JP2003131034A - Polarizing plate and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate having excellent durability without rapidly increasing ray transmittance even under a high temperature. SOLUTION: The manufacturing method for obtaining a polarizer by sticking a polarizer protection film having moisture permeability of 5 g/(m<2> .24 hr) or greater and 500 g/(m<2> .24 hr) in 25 deg.C×90%RH onto at least an one-sided face of the polarizer film through an adhesive solution, and drying the adhesive solution, is characterized in that it is dried at 50 deg.C or lower until heating weight reduction for 120 deg.C×60 min. per area of an adhesion sticking face is 1.3 g/m<2> or less, and the polarizing plate obtained therefrom is provided. And, the polarizing plate adhering and sticking the polarizer protection film having moisture permeability of 5 g/m<2> .24 hr) or greater and 500 g/(m<2> .24 hr) or less in 25 deg.C×90%RH on at least an one-sided face of the polarizer film, is characterized in that heating weight reduction for 120 deg.C×60 min. per area of an adhesion and sticking is 0 g/m<2> or greater and 1.3 g/m<2> or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polarizing plate and a method for manufacturing the same.

[0002]

2. Description of the Related Art A linearly polarizing plate is a material having a function of transmitting only linearly polarized light having a specific vibration direction out of transmitted light and blocking other linearly polarized light, and constitutes a liquid crystal display device, for example. Widely used as one of the parts. As such a linear polarizing plate, one having a structure in which a polarizer film and a polarizer protective film are laminated is generally used.

The above-mentioned polarizer film is a film having a function of transmitting only linearly polarized light having a specific vibration direction. For example, a polyvinyl alcohol (hereinafter referred to as PVA) film is stretched to obtain iodine or a dichroic dye. Films dyed with are commonly used.

The above-mentioned polarizer protective film has a function of holding the polarizer film and imparting practical strength to the entire polarizing plate. For example, a triacetyl cellulose (hereinafter referred to as TAC) film is used. It is commonly used. The polarizer protective film may also be referred to as a support or a support film.

The polarizer film and the polarizer protective film are bonded together via an adhesive layer, and the polarizer protective film is used in a form laminated on one side or both sides of the polarizer film. A water-soluble PVA-based adhesive or the like is generally used as the adhesive forming the adhesive layer. As an industrial laminating method, a polarizer film and a polarizer protective film are roll-conveyed, and an adhesive is applied between both films in the laminating step to bond them by pressure adhesion, and then through a predetermined drying step. A method of obtaining an integrated polarizing plate is generally used.

Since the polarizing film tends to have a reduced polarization performance due to moisture absorption, a film material having a smaller water vapor transmission rate (moisture permeability) than that of a conventional TAC film is used as a polarizer protective film, so that Attempts have been made to suppress moisture absorption from the outside to reduce performance deterioration of the polarizer film.

[0007] For example, in Japanese Patent Laid-Open No. 7-77608, the moisture permeability at 80 ° C. and 90% RH is 200 g / (m).
²・ 24hr ・ 100μ) or less and the photoelastic coefficient is 1
Disclosed is an invention for improving the wet heat resistance of a polarizing plate by using a polarizer protective film having a density of x10 ^-11 cm ² / dyne or less.

[0008]

However, when a polarizer film and a polarizer protective film having a low moisture permeability are adhered and dried by a conventional method, the degree of polarization is drastically lowered during the drying of the polarizing plate and the light transmission. There was a problem that the rate would rise.

[0009]

The inventors of the present invention have made diligent studies to solve the above problems, and as a result, the water or residual solvent mainly derived from the adhesive trapped in the polarizing plate causes the above problems. That is, after the polarizer film and the polarizer protective film having a small water vapor transmission rate are adhered, the above problem can be solved by gently drying until the water content (solvent content) of the polarizing plate becomes a specific value or less. Heading out, the present invention has been completed.

Further, the present inventors have to proceed to dry a polarizing plate obtained by laminating a polarizer film and a polarizer protective film having low moisture permeability to a specific water content (solvent content). It was found that the light transmittance during heating, which is considered to be caused by the loss of iodine or dichroic dye in the polarizer film, easily occurs.

In the present specification, the above-mentioned water content (solvent content) is evaluated as a reduction in weight by heating when a polarizing plate is heated at 120 ° C. for 60 minutes, and the following method for producing a polarizing plate and the polarizing plate are disclosed. To do.

Namely, the present invention is, at least on one surface of a polarizer film, moisture permeability 5 g / at 25 ℃ · 90% RH (m 2 · 24hr) or 500g / (m ² · 24h
r) In the production method of laminating the following polarizer protective film via an adhesive solution and drying the adhesive solution to obtain a polarizing plate, heating at 120 ° C. × 60 minutes per area of the adhesive laminating surface 50 until weight loss is 1.3g / m ² or less
It relates to a method for producing a polarizing plate, which comprises drying at a temperature of ℃ or less.

In one embodiment of the method for producing a polarizing plate of the present invention, the adhesive solution is an aqueous adhesive solution, and
In one embodiment of the other aspect, the adhesive solution contains a polyvinyl alcohol-based adhesive.

Further, the present invention is a polarizing plate obtained by the above-mentioned manufacturing method, wherein the amount of change in light transmittance before and after heating at 70 ° C. for 5 minutes is −1.0% or more and + 1.0% or less. A polarizing plate characterized by the above.

Furthermore, according to the present invention, the moisture permeability at 25 ° C. and 90% RH is 5 g / (m ² · 24 hr) or more and 500 g / (m ² · 2) on at least one surface of the polarizer film.
It is a polarizing plate in which a polarizer protective film of 4 hr) or less is adhered and adhered, and 120 ° C. × 60 per area of the adhered and adhered surface.
There is provided a polarizing plate characterized in that the weight loss by heating per minute is 0 g / m ² or more and 1.3 g / m ² or less.

The amount of change in light transmittance of the polarizing plate before and after heating at 70 ° C. for 5 minutes is preferably −1.0% or more +
It is 1.0% or less.

Here, the adhesive used for adhering the polarizer film and the polarizer protective film together is preferably a water-based adhesive.

Further, as the water-based adhesive, a polyvinyl alcohol-based adhesive is preferable.

The polarizer protective film used in the present invention is preferably a polarizer protective film obtained by a melt molding method.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The polarizing plate of the present invention is obtained by laminating a specific polarizer protective film on at least one surface of a polarizer film via an adhesive layer.

The polarizer film used in the present invention is a uniaxially oriented PVA-based film in which iodine or a dichroic dye is adsorbed and oriented, and a boron compound-treated film can also be used. PVA is usually
It is produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (including salt, ester, amide, nitrile, etc.), olefin It may contain a component copolymerizable with vinyl acetate, such as compounds, vinyl ethers and unsaturated sulfonates.

The degree of saponification in PVA is 85 to 100.
Practically, it is mol%, preferably 98 to 100 mol%. The average degree of polymerization of PVA is 1100 or more, preferably 1500 or more, and more preferably 260.
High degree of polymerization PVA of 0-5000 is advantageous. When the average degree of polymerization is less than 1100, initial polarization performance (degree of polarization, transmittance)
May decrease, and the polarization performance may deteriorate under high temperature and high humidity conditions. If the degree of polymerization is too high, the processability of the obtained film is deteriorated, which is not preferable.

As a method for producing a PVA-based polarizer film, a stock solution of PVA dissolved in water or an organic solvent is cast to form a film, which is then stretched and dyed with iodine or an azo-based, anthraquinone-based or tetrazine-based dichroic dye. Examples thereof include a method of dyeing with a dye, simultaneous stretching and dyeing, or a method of treating with a boron compound after dyeing and stretching.

The solvent used for preparing the stock solution is
Water, dimethyl sulfoxide, N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol,
Polyhydric alcohols such as tetraethylene glycol and trimethylolpropane, amines such as ethylenediamine and diethylenetriamine, and mixtures thereof are used.

A small amount, for example, 5 to 30 is contained in the above organic solvent.
It is permissible to include water in a weight percentage. PV in undiluted solution
It is practical that the concentration of A is about 5 to 20% by weight. The PVA film forming stock solution obtained using the solvent is formed into a film by any method such as a casting method or an extrusion method. The film forming method is a dry / wet film forming method, that is, the solution is once discharged from the mouth slit into the air or an atmosphere of an inert gas such as nitrogen, helium, or argon, and then introduced into a coagulation bath. Form an unstretched film. Alternatively, the film-forming solution discharged from the die may be introduced into the coagulation bath after the solvent is partially dried on a roller, a belt conveyor or the like.

The solvent used for the coagulation bath is PVA.
Those which are miscible with the solvent of, for example, alcohols such as methanol, ethanol, propanol and butanol,
Acetone, benzene, toluene etc. are mentioned.

As a method of obtaining a PVA-based film, a so-called gel stretching method other than the above can be adopted. That is, PVA is dissolved in a solvent so that the polymer concentration is 30% by weight or less to prepare a PVA film-forming stock solution. The solution is discharged into air or an inert gas atmosphere through a slit-shaped die and then introduced onto a roller or belt conveyor whose surface is cooled or into a coagulating liquid to form a gelled film. The gelled film is desolvated and then stretched. The film forming method is almost the same as the dry / wet film forming method, but there is a difference in forming a gelled film so that the polymer concentration does not change from the stock solution.

Examples of the solvent for the PVA film-forming stock solution in this case include glycerin, ethylene glycol, tetraethylene glycol, polyhydric alcohols such as trimethylolpropane, benzenesulfonamide, and caprolactam.

The PVA-based unstretched film obtained as described above is then stretched and dyed. Stretching and dyeing may be performed separately or simultaneously. When they are performed separately, the order of stretching and dyeing is arbitrary. It is desirable that the stretching is 3.5 times or more, preferably 4.5 times or more in the uniaxial direction. At this time, some stretching (stretching to a degree that prevents shrinkage in the width direction or more) may be performed in the direction perpendicular to the above. The temperature condition during stretching is 5
It is suitable to select from the range of 0 to 150 ° C.

The dyeing of the film, that is, the adsorption of the polarizing element is performed by bringing the liquid containing the polarizing element into contact with the film. Usually, an aqueous solution of iodine-potassium iodide or an aqueous solution of an azo-based, anthraquinone-based, tetrazine-based dichroic dye or the like is used. The iodine concentration was 0.01 to 1.0% by weight, and the potassium iodide concentration was 0.1.
5 to 10% by weight, the weight ratio of iodine to potassium iodide is suitably 20 to 100 with respect to iodine 1, and the concentration of the dichroic dye is suitably 0.01 to 0.3% by weight. Practical dyeing time is about 30 to 500 seconds. A small amount of an organic solvent compatible with water may be contained in addition to the water solvent.

As the contact means, any means such as dipping, coating and spraying can be applied. The stretched and dyed film is then treated with a boron compound. Boric acid and borax are practical as the boron compound. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.5 to 2.0 mol / l.

The treatment method is preferably dipping, but of course the coating method and spraying method are also practical. The processing temperature is 50 to 7
The temperature is preferably 0 ° C. and the treatment time is preferably about 5 to 20 minutes, and if necessary, a stretching operation may be performed during the treatment or after the treatment.

The thickness of the polarizer protective film used in the present invention is usually 20 to 300 μm, preferably 30.
To 200 μm, and more preferably 40 to 100 μm. If the polarizer protective film is too thin, the film strength will decrease, undesired birefringence will occur due to shrinkage of the polarizer film, and it will not be able to be mechanically supported, and the curl will increase in the durability test of the polarizing plate. There is a point. On the other hand, if the polarizer protective film is too thick, the polarizing plate obtained will also be thicker, and the transparency will be reduced, the retardation expressed by the product of the birefringence and the thickness will be increased, and the moisture permeability will be small, so that the adhesion described There are problems that the drying of the agent solution is delayed and it takes time to develop the adhesive strength. If the phase difference increases, a problem occurs that the contrast decreases when the liquid crystal display is used.

25 ° C./90% of the above polarizer protective film
The water vapor permeability in RH is preferably 500 g / (m ² · 24 hr) or less. More preferably 300 g /
(M ² · 24 hr) or less, more preferably 200 g /
(M ² · 24 hr) or less. Water vapor transmission rate is 500g /
If it exceeds (m ² · 24 hr), under the conditions of high temperature and high humidity, external moisture passing through the polarizer protective film may permeate into the polarizer film to deteriorate the performance of the polarizing plate. On the other hand, for the adhesion of the polarizer film and the polarizer protective film, an aqueous adhesive is often used, and if the water vapor transmission rate is too low, the drying of the aqueous adhesive becomes slow, and it takes time to develop the adhesive strength. Such a problem occurs. Therefore, the water vapor transmission rate at 25 ° C / 90% RH is 5g /
(M ² · 24 hr) or more is preferable, and more preferably 1
0 g / (m ² · 24 hr) or more, more preferably 30
g / (m ² · 24 hr) or more. Further, the water vapor transmission rate at high temperature is also important, and the water vapor transmission rate at 80 ° C. and 90% RH is preferably 1000 g / (m ² · 24 hr) or less. More preferably 800 g / (m ² · 24 hr)
Or less, more preferably 600 g / (m ² · 24 hr)
It is the following. Moisture vapor transmission rate is 1000g / (m ² · 24hr)
If it exceeds, the external moisture that has passed through the polarizer protective film may permeate into the polarizer film under the conditions of high temperature and high humidity to deteriorate the performance of the polarizing plate. On the other hand, for the adhesion of the polarizer film and the polarizer protective film, an aqueous adhesive is often used, and if the water vapor transmission rate is too low, the drying of the aqueous adhesive becomes slow, and it takes time to develop the adhesive strength. Such a problem occurs. Therefore, when industrially dried, in order to obtain a polarizing plate with high productivity, 80 ° C.
The water vapor transmission rate at 0% RH is 10 g / (m ² · 24h
r) or more, more preferably 50 g / (m ² ·
24 hr) or more, more preferably 100 g / (m ² ·
24 hours or more.

From the viewpoint that the polarizing performance of the polarizing plate of the present invention can be sufficiently ensured, the retardation value of the polarizer protective film is preferably 20 nm or less, more preferably 1 nm.
It is 0 nm or less, more preferably 5 nm or less. The retardation in the film thickness direction of the polarizer protective film is also important for improving the viewing angle characteristics of the obtained polarizing plate. The retardation in the thickness direction is preferably 50 nm or less, more preferably 30 nm or less, and further preferably 10 nm or less. Regarding the retardation in the film thickness direction, the maximum in-plane refractive index is nx, the refractive index in the direction orthogonal to nx is ny, and the refractive index in the film thickness direction is n.
where z and film thickness are d, | (nx + ny)
It is represented by / 2-nz | xd.

From the viewpoint that the amount of transmitted light of the polarizing plate of the present invention can be sufficiently secured, the light transmittance of the polarizer protective film is preferably 85% or more, and the haze is 2%.
The following is preferable.

Ideally, the light transmittance is 100%,
In reality, 95% or a little lower than 95% does not cause a big problem as a polarizer protective film. However, if it is less than 85%, the displayed image becomes dark when used as a polarizing plate, which is not practical. Therefore, the light transmittance is preferably 85% or more, more preferably 87% or more, and particularly preferably 89% or more.

The haze is ideally 0%, but in reality, even if 0.1% or a little over 0.1%, it does not pose a big problem as a polarizer protective film. However, if it exceeds 2%, the display image when used as a polarizing plate becomes unclear, which is not preferable. Therefore, the haze is preferably 2% or less, more preferably 1.5% or less, and particularly preferably 1% or less.

The selection of the film satisfying the above-mentioned characteristics such as moisture permeability, retardation value and light transmittance is not determined only by the film composition, but the thickness of the film and the conditions for producing the film also affect the resin composition. As the polycarbonate resin, polyarylate resin, polysulfone resin,
Polyethersulfone resin, cycloolefin resin, polystyrene resin, polyacrylate resin, polymethacrylate resin, polyester resin, resin composition composed of polyphenylene ether resin and polystyrene resin, or aliphatic imide resin and acrylonitrile -The resin composition which consists of styrene-type resin can be illustrated, These can be used individually or in mixture.

When these resins are used as a polarizer protective film, shrinkage stress of the polarizer film may cause an unfavorable retardation in the polarizer protective film.
By using a thermoplastic resin having a small absolute value of the photoelastic coefficient, it is possible to suppress the occurrence of a phase difference. The preferred absolute value of the photoelastic coefficient is generally 50 × 10 ^-13 cm ²
/ Dyne or less, more preferably 20 × 10 ^-13
cm ² / dyne, more preferably 10 × 10 ^-13 cm
^{It is 2} / dyne or less.

Examples of such preferable resins include cycloolefin resins, polystyrene resins, polyacrylate resins, polymethacrylate resins, polyester resins, resin compositions comprising polyphenylene ether resins and polystyrene resins, or aliphatic resins. A resin composition composed of an imide-based resin and an acrylonitrile-styrene-based resin can be mentioned. In addition to the water vapor transmission rate, it is easy to obtain a film excellent in the above-mentioned retardation value, light transmittance, and haze characteristics, and therefore, JP-A-8-231780 and JP-A-5-22 are used.
Olefin as described in JP 02253-
A resin composition composed of an aliphatic imide resin such as a maleimide resin or a glutarimide resin and an acrylonitrile-styrene resin is particularly preferable. Other particularly preferable resins are cycloolefin resins described in JP-A-4-301415 and JP-A-7-287123, which contain polar groups such as methoxycarbonyl group, nitrile group and carboxymethyl group. The cycloolefin-based resin having is preferable. In particular, a cycloolefin resin composed of a monomer such as 5-methoxycarbonyl-2-norbornene, 5-methyl-5-methoxycarbonyl-2-norbornene, 5-cyano-2-norbornene is preferable. Examples of these resins include, for example, Mitsui Petrochemical Co., Ltd., trade name “APEL”, Nippon Zeon Co., Ltd., trade name “Z
"EONOR", manufactured by JSR, product name "ART
"ON" and the like are marketed as commercial products.

The heat resistance of a preferred resin can be evaluated by the glass transition temperature of the resin, and is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 1.
It is 50 ° C or higher. When the glass transition temperature is less than 100 ° C, there is a risk of thermal deformation when used as a polarizing plate.
Further, the upper limit of the preferable heat resistance is not particularly limited as long as the processability required for forming a film can be maintained, but it is generally preferably 350 ° C or lower, and more preferably 300 ° C.
Hereafter, it is more preferably 250 ° C. or lower.

The polarizer protective film used in the present invention contains known additives such as a plasticizer, a heat stabilizer, an ultraviolet absorber and a filler, and other compounds, if necessary, within a range that does not impair the above properties. be able to.

The polarizer protective film used in the present invention can be obtained by forming a film by a melt molding method using the resin composition containing the resin and additives and other compounds used as necessary. it can. In the prior art, the solution casting method may be used because it is relatively easy to obtain a film with a small film thickness unevenness, but since a solvent is required, productivity and work environment deteriorate, High cost, large water vapor transmission rate due to the solvent remaining in the film, and also may impair the dimensional stability of the obtained polarizing plate because the heating dimensional change rate of the film may increase, Not preferable. In contrast, film formation by the melt molding method does not require the use of a solvent, so productivity and work environment are good,
The production cost is low, and the obtained film is 80 ℃ ×
The heating dimensional change rate in 5 hours is -0.05% to +0.
Since it shows a small heating dimensional change rate of 05%, preferably -0.01% to + 0.01%, a polarizing plate excellent in dimensional stability can be obtained, which is preferable. In the case of forming a film by the melt molding method, the molding temperature is usually 200 ° C. or higher.
Pre-drying the resin or pellets to be used prior to forming a film is useful for preventing defects such as foaming of the film. As the melt molding method, a known method such as a melt extrusion method such as a T-die method or an inflation method, a calender method, a heat pressing method, an injection molding method can be adopted, and among them, from the viewpoint of industrial productivity, The melt extrusion method is preferred. In particular, the melt extrusion method using a T die is preferable in that a wide film having good thickness accuracy can be easily obtained. Film formation by the melt extrusion method can be carried out by, for example, introducing the resin composition into an extruder to melt it, extruding it into a film form through a T-die or the like, and then cooling and solidifying to form a film. At this time, the resin composition extruded in a film shape is cast on a support such as a roll or a belt having a smooth surface to be solidified, and the resin composition extruded in a film shape is supported by a support having a smooth surface. A method of sandwiching and solidifying can also be used.

The film used as the above-mentioned polarizer protective film is uniaxially, biaxially or polyaxially stretched by a known stretching method, for example, according to the purpose of increasing the strength and the like. It may be preferable to perform the alignment treatment. When the stretching treatment is performed to increase the strength while keeping the anisotropy of the strength in the film plane as small as possible, it may be preferable to perform biaxial or multiaxial stretching.

The film used as the polarizer protective film may be subjected to an easy-adhesion treatment in order to increase the adhesive strength with the polarizer film. Examples thereof include alkali saponification treatment, corona discharge treatment, UV ozone treatment, plasma treatment, flame treatment, and coating of an easily adhesive layer. As the easily-adhesive layer that is preferably applied, a copolymer having a carboxyl group-containing monomer such as acrylic acid, methacrylic acid, or maleic anhydride described in JP-A-6-94915 as a repeating unit, Hydrophilic cellulose derivative and hydrophilic PVA described in JP-A-6-118232
Hydrophilic polymer compounds such as derivatives, JP-A-9-19712
8, maleic anhydride-containing copolymers described in JP-A No. 8-281333 and JP-A No. 2001-21
Examples thereof include the cellulose derivative described in Japanese Patent No. 5331 and the polyurethane resin described in Japanese Patent Application Laid-Open No. 2001-174637. The easily-adhesive layer may contain known additives such as a plasticizer, a heat stabilizer, an ultraviolet absorber and a filler, and other compounds, if necessary, within a range that does not impair the above properties. When applying an easy-adhesion layer, the film may be subjected to a surface treatment such as corona discharge treatment, UV ozone treatment, plasma treatment, or flame treatment before coating, if necessary. Surface treatment such as alkali saponification treatment, corona discharge treatment, UV ozone treatment, plasma treatment, and flame treatment may be performed.

When a water-based adhesive is used, a hydrophilic polymer compound, a urethane resin, a resin having a hydrolyzable functional group, or the like can be preferably used as the easily adhesive layer. Among them, a resin having a hydrolyzable functional group is preferable because the adhesiveness to the polarizer protective film is easily obtained. Furthermore, when a resin having a hydrolyzable functional group is used as the easy-adhesion layer, it is extremely strong even if the conventional PVA-based adhesive is used as it is by subjecting it to an alkali saponification treatment similar to known TAC. Adhesiveness with the polarizer can be obtained. Examples of the resin having a hydrolyzable functional group that forms the easy-adhesion layer include cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose ester resins such as cellulose acetate phthalate, methyl cellulose,
Cellulose ether resins such as ethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, nitrocellulose resins, or derivatives of these cellulose resins, polyvinyl ester resins such as polyvinyl acetate and vinyl propionate, And saponified product thereof, olefin-vinyl ester resin and saponified product of olefin such as ethylene and propylene and vinyl ester such as vinyl acetate and vinyl propionate, isobutene-maleic anhydride resin and hydrolyzate thereof, alkali metal salt, Polyacrylate and polymethacrylate resins and copolymers thereof with methyl methacrylate, methyl acrylate, etc. can be preferably used In particular, a cellulosic resin is a preferable resin because it has relatively high heat resistance and the saponification layer on the surface of the easily adhesive layer has excellent water resistance.

The thickness of the easily adhesive layer is preferably 0.01 to 10 μm, more preferably 0.1 to 1 μm. If the thickness of the easy-adhesion layer is less than 0.01 μm, the effect of improving the adhesiveness may decrease. If the thickness of the easy-adhesion layer exceeds 10 μm, not only the obtained polarizing plate becomes unnecessarily thick, but it may cause deterioration in durability such as moisture resistance.

The method of applying the easy-adhesion layer is not particularly limited. A method in which the resin is dispersed and dissolved in an appropriate solvent and then coated, a method in which a film made of the resin is laminated on the polarizer protective film by heat or the like, and when the polarizer protective film is formed into a film, A known laminating method such as a method of laminating by extrusion can be used.

When the resin is dissolved or dispersed in a solvent for coating, a known coating method can be used. Illustrating a preferred coating method,
Bar coater, doctor knife, meir bar, roll,
Examples include T-die and comma coater. A known solvent can be used for coating. Generally, aromatic compounds such as toluene, xylene and anisole, cyclic ether compounds such as dioxane, dioxolane, tetrahydrofuran and pyran, ethylene glycol dimethyl ether,
Glycol ether solvents such as diethylene glycol dimethyl ether, ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone, carbonate ester solvents such as dimethyl carbonate, and alcohol solvents such as methanol and isopropanol can be used. Further, a halogenated hydrocarbon solvent such as dichloromethane or trichloroethane, or a non-halogen solvent having a high polarity such as dimethylformamide or dimethylacetamide can also be used. These solvents may be mixed with each other, and the evaporation rate may be controlled by combining a solvent having a low boiling point and a solvent having a high boiling point, in order to obtain the easily adhesive layer having excellent surface properties. Is the preferred method. The solid content concentration of the solution can be appropriately adjusted depending on the appearance of the coating film and the required thickness of the resin layer, but it is generally 0.1 to 50% by weight, and preferably 1 to 10% by weight. . After coating the polarizer protective film with the solution, the easy-adhesion layer is dried in a drying oven, and if necessary, further heated or irradiated with ultraviolet rays or an electron beam to cure the easy-adhesion layer. The residual solvent amount of the easy-adhesion layer is preferably 5% by weight or less, more preferably 1% or less, still more preferably 0.5% or less.

As the adhesive forming the adhesive layer of the polarizing plate of the present invention, known adhesives can be used. Examples thereof include PVA-based adhesives such as PVA and polyvinyl butyral, and acrylic-based, polyurethane-based, and epoxy-based adhesives. The above-mentioned adhesives are known as other polymers, plasticizers, heat stabilizers, UV absorbers, cross-linking agents, fillers, etc. within a range that does not impair the effects of the present invention in order to improve durability and adhesiveness. Additives may be included. The preferred adhesive is PVA, which has a saponification degree of 90 mol% to 100 mol% and a polymerization degree of 1500 to 4000.
A can be preferably used. When the saponification degree is less than 90 mol%, the polarizer film and the polarizer protective film may be delaminated under high temperature and high humidity conditions when used as a polarizing plate. If the degree of polymerization is less than 1500, the adhesive strength may decrease. When the degree of polymerization exceeds 4000, the viscosity at the time of application becomes high, the thickness tends to be non-uniform, the adhesive strength varies, and the performance stability may deteriorate. An adhesive is often used as an adhesive solution by dissolving it in water or an organic solvent, but an adhesive aqueous solution prepared by dissolving an aqueous adhesive in water can be preferably used without contaminating the working environment. .

The polarizing plate of the present invention can be obtained by adhering a polarizer film and a polarizer protective film using the above adhesive. As a method of adhering the polarizer film and the polarizer protective film, for example, after applying an adhesive to the polarizer film, a method of laminating the polarizer protective film, after applying the adhesive to the polarizer protective film, Any method such as a method of sticking a polarizer film is adopted. As a method for applying the adhesive to the polarizer film or the polarizer protective film, a conventionally known method can be used and is not particularly limited as long as it is a method for forming a uniform adhesive layer.

The thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.1 to 5 μm, still more preferably 0.5 to 1 μm. If the adhesive layer is less than 0.01 μm, the adhesive strength may be reduced. If the adhesive layer has a thickness of more than 10 μm, it may cause deterioration of durability such as moisture resistance.

The drying temperature after bonding the polarizer film and the polarizer protective film used in the present invention is preferably 50 ° C. or lower. More preferably, it is 40 ° C. or lower. If the drying temperature exceeds 50 ° C., the light transmittance may drastically increase during the drying, and the degree of polarization may decrease. On the other hand, the lower limit of the preferable drying temperature is not limited, but if the temperature is less than room temperature, the moisture permeability of the polarizer protective film is small, and thus the drying is slow, which causes a problem that it takes time to develop the adhesive strength. Generally, it is preferably 10 ° C or higher, more preferably 30 ° C or higher. After adhering the polarizer film and the polarizer protective film in this way, it is gently dried to give 1 per area of the laminated area of the polarizer film and the polarizing plate protective film.
20 ℃ × 60 minutes heating weight loss is preferably 1.3g
/ M ² or less, more preferably 1.0 g / m ² or less, and further preferably 0.7 g / m ² or less. By drying at 50 ° C. or lower until the weight loss upon heating falls within these ranges, a rapid increase in light transmittance can be suppressed even if the polarizing plate is subsequently heated at a high temperature. For example, the increase in light transmittance before and after heating at 70 ° C. for 5 minutes can be 1.0% or less. The increase in the light transmittance in this case is considered to be due to the escape of iodine or the dichroic dye from the polarizer film, which causes the deterioration of the polarization performance. Therefore, it is preferable that the change amount of the light transmittance is smaller when the increase is expressed as a positive value and the decrease is expressed as a negative value. However, if the light transmittance is lower than that before the heating, there is a possibility that coloring due to heating has occurred. Therefore, the amount of change in light transmittance is preferably −1.0% or more and + 1.0% or less.

Further, a polarizing plate in which the weight loss upon heating at 120 ° C. for 60 minutes per area of the adhesive bonding surface is 0 g / m ² or more and 1.3 g / m ² or less, irrespective of the drying temperature of the adhesive,
The increase in light transmittance before and after heating at 70 ° C. for 5 minutes is small, which is preferable. Above all, the polarizing plate in which the variation of the light transmittance is in the range of -1.0% or more and + 1.0% or less can be a polarizing plate suitable for a liquid crystal display device used in various environments.

[0057]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The methods for measuring the physical properties shown in Examples, Comparative Examples and Reference Examples are as follows.

<Glass Transition Temperature> JIS K7121
Compliant with Shimadzu Shimadzu heat flux differential scanning calorimeter D
It measured using SC-50 at a temperature rising rate of 20 ° C./min.

<Phase Difference Value> Measurement was performed at a measurement wavelength of 515 nm using a micro polarization spectrophotometer TFM-120AFT manufactured by Oak Manufacturing Co., Ltd.

<Light transmittance and haze> JIS K
Compliant with 7105, turbidimeter ND manufactured by Nippon Denshoku Industries Co., Ltd.
It measured using H-300A.

<Heating dimensional change rate> The heating dimensional change rate at 80 ° C. for 5 hours was measured as follows.

Two test pieces each having a width of 120 mm and a length of 120 mm were taken and marked in the longitudinal (MD) direction and the transverse (TD) direction. Punch a 1 mmφ hole in each of the four corners of the test piece.
Open at 0mm intervals, and open this at 20 ± 2 ℃, relative humidity 60 ±
Humidification was performed in a 5% room for 3 hours or more. Using a three-dimensional length measuring instrument AE112 manufactured by Mitoyo Seisakusho, the original size (L ₁ ) of the punch interval was measured to the minimum scale of 1/1000 mm.
Next, place the test pieces sandwiched between aluminum foils at 80 ° C ±
Place it in a dryer at 1 ℃ for 5 hours and heat it for 20 ± 2
After the humidity was controlled in a room at 60 ° C. and a relative humidity of 60 ± 5% for 3 hours or more, the dimension (L ₂ ) of the punch interval after the heat treatment was measured by a three-dimensional length measuring machine. Then, the heat shrinkage rate was calculated by the following formula, and the average value was obtained. Heating dimensional change rate (%) = (L ₂ −L ₁ ) / L ₁ × 100 A negative value corresponds to the shrinkage of the film, and a positive value corresponds to the elongation.

<Moisture Permeability> The moisture permeability was measured according to JIS Z0208 (cup method) under the conditions of 25 ° C. and 90% RH.

<Contact angle> FA manufactured by Kyowa Interface Science Co., Ltd.
It measured using CE contact angle meter CA-S150 type.

<Reduction in Weight of Polarizing Plate Heated Per Bonding Area> A part of the polarizing plate having a polarizer protective film on both sides prepared in each example was cut into a size of 40 mm × 40 mm, and its mass W ₁ (mg), And the polarizing plate at 120 ° C. for 60
The mass W ₂ (mg) after heat treatment for minutes was measured, and the water content was calculated by the following formula. Heating weight loss (g / m ² ) = 1000 × (W ₁ −W ₂ ) /
(40 × 40 × 2) <polarizing plate light transmittance variation of> light transmittance after light transmittance T _1, and a polarizing plate was then heated for 5 minutes at 70 ° C. of the polarizing plate after drying T ₂ Was measured and the amount of change was calculated by the following formula. Amount of change in light transmittance (%) = T ₂ −T ₁

The polarizer film was prepared as follows. PVA film with a thickness of 50 μm (manufactured by Nippon Synthetic Chemical Industry Co., Ltd .: Nigo Vinylon Film, # 5000U)
Was longitudinally uniaxially stretched 4 times and immersed in an aqueous solution containing 0.075% by weight of iodine and 5% by weight of potassium iodide at room temperature for 1 minute while maintaining a tension state. Furthermore, boric acid 7.
A polarizer film was obtained by immersing in an aqueous solution containing 5% by weight and 6% by weight potassium iodide at 50 ° C. for 5 minutes for crosslinking treatment.

Example 1 60 parts by weight of an alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content 50 mol%, glass transition temperature 157 ° C.), and acrylonitrile and styrene contents of 24 parts by weight, respectively. %, 76% by weight of acrylonitrile-styrene copolymer (40 parts by weight) was melt-kneaded to obtain a resin composition, and a T-die extruder (cylinder diameter 40 mm, L / D2
Approximately 170 μm in thickness, made into a melt extruded film using 4)
I got the original film. The retardation value of this original film is 0 nm, the light transmittance is 92%, the haze is 0.3%, and the heating dimensional change rate at 80 ° C. for 5 hours is − in the MD direction.
It was 0.007% and + 0.008% in the TD direction.

This raw film was stretched at a stretching speed of 10c using a stretching tester (Toyo Seiki Seisakusho: X4HD-HT).
m / min, stretching ratio 1.8 times, stretching temperature 140 ° C., free-end longitudinal uniaxial stretching, and then free-end uniaxial stretching in a direction orthogonal to the previous stretching direction under the same stretching conditions. A stretched film of 50 μm was obtained. The retardation value of this stretched film was 2 nm, the light transmittance was 92%, and the haze was 0.4.
%, The rate of dimensional change by heating at 80 ° C. for 5 hours was −0.002% in the MD direction and + 0.004% in the TD direction. Also, the moisture vapor transmission rate at 25 ° C and 90% RH is 69 g / (m
Was ² · 24hr).

On this polymer film, cellulose acetate propionate (acetyl group substitution degree 0.17, propionyl group substitution degree 2.66) was mixed with toluene / methyl ethyl ketone mixed solvent (toluene: methyl ethyl ketone (weight ratio) = 1: 1). After casting a solution (concentration: 10% by weight) dissolved in (1), the mixture was heat-treated at 120 ° C. for 10 minutes to obtain a polarizer protective film in which a cellulose ester layer was laminated on a polymer film. The thickness of the cellulose ester layer is 1μ
It was m.

The obtained polarizer protective film was treated with 60 ± 5
After dipping in a 10 wt% sodium hydroxide aqueous solution kept at 0 ° C for 2 minutes, it was thoroughly washed with water to obtain a saponified polarizer protective film. The contact angle of the surface of the cellulose ester layer of the film with pure water was 21 °.

The above-mentioned polarizer protective films were provided on both sides of the polarizer film so that the cellulose ester layer was on the polarizer film side, and the degree of polymerization was 1700 and the degree of saponification was 9
After laminating with a 6 wt% aqueous solution of an adhesive consisting of 8.5 mol% PVA and bringing them into close contact with a rolling roll, they are allowed to stand at room temperature for 24 hours.
After that, it was dried at 40 ° C. for 24 hours to obtain a polarizing plate.
The weight loss on heating per bonded area before drying at 40 ° C. was 1.47 g / m ² , and the weight loss on heating per bonded area of the polarizing plate obtained after drying at 40 ° C. for 24 hours was 0.97.
It was g / m ² . The light transmittance is 42.4% before drying at 40 ° C and 42.5% after drying at 40 ° C for 24 hours.
Met.

Further, as a result of heating the obtained polarizing plate at 70 ° C. for 5 minutes, the light transmittance was 42.6%, and the change amount was + 0.1%.

Example 2 A polarizing plate was obtained in the same manner as in Example 1 except that the polarizing plate was dried at room temperature for 24 hours and at 70 ° C. for 5 minutes. The weight loss on heating per bonded area before drying at 70 ° C is 1.78 g / m ^2, which is 70 ° C.
The weight loss on heating of the polarizing plate obtained after drying for 5 minutes at 1.22 g / m ² was 1.22 g / m ² . The light transmittance is
It was 42.4% before drying at 70 ° C and 43.6% after drying at 70 ° C for 5 minutes.

Further, as a result of heating the obtained polarizing plate at 70 ° C. for 5 minutes, the light transmittance was 43.8%, and the change amount was + 0.2%.

Comparative Example 1 The polarizing plate was dried at room temperature for 24 hours.
A polarizing plate was formed in the same manner as in Example 1 except that only the space was provided.
Obtained. Reduction of heating weight per bonding area before drying at room temperature
Is 2.44 g / m ²And after 24 hours of drying at room temperature
The weight loss by heating of the obtained polarizing plate per laminated area was 1.7.
8 g / m²Met. Light transmittance is before drying at room temperature
42.4%, after drying for 24 hours at room temperature is 42.4%
there were.

Further, as a result of heating the obtained polarizing plate at 70 ° C. for 5 minutes, the light transmittance was 43.6%, and the change amount was + 1.2%.

(Reference Example 1) Thickness 80 μm, 25 ° C./90
Water vapor transmission rate at RH is 516g / (m ² · 24hr)
The TAC film of No. 2 was immersed in a 10% by weight sodium hydroxide aqueous solution kept at 60 ± 5 ° C. for 2 minutes and then thoroughly washed with water to obtain a saponified TAC film (TAC saponified film). The contact angle of the surface of the TAC saponified film with pure water was 19 °.

TAC is provided on each side of the polarizer film.
The saponified film was laminated via the PVA-based adhesive aqueous solution used in Example 1, adhered with a rolling roll, and then dried at room temperature for 24 hours to bond the polarizer film and the TAC saponified film to each other. The obtained polarizing plate was obtained. The resulting polarizing plate had a reduced heating weight of 2.28 g / m ² and a light transmittance of 42.
It was 4%.

Further, as a result of heating the obtained polarizing plate at 70 ° C. for 5 minutes, the light transmittance was 42.5%, and the change amount was + 0.1%.

Reference Example 2 A polarizing plate was obtained in the same manner as in Reference Example 1 except that the polarizing plate was dried at room temperature for 24 hours and at 40 ° C. for 24 hours. The weight loss of the obtained polarizing plate upon heating was 1.38 g / m ² , and the light transmittance was 42.5%.

Further, as a result of heating the obtained polarizing plate at 70 ° C. for 5 minutes, the light transmittance was 42.6%, and the change amount was + 0.1%.

[0082]

According to the production method of the present invention, when a polarizer protective film having a low moisture permeability is bonded and bonded to form a polarizing plate,
A sharp increase in light transmittance does not occur during drying of the adhesive, and a polarizing plate having excellent polarization can be prepared. Further, the obtained polarizing plate has an excellent durability, in which the light transmittance does not sharply increase even at high temperatures.

Further, the polarizing plate of the present invention, which has a specific heating weight reduction range, does not have a sharp increase in light transmittance even at high temperature, and has excellent durability.

Claims (10)

[Claims] 1. A polarizer film having at least one surface on which two 2
Water vapor transmission rate at 5 ° C / 90% RH is 5g / (m ² · 24
In the manufacturing method for laminating a polarizer protective film of not less than hr) and not more than 500 g / (m ² · 24 hr) via an adhesive solution, and drying the adhesive solution to obtain a polarizing plate, the area of the adhesive bonding surface. A method for producing a polarizing plate, which comprises drying at a temperature of 50 ° C. or lower until the weight loss by heating per 120 ° C. × 60 minutes is 1.3 g / m ² or lower. 2. The method for producing a polarizing plate according to claim 1, wherein the adhesive solution is an aqueous adhesive solution. 3. The method for producing a polarizing plate according to claim 1, wherein the adhesive solution contains a polyvinyl alcohol-based adhesive. 4. The method for producing a polarizing plate according to claim 1, wherein the polarizer protective film is a polarizer protective film obtained by a melt molding method. 5. A polarizing plate obtained by the manufacturing method according to claim 1, wherein a change in light transmittance before and after heating at 70 ° C. for 5 minutes is −1.0% or more. +
A polarizing plate characterized by being 1.0% or less. 6. A polarizer film, on at least one side of which a 2 is formed.
Water vapor transmission rate at 5 ° C / 90% RH is 5g / (m ² · 24
It is a polarizing plate to which a polarizer protective film of not less than hr) and not more than 500 g / (m ² · 24 hr) is adhered and adhered, and the weight loss by heating at 120 ° C. × 60 minutes per area of the adhered and adhered surface is 0 g / m ² A polarizing plate which is 1.3 g / m ² or less. 7. The polarizing plate according to claim 6, wherein the amount of change in light transmittance before and after heating at 70 ° C. for 5 minutes is −1.0% or more and + 1.0% or less. 8. The polarizing plate according to claim 6 or 7, wherein the adhesive used for adhesive bonding is a water-based adhesive. 9. The polarizing plate according to claim 8, wherein the water-based adhesive is a polyvinyl alcohol-based adhesive. 10. The polarizing plate according to claim 6, wherein the polarizer protective film is a polarizer protective film obtained by a melt molding method.