KR20200046016A - Polarizing plate, liquid crystal display device and manufacturing method thereof, and polyvinyl alcohol-based polarizing film - Google Patents

Abstract

Provided is a high-quality polyvinyl alcohol-based polarizing plate excellent in balance in heat resistance durability and polarization performance, a liquid crystal display device having the polarizing plate and a manufacturing method thereof, and a polyvinyl alcohol-based polarizing film used in the polarizing plate. The polarizing plate is provided with a polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher, and a protective film provided on at least one side of the polyvinyl alcohol-based polarizing film. In the liquid crystal display device, the polarizing plate and the image display device are stacked. The manufacturing method of this liquid crystal display device is a polyvinyl alcohol-based polarizing film having a glass transition temperature of less than 95 ° C., and a laminate of the image display device is subjected to a drying treatment, and the polyvinyl constituting the polarizing plate is formed. The glass transition temperature of the alcohol-based polarizing film is controlled to 95 ° C or higher.

Description

Polarizing plate, liquid crystal display device and manufacturing method thereof, and polyvinyl alcohol-based polarizing film

The present invention relates to a polarizing plate, a liquid crystal display device and a manufacturing method thereof, and a polyvinyl alcohol-based polarizing film. More specifically, the present invention relates to a polarizing plate (polyvinyl alcohol-based polarizing plate) having a polyvinyl alcohol-based polarizing film which is excellent in the balance between optical properties and heat resistance and durability.

Recently, the development of liquid crystal display devices has been widely used in smart phones, tablets, personal computers, liquid crystal TVs, projectors, vehicle panels, and the like. A polarizing plate is used in the liquid crystal display device. As the polarizing plate, a protective film is laminated on a polarizing film obtained by adsorbing and aligning iodine or dichroic dye onto a polyvinyl alcohol-based film. In recent years, as the use of liquid crystal display devices has expanded, the use environment of both the temperature range and the humidity range has been widened more broadly than in the prior art. Therefore, a polarizing plate having higher heat resistance and exhibiting high polarization degree is required because of this. Getting

As a method of improving the heat resistance durability of the polarizing plate, for example, a polarizing film using a specific azo-based dye is used (for example, see Patent Document 1), or iodine is adsorbed and oriented, and also contains a dichroic organic dye. A method using a film (for example, see Patent Document 2) has been proposed.

In addition, a polarizer comprising an polarizer in which iodine is adsorbed and oriented, the phase difference value Ri of iodine is 160 nm or more, and a polarizing plate having specific optical properties (for example, see Patent Document 3), a weight ratio of iodine and potassium, and an elemental amount of boron The polarizing plate which prescribed | regulated (for example, refer patent document 4) is also proposed as a polarizing plate excellent in heat resistance durability.

Patent document 1 WO 2016 / 186196A Patent document 2 JP 2012-3172A Patent document 3 JP 2016-139151A Patent document 4 WO 2016 / 060087A

However, in the disclosed technique of Patent Document 1, although a polarizing film having high heat resistance and durability can be obtained by using a specific dye, the polarization degree is as low as 99.9% and there is a problem of insufficient contrast.

In Patent Document 2, it is also possible to obtain a polarizing film having high polarization performance, but in the manufacturing process, it is necessary to install two or more dyeing tanks, which are dyed with dichroic dyes and dyed with iodine, In order to adjust the color tone of the polarizing film, since strong concentration management of two or more types of dyeing tanks is also necessary, there is a problem that productivity is low.

In addition, in the disclosed technique of Patent Document 3, the degradation of the optical properties of the heat resistance test at about 85 ° C can be suppressed, but there is a problem that the heat resistance durability under more severe temperature conditions cannot be improved.

Even in the disclosed technique of Patent Document 4, the absorbance at 700 nm when left at 105 ° C for 30 minutes can be maintained at 2.3 or more, but the heat resistance and durability when exposed to high temperature over a longer period of time cannot be improved. There is a problem.

Accordingly, in the present invention, under such a background, a high-quality polyvinyl alcohol-based polarizing plate excellent in balance in heat resistance durability and polarization performance, a liquid crystal display device having the polarizing plate and a method for manufacturing the same, and polyvinyl alcohol-based polarizing used in the polarizing plate Provide a film.

As a result of repeated studies in view of such circumstances, the present inventors have used a polarizing plate having a polyvinyl alcohol-based polarizing film having a higher glass transition temperature than a conventional polyvinyl alcohol-based polarizing plate, which is balanced for heat resistance and polarization performance. It has been found that a polyvinyl alcohol-based polarizing plate having excellent properties can be obtained.

That is, the present invention makes the following [1] to [6] the gist.

[1] A polarizing plate comprising a polyvinyl alcohol-based polarizing film and a protective film provided on at least one surface of the polyvinyl alcohol-based polarizing film, wherein the glass transition temperature of the polyvinyl alcohol-based polarizing film is 95 ° C or higher.

[2] The polarizing plate according to [1] above, wherein the moisture content is 2% by weight or less.

[3] The polarizing plate according to [1] or [2], wherein the polyvinyl alcohol-based polarizing film has a boric acid content of 20% by weight or more.

[4] A liquid crystal display device comprising the polarizing plate according to any one of [1] to [3] above, and an image display device.

[5] In the method for producing a liquid crystal display device according to the above [4], a drying process is performed on a laminate of a polarizing plate having a polyvinyl alcohol-based polarizing film having a glass transition temperature of less than 95 ° C and an image display device. That is, the method of manufacturing a liquid crystal display device for controlling the glass transition temperature of the polyvinyl alcohol-based polarizing film constituting the polarizing plate to 95 ℃ or more.

[6] A polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher.

Since the polarizing plate of the present invention has a polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher, it is excellent in heat resistance and polarization performance, and can stably exhibit performance under very high temperature conditions of 95 ° C or higher. It is.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these embodiments.

One embodiment of the polarizing plate of the present invention has a polyvinyl alcohol-based polarizing film having a glass transition temperature (Tg) of 95 ° C or higher, and a protective film provided on at least one side of the polyvinyl alcohol-based polarizing film. This is the biggest feature of the present invention.

The glass transition temperature (Tg) of the polyvinyl alcohol-based polarizing film is required to be 95 ° C or higher, preferably from 100 ° C or higher from the viewpoint of heat resistance, particularly preferably 105 ° C or higher, and the upper limit is usually 125 ° C. That is, when the glass transition temperature (Tg) is less than the lower limit, the heat resistance durability of the polarizing plate becomes insufficient, and the object of the present invention cannot be achieved.

The glass transition temperature (Tg) was measured by heating a polyvinyl alcohol-based polarizing film (polarizing plate) using a DSC (Q2000 manufactured by TA Instruments, sample 5 mg) at a heating rate of 5 ° C / min from -80 ° C to 155 ° C. Is the value.

The production of the polyvinyl alcohol-based polarizing film, first, a polyvinyl alcohol-based resin as a raw material to obtain a polyvinyl alcohol-based film, and then, the polyvinyl alcohol-based film as a disk swelling, dyeing, boric acid crosslinking, stretching, It is carried out through processes such as washing and drying.

Here, an example of the manufacturing method of the polyvinyl alcohol-based polarizing film will be described in detail in the order of the steps.

(Material for forming polyvinyl alcohol-based film)

First, the polyvinyl alcohol-based resin that is a material for forming the polyvinyl alcohol-based film will be described.

As the polyvinyl alcohol-based resin, an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (typically, 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may also be used. As a component copolymerizable with vinyl acetate, for example, unsaturated carboxylic acids (for example, salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n -Butene, isobutene, etc.), vinyl ethers, unsaturated sulfonic acid salts, and the like. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in this side chain is, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) Method of saponifying and decarbonizing a copolymer of vinyl acetate and vinylethylene carbonate, (iii) Saponifying and de-ketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane And (i 하는) a method of saponifying a copolymer of vinyl acetate and glycerin monoaryl ether.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000 from the viewpoint of production of the polyvinyl alcohol-based polarizing film, particularly preferably 110 to 280,000, more preferably 120,000 to 26 It is only. That is, if this weight average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is used as an optical film. If it is too large, the polyvinyl alcohol-based polarizing film is obtained from the polyvinyl alcohol-based film. There is a tendency that stretching at the time of manufacturing becomes difficult. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is a weight average molecular weight measured by GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin is preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, from the viewpoint of the optical performance of the polyvinyl alcohol-based polarizing film. , Particularly preferably 99.8 mol% or more. That is, if this average saponification degree is too small, the polyvinyl alcohol-based polarizing film produced from the polyvinyl alcohol-based film tends to have insufficient optical performance.

Here, the average saponification degree is measured according to JIS K 6726.

As the polyvinyl alcohol-based resin, two or more kinds of modified species, modified amount, weight average molecular weight, average saponification degree and the like may be used in combination.

Subsequently, an aqueous polyvinyl alcohol-based resin solution is prepared using the polyvinyl alcohol-based resin. The aqueous solution of the polyvinyl alcohol-based resin will be described.

The aqueous solution of the polyvinyl alcohol-based resin is obtained by dissolving the aforementioned polyvinyl alcohol-based resin in a solvent such as water. In addition to water as the solvent, polyhydric alcohols such as dimethyl sulfoxide (DMSO); N-methylpyrrolidone; glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, for example. Amines such as ethylene diamine and diethylene triamine; and mixtures of these may be used in combination.

In the aqueous solution of the polyvinyl alcohol-based resin, in addition to the polyvinyl alcohol-based resin, a plasticizer generally used, such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, if necessary, It is possible to contain at least one nonionic, anionic, and cationic surfactant, and it is preferable from the viewpoint of film forming properties to contain them. One type selected from these may be used alone or two or more types may be used together.

The resin concentration of the aqueous polyvinyl alcohol-based resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight from the viewpoint of productivity. That is, if the resin concentration of this aqueous solution is too low, the drying load tends to increase, and productivity tends to decrease. If it is too high, the viscosity tends to be too high, and a uniform solution tends to be impossible.

The obtained aqueous polyvinyl alcohol-based resin solution is usually defoamed. As the defoaming method, for example, a method such as static defoaming or defoaming with a multi-screw extruder can be given. As the multi-screw extruder, it may be a multi-screw extruder having a vent, and a twin-screw extruder having a vent is usually used.

(Method for producing polyvinyl alcohol-based film)

After the defoaming treatment, a polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die by a certain amount, discharged and cast onto a rotating cast drum, and is formed by a continuous cast method. Then, a polyvinyl alcohol-based film is obtained by drying the formed film. The manufacturing method of this polyvinyl alcohol-type film is demonstrated.

The continuous casting method is, for example, a method in which a polyvinyl alcohol-based resin aqueous solution is discharged from a T-shaped slit die and cast into a rotating cast drum, endless belt, resin film or the like to form a flexible film.

The surface temperature of the cast type such as the cast drum is preferably 40 to 99 ° C, particularly preferably 60 to 95 ° C. Drying of the film formed into a cast form is carried out by conveying the surface and the back surface of the film while alternately contacting the outer circumferential portions of a plurality of lines of heat rolls. After drying with this heat roll, the film may be heat treated. The heat treatment is preferably performed at 60 to 150 ° C, particularly preferably 80 to 130 ° C. The film subjected to the drying and heat treatment as necessary is formed by cutting and removing (slit) both ends of the film to form the polyvinyl alcohol-based film. Then, the polyvinyl alcohol-based film is wound on a core tube to form a film roll.

The thickness of the polyvinyl alcohol-based film is preferably 5 to 75 μm, particularly preferably 10 to 60 μm from the viewpoint of thinning of the polarizing film, and more preferably 15 to 60 μm from the viewpoint of durability.

Moreover, it is preferable that the width of the said polyvinyl alcohol-type film is 4 m or more, More preferably, it is 4.5 m or more from a viewpoint of large-scale, and it is 4.5-6 m especially preferably from a viewpoint of avoidance of fracture.

Further, the length of the polyvinyl alcohol-based film is preferably 4 km or more, more preferably 4.5 km or more from the viewpoint of large-scale, and particularly preferably 4.5 to 50 km from the viewpoint of transport weight.

(Method for producing polyvinyl alcohol-based polarizing film)

Hereinafter, a method of manufacturing an embodiment of the polyvinyl alcohol-based polarizing film of the present invention obtained using the polyvinyl alcohol-based film will be described.

The production of the polyvinyl alcohol-based polarizing film is carried out through a process such as swelling, dyeing, boric acid crosslinking, stretching, washing, drying, etc. by continuously releasing and transporting the polyvinyl alcohol-based film from the film roll. These processes will be described.

The swelling process is performed before the dyeing process. The swelling process is usually performed by immersing the polyvinyl alcohol-based film in a treatment liquid in a water bath. In addition to being able to clean the surface of the polyvinyl alcohol-based film by the swelling process, swelling the polyvinyl alcohol-based film also has an effect of preventing staining and the like. Water is usually used as the treatment liquid. If the main component is water, this treatment liquid may contain a small amount of an additive such as an iodide compound or a surfactant, or alcohol. The temperature of the treatment liquid is usually about 10 to 45 ° C, and the immersion time in the treatment liquid is usually about 0.1 to 10 minutes.

The dyeing process is usually carried out by immersing the polyvinyl alcohol-based film in a liquid containing iodine or a dichroic dye. As the liquid, an aqueous solution of iodine-potassium iodide is usually used. The concentration of iodine is 0.1 to 2 g / L, and the concentration of potassium iodide is 1 to 100 g / L. The dyeing time is practical for about 30 to 500 seconds. The temperature of the liquid is preferably 5 to 50 ° C. In addition to the aqueous solvent, the aqueous solution may contain a small amount of an organic solvent compatible with water.

The boric acid crosslinking step is usually carried out by immersing the polyvinyl alcohol-based film in a liquid containing a boron compound such as boric acid or borax. The liquid is an aqueous solution or a water-organic solvent mixture, and the concentration of the boron compound in the liquid is about 10 to 100 g / L. It is preferable from the viewpoint of stabilization of the polarization performance that potassium iodide coexist in the liquid. The temperature of the liquid is about 30 to 70 ° C, and the immersion time in the liquid is preferably about 0.1 to 20 minutes.

The stretching step may be performed independently, or may be carried out during at least a part of the swelling step, the dyeing step, and the boric acid crosslinking step. In addition, it is preferable that the total draw ratio is 3 to 10 times in the uniaxial direction, preferably 3.5 to 6 times. At this time, some stretching (a degree of preventing shrinkage in the width direction or stretching beyond) may also be performed in the direction perpendicular to the stretching direction. The temperature of rotation of the polyvinyl alcohol-based film to be stretched during stretching is preferably 40 to 170 ° C.

The washing step is carried out, for example, by dipping the polyvinyl alcohol-based film in an aqueous iodide solution such as water or potassium iodide. A precipitate generated on the surface of the polyvinyl alcohol-based film can be removed by a washing process. When a potassium iodide aqueous solution is used, the potassium iodide concentration is usually about 1 to 80 g / L. The temperature of the aqueous iodide solution during washing is usually 5 to 50 ° C, preferably 10 to 45 ° C. The immersion time in the water or aqueous iodide solution is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, water washing and washing with an aqueous potassium iodide solution may be performed in appropriate combination.

The drying process is usually carried out by drying the polyvinyl alcohol-based film in an atmosphere at an atmosphere temperature of 40 to 100 ° C, preferably 70 to 98 ° C for 0.5 to 20 minutes.

Here, as a method of controlling the glass transition temperature of the polyvinyl alcohol-based polarizing film to be made high, (1) in the boric acid crosslinking step, by increasing the concentration of boric acid in the liquid immersing the polyvinyl alcohol-based film, poly produced Method of increasing the boric acid content in the vinyl alcohol-based polarizing film, (2) a method of increasing the crosslink density of the polyvinyl alcohol-based polarizing film, and (3) moisture content of the polyvinyl alcohol-based polarizing film using a drying agent such as phosphorus pentoxide. And (4) a method of adjusting the atmosphere temperature and drying time in the drying step.

Among these, the above methods (1) and (4) are preferred from the viewpoint of ease of adjustment.

In the case of the method (1), the concentration of boric acid in the liquid is preferably 20 to 90 g / L from the viewpoint of setting the glass transition temperature to 95 ° C. or higher, and from 30 to 80 g / L from the viewpoint of achieving both heat resistance and elongation. It is more preferable to be.

By increasing the concentration of boric acid in the liquid as described above, it is possible to increase the boric acid content in the polyvinyl alcohol-based polarizing film produced. The boric acid content is preferably 20% by weight or more, particularly preferably 20 to 30% by weight, and more preferably 21 to 29% by weight.

If the boric acid content is too small, the heat resistance and durability of the polyvinyl alcohol-based polarizing film tends to be insufficient, and if too large, the polyvinyl alcohol-based polarizing film produced during the production of the polyvinyl alcohol-based polarizing film tends to crack. Tend to lose.

In the case of the method (4), from the viewpoint of setting the glass transition temperature to 95 ° C or higher, the atmosphere temperature of the drying step is preferably 50 to 99 ° C, particularly preferably from the viewpoint of heat resistance and durability, 60 to 98 ° C, and drying The time is preferably 1 to 15 minutes, particularly preferably 1.5 to 10 minutes.

By this drying step, the moisture content of the polyvinyl alcohol-based polarizing film can be 2.0% by weight or less.

In this way, a polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher is obtained.

The polarization degree of this polyvinyl alcohol-based polarizing film is preferably 99.9% or more, particularly preferably 99.92% or more. If the polarization degree is too low, there is a tendency that the contrast in a liquid crystal display device such as a liquid crystal display cannot be secured.

In addition, the single transmittance of the polyvinyl alcohol-based polarizing film is preferably 42% or more. When this simple substance transmittance is too low, there is a tendency that high luminance of a liquid crystal display device such as a liquid crystal display cannot be achieved.

The simplex transmittance is a value obtained by measuring the light transmittance of a single polyvinyl alcohol-based polarizing film using a spectrophotometer.

〔Manufacturing method of polarizing plate〕

And a polarizing plate provided with a protective film on at least one side is obtained by bonding an optically isotropic protective film to one or both surfaces of the obtained polyvinyl alcohol-based polarizing film through an adhesive.

Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, and poly-4- And resin films or resin sheets such as methyl pentene and polyphenylene oxide.

The bonding of the polyvinyl alcohol-based polarizing film and the protective film is carried out by a known method, but, for example, a liquid adhesive composition is uniformly coated on the polyvinyl alcohol-based polarizing film, protective film, or both. Then, it is carried out by bonding and compressing both, and irradiating with heating or active energy rays.

The polarizing plate preferably has a moisture content of 2% by weight or less, particularly preferably 1.5% by weight or less, and more preferably 1% by weight or less from the viewpoint of increasing the heat resistance and durability of the polyvinyl alcohol-based polarizing film. The lower limit of the water content is usually 0.1% by weight.

When the moisture content is too high, the heat resistance of the polyvinyl alcohol-based polarizing film tends to be insufficient.

As a method of adjusting the moisture content to be low, (a) a method of continuously drying the polarizing plate, (b) a method of heat-treating in a high-temperature storage after winding the polarizing plate once, (c) vacuum drying treatment after chip-cutting the polarizing plate And the like.

Among these, the method (a) is preferable in order to uniformly control the moisture content in the width direction and the length direction.

In the case of the method (a), the atmospheric temperature in the drying treatment is usually 60 to 100 ° C, and preferably 70 to 95 ° C from the viewpoint of optical properties. Moreover, drying time is 1 to 10 minutes normally, Preferably it is 2 to 8 minutes. In this drying treatment, it is preferable to use two or more stages of drying treatment with different atmospheric temperature and drying time, and it is particularly preferable from the viewpoint of the appearance of the polarizing plate to increase the atmospheric temperature of the drying treatment in the subsequent stage. Specifically, for example, it is preferable that the atmospheric temperature of the first stage drying treatment is 60 to 80 ° C, and the atmospheric temperature of the second stage drying treatment is 80 to 100 ° C.

In the case of the method (c), the vacuum drying treatment after chip-cutting the polarizing plate is preferably carried out at an ambient temperature of 40 to 60 ° C for about 15 minutes to 36 hours.

The polarization degree of the polarizing plate is preferably 99.9% or more, particularly preferably 99.92% or more. If the polarization degree is too low, there is a tendency that the contrast in a liquid crystal display device such as a liquid crystal display cannot be secured.

In addition, the degree of polarization is generally a direction in which two polarizing plates are aligned so that their orientation directions are the same, and the light transmittance (H ₁₁ ) measured at wavelength λ and the two polarizing plates are orthogonal to each other. In the state of being superimposed as above, the light transmittance (H ₁ ) measured at the wavelength λ is calculated according to the following formula.

Polarization = (((H ₁₁ -H ₁ ) / (H ₁₁ + H ₁ )) ^1/2

In addition, the simple substance transmittance of the polarizing plate is preferably 42% or more. When this simple substance transmittance is too low, there is a tendency that high luminance of a liquid crystal display device such as a liquid crystal display cannot be achieved.

The simplex transmittance is a value obtained by measuring the light transmittance of a single polyvinyl alcohol-based polarizing plate using a spectrophotometer.

〔Liquid crystal display device〕

One embodiment of the liquid crystal display device of the present invention is provided with the polarizing plate.

That is, the liquid crystal display device is one in which an image display device such as the polarizing plate and a liquid crystal cell is laminated through an adhesive layer.

If necessary, components such as a lighting system may be added to the liquid crystal display device.

As said liquid crystal cell, TN type, STN type, VA type, IPS type etc. are mentioned, for example.

Since the liquid crystal display device is provided with the polarizing plate having a polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher, it is possible to stably display an image even under very high temperature conditions of 95 ° C or higher.

〔Manufacturing method of liquid crystal display device〕

When the glass transition temperature of the polyvinyl alcohol-based polarizing film constituting the polarizing plate in the liquid crystal display device is less than 95 ° C, the liquid crystal display device may be manufactured as follows.

That is, if the glass transition temperature is a polarizing plate having a polyvinyl alcohol-based polarizing film of less than 95 ° C, the liquid crystal cell is laminated through an adhesive layer, and the laminate is subjected to a drying treatment or a vacuum drying treatment. The glass transition temperature of the polyvinyl alcohol-based polarizing film is 95 ° C or higher.

In this case, the atmosphere temperature in the drying treatment is preferably 60 to 100 ° C, and the drying time is 0.5 to 10 minutes. The atmospheric temperature in the vacuum drying treatment is preferably 50 to 80 ° C, and the drying time is 10 to 120 minutes.

Note that the vacuum drying treatment is a drying treatment under vacuum (absolute pressure of 1 kPa or less).

The polarizing plate has excellent heat resistance and polarization performance, so it is a portable information terminal, PC, television, projector, signage, electronic desk calculator, electronic clock, word processor, electronic paper, game machine, video, camera, photo album, thermometer, audio, automobile B. Liquid crystal display devices such as machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc. It is preferably used.

(Example)

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless the gist is exceeded. About each property, it measured as follows.

<Measurement conditions>

(1) Moisture content (% by weight)

The obtained polarizing plate was weighed 100 mg, placed in a 2 ml vial bottle, and then, anhydrous ethanol was added, sealed, and heated at 60 ° C. for 24 hours. Then, it cooled to room temperature (25 degreeC), and the moisture content of the polarizing plate was measured using the micro-moisture measuring device CA-200 (made by Mitsubishi Chemical Analtech).

(2) Glass transition temperature of polyvinyl alcohol-based polarizing film (℃)

The obtained polyvinyl alcohol-based polarizing film was heated using a DSC (Q2000, manufactured by TA Instruments, sample 5 mg) at -80 ° C to 155 ° C at a heating rate of 5 ° C / min to increase the glass transition temperature of the polyvinyl alcohol-based polarizing film. Measured.

(3) Boric acid content (% by weight)

The obtained polyvinyl alcohol-based polarizing film was dried at 105 ° C. for 2 hours, 100 mg was weighed, 30 ml of water was added, and then heated and dissolved. After the obtained solution was cooled to 25 ° C, 5 ml of glycerin was added and stirred, and then titrated with 0.1 mol / L aqueous sodium hydroxide solution to calculate the following formula.

Boric acid content (% by weight) = 61.83 x 0.1 x f x V / weight of polyvinyl alcohol-based polarizing film x 100

f: Factor of 0.1 mol / L aqueous sodium hydroxide

V: Appropriate amount (ml)

(4) Polarization degree (%), simple substance transmittance (%)

A test piece having a length of 4 cm x a width of 4 cm was cut out from the center portion in the width direction of the obtained polarizing plate, and the polarization degree (%) and simple substance transmittance (%) were measured using an automatic polarizing film measuring apparatus (VAP7070 manufactured by Jasko Corporation).

(5) Heat resistance endurance test

Both surfaces of the obtained polarizing plate were sandwiched with glass and put into a dryer at 105 ° C. The appearance was visually observed after 150 hours and evaluated according to the following criteria.

(Evaluation standard)

○ There was no discoloration at all

△ ... There was faint discoloration

There was clearly discoloration.

<Example 1>

(Preparation of polyvinyl alcohol-based polarizing film and polarizing plate)

The polyvinyl alcohol-based film having a film thickness of 45 µm was continuously released from the film roll and conveyed in the horizontal direction, while being immersed in a water bath having a water temperature of 25 ° C. and swollen to stretch 1.7 times in the flow direction (MD). Subsequently, the mixture was immersed in a 30 ° C aqueous solution consisting of 1.2 g / L of iodine and 30 g / L of potassium iodide and stretched 1.6 times in the flow direction (MD) while dyeing, followed by the composition of 50 g / L of boric acid and 30 g / L of potassium iodide. It was immersed in an aqueous solution (55 DEG C) and uniaxially stretched 2.1 times in the flow direction (MD) while crosslinking boric acid. Then, washing was performed with an aqueous potassium iodide solution and dried at an ambient temperature of 60 ° C for 2 minutes to obtain a polyvinyl alcohol-based polarizing film having a total draw ratio of 5.7 times. Table 1 shows the properties of the obtained polyvinyl alcohol-based polarizing film.

Subsequently, a polyvinyl alcohol aqueous solution was used as an adhesive on both sides of the obtained polyvinyl alcohol-based polarizing film, a triacetyl cellulose film having a film thickness of 40 µm was dried, and the mixture was dried at an ambient temperature of 95 ° C. for 2 minutes to obtain a unit transmittance of 42.8%, A polarizing plate having a polarization degree of 99.95% was obtained. Table 1 shows properties of the polyvinyl alcohol-based polarizing film and the polarizing plate.

<Example 2>

The polyvinyl alcohol-based film having a film thickness of 45 µm was continuously released from the film roll and conveyed in a horizontal direction, while being immersed in a water bath having a water temperature of 25 ° C. and swollen, stretched 1.7 times in the flow direction (MD). Subsequently, the mixture was immersed in a 30 ° C aqueous solution consisting of 1.2 g / L of iodine and 30 g / L of potassium iodide and stretched 1.6 times in the flow direction (MD) while dyeing, followed by the composition of 50 g / L of boric acid and 30 g / L of potassium iodide. It was immersed in an aqueous solution (55 ° C) and uniaxially stretched 2.2 times in the flow direction (MD) while crosslinking boric acid. Then, washing was performed with an aqueous potassium iodide solution, and dried at 60 ° C for 2 minutes to obtain a polyvinyl alcohol-based polarizing film having a total draw ratio of 6.0 times. Table 1 shows the properties of the obtained polyvinyl alcohol-based polarizing film.

Subsequently, on both sides of the obtained polyvinyl alcohol-based polarizing film, a polyvinyl alcohol aqueous solution was used as an adhesive, a triacetyl cellulose film having a film thickness of 40 µm was adhered, dried at 80 ° C. for 5 minutes, and then again atmosphere. It was dried at a temperature of 95 ° C. for 1 minute to obtain a polarizing plate having a single transmittance of 42.9% and a polarization degree of 99.96%. Table 1 shows properties of the polyvinyl alcohol-based polarizing film and the polarizing plate.

<Example 3>

After drying the triacetyl cellulose film, drying was performed in the same manner as in Example 2 except that the temperature was 80 minutes at 80 ° C to obtain a polyvinyl alcohol-based polarizing plate.

After the adhesive layer was provided on one surface of the obtained polarizing plate, chip cutting was performed to obtain a polarizing plate chip having a length of 10 cm and a width of 5 cm. The polarizing plate chip was vacuum dried at 40 ° C for 16 hours. Table 1 shows properties of the obtained polarizing plate.

<Comparative Example 1>

A polarizing plate was obtained in the same manner as in Example 2 except that drying after laminating the triacetylcellulose film in Example 2 was performed at 80 ° C for 2 minutes at ambient temperature. Table 1 shows properties of the polyvinyl alcohol-based polarizing film and the polarizing plate.

The polarizing plates of Examples 1 to 3 show that the polyvinyl alcohol-based polarizing film containing glass had a glass transition temperature of 95 ° C or higher, which is higher than usual, so that there was no discoloration at all during the heat resistance test and excellent heat resistance.

On the other hand, in the polarizing plate of Comparative Example 1, since the glass transition temperature of the polyvinyl alcohol-based polarizing film contained is less than 95 ° C, it can be seen that discoloration occurs during the heat resistance test.

<Example 4>

On both sides of the polarizing film obtained in Example 1, a polyvinyl alcohol aqueous solution was used as an adhesive, a triacetyl cellulose film having a film thickness of 40 µm was dried, and the mixture was dried at 80 ° C for 2 minutes for a single group, and transmittance was 42.8%. 99.94% of a polarizing plate was obtained.

After the adhesive layer was provided on one surface of the obtained polarizing plate, it was bonded to a liquid crystal display device, and a laminate of these polarizing plates and a liquid crystal display device was formed. Subsequently, the laminated body was vacuum-dried at atmospheric temperature 60 degreeC for 45 minutes using a vacuum dryer. Thereafter, a glass substrate was pasted on the polarizing plate of the laminate, and a heat resistance durability test was performed for 150 hours in a dryer having an atmosphere temperature of 105 ° C. Table 2 shows the results.

Moreover, when the polarizing plate was peeled from the said laminated body after the vacuum drying process produced separately, the moisture content and the glass transition temperature were measured, the moisture content was 2.0 weight%, and the glass transition temperature of the polarizing film was 98 degreeC.

<Example 5>

The laminate obtained in Example 4 was vacuum dried at 70 ° C. for 60 minutes using a vacuum dryer. Thereafter, a glass substrate was pasted on the polarizing plate of the laminate, and a heat resistance durability test was performed in a dryer at an atmosphere temperature of 105 ° C for 150 hours. Table 2 shows the results.

Moreover, the polarizing plate was peeled from the laminated body after the vacuum drying process separately produced, and the moisture content and the glass transition temperature were measured. The moisture content was 0.9% by weight, and the glass transition temperature of the polarizing film was 114 ° C.

<Comparative Example 2>

The layered product obtained in Example 4 was vacuum dried for 15 minutes at 70 ° C at an ambient temperature using a vacuum dryer. Thereafter, a glass substrate was pasted on the polarizing plate of the laminate, and a heat resistance durability test was performed in a dryer at an atmosphere temperature of 105 ° C for 150 hours. Table 2 shows the results.

Moreover, the polarizing plate was peeled from the laminate after the vacuum drying treatment separately produced, and the moisture content and the glass transition temperature were measured. The moisture content was 2.3% by weight, and the glass transition temperature of the polarizing film was 93 ° C.

Evaluation criteria of the heat resistance durability test of the said laminated body in Examples 4, 5, and Comparative Example 2 are as follows.

(Evaluation standard)

○ There was no discoloration at all

△ ... There was faint discoloration

There was clearly discoloration.

In Examples 4 and 5, since the glass transition temperature of the polyvinyl alcohol-based polarizing film in the polarizing plate was 95 ° C or higher, it was found that the laminate using the polarizing plate had no discoloration at all during the heat resistance test and was excellent in heat resistance. .

On the other hand, in Comparative Example 2, since the glass transition temperature of the polyvinyl alcohol-based polarizing film in the polarizing plate is less than 95 ° C, it can be seen that discoloration occurs in the laminate using the polarizing plate during the heat resistance test.

Although the specific form in this invention was shown in the said Example, the said Example is only a mere illustration and is not interpreted limitedly. Various modifications apparent to those skilled in the art are also intended to be within the scope of the present invention.

The polarizing plate of the present invention is excellently balanced in heat resistance and polarization performance, and is preferably used for various liquid crystal display devices, vehicle applications requiring high durability and polarization performance, and display applications for industrial instruments required in various environments.

Claims (6)

A polarizing plate comprising a polyvinyl alcohol-based polarizing film and a protective film provided on at least one side of the polyvinyl alcohol-based polarizing film, wherein the glass transition temperature of the polyvinyl alcohol-based polarizing film is 95 ° C or higher. Polarizer. The method according to claim 1,
A polarizing plate having a moisture content of 2% by weight or less. The method according to claim 1 or 2,
The polarizing plate, characterized in that the boric acid content of the polyvinyl alcohol-based polarizing film is 20% by weight or more. A liquid crystal display device comprising the polarizing plate according to any one of claims 1 to 3 and an image display device. In the method of manufacturing a liquid crystal display device according to claim 4, the polarizing plate having a polyvinyl alcohol-based polarizing film having a glass transition temperature of less than 95 ° C. and an image display device is subjected to a drying treatment to constitute the polarizing plate. Method of manufacturing a liquid crystal display device, characterized in that for controlling the glass transition temperature of the polyvinyl alcohol-based polarizing film to 95 ℃ or more. A polyvinyl alcohol-based polarizing film having a glass transition temperature of 95 ° C or higher.