JP6721410B2 - Protective film, film laminate, and polarizing plate - Google Patents

Description

The present invention relates to a protective film, a film laminate, and a polarizing plate using an energy ray-curable composition.

In recent years, displays such as liquid crystal and organic EL used in TVs and mobile devices have become thinner and thinner, and technological development has been advanced toward the ultimate thinness of components used in these displays, especially polarizing plates. ing. The polarizing plate is generally a polarizing film made of a polyvinyl alcohol (hereinafter, referred to as PVA)-based film that adsorbs iodine and is uniaxially stretched, and an optical film such as triacetyl cellulose (hereinafter, referred to as TAC) is provided on both surfaces of the polarizing film. The protective film is made of an adhesive.

By the way, in a liquid crystal display, a dimensional change occurs because the polarizing film undergoes a significant dimensional change when exposed to an environment where stress relaxation and moisture absorption/dehumidification occur (for example, under high temperature, high temperature/high humidity, low temperature, high temperature/low temperature cycle). A film having a three-dimensionally controlled retardation value is used in order to obtain good contrast and a wide viewing angle for the purpose of suppressing the above.
In particular, in a liquid crystal display in which the driving mode of the liquid crystal cell is IPS or FFS, a wide viewing angle can be obtained in principle of driving, and thus it is not necessary to use a retardation film. In this case, a portion corresponding to the retardation film is used. As the film, a film having a retardation value in the in-plane direction and the retardation value in the thickness direction close to zero (so-called zero retardation film) can be used.

The zero retardation film is generally obtained by forming a film of a thermoplastic resin or the like without stretching, but since they are not stretched, cohesive force due to molecular orientation cannot be obtained, and The dimensional change cannot be sufficiently suppressed.

An acrylic resin is mentioned as a resin having a high cohesive force in relation to such a problem, and Patent Document 1 proposes forming an acrylic resin into a film without performing a molecular orientation treatment.

JP, 2011-242581, A

However, with the above method, although a film having a retardation value close to zero can be obtained, the tensile modulus of elasticity is excessively high, and thus the film is brittle and easily broken. The film is given flexibility by adding rubber elastic particles in order to modify the brittle property, and the tensile modulus of elasticity of the obtained acrylic resin film eventually becomes low due to this effect. Will end up. A polarizing plate laminated with such a film having a low tensile elastic modulus can be polarized by exposing it to an environment where stress relaxation and moisture absorption/dehumidification occur (for example, under high temperature, high temperature/high humidity, low temperature, high temperature/low temperature cycle). There is a problem that the film undergoes a large dimensional change.

In view of the above problems, the problem of the present invention is that the retardation value in the in-plane direction and the thickness direction of the film is close to zero, and the tensile modulus is high without molecular orientation treatment, and the water-soluble adhesive or energy is used. It is an object of the present invention to provide a protective film that can obtain good adhesion to a polarizing film using a line-curable adhesive.

In order to solve the above problems, the inventors of the present invention have conducted extensive studies, and as a result, a protective film obtained by applying a specific energy ray-curable composition to a substrate film, and curing and then peeling the composition from the substrate film. Have found that the retardation values in the in-plane direction and the thickness direction are close to zero, and have a high tensile elastic modulus without molecular orientation treatment.

The present invention includes the following modes.
A protective film formed by a block A composed of repeating units I or II having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or
A protective film formed by the block A and a block B comprising a repeating unit having a structure derived from a (meth)acrylate group-containing raw material which is a monomer b,
The urethane (meth)acrylate I is a reaction product of a hydroxyl group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylate II is a reaction product of an isocyanate group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylates I and II have a plurality of types of saturated cycloaliphatic structures,
The (meth)acrylate group-containing raw material has a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less,
The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. is 0 nm or more and 10 nm or less, and the retardation value (Rth) in the thickness direction at a wavelength of 590 nm at 23° C. is -10 nm or more and 10 nm or less. And a protective film.
On at least one side of the protective film,
(1) A film substrate that supports the protective film,
(2) A hard coat layer having scratch resistance,
(3) An antiglare layer that scatters light, and
(4) A film comprising any one of a high refractive index layer provided on the protective film and an antireflection layer composed of a low refractive index layer provided on the high refractive index layer. Laminate.
A polarizing plate comprising the above-mentioned protective film on at least one surface of a polarizing film.

The protective film according to the present invention has a retardation value close to zero in the in-plane direction and the thickness direction, and has a high tensile elastic modulus without molecular orientation treatment, so that the polarizing film can be bonded to the polarizing film. Even in an environment where stress relaxation or moisture absorption/dehumidification occurs (for example, under high temperature, high temperature/high humidity, low temperature, or high temperature/low temperature cycle), the dimensional change of the polarizing film is suppressed.

Hereinafter, the protective film, the film laminate and the polarizing plate according to the present invention, and the production methods thereof will be described, but the present invention is not construed as being limited to these descriptions.

"Protective film"
The protective film according to the present invention is a polymer formed by a block A composed of repeating units having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or the block A and a monomer b (meth). ) A copolymer formed by a block B comprising a repeating unit having a structure derived from an acrylate group-containing raw material, wherein the repeating unit of the block A has a plurality of types of saturated cyclic aliphatic structures, The repeating unit is composed of a (meth)acrylate group-containing raw material having a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less.
That is, in the protective film, a matrix forming a polymer or a copolymer has a block A composed of repeating units having a structure derived from urethane (meth)acrylate I or II and a (meth)acrylic equivalent of 90 g/ It is formed by a block B composed of a (meth)acrylate group-containing raw material monomer unit having an eq or more and 500 g/eq or less. In addition, the monomers a and b may be structural isomers thereof, or may be a mixture of the monomers a and b and structural isomers thereof.

[Block A]
The structure derived from urethane (meth)acrylate I or II according to block A means a urethane (meth)acrylate I or II monomer unit, that is, (meth)acrylate in urethane (meth)acrylate I or II as a monomer. It means a structure in which the double bond of the group is cleaved, and since it has sites where the double bond of the (meth)acrylate group is cleaved mainly at both ends, it is bifunctional.

The repeating unit of the block A has a urethane bond (-NH-CO-O-). The number of the urethane bonds is not particularly limited and is, for example, 1-8. The urethane bond is a polar group, and the urethane bonds in each repeating unit come close to each other due to intermolecular force. On the other hand, the saturated cyclic aliphatic structure has a high molecular weight because it is a non-polar cyclic structure, and is a skeleton that is harder in terms of molecular structure than a saturated aliphatic chain. It is considered that the high molecular weight and hardness of the saturated cycloaliphatic structure contribute to the intermolecular interaction between the urethane bonds, so that the intermolecular force causes a high cohesive force. As a result, the protective film composed of the above repeating unit has a high tensile elastic modulus without stretching.

The urethane (meth)acrylate I or II monomer unit has a plurality of types of saturated cycloaliphatic structures. The saturated cycloaliphatic structure is not particularly limited, but a saturated cycloaliphatic structure having 5 or more membered rings is preferable from the viewpoint of enhancing the cohesive force due to the molecular weight. Although the upper limit of the number of member rings is not particularly limited, it is, for example, 15 member rings or less, preferably 10 member rings or less, from the viewpoint of easiness of synthesizing a monomer as a raw material of the protective film. When the saturated cyclic aliphatic structure has a plurality of cyclic structures, the number of membered rings represents the number of member rings of the maximum cyclic structure, and the saturated cyclic aliphatic structure has a bicyclo ring or a tricyclo ring. , Means the number of members in the ring structure excluding the carbon of the bridge connecting the bridgehead carbons. For example, in the case of a tricyclodecane ring, the number of members is 9.

The main chain of the cyclic structure of the saturated cycloaliphatic structure may be formed only by carbon atoms, or may be formed by oxygen atoms and/or nitrogen atoms in addition to carbon atoms. In addition, a linear and/or branched structure having 1 to 10 carbon atoms may be added to the carbon atom of the cyclic structure.

Examples of the saturated cycloaliphatic structure include a 3,5,5-trimethylcyclohexane ring, a tricyclodecane ring, an adamantane ring and a norbornene ring. The saturated cycloaliphatic structure may be bonded to the urethane bonding group via a saturated aliphatic chain, and the rigidity of the repeating unit can be suitably adjusted by changing the carbon number of the saturated aliphatic chain. The saturated aliphatic chains, have a linear structure and branched structure, as an example of a linear _{structure, - (CH 2) n -} (n is an integer of 1 to 10), with the repeating unit From the viewpoint of reducing the flexibility and increasing the rigidity, —CH ₂ — or —(CH ₂ ) ₂ — is particularly preferable. On the other hand, examples of the branched chain structure include a structure in which hydrogen on at least one carbon of the above linear structure is substituted with a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or the like.

When the 3,5,5-trimethylcyclohexane ring described above is bonded to two urethane bonds via a methylene chain, the 3-methylene-3,5,5-trimethylcyclohexane ring is bonded to each urethane bond. Thus, when the tricyclodecane ring is bonded to two urethane bonds via the methylene chain, the dimethylenetricyclodecane ring is bonded to each urethane bond.

The 3-methylene-3,5,5-trimethylcyclohexane ring and the dimethylenetricyclodecane ring are preferred ring structures, and a protective film containing the ring structure in a polymer chain has a high tensile modulus without stretching. Is preferably expressed.

The main chain of the repeating unit preferably contains a saturated aliphatic chain having 5 to 10 carbon atoms in addition to the saturated cyclic aliphatic structure. When the saturated aliphatic chain has 5 or more carbon atoms, the saturated aliphatic chain having a long chain length and flexibility imparts flexibility to the repeating unit and reduces the brittleness of the protective film. On the other hand, when the carbon number is 10 or less, it is possible to suppress a decrease in tensile elastic modulus due to excessive flexibility imparted. The saturated aliphatic chain may have a linear structure or a branched structure. The saturated aliphatic chain constitutes a part of the repeating unit with a structure having a urethane bond or an ester bond, for example.

Examples of the straight chain _{structure, - (CH 2) n1 -} (n1 is an integer of 5-10) include, in particular, - _{(CH 2) 5} - is preferably. On the other hand, examples of the branched chain structure include a structure in which hydrogen on at least one carbon of the above linear structure is substituted with a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or the like.

As an example of the repeating unit, a structure including the following structure A containing a saturated cycloaliphatic structure R ¹ and the following structure C containing a saturated cycloaliphatic structure R ³ can be exemplified.
^{-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 3 -O- ··· (Structure C)
As the repeating unit, for example, (1) R ¹ -containing diisocyanate, (2) R ³ -containing diol, and (3) hydroxyl group-containing alkyl (meth) acrylate or isocyanate group-containing alkyl (meth) acrylate are used. It can be obtained from the urethane (meth)acrylate thus obtained, and can be easily produced. As an example, the ratio of the structure A and the structure C may be m+1:m or m:m+1, and m represents an integer of 1 to 4.

Further, the repeating unit may further include the following structure B containing the following saturated aliphatic chain R ² .
^-O-R 2 -CO- ··· (Structure B)
The repeating unit is, for example, a diisocyanate containing R ¹ , an ester (optionally used) containing R ² , a diol containing R ³ , a hydroxyl group-containing alkyl (meth)acrylate, or an isocyanate group-containing alkyl ( It can be obtained from urethane (meth)acrylate obtained by using (meth)acrylate, and can be easily produced. As an example, the ratio of the structure A, the structure B, and the structure C can be m+1:m(r+s):m, m:m(r+s):m+1, and m:k+n:m+1. The above m represents an integer of 1 to 4, r and s each represent an integer of 0 to 2, the sum of r and s is 1 to 2, k represents an integer of 0 to 2, and n Represents an integer of 0 to 2.

（一般式（１）中、Ｒ^１は飽和環状脂肪族構造を示し、Ｒ^２は炭素数５〜１０の直鎖または分岐鎖状の飽和脂肪族鎖を示し、Ｒ^３は、Ｒ^１と異なる飽和環状脂肪族構造を示し、Ｒ^４は水素原子またはメチル基を示し、Ｒ^５は、水素原子、メチル基またはエチル基を示し、ｍは１〜４の整数を示し、ｒおよびｓはそれぞれ０〜２の整数を示し、かつ、ｒとｓとの和は１〜２であり、ｘは０〜３の整数を示す） Specific examples of the repeating unit having the above saturated cycloaliphatic structure and saturated aliphatic chain are shown below. As shown in the general formula (1), the structure derived from (meth)acrylate means a (meth)acrylate structure H ₂ C═CH—CO ₂ — (or H ₂ C═C(CH ₃ )—CO ₂ —. ) Is a structure in which the carbon-carbon double bond is cleaved to become a single bond.

(In the general formula (1), R ¹ represents a saturated cycloaliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. Shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and r and s each represent 0. Represents an integer of 2 and the sum of r and s is 1 to 2 and x represents an integer of 0 to 3).

When m in the general formula (1) is an integer of 1 to 4, the tensile elastic modulus is further increased. m is more preferably 1 or 2, and further preferably 1. The same applies to general formulas (2) and (3) described later.

In the general formula (1), R ¹ is a 3-methylene-3,5,5-trimethylcyclohexane ring, R ² is —(CH ₂ ) ₅ —, and R ³ is a dimethylenetricyclodecane ring. And R ⁴ and R ⁵ are hydrogen atoms, r and s are 1, and x is 1.

（一般式（２）中、Ｒ^１は飽和環状脂肪族構造を示し、Ｒ^２は炭素数５〜１０の直鎖または分岐鎖状の飽和脂肪族鎖を示し、Ｒ^３は、Ｒ^１と異なる飽和環状脂肪族構造を示し、Ｒ^４は水素原子またはメチル基を示し、Ｒ^５は、水素原子、メチル基またはエチル基を示し、ｍは１〜４の整数を示し、ｒおよびｓはそれぞれ０〜２の整数を示し、かつ、ｒとｓとの和は１〜２であり、ｘは０〜３の整数を示す） Other specific examples of the repeating unit are shown below.

(In the general formula (2), R ¹ represents a saturated cyclic aliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. Shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and r and s each represent 0. Represents an integer of 2 and the sum of r and s is 1 to 2 and x represents an integer of 0 to 3).

In the general formula (2), R ¹ is a 3-methylene-3,5,5-trimethylcyclohexane ring, R ² is —(CH ₂ ) ₅ —, and R ³ is a dimethylenetricyclodecane ring. And R ⁴ and R ⁵ are hydrogen atoms, r and s are 1 and x is 1, and suitable repeating units are shown below.

（一般式（３）中、Ｒ^１は飽和環状脂肪族構造を示し、Ｒ^２は炭素数５〜１０の直鎖または分岐鎖状の飽和脂肪族鎖を示し、Ｒ^３は、Ｒ^１と異なる飽和環状脂肪族構造を示し、Ｒ^４は水素原子またはメチル基を示し、Ｒ^５は、水素原子、メチル基またはエチル基を示し、ｍは１〜４の整数を示し、ｋは０〜２の整数を示し、ｎは０〜２の整数を示し、ｘは０〜３の整数を示す） Other specific examples of the repeating unit are shown below.

(In the general formula (3), R ¹ represents a saturated cyclic aliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. It shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and k represents 0 to 2 Represents an integer, n represents an integer of 0 to 2, and x represents an integer of 0 to 3)

In the general formula (3), R ¹ is a 3-methylene-3,5,5-trimethylcyclohexane ring, R ² is —(CH ₂ ) ₅ —, and R ³ is a dimethylenetricyclodecane ring. And R ⁴ and R ⁵ are hydrogen atoms, k and n are 1, and x is 1, suitable repeating units are shown below.

[Block B]
The structure derived from the (meth)acrylate group-containing raw material according to the block B means a (meth)acrylate group-containing raw material monomer unit, that is, 2 of the (meth)acrylate groups in the (meth)acrylate group-containing raw material that is a monomer. It means a structure in which a heavy bond is polymerized.

The (meth)acrylate group-containing raw material for producing the block B has a (meth)acrylic equivalent of preferably 90 g/eq or more and 500 g/eq or less, and 90 g/eq or more and 400 g or more so that the tensile elastic modulus of the protective film is at a high level. /Eq or less is more preferable, and 90 g/eq or more and 300 g/eq or less is particularly preferable. When the (meth)acrylic equivalent is more than 500 g/eq, the three-dimensional crosslinked structure formed by polymerizing the (meth)acrylate group is reduced, and as a result, the tensile elastic modulus of the protective film made of the above copolymer is increased. Will be reduced.

The (meth)acrylate group-containing raw material is not particularly limited in molecular structure as long as the (meth)acrylic equivalent is in the range of 90 g/eq or more and 500 g/eq or less, and is composed of plural kinds of (meth)acrylate group-containing raw materials. It may be. At this time, the (meth)acrylic equivalent of the (meth)acrylate group-containing raw material is calculated as a value obtained by averaging the (meth)acrylic equivalents of a plurality of types of (meth)acrylate group-containing raw materials by mass ratio (for example, When the (meth)acrylic equivalent 200 g/eq is 70% by mass and the (meth)acrylic equivalent 400 g/eq is 30% by mass, the (meth)acrylic equivalent is 260 g/eq).

Here, the (meth)acrylic equivalent is a value obtained by dividing the molecular weight in the theoretical structure of the (meth)acrylate group-containing raw material by the number of (meth)acrylic functional groups, and when the value is large, the (meth)acrylic functional group contained in the monomer. Since the proportion of the groups is reduced, the three-dimensional crosslinked structure formed by polymerizing the (meth)acrylate group is reduced.

An example of the (meth)acrylate group-containing raw material will be shown. The structure is not limited to the following as long as the (meth)acrylic equivalent is in the range of 90 g/eq or more and 500 g/eq or less.
Monofunctional (meth)acrylate group-containing raw materials include: alkyl (meth)acrylates such as methyl methacrylate, ethyl (meth)acrylate, propyl (meth)acrylate and isopropyl (meth)acrylate;
Cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, benzyl (meth)acrylate, etc. Saturated/unsaturated cyclic (meth)acrylate,
A hydroxyl group containing 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polycaprolactone-modified hydroxyethyl (meth)acrylate, pentaerythritol mono(meth)acrylate, or the like; (Meth)acrylate etc. are mentioned.
As the bifunctional (meth)acrylate group-containing raw material, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1 , 10-decanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A type di (Meth)acrylate, bisphenol F-type di(meth)acrylate, polybutadiene di(meth)acrylate, hydrogenated polybutadiene di(meth)acrylate, isocyanuric acid di(meth)acrylate, polyester di(meth)acrylate composed of diol and dicarboxylic acid , Polyurethane di(meth)acrylate composed of diol and diisocyanate.
As the polyfunctional (meth)acrylate group-containing raw material, pentaerythritol tri(meth)acrylate, ethoxy modified pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylol Propane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, isocyanuric acid tri(meth)acrylate, polyester (meth)acrylate consisting of polyol and polycarboxylic acid, polyurethane (meth)acrylate consisting of polyol and polyisocyanate, dendrimer Examples thereof include a (meth)acrylate having a structure and an acrylic oligomer having a (meth)acrylate in a side chain.

[Relationship between blocks A and B]
The site derived from the (meth)acrylate of the block A is bonded to another site derived from the (meth)acrylate group-containing raw material of the block A or the block B, and the same applies to the block B (-block A -Block A- or-block A-block B-or-block B-block B-).

The mass ratio of the urethane (meth)acrylate and the (meth)acrylate group-containing raw material, which is a monomer that becomes the repeating unit of the block A and the block B, is not particularly limited, but the tensile elastic modulus of the protective film due to the block B is Urethane (meth)acrylate:(meth)acrylate group-containing raw material=90:10 to 10:90 is preferable, 80:20 to 20:80 is more preferable, and 70:30 to 30 : 70 is particularly preferable.

Further, the proportion of the polymer and the copolymer in the protective film according to the present invention is preferably high from the viewpoint of increasing the tensile elastic modulus of the protective film, and is 70% by mass or more and 99% by mass or more with respect to the total mass of the protective film. It is preferably 0.5% by mass or less, and more preferably 80% by mass or more and 99.5% by mass or less.

The structure of the repeating unit (block A and block B) in the protective film according to the present invention can be determined by analyzing the protective film by pyrolysis GC-MS and FT-IR. .. In particular, pyrolysis GC-MS is useful because it can detect the monomer unit contained in the protective film as a monomer component.

[Silica particles]
The protective film according to the present invention preferably contains silica particles. This improves the hydrophilicity of the surface of the protective film and improves the adhesiveness with the water-soluble adhesive. The silica particles may be ordinary silica (SiO ₂ ) having no organic substituent or organic silica particles having an organic substituent.

The silica particles having a particle diameter of 5 nm to 300 nm can be preferably used. Further, for the purpose of improving affinity with a monomer, reacting with a monomer, or the like, by reacting a silane coupling agent with ordinary silica particles, a silanol group on the surface of the silica particles, an alkylene group, a phenyl group, It is also possible to modify it into organic silica particles having an organic functional group such as a vinyl group, a (meth)acrylic group and a glycidyl group. Among them, a vinyl group which is a reactive group, a (meth)acrylic group, silica particles modified with a glycidyl group (hereinafter referred to as reactive silica particles) are polymerized with a monomer to form a three-dimensional crosslinked structure, Silica particles are less likely to fall off from the protective film, and stronger adhesiveness is obtained, which is preferable.

Specific examples of the silane coupling agent include hexyltriethoxysilane, triethoxyphenylsilane, triethoxyvinylsilane, triethoxy(3-methacryloyloxypropyl)silane, 3-(acryloxy)propyltrimethoxysilane, triethoxy(3- Glycidyloxypropyl)silane and the like can be used, and these can be used alone or in combination of two or more kinds as appropriate.

The addition amount of the silica particles is not particularly limited as long as the adhesiveness with the PVA polarizing film using the water-soluble adhesive is satisfied, and is usually 1 to 60 mass% in the protective film, preferably 3 to It is in the range of 40% by mass, more preferably 5 to 20% by mass.

Since the silanol groups of the organic silica particles are modified with an organic functional group, by subjecting the surface of the protective film containing the organic silica particles to plasma treatment or corona treatment, silanol groups modified with organic functional groups are obtained. Returns to the original silanol group and can be bonded to the PVA polarizing film using a water-soluble adhesive.

The strength of the plasma treatment or the corona treatment is not particularly limited, but treatment with a strength such that the water contact angle on the surface of the protective film after treatment is 30° or less is not suitable for the PVA polarizing film using the water-soluble adhesive. It is preferable in terms of adhesiveness. The specific treatment strength varies greatly depending on the treatment method, the type of organic silica particles and the addition amount, but the treatment amount is generally in the range of 200 to 1000 watt·min/m ² .

The monomers a and b and the reactive silica particles forming the protective film according to the present invention can be cured as they are by irradiation with ionizing radiation. However, when curing by irradiation with ultraviolet rays, addition of a photopolymerization initiator is not necessary. is necessary. As the photopolymerization initiator, acetophenone-based, benzophenone-based, thioxanthone-based, benzoin, radical polymerization initiators such as benzoin methyl ether, aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, cationic polymerization initiation of metallocene compounds, etc. The agents can be used alone or in appropriate combination.
In order to obtain a protective film containing silica particles, for example, a method of mixing silica sol and the monomer a, or the monomers a and b, and then curing the mixture may be used. The silica sol is a dispersion medium in which silica particles are dispersed, and typically colloidal silica can be used.

[Physical properties of additives and protective film]
The protective film according to the present invention contains various additives such as a UV absorber, a leveling agent and an antistatic agent as long as the film forming property of the protective film, the retardation value in the in-plane direction and the thickness direction, and the tensile modulus are not impaired. It may be contained. With this, it is possible to impart the ultraviolet absorption property, the peeling property, and the antistatic property to the protective film.

As the ultraviolet absorber, known ones can be used, and examples thereof include benzophenone type, benzotriazole type, hindered amine type and the like. Known leveling agents and antistatic agents can be used.

Since the protective film according to the present invention is formed into a thin film, the film thickness is, for example, 5 μm or more and 80 μm or less, more preferably 6 μm or more and 50 μm or less, and particularly preferably 7 μm or more and 30 μm or less.

The retardation value of the protective film according to the present invention is the refractive index in the direction in which the refractive index in the film surface is maximum (that is, the slow axis direction), nx, and the refractive index in the direction orthogonal to the slow axis in the surface. When ny is the refractive index in the thickness direction, nz is the thickness direction, and d is the thickness, the in-plane retardation value (Re) and the thickness direction retardation value (Rth) are respectively expressed by the following equations (i) and (ii). Is defined.
Re=(nx−ny)×d (i)
Rth=[(nx+ny)/2-nz]×d (ii)

The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. of the protective film according to the present invention is 0 nm or more and 10 nm or less, and more preferably 0 nm or more and 5 nm or less. Further, the retardation value (Rth) in the thickness direction at a wavelength of 590 nm at 23° C. is −10 nm or more and 10 nm or less, and more preferably −5 nm or more and 5 nm or less.

The protective film according to the present invention is excellent in tensile elastic modulus, and the tensile elastic modulus is, for example, 1500 MPa or more, more preferably 2500 MPa or more. The upper limit is not particularly limited, but is, for example, 4500 MPa.

<Film laminate>
Next, the film laminate will be described. The film laminate according to the present invention, on at least one surface of the protective film,
(1) A film substrate that supports the protective film,
(2) A hard coat layer having scratch resistance,
(3) An antiglare layer that scatters light, and
(4) An antireflection layer including a high refractive index layer provided on the protective film and a low refractive index layer provided on the high refractive index layer.
Of course, the film laminate may have any of the above (1) to (4) on both sides of the protective film. That is, a layer of the same kind on both sides (for example, (1) on the front surface of the protective film, (1) on the back surface) or a different layer (for example, (1) on the front surface of the protective film, (2) on the back surface, or (2) and (3) on the back side may be provided. Furthermore, (1) to (4) are provided with other layers (1) to (4), and may have a laminated structure. Hereinafter, (1) to (4) will be described.

[Film substrate]
The protective film according to the present invention can be integrally handled in a state of being laminated with another film. When a film laminate is produced by forming a protective film on a film substrate by a coating method such as a roll coating method or a gravure coating method, the film substrate should be used as it is as a part of the film laminate. Can also

The film substrate plays a role of supporting the protective film, and it is preferable to have a release layer on the side on which the protective film is laminated so that the protective film is finally peeled off and removed. In addition, when the film base material is provided with a functional layer via a release layer, after the protective film is attached to the functional layer side of the film base material, the film base material is peeled and removed. Is not transferred to the film substrate side and is transferred to the protective film side.

Normally, the protective film may be inspected for optical properties in various manufacturing processes that process up to the display device after it is attached to the polarizing film, so the influence on the optical property evaluation as a polarizing plate may be minimized. It is preferable that the film substrate has transparency so that it can be formed.
Moreover, since the protective film and the polarizing film are usually bonded together with an ultraviolet curable adhesive, it is preferable that the film base material does not have an ultraviolet absorbing ability so as not to hinder the ultraviolet irradiation. In addition, the optical properties may be inspected in various manufacturing processes in which other films are provided on the polarizing plate to process the display device, and the influence on the optical property measurement of the polarizing film and the protective film, which is the basic configuration of the polarizing plate. It is preferred that the film substrate be transparent so that From such a viewpoint, a polyester film substrate having a release layer is preferably used as the film substrate.

The polyester film substrate may have a release layer as described above, or may have another functional layer formed in addition to the release layer. Examples of the functional layer include a hard coat layer (HC layer), an antiglare layer (AG layer), and an antireflection layer (LR layer). These layers were formed on the release layer of the polyester film, and after being laminated with the protective film, the polyester base material provided with the release layer was peeled off to laminate each functional layer and the protective film. A film laminate can be easily obtained.

[Hard coat layer]
The hard coat layer has a hard coat property. The hard coat property in the present invention is based on JIS K5600:1999, the hard coat layer surface has a scratch hardness of 2H or more by a pencil method under the condition of a load of 500 g and a speed of 1 mm/s, or
After rubbing the surface of the hard coat layer 10 times with steel wool (Nippon Steel Wool Co., Ltd., count #0000) under a load of 250 g/cm ² , at least one of 10 or less scratches was visually evaluated. Refers to the state.

As a resin component constituting the hard coat layer, an ionizing radiation curable resin is suitable because it can be efficiently cured by a simple processing operation, and after curing, it gives a film having sufficient strength and transparency. Ionizing radiation curable resins can be used without particular limitation.
The ionizing radiation-curable resin can be cured as it is by irradiation with ionizing radiation, but when curing by irradiation with ultraviolet rays, it is necessary to add a photopolymerization initiator. As the photopolymerization initiator in this case, the same one as described in the section of the protective film can be used.

The thickness of the hard coat layer is not particularly limited as long as the hard coat property is exhibited, but is generally 1 μm or more and 10 μm or less.

Various additives may be added to the hard coat layer in order to impart functions other than the hard coat property. As an example, a fluorine-based or silicone-based leveling agent added to improve releasability when peeling from a polyester film substrate, or added to prevent dust adhesion due to peeling charge at the time of peeling, electronic Conjugate type, metal oxide type or ionic type antistatic agents may be appropriately selected and used according to the required function. The same applies to the antiglare layer and the low refractive index layer described below, in which an additive can be used.

[Anti-glare layer]
The antiglare layer has an antiglare function that scatters light, and realizes the antiglare function by external haze and/or internal haze. The antiglare layer has unevenness formed on the surface or inside. It contains translucent fine particles, or both.

The method for forming irregularities on the surface of the antiglare layer for producing the external haze is not particularly limited, but on the polyester film substrate on which irregularities are formed, an ionizing radiation curable resin is applied, and after application. The method of curing is preferable because the shape of the unevenness can be easily controlled.
The shape of the surface irregularities on the polyester substrate side of the antiglare layer is determined by the required antiglare property. A more preferable shape of the unevenness is based on roughness, JIS B0601:2001, and can be defined by parameters Ra and Sm and an average inclination angle. Ra: 0.01 μm or more, Sm: 50 μm or more and 500 μm or less, average Inclination angle: More preferably 0.1° or more and 3.0° or less.

The thickness of the antiglare layer is not particularly limited as long as the antiglare property is exhibited, but is generally 1 μm or more and 10 μm or less. The antiglare layer may have hard coat properties in addition to antiglare properties. In this case, hard coat properties are imparted by adjusting the resin component used.

[Antireflection layer]
The antireflection layer is composed of a low refractive index layer and a high refractive index layer. The low refractive index layer is a layer having a lower refractive index than the adjacent high refractive index layer (hard coat layer, antiglare layer, or protective film), and has a low refractive index when laminated with the high refractive index layer. It contributes to prevent reflection of light from the layer side. It should be noted that the high refractive index and the low refractive index here do not specify the absolute refractive index, but the high refractive index and the low refractive index are defined to be relatively high or relatively low. It is said that the reflectance is lowest when both have the following relationship (iii).
n2=(n1) ^1/2 ...(iii)
(N1 is the refractive index of the high refractive index layer, n2 is the refractive index of the low refractive index layer)

The film thickness of the low refractive index layer is not particularly limited as long as the antireflection function is exhibited in relation to the high refractive index layer, but is generally 0.05 μm or more and 0.2 μm or less, and the film thickness of the high refractive index layer is Is generally preferably 0.05 μm or more and 10 μm or less. The low-refractive index layer exhibits an antireflection function in relation to the high-refractive index layer, but it may have a hard coat property depending on the selection of raw materials. Further, the high refractive index layer may have a hard coat property or may further have an antiglare property depending on the selection of raw materials.

"Polarizer"
Next, a polarizing plate provided with the protective film of the present invention will be described. The polarizing plate according to the present invention includes the protective film on at least one surface of a polarizing film.

The polarizing film is a film made of a PVA-based resin and has a property of transmitting light having a vibrating surface in a certain direction and absorbing light having a vibrating surface orthogonal to the light incident on the polarizing film. Specifically, the dichroic dye is adsorbed and oriented on the PVA resin. A polarizing film can be produced by subjecting a film made of the PVA resin to uniaxial stretching, dyeing with a dichroic dye, and boric acid crosslinking treatment after dyeing.

An energy ray-curable adhesive or a water-soluble adhesive is preferably used for bonding the polarizing film and the protective film.

Energy ray-curable adhesives are known in the art, as long as they are supplied in a liquid coatable state, they are polymerized and cured by energy rays of epoxy type, urethane type, acrylic type, etc., which have been conventionally used for manufacturing a polarizing plate. You can use one.
As the water-soluble adhesive, PVA-based adhesives such as polyvinyl alcohol and polyvinyl butyral can be used.

The polarizing plate according to the present invention includes the above-mentioned protective film on at least one surface, and includes a configuration in which the protective film is provided on both surfaces of the polarizing plate. The protective film has a low retardation value in the in-plane direction and the thickness direction and has a high tensile elastic modulus without molecular orientation treatment, so that the internal stress relaxation of the polarizing film or the environment in which moisture absorption/dehumidification occurs (for example, high temperature). Temperature, high temperature/high humidity, low temperature, high temperature/low temperature cycle, etc.), the dimensional change of the polarizing film is suppressed.

<<Method for producing protective film and film laminate>>
[Protective film forming process]
The method for producing the protective film according to the present invention is not particularly limited as long as the protective film can be produced, but an example thereof includes a method including a protective film forming step including the following steps (A1) and (A2).
Step (A1): The energy ray-curable composition is applied on the film substrate or on the release layer of the film substrate.
Step (A2): After coating, the energy ray-curable composition is cured to form a protective film.

The energy ray-curable composition contains, as an essential component, the monomer a associated with the block A, or the monomer a associated with the block A and the monomer b associated with the block B. The monomers a and b are raw materials for the protective film, and the repeating units described in the above <<protective film>> are formed by polymerizing or copolymerizing the monomers.

The monomer a of the block A is urethane (meth)acrylate I or II, and as an example, the following structure A having a saturated cyclic aliphatic structure R ¹ and structure B having the following saturated aliphatic chain R ² (optionally included) be), and can be exemplified a structure comprising the following structure C having a saturated cyclic aliphatic structure R ^3. The structure B is an optional component.
^{-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 2 -CO- ··· (Structure B)
^-O-R 3 -O- ··· (Structure C)

The urethane (meth)acrylates I and II are, for example, a diisocyanate containing R ¹ , an ester containing R ² (optionally used), a diol containing R ³ , a hydroxyl group-containing alkyl (meth)acrylate, or It can be obtained by using an isocyanate group-containing alkyl (meth)acrylate and can be easily produced.

As an example, the ratio of the structure A, the structure B, and the structure C can be m+1:m(r+s):m, m:m(r+s):m+1, or m:k+n:m+1. The above m represents an integer of 1 to 4, r and s each represent an integer of 0 to 2, the sum of r and s is 1 to 2, k represents an integer of 0 to 2, and n Represents an integer of 0 to 2.

The method for synthesizing the urethane (meth)acrylates I and II is not particularly limited, but as an example, first, a bifunctional intermediate is synthesized and then a hydroxyl group-containing alkyl (meth)acrylate or an isocyanate group-containing alkyl (meth) is synthesized. A method of synthesizing acrylate at both ends of the intermediate can be mentioned.

Specifically, exemplifying a method of synthesizing the urethane (meth)acrylate I corresponding to the repeating unit of the general formula (1), [1] an ester having R ² and a diol having R ³ are m The reaction is carried out at a molar ratio of (r+s):m, and further, m+1 mol of a diisocyanate having R ¹ is reacted to obtain an intermediate having —N═C═O groups at both ends. [2] Then, by reacting 1 mol of the above intermediate with 2 mol of a hydroxyl group-containing alkyl (meth)acrylate, both ends of the repeating unit represented by the general formula (1) are not cleaved (both H ₂ C=CH-) urethane (meth)acrylate I with terminals is obtained.

As an example of the method for synthesizing the urethane (meth)acrylate II corresponding to the repeating unit of the general formula (2), [1] a diisocyanate having R ¹ and an ester having R ² are mixed in m:m(r+s) The reaction is carried out at a molar ratio, and further a diol having m+1 mol of R ³ is reacted to obtain an intermediate having hydroxyl groups at both ends. [2] Then, by reacting 1 mol of the intermediate with 2 mol of an isocyanate group-containing alkyl (meth)acrylate, both terminals of the repeating unit represented by the general formula (2) are not cleaved (both The end is H ₂ C=CH-)
Urethane (meth)acrylate II is obtained.

As an example of a method for synthesizing a urethane (meth)acrylate II corresponding to the repeating unit of the general formula (3), [1] a diisocyanate having R ¹ and a diol having R ³ are reacted at a molar ratio of m:m+1. Then, an intermediate having hydroxyl groups at both ends is obtained. [2-1] After that, 1 mol of the above intermediate is reacted with 2 mol of an isocyanate group-containing alkyl (meth)acrylate, or [2-2] 1 mol of the above intermediate is added to k+n mol. After reacting the ester having R ² with 2 mol of the isocyanate group-containing alkyl (meth)acrylate, or [2-3] with respect to 2 mol of the isocyanate group-containing alkyl (meth)acrylate, k+n mol The urethane (meth)acrylate obtained by reacting the ester having R ² of 1 is reacted with 1 mol of the above-mentioned intermediate, or by any method of the repeating unit represented by the general formula (3). both ends is not cleaved (both terminals H _{2 C} = CH-) urethane (meth) acrylate II is obtained.

Although the synthetic procedure of each raw material is shown above, the synthetic procedure of urethane (meth)acrylates I and II according to the present invention is not limited to these, and the raw materials may be mixed at the same time. However, the above synthetic procedure is excellent in that the molecular weight is easily controlled.

The monomer b that forms the block B has been described as a specific example of the (meth)acrylate group-containing raw material, and thus the description thereof will not be repeated.

The energy ray-curable composition is prepared by adding a photopolymerization initiator that initiates the polymerization of the monomers to the monomers a and b that generate the repeating units of the block A and the block B. As a photopolymerization initiator, acetophenone-based, benzophenone-based, thioxanthone-based, benzoin, radical polymerization initiators such as benzoin methyl ether, aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, cationic polymerization initiation of metallocene compounds, etc. The agents can be used alone or in appropriate combination.

Various additives such as the ultraviolet absorber, the leveling agent and the antistatic agent described above in <<Protective Film>> may be added to the energy ray-curable composition.

In the energy ray-curable composition, the respective proportions of the monomer (the total amount of the monomers a and b that form the block A and the block B), the photopolymerization initiator and the optional additives are different depending on the type of each material, and are unique. However, as an example, the above monomer is 50% by mass or more and 99% by mass or less, the photopolymerization initiator is 0.5% by mass or more and 10% by mass or less, and various additives are 0.01% by mass. It can be 50 mass% or less. Further, an organic solvent such as toluene may be added to the energy ray curable composition. Furthermore, silica sol may be added to the energy ray-curable composition.

The mass ratio of the urethane (meth)acrylates I and II that are the monomers a that generate the block A to the (meth)acrylate group-containing raw material that is the monomers b that generate the block B is the tensile ratio of the protective film due to the block B. Urethane (meth)acrylates I and II: (meth)acrylate group-containing raw material=90:10 to 10:90 are preferable, and 80:20 to 20:80 are more preferable in order to make the degree of elastic modulus improvement suitable. , 70:30 to 30:70 are particularly preferable.

In order to apply the prepared energy ray-curable composition on the film substrate or on the release layer of the film substrate, considering continuous productivity, a coating method such as a roll coating method or a gravure coating method is used. It is preferable to use. By the coating method, the energy ray-curable composition can be applied so as to form a thin film, for example, a protective film having a thickness of 80 μm or less, preferably 50 μm or less, more preferably 30 μm or less.

The curing in the step (A2) can be performed by irradiating with ultraviolet rays from an ultraviolet ray irradiation device. The ultraviolet light source used is not particularly limited, but has a light emission distribution at a wavelength of 400 nm or less, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excited mercury lamp, a metal halide lamp, etc. Can be used. When a composition containing an acrylic compound as an energy ray-curable component is used, a high-pressure mercury lamp or metal halide lamp having a large amount of light of 400 nm or less is preferably used as an ultraviolet light source in consideration of the absorption wavelength exhibited by a general polymerization initiator. ..

By curing the energy ray-curable composition, a protective film is formed on the film substrate or on the release layer of the film substrate, and a film laminate in which the protective film is laminated on the film substrate is obtained. .. Furthermore, a single protective film can be obtained by peeling the protective film from the film laminate.

[Functional layer forming process]
As a variation of the method for producing a film laminate, there is a production method including a functional layer forming step (B) before the protective film forming steps (A1) and (A2). In the functional layer forming step (B), the energy ray-curable composition, which is a raw material of the functional layer, is applied onto the film base material or the release layer of the film base material and cured to function as a film base material. Form the layers.

The functional layer is not particularly limited, and examples thereof include the hard coat layer, antiglare layer and antireflection layer described above. The energy ray-curable composition that is a raw material of the functional layer includes the resin described above in the description of the hard coat layer, the antiglare layer, and the antireflection layer.

In order to apply the energy ray-curable composition, which is the raw material of the functional layer, onto the film substrate or onto the release layer of the film substrate, considering continuous productivity, roll coating, gravure coating, etc. It is preferable to use the above coating method. Depending on the energy ray-curable composition to be used, a method may be used in which heating is optionally performed, and then crosslinking and curing are performed by ultraviolet irradiation or the like.

When the functional layer is formed on the film substrate in the functional layer forming step, the energy ray-curable composition is applied to the functional layer side of the film substrate in the protective film forming step (A1). When the functional layer has a plurality of layers, it is usually applied on the side of the functional layer formed last.

When a film substrate having irregularities is used, the functional layer formed on the film substrate has irregularities and functions as an antiglare layer having antiglare properties.

<<Method of manufacturing polarizing plate>>
The polarizing plate according to the present invention includes the protective film according to the present invention on at least one surface of the polarizing film. In the method for producing a polarizing plate according to the present invention, it is important that the protective film is attached to the polarizing film, and the attaching method may be a known method and is not particularly limited.

Although the protective film may be used alone as the protective film, it is preferable to use the protective film together with the film laminate, that is, the film substrate, from the viewpoint of easy handling.

For example, after the protective film forming step, or after the functional layer forming step and the protective film forming step, after obtaining a laminate including a protective film, if a polarizing film is attached to the protective film side of the film laminate The polarizing plate according to the present invention can be obtained.

The steps involved in the method for producing a polarizing plate using the energy ray-curable adhesive will be described more specifically. The following steps (C1-1) to (C4) are performed after the protective film forming step or after the functional layer forming step and the protective film forming step.

(C1-1) A coating step of applying an ultraviolet curable adhesive to the protective film side (or polarizing film) of the film laminate,
(C2-1) A laminating step in which a polarizing film (or the protective film side of the film laminate) is overlaid and pressed on the ultraviolet curable adhesive surface applied in the applying step,
(C3-1) Curing by curing the ultraviolet curable adhesive by irradiating the film laminate, in which the protective film is bonded to the polarizing film via the ultraviolet curable adhesive, with ultraviolet rays from the ultraviolet irradiation device. Process,
(C4) A peeling step of peeling and removing the film base material (support base material) from the laminated film as necessary.

In the coating step (C1-1), an ultraviolet curable adhesive is applied to the protective film side of the film laminate, which is the bonding surface of the polarizing film (or, instead of the protective film side of the film laminate, polarized light is used). Apply UV curable adhesive to the film). When the applied ultraviolet curable adhesive has been diluted with water, an organic solvent or the like, it is appropriately dried by a method such as heating. As the coating machine used here, a known one can be appropriately used, and examples thereof include a coating machine using a gravure roll.

In the laminating step (C2-1), after passing through the coating step (C1-1), the polarizing film is laminated on the adhesive-coated surface of the film laminate and laminating is performed (coating step (C When the UV-curable adhesive is applied to the polarizing film in C1-1), the protective film side of the film laminate is laminated on the surface of the UV-curable adhesive and the bonding is performed while applying pressure). A known means can be used for pressurization in the laminating step, but from the viewpoint that pressurization can be carried out while being continuously conveyed, a method of sandwiching between a pair of nip rolls is preferably used. The pressure is preferably about 150 to 500 N/cm as a linear pressure when sandwiched by a pair of nip rolls.

In the curing step (C3-3), after the film laminate is attached to the polarizing film, ultraviolet rays are irradiated from the ultraviolet irradiation device to cure the ultraviolet curable adhesive. Ultraviolet rays are irradiated through the polarizing film or the protective film. The ultraviolet light source used is not particularly limited, but has a light emission distribution at a wavelength of 400 nm or less, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excited mercury lamp, a metal halide lamp, etc. Can be used. When an adhesive containing an acrylic compound as an energy ray-curable component is used, a high pressure mercury lamp or a metal halide lamp having a large amount of light of 400 nm or less is preferably used as an ultraviolet light source in consideration of the absorption wavelength of a general polymerization initiator. ..

The peeling step (C4) is a step that is appropriately performed as necessary, and peels and removes the film base material laminated on the protective film in this step (when the film base material has a plurality of layers, a film base). A part of the material is peeled and removed) to obtain a polarizing plate. In the case where the polarizing plate is further processed and the surface of the protective film is desired to be protected in the post-processing step, the film base material may be peeled off after the processing is completed.

The steps involved in the method for producing a polarizing plate using a water-soluble adhesive will be described more specifically. The following steps (C1-2) to (C4) are performed after the protective film forming step, or after the functional layer forming step and the protective film forming step.

(C1-2) A treatment step of performing plasma treatment or corona treatment on the protective film side of the film laminate, if necessary.
(C2-2) A laminating step in which the plasma-treated or corona-treated surface and the polarizing film are overlapped with each other via a water-soluble adhesive and pressed,
(C3-2) A curing step of heating and drying the film laminate in which the protective film is laminated on the polarizing film via the water-soluble adhesive to cure the water-soluble adhesive,
(C4) A peeling step of peeling and removing the film base material (support base material) from the laminated film as necessary.

In the treatment step (C1-2), plasma treatment or corona treatment is performed on the protective film side of the film laminate, if necessary. When using an unmodified silica sol having no organic substituent, this step is unnecessary. As the processing apparatus used here, a known apparatus can be appropriately used, and a plasma processing or corona processing apparatus capable of performing processing at a processing strength such that the water contact angle after plasma processing or corona processing is 30° or less is mentioned. To be

In the laminating step (C2-2), after passing through the treatment step (C1-2), the polarizing film is laminated on the surface of the film laminate subjected to the surface treatment via a water-soluble adhesive and laminated while applying pressure. Is performed. A known means can be used for pressurization in the laminating step, but from the viewpoint that pressurization can be carried out while being continuously conveyed, a method of sandwiching between a pair of nip rolls is preferably used. The pressure is preferably about 150 to 500 N/cm as a linear pressure when sandwiched by a pair of nip rolls.

In the curing step (C3-2), after the film laminate is attached to the polarizing film, heat treatment is performed to cure the water-soluble adhesive. Since the water-soluble adhesive uses water as a solvent, the polarizing plate manufacturing apparatus using a conventional protective film can be used as it is.

Hereinafter, the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited to the contents of the Examples. The protective film obtained by peeling the polyester film substrate from the obtained film laminate is measured, and the thickness of the protective film, the in-plane direction and the retardation value in the thickness direction, and the tensile elastic modulus are respectively measured by the following measuring methods. It was measured.

[Film thickness]
The thickness of the protective film was measured using a digital linear gauge D-10HS and a digital counter C-7HS (manufactured by Ozaki Seisakusho Co., Ltd.).
[Phase difference value in in-plane direction and thickness direction]
Using a phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.), based on the above formulas (i) and (ii), a phase difference value (Re) in the in-plane direction at a measurement wavelength of 590 nm at 23° C. and The retardation value (Rth) in the thickness direction was measured.
(Tensile modulus)
The protective film was cut into a size of 15 mm × 160 mm, and the long side was taken as the pulling direction, using "Tensilon RTF-24" (manufactured by Yamato Scientific Co., Ltd.) so that the distance between the grips was 100 mm. Hold both ends of the grip in a grip and measure the tensile modulus from the maximum slope of the stress-strain curve at a temperature of 23°C ± 5°C, relative humidity of 50% RH ± 10% RH, measuring load range of 40 N, and measuring speed of 20 mm/min. I asked.
[Adhesiveness with polarizing film]
Adhesion with energy ray curable adhesive:
"Unidick V-9510" (manufactured by DIC) as an energy ray curable adhesive was applied to the protective film with a bar coater to a thickness of about 2 µm, and then the applied surface was bonded with a PVA-based polarizing film and a laminator. Then, a high pressure mercury lamp was irradiated from the protective film side under the conditions of a peak illuminance of 800 mW/cm ² and an integrated light amount of 2000 mJ/cm ² to perform ultraviolet curing to obtain a polarizing plate. The protective film was manually peeled off from this polarizing plate, and when it was not peeled off, it was judged as ∘, when there was a strong resistance when peeled off, and when it was not adhered in the first place or when it was easily peeled off, it was judged as x.
Adhesion with water-soluble adhesive:
The surface of the protective film is corona-treated at a strength of 500 mW·min/m ² , and a PVA aqueous solution (solid content 3%) is applied on the corona-treated surface with a bar coater to a thickness of about 0.2 μm. Was laminated with a PVA-based polarizing film with a laminator and dried at 80° C. for 5 minutes to obtain a polarizing plate. The protective film was manually peeled off from this polarizing plate, and when it was not peeled off, it was judged as ∘, when there was a strong resistance when peeled off, and when it was not adhered in the first place or when it was easily peeled off, it was judged as x.

[Production Example 1: Synthesis of Block A Monomer]
Synthesis of compound 1a:
196.29 g (1 mol) of tricyclodecane dimethanol and 228.28 g (2 mol) of ε-caprolactone were charged in a flask, the temperature was raised to 120° C., and 50 ppm of monobutyltin oxide was added as a catalyst. Then, the reaction was performed under a nitrogen stream until the amount of remaining ε-caprolactone was 1% or less by gas chromatography to obtain diol (1).

In a separate flask was charged 444.56 g (2 mol) of isophorone diisocyanate, 424.57 g (1 mol) of diol (1) was added at a reaction temperature of 70°C, and 2-hydroxyethyl was added when the remaining isocyanate group became 5.7%. Acrylate 232.24 g (2 mol) and dibutyl tin laurate 0.35 g were added and reacted until the residual isocyanate group became 0.1% to obtain a urethane acrylate (compound 1a) which is a monomer to generate a repeating unit (compound 1a Is the same as the structure in which m is 1 in the general formula (1a) except that both terminals are acrylate groups).

[Production Example 2: Synthesis of Block A Monomer]
Synthesis of compound 1b:
Compound 1b, which is a monomer giving a repeating unit, was obtained in the same manner as in Production Example 1 except that the synthesis amount of diol (1) was doubled and the amount of isophorone diisocyanate used was changed from 2 mol to 3 mol. (Compound 1b has the same structure as m in general formula (1a) except that both ends are acrylate groups).

[Production Example 3: Synthesis of Block A Monomer]
Synthesis of compound 1c:
Compound 1c was obtained in the same manner as in Production Example 1 except that the amount of diol (1) synthesized was changed to 3 times and the amount of isophorone diisocyanate used was changed from 2 mol to 4 mol. Except that is an acrylate group, has the same structure as m in formula (1a)).

[Production Example 4: Synthesis of block A monomer for comparison]
Synthesis of compound 2:
196.29 g (1 mol) of tricyclodecane dimethanol and 228.28 g (2 mol) of ε-caprolactone were charged in a flask, the temperature was raised to 120° C., and 50 ppm of monobutyltin oxide was added as a catalyst. Then, the reaction was performed under a nitrogen stream until the amount of remaining ε-caprolactone was 1% or less by gas chromatography to obtain a diol (2).

In a separate flask, 420.54 g (2 mol) of trimethylhexamethylene isocyanate was charged, 424.57 g (1 mol) of diol (2) was added at a reaction temperature of 70° C., and when the residual isocyanate group became 5.7%, 2- 232.24 g (2 mol) of hydroxyethyl acrylate and 0.35 g of dibutyltin laurate are added, and the reaction is carried out until the remaining isocyanate group becomes 0.1%, which is a monomer represented by the following general formula (4a) to give a repeating unit. Urethane acrylate (Compound 2, acrylic equivalent 538 g/eq) was obtained. Compound 2 has one type of saturated cycloaliphatic structure and does not form block A.

[Production Example 5: Synthesis of Block B Monomer]
Synthesis of compound 3:
114.14 g (1 mol) of ε-caprolactone and 116.12 g (1 mol) of 2-hydroxyethyl acrylate were reacted at 120° C. under a nitrogen stream to give 100 parts by mass of 114.14 g (1 mol) of ε-caprolactone. As a catalyst, 5 parts by mass of spherical activated carbon BAC manufactured by Kureha Co., Ltd. was added, and in order to suppress radical polymerization of 2-hydroxyethyl acrylate, 500 ppm of 4-methoxyphenol was added to the entire polymerization system. Then, the reaction was carried out until the amount of ε-caprolactone was 1% or less by gas chromatography, to obtain ε-caprolactone-modified hydroxyethyl acrylate (3).
Into another flask was charged 624.77 g (1 mol) of isophorone diisocyanate trimer, 690.78 g (3 mol) of ε-caprolactone modified hydroxyethyl acrylate (3) and 0.35 g of dibutyltin laurate were added at a reaction temperature of 70° C. The reaction was carried out until the content became 0.1% to obtain urethane acrylate (compound 3, acrylic equivalent of 452 g/eq), which is a monomer for generating a repeating unit, represented by the following general formula (5a).

[Production Example 6: Synthesis of organic silica particles]
Synthesis of compound 4:
600 g of commercially available MEK (methyl ethyl ketone)-dispersed colloidal silica (primary particle diameter: 10 to 15 nm, solid content 30%) and 24.0 g (0.1 mol) of triethoxyphenylsilane were placed in a flask and sufficiently charged. After reacting at 30° C. for 24 hours with stirring, the dispersion medium was volatilized so that the solid content ratio of the reaction product was 40% to obtain a dispersion liquid containing organic silica particles (Compound 4).

[Production Example 7: Synthesis of reactive silica particles]
Synthesis of compound 5:
600 g of commercially available MEK (methyl ethyl ketone)-dispersed colloidal silica (primary particle size: 10 to 15 nm, solid content 30%) and trimethoxy(3-methacryloyloxypropyl)silane 24.8 g (0.1 mol) as silica particles in a flask. After reacting at 30° C. for 24 hours with sufficient stirring, the dispersion medium is volatilized so that the solid content ratio of the reaction product is 40% to obtain a dispersion liquid containing reactive silica particles (compound 5). It was

[Example 1]
An energy ray-curable composition (P1) for forming a protective film described below was applied to the release layer side of a non-silicone release PET SG-1 (38 μm thickness) manufactured by Panac Co. using an applicator. The energy ray-curable composition (P1) is diluted with toluene and has a solid content ratio (NV) of 50%.

The coating thickness of the energy ray-curable composition (P1) was adjusted so that the film thickness after drying was 10 μm to 15 μm. Dry the coating film in a clean oven set to a drying oven temperature of 100°C, and then irradiate it with a high-pressure mercury lamp under a nitrogen atmosphere under the conditions of a peak illuminance of 326 mW/cm ² and an accumulated light amount of 192 mJ/cm ^2. UV curing was performed to obtain a film laminate having a protective film formed on one side of the PET film. Table 4 shows the evaluation results of this film laminate.

[Examples 2 to 12, Comparative Examples 1 to 4]
94.5 parts by mass of the compound 1a described in Table 1 was changed to the compounds described in the formulation of Table 3 and the corresponding parts by mass, and a protective film was formed on one side of the PET film in the same manner as in Example 1 except for the change. The film laminated body in which was formed was obtained. Table 4 shows the evaluation results of this film laminate.

[Example 13]
A film laminate having a protective film formed on one side of a PET film was obtained in the same manner as in Example 1 except that the energy ray-curable composition (P2) shown in Table 2 was used. Table 4 shows the evaluation results of this film laminate. Since the dispersion liquid of compound 4 shown in Table 2 has a solid content of 40%, P2 contains 5 parts by mass of compound 4.

[Examples 14 to 18]
The compound 1a described in Table 2 and the dispersion liquid of the compound 4 were changed to the compounds described in the formulation table of Table 3 and the corresponding parts by mass, and a PET film was prepared in the same manner as in Example 1 except for the change. A film laminate having a protective film formed on one surface was obtained. Table 4 shows the evaluation results of this film laminate.

Compound 6 shown in the formulation table of Table 3 is a monomer having an acrylic equivalent of 196 g/eq, and its structure is represented by the following general formula (6a).

Compound 7 described in the formulation table of Table 3 is a monomer having an acrylic equivalent of 99 g/eq, and its structure is represented by the following general formula (7a).

Compound 8 described in the formulation of Table 3 is UA-160TM (urethane acrylate manufactured by Shin-Nakamura Chemical Co., Ltd., theoretical molecular weight 1600, acrylic functional group 2), and since the acrylic equivalent is 800 g/eq, block B is produced. Do not let

As shown in Table 4, when the compound 1a of Example 1 was used, a protective film having an absolute value of Re and Rth both close to zero and a very high tensile modulus was obtained. The protective films composed of the compounds 1b and 1c in Examples 2 and 3 achieved a high tensile elastic modulus, although it was inferior to that of Example 1 (compound 1a).

The cured film formed in Comparative Example 1 was very soft, and a protective film having a low tensile modulus was obtained. When synthesizing the compound 2, since a diisocyanate having a branched saturated aliphatic chain which is a flexible skeleton was used, the repeating unit of the compound 2 contains only one type of saturated cyclic aliphatic structure. Therefore, it is considered that the cohesive force between the repeating units was weakened and a flexible cured film was formed.

The cured film formed in Comparative Example 2 was very hard and fragile, and collapsed when peeled from the PET film. Therefore, it is possible to measure the film thickness, retardation value, tensile elastic modulus, and adhesiveness with the polarizing film. could not. Since compound 6 does not have a urethane bond (-NH-CO-O-), cohesive force between repeating units was not obtained, and only a three-dimensional network covalent bond was formed due to the curing of the acrylic group. It is considered that a hardened film with high brittleness was formed due to the influence.

Examples 4 to 12 used Compounds 3, 6 and 7 each having an acrylic equivalent of 99 g/eq to 452 g/eq as the compound which produces the block B, so that Re and Rth are both close to zero and very high. A protective film having a tensile modulus was obtained.

On the other hand, the cured film formed in Comparative Example 3 was very soft and a protective film having a low tensile modulus was obtained. Since the acrylic equivalent of the compound 8 that produces the comparative block B was as large as 800 g/eq, it is considered that the effect was that the three-dimensional crosslinked structure was not sufficiently formed due to the curing of the acrylic group.
Further, the cured film formed in Comparative Example 4 was a very soft protective film having a low tensile elastic modulus because Compound 2 had a flexible skeleton as in the above description.

Since Examples 13 to 18 contained silica particles in the protective film, even the water-soluble adhesives were bonded to the polarizing film. In particular, since Examples 14 to 18 used the compound 5 which is a reactive silica particle, very good adhesiveness with a water-soluble adhesive was obtained.

As is clear from the above Examples and Comparative Examples, the repeating unit forming the protective film is made of urethane (meth)acrylate and (meth)acrylate group-containing raw materials, and the urethane (meth)acrylate contains a plurality of saturated types. It is very important that the (meth)acryl equivalent of the (meth)acrylate group-containing raw material has a cyclic aliphatic structure and is 90 g/eq or more and 500 g/eq or less, and the usefulness of the protective film according to the present invention is To be understood.

The protective film according to the present invention has a high tensile elastic modulus without undergoing a molecular orientation treatment, therefore, an application requiring high durability against a harsh temperature and humidity environment, in particular, as a constituent member of a polarizing plate. It is useful and can be used in various fields.

Claims (9)

A protective film formed by a block A composed of repeating units I or II having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or
A protective film formed by the block A and a block B comprising a repeating unit having a structure derived from a (meth)acrylate group-containing raw material which is a monomer b,
The urethane (meth)acrylate I is a reaction product of a hydroxyl group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylate II is a reaction product of an isocyanate group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylates I and II have a plurality of types of saturated cycloaliphatic structures,
The (meth)acrylate group-containing raw material has a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less,
The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. is 0 nm or more and 10 nm or less, and the thickness direction retardation value (Rth) at a wavelength of 590 nm at 23° C. is -10 nm or more and 10 nm or less ,
The repeating units I and II are
The following structure A containing a saturated cycloaliphatic structure R ¹ , and
Comprises the following structure C that includes a saturated cyclic aliphatic structure R ^{3,
-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 3 -O- ··· (Structure C)
The repeating units I and II are
Further, including the following structure B containing a saturated aliphatic chain R ² ,
^-O-R 2 -CO- ··· (Structure B)
The protective film , wherein the repeating unit I has a structure represented by the following general formula (1) .

(In the general formula (1), R ¹ represents a saturated cycloaliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. Shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and r and s each represent 0. Represents an integer of 2 and the sum of r and s is 1 to 2 and x represents an integer of 0 to 3). A protective film formed by a block A composed of repeating units I or II having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or
A protective film formed by the block A and a block B comprising a repeating unit having a structure derived from a (meth)acrylate group-containing raw material which is a monomer b,
The urethane (meth)acrylate I is a reaction product of a hydroxyl group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylate II is a reaction product of an isocyanate group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylates I and II have a plurality of types of saturated cycloaliphatic structures,
The (meth)acrylate group-containing raw material has a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less,
The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. is 0 nm or more and 10 nm or less, and the thickness direction retardation value (Rth) at a wavelength of 590 nm at 23° C. is -10 nm or more and 10 nm or less ,
The repeating units I and II are
The following structure A containing a saturated cycloaliphatic structure R ¹ , and
Comprises the following structure C that includes a saturated cyclic aliphatic structure R ^{3,
-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 3 -O- ··· (Structure C)
The repeating units I and II are
Further, including the following structure B containing a saturated aliphatic chain R ² ,
^-O-R 2 -CO- ··· (Structure B)
The protective film , wherein the repeating unit II has a structure represented by the following general formula (2) .

(In the general formula (2), R ¹ represents a saturated cyclic aliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. Shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and r and s each represent 0. Represents an integer of 2 and the sum of r and s is 1 to 2 and x represents an integer of 0 to 3). A protective film formed by a block A composed of repeating units I or II having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or
A protective film formed by the block A and a block B comprising a repeating unit having a structure derived from a (meth)acrylate group-containing raw material which is a monomer b,
The urethane (meth)acrylate I is a reaction product of a hydroxyl group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylate II is a reaction product of an isocyanate group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylates I and II have a plurality of types of saturated cycloaliphatic structures,
The (meth)acrylate group-containing raw material has a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less,
The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. is 0 nm or more and 10 nm or less, and the thickness direction retardation value (Rth) at a wavelength of 590 nm at 23° C. is -10 nm or more and 10 nm or less ,
The repeating units I and II are
The following structure A containing a saturated cycloaliphatic structure R ¹ , and
Comprises the following structure C that includes a saturated cyclic aliphatic structure R ^{3,
-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 3 -O- ··· (Structure C)
The repeating units I and II are
Further, including the following structure B containing a saturated aliphatic chain R ² ,
^-O-R 2 -CO- ··· (Structure B)
The protective film , wherein the repeating unit II has a structure represented by the following general formula (3) .

(In the general formula (3), R ¹ represents a saturated cyclic aliphatic structure, R ² represents a linear or branched saturated aliphatic chain having 5 to 10 carbon atoms, and R ³ is different from R ^1. It shows a saturated cycloaliphatic structure, R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 1 to 4, and k represents 0 to 2 Represents an integer, n represents an integer of 0 to 2, and x represents an integer of 0 to 3) A protective film formed by a block A composed of repeating units I or II having a structure derived from urethane (meth)acrylate I or II which is a monomer a, or
A protective film formed by the block A and a block B comprising a repeating unit having a structure derived from a (meth)acrylate group-containing raw material which is a monomer b,
The urethane (meth)acrylate I is a reaction product of a hydroxyl group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylate II is a reaction product of an isocyanate group-containing alkyl (meth)acrylate, a diol and a diisocyanate,
The urethane (meth)acrylates I and II have a plurality of types of saturated cycloaliphatic structures,
The (meth)acrylate group-containing raw material has a (meth)acrylic equivalent of 90 g/eq or more and 500 g/eq or less,
The in-plane retardation value (Re) at a wavelength of 590 nm at 23° C. is 0 nm or more and 10 nm or less, and the thickness direction retardation value (Rth) at a wavelength of 590 nm at 23° C. is -10 nm or more and 10 nm or less ,
The repeating units I and II are
The following structure A containing a saturated cycloaliphatic structure R ¹ , and
Comprises the following structure C that includes a saturated cyclic aliphatic structure R ^{3,
-CO-NH-R 1 -NH-} CO- ··· ( Structure A)
^-O-R 3 -O- ··· (Structure C)
The repeating units I and II are
Further, including the following structure B containing a saturated aliphatic chain R ² ,
^-O-R 2 -CO- ··· (Structure B)
A protective film , further comprising silica particles . The protective film according to claim 4 , wherein the silica particles are organic silica particles having an organic substituent. Said R ¹ is 3-methylene-3,5,5 a-trimethyl cyclohexane ring, R ³ is as defined in any one of claims 1 to 5, characterized in that a dimethylene tricyclodecane ring Protective film. The tensile elastic modulus is 1500 MPa or more, and the protective film according to any one of claims 1 to 6 . On at least one surface of the protective film according to any one of claims 1 to 7 ,
(1) A film substrate that supports the protective film,
(2) A hard coat layer having scratch resistance,
(3) An antiglare layer that scatters light, and
(4) A film comprising any one of a high refractive index layer provided on the protective film and an antireflection layer composed of a low refractive index layer provided on the high refractive index layer. Laminate. A polarizing plate comprising the protective film according to any one of claims 1 to 7 on at least one surface of the polarizing film.