KR20140138647A - Method for producing polarizing plate - Google Patents

Abstract

The present invention relates to a process for producing a polarizing film by dyeing and crosslinking a polyvinyl alcohol film and then drying the polarizing film by a first drying step of drying the polarizing film and bonding a protective film to at least one surface of the polarizing film through an adhesive layer to form a laminate And a second drying step of drying the laminate to produce a polarizing plate, wherein the thickness Tb of the polarizing film in the polarizing plate after the second drying step, after the first drying step and before the polarizing film before the bonding step The ratio Ta / Tb of the thickness Ta is 1.02 to 1.30.

Description

METHOD FOR PRODUCING POLARIZING PLATE [0002]

The present invention relates to a method for producing a polarizing plate.

BACKGROUND ART [0002] Liquid crystal display devices are used in various display devices by taking advantage of features such as low power consumption, low voltage operation, light weight and thinness. The liquid crystal display device is made up of many materials such as a liquid crystal cell, a polarizing plate, a phase difference film, a light condensing sheet, a diffusion film, a light guide plate, and a light reflection sheet. Therefore, improvements have been actively made with the aim of reducing the number of constituent films or thinning the thickness of the film or sheet, aiming at improvement in productivity, light weight, brightness and the like.

The polarizing plate usually has a structure in which a protective film is laminated on both sides or one side of a polarizing film including a polyvinyl alcohol-based resin in which dichroic dye is adsorbed and oriented. For example, Japanese Unexamined Patent Publication (Kokai) No. 2004-341503 (Patent Document 1) discloses a polarizing plate having good color and good durability. The polyvinyl alcohol film is subjected to iodine dyeing and then crosslinked in an aqueous solution of boric acid, Discloses a polarizing plate in which a protective film is provided on the surface of a polarizer produced by axial stretching.

Japanese Patent Application Laid-Open No. 2002-40256 (Patent Document 2) discloses a polarizing plate in which a thickness of a disc of a synthetic resin film, a thickness of only a polarizer after bonding a protective film, and a total stretching magnification are established to be constant .

Japanese Patent Application Laid-Open No. 2004-341503 Japanese Patent Application Laid-Open No. 2002-40256

In the method of producing a polarizing plate as described in Patent Documents 1 and 2, a drying treatment is usually carried out after the crosslinking treatment to adjust the moisture content of the polarizing film to an appropriate range, and the polarizing film and the protective film are bonded through an aqueous adhesive , And drying treatment is performed to remove the solvent of the adhesive. Although the drying treatment may reduce the thickness of the polarizing film, it is preferable to contribute to the thinning of the polarizing plate in this respect, but the width of the polarizing film shrinks due to the drying treatment and the effective area of the polarizing plate becomes narrow .

An object of the present invention is to provide a manufacturing method for producing a polarizing plate having sufficient optical performance by controlling the drying process so as to suppress the width of the polarizing film from shrinking while reducing the thickness of the polarizing film.

As a result of intensive studies, the inventors of the present invention have found that a first drying step is carried out for a polarizing film after a crosslinking treatment and before a protective film is bonded, and a second drying step for a laminated body obtained by bonding a protective film to a polarizing film The degree of drying in the first drying step and the second drying step is controlled so that the thickness of the polarizing film after each drying step satisfies a predetermined relationship so that the width of the polarizing film Can be suppressed and a polarizing plate having more excellent optical performance can be produced, and thus the present invention has been accomplished.

That is, the present invention relates to a process for dyeing a polyvinyl alcohol-based film with a dichroic dye, a step of dyeing the dyed polyvinyl alcohol-based film in a solution containing a cross-linking agent to effect crosslinking, And a first drying step of drying the polarizing film to form a polarizing film comprising a polyvinyl alcohol film and then bonding a protective film to at least one surface of the polarizing film through an adhesive layer to form a laminated body A bonding step and a second drying step for drying the laminate are sequentially performed to produce a polarizing plate including a laminate, wherein the polarizing plate after the second drying step is subjected to a first drying step And the ratio Ta / Tb of the thickness Ta of the polarizing film before the bonding step is 1.02 to 1.30.

By controlling the degree of drying of the first drying step and the second drying step so that the thickness of the polarizing film satisfies the above-described relationship, it is possible to suppress the width of the polarizing film while reducing the thickness of the polarizing film.

The ratio of the width Wb of the polarizing film to the width Wb of the polarizing film after the first drying step and the width Wa of the polarizing film before the bonding step is 0.960 or more and less than 1.000, It is desirable to control the degree of drying of the drying process.

Further, in order to control as described above, it is preferable to perform the first drying step so that the moisture content of the polarizing film after the first drying step and before the bonding step becomes 12 to 45%.

In the present invention, it is preferable that the content of boron in the polarizing film of the finally obtained polarizing plate is 2.5 to 4.5% by weight.

In the present invention, it is preferable that the second drying step includes a step of performing the treatment at a drying temperature higher than the maximum drying temperature of the first drying step. In the present invention, it is preferable that the second drying step includes a step of performing the treatment at a drying temperature higher than the drying temperature at the start of the process.

Further, in the present invention, it is also possible to further have a removing step of cutting and removing both ends of the polyvinyl alcohol-based film before the bonding step.

According to the production method of the present invention, it is possible to produce a polarizing plate having a thin and excellent polarization performance while suppressing the contraction of the width of the polarizing film produced in the production step.

The method for producing a polarizing plate of the present invention comprises a dyeing step of dyeing a polyvinyl alcohol film with a dichromatic dye, a crosslinking step of dipping the dyed polyvinyl alcohol film in a solution containing a crosslinking agent to effect crosslinking, And a first drying step of drying the polyvinyl alcohol film are sequentially performed to produce a polarizing film comprising a polyvinyl alcohol film and then a protective film is bonded to at least one surface of the polarizing film through an adhesive layer to form a laminate And a second drying step of drying the laminate are performed in this order to produce a polarizing plate including a laminate. In the production method of the present invention, the ratio of the thickness Ta of the polarizing film before the bonding step to the thickness Ta of the polarizing film after the first drying step with respect to the thickness Tb of the polarizing film after the second drying step is 1.02 to 1.30, And controls the degree of drying in the drying step and the second drying step. Hereinafter, the respective materials and respective steps used in the present invention will be described in detail.

(Polyvinyl alcohol film)

The polyvinyl alcohol-based resin forming the polyvinyl alcohol-based film used in the production method of the present invention is exemplified by a saponified polyvinyl acetate-based resin. The degree of saponification is usually at least 85 mol%, preferably at least 90 mol%, more preferably from 99 mol% to 100 mol%. Examples of the polyvinyl acetate resin include polyvinyl acetate as a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, and preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Normally, an unoriented film of a polyvinyl alcohol-based film having a thickness of 20 탆 to 100 탆, preferably 30 탆 - 80 탆 is used as a starting material for producing a polarizing film. Further, a stretched film which has been subjected to stretching treatment in advance may be used. The width of the film is practically 1500 to 6000 mm industrially.

In one embodiment of the present invention, a polarizing film is produced by first performing a swelling process, a dyeing process, a crosslinking process, a washing process, and a first drying process using an unstretched polyvinyl alcohol film. In the case of using an unstretched film, the film is subjected to a wet or dry stretching treatment in any one step or as a separate step. The stretching can be performed by a known stretching method. Examples of known stretching methods include inter-roll stretching in which a main speed difference is applied between two nip rolls for transporting a film, a thermal roll stretching method and a tenter stretching method as described in Japanese Patent No. 2731813, and the like. Even in the case of using a stretched film, stretching processing may be further performed. The thickness of the polarizing film finally obtained through the first drying step is, for example, 5 to 50 占 퐉.

[Swelling Process]

The swelling process is performed for the purpose of removing foreign substances on the film surface, removing the plasticizer in the film, imparting easy dyeability in the subsequent dyeing process, plasticizing the film, and the like. The processing conditions are within a range that can achieve these purposes and are determined within a range that does not cause problems such as extreme melting of the film and loss of transparency. When the film stretched in advance in a gas is swelled, the film is immersed in an aqueous solution of, for example, 20 占 폚 to 70 占 폚, preferably 30 占 폚 to 60 占 폚. The immersion time of the film is preferably 30 seconds to 300 seconds, more preferably 60 seconds to 240 seconds. In the case of swelling the unstretched original film, the film is immersed in an aqueous solution of, for example, 10 캜 to 50 캜, preferably 20 캜 to 40 캜. The immersion time of the film is preferably 30 seconds to 300 seconds, more preferably 60 seconds to 240 seconds.

The uniaxial stretching of the polyvinyl alcohol-based film may be performed in the swelling step. In this case, the draw ratio is usually 1.2 to 3.0 times, preferably 1.3 to 2.5 times.

In the swelling process, the film tends to swell in the width direction to cause wrinkles in the film. Therefore, it is preferable to use an expander roll, a spiral roll, a crown roll, a cloth guider, It is preferable to carry the film while grasping the film with a known widening device such as a bar or a tenter clip. In order to stabilize the film transportation during the swelling bath, the water stream in the swelling bath is controlled by an underwater shower, or an EPC apparatus (Edge Position Control apparatus: an apparatus for detecting the end of the film and preventing the film from skewing) It is also useful to use it in combination. In this process, since the film swells and expands even in the traveling direction of the film, when the film is not actively stretched, in order to eliminate the looseness of the film in the carrying direction, for example, It is preferable to take measures such as adjustment. In addition to the pure water, boric acid (described in JP-A No. 10-153709), chloride (described in JP-A No. 06-281816), inorganic acid, inorganic salt, An organic solvent, an alcohol, or the like in an amount of 0.01 wt% to 10 wt% may be used.

[Dyeing Process]

The dyeing step with the dichroic dye is carried out for the purpose of adsorbing and orienting the dichroic dye on the film. The processing conditions are within a range that can achieve these purposes and are determined within a range that does not cause problems such as extreme melting of the film and loss of transparency. When iodine is used as the dichroism dye, the concentration of iodine / potassium iodide / water = 0.003 to 0.2 / 0.1 to 10/100, for example, at a temperature of 10 to 45 캜, preferably 20 to 35 캜, For 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may also be used in combination with potassium iodide. Further, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, and the like may be coexistent. When boric acid is added, it is distinguished from the boric acid treatment described below in that it contains iodine. If it contains 0.003 part by weight or more of iodine per 100 parts by weight of water, it can be regarded as a dyeing bath.

When a water-soluble dichroic dye is used as the dichroic dye, for example, a dye having a dichroic dye / water concentration of 0.001 to 0.1 / 100 at a temperature of 20 캜 to 80 캜, preferably 30 캜 to 70 캜, Second to 600 seconds, preferably 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may have a dyeing aid or the like, for example, an inorganic salt such as sodium sulfate, or a surfactant. The dichroic dye may be used singly or two or more dichroic dyes may be used at the same time.

When the unstretched polyvinyl alcohol film is treated in the order of the swelling process, the dyeing process and the crosslinking process, the film can be stretched in the dyeing bath. The stretching ratio of the total of the stretching magnifications combined in the dyeing step is usually 1.6 to 4.5 times, preferably 1.8 to 4.0 times. In addition, when the stretching ratio of the total of the stretching magnifications combined in the dyeing step is less than 1.6 times, the frequency of breaking of the film is increased, and the yield tends to deteriorate.

Stretching is performed by a method in which the nip rolls before and after the dyeing bath have a main speed difference or the like. In addition, as in the case of the swelling step, a widening roll (expander roll), a spiral roll, a crown roll, a cloth guider, a bent bar or the like may be provided in the dyeing bath and / or the dyeing bath entrance.

[Crosslinking Process]

The crosslinking step is carried out by immersing a polyvinyl alcohol-based film dyed with a dichroic dye into an aqueous solution containing 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye is iodine, iodide is preferably contained in an amount of 1 to 30 parts by weight. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may be coexistent.

The crosslinking step is carried out for water resistance and color adjustment (such as prevention of blue light) by crosslinking. For hydration by crosslinking, a crosslinking agent such as glyoxal, glutaraldehyde and the like may be used in addition to boric acid or boric acid, if necessary. The crosslinking step for water resistance may also be referred to as a waterproofing step, an immobilization step or the like. In addition, the crosslinking process for color adjustment may be referred to as a complementary process or a re-dyeing process.

The crosslinking step is carried out by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath, depending on the purpose. The crosslinking process for water resistance and the crosslinking process for color adjustment are not particularly discriminated but are carried out under the following conditions. When the swelling step is carried out by using an unstretched film and then the dyeing step and the crosslinking step are carried out. When the crosslinking step is aimed at water resistance, boric acid is added in an amount of 3 to 10 parts by weight And a boric acid treatment bath containing iodide in an amount of 1 to 20 parts by weight is usually used at a temperature of 50 캜 to 70 캜, preferably 53 캜 to 65 캜. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds. Further, in the case where the swelling step is carried out by using a previously stretched film, and then the dyeing step and the crosslinking step are carried out, the temperature of the boric acid treating bath is usually from 50 캜 to 85 캜, preferably from 55 캜 to 80 캜.

After the crosslinking treatment for water resistance, a crosslinking treatment for color adjustment may be performed. For example, when the dichroic dye is iodine, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodine is added to 100 parts by weight of water Lt; 0 > C to 45 < 0 > C. The immersing time is usually 1 to 300 seconds, preferably 2 to 100 seconds.

These crosslinking treatments may be performed a plurality of times, usually in two to five times. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above-mentioned range. The boric acid treatment for the water resistance and the boric acid treatment for the color adjustment may be performed in a plurality of steps, respectively. At that time, in order to sufficiently attain the effect of the present invention, it is preferable to set the boron content in the polarizing film to 2.5 to 4.5 wt%. In this case, the boric acid concentration in the crosslinking step is preferably 2.0 to 5.0 parts by weight .

The final integrated stretching magnification of the stretching of the polarizing film in the present embodiment is usually 4.5 to 7 times, preferably 5 to 6.5 times.

[Washing step]

After the crosslinking step, it is provided in the washing step. The water washing step is carried out, for example, by immersing a polyvinyl alcohol-based film treated with boric acid for water resistance and / or color tone adjustment in water, spraying water as a shower, or using immersion and spray in combination. The temperature of the water in the washing step is usually about 2 to 40 占 폚, and the immersing time is preferably 2 to 120 seconds.

[First drying step]

After the washing step, the polyvinyl alcohol-based film is provided in the first drying step. The thickness of the polyvinyl alcohol-based film is reduced by the first drying step. In the present invention, the degree of proper drying is indicated by the ratio of the thickness. That is, in the present invention, the relationship between the thickness Tb of the polarizing film in the polarizing plate after the second drying step, which will be described later, and the ratio Ta / Tb of the thickness Ta of the polarizing film before the bonding step after the first drying step is 1.02 to 1.30 The drying temperature and the drying time of the first drying step and the second drying step described later are controlled. The drying temperature in the first drying step may be, for example, 20 to 90 DEG C, and the drying time may be, for example, 10 to 300 seconds. In the first drying step, the drying temperature is preferably 20 to 70 DEG C and the drying time is preferably 10 to 120 seconds.

In the first drying step, the moisture content of the polarizing film is adjusted to be 12 to 45%, more preferably adjusted to 15 to 40%. If it is lower than 12%, the effect of decreasing the thickness in the second drying step, which will be described later, becomes small. If it is higher than 45%, the adhesion with the protective film is difficult to manifest sufficiently, Thereby causing a problem of contamination of the process. In the first drying step, there may be a plurality of zones having different temperatures. By combining a plurality of drying steps having different temperatures and times, the polarizing film can be easily dried to a desired moisture content, and can be appropriately colored.

Here, the moisture content refers to the amount of water required by the dry weight method and is obtained from the change in water content before and after the heat treatment at 105 占 폚 for 120 minutes,

Moisture content = (weight before heat treatment - weight after heat treatment) / weight before heat treatment x 100 (weight / weight%)

Can be obtained.

The drying method in the first drying step includes various methods such as a method of spraying hot air, a method of bringing into contact with a heat roll, a method of heating with an IR heater, all of which can be preferably used. The method of bringing the film into contact with a hot roll is preferable from the viewpoints of shortening the drying time since the drying efficiency is improved and suppressing shrinkage in the width direction of the film to enable wide width. The drying temperature in the drying step means the atmospheric temperature in the drying furnace in the case of a drying apparatus in which a drying furnace is installed such as a method of spraying hot air or an IR heater and in the case of a contact type drying equipment such as a heat roll , And the surface temperature of the heat roll. The polarizing film is produced through the above steps.

[Removal process]

In the production process of the polarizing film, there may be a thickness unevenness at both end portions of the polyvinyl alcohol-based film. In this case, there may be a removal step of cutting off both end portions where thickness unevenness is remarkable. The removing step may be performed, for example, after the crosslinking step, before the first drying step, or after the first drying step and before the bonding step described below. In the present invention, since the width of the polarizing film can be suppressed from shrinking, a polarizing film having a sufficient width and a uniform thickness can be produced even if both ends are removed by a removing step. Using the thus prepared polarizing film, the polarizing plate is further produced through the following steps.

[Joining process]

A protective film is bonded to one side or both sides of the polarizing film through an adhesive layer.

(Protective film)

Examples of the material constituting the protective film include a cycloolefin resin, a cellulose acetate resin, a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate, polycarbonate resin, acrylic resin Resin, and polypropylene, which are conventionally widely used in the field. When a protective film is bonded to both sides of a polarizing film, each protective film may be the same or may be a different kind of film.

The cycloolefin-based resin is a thermoplastic resin (also referred to as a thermoplastic cycloolefin-based resin) having a unit of a monomer containing a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene monomer. The cycloolefin resin may be a hydrogenated product of a ring-opening polymer of the cycloolefin or a ring-opening copolymer using two or more cycloolefins, or an addition polymer with a cycloolefin, a chain olefin, or an aromatic compound having a vinyl group. It is also effective that a polar group is introduced.

When a copolymer of a cycloolefin and an aromatic compound having a chain olefin and / or a vinyl group is used, examples of the chain olefin include ethylene and propylene. Examples of the aromatic compound having a vinyl group include styrene, Substituted styrene, and the like. In such a copolymer, the unit of the monomer containing the cycloolefin may be 50 mol% or less (preferably 15 to 50 mol%). In particular, in the case of using a ternary copolymer of a cycloolefin, a chain olefin and an aromatic compound having a vinyl group, the unit of the monomer containing the cycloolefin can be a relatively small amount as described above. In such a terpolymer, the unit of the monomer containing the chain olefin is usually 5 to 80 mol%, and the unit of the monomer containing the vinyl group-containing aromatic compound is usually 5 to 80 mol%.

Examples of the cycloolefin resin include commercially available products such as Topas (manufactured by Ticona), Aton (manufactured by JSR Corporation), Zeonor (manufactured by Nippon Zeon Co., Ltd.), Zeonex (ZEONEX) (manufactured by Nippon Zeon Co., Ltd.), APEL (manufactured by Mitsui Chemicals, Inc.), and OXIS (manufactured by Okura Kogyo Co., Ltd.). When the cycloolefin resin is formed into a film, known methods such as a solvent casting method and a melt extrusion method are suitably used. Further, a preformed cycloolefin such as, for example, Essen (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), Zeonor film (manufactured by Optesis) A commercially available product of a resin film may also be used.

The cycloolefin-based resin film may be uniaxially or biaxially stretched. By stretching, an arbitrary retardation value can be imparted to the cycloolefin-based resin film. The stretching is usually performed continuously while unwinding the film roll, and is stretched in the heating furnace in the direction of advancement of the roll (longitudinal direction of the film), in the direction perpendicular to the progressing direction thereof (width direction of the film), or both. The temperature of the heating furnace is usually in the range of the glass transition temperature + 100 deg. C in the vicinity of the glass transition temperature of the cycloolefin resin. The magnification of the stretching is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

When the cycloolefin-based resin film is in a roll-wound state, since the films tends to adhere to each other and blockage tends to occur, roll-winding is usually carried out after the protective film is bonded. Since the cycloolefin-based resin film generally has a low surface activity, the surface to be bonded to the polarizing film is preferably subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet ray irradiation treatment, frame (flame) treatment and saponification treatment Do. Among them, a plasma treatment, particularly an atmospheric pressure plasma treatment and a corona treatment, which can be carried out relatively easily, is preferable.

The cellulose acetate resin is a partial or complete esterified product of cellulose, and examples thereof include films containing acetic acid ester, propionic acid ester, butyric acid ester, mixed ester thereof and the like of cellulose. More specifically, a triacetylcellulose film, a diacetylcellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film and the like can be given. Examples of such a cellulose ester based resin film include commercially available products such as Fuji Tack TD80 (manufactured by Fuji Film), Fuji Tack TD80UF (manufactured by Fuji Film), Fuji Tack TD80UZ (manufactured by Fuji Film Co., Ltd.) , KC8UYW (manufactured by KONICA MINOLTA OPT Co., Ltd.), KC8UY (manufactured by Konica Minolta Optical Co., Ltd.), Fujitack TD60UL (manufactured by Fuji Film Co., Ltd.), KC4UYW Ltd.) and the like can be preferably used.

As the protective film, a cellulose acetate resin film imparted with a retardation property is also preferably used. Examples of commercial products of the cellulose acetate based resin film to which such retardation characteristics are imparted include WV BZ 438 (manufactured by Fuji Film), KC4FR-1 (manufactured by Konica Minolta Opt), KC4CR-1 (manufactured by Konica Minolta Opt ), KC4AR-1 (manufactured by Konica Minolta Opt.), And the like. Acetic acid cellulose is also referred to as acetylcellulose or cellulose acetate.

The thickness of the protective film used in the polarizing plate manufacturing method of the present invention is preferably small, but if it is too thin, the strength is lowered and the workability is lowered. On the other hand, if the thickness is too large, the transparency may deteriorate or the curing time required after lamination may be prolonged. Therefore, the suitable thickness of the protective film is, for example, 5 to 200 占 퐉, preferably 10 to 150 占 퐉, and more preferably 10 to 100 占 퐉.

A surface treatment such as a corona treatment, a flame treatment, a plasma treatment, an ultraviolet treatment, a primer coating treatment or a saponification treatment is performed on the polarizing film and / or the protective film to improve the adhesion between the adhesive and the polarizing film and / It is possible.

The protective film may be subjected to surface treatment such as anti-glare treatment, anti-reflection treatment, hard coating treatment, antistatic treatment and antifouling treatment, either singly or in combination of two or more kinds. In addition, the protective film and / or protective film surface protective layer may contain an ultraviolet absorber such as a benzophenone-based compound or a benzotriazole-based compound or a plasticizer such as a phenylphosphate-based compound or a phthalic acid ester compound.

In addition, the protective film can have optical functions such as a function as a retardation film, a function as a luminance enhancement film, a function as a reflective film, a function as a transflective film, a function as a diffusion film, and a function as an optical compensation film. In this case, for example, such functions can be obtained by laminating an optical functional film such as a retardation film, a luminance enhancement film, a reflection film, a transflective film, a diffusion film, or an optical compensation film on the surface of a protective film , The protective film itself may be provided with such a function. It is also possible to have a plurality of functions in a protective film, such as a diffusion film having the function of a brightness enhancement film.

For example, the stretching treatment described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc. is performed on the above-mentioned protective film, or the treatment described in Japanese Patent No. 3168850 is performed to give a function as a retardation film . The retardation characteristics in the retardation film can be suitably selected, for example, in the range of the front retardation value of 5 to 100 nm and the thickness retardation value of 40 to 300 nm. It is also possible to form fine holes by the method described in Japanese Patent Application Laid-Open Nos. 2002-169025 and 2003-29030, or to use two or more cholesteric layers having different center wavelengths By superimposing the steric liquid crystal layers, a function as a brightness enhancement film can be provided.

When a metal thin film is formed on the protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the above-mentioned protective film with a resin solution containing fine particles, a function as a diffusion film can be given. In addition, a function as an optical compensation film can be imparted by coating and orienting a liquid crystal compound such as a discotic liquid crystal compound on the above protective film. In addition, the protective film may contain a compound exhibiting a retardation. Further, various optical functional films may be directly bonded to the polarizing film by using a suitable adhesive. Examples of commercially available optical functional films include a luminance enhancement film such as DBEF (available from 3M Company, Japan, available from Sumitomo 3M Ltd.), a WV film (manufactured by Fuji Film Co., Ltd.) (Trade name) manufactured by Sekisui Chemical Co., Ltd.), VA-TAC (manufactured by Komica Minolta Optical Co., Ltd.) (Manufactured by Sumitomo Chemical Co., Ltd.), and Sumikarite (manufactured by Sumitomo Chemical Co., Ltd.).

(Adhesive layer)

Examples of the adhesive constituting the adhesive layer include an aqueous adhesive, an active energy ray-curable adhesive, and the like. When an aqueous adhesive is used, it is preferable to dry the polarizing film and dry the adhesive simultaneously in the second drying step.

As the water-based adhesive, for example, a polyvinyl alcohol-based resin aqueous solution, an aqueous two-component type urethane emulsion adhesive, and the like can be given. The polyvinyl alcohol-based resin used as the adhesive includes a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate which is a homopolymer of vinyl acetate, a vinyl alcohol obtained by saponifying a copolymer of vinyl acetate and another monomer copolymerizable therewith Based copolymers, and further modified polyvinyl alcohol polymers obtained by partially modifying hydroxyl groups thereof. As the water-based adhesive, polyaldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound and the like may be added as an additive. When such an aqueous adhesive is used, the adhesive layer obtained therefrom is usually much thinner than 1 占 퐉. The water-based adhesive is applied at a temperature of 15 to 40 캜 after its production, and the bonding temperature is usually in the range of 15 to 30 캜.

Examples of the active energy ray curable adhesive include adhesives including an epoxy resin composition containing an epoxy resin which is cured by irradiation with an active energy ray in view of weatherability, refractive index, cationic polymerizability, and the like. However, the present invention is not limited thereto. Various active energy ray curable adhesives (organic solvent adhesives, hot melt adhesives, solventless adhesives, etc.) conventionally used in the production of polarizing plates can be employed.

[Second drying step]

After the bonding step, a laminate including a polarizing film and a protective film is provided in the second drying step to produce a polarizing plate. The adhesive is dried by the second drying step, or the polarizing plate is dried so as to have an appropriate moisture content. By the second drying step, the thickness of the polyvinyl alcohol-based film is further reduced. In the present invention, the degree of proper drying is indicated by the ratio of the thickness. That is, as described above, after the first drying step and the ratio Ta / Tb of the thickness Ta of the polarizing film before the bonding step to the thickness Tb of the polarizing film in the polarizing plate after the second drying step satisfy the relationship of 1.02 to 1.30 The drying temperature and the drying time of the second drying step are controlled.

In the present invention, the degree of adequate drying is also indicated by the ratio of the width. That is, as described above, when the ratio Wb / Wa of the width Wb of the polarizing film in the polarizing plate after the first drying step and before the joining step with respect to the width Wa of the polarizing film after the second drying step satisfies the relationship of 0.960 or more and less than 1.000 The drying temperature and the drying time of the second drying step are controlled. The drying temperature in the second drying step may be, for example, 30 to 100 ° C, and the drying time may be 60 to 1200 seconds, for example. The drying method in the second drying step is similar to the first drying step described above. In the second drying step, it is preferable to provide a plurality of zones having different temperatures. By combining a plurality of drying steps with different temperatures and times, the polarizing plate can be easily dried up to a desired moisture content, and the color of the polarizing plate, Can be appropriately adjusted. The second drying step preferably includes a step of performing the treatment at a drying temperature higher than the maximum drying temperature of the first drying step. It is preferable that the second drying step includes a step of performing the treatment at a drying temperature higher than the drying temperature at the start of the process.

The water content of the finally obtained polarizing plate is preferably 1.5 to 3.0%. Outside of this range, problems of curling and appearance defects tend to occur. Particularly when the content is higher than 3.0%, the effect of reducing the thickness may be reduced.

When the ratio of the thickness to the ratio Ta / Tb is less than 1.02, most of the drying to adjust the moisture content of the polarizing film is performed in the first drying step. However, the greater the degree of drying in the first drying step, the greater the shrinkage of the width of the polarizing film becomes, which is not preferable. Therefore, in the present invention, by including the step of performing the treatment at the drying temperature higher than the maximum drying temperature of the first drying step in the second drying step, only a part of the drying for achieving the moisture content of the appropriate polarizing film is performed in the first drying step , And the second drying step performed after the protective film is bonded, the remaining moisture is adjusted as the final product and the remaining drying is performed, so that the shrinkage of the width of the polarizing film can be suppressed.

It is preferable that the second drying step includes a step of performing the treatment at a drying temperature higher than the drying temperature at the start of the process. That is, in the second drying step in which a plurality of zones are provided, it is preferable that after the second zone, a zone to be treated at a higher temperature than the first zone is desired. For example, the temperature of the first zone is less than 60 deg. C, and in the second zone and after, the temperature of at least one of the drying channels is 60 deg. C or more and the temperature is 60 deg. C or more, Lt; RTI ID = 0.0 > 60 C < / RTI > By doing so, after the polarizing film and the protective film are allowed to adhere, the thickness of the polarizing film can be sufficiently shrunk.

On the other hand, when the ratio of the thickness Ta / Tb is more than 1.30, the degree of drying in the first drying step is insufficient and the drying conditions in the second drying step should be strict. In the second drying step The occurrence of wrinkles on the surface of the polarizing plate, the process contamination such as film breakage, and the quality deterioration of the polarizing plate may be deteriorated.

As described above, by controlling the degree of drying in the first drying step and the second drying step, the polarizing plate can be manufactured so as to satisfy the relationship of the thickness ratio. The degree of shrinkage of the width of the polarizing film can be suppressed. In the case of using an aqueous adhesive in the bonding of the protective film, the drying step for evaporating the solvent of the adhesive may be the second drying step.

The polarizing plate thus produced has a polarizing film and a protective film bonded to at least one surface of the polarizing film and can be used as a polarizing plate of a liquid crystal display device. Further, according to the production method of the present invention, it is possible to produce a polarizing plate having optical properties such that, for example, the visual sensitivity-corrected single transmittance is 41.5% or more and the visual sensitivity correction polarization degree is 99.99% or more. Since the polarizing plate has such an optical characteristic, when a polarizing plate is used as a polarizing plate of a liquid crystal display device, a display of a good contrast ratio can be obtained.

Example

[Example 1]

(Production of polarizing film)

A polyvinyl alcohol film (Kurarabinetron VF-PS # 7500, degree of polymerization of 2,400, degree of saponification of 99.9 mol% or more) having a thickness of 75 탆 was immersed in pure water at 30 캜 while keeping the tension so that the film did not become loose, (Swelling process). Subsequently, uniaxial stretching was carried out while immersing iodine / potassium iodide / water in an aqueous solution having a weight ratio of 0.04 / 2.0 / 100 at 30 ° C (dyeing step), and potassium iodide / boric acid / And then immersed in an aqueous solution at 56 deg. C and subjected to crosslinking treatment to perform uniaxial stretching (cross-linking step and stretching step) until the total elongation percentage from the disc was 5.7 times. Subsequently, the substrate was immersed in an aqueous solution at 40 占 폚 in which potassium iodide / boric acid / water was 9 / 2.9 / 100 by weight, washed with pure water at 5 占 폚 and then dried under a drying condition of 30 占 폚 and a drying time of 50 seconds To obtain a polarizing film (first drying step). The obtained polarizing film had a thickness (Ta) of 33.1 탆, a width (Wa) of 225 mm and a water content of 30%.

(Preparation of adhesive)

(4% aqueous solution viscosity of 12.4 mPa · sec and saponification degree of 99.1 mol%, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.) was dissolved in deionized water, , 10% aqueous solution. The acetoacetyl group-modified polyvinyl alcohol-based resin aqueous solution and the sodium glyoxylate serving as a crosslinking agent were mixed so that the weight ratio of the former solids was 1: 0.1. Further, 100 parts of water was mixed with 100 parts of acetoacetyl modified polyvinyl alcohol And diluted with pure water so that one part of the resin was added to prepare an adhesive composition.

(Production of polarizing plate)

A film (KC8UX2MW, manufactured by Konica Minolta Opt) having a thickness of 80 占 퐉 and containing triacetylcellulose saponified on both sides of the obtained polarizing film was bonded with a nip roll through the adhesive and dried at 75 占 폚, And dried for a drying time of 150 seconds (second drying step) to obtain a polarizing plate. The polarizing film of the obtained polarizing plate had a thickness (Tb) of 27.0 mu m, a width (Wb) of 221 mm and a boron content of 3.8 wt%. That is, Ta / Tb was 1.23 and Wb / Wa was 0.982.

(Optical Properties of Polarizer)

To obtain the optical performance of the obtained polarizing plate, a polarizing plate was set on an ultraviolet visible spectrophotometer V7100 manufactured by Nippon Bunko Co., Ltd. and the ultraviolet visible spectrum of the polarizing plate in the transmission direction and the absorption direction was measured. The mass transmittance and the degree of polarization (visual sensitivity correction polarization degree) were calculated in accordance with JIS-Z8729. The optical characteristics of the polarizing plate of Example 1 were 42.5% for the visual sensitivity-corrected single-unit transmittance and 99.995% for the visibility-corrected polarization degree.

[Example 2]

(Production of polarizing film)

A polarizing film was produced in the same manner as in Example 1, except that the drying conditions in the first drying step were set at a drying temperature of 50 캜 and a drying time of 50 seconds. The obtained polarizing film had a thickness (Ta) of 32.1 占 퐉, a width (Wa) of 219 mm and a moisture content of 16%.

(Production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film of the obtained polarizing plate had a thickness (Tb) of 28.0 m, a width (Wb) of 217 mm and a boron content of 3.8% by weight. That is, Ta / Tb was 1.15 and Wb / Wa was 0.991. The optical characteristics of the polarizing plate of Example 2 were 42.5% for the visibility-corrected single-unit transmittance and 99.997% for the visibility-corrected polarized light.

[Example 3]

(Production of polarizing film)

A polarizing film was produced in the same manner as in Example 1. The obtained polarizing film had a thickness (Ta) of 33.1 占 퐉, a width (Wa) of 225 mm and a water content of 30% as in Example 1.

(Production of polarizing plate)

A polarizing plate was produced in the same manner as in Example 1 except that the drying conditions in the second drying step were set at a drying temperature of 90 캜 and a drying time of 150 seconds. The polarizing film of the resulting polarizing plate had a thickness (Tb) of 26.6 占 퐉, a width (Wb) of 219 mm and a boron content of 3.8% by weight. That is, Ta / Tb was 1.24 and Wb / Wa was 0.973. The optical characteristics of the polarizing plate of Example 3 were as follows: the visual sensitivity-corrected single-unit transmittance was 42.5%, and the visibility-corrected polarized light intensity was 99.996%.

[Example 4]

(Production of polarizing film)

A polarizing film was produced in the same manner as in Example 2 except that the weight ratio of potassium iodide / boric acid / water in the crosslinking treatment was 12 / 3.1 / 100. The obtained polarizing film had a thickness (Ta) of 32.8 占 퐉, a width (Wa) of 226mm and a moisture content of 22%.

(Production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 2. The polarizing film of the resulting polarizing plate had a thickness (Tb) of 27.2 占 퐉, a width (Wb) of 223 mm and a boron content of 3.2% by weight. That is, Ta / Tb was 1.21 and Wb / Wa was 0.987. The optical characteristics of the polarizing plate of Example 4 were 42.5% of the visual sensitivity-corrected single-unit transmittance and 99.993% of the visual sensitivity-corrected polarization degree.

[Comparative Example 1]

(Production of polarizing film)

A polarizing film was produced in the same manner as in Example 1, except that the drying conditions in the first drying step were set at a drying temperature of 80 캜 and a drying time of 150 seconds. The obtained polarizing film had a thickness (Ta) of 29.5 占 퐉, a width (Wa) of 213 mm and a moisture content of 9%.

(Production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film of the obtained polarizing plate had a thickness (Tb) of 29.5 占 퐉, a width (Wb) of 213 mm and a boron content of 3.9% by weight. That is, Ta / Tb was 1.00 and Wb / Wa was 1.00. In the optical characteristics of the polarizing plate of Comparative Example 1, the visual sensitivity-corrected single-unit transmittance was 42.5% and the visibility-corrected polarized light intensity was 99.996%.

[Comparative Example 2]

(Production of polarizing film)

A polarizing film was produced in the same manner as in Comparative Example 1 except that the total stretching magnification was 5.0 times. The obtained polarizing film had a thickness (Ta) of 34.4 占 퐉, a width (Wa) of 227 mm and a moisture content of 9.5%.

(Production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film of the obtained polarizing plate had a thickness (Tb) of 34.2 占 퐉, a width (Wb) of 227 mm and a boron content of 3.9% by weight. That is, Ta / Tb was 1.01 and Wb / Wa was 1.00. In the optical characteristics of the polarizing plate of Comparative Example 2, the visual sensitivity-corrected single-unit transmittance was 42.5% and the visibility-corrected polarized light intensity was 99.980%.

Table 1 below shows the results of Examples 1 to 4 and Comparative Examples 1 and 2.

As can be seen from Table 1, the drying conditions of the first drying step and the second drying step were thinner than those of the first and second comparative examples 1 and 2 according to Examples 1 to 4 in which the Ta / Tb was adjusted to be 1.02 to 1.30, It was found that a polarizing plate having a wide polarizing film and a good optical performance was obtained.

The polarizing plate produced by the manufacturing method of the present invention can be effectively applied to various display devices including a liquid crystal display device.

Claims (7)

A dyeing step of dyeing a polyvinyl alcohol-based film with a dichroic dye,
A crosslinking step of immersing the dyed polyvinyl alcohol-based film in a solution containing a crosslinking agent and crosslinking;
And a first drying step of drying the crosslinked polyvinyl alcohol-based film are sequentially performed to produce a polarizing film comprising a polyvinyl alcohol-based film,
A bonding step of bonding a protective film to at least one surface of the polarizing film through an adhesive layer to form a laminated body;
And a second drying step of drying the laminate are performed in this order to form a polarizing plate including the laminate,
Wherein the ratio of the thickness Ta of the polarizing film to the thickness Tb of the polarizing film in the polarizing plate after the second drying step after the first drying step and before the bonding step is 1.02 to 1.30. The method of claim 1, wherein the ratio Wb / Wa of the width Wb of the polarizing film in the polarizing plate after the first drying step to the width Wa of the polarizing film before the bonding step is not less than 0.960 and not more than 1.000 ≪ / RTI > The method of manufacturing a polarizing plate according to claim 1 or 2, wherein the polarizing film after the first drying step and before the bonding step has a water content of 12 to 45%. The method of producing a polarizing plate according to any one of claims 1 to 3, wherein the content of boron in the polarizing film of the polarizing plate after the second drying step is 2.5 to 4.5 wt%. The method of manufacturing a polarizing plate according to any one of claims 1 to 4, wherein the second drying step includes a step of performing a treatment at a drying temperature higher than a maximum drying temperature of the first drying step. The method of manufacturing a polarizing plate according to any one of claims 1 to 5, wherein the second drying step includes a step of performing a treatment at a drying temperature higher than a drying temperature at the start of the process. The method of manufacturing a polarizing plate according to any one of claims 1 to 6, further comprising a removing step of cutting and removing both ends of the polyvinyl alcohol film before the joining step.