecular weight means the average value thereof.

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

When the heat-resistant acrylic resin is a heat-resistant acrylic resin (hereinafter also referred to as "heat-resistant acrylic resin (1)") which does not contain an aromatic vinyl monomer as a monomer component, the heat-resistant acrylic resin ( The content of the acrylic monomer component in 1) is preferably 40% by mass or more based on the total monomer component constituting the heat-resistant acrylic resin (1). As the acrylic resin (1), for example, a methacrylate selected from cyclohexyl methacrylate, dimethylcyclohexyl methacrylate or methyl methacrylate; methyl acrylate or ethyl acrylate; One or more monomers of acrylate such as butyl acrylate, isopropyl acrylate or 2-ethylhexyl acrylate are polymerized.

The weight average molecular weight of the acrylic resin (1) is preferably 50,000 or more and 200,000 or less, more preferably 70,000 or more and 150,000 or less. By setting the weight average molecular weight to the above range, the obtained protective sheet can have excellent strength, and the protective sheet has excellent moldability and fluidity during molding.

Further, the heat-resistant acrylic resin constituting the matrix phase is a combination of a heat-resistant acrylic resin containing an aromatic vinyl monomer as a monomer component and an acrylic resin containing no aromatic aromatic monomer as a monomer component. In the case of the resin (1), other acrylic resins may be further used in combination. In this case, the content of the other acrylic resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less based on 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 parts by mass or more and 50 parts by mass or less, more preferably 0.1 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the total resin constituting the matrix phase, and particularly preferably 0.1 part by mass or more and 35 parts by mass or less. Further, the content of the heat-resistant acrylic resin is preferably 50 parts by mass or more and 99.9 parts by mass or less, more preferably 60 parts by mass or more and 99.9 parts by mass or less, more preferably 100 parts by mass or less based on 100 parts by mass of the total resin constituting the matrix phase. 65 parts by mass or more and 99.9 parts by mass or less. By setting the content of the heat-resistant acrylic resin in the matrix phase to the above range, the heat resistance of the obtained protective sheet can be improved. Further, by using a heat-resistant acrylic resin having a ring structure in its main chain, the heat resistance of the protective sheet can be increased.

<Disperse phase>

The above dispersed phase contains an acrylic rubber as a main polymer. The acrylic rubber means a rubber containing an acrylic monomer such as acrylic acid, methacrylic acid, or the like as a monomer component. The acrylic rubber may be composed only of an acrylic monomer, or may be composed of an acrylic monomer and another monomer. Examples of the acrylic monomer include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, allyl methacrylate, methyl acrylate, ethyl acrylate, isopropyl acrylate, and acrylic acid. N-butyl ester and the like. Examples of the other monomer include styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 2,4-diethylstyrene, and 4-butoxystyrene. An aromatic vinyl compound such as N,N-dimethylaminostyrene; an α,β-ethylenically unsaturated nitrile compound such as acrylonitrile, methacrylonitrile or dicyandiethylene; and ethylene such as vinyl acetate or vinyl propionate An ester compound; a vinyl ether compound such as ethylvinylether, cetylvinylether or hydroxybutylvinylether. These other monomers may be used alone or in combination of two or more.

The acrylic rubber may be crosslinked by using a crosslinking agent. Examples of the crosslinking agent include sulfur; organic peroxides such as 2,4-dichloroperbenzoic acid benzoquinone, benzoyl peroxide, and di-terternary butyl peroxydiisopropylbenzene; Organic sulfur compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide; p-quinone dioxime, p,p'-dibenzidine (p,p) '-dibenzoylquinone dioxime) is an anthracene compound; a polyamine such as hexamethylenediamine carbamate or the like. When a crosslinking agent is used, for example, a sulfur-adding accelerator such as biphenyl hydrazine, zinc dimethyldithiocarbamate, 2-hydrothiobenzothiazole or dibenzothiazyl sulfide may be used.

The average particle diameter of the dispersed phase is 1 nm or more and less than 50 nm, preferably 2 nm or more and less than 50 nm, more preferably 3 nm or more and less than 50 nm. If the average particle diameter of the dispersed phase does not reach the above lower limit, the flexibility of the protective sheet may decrease. On the other hand, when the average particle diameter exceeds the above upper limit, the transparency of the protective sheet may deteriorate.

In the protective sheet, the content of the dispersed phase is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, and still more preferably 20% by mass or more and 30% by mass based on the protective sheet. %the following. If the content of the dispersed phase does not reach the above lower limit, the flexibility of the protective sheet may decrease. On the other hand, if the content of the dispersed phase exceeds the above upper limit, the transparency of the protective sheet may deteriorate.

This dispersed phase can be employed in a multilayer structure. The multilayer structure may, for example, adopt a two-layer structure composed of a core-shell structure, a three-layer structure composed of a central hard layer and a soft layer and an outermost hard layer, or further between the soft layer and the outermost hard layer. The four-layer structure of the middle hard layer.

The above two-layer structure may be formed, for example, as a core-shell structure composed of a core layer and a shell layer, wherein the core layer is composed of a rubbery polymer, and the outer shell layer is composed of an acrylic resin-based glassy polymer. Further, the rubber-like polymer used for the core layer is not particularly limited as long as it is rubbery at normal temperature, and for example, a rubbery polymer containing butadiene as a main component (for example, butadiene homopolymer, butyl) may be used. a diene-aromatic ethylene copolymer or the like, or a rubbery polymer mainly composed of an alkyl acrylate (for example, butyl acrylate-styrene copolymer, 2-ethylhexyl acrylate-styrene copolymer, etc.) . Further, it is preferred to use a butadiene-styrene copolymer, whereby strength, productivity, and transparency can be improved. Further, the glassy polymer used for the outer shell layer is not particularly limited as long as it is a glass-like acrylic polymer at normal temperature, and for example, methyl methacrylate homopolymer or methyl methacrylate-acrylic acid can be used. Ester copolymers and the like.

Further, the dispersed phase having a multilayer structure of three or more layers may be composed of a soft layer composed of a rubbery polymer and a hard layer composed of a glassy polymer having three or more layers. The rubbery polymer used for the soft layer and the glassy polymer used for the hard layer can be described using the rubber particles of the above two-layer structure.

Further, in addition to the effect of the present invention, other copolymers may be mixed in addition to the heat-resistant acrylic resin constituting the matrix phase and the acrylic rubber constituting the dispersed phase. Further, examples of the other copolymer include a polyolefin resin such as polyethylene or polypropylene; a polyamide resin; a polyphenylene sulfide resin; a polyether ether ketone resin; and a polyester, polyfluorene, and polyphenylene oxide. Thermoplastic resins such as polyphenylene oxide, polyimine, polyetherimide, and polyacetal; and thermosetting resins such as phenol resin, melamine resin, oxime resin, and epoxy resin. Other copolymers may be used singly or in combination. Further, the content of the other copolymer is preferably 20 parts by mass or less based on 100 parts by mass of the matrix phase.

<UV absorber>

The protective sheet contains an ultraviolet absorber in the matrix phase. By providing the protective sheet with an ultraviolet absorber in the matrix, it is possible to have an effect of making the protective sheet less yellow. Further, when the protective sheet is formed in two layers of the sheet-like polarizing element to form a polarizing plate, it is possible to suppress ultraviolet rays from penetrating the polarizing element. Further preferably, the dispersed phase further contains the ultraviolet absorber. By further including the ultraviolet absorbing agent in the dispersion layer, the dispersion uniformity of the ultraviolet absorbing agent in the protective sheet can be improved, and when the protective sheet is formed on the two-layer layer of the sheet-shaped polarizing element to form a polarizing plate, ultraviolet ray penetration can be further suppressed. Polarized component.

As the ultraviolet absorber, a compound having a phenolic hydroxyl group, a branched alkyl group having 4 to 12 carbon atoms, or a linear alkoxy group having 4 to 12 carbon atoms is used. Since the phenolic hydroxyl group of the ultraviolet absorber has a high polarity, the affinity for the heat-resistant acrylic resin having a highly polar ester group is high. The branched alkyl group or the linear alkoxy group of the above ultraviolet absorber has a low polarity and contains a carbon chain of a moderate length, and therefore has high affinity for an acrylic rubber which is easy to interact with the carbon chain. Therefore, the above ultraviolet absorber is likely to exist at the interface between the heat resistant acrylic resin and the acrylic rubber. Therefore, the above ultraviolet absorbent is uniformly dispersed in the matrix of the protective sheet. As a result, the protective sheet can exhibit excellent ultraviolet absorbing ability.

As a UV absorber, a benzotriazole-based compound, a diphenylketone-based compound, a benzoate-based compound, and three The compound has high transparency and is excellent in preventing deterioration of the polarizing plate. In particular, it is more preferred to use an ultraviolet absorber composed of a benzotriazole-based compound having less coloration and higher transparency.

In addition, the ultraviolet absorber may be appropriately selected from the compounds represented by the following general formulae (1) to (5).

In the formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms. However, none of R ¹ to R ⁴ is a hydrogen atom. X ¹ is a hydrogen atom or a halogen atom.

In the formula (2), R ⁵ and R ⁶ each independently represent a hydrogen atom, a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms. However, there is no case where both of R ⁵ and R ⁶ are hydrogen atoms. R ⁷ is a methylene group or an alkylene having 2 to 4 carbon atoms. X ² and X ³ each independently represent a hydrogen atom or a halogen atom.

In the formula (3), R ⁸ to R ¹⁰ are a hydrogen atom, a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms. However, it is not the case that all of R ⁸ to R ¹⁰ are hydrogen atoms.

In the formula (4), R ¹¹ is a hydrogen atom or a hydroxyl group. R ¹² is a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms.

In the formula (5), R ¹³ to R ¹⁶ each independently represent a hydrogen atom, a branched alkyl group having 4 to 12 carbon atoms or a linear alkoxy group having 4 to 12 carbon atoms. However, it is not the case that all of R ¹³ to R ¹⁶ are hydrogen atoms.

More specifically, the ultraviolet absorber can be appropriately selected from the compounds represented by the following general formulae (1-1) to (2-1). The following general formula (1-1) is a specific example of the above formula (1), and the following formula (2-1) is a specific example of the above formula (2), and the following formula (3-1) is In the specific example of the above formula (3), the following general formula (4-1) is a specific example of the above formula (4), and the following formula (5-1) is a specific example of the above formula (5).

Further, the ultraviolet absorber preferably has a melting point of 110 ° C or higher, more preferably 120 ° C or higher, still more preferably 130 ° C or higher. When the melting point of the ultraviolet absorber is not less than the above lower limit, the amount of volatilization during heating and melting is small, and the ultraviolet absorber is less likely to be deposited and aggregated at the forming outlet such as the extrusion port, and the stain is less likely to occur during sheet forming. Does not hinder the transparency of the film.

The content of the ultraviolet absorber is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and still more preferably 2% by mass or more and 8% by mass or less based on the amount of the matrix phase. . If the content of the ultraviolet absorber is less than the above lower limit, the obtained protective sheet may not be obtained. Fully absorb the ray of ultraviolet rays. When the content of the ultraviolet absorber exceeds the above upper limit, the heat resistance of the protective sheet may be lowered.

<microparticle>

The protective sheet contains fine particles in the matrix phase. The material of the fine particles is preferably cerium oxide. Others may also use titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium citrate, water and calcium citrate, aluminum citrate, magnesium citrate. Organic materials such as inorganic materials such as calcium phosphate or crosslinked polymers. Further, the material of the fine particles may be ruthenium dioxide because it is preferable because the haze of the protective sheet is lowered. Further, from the viewpoint of reducing the haze of the protective sheet, it is preferable to use a material obtained by surface treatment of an organic material using a material of cerium oxide. Examples of the organic substance used for the surface treatment include halosilanes, alkoxysilanes, silazane, decane, and the like. For example, the product name "sylophobic" (manufactured by Fuji Silysia Chemical Co., Ltd.), "Aerosil 200V" (manufactured by Nippon Aerosil Co., Ltd.), and "Aerosil R927V" (manufactured by Nippon Aerosil Co., Ltd.) are mentioned. These may be used singly or in combination.

The average particle diameter of the fine particles is preferably 0.005 μm or more and 2 μm or less, and more preferably 0.05 μm or more and 1 μm or less. Further, the fine particles are disposed 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 or less, and more preferably 0.02 μm or more and 0.05 μm or less. Further, the fine particles are extended (micro-extended) by the sheet when the protective sheet is formed, and the fine particles are protruded from the surface as described above.

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 particularly preferably 0.1% by mass or more and 0.3% by mass or less based on the protective sheet.

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

<protection sheet>

The protective sheet is formed by extrusion molding, for example, a mixture of a heat-resistant acrylic resin forming a matrix phase and an acrylic rubber forming a dispersed phase. Here, the protective sheet is formed into a sheet by micro-extension after extrusion. The extension is preferably a uniaxial extension. Further, the elongation due to the micro extension is 1% or more and 5% or less. In order to achieve this elongation, for example, extrusion molding is carried out in such a manner that the drawing speed at which the sheet formed by cooling is stretched is 0.3% faster than the extrusion speed at which the molten material is extruded during extrusion molding. Thus, it is easy to arrange in a state where the fine particles protrude from the surface of the protective sheet by micro-extension after extrusion, and the slipperiness of the protective sheet can be improved. Moreover, since it is slightly extended, the transparency of the protective sheet can be maintained.

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, still more 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 to the above range, it is possible to impart sufficient toughness to the protective sheet, and it is possible to easily improve the usability such as retraction of the protective sheet.

The thickness of the polarizing plate produced by bonding the protective sheet to the polarizing element is preferably 150 μm or more and 800 μm or less, more preferably 180 μm or more and 700 μm or less, and still more preferably 200 μm or more and 600 μm or less. By setting the thickness of the polarizing plate to the above range, it is possible to impart sufficient toughness to the protective sheet, and it is possible to easily improve the usability such as retraction of the protective sheet.

In the protective sheet, the retardation value (Re) in the plane direction is preferably 0 nm or more and 15 nm or less. Further, the retardation value (Rth) in the thickness direction is preferably -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 the equations (a) and (b), respectively.

Re1=(nx1-ny1)×d[nm] (a)

Rth1={(nx1+ny1)/2-nz1}×d[nm] (b)

Here, nx1 is the principal refractive index of the protective sheet in the planar direction. Ny1 is the refractive index perpendicular to nx1. Nz1 is the main refractive index in the thickness direction of the protective sheet. d is the thickness of the protective sheet.

Further, in the protective sheet, the transmittance of light having a wavelength of 380 nm is preferably 60% or less, more preferably 20%, still more preferably 8% or less, and particularly preferably 5% or less. Since the transmittance of the light having the wavelength of 380 nm is not more than the above upper limit, the protective sheet can surely absorb ultraviolet rays. Further, the transmittance is a ratio of incident light of a specific wavelength to a sample (protective sheet).

Further, in the protective sheet, the transmittance of light having a wavelength of 420 nm is preferably 90% or more, and more preferably 91% or more. Further, in the protective sheet, the transmittance of light having a wavelength of 550 nm is preferably 91% or more, more preferably 92% or more. The transmittance of the light of the specific wavelength is at least the above-mentioned lower limit value, so that visible light rays can be efficiently penetrated, and can be effectively applied to display light when used in an optical system of a liquid crystal display device.

<Polarizing plate>

The protective sheet can be used as a polarizing plate protective sheet. Fig. 1 is a cross-sectional view showing a polarizing plate according to an embodiment of the present invention. As shown in FIG. 1, the polarizing plate has a pair of protective sheets 1, and a polarizing element 2 in which a plate shape is inserted between the pair of protective sheets 1. The protective sheet 1 and the polarizing element 2 are attached to each other by an adhesive such as an aqueous paste (not shown). For example, a pair of protective sheets 1 are laminated on both sides of the polarizing element 2 via an adhesive, thereby forming a polarizing plate.

<Liquid crystal display element>

The polarizing plate having the above protective sheet 1 can be used in a liquid crystal display device. Fig. 2 is a cross-sectional view showing a liquid crystal display element of an embodiment of the present invention. As shown in FIG. 2, the liquid crystal display element has a liquid crystal panel 3, and one pair of polarizing plates are disposed on each of both surfaces of the liquid crystal panel 3. In the above-described manner, the polarizing plate is a plate in which the polarizing element 2 inserted between the pair of protective sheets 1 and the pair of protective sheets 1 is laminated with an adhesive. The liquid crystal panel 3 and the pair of polarizing plates are respectively attached to the adhesive 4 such as an ultraviolet effect type adhesive.

<Other Embodiments>

Further, the present invention is not limited to the above embodiment, and various design changes can be made, and matting processing can be applied to one surface or both surfaces of the protective sheet. Thereby, the effect of attaching the surface to which the matte processing is applied to another member via an adhesive or the like can be exhibited. In the polarizing plate of FIG. 3, a matting layer 5 is formed on each of a pair of protective sheets 1. On the other hand, the polarizing element 2 is disposed between the matting layers 5 of the pair of protective sheets 1, and the matting layer 5 and the polarizing element 2 are adhered by a water-based adhesive (not shown). The matte layer 5 can be formed using a matting agent. Specifically, a matting agent-containing coating liquid can be applied to one surface of the protective sheet 1 to form the matte layer 5. In addition, the matting agent may use organic or inorganic fine particles such as cerium oxide, talc, calcium carbonate, precipitated barium sulfate, alumina, acid white clay, clay, magnesium carbonate, carbon black, tin oxide, titanium white (titane). White), urea powder resin, and the like.

Further, as shown in Fig. 3, a configuration in which a hard coat layer 6 is formed on a single-layer layer of the protective sheet may be employed. In the polarizing plate of Fig. 3, in one of the pair of protective sheets 1, the surface layer of the protective sheet 1 on the side opposite to the polarizing element 2 has a hard coat layer 6. Thereby, the scratch resistance of the protective sheet 1 can be improved. Further, the hard coat layer 6 is formed by applying an acrylic paint. Thereby, the transparency of the hard coat layer 6 can also be ensured, and the transparency of the protective sheet 1 can be maintained.

[Example 1]

Hereinafter, the present invention is not limited to the embodiments, but is specifically described based on the embodiments of the present invention.

The acrylic rubber and the ultraviolet absorber were added to the heat-resistant acrylic resin, and the T-die device extruder was used to adjust the number of revolutions of the screw, the resin temperature in the cylinder of the extruder, and the T die ( The temperature of the T-die is extruded to obtain a plurality of types of protective sheets. As the ultraviolet absorber, TINUVIN 360 and TINUVIN 1577 manufactured by BASF Japan Co., Ltd. and SEESORB707 and SEESORB 709 manufactured by SHIPRO Chemical Co., Ltd. were used. A protective sheet having a thickness of 40 μm in a plurality of types is obtained by using one or two of the above-mentioned four types of ultraviolet absorbers and changing the amount of the above-mentioned four types of ultraviolet ray absorbents. The transmittance Tt (%) of the light of the wavelengths of 380 nm, 420 nm, and 550 nm was measured for each of the obtained protective sheets. The measured results are shown in Tables 1 and 2 below.

As can be understood from the above Tables 1 and 2, the protective sheets of the respective embodiments have low transmittance of light having a wavelength of 380 nm, and high transmittance of light having a wavelength of 420 nm and 550 nm, so that visible light can be easily penetrated and the ultraviolet absorbing ability is high.

[Industrial availability]

The polarizing plate of the present invention can be utilized as a liquid crystal display element assembled in a liquid crystal display device. The protective sheet of the present invention can be utilized as an element of a polarizing plate.

1. . . Protective sheet

2. . . Polarizing element

3. . . LCD panel

4. . . Follower

5. . . Matting layer

6. . . Hard coating

Fig. 1 is a cross-sectional view showing a polarizing plate according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view showing a liquid crystal display element of an embodiment of the present invention.

Figure 3 is a cross-sectional view showing a polarizing plate according to another embodiment of the present invention.

1. . . Protective sheet

2. . . Polarizing element

Claims (8)

A protective sheet comprising a matrix phase containing a heat resistant acrylic resin as a main polymer, and an island structure protective sheet containing an acrylic rubber as a dispersed phase of a main polymer, the matrix phase containing an ultraviolet absorber, the ultraviolet absorption A compound having a phenolic hydroxyl group and a branched alkyl group having 7 to 12 carbon atoms, wherein the ultraviolet absorber has a melting point of 110 ° C or higher, and the ultraviolet absorber has a content of 0.5% by mass or more based on the matrix phase. 10% by mass or less, the protective sheet is formed by extrusion molding, and the ultraviolet absorber is uniformly dispersed in the matrix phase. The protective sheet of claim 1, wherein the dispersed phase contains the ultraviolet absorber. The protective sheet of claim 1, wherein the content of the dispersed phase is 5% by mass or more and 40% by mass or less. The protective sheet of the first aspect of the patent application has a retardation value in the plane direction of 0 nm or more and 15 nm or less, and a retardation value in the thickness direction of -15 nm or more and 0 nm or less. The protective sheet of claim 1, wherein the heat-resistant acrylic resin has a ring structure in the main chain. For example, the protective sheet of the first application of the patent scope has a matting process on one or both sides. For example, the protective sheet of claim 1 has a layered on one side A hard coat layer formed by applying an acrylic paint. A polarizing plate comprising a sheet-shaped polarizing element and a pair of protective sheets of the first aspect of the patent application scope in which the adhesive layer is laminated on both sides of the polarizing element.