JP5582947B2 - Polarizing plate, liquid crystal display using the same, and protective film for moisture and heat resistant polarizing plate - Google Patents

Description

  The present invention relates to a polarizing plate and a liquid crystal display device using the polarizing plate, and more specifically, a polarizing plate that hardly causes light leakage due to distortion such as wet heat, and a liquid crystal display having high image display quality using the polarizing plate. Relates to the device. Moreover, this invention relates also to the protective film for heat-and-moisture resistant polarizing plates.

  As the polarizing plate, a polarizing film formed by adsorbing iodine or the like on polyvinyl alcohol is widely used. The polarizing plate usually has a laminated structure in which a polarizing film made of a polyvinyl alcohol film or the like and a protective film for protecting the polarizing film are bonded to both surfaces of the polarizing film. Various versatile triacetyl cellulose films are used as the protective film.

  On the other hand, image display devices such as liquid crystal display devices using polarizing plates are becoming thinner and the distance between the backlight unit and the display panel unit tends to be shorter. As a result, the polarizing plate disposed in the vicinity of the backlight unit is distorted by heat from the backlight, which contributes to a deterioration in display characteristics. In addition, the usage environment of the image display apparatus is diversified, and the demand for the polarizing plate to be compatible with use in a high temperature / high humidity environment is increasing.

As a polarizing plate with improved durability at high temperatures, a polarizing plate using a predetermined adhesive layer for adhesion to a protective film has been proposed (Patent) Reference 1). As described in [0047] of Patent Document 1, in Patent Document 1, durability of the polarizing plate at high temperature is improved by reducing the moisture content of the polarizer.
Moreover, as a polarizing plate with improved heat and humidity resistance, a polarizing plate is proposed in which a stretched polyethylene terephthalate film is laminated on a polarizing film via a predetermined adhesive layer (Patent Document 2). The wet heat resistance of the polarizing plate is improved by using a stretched polyethylene terephthalate film having a relatively low moisture permeability as a protective film instead of the triacetyl cellulose film having a relatively high moisture permeability.
The polarizing plate has a polarizing film, a pressure-sensitive adhesive layer, and an optical compensation sheet as a polarizing plate in which light leakage due to distortion due to wet heat or the like is reduced, and the photoelastic coefficient of the pressure-sensitive adhesive layer and the optical compensation sheet A polarizing plate has been proposed in which the elastic modulus satisfies a predetermined relationship (Patent Document 3). As shown in FIG. 1 and FIG. 2 of Patent Document 3, this pressure-sensitive adhesive layer is used for bonding a laminate including a polarizer film and an optical compensation sheet to another member such as a liquid crystal cell. Is a layer.

JP 2009-282137 A JP 2010-91602 A JP 2008-181105 A

A cellulose acylate film such as a triacetyl cellulose film conventionally used as a protective film for a polarizing plate is available at a low cost and has excellent handleability. Therefore, it is very useful in the industry of this technical field that the wet heat resistance of the polarizing plate can be improved while using the cellulose acylate film as a protective film.
This invention makes it a subject to provide the technique which improves the heat-and-moisture resistance of the polarizing plate which has a cellulose acylate film as a protective film.
More specifically, the present invention provides a polarizing plate having a cellulose acylate film with improved wet heat resistance, a liquid crystal display device with reduced luminance unevenness due to wet heat, and a cellulose acylate film. It is an object of the present invention to provide a protective film for a heat-and-moisture-resistant polarizing plate using

Means for solving the above-mentioned problems are as follows.
[1] A polarizing plate, a polarizing plate having at least a cellulose acylate film having a total of 10% or more of stretching ratios in the TD direction and MD direction, and a layer having a negative photoelastic coefficient on one surface thereof.
[2] The polarizing plate according to [1], wherein the cellulose acylate film has a thickness exceeding 77 μm.
[3] The polarizing plate according to [1] or [2], wherein an average elastic modulus in the transverse direction and the longitudinal direction of the cellulose acylate film is 3800 MPa or more.
[4] The polarizing plate according to any one of [1] to [3], wherein the layer having a negative photoelastic coefficient is an adhesive layer that bonds the cellulose acylate film and the polarizing film.
[5] The polarizing plate according to [4], wherein the adhesive layer is made of an acrylic adhesive composition.
[6] The polarizing plate according to any one of [1] to [3], wherein the layer having a negative photoelastic coefficient is a polymer film containing a cyclic olefin resin.
[7] The polarizing plate according to any one of [1] to [3], wherein the layer having a negative photoelastic coefficient is a polymer film containing an acrylic resin.
[8] A liquid crystal display device comprising at least a polarizing plate according to any one of [1] to [7] and a liquid crystal cell.
[9] The liquid crystal display device according to [8], wherein the polarizing plate is disposed on a light source side of the liquid crystal cell.
[10] The liquid crystal display device according to [8] or [9], wherein the cellulose acylate film and the layer having a negative photoelastic coefficient included in the polarizing plate are disposed between the liquid crystal cell and a polarizing film.
[11] A protective film for a moisture and heat resistant polarizing plate having at least a cellulose acylate film having a total stretching ratio of 10% or more in the TD direction and MD direction and a layer having a negative photoelastic coefficient.
[12] The protective film for moisture and heat resistant polarizing plates according to [11], wherein the cellulose acylate film has a thickness exceeding 77 μm.
[13] The protective film for heat and heat resistant polarizing plates according to [11] or [12], wherein the layer having a negative photoelastic coefficient is a polymer film containing a cyclic olefin resin.
[14] The protective film for heat and heat resistant polarizing plates according to [11] or [12], wherein the layer having a negative photoelastic coefficient is a polymer film containing an acrylic resin.

ADVANTAGE OF THE INVENTION According to this invention, the technique which improves the heat-and-moisture resistance of the polarizing plate which has a cellulose acylate film as a protective film can be provided.
More specifically, according to the present invention, a polarizing plate having a cellulose acylate film with improved wet heat resistance, a liquid crystal display device with reduced luminance unevenness due to wet heat, and cellulose acylate are provided. A protective film for a heat-and-moisture resistant polarizing plate using a rate film can be provided.

It is a cross-sectional schematic diagram of an example of the polarizing plate of this invention. It is a cross-sectional schematic diagram of the other example of the polarizing plate of this invention.

The present invention is described in detail below. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
In the present specification, the terms “adhesive” and “pressure-sensitive adhesive” are used separately. “Adhesive” means an agent that joins and integrates two members by solidifying by a chemical reaction or the like. On the other hand, “adhesive” means an agent that joins two members by their high viscosity without going through a solidification process. The state of the adhesive changes before and after joining, but the state of the adhesive does not change before and after joining.
1. TECHNICAL FIELD The present invention relates to a polarizing film, a polarizing plate having at least a cellulose acylate film having a total stretching ratio of 10% or more in the TD direction and MD direction on one surface thereof, and a layer having a negative photoelastic coefficient. About. In the present invention, a cellulose acylate film having a positive photoelastic coefficient and a layer having a negative photoelastic coefficient are disposed on one surface of the polarizing film. Even when the polarizing plate is distorted by the heat from the backlight or the like, the birefringence generated in each of the polarizing plates cancels out, so that fluctuations in the polarizing plate characteristics due to the distortion can be reduced. However, if the thickness of the cellulose acylate film is large, correction of birefringence by the negative photoelastic coefficient layer becomes insufficient, and it is practically recognized as a variation in polarization characteristics. In the present invention, as a cellulose acylate film, a negative photoelastic coefficient layer is corrected by using a stretched cellulose acylate film subjected to a stretching treatment in which the total stretching ratio in the TD direction and the MD direction is 10% or more. The effect is fully demonstrated.

1 and 2 are schematic cross-sectional views of first and second examples of the polarizing plate of the present invention. In addition, the relative relationship of the thickness of each layer does not necessarily correspond with the relative relationship of an actual polarizing plate. The same applies to FIG.
A polarizing plate 10 shown in FIG. 1 has a polarizing film 12, a layer 14 having a negative elastic modulus on one surface thereof, and a cellulose acylate film 16, and a protective film made of an arbitrary polymer film on the other surface. It has a film 18. A polarizing plate 10 ′ shown in FIG. 2 is a polarizing plate having the same configuration except that the positions of the layer 14 having a negative elastic modulus and the cellulose acylate film 16 are exchanged.

  1 and 2, the cellulose acylate film 16 is a stretched cellulose acylate film subjected to a stretching treatment in which the total stretching ratio in the TD direction and the MD direction is 10% or more. It is. The cellulose acylate film 16 functions as a protective film for the polarizing film 12 or as a part of the protective film. The cellulose acylate film 16 has a positive photoelastic coefficient. When distortion occurs due to wet heat, birefringence occurs and contributes to luminance leakage. However, since the negative photoelastic coefficient layer 14 exists in the polarizing plates 10 and 10 ′, the cellulose acylate 16 Birefringence generated by distortion or the like can be corrected. Details of the cellulose acylate film that can be used in the present invention will be described later.

  A polarizing plate 10 of the first example shown in FIG. 1 includes a layer 14 having a negative photoelastic coefficient between a polarizing film 12 and a cellulose acylate film 16. In this example, the negative photoelastic coefficient layer 14 may be, for example, an adhesive layer for bonding the cellulose acylate film 16 to the polarizing film 12. It is preferable that the negative photoelastic coefficient layer 14 is an adhesive layer because the polarizing plate can be thinned. An example of a material that can be used to form a negative photoelastic coefficient adhesive layer is an acrylic adhesive. Details of materials that can be used for forming the adhesive layer having a negative photoelastic coefficient will be described later.

  Of course, in the first example shown in FIG. 1, the negative photoelastic coefficient layer 14 may be a polymer film having a negative photoelastic coefficient.

  A polarizing plate 10 ′ of the second example shown in FIG. 2 has a negative photoelastic coefficient layer 14 on a cellulose acylate film 16. In this example, the negative photoelastic coefficient layer 14 may be, for example, a polymer film having a negative photoelastic coefficient. Examples of materials that can be used to make a polymer film with a negative photoelastic coefficient include cyclic polyolefins and acrylic resins. Details of these materials will be described later.

  In addition, the polarizing plate of this invention is not limited to the structure shown in FIG.1 and FIG.2. If necessary, it may have other functional layers (for example, an antireflection layer, an optically anisotropic layer, an antistatic layer, a hard coat layer, etc.). In addition, an adhesive layer may be separately disposed between the respective layers. Moreover, you may have the adhesive layer for joining with a liquid crystal cell in the outermost surface.

Next, various materials and methods that can be used for producing the polarizing plate of the present invention will be described.
(1) Cellulose acylate film The polarizing plate of the present invention has a cellulose acylate film as a protective film of a polarizing film or as a part of the protective film. In the present specification, the “cellulose acylate film” refers to a film containing one or more cellulose acylates as a main component. In addition, “containing as a main component” refers to a component having the highest mass fraction in an embodiment in which one component is a raw material and in an embodiment having two or more components.

The photoelastic coefficient of the cellulose acylate film used in the present invention is positive. The photoelastic coefficient of the cellulose acylate film is, for example, about 5 × 10 ⁻¹² Pa ^{−1 to} 25 × 10 ⁻¹² Pa ⁻¹ , and 10 × 10 ⁻¹² Pa ^{−1 to} 20 × 10 ⁻¹² Pa. ^{−1 and} about 12 × 10 ⁻¹² Pa ⁻¹ to 18 × 10 ⁻¹² Pa ⁻¹ . The photoelastic coefficient of the cellulose acylate film is determined by a plurality of factors such as the type and content of cellulose acylate used as a main component, additives and content thereof, film thickness, production method and conditions thereof. By determining these, a cellulose acylate film having a photoelastic coefficient in the above range can be obtained.
In addition, the photoelastic coefficient of a cellulose acylate film can be known by measuring a phase difference with an ellipsometer M-150 manufactured by JASCO Corporation while applying a weight to a film sample. The same applies to the following layers having a negative photoelastic coefficient.

  There is no restriction | limiting in particular about the thickness of the cellulose acylate film used for this invention. For example, a cellulose acylate film having a thickness exceeding 77 μm can be used. The thickness of the cellulose acylate film is preferably 82 to 150 μm, more preferably 86 to 120 μm.

  There is no restriction | limiting in particular as a cellulose acylate used as a raw material of the said cellulose acylate film. Any film can be used as long as it can form a transparent film. Cellulose acylate obtained from any raw material cellulose such as cotton linter and wood pulp (hardwood pulp, conifer pulp) can be used, and may be used by mixing in some cases. Detailed descriptions of these raw material celluloses can be found, for example, by Marusawa and Uda, “Plastic Materials Course (17) Fibrous Resin”, published by Nikkan Kogyo Shimbun (published in 1970), and the Japan Institute of Invention and Technology Publication No. 2001 The cellulose described in No.-1745 (pages 7 to 8) can be used.

  The raw material cellulose acylate may be acylated by one kind of acyl group or may be acylated by two or more kinds of acyl groups. It is preferable to have an acyl group having 2 to 4 carbon atoms as a substituent. When two or more types of acyl groups are used, one of them is preferably an acetyl group, and the acyl group having 2 to 4 carbon atoms is preferably a propionyl group or a butyryl group. Cellulose acylate having these acyl groups has good solubility, and a good solution can be prepared particularly by using a non-chlorine organic solvent. Furthermore, it is possible to prepare a solution having a low viscosity and good filterability.

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by acylating part or all of these hydroxyl groups with an acyl group. The degree of acyl substitution means the sum of the ratios of acylation of the hydroxyl groups of cellulose located at the 2-position, 3-position and 6-position (100% acylation at each position is substitution degree 1).

  The acyl group having 2 or more carbon atoms may be an aliphatic group or an allyl group, and is not particularly limited. These are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters, and the like, each of which may further have a substituted group. Preferred examples of these include acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, isobutanoyl group Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group (when the cellulose acylate is cellulose acetate).

  In the acylation of cellulose, when an acid anhydride or acid chloride is used as an acylating agent, an organic acid such as acetic acid or methylene chloride is used as an organic solvent as a reaction solvent.

As the catalyst, when the acylating agent is an acid anhydride, a protic catalyst such as sulfuric acid is preferably used, and when the acylating agent is an acid chloride (for example, CH ₃ CH ₂ COCl), Basic compounds are used.

The most common industrial synthesis method of cellulose mixed fatty acid ester is to use cellulose corresponding to fatty acid corresponding to acetyl group and other acyl groups (acetic acid, propionic acid, valeric acid, etc.) or their anhydrides. This is a method of acylating with a mixed organic acid component.
Examples of the method for producing cellulose acylate that can be used in the present invention include, for example, the method described in JP-A-10-45804.

An example of a cellulose acylate film that can be used in the present invention is a cellulose acylate film that consists of or has a low substitution degree layer containing as a main component a cellulose acylate that satisfies the following formula (I).
(1) 2.0 <Z1 <2.7
(In formula (1), Z1 represents the total acyl substitution degree of the cellulose acylate of the low substitution degree layer.)

The low substitution layer may have a high substitution layer containing, as a main component, cellulose acylate satisfying the following formula (2) on at least one surface thereof.
(2) 2.7 <Z2
(In formula (2), Z2 represents the total acyl substitution degree of the cellulose acylate of the high substitution degree layer.)

Examples of the cellulose acylate used for forming the low substitution degree layer include cellulose acylate satisfying the following formulas (3) and (4).
Formula (3) 1.0 <X1 <2.7
(In Formula (3), X1 represents the substitution degree of the acetyl group of the cellulose acylate in the low substitution degree layer.)
Formula (4) 0 <= Y1 <1.5
(In Formula (4), Y1 represents the total substitution degree of acyl groups having 3 or more carbon atoms in the cellulose acylate of the low substitution degree layer.)
Note that the relationship X1 + Y1 = Z1 holds between X1 and Y1 and Z1 in the formula (1).

Examples of the cellulose acylate used for forming the high substitution degree layer include cellulose acylate satisfying the following formulas (5) and (6).
Formula (5) 1.2 <X2 <3.0
(In Formula (5), X2 represents the substitution degree of the acetyl group of the cellulose acylate in the high substitution degree layer.)
Formula (6) 0 <= Y2 <1.5
(In Formula (6), Y2 represents the total substitution degree of acyl groups having 3 or more carbon atoms in the cellulose acylate of the high substitution degree layer.)
Note that the relationship of X2 + Y2 = Z2 holds between X2 and Y2 and Z2 in the formula (2).

  The cellulose acylate film may contain one or more additives as desired. Examples of the additive include a plasticizer, an optical property adjuster (a wavelength dispersion adjuster, a retardation increasing agent, a retardation reducing agent, etc.), fine particles, a UV absorber, an antioxidant, and the like.

  The cellulose acylate film used in the present invention is a stretched cellulose acylate film that has been subjected to a stretching treatment in which the total stretching ratio in the TD direction and the MD direction is 10% or more. The total stretching ratio in the TD direction and MD direction is preferably 15 to 50%, more preferably 20 to 40%. In addition, the draw ratio of MD direction (conveyance direction) and TD direction (direction orthogonal to a conveyance direction) is defined as follows. The draw ratio in the MD direction is calculated as (speed) / (speed of casting support) immediately after winding of the film after drying. Further, the stretching ratio in the TD direction is calculated as (film width) when the film comes out of the stretching device / (film width when both ends in the width direction of the film are held by the stretching device).

  The stretching treatment for the cellulose acylate film may be either uniaxial stretching or biaxial stretching. In the embodiment in which the cellulose acylate film is used for optical compensation of the birefringence of the liquid crystal cell, it is preferable that the cellulose acylate film exhibits retardation that contributes to optical compensation, and the retardation is set to a desired range by stretching. be able to.

  As long as the above stretching conditions are satisfied, it may be a cellulose acylate film produced by any method such as a solution casting method or a melt casting method. Moreover, you may utilize a commercial item.

In addition, the cellulose acylate film used in the present invention preferably has a higher elastic modulus because it can reduce distortion due to wet heat. More specifically, the average elastic modulus in the transverse direction and the longitudinal direction of the cellulose acylate film is preferably 3800 MPa or more, more preferably 4000 MPa or more, and further preferably 4200 MPa or more. The upper limit is not particularly limited, but is generally less than 6000 MPa. The “average elastic modulus in the transverse direction and the longitudinal direction” of the cellulose acylate film can be measured by the following method.
First, a film sample 10 mm × 150 mm is prepared. The sample was conditioned for 2 hours or more at a temperature of 25 ° C. and a relative humidity of 60%, and then using a tensile tester (Strograph-R2 (manufactured by Toyo Seiki)), the distance between chucks was 50 mm, the temperature was 25 ° C., and the stretching speed. The elastic modulus is measured under the condition of 10 mm / min. The elastic modulus in the horizontal direction is measured by pulling a sample having a width of 150 mm and a length of 10 mm in the horizontal direction, and the elastic modulus in the vertical direction is measured by pulling a sample having a width of 10 mm and a length of 150 mm in the vertical direction. The average elastic modulus can be calculated.
For example, there are many cases where a difference occurs in elastic modulus between a transport direction (MD direction) and a direction perpendicular to the transport direction (MD direction) when the long cellulose acylate film is continuously transported. The cellulose acylate film used in the present invention preferably has an average elastic modulus in the MD direction and TD direction in the above range.

There is no restriction | limiting in particular about the optical characteristic of the said cellulose acylate film utilized for this invention. In the embodiment in which the polarizing plate of the present invention is disposed with the cellulose acylate film between the liquid crystal cell and the polarizing film, the retardation of the cellulose acylate film affects the display characteristics. Accordingly, it is preferable to adjust the in-plane retardation Re and the thickness direction retardation Rth to desired ranges. Hereinafter, in the embodiment in which the polarizing plate of the present invention is arranged such that the cellulose acylate film is disposed between the liquid crystal cell and the polarizing film, the preferred ranges of Re and Rth of the cellulose acylate film are classified according to the mode of the liquid crystal cell. Illustrate. However, it is not limited to the following ranges.
In an embodiment in which the polarizing plate of the present invention is disposed only on the backlight side of the VA mode liquid crystal cell, the cellulose acylate film has an Re of 20 to 100 nm (more preferably 40 to 80 nm) and an Rth of 100 to 300 nm ( More preferably, it is 150 to 250 nm). In this embodiment, among the protective films of the other polarizing plate, the protective film disposed between the liquid crystal cell and the polarizing film is preferably optically isotropic.
In an embodiment in which the polarizing plate of the present invention is disposed on both the display surface side and the backlight side of the VA mode liquid crystal cell, the cellulose acylate film has an Re of 20 to 80 nm (more preferably 30 to 60 nm), and Rth. Is 80 to 200 nm (more preferably 110 to 170 nm).
In an embodiment in which the polarizing plate of the present invention is disposed on both the display surface side and the backlight side of the IPS mode liquid crystal cell, the cellulose acylate film has Re of 0 to 10 nm (more preferably 0 to 6 nm), and Rth. Is preferably 0 to 50 nm (more preferably 0 to 20 nm).

  The cellulose acylate film may be subjected to a surface treatment or the like in order to improve adhesion with a layer having a negative photoelastic coefficient and / or adhesion with a polarizing film. Examples of the surface treatment include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, or ultraviolet irradiation treatment.

(2) Layer with negative photoelastic coefficient The polarizing plate of the present invention has a layer with a negative photoelastic coefficient. The photoelastic coefficient of the layer is preferably −20 × 10 ⁻¹² Pa ⁻¹ to ⁻² × 10 ⁻¹² Pa ⁻¹ , and −15 × 10 ⁻¹² Pa ⁻¹ to ⁻² × 10 ^−12. It is more preferably Pa ⁻¹ , and further preferably −10 × 10 ⁻¹² Pa ⁻¹ to −3 × 10 ⁻¹² Pa ⁻¹ . When the photoelastic coefficient is within this range, birefringence caused by deformation of the cellulose acylate film can be sufficiently corrected.

The material used for forming the layer having a negative photoelastic coefficient is not particularly limited as long as a transparent layer having a negative photoelasticity can be formed. It may be a layer formed by coating such as an adhesive layer, or may be a self-supporting polymer film.
Each example will be described below.

Adhesive layer:
The layer having a negative photoelastic coefficient may be an adhesive layer. The layer having a negative photoelastic coefficient is preferably an adhesive layer that is disposed between the polarizing film and the cellulose acylate film and joins the two. Examples of the adhesive layer having a negative photoelastic coefficient include an adhesive layer made of an acrylic adhesive. Conventionally, a polyvinyl alcohol-based adhesive that has been frequently used for bonding a cellulose acylate film and a polarizing film cannot form a layer having a negative photoelastic coefficient.

An acrylic adhesive is acrylic acid or methacrylic acid (hereinafter collectively referred to as “(meth) acrylic acid”) or derivatives thereof (examples of derivatives include (meth) acrylic acid esters), or (meta ) It means a reactive adhesive mainly composed of a polymer of acrylic acid or a derivative thereof. One example is radical polymerization of an acrylic monomer composition containing a (meth) acrylic acid ester as a main component and a small amount of a (meth) acrylic monomer having a functional group in the presence of a polymerization initiator. And an acrylic adhesive containing an acrylic resin and a crosslinking agent. The (meth) acrylic acid ester as the main component of the acrylic resin has the following formula:
CH ₂ = C (R ¹ ) COOR ²
Can be expressed as In the formula, R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkyl group having 1 to 14 carbon atoms or an aralkyl group, and the hydrogen atom of the alkyl group of R ² or the hydrogen atom of the aralkyl group represents a carbon atom. It may be substituted by an alkoxy group of formula 1-10.
Specific examples of the (meth) acrylic acid ester include butyl acrylate in which R ¹ is H and R ² is an n-butyl group; acrylic in which R ¹ is H and R ² is a 2-ethylhexyl group 2-ethylhexyl acid.

  The (meth) acrylic monomer having the functional group used for the production of the acrylic resin is composed of a polar functional group such as a hydroxyl group, a carboxyl group, an amino group, and an epoxy group, and one olefinic double bond (usually Is a monomer having a (meth) acryloyl group) in the molecule. Specific examples thereof include 2-hydroxyethyl (meth) acrylate as having a hydroxyl group; acrylic acid as having a carboxyl group.

  Furthermore, in the production of the acrylic resin, a small amount of a monomer having a plurality of (meth) acryloyl groups in the molecule can be copolymerized. Examples thereof include 1,4-butanediol di (meth) acrylate and the like. Can be mentioned.

  In the production of the acrylic resin as the main component of the adhesive, only one kind of each of the (meth) acrylic acid ester and the (meth) acrylic monomer having a functional group may be used. Multiple types may be used in combination. In addition, a combination of a plurality of acrylic resins that are copolymers of (meth) acrylic acid esters and (meth) acrylic monomers having functional groups, or other acrylic resins in addition to the acrylic resins that are the copolymers. For example, an acrylic resin composition obtained by blending, for example, an acrylic resin composed of a single or copolymer of a (meth) acrylic monomer having no functional group, can be used as the resin component of the pressure-sensitive adhesive.

  Examples of the crosslinking agent blended in the acrylic adhesive may include an isocyanate compound, an epoxy compound, a metal chelate compound, an aziridine compound, and the like. Isocyanate compounds should be used in the form of adducts, dimers, trimers, etc., in which the compounds have at least two isocyanato groups (—NCO) in the molecule, as well as those reacted with polyols. Can do. As specific examples of the crosslinking agent, there are a trimethylolpropane adduct of hexamethylene diisocyanate and a trimethylolpropane adduct of tolylene diisocyanate as diisocyanate compounds, each used as a solution dissolved in an organic solvent such as ethyl acetate. There are many cases. These crosslinking agents may be used alone or in combination of two or more.

  The weight average molecular weight of the acrylic resin contained in the acrylic adhesive is usually about 600,000 to 2,000,000 in terms of standard polystyrene using gel permeation chromatography (GPC), and 800,000 to 1,800,000. Is preferred.

  The acrylic resin is dissolved in an organic solvent such as ethyl acetate, and a crosslinking agent is added to obtain an acrylic adhesive solution. Further, if necessary, one or more of silane coupling agents, weathering stabilizers, tackifiers, plasticizers, softeners, pigments, and inorganic fillers, and further light diffusing fine particles such as organic beads are included. be able to.

  The adhesive layer is formed by applying an adhesive composition containing an acrylic adhesive prepared as a coating solution to the surface of the cellulose acylate film or polarizing film, and optionally heating the organic solvent under heating. It is formed by leaving and solidifying. Once the adhesive layer is formed on the temporary support, it may be transferred onto a cellulose acylate film or a polarizing film.

  Although there is no restriction | limiting in particular about the thickness of an adhesive bond layer, it is preferable that it is 0.1-40 micrometers, and it is more preferable that it is 0.5-20 micrometers.

Polymer film:
The layer having a negative photoelastic coefficient used in the present invention may be a polymer film. Examples of the polymer film having a negative photoelastic coefficient include (1) a polymer film containing a cyclic olefin-based resin, and (2) at least selected from a lactone ring unit, a maleic anhydride unit, and a glutaric anhydride unit. A polymer film containing an acrylic resin containing one unit is included. However, it is not limited to these.

(1) Polymer Film Containing Cyclic Olefin Resin Used for the production of a polymer film containing cyclic olefin resin usable in the present invention as a main component (hereinafter sometimes referred to as “cyclic olefin polymer film”). Examples of the cyclic olefin resins include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrides of these polymers. . Preferred examples include an addition (co) polymer cyclic olefin resin containing at least one repeating unit represented by the following general formula (II), and, if necessary, a repeating unit represented by the general formula (I) An addition (co) polymer cyclic olefin resin further comprising at least one of the above is included. Another preferred example includes a ring-opening (co) polymer containing at least one cyclic repeating unit represented by the general formula (III).

In formula, m represents the integer of 0-4. R ^{1 to} R ⁶ are a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, X ^{1 to} X ³ and Y ^{1 to} Y ³ are a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, a halogen atom, and a halogen atom. substituted hydrocarbon group having 1 to 10 carbon _{atoms, - (CH 2) n COOR} 11, - (CH 2) n OCOR 12, - (CH 2) n NCO, - (CH 2) n NO 2, - ( _{CH 2) n CN, - (} CH 2) n CONR 13 R 14, - (CH 2) n NR 13 R 14, - (CH 2) n OZ, - (CH 2) n W or X ¹ and Y ^1, Alternatively, (—CO) ₂ O and (—CO) ₂ NR ¹⁵ composed of X ² and Y ² or X ³ and Y ³ are shown. R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , and R ¹⁵ are hydrogen atoms, hydrocarbon groups having 1 to 20 carbon atoms, Z is a hydrocarbon group or a hydrocarbon group substituted with halogen, and W is SiR ¹⁶ _p. D _3-p (R ¹⁶ is a hydrocarbon group having 1 to 10 carbon atoms, D is a halogen atom —OCOR ¹⁶ or —OR ¹⁶ , p is an integer of 0 to 3), and n is an integer of 0 to 10 .

  Norbornene-based addition (co) polymers are disclosed in JP-A No. 10-7732, JP-T-2002-504184, US2004229157A1 or WO2004 / 070463A1. It can be obtained by addition polymerization of norbornene-based polycyclic unsaturated compounds. If necessary, norbornene-based polycyclic unsaturated compounds and ethylene, propylene, butene; conjugated dienes such as butadiene and isoprene; nonconjugated dienes such as ethylidene norbornene; acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride It is also possible to carry out addition polymerization with linear diene compounds such as acid, acrylic acid ester, methacrylic acid ester, maleimide, vinyl acetate and vinyl chloride. This norbornene-based addition (co) polymer is marketed by Mitsui Chemicals, Inc. under the name of Apel, and has different glass transition temperatures (Tg) such as APL8008T (Tg70 ° C), APL6013T (Tg125 ° C) or APL6015T ( Grades such as Tg145 ° C). Pellets such as TOPAS 8007, 6013, and 6015 are sold by Polyplastics Co., Ltd. Further, Appear 3000 is sold by Ferrania.

Norbornene-based polymer hydrides are disclosed in JP-A-1-240517, JP-A-7-196736, JP-A-60-26024, JP-A-62-19807, JP-A-2003-159767, or JP-A-2004-309979. As disclosed in No. 1, etc., the polycyclic unsaturated compound can be produced by addition polymerization or metathesis ring-opening polymerization and then hydrogenation.
In the above formula, R ^{5 to} R ⁶ are preferably a hydrogen atom or —CH ₃ , X ³ and Y ³ are preferably a hydrogen atom, Cl, —COOCH ₃ , and other groups are appropriately selected. This norbornene-based resin is sold under the trade name Arton G or Arton F by JSR Corporation, and from Zeon Corporation, Zeonor ZF14, ZF16, Zeonex 250 or Zeonex. They are commercially available under the trade name 280 and can be used.

  The cyclic olefin polymer film may be a polymer film produced by either a solution casting method or a melt casting method. An example is a polymer film prepared by a solution casting method using a solution (dope) prepared by dissolving the cyclic olefin resin in an organic solvent. Fine particles may be dispersed in the dope. Examples of the fine particles include fine particles of an inorganic compound and fine particles of a polymer compound. Examples of inorganic compounds include fine powders of inorganic substances such as barium sulfate, manganese colloid, titanium dioxide, strontium barium sulfate, and silicon dioxide, but also, for example, synthetic silica obtained by a wet method or gelation of silicic acid. Examples thereof include titanium dioxide (rutile type and anatase type) produced by silicon dioxide, titanium slug and sulfuric acid. It can also be obtained by pulverizing from an inorganic substance having a relatively large particle size, for example, 20 μm or more, and then classifying (vibration filtration, wind classification, etc.). Inorganic fine particles containing silicon are preferred in that the turbidity is lowered and the haze of the film can be reduced. Most of the fine particles such as silicon dioxide are surface-treated with an organic substance, but such one is preferable because it can reduce the surface haze of the film. Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like. Examples of the polymer compound include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, starch, and the like, and pulverized and classified products thereof. Further, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray dry method or a dispersion method, or fine particles of an inorganic compound can also be used.

  The method for preparing the dope and the method for producing a polymer film by a solution casting method using the dope are described in detail in JP-A-2007-77243, and can be referred to.

(2) Polymer Film Containing Acrylic Resin Acrylic Resin Used for Production of Polymer Film Containing As Main Component Acrylic Resin that can be Used in the Present Invention (Hereinafter, It may be referred to as “Acrylic Polymer Film”) Examples include a polymer film containing an acrylic resin containing at least one unit selected from a lactone ring unit, a maleic anhydride unit, and a glutaric anhydride unit.

  The acrylic resin is not particularly limited as long as it is a resin obtained by polymerizing a monomer composition containing (meth) acrylic acid ester as a main component. Moreover, what has 2 or more types of acrylic polymers as a main component may be sufficient. Examples of the (meth) acrylic acid ester include a compound represented by the following general formula (10).

In the formula, R ⁴ and R ⁵ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. Examples of the compound having a structure represented by the above general formula include methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, 2- (hydroxy Methyl) normal butyl acrylate, 2- (hydroxymethyl) acrylate tertiary butyl and the like. Among these, methyl 2- (hydroxymethyl) acrylate and 2- (hydroxymethyl) ethyl acrylate are preferable, and methyl 2- (hydroxymethyl) acrylate is particularly preferable in terms of a high moist heat resistance improving effect. As for the compound represented by General formula (2), only 1 type may be used and 2 or more types may be used together.

  Other examples of (meth) acrylic acid esters include acrylic acid such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate. Esters; methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate; and the like. These may be used alone or in combination of two or more.

  Among these, a compound having a structure represented by the above general formula (10), methyl methacrylate, is more preferable because it has excellent resistance to moist heat and transparency. Further, when it is desired to increase the positive birefringence (positive phase difference), benzyl (meth) acrylate is preferred.

  The acrylic resin may have other units in addition to the units derived from the (meth) acrylic acid ester described above. Specific examples include a unit derived from a hydroxyl group-containing monomer, an unsaturated carboxylic acid, and a monomer represented by the following general formula (11).

In the formula, R ⁶ represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an —OAc group, a —CN group, a —CO—R ⁷ group, or —C—. Represents an O—R ⁸ group, an Ac group represents an acetyl group, and R ⁷ and R ⁸ represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms.

  The hydroxyl group-containing monomer is not particularly limited as long as it is a hydroxyl group-containing monomer other than the monomer represented by the general formula (10). For example, methallyl alcohol, allyl alcohol, 2-hydroxymethyl 2- (hydroxyalkyl) acrylic acid esters such as allyl alcohol such as 1-butene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, methyl 2- (hydroxyethyl) acrylate; 2- (hydroxyethyl) acrylic acid Such as 2- (hydroxyalkyl) acrylic acid; and the like. These may be used alone or in combination of two or more.

  Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, α-substituted methacrylic acid and the like. These may be used alone or in combination of two or more. May be. Among these, acrylic acid and methacrylic acid are preferable in that the effects of the present invention are sufficiently exhibited.

  Examples of the compound represented by the general formula (11) include styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate, and these may be used alone. Two or more kinds may be used in combination. Of these, styrene and α-methylstyrene are particularly preferable.

  The acrylic polymer film may be a polymer film produced by either a solution casting method or a melt casting method. An example is a polymer film produced by a melt casting method. Details of the acrylic polymer that can be used as a raw material for the acrylic polymer film and details of a method for producing an acrylic polymer film by a melt film forming method using the acrylic polymer film are described in JP-A-2008-9378. Can be referred to.

  Although there is no restriction | limiting in particular about the thickness of the polymer film utilized for a layer with a negative photoelastic coefficient, Generally, it is preferable that it is 20-55 micrometers, and it is more preferable that it is 30-45 micrometers.

  The polymer film used for the layer having a negative photoelastic coefficient may contain one or more additives as required together with the main component polymer. The example of the additive which can be used is the same as the example of the additive which can be added to the said cellulose acylate film.

  The polymer film used for the layer having a negative photoelastic coefficient may be optically isotropic or optically anisotropic. When an optically anisotropic polymer film is used, depending on the arrangement, optical compensation is affected. Therefore, in consideration of the optical properties of the cellulose acylate film used in combination, a preferable range of the optical properties of the polymer film is determined. Can be determined.

Polarizing film:
There is no restriction | limiting in particular about the polarizing film which the polarizing plate of this invention has. Any of iodine-based polarizing films, dye-based polarizing films using dichroic dyes, and polyene-based polarizing films can be used. The iodine-based polarizing film and the dye-based polarizing film are generally produced by adsorbing iodine or a dichroic dye to polyvinyl alcohol and stretching it.

Protective film:
In the polarizing plate of the present invention, the cellulose acylate film and a layer having a negative photoelastic coefficient are disposed on one surface of the polarizing film, and the cellulose acylate film is independent or has a photoelastic coefficient. Acts as a protective film for the polarizing film together with the negative polymer film. It is preferable that a protective film is also disposed on the other surface of the polarizing film. When the polarizing plate of the present invention is incorporated in a liquid crystal display device, it is preferable that the cellulose acylate film and a layer having a negative photoelastic coefficient are disposed between the polarizing film and the liquid crystal cell.

  There is no restriction | limiting in particular about the protective film arrange | positioned on the other surface of a polarizing film. Depending on the application, it can be selected from various polymer films. Depending on the application, it is required to use a polymer film excellent in optical performance transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. Examples of the main component polymer of the protective film include cellulose acylate, polycarbonate polymer, polyester polymer such as polyethylene terephthalate and polyethylene naphthalate, acrylic polymer such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene copolymer (AS Resin) and the like. Polyolefins such as polyethylene and polypropylene, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers, polyethersulfone polymers , Polyether ether ketone polymer, polyphenylene sulfide polymer, vinylidene chloride polymer, vinyl alcohol polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or a polymer mixed with the above polymers. included. Moreover, you may use the polymer film marketed.

Manufacturing method of polarizing plate:
There is no restriction | limiting in particular about the manufacturing method of the polarizing plate of this invention. You may manufacture continuously in elongate form. In the aspect in which the layer having a negative photoelastic coefficient is an adhesive layer, after the adhesive layer is formed on the surface of the cellulose acylate film or the polarizing film, the cellulose acylate film and the polarizing film are bonded to the adhesive layer. It can manufacture by joining via. A protective film may be bonded to the other surface of the polarizing film simultaneously with, or before or after the bonding of the cellulose acylate film and the polarizing film. In addition, in the aspect in which the layer having a negative photoelastic coefficient is made of a polymer film, after the cellulose acylate film is bonded to the polarizing film, the polymer film having a negative photoelastic coefficient is bonded to the surface of the cellulose acylate film. Alternatively, the cellulose acylate film and the polymer film having a negative photoelastic coefficient may be bonded and then bonded to the polarizing film. In the latter embodiment, the cellulose acylate film side may be bonded to the polarizing film, or the polymer film side having a negative photoelastic coefficient may be bonded to the polarizing film.

2. Liquid crystal display device TECHNICAL FIELD This invention relates also to the liquid crystal display device which has the polarizing plate of this invention. The polarizing plate of the present invention is preferably disposed on the light source side, which is easily affected by heat, since fluctuations in polarization characteristics due to wet heat are reduced. Further, the cellulose acylate film and the layer having a negative photoelastic coefficient of the polarizing plate are preferably disposed between the liquid crystal cell and the polarizing film. The mode of the liquid crystal display device of the present invention is not particularly limited, and includes TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroelectric Liquid Crystal), ), Super Twisted Nematic (STN), Vertically Aligned (VA), and Hybrid Aligned Nematic (HAN) liquid crystal display devices in any display mode can reduce luminance leakage due to wet heat.

3. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film for a wet heat resistant polarizing plate having at least a cellulose acylate film having a total stretching ratio of 10% or more in the TD direction and MD direction and a layer having a negative photoelastic coefficient. Also related to film. By using the protective film of the present invention, it is possible to reduce variation in polarization characteristics due to wet heat of the polarizing plate. Regarding the cellulose acylate film having a total of 10% or more of the stretching ratio in the TD direction and the MD direction and the layer having a negative photoelastic coefficient, which can be used in the protective film for a heat-and-moisture resistant polarizing plate of the present invention, These examples are the same as the examples used for the polarizing plate, and preferred examples are also the same.

The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
In addition, about the following characteristic, it measured by the following method, respectively.
(Re and Rth)
Re (λ) and Rth (λ) represent in-plane retardation at wavelength λ and retardation in the thickness direction, respectively. Re (λ) is measured with KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments Co., Ltd.) by making light of wavelength λ nm incident in the normal direction of the film. In selecting the measurement wavelength λnm, the wavelength selection filter can be exchanged manually, or the measurement value can be converted by a program or the like. When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method. This measuring method is also partially used for measuring the average tilt angle on the alignment film side of the discotic liquid crystal molecules in the optically anisotropic layer, which will be described later, and the average tilt angle on the opposite side.
Rth (λ) is the film surface when Re (λ) is used and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) (if there is no slow axis) Measurement is performed at a total of 6 points by injecting light of wavelength λ nm from each inclined direction in steps of 10 degrees from the normal direction to 50 ° on one side with respect to the film normal direction (with any rotation direction as the rotation axis). Then, KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value. In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative. The retardation value is measured from two inclined directions with the slow axis as the tilt axis (rotation axis) (if there is no slow axis, the arbitrary direction in the film plane is the rotation axis). Rth can also be calculated from the following formula (A) and formula (B) based on the value, the assumed value of the average refractive index, and the input film thickness value.

なお、上記のＲｅ（θ）は法線方向から角度θ傾斜した方向におけるレターデーション値をあらわす。また、式（Ａ）におけるｎｘは、面内における遅相軸方向の屈折率を表し、ｎｙは、面内においてｎｘに直交する方向の屈折率を表し、ｎｚは、ｎｘ及びｎｙに直交する方向の屈折率を表す。
Ｒｔｈ＝（（ｎｘ＋ｎｙ）／２−ｎｚ）×ｄ・・・・・・・・・・・式（Ｂ）

Note that Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. In the formula (A), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction orthogonal to nx in the plane, and nz is the direction orthogonal to nx and ny. Represents the refractive index.
Rth = ((nx + ny) / 2−nz) × d (Equation (B)

  When the film to be measured is a film that cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film without a so-called optical axis, Rth (λ) is calculated by the following method. Rth (λ) is from −50 ° to the normal direction of the film, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotary axis). Measured at 11 points by making light of wavelength λ nm incident in 10 ° steps up to + 50 °, and based on the measured retardation value, average refractive index assumption value and input film thickness value. KOBRA 21ADH or WR is calculated. In the above measurement, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. If the average refractive index is not known, it can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

(Degree of acetyl substitution)
The degree of acetyl substitution was measured according to ASTM D-817-91. The viscosity average degree of polymerization was measured by Uda et al.'S intrinsic viscosity method {Kazuo Uda, Hideo Saito, "Journal of Textile Society", Vol. 18, No. 1, 105-120 (1962)}.

1. Preparation of Cellulose Acylate Film 1-1 Production of Cellulose Acylate Film 1 An inner layer dope and an outer layer dope having the following compositions were prepared.
Composition of inner layer dope:
Cellulose acetate C-1
(Acetyl substitution degree 2.81, number average molecular weight 88000) 100 parts by weight Optical developer A 6.7 parts by weight Triphenyl phosphate 6.8 parts by weight Biphenyl diphenyl phosphate 4.9 parts by weight Brewing dye B having the following structure 000078 parts by mass Dichloromethane 439.1 parts by mass Methanol 65.6 parts by mass

Composition of outer layer dope:
Cellulose acetate C-1
(Acetyl substitution degree 2.81, number average molecular weight 88000) 100 parts by weight Optical developer A 6.7 parts by weight Triphenyl phosphate 6.8 parts by weight Biphenyl diphenyl phosphate 4.9 parts by weight Brewing dye B having the following structure 000078 parts by mass Silica particles having an average particle diameter of 16 nm (“aerosol R972” manufactured by Nippon Aerosil Co., Ltd.) 0.14 parts by mass Dichloromethane 424.5 parts by mass Methanol 63.4 parts by mass

  The outer layer and inner layer dope solutions having the above composition are uniformly and simultaneously laminated on a stainless steel band support with a width of 2000 mm so as to form a three-layer structure of an outer layer on the support surface side, an inner layer, and an outer layer on the air interface side using a band casting apparatus. Casted. With the stainless steel band support, the solvent was evaporated until the residual solvent amount was 40% by mass, and the stainless steel band support was peeled off. Stretching is applied to stretch so that the longitudinal (MD) stretch ratio is 1.02, then both ends are held by a tenter, and the stretch ratio in the width (TD) direction is 1.22 times. (I.e., the sum of the draw ratios in the TD direction and MD direction was 25%), and the film was stretched in the transverse direction (lateral stretching) at a rate of 45% / min. The residual solvent amount at the start of stretching was 30% by mass. It was made to dry for 35 minutes in a 115 degreeC drying zone, conveying after extending | stretching. After drying, it was slit to a width of 1340 mm, and a cellulose acylate film having a thickness of 82 μm and a thickness ratio of each layer of the support surface side outer layer: inner layer: air interface side outer layer = 3: 94: 3 was obtained. This was used as the cellulose acylate film 1.

1-2 Manufacture of Cellulose Acylate Film 2 The thickness is 91 μm in the same manner as the cellulose acylate film 1 except that the draw ratio is lowered and the total draw ratio in the TD direction and MD direction is changed to 10%. A film was prepared. This was used as the cellulose acylate film 2.

1-3 Production of Cellulose Acylate Film 3 for Comparative Example A main dope liquid D-3 having the following composition was prepared. Methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate was added to a pressurized dissolution tank containing a solvent while stirring. This was heated and stirred to completely dissolve, and a plasticizer and an ultraviolet absorber were further added and dissolved. This was designated as Azumi Filter Paper No. The main dope liquid D-3 was prepared by filtering using 244.
<Composition of dope D-3>
Methylene chloride 440 parts by mass Ethanol 40 parts by mass Cellulose acetate (acetyl group substitution degree 2.9) 100 parts by mass Triphenyl phosphate (plasticizer) 9.5 parts by mass Ethylphthalylethyl glycolate (plasticizer) 2.2 parts by mass Tinuvin 326 (ultraviolet absorber; manufactured by Specialty Chemicals) 0.4 parts by mass Tinuvin 109 (ultraviolet absorber; manufactured by Specialty Chemicals) 0.7 parts by mass of tinuvin 171 (ultraviolet absorber; Specialty Chemicals) Made) 0.6 parts by mass

The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to prepare a fine particle dispersion having the following composition.
<Composition of fine particle dispersion>
Fine particles (Aerosil R972V (made by Nippon Aerosil Co., Ltd.)) 11 parts by mass Ethanol 89 parts by mass

Next, cellulose acetate (acetyl group substitution degree: 2.9) was added to a dissolution tank containing methylene chloride, and the mixture was heated and completely dissolved, and this was then added to Azumi Filter Paper No. Filtered using 244. While finely stirring the solution after filtration, the fine particle dispersion prepared above was slowly added thereto. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.
Methylene chloride 99 parts by weight Cellulose triacetate (acetyl group substitution degree 2.9) 4 parts by weight Fine particle dispersion 11 parts by weight

  Add 100 parts by mass of the main dope solution D-3 and 2 parts by mass of the fine particle additive solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting apparatus. Used and cast uniformly on a stainless steel band support having a width of 2 m. On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off. The residual solvent at the time of peeling was 30%. After stretching, hold for several seconds while maintaining its width, release the width holding after relaxing the tension in the width direction, further carry for 30 minutes in the third drying zone set at 125 ° C., and perform drying, A film having a width of 1.5 m, a knurling having a width of 1 cm at the end and a height of 8 μm was prepared. This was used as the cellulose acylate film 3.

1-4 Cellulose acylate film 4 for comparative example
A commercially available triacetyl cellulose film (“TD80” manufactured by Fuji Film Co., Ltd.) was prepared. This was used as the cellulose acylate film 4.

2. Preparation of layer having negative photoelastic coefficient 2-1 Production of polymer film N1 having negative photoelastic coefficient Synthesis of cyclic olefin-based resin P-1:
180 parts by mass of purified toluene and 100 parts by mass of norbornene-5-methanol acetate were charged into the reaction kettle. Next, 0.04 parts by mass of palladium (II) acetylacetonate, 0.04 parts by mass of tricyclohexylphosphine, and 0.20 parts by mass of dimethylaluminum tetrakis (pentafluorophenyl) borate dissolved in 80 parts by mass of toluene were added. The reaction kettle was charged. The reaction was allowed to proceed for 18 hours at 90 ° C. with stirring. After completion of the reaction, the reaction mixture was put into excess ethanol to form a polymer precipitate. The polymer (P-1) obtained by purifying the precipitate was vacuum dried at 65 ° C. for 24 hours.
When the obtained polymer (P-1) was dissolved in tetrahydrofuran and the molecular weight was measured by gel permeation chromatography, the number average molecular weight in terms of polystyrene was 79,000 and the mass average molecular weight was 205,000. .

The following composition was put into a mixing tank, stirred to dissolve each component, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm to obtain a cyclic olefin resin solution.
(Cyclic olefin resin solution)
Cyclic olefin resin P-1 150 parts by mass Dichloromethane 380 parts by mass Methanol 70 parts by mass

Next, the following composition containing the cyclic olefin resin solution prepared by the above method was charged into a disperser to prepare a fine particle dispersion M-1.
(Fine particle dispersion)
2 parts by mass of silica particles having a primary average particle diameter of 16 nm (aerosil R972, manufactured by Nippon Aerosil Co., Ltd.)
Dichloromethane 73 parts by mass Methanol 10 parts by mass Cyclic olefin resin solution 10 parts by mass

100 parts by mass of the cyclic olefin-based resin solution and 1.43 parts by mass of the fine particle dispersion were mixed to prepare a dope for film formation. The above-mentioned dope was cast using a band casting machine at a production rate of 20 m / min. A film peeled off from the band with a residual solvent amount of about 25% by mass was stretched in the width direction at a stretch rate of 2% using a tenter, and hot air was applied while holding the film so as not to cause wrinkles. Dried.
Thereafter, the tenter conveyance was shifted to the roll conveyance, and the film was further dried and wound at 120 to 140 ° C. to obtain a cyclic olefin polymer film. This film was used as the polymer film N1.

2-2 Production of polymer film N2 having a negative photoelastic coefficient An acrylic resin (Asahi Kasei Chemicals Co., Ltd. 80N) was prepared, and this was applied to a Technobel T-die mounting extruder (KZW15TW-25MG-NH type / 150 mm T width die mounting / Using a lip thickness of 0.5 mm, the resin temperature in the cylinder of the extruder was adjusted to 247 ° C., the temperature of the T die was adjusted to 250 ° C., and extrusion molding was performed to obtain an unstretched film. This was used as a polymer film N2.

2-3 Formation of Adhesive Layer N3 with Negative Photoelastic Coefficient An ultraviolet curable acrylic adhesive UV-3400 (manufactured by Toa Gosei Co., Ltd.) is applied on the PEN film so as to have a predetermined thickness, and then each cellulose After laminating with an acylate film and irradiating ultraviolet light of 400 mJ / cm ² from the cellulose acylate film side to cure the adhesive, the PEN film was peeled off. The obtained film had no peeling failure part. The adhesive layer thus formed is referred to as an adhesive layer N3.

  The following table summarizes the properties of the films produced above. As for the photoelastic coefficient of the adhesive layer N3, an adhesive is formed to a thickness of about 40 μm on a sheet (silicon sheet, release film, etc.) having low adhesion to the adhesive, and peeled off from the sheet. And the photoelastic coefficient was calculated | required like other films. In addition, the thickness of the adhesive layer N3 described in the following table is the thickness of the adhesive layer N3 formed when manufacturing the polarizing plates of Examples and Comparative Examples described later.

About the cellulose acylate films 1-4, after performing the following alkali saponification processes, it used for preparation of a polarizing plate.
Alkali saponification treatment:
Each film was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55 ° C. for 2 minutes, then washed with water, and then immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25 ° C. for 30 seconds. did. Thereafter, the film was further neutralized by passing a washing bath under running water for 30 seconds. Then, draining with an air knife was repeated three times, and after dropping the water, it was retained in a drying zone at 70 ° C. for 15 seconds and dried. In this manner, each cellulose acylate film was saponified.

2. Production of Polarizing Plate 2-1 Production of Polarizing Plate 1N1 to 1N4 Production of Polarizer:
According to Example 1 of Unexamined-Japanese-Patent No. 2001-141926, the 20-micrometer-thick polarizer was produced by making iodine adsorb | suck to the stretched polyvinyl alcohol film.

Production of polarizing plate 1N1:
Using a polyvinyl alcohol-based adhesive, the cellulose acylate film 1 was attached to one side of the polarizer and the cellulose acylate film 4 was attached to the other side, and dried at 70 ° C. for 10 minutes or more to obtain a laminate 1. The polymer film N1 was joined to the surface of the cellulose acylate film 1 of the laminate 1 using a pressure sensitive adhesive (SK2057 manufactured by Soken Chemical Co., Ltd.). In this way, a polarizing plate 1N1 was produced.

Production of polarizing plate 1N2:
A polymer film N2 was further bonded to the surface of the cellulose acylate film 1 of the laminate 1 produced in the same manner as described above using an adhesive (SK2057 manufactured by Soken Chemical Co., Ltd.). In this way, a polarizing plate 1N2 was produced.

Production of polarizing plate 1N3:
Using the adhesive for the adhesive layer N3, the cellulose acylate film 1 is bonded to one side of the polarizer, and the cellulose acylate film 4 is pasted to the other side using a polyvinyl alcohol-based adhesive, and 10 minutes at 70 ° C. This was dried to prepare a polarizing plate. In this way, a polarizing plate 1N3 was produced. The thickness of the adhesive layer N3 was 10 μm.

Production of polarizing plate 1N4:
In the same manner as described above, using a polyvinyl alcohol-based adhesive, the cellulose acylate film 1 is attached to one side of the polarizer, the cellulose acylate film 4 is attached to the other side, and dried at 70 ° C. for 10 minutes or more. 1 was obtained. This laminate 1 was used as a polarizing plate 1N4.

2-2 Production of Polarizing Plates 2N1 to 2N4 Except that the cellulose acylate film 1 was replaced with the cellulose acylate film 2, the polarizing plates 2N1 to 2N4 were produced in the same manner as the polarizing plates 1N1 to 1N4, respectively.

2-3 Production of Polarizing Plates 3N1 to 3N4 Polarizing plates 3N1 to 3N4 were produced in the same manner as the polarizing plates 1N1 to 1N4, respectively, except that the cellulose acylate film 1 was replaced with the cellulose acylate film 3.

2-4 Production of Polarizing Plate 0 Using a polyvinyl alcohol-based adhesive, the cellulose acylate film 4 was attached to both sides of the polarizer and dried at 70 ° C. for 10 minutes or more to produce a polarizing plate. This was used as polarizing plate 0.

3. Production and evaluation of liquid crystal display device 3-1 Production and evaluation of VA mode liquid crystal display device (single sheet type) Production of VA mode liquid crystal cell:
A cell gap between the substrates is set to 3.6 μm, and a liquid crystal material having negative dielectric anisotropy (“MLC6608”, manufactured by Merck & Co., Inc.) is dropped and sealed between the substrates to form a liquid crystal layer between the substrates. Made. The retardation of the liquid crystal layer (that is, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn) was set to 300 nm. The liquid crystal material was aligned so as to be vertically aligned. In this way, a VA mode liquid crystal cell was produced.

Bonding of liquid crystal cell and polarizing plate:
In the liquid crystal display device using the VA mode liquid crystal cell, the polarizing plate 0 is used as the upper polarizing plate (display surface side) polarizing plate, and the polarizing plates 1N1 to 1N4, 2N1 to 2N4 are used as the lower polarizing plate (backlight side), Any of 3N1 to 3N4 was joined. In addition, when bonding the polarizing plates 1N1 to 1N4, 2N1 to 2N4, or 3N1 to 3N4, the cellulose acylate film 1, the cellulose acylate film 2, or the cellulose acylate film 3 was bonded to the liquid crystal cell side. The upper polarizing plate and the lower polarizing plate were attached to the liquid crystal cell via an adhesive (SK2057 manufactured by Soken Chemical Co., Ltd.). The crossed nicols were arranged so that the transmission axis of the upper polarizing plate was in the vertical direction and the transmission axis of the lower polarizing plate was in the horizontal direction. In this way, VA mode liquid crystal display devices 1N1 to 1N4, 2N1 to 2N4, and 3N1 to 3N4 were produced, respectively.

Rating:
A rectangular wave voltage of 55 Hz was applied to the liquid crystal cell of each manufactured liquid crystal display device. A normally black mode with 5 V white display and 0 V black display was set.
Each liquid crystal display device was allowed to stand for 24 hours in an environment of a temperature of 50 ° C. and a humidity of 95%, and then continuously lit for 24 hours. Thereafter, light leakage generated in an elliptical shape at the center of the screen during black display was observed from the front direction (normal direction with respect to the display surface) and evaluated according to the following criteria. The results are shown in the following table.
9: The degree of light leakage is very weak and can withstand actual use. Display quality is good.
8: The degree of light leakage is weak and can withstand actual use.
7: The degree of light leakage is weak and can withstand actual use. The degree of light leakage is worse than 8.
6: The degree of light leakage is weak and can withstand actual use. The degree of light leakage is worse than 7.
5: The degree of light leakage is weak and can withstand actual use. The degree of light leakage is worse than 6.
4: The degree of light leakage is weak and it can withstand actual use. The degree of light leakage is an allowable lower limit.
3: Light leakage is strong and cannot withstand actual use.
2: Light leakage is strong and cannot withstand actual use. The degree of light leakage is worse than 3.
1: Light leakage is strong and cannot withstand actual use. The degree of light leakage is worse than 2.

From the results shown in the above table, a VA mode liquid crystal display device 1N1 using polarizing plates 1N1 to 1N3 or 2N1 to 2N3 having a cellulose acylate film 1 or 2 having a total stretching ratio in the TD and MD directions of 10% or more. Since ˜1N3 and 2N1 to 2N3 are added with film N1, film N2 or adhesive layer N3 having a negative photoelastic coefficient, polarizing plate 1N4 without a layer having a negative photoelastic coefficient is used. It can be understood that light leakage is significantly reduced as compared with the VA mode liquid crystal display device 1N4.
On the other hand, the VA mode liquid crystal display devices 3N1 to 3N3 using the polarizing plates 3N1 to 3N3 having the cellulose acylate film 3 having a total of stretching ratios in the TD and MD directions of less than 10% are films having a negative photoelastic coefficient. Even when N1, the film N2 or the adhesive layer N3 was added, the light leakage was slightly reduced and was not satisfactory in practical use.

DESCRIPTION OF SYMBOLS 10, 10 'Polarizing plate 12 Polarizing film 14 Photoelastic coefficient negative layer 16 Cellulose acylate film 18 whose total of draw ratio of TD and MD direction is 10% or more Protective film

Claims (8)

A polarizing plate comprising at least a polarizing film, a cellulose acylate film having a total stretching ratio of 10% or more in the TD direction and MD direction on one surface thereof, and a layer having a negative photoelastic coefficient , wherein the light The polarizing plate whose layer whose elasticity modulus is negative is a polymer film containing cyclic olefin system resin . The polarizing plate according to claim 1, wherein the cellulose acylate film has a thickness exceeding 77 μm. The polarizing plate according to claim 1, wherein the cellulose acylate film has an average elastic modulus in a horizontal direction and a vertical direction of 3800 MPa or more. At least a liquid crystal display device and the polarizing plate; and a liquid crystal cell to any one of claims 1-3. The liquid crystal display device according to claim 4 , wherein the polarizing plate is disposed on a light source side of the liquid crystal cell. The liquid crystal display device according to claim 4 or 5 , wherein the cellulose acylate film and the layer having a negative photoelastic coefficient of the polarizing plate are disposed between the liquid crystal cell and a polarizing film. A protective film for a moisture and heat resistant polarizing plate having at least a cellulose acylate film having a total stretching ratio in the TD direction and MD direction of 10% or more and a layer having a negative photoelastic coefficient, wherein the photoelastic coefficient is negative. The protective film for a heat-and-moisture resistant polarizing plate, wherein the layer is a polymer film containing a cyclic olefin-based resin . The protective film for a heat-and-moisture resistant polarizing plate according to claim 11, wherein the cellulose acylate film has a thickness exceeding 77 μm.

Images