TW201339663A - Method for producing polarizing plate - Google Patents

Abstract

The present invention is a method for producing a polarizing plate, wherein: a polarizing film is produced by dyeing and crosslinking a polyvinyl alcohol film and then drying the polyvinyl alcohol film in a first drying step; and a polarizing plate is produced by carrying out a bonding step in which a laminate is formed by bonding a protective film on at least one surface of the polarizing film with an adhesive layer being interposed therebetween, and a second drying step in which the laminate is dried. The ratio of the thickness (Ta) of the polarizing film before the bonding step but after the first drying step to the thickness (Tb) of the polarizing film in the polarizing plate after the second drying step, namely Ta/Tb is from 1.02 to 1.30.

Description

Method for manufacturing polarizing plate

The present invention relates to a method of manufacturing a polarizing plate.

The liquid crystal display device is applied to various display devices by utilizing characteristics such as low power consumption, low voltage operation, light weight, and thinness. The liquid crystal display device includes a plurality of materials such as a liquid crystal cell, a polarizing plate, a retardation film, a condensing sheet, a diffusion film, a light guide plate, and a light reflection sheet. Therefore, improvement in productivity, weight reduction, and improvement in brightness is actively performed by reducing the number of sheets constituting the film or reducing the thickness of the film or sheet.

The polarizing plate usually has a configuration in which a protective film is laminated on both surfaces or a single surface of a polarizing film that adsorbs a polyvinyl alcohol-based resin having a dichroic dye. For example, in the polarizing plate which is excellent in hue and excellent in durability, it is disclosed that the polyvinyl alcohol film is dyed with iodine and then in a boric acid aqueous solution, as disclosed in Japanese Laid-Open Patent Publication No. 2004-341503 (Patent Document 1). A polarizing plate provided with a protective film on the surface of the polarizing element which is formed by cross-linking and uniaxially extending.

In Japanese Patent Laid-Open Publication No. 2002-40256 (Patent Document 2), it is disclosed that the thickness of the original sheet of the synthetic resin film and the thickness of only the polarizing element after bonding the protective film and the total stretching ratio are established. A polarizing plate with a certain relationship.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-341503

Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-40256

In the method for producing a polarizing plate described in Patent Documents 1 and 2, in order to perform a drying treatment after the crosslinking treatment, the water content of the polarizing film is set to an appropriate range, and the polarizing film is bonded and protected by a water-based adhesive. After the film, a drying treatment is performed in order to remove the solvent of the adhesive. According to the drying treatment, the thickness of the polarizing film can be reduced. Therefore, it is preferable to contribute to the thinning of the polarizing plate in this respect. However, the width of the polarizing film shrinks due to the drying process, and the effective use area of the polarizing plate is narrowed. situation.

An object of the present invention is to provide a method for producing a polarizing plate having sufficient optical properties by controlling the drying process so as to reduce the thickness of the polarizing film and suppress the shrinkage of the width of the polarizing film.

The inventors of the present invention have conducted intensive studies and found that the first drying step including the polarizing film before the bonding treatment after the crosslinking treatment is performed, and the laminated body after the protective film is bonded to the polarizing film The drying process of the second drying step is performed to control the degree of drying of the first drying step and the second drying step so that the thickness of the polarizing film after each drying step satisfies a specific relationship, thereby reducing the thickness of the polarizing film and suppressing it. The shrinkage of the width of the polarizing film can further produce a polarizing plate having excellent optical properties, thereby completing the present invention.

That is, the present invention is a method for producing a polarizing plate, which is a dyeing step of dyeing a polyvinyl alcohol-based film with a dichroic dye, and immersing the dyed polyvinyl alcohol-based film in a crosslinking agent-containing layer. a cross-linking step of crosslinking in the solution and a first drying step of drying the crosslinked polyvinyl alcohol-based film to produce a polarizing film comprising a polyvinyl alcohol-based film, followed by sequentially passing through the adhesive layer a bonding step of bonding a protective film to at least one surface of the polarizing film to form a laminated body, and a second drying step of drying the laminated body to produce a polarizing plate including a laminated body; and after the first drying step Pre-step polarizing film The ratio Ta/Tb of the thickness Ta to the thickness Tb of the polarizing film in the polarizing plate after the second drying 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 relationship, the thickness of the polarizing film can be reduced and the shrinkage of the width of the polarizing film can be suppressed.

Moreover, it is preferable that the ratio Wb/Wa of the width Wb of the polarizing film in the polarizing plate after the second drying step to the width Wa of the polarizing film before the first drying step and before the bonding step is 0.960 or more and less than The method of 1.000 controls the degree of drying of the first drying step and the second drying step.

Further, in order to control in the above manner, it is preferred to carry out the first drying step so that the water content of the polarizing film after the first drying step and before the bonding step is 12 to 45%.

Further, in the present invention, it is preferred that the polarizing film in the polarizing plate finally obtained has a boron content of 2.5 to 4.5 wt%.

In the present invention, preferably, the second drying step includes a step of treating at a drying temperature higher than a highest drying temperature of the first drying step. Further, in the invention, it is preferable that the second drying step includes a step of performing treatment at a drying temperature higher than a drying temperature at the start of the step.

Moreover, in the present invention, the removal step of cutting both ends of the polyvinyl alcohol-based film before the bonding step may be further included.

According to the production method of the present invention, it is possible to manufacture a polarizing plate which is thin and has excellent polarizing performance while suppressing shrinkage of the width of the polarizing film which is generated in the manufacturing stage.

The method for producing a polarizing plate of the present invention is as follows: sequentially performing polyvinyl alcohol a dyeing step of dyeing a 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 crosslinking the polyvinyl alcohol-based film After the polarizing film including the polyvinyl alcohol-based film is produced in the first drying step of drying, the bonding step of bonding the protective film to at least one surface of the polarizing film via the adhesive layer to form a laminated body, and laminating The second drying step of the body drying produces a polarizing plate including a laminate. In the manufacturing method of the present invention, the ratio Ta/Tb of the thickness Ta of the polarizing film after the first drying step and before the bonding step to the thickness Tb of the polarizing film in the polarizing plate after the second drying step is 1.02~ In the manner of 1.30, the degree of drying in the first drying step and the second drying step is controlled. Hereinafter, each material and each step used in the present invention will be described in detail.

(polyvinyl alcohol film)

The polyvinyl alcohol-based resin of the polyvinyl alcohol-based film used in the production method of the present invention is usually saponified with a polyvinyl acetate-based resin. The degree of saponification is usually 85 mol% or more, preferably 90 mol% or more, more preferably 99 mol% to 100 mol%. As the polyvinyl acetate-based resin, in addition to the polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and other monomers copolymerizable therewith, for example, an ethylene-vinyl acetate copolymer, may be mentioned. Wait. Examples of the other monomer which can be copolymerized include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually from 1,000 to 10,000, preferably from about 1,500 to 5,000.

These polyvinyl alcohol-based resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral or the like which is modified with an aldehyde may be used. As a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol-based film having a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm, is usually used. Further, a stretched film which has been subjected to elongation treatment in advance may also be used. In the industry, the width of the film is practical from 1500 mm to 6000 mm.

As an embodiment of the present invention, first, a polarizing film is produced by a swelling step, a dyeing step, a crosslinking step, a water washing step, and a first drying step using an unstretched polyvinyl alcohol film. In the case where an unstretched film is used, the stretching treatment is carried out in either step or as a separate step in a wet or dry manner. The extension can be carried out by a known extension method. As a known extension method, there is a roll-to-roll extension in which a circumferential speed difference is set between two nip rolls of a transfer film, a hot roll extension method described in Japanese Patent No. 2731813, a tenter stretching method, and the like. Even in the case of using a stretched film, the stretching treatment can be further carried out. The thickness of the polarizing film finally obtained through the first drying step is, for example, 5 to 50 μm.

[swelling step]

The swelling step is carried out for the purpose of removing foreign matter on the surface of the film, removing the plasticizer in the film, imparting dyeability in the subsequent dyeing step, plasticizing the film, and the like. The treatment conditions are determined within a range in which such a purpose can be achieved without causing adverse effects such as extreme dissolution or devitrification of the membrane. In the case where the film which has been previously extended in the gas is swollen, for example, the film is immersed in an aqueous solution of 20 to 70 ° C, preferably 30 to 60 ° C. The immersion time of the film is preferably from 30 seconds to 300 seconds, and more preferably from about 60 seconds to 240 seconds. When the unextended green film is swollen, for example, the film is immersed in an aqueous solution of 10 ° C to 50 ° C, preferably 20 ° C to 40 ° C. The immersion time of the film is preferably from 30 seconds to 300 seconds, and more preferably from about 60 seconds to 240 seconds.

In the swelling step, uniaxial stretching of the polyvinyl alcohol film can also be carried out. In this case, the stretching ratio is usually 1.2 to 3.0 times, preferably 1.3 to 2.5 times.

In the swelling step, since the film is likely to be swollen in the width direction to cause wrinkles on the film, it is preferable to use an expander roller, a spiral roller, a crown roll, and a guide cloth. A known spreader such as a cloth guider, a bend bar, or a tenter clip removes the wrinkles of the film and conveys the film. In order to stabilize the film transport in the swelling bath, it is also useful to control the swelling by a water shower (shower). The water flow in the bath or the EPC device (edge position control device: an end portion of the film to detect the bending of the film) and the like. In this step, since the film is swollen and expanded in the direction in which the film is moved, when the film is not actively extended, in order to eliminate the relaxation of the film in the transport direction, it is preferable to carry out, for example, control before and after the treatment tank. The speed of the roller and the like. In addition, in addition to the pure water, boric acid may be added to the swelling bath to be used in the range of 0.01% by weight to 10% by weight (described in Japanese Patent Laid-Open No. Hei 10-153709), and chloride (Japan) An aqueous solution of an inorganic acid, an inorganic salt, a water-soluble organic solvent, or an alcohol is described in JP-A-06-281816.

[staining step]

The dyeing step by the dichroic dye is carried out for the purpose of adsorbing the dichroic dye on the film and orienting it. The treatment conditions are determined within a range in which such a purpose can be achieved without causing adverse effects such as extreme dissolution or devitrification of the membrane. When iodine is used as the dichroic dye, for example, at a temperature of 10 ° C to 45 ° C, preferably 20 ° C to 35 ° C, and by weight ratio, iodine / potassium iodide / water = 0.003 ~ 0.2 / 0.1 The immersion treatment is carried out at a concentration of ~10/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. Other iodides such as zinc iodide may be used instead of potassium iodide. Further, other iodides may be used in combination with potassium iodide. Further, a compound other than the iodide such as boric acid, zinc chloride, cobalt chloride or the like may be allowed to coexist. In the case of adding boric acid, it can be distinguished from the following boric acid treatment in terms of containing iodine. If it contains 0.003 part by weight or more of iodine with respect to 100 parts by weight of water, it can be used as a dyeing tank.

When a water-soluble dichroic dye is used as the dichroic dye, for example, at a temperature of from 20 ° C to 80 ° C, preferably from 30 ° C to 70 ° C, and by weight ratio, dichroic dye/water The immersion treatment is carried out at a concentration of 0.001 to 0.1/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. The dichroic dye may be used singly or in combination of two or more kinds of dichroic dyes.

When the unstretched polyvinyl alcohol-based film is treated in the order of the swelling step, the dyeing step, and the crosslinking step, the film may be stretched in the dyeing tank. The cumulative stretching ratio obtained by totaling the stretching ratio in the dyeing step is usually 1.6 to 4.5 times, preferably 1.8 to 4.0 times. In addition, when the cumulative stretching ratio obtained by totaling the stretching ratio in the dyeing step is less than 1.6 times, the frequency of cracking of the film tends to increase, and the yield tends to deteriorate.

The extension is performed by a method such as generating a circumferential speed difference between the nip rolls before and after the dyeing tank. Further, in the same manner as the swelling step, an expander roller, a spiral roller, a medium-high roller, a cloth guide, a bending bar, or the like may be placed in the dye bath and/or the entrance and exit of the dye bath.

[Crosslinking step]

The crosslinking step is carried out by immersing the polyvinyl alcohol-based film dyed with the dichroic dye in 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, it preferably contains 1 to 30 parts by weight of the iodide. Examples of the iodide include potassium iodide, zinc iodide, and the like. Further, a compound other than the iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate or the like may be allowed to coexist.

The crosslinking step is carried out in order to perform water resistance, hue adjustment (preventing bluish blue, etc.) by crosslinking. In the water resistance by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde may be used in addition to or in addition to boric acid. Further, the crosslinking step for water resistance is sometimes referred to by a name such as a water resistance step and an immobilization step. Further, the cross-linking step for hue adjustment is sometimes referred to by a name such as a complementary color step or a re-dyeing step.

The crosslinking step is carried out by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath according to the purpose. The crosslinking step for water resistance and the crosslinking step for hue adjustment are not particularly distinguished and are carried out under the following conditions. When the swelling step is carried out using an unstretched film, followed by the dyeing step and the crosslinking step, and the crosslinking step is for the purpose of hydration resistance, 3 to 10 parts by weight of boric acid and iodine are used with respect to 100 parts by weight of water. The boric acid treatment bath of 1 to 20 parts by weight of the compound is usually carried out at a temperature of from 50 ° C to 70 ° C, preferably from 53 ° C to 65 ° C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more Good for 20~200 seconds. Further, in the case where the swelling step is carried out using a pre-stretched film, and then the dyeing step and the crosslinking step are carried out, the temperature of the boric acid treatment bath is usually from 50 ° C to 85 ° C, preferably from 55 ° C to 80 ° C.

The cross-linking treatment for hue adjustment can also be carried out after the cross-linking treatment for water resistance. For example, when the dichroic dye is iodine, for the purpose of hue adjustment, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide per 100 parts by weight of water is used, usually at 10 ° C. It is carried out at a temperature of 45 °C. The immersion time is usually from 1 to 300 seconds, preferably from 2 to 100 seconds.

The cross-linking treatment can be performed plural times, usually 2 to 5 times in many cases. In this case, the aqueous solution composition and the temperature of each of the boric acid treatment tanks used may be the same or different in the above range. The above-described boric acid treatment for water resistance and boric acid treatment for hue adjustment may be carried out in a plurality of steps. In this case, in order to sufficiently obtain the effects of the present invention, it is preferred to set the boron content in the polarizing film to 2.5 to 4.5% by weight. In this case, it is preferred to carry out the crosslinking step with respect to 100 parts by weight of water. The boric acid concentration in the medium is set to 2.0 to 5.0 parts by weight.

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

[washing step]

It is supplied to the water washing step after the crosslinking step. The water washing step is carried out, for example, by immersing the boric acid-treated polyvinyl alcohol-based film for water hydration and/or color tone adjustment in water, spraying the water with a water sprayer, or using both immersion and spraying. The temperature of the water in the water washing step is usually about 2 to 40 ° C, and the immersion time is preferably 2 to 120 seconds.

[First drying step]

After the water washing step, the polyvinyl alcohol-based film is supplied to the first drying step. The thickness of the polyvinyl alcohol-based film is lowered by the first drying step. In the present invention, the degree of dryness is indicated by the ratio of the thicknesses. That is, in the present invention, after the first drying step and the bonding step The first drying step and the second drying described below are controlled so that the ratio Ta/Tb of the thickness Ta of the front polarizing film to the thickness Tb of the polarizing film in the polarizing plate after the second drying step satisfies the relationship of 1.02 to 1.30. Drying temperature and drying time of the step. The drying temperature in the first drying step can be set, for example, to 20 to 90 ° C, and the drying time can be set, for example, to 10 to 300 seconds. In the first drying step, the drying temperature is preferably 20 to 70 ° C, and the drying time is 10 to 120 seconds.

The moisture content of the polarizing film in the first drying step is adjusted to 12 to 45%, more preferably 15 to 40%. When the amount is less than 12%, the effect of lowering the thickness in the second drying step described below becomes small, and when it is higher than 45%, it is difficult to sufficiently exhibit the adhesion to the protective film, and the appearance is liable to be poor or The film breaks in the line and contaminates the steps and the like. The first drying step may also include a plurality of regions of 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 colorization is moderately performed.

The water content referred to herein means the water content obtained by the dry weight method, and is obtained by changing the water content before and after the heat treatment at 105 ° C for 120 minutes, and can be obtained by the following formula: moisture content = (weight before heat treatment) - weight after heat treatment) / weight before heat treatment × 100 (weight/weight%)

Calculated and calculated.

The drying method in the first drying step may be any of various methods such as a method of blowing hot air, a method of contacting a heat roll, and a method of heating by an IR (Infra-red) heater, and any of them may be preferably used. The method of drying in contact with the heat roller improves the drying efficiency, so that the drying time can be shortened, and the shrinkage in the width direction of the film can be suppressed, and the width can be increased. In addition, the drying temperature in the drying step refers to the case where the drying apparatus of the drying furnace is provided as in the method of blowing hot air or the IR heater, etc., and refers to the ambient temperature in the drying furnace, such as the contact type of the hot roll. In the case of a drying device, it refers to the surface temperature of the heat roller. A polarizing film was produced through the above steps.

[Removal steps]

In the production step of the polarizing film, thickness unevenness may occur in both end portions of the polyvinyl alcohol-based film. Therefore, in this case, a removal step of cutting both ends of the thickness unevenness may be included. . The removal step can be carried out, for example, after the crosslinking step and before the first drying step, or after the first drying step and before the bonding step described. In the present invention, since the shrinkage of the width of the polarizing film can be suppressed, even if both ends are removed by the removing step, the width is sufficiently wide, and a polarizing film having a more uniform thickness can be produced. Using the polarizing film manufactured in the above manner, a polarizing plate was further produced through the following procedure.

[Finishing step]

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

(protective film)

Examples of the material constituting the protective film include a cycloolefin resin, a cellulose acetate resin, and a polycondensation such as polyethylene terephthalate or polyethylene naphthalate or polybutylene terephthalate. A film material which has been widely used in the field, such as an ester resin, a polycarbonate resin, an acrylic resin, and polypropylene. When the protective film is bonded to both surfaces of the polarizing film, the protective films may be the same or different types of films.

The cycloolefin-based resin, for example, has a Alkene A thermoplastic resin (also referred to as a thermoplastic cycloolefin resin) containing a unit of a monomer of a cyclic olefin (cycloolefin) of an olefinic monomer. The cycloolefin resin may be a ring-opening polymer of the above cycloolefin or a hydrogenated product of a ring-opening copolymer of two or more kinds of cyclic olefins, or a cyclic olefin, a chain olefin, an aromatic compound having a vinyl group or the like. Addition polymer. Also, it is effective to introduce a polar base.

In the case of using a copolymer of a cyclic olefin and a chain olefin or/and a vinyl compound having a vinyl group, examples of the chain olefin include ethylene and propylene, and examples of the aromatic compound having a vinyl group include Styrene, α-methylstyrene, nucleoalkyl-substituted styrene, and the like. In such a copolymer, the unit of the monomer containing a cycloolefin may be 50 mol% The following (preferably 15 to 50% by mole). Particularly in the case of using a terpolymer of a cyclic olefin and a chain olefin and an aromatic compound having a vinyl group, the unit of the monomer containing a cyclic olefin can be set to a relatively small amount as described above. In the terpolymer, the unit of the monomer containing a chain olefin is usually 5 to 80 mol%, and the unit of the monomer containing the aromatic compound having a vinyl group is usually 5 to 80 mol%.

As the cycloolefin-based resin, a commercially available product such as Topas (manufactured by Ticona Co., Ltd.), ARTON (manufactured by JSR Co., Ltd.), ZEONOR (manufactured by Nippon Zeon Co., Ltd.), and ZEONEX (Japan Rygne Co., Ltd.) can be preferably used. Manufactured by the company, APEL (manufactured by Mitsui Chemicals Co., Ltd.), OXIS (manufactured by Okura Industrial Co., Ltd.), etc. When a film is formed by forming a film of such a cycloolefin resin, a known method such as a solvent casting method or a melt extrusion method can be suitably used. Further, a cycloolefin-based resin obtained by preliminarily forming a film, such as S-SINA (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), or ZEONOR Film (manufactured by Optes Co., Ltd.), may be used. A commercially available product of the film.

The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By extending, an arbitrary phase difference value can be given to the cycloolefin type resin film. The stretching is generally performed while the film roll is being wound up, and is extended by the heating furnace in the forward direction of the roll (the longitudinal direction of the film), the direction perpendicular to the advancing direction (the width direction of the film), or both. The temperature of the heating furnace is usually in the range from the vicinity of the glass transition temperature of the cycloolefin-based resin to the glass transition temperature + 100 °C. The magnification of the extension 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, the film tends to adhere to each other and tends to cause adhesion. Therefore, the film is usually wound after the protective film is bonded. Further, since the cycloolefin resin film generally has poor surface activity, it is preferred to carry out surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, or saponification treatment on the surface adjacent to the polarizing film. Among them, it is preferred that the plasma treatment can be carried out relatively easily, especially Atmospheric piezoelectric slurry treatment and corona treatment.

The cellulose acetate-based resin is a partial or complete esterified product of cellulose, and examples thereof include a film containing cellulose acetate, propionate, butyrate, or a mixed ester thereof. More specifically, a triethylene fluorene cellulose film, a diethyl fluorene cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, etc. are mentioned. As such a cellulose ester-based resin film, a commercially available product such as FUJITAC TD80 (manufactured by FUJI FILM Co., Ltd.), FUJITAC TD80UF (manufactured by FUJI FILM Co., Ltd.), and FUJITAC TD80UZ (FUJI FILM Co., Ltd.) can be preferably used. Co., Ltd.), KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.), KC8UY (manufactured by Konica Minolta Opto Co., Ltd.), FUJITAC TD60UL (manufactured by FUJI FILM Co., Ltd.), KC4UYW (manufactured by Konica Minolta Opto Co., Ltd.), KC6UAW (manufactured by Konica Minolta Opto Co., Ltd.), etc.

Moreover, as the protective film, a cellulose acetate-based resin film to which phase difference characteristics are imparted can be preferably used. The commercially available product of the cellulose acetate-based resin film to which the phase difference property is imparted is, for example, WV BZ 438 (manufactured by FUJI FILM Co., Ltd.), KC4FR-1 (manufactured by Konica Minolta Opto Co., Ltd.), and KC4CR-1. (manufactured by Konica Minolta Opto Co., Ltd.), KC4AR-1 (manufactured by Konica Minolta Opto Co., Ltd.), and the like. Cellulose acetate is also known as acetaminophen or cellulose acetate.

The thickness of the protective film used in the method for producing a polarizing plate of the present invention is preferably thin, but if it is too thin, the strength is lowered, and the workability is poor. On the other hand, if it is too thick, there arises a problem that transparency is lowered or the curing time required after lamination is long. Therefore, the appropriate thickness of the protective film is, for example, 5 to 200 μm, preferably 10 to 150 μm, more preferably 10 to 100 μm.

In order to improve the adhesion between the adhesive and the polarizing film and/or the protective film, corona treatment, flame treatment, plasma treatment, ultraviolet treatment, primer coating treatment, saponification treatment, etc. may be performed on the polarizing film and/or the protective film. Surface treatment.

Further, two or more kinds of surface treatments such as anti-glare treatment, anti-reflection treatment, hard coating treatment, antistatic treatment, and antifouling treatment may be carried out separately or in combination on the protective film. Further, the protective film and/or the protective film surface protective layer may contain a UV absorber such as a benzophenone compound or a benzotriazole compound, or a plasticizer such as a phenyl phosphate compound or a phthalate compound. .

Further, the protective film can have a function as a retardation film, a function as a brightness enhancement film, a function as a reflection film, a function as a semi-transmissive reflection film, a function as a diffusion film, and a function as an optical compensation film. Features. In this case, for example, by an optical functional film such as a surface layer retardation film, a brightness enhancement film, a reflection film, a semi-transmissive reflection film, a diffusion film, or an optical compensation film on the surface layer of the protective film, in addition to the above functions, The above function can also be imparted to the protective film itself. Further, the protective film may have a plurality of functions as in the case of a diffusion film having a function of a brightness enhancement film.

For example, the protective film described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, and the like, or the processing described in Japanese Patent No. 3168850, can be used as a function of a retardation film. . The phase difference characteristic in the retardation film can be appropriately selected, for example, from 5 to 100 nm in the front phase difference value and from 40 to 300 nm in the thickness direction. Further, on the above-mentioned protective film, fine pores are formed by a method as described in JP-A-2002-169025 or JP-A-2003-29030, or the center wavelength of the reflection is different by overlapping. Two or more layers of the cholesteric liquid crystal layer can impart a function as a brightness enhancement film.

When a metal thin film is formed on the protective film by vapor deposition, sputtering, or the like, it can be provided as a reflective film or a semi-transmissive reflective film. By applying a resin solution containing fine particles to the above protective film, it is possible to impart a function as a diffusion film. In addition, by applying a liquid crystal compound such as a discotic liquid crystalline compound to the protective film and aligning it, it is possible to provide a function as an optical compensation film. Further, the protective film may contain a compound exhibiting a phase difference. Further, various optical functional films can be directly bonded to each other by using an appropriate adhesive. On the polarizing film. As a commercially available product of the optical functional film, for example, a brightness enhancement film such as DBEF (manufactured by 3M Company, available from Sumitomo 3M Co., Ltd. in Japan), and a viewing angle improving film such as WV Film (manufactured by FUJI FILM Co., Ltd.) , ARTON Film (manufactured by JSR Co., Ltd.), ZEONOR Film (manufactured by Optes Co., Ltd.), S-SINA (manufactured by Sekisui Chemical Co., Ltd.), VA-TAC (manufactured by Konica Minolta Opto Co., Ltd.), Sumikalite (Sumitomo) A retardation film, etc., manufactured by Chemical Co., Ltd.).

(adhesive layer)

Examples of the adhesive constituting the adhesive layer include a water-based adhesive, an active energy ray-curable adhesive, and the like. In the case of using a water-based adhesive, it is preferred to simultaneously perform drying of the polarizing film and drying of the adhesive in the second drying step.

Examples of the water-based adhesive include a polyvinyl alcohol-based resin aqueous solution and an aqueous two-liquid urethane-based latex adhesive. In the polyvinyl alcohol-based resin used as the adhesive, in addition to the vinyl alcohol homopolymer obtained by saponifying the polyvinyl acetate which is a homopolymer of vinyl acetate, vinyl acetate is also available. The vinyl alcohol-based copolymer obtained by the saponification treatment of the copolymer of the other monomer copolymerized with the copolymer, and the modified polyvinyl alcohol-based polymer obtained by modifying the hydroxyl group. A polyvalent aldehyde, a water-soluble epoxy compound, a melamine-based compound, a zirconia compound, a zinc compound or the like may be added as an additive to the aqueous binder. In the case of using such a water-based adhesive, the adhesive layer obtained therefrom is usually much thinner than 1 μm. After the water-based adhesive is prepared, it is applied at a temperature of 15 to 40 ° C, and the bonding temperature is usually in the range of 15 to 30 ° C.

An epoxy resin composition containing an epoxy resin which is cured by irradiation with an active energy ray is used as an adhesive agent for an active energy ray-curing type, in terms of weather resistance, refractive index, cationic polymerization property, and the like. Follow-up agent. However, the present invention is not limited thereto, and various active energy ray-curable adhesives (organic solvent-based adhesives, hot-melt adhesives, solvent-free adhesives, and the like) which have been used in the production of polarizing plates have been used.

[2nd drying step]

After the bonding step, the laminate including the polarizing film and the protective film is supplied to the second drying step to produce a polarizing plate. In the second drying step, the adhesive is dried, and the polarizing plate is dried so as to have a suitable moisture content. Further, the thickness of the polyvinyl alcohol-based film can be reduced by the second drying step. In the present invention, the degree of dryness is indicated by the ratio of the thicknesses. That is, as described above, the ratio Ta/Tb of the thickness Ta of the polarizing film after the first drying step and before the bonding step to the thickness Tb of the polarizing film in the polarizing plate after the second drying step satisfies 1.02 to 1.30. The relationship between the drying temperature and the drying time of the second drying step is controlled.

Further, in the present invention, the degree of drying is also indicated by the ratio of the widths. In other words, as described above, the ratio Wb/Wa of the width Wb of the polarizing film in the polarizing plate after the second drying step to the width Wa of the polarizing film after the first drying step and before the bonding step satisfies 0.960 or more. The drying temperature and drying time of the second drying step are controlled in a manner of up to 1.000. The drying temperature in the second drying step can be set, for example, to 30 to 100 ° C, and the drying time can be set, for example, to 60 to 1200 seconds. The drying method in the second drying step is the same as the first drying step described above. Preferably, the second drying step is provided with a plurality of regions having different temperatures. By combining a plurality of drying steps with different temperatures and times, the polarizing plate can be easily dried to a desired moisture content, and the polarizing plate can be appropriately adjusted. Hue, appearance quality, curl. Preferably, the second drying step comprises the step of treating at a drying temperature higher than the highest drying temperature of the first drying step. Further, it is preferable that the second drying step includes a step of performing treatment at a drying temperature higher than a drying temperature at the start of the step.

Preferably, the polarizing plate finally obtained has a water content of 1.5 to 3.0%. When it is out of this range, the problem of curling or poor appearance is liable to occur, and in particular, when it is more than 3.0%, the effect of reducing the thickness becomes small.

When the ratio Ta/Tb of the above thickness is less than 1.02, most of the drying performed to adjust the water 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 more pronounced the shrinkage of the width of the polarizing film, and thus Poor. Therefore, in the present invention, in the second drying step, only the moisture content of the polarizing film to be suitable is set by the step of treating at a drying temperature higher than the highest drying temperature of the first drying step. A part of the drying is performed in the first drying step, and the second drying step performed after bonding the protective film is performed as a final product to adjust the remaining moisture to a suitable moisture content, thereby suppressing the width of the polarizing film. The contraction is preferred.

Further, it is preferred to carry out the treatment in the second drying step at a drying temperature higher than the drying temperature at the start of the step. That is, it is preferable that the second drying step in which a plurality of regions are provided is included in the region which is processed at a temperature higher than the first region after the second region. For example, the temperature of the first region is less than 60 ° C, and after the second region, the temperature of at least one of the drying furnaces is 60 ° C or higher, and the drying furnace having the temperature of 60 ° C or higher is preferably set at 60 ° C. Range of °C~100°C. By doing so, the thickness of the polarizing film can be sufficiently contracted after the polarizing film and the protective film are followed.

On the other hand, when the ratio Ta/Tb of the above thickness exceeds 1.30, there is a case where the degree of drying in the first drying step is insufficient, and it is necessary to set the drying condition of the second drying step to a stricter condition, resulting in The problem of contamination such as generation of wrinkles or film breakage in the second drying step, and deterioration in quality such as poor appearance of the polarizing plate.

As described above, by controlling the degree of drying of 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 described above. Further, the degree of shrinkage of the width of the polarizing film can be suppressed. When a water-based adhesive is used for bonding the protective film, the drying step for evaporating the solvent of the adhesive may be a second drying step.

The polarizing plate manufactured in the above manner includes a polarizing film and a protective film attached 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, for example, a polarizing plate having an optical property of a visibility correction monomer transmittance of 41.5% or more and a visibility correction polarization degree of 99.99% or more can be produced. By using the polarizing plate to have such an optical characteristic, when the polarizing plate is used as a polarizing plate of a liquid crystal display device, Get a good contrast display.

Example

[Example 1]

(production of polarizing film)

A polyvinyl alcohol film (Kuraray Vinylon VF-PS #7500, polymerization degree 2,400, saponification degree: 99.9 mol% or more) having a thickness of 75 μm was immersed in pure water at 30 ° C in a state in which the film was not relaxed. And the film is sufficiently swollen (swelling step). Then, one side was immersed in an aqueous solution of 30% by weight of iodine/potassium iodide/water in a weight ratio of 0.04/2.0/100, followed by uniaxial stretching (dyeing step), and one side was immersed in potassium iodide/boric acid/water. The cross-linking treatment was carried out in an aqueous solution of 56° C. in a weight ratio of 12/4.2/100, and uniaxially stretched until the cumulative stretching ratio from the original sheet was 5.7 (crosslinking step and stretching step). Next, it was immersed in an aqueous solution of potassium iodide/boric acid/water in a weight ratio of 9/2.9/100 at 40 ° C, followed by washing with pure water of 5 ° C, at a drying temperature of 30 ° C and a drying time of 50. The drying treatment was carried out under dry conditions of seconds to obtain a polarizing film (first drying step). The obtained polarizing film had a thickness (Ta) of 33.1 μm, a width (Wa) of 225 mm, and a water content of 30%.

(preparation of adhesive)

Ethyl acetonitrile-modified polyvinyl alcohol-based resin (trade name "GOHSEFIMER Z-200", manufactured by Nippon Synthetic Chemical Co., Ltd., 4% aqueous solution viscosity 12.4 mPa.sec, saponification degree: 99.1 mol%) was dissolved in Pure water was used to prepare a 10% aqueous solution. The acetonitrile-modified polyvinyl alcohol-based resin aqueous solution and the sodium glyoxylate which is a crosslinking agent are mixed in such a manner that the weight ratio of the solid content of the latter is 1:0.1, and further, relative to water 100. An adhesive composition was prepared by diluting with a pure water in the form of a acetonitrile-modified polyvinyl alcohol-based resin in a portion.

(production of polarizing plate)

The thickness of the triacetyl cellulose subjected to saponification treatment is 80 μm by nip rolls The film (KC8UX2MW, manufactured by Konica Minolta Opto Co., Ltd.) was bonded to both sides of the previously obtained polarizing film via the above-mentioned adhesive, and dried under the drying conditions of a drying temperature of 75 ° C and a drying time of 150 seconds (second drying). Step) to obtain a polarizing plate. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 27.0 μm, a width (Wb) of 221 mm, and a boron content of 3.8 wt%. That is, Ta/Tb is 1.23, and Wb/Wa is 0.982.

(Optical characteristics of polarizing plate)

In order to determine the optical properties of the obtained polarizing plate, an ultraviolet-visible spectrophotometer V7100 manufactured by JASCO Corporation was placed on a polarizing plate, and the ultraviolet visible spectrum of the polarizing plate in the direction of penetration and the direction of absorption was measured. The monomer transmittance and the degree of polarization (visibility correction polarization) were determined by calculation according to JIS-Z8729. In the optical characteristics of the polarizing plate of Example 1, the visibility correction monomer transmittance was 42.5%, and the visibility correction polarization degree was 99.995%.

[Embodiment 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 50 ° C and a drying time of 50 seconds. The obtained polarizing film had a thickness (Ta) of 32.1 μm, a width (Wa) of 219 mm, and a water content of 16%.

(production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 28.0 μm, a width (Wb) of 217 mm, and a boron content of 3.8 wt%. That is, Ta/Tb was 1.15, and Wb/Wa was 0.991. In the optical characteristics of the polarizing plate of Example 2, the visibility correction monomer transmittance was 42.5%, and the visibility correction polarization degree was 99.997%.

[Example 3]

(production of polarizing film)

A polarizing film was produced in the same manner as in Example 1. The polarizing film obtained had a thickness (Ta) of 33.1 μm, a width (Wa) of 225 mm, and a water content of 30% in the same manner 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 changed to a drying temperature of 90 ° C and a drying time of 150 seconds. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 26.6 μm, a width (Wb) of 219 mm, and a boron content of 3.8 wt%. That is, Ta/Tb was 1.24, and Wb/Wa was 0.973. In the optical characteristics of the polarizing plate of Example 3, the visibility correction monomer transmittance was 42.5%, and the visibility correction polarization degree 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 μm, a width (Wa) of 226 mm, and a water content of 22%.

(production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 2. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 27.2 μm, a width (Wb) of 223 mm, and a boron content of 3.2 wt%. That is, Ta/Tb was 1.21, and Wb/Wa was 0.987. In the optical characteristics of the polarizing plate of Example 4, the visibility correction monomer transmittance was 42.5%, and the visibility correction polarization degree was 99.993%.

[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 changed to a drying temperature of 80 ° C and a drying time of 150 seconds. The obtained polarizing film had a thickness (Ta) of 29.5 μm, a width (Wa) of 213 mm, and a water content of 9%.

(production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 29.5 μm, a width (Wb) of 213 mm, and a boron content of 3.9 wt%. That is, Ta/Tb is 1.00, and Wb/Wa is 1.00. In the optical characteristics of the polarizing plate of Comparative Example 1, it can be seen The corrected monomer transmittance was 42.5%, and the visibility corrected polarization 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 cumulative stretching ratio was 5.0. The obtained polarizing film had a thickness (Ta) of 34.4 μm, a width (Wa) of 227 mm, and a water content of 9.5%.

(production of polarizing plate)

A polarizing plate was obtained in the same manner as in Example 1. The polarizing film obtained in the polarizing plate had a thickness (Tb) of 34.2 μm, a width (Wb) of 227 mm, and a boron content of 3.9 wt%. That is, Ta/Tb is 1.01, and Wb/Wa is 1.00. In the optical characteristics of the polarizing plate of Comparative Example 2, the visibility correction monomer transmittance was 42.5%, and the visibility correction polarization degree was 99.980%.

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

As can be seen from Table 1, according to Examples 1 to 4 in which the drying conditions of the first drying step and the second drying step were adjusted such that Ta/Tb was 1.02 to 1.30, it was found to be thinner than Comparative Examples 1 and 2. A polarizing film of a polarizing film which is wide and has excellent optical properties.

Industrial availability

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

Claims (7)

A method for producing a polarizing plate, comprising: performing a dyeing step of dyeing a polyvinyl alcohol-based film with a dichroic dye, and immersing the dyed polyvinyl alcohol-based film in a solution containing a crosslinking agent; After the cross-linking step of crosslinking and the first drying step of drying the crosslinked polyvinyl alcohol-based film to produce a polarizing film containing a polyvinyl alcohol-based film, the protective film is sequentially attached via the adhesive layer. a bonding step of forming a laminate on at least one surface of the polarizing film and a second drying step of drying the laminate to produce a polarizing plate comprising the laminate; and after the first drying step and the bonding The ratio Ta/Tb of the thickness Ta of the polarizing film before the step to the thickness Tb of the polarizing film in the polarizing plate after the second drying step is 1.02 to 1.30. The method for producing a polarizing plate according to claim 1, wherein a width Wb of the polarizing film in the polarizing plate after the second drying step is larger than a width of the polarizing film after the first drying step and before the bonding step The ratio W of Wb/Wa is 0.960 or more and less than 1.000. The method for producing 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 for producing a polarizing plate according to any one of claims 1 to 3, wherein a boron content of the polarizing film in the polarizing plate after the second drying step is 2.5 to 4.5 wt%. The method for producing a polarizing plate according to any one of claims 1 to 4, wherein the second drying step is carried out at a drying temperature higher than a highest drying temperature of the first drying step The steps to proceed. The method of producing a polarizing plate according to any one of claims 1 to 5, wherein the second drying step comprises a step of treating at a drying temperature higher than a drying temperature at the beginning of the step. The method for producing a polarizing plate according to any one of claims 1 to 6, further comprising a step of removing the both ends of the polyvinyl alcohol film before the bonding step.