JP2013178356A - Method for manufacturing polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing plate having sufficient optical performance by controlling a drying process to suppress shrinkage in the width of a polarizing film while reducing the thickness of the polarizing film.SOLUTION: The method for manufacturing a polarizing plate comprises: preparing a polarizing film by dyeing and crosslinking a polyvinyl alcohol film and then drying in a first drying step; laminating a protective film in a lamination step via an adhesive layer to at least one surface of a polarizing film to form a laminate; and drying the laminate in a second drying step. In the method, a ratio Ta/Tb, which is a ratio of the thickness Ta of the polarizing film after the first drying step and before the lamination step to the thickness Tb of the polarizing film in the polarizing plate after the second drying step, is from 1.02 to 1.30.

Description

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

  Liquid crystal display devices are used in various display devices by taking advantage of features such as low power consumption, operation at a low voltage, light weight and thinness. The liquid crystal display device is composed of many 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 reflecting sheet. Therefore, improvements aimed at productivity, weight reduction, brightness improvement, etc. are actively performed by reducing the number of constituent films 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 sides or one side of a polarizing film made of a polyvinyl alcohol-based resin having a dichroic dye adsorbed and oriented. For example, in Patent Document 1, as a polarizing plate having good hue and good durability, a polyvinyl alcohol film is iodine-dyed, and then crosslinked in a boric acid aqueous solution and uniaxially stretched on the surface of a polarizer. A polarizing plate provided with a protective film is disclosed.

  Patent Document 2 discloses a polarizing plate that establishes a certain relationship between the thickness of the synthetic resin film, the thickness of only the polarizer after the protective film is bonded, and the total draw ratio. It is disclosed.

JP 2004-341503 A JP 2002-40256 A

  In the method for producing a polarizing plate as described in Patent Documents 1 and 2, usually, after the crosslinking treatment, the polarizing film is subjected to a drying treatment in order to bring the moisture content of the polarizing film into an appropriate range. Is bonded via a water-based adhesive, and then a drying process is performed to remove the solvent of the adhesive. Since the thickness of the polarizing film can be reduced by the drying treatment, this is preferable in order to contribute to the thinning of the polarizing plate. However, the width of the polarizing film is reduced by the drying treatment, and the effective use area of the polarizing plate is reduced. Sometimes narrowed.

  The present invention provides a production method for producing a polarizing plate having sufficient optical performance by controlling the drying treatment so as to suppress the shrinkage of the width of the polarizing film while reducing the thickness of the polarizing film. With the goal.

  As a result of intensive studies, the present inventor conducted a first drying step performed on the polarizing film after the crosslinking treatment and before the protective film was bonded, and the lamination after the protective film was bonded to the polarizing film. About the drying process including the 2nd drying process performed with respect to a body, the drying degree of a 1st drying process and a 2nd drying process is controlled so that the thickness of the polarizing film after each drying process may satisfy | fill a predetermined relationship. Thus, the present inventors have found that a polarizing plate having excellent optical performance can be produced by suppressing the shrinkage of the width of the polarizing film while reducing the thickness of the polarizing film.

  That is, the present invention includes a dyeing process for dyeing a polyvinyl alcohol film with a dichroic dye, a crosslinking process in which the dyed polyvinyl alcohol film is immersed in a solution containing a crosslinking agent, and the crosslinked polyvinyl alcohol. A first drying step for drying the film, and producing a polarizing film comprising a polyvinyl alcohol film, and then laminating a protective film on at least one surface of the polarizing film via an adhesive layer. The manufacturing method which manufactures the polarizing plate which consists of a bonding process which forms a body, and the 2nd drying process which dries the said laminated body in order, and manufactures a laminated body, Comprising: Polarized light in the polarizing plate after a 2nd drying process The ratio Ta / Tb of the thickness Ta of the polarizing film after the first drying step and before the bonding step with respect to the film thickness Tb is 1.02 to 1.3. It is.

  By controlling the degree of drying between the first drying step and the second drying step so that the thickness of the polarizing film satisfies the above relationship, the width of the polarizing film is suppressed from shrinking while the thickness of the polarizing film is reduced. can do.

  Further, 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 is 0.960 or more and 1.000. It is preferable to control the degree of drying in the first drying step and the second drying step so as to be less than the minimum.

  In addition, in order to control as mentioned 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 is 12 to 45%.

  Moreover, in this invention, it is preferable that the content rate of the boron of the polarizing film in the polarizing plate finally obtained is 2.5-4.5 wt%.

  In the present invention, 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. In the present invention, the second drying step preferably includes a step of performing treatment at a drying temperature higher than the drying temperature at the start of the step.

  Moreover, in this invention, you may have further the removal process of cut | disconnecting and removing the both ends of a polyvinyl alcohol-type film before a bonding process.

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

  The method for producing a polarizing plate of the present invention includes a dyeing step of dyeing a polyvinyl alcohol film with a dichroic dye, a crosslinking step of immersing the dyed polyvinyl alcohol film in a solution containing a crosslinking agent, and crosslinking. The first drying step of drying the polyvinyl alcohol film is sequentially performed to produce a polarizing film made of the polyvinyl alcohol film, and then a protective film is bonded to at least one surface of the polarizing film via an adhesive layer. It is a manufacturing method which manufactures the polarizing plate which performs the bonding process which forms a laminated body, and the 2nd drying process which dries a laminated body in order, and consists of a laminated body. In the production 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 is 1 with respect to the thickness Tb of the polarizing film in the polarizing plate after the second drying step. The degree of drying in the first drying step and the second drying step is controlled so as to be 0.02 to 1.30. Hereinafter, details of each material and each process used in the present invention will be described.

(Polyvinyl alcohol film)
Examples of the polyvinyl alcohol-based resin that forms the polyvinyl alcohol-based film used in the production method of the present invention are typically saponified polyvinyl acetate-based resins. The degree of saponification is usually 85 mol% or more, preferably 90 mol% or more, more preferably 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. 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 10,000, preferably about 1500 to 5,000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used. Usually, as a starting material for manufacturing a polarizing film, an unstretched film of a polyvinyl alcohol film having a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm is used. A stretched film that has been previously stretched may be used. Industrially, the width of the film is practically 1500 mm to 6000 mm.

  As one embodiment of the present invention, first, using a non-stretched polyvinyl alcohol film, a polarizing film is produced by performing a swelling process, a dyeing process, a crosslinking process, a washing process, and a first drying process. When an unstretched film is used, the stretching process is performed either in any step or as a separate step in a wet or dry manner. Stretching can be performed by a known stretching method. Known stretching methods include inter-roll stretching that stretches with a difference in peripheral speed between two nip rolls that transport the film, a hot roll stretching method as described in Japanese Patent No. 2731813, a tenter stretching method, and the like. . Even when a stretched film is used, a stretching process may be further performed. The thickness of the polarizing film finally obtained through the first drying step is, for example, 5 to 50 μm.

[Swelling process]
The swelling step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next dyeing step, and plasticizing the film. The processing conditions are determined in such a range that these objectives can be achieved and in which a problem such as extreme dissolution and devitrification of the film does not occur. When the film previously stretched in the gas is swollen, for example, the film is immersed in an aqueous solution at 20 ° C. to 70 ° C., preferably 30 ° C. to 60 ° C. The immersion time of the film is preferably about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. When the unstretched raw film is swollen, for example, the film is immersed in an aqueous solution at 10 ° C to 50 ° C, preferably 20 ° C to 40 ° C. The immersion time of the film is preferably about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

  You may uniaxially stretch a polyvinyl alcohol-type film in a swelling process. 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, problems such as the film swelling in the width direction and wrinkling into the film are likely to occur, so known widening devices such as widening rolls (expander rolls), spiral rolls, crown rolls, cross guiders, bend bars, tenter clips, etc. It is preferable to transport the film while removing the wrinkles of the film. In order to stabilize the film transport in the swelling bath, the water flow in the swelling bath is controlled by an underwater shower, or an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents the film from meandering. ) Etc. are also useful. In this process, since the film swells and expands in the film running direction, if the film is not actively stretched, for example, the speed of the transport roll before and after the treatment tank is set to eliminate sagging of the film in the transport direction. It is preferable to take measures such as control. In addition to pure water, boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble are used as the swelling bath to be used. It is also possible to use an aqueous solution to which an organic solvent, alcohols and the like are added in an amount of 0.01 wt% to 10 wt%.

[Dyeing process]
The dyeing step with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The processing conditions are determined in such a range that these objectives can be achieved and in which a problem such as extreme dissolution and devitrification of the film does not occur. 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 in a weight ratio, iodine / potassium iodide / water = 0.003 to 0.2 / 0. The immersion treatment is performed at a concentration of 1 to 10/100 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 be used in combination with potassium iodide. In addition, compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, the temperature is 20 ° C. to 80 ° C., preferably 30 ° C. to 70 ° C., and the dichroic dye / water = 0.001 to. The immersion treatment is performed at a concentration of 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 have a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used at the same time.

  When an unstretched polyvinyl alcohol film is processed in the order of a swelling process, a dyeing process, and a crosslinking process, the film can be stretched also in a dyeing tank. The total draw ratio combined with the draw ratio in the dyeing step is usually 1.6 to 4.5 times, preferably 1.8 to 4.0 times. In addition, when the integrated draw ratio including the draw ratio in the dyeing process is less than 1.6 times, the frequency of film breakage increases, and the yield tends to deteriorate.

  Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling step, a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar, and the like can be installed in the dyeing bath and / or at the dyeing bath entrance / exit.

[Crosslinking process]
The crosslinking step is performed by immersing a polyvinyl alcohol film dyed with a dichroic dye in an aqueous solution containing 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain 1 to 30 parts by weight of iodide. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  The crosslinking step is carried out for water resistance and hue adjustment (for example, preventing bluish tint) due to crosslinking. For water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde other than boric acid or together with boric acid can be used as necessary. In addition, the bridge | crosslinking process for water resistance may be called with names, such as a water resistance process and an immobilization process. In some cases, the crosslinking process for hue adjustment is referred to as a complementary color process, a re-dying process, or the like.

  The crosslinking step is performed by appropriately changing the concentrations 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 adjusting the hue are not particularly distinguished, but are carried out under the following conditions. When a swelling process is performed using an unstretched film, and then a dyeing process and a crosslinking process are performed, and the crosslinking process aims at water resistance, 3 to 10 boric acid is added to 100 parts by weight of water. A boric acid treatment bath containing 1 part by weight and 1 to 20 parts by weight of iodide is used, and it is usually performed at a temperature of 50 ° C to 70 ° C, preferably 53 ° C to 65 ° C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds. In addition, when performing a swelling process using the film extended | stretched previously, and performing a dyeing process and a bridge | crosslinking process after that, the temperature of a boric-acid treatment bath is 50 to 85 degreeC normally, Preferably it is 55 to 80 degreeC. .

  You may perform the crosslinking process for hue adjustment after the crosslinking process for water resistance. For example, when the dichroic dye is iodine, for the purpose of adjusting the hue, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide for 100 parts by weight of water is used. It is usually used at a temperature of 10 ° C to 45 ° C. The immersion time is usually 1 to 300 seconds, preferably 2 to 100 seconds.

  These cross-linking treatments may be performed a plurality of times and are usually performed 2 to 5 times in many cases. 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 range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively. At that time, in order to sufficiently obtain the effects of the present invention, the boron content in the polarizing film is preferably set to 2.5 to 4.5% by weight. In this case, the boric acid concentration in the crosslinking step is set to 100% by weight of water. It is preferable to set it as 2.0-5.0 weight part with respect to a part.

  The final integrated draw ratio of the polarizing film in this embodiment is usually 4.5 to 7 times, preferably 5 to 6.5 times.

[Washing process]
After the crosslinking step, it is subjected to a water washing step. The water washing step is performed, for example, by immersing a polyvinyl alcohol film treated with boric acid for water resistance and / or color tone adjustment in water, spraying water as a shower, or using both immersion and spraying. The water temperature 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 film is subjected to the first drying step. The thickness of the polyvinyl alcohol film is reduced by the first drying step. In the present invention, an appropriate degree of drying is represented by a thickness ratio. That is, in 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 is relative to the thickness Tb of the polarizing film in the polarizing plate after the second drying step described later. The drying temperature and drying time of the first drying step and the second drying step described later are controlled so as to satisfy the relationship of 1.02 to 1.30. The drying temperature in the first drying step can be set to 20 to 90 ° C., for example, and the drying time can be set to 10 to 300 seconds, for example. In the first drying step, it is preferable that the drying temperature is 20 to 70 ° C. and the drying time is 10 to 120 seconds.

  In the first drying step, the moisture content of the polarizing film is adjusted to 12 to 45%, more preferably 15 to 40%. If it is lower than 12%, the effect of reducing the thickness in the second drying step described later is reduced, and if it is higher than 45%, adhesion with the protective film is not sufficiently exhibited, resulting in poor appearance and film in the line. The problem of breaking and contaminating the process is likely to occur. The first drying step may include a plurality of zones having different temperatures. By combining a plurality of drying steps with different temperatures and times, the polarizing film can be easily dried to a desired moisture content and can be appropriately colored.

The moisture content here refers to the moisture content determined by the dry weight method, and is obtained from the change in moisture content before and after the heat treatment at 105 ° C. for 120 minutes.
Moisture content = (weight before heat treatment−weight after heat treatment) / weight before heat treatment × 100 (weight / weight%)
Can be obtained by calculation.

  The drying method in the first drying step includes various methods such as a method of blowing hot air, a method of contacting with a hot roll, and a method of heating with an IR heater, and any of them can be suitably used. The method of drying by contacting with a heat roll is preferable in that the drying time can be shortened because the drying efficiency is improved, and the film can be widened by suppressing shrinkage in the width direction of the film. is there. The drying temperature in the drying process means the atmospheric temperature in the drying furnace in the case of a drying facility provided with a drying furnace such as a method of blowing hot air or an IR heater, and is a contact type drying such as a hot roll. In the case of equipment, it means the surface temperature of the hot roll. A polarizing film is manufactured through the above process.

[Removal process]
In the manufacturing process of a polarizing film, since a thickness nonuniformity may arise in the both ends of a polyvinyl-alcohol-type film, in this case, you may have a removal process which cut | disconnects and removes the both ends where a thickness nonuniformity is remarkable. The removing step can be performed, for example, after the crosslinking step and before the first drying step, or after the first drying step and before the bonding step described below. In the present invention, since the shrinkage of the width of the polarizing film can be suppressed, a polarizing film having a sufficient width and a uniform thickness can be produced even if both ends are removed by the removing step. . A polarizing plate is produced through the following steps using the polarizing film produced as described above.

[Bonding process]
A 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 cycloolefin resins, cellulose acetate resins, polyethylene terephthalate, polyethylene naphthalate, polyester resins such as polybutylene terephthalate, polycarbonate resins, acrylic resins, and polypropylene. Mention may be made of film materials that have been widely used in the field. When a protective film is bonded on both surfaces of a polarizing film, each protective film may be the same and 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 monomer unit made of a cyclic olefin (cycloolefin), such as norbornene or a polycyclic norbornene-based monomer. The cycloolefin-based resin may be a hydrogenated product of the above-mentioned cycloolefin ring-opening polymer or a ring-opening copolymer using two or more cycloolefins, and has a cycloolefin, a chain olefin, and a vinyl group. An addition polymer with an aromatic compound or the like may be used. Those having a polar group introduced are also effective.

  When using a copolymer of a cycloolefin and a chain olefin or / and an aromatic 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 Examples include styrene, α-methylstyrene, and nuclear alkyl-substituted styrene. In such a copolymer, the monomer unit composed of cycloolefin may be 50 mol% or less (preferably 15 to 50 mol%). In particular, when a terpolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group is used, the amount of the monomer unit composed of cycloolefin can be made relatively small as described above. In such a terpolymer, the monomer unit composed of a chain olefin is usually 5 to 80 mol%, and the monomer unit composed of an aromatic compound having a vinyl group is usually 5 to 80 mol%.

  Cycloolefin-based resins may be commercially available products such as Topas (manufactured by Ticona), Arton (manufactured by JSR), ZEONOR (manufactured by Nippon Zeon), ZEONEX (manufactured by Nippon Zeon ( Co., Ltd.), Apel (manufactured by Mitsui Chemicals, Inc.), Oxis (OXIS) (manufactured by Okura Kogyo Co., Ltd.) and the like can be suitably used. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, for example, commercially available cycloolefin resin films such as Essina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), Zeonoa Film (manufactured by Optes Co., Ltd.), etc. You may use goods.

  The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By stretching, an arbitrary retardation value can be given to the cycloolefin-based resin film. Stretching is usually performed continuously while unwinding a film roll, and in a heating furnace, the roll traveling direction (film longitudinal direction), the direction perpendicular to the traveling direction (film width direction), or both Stretched. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cycloolefin resin to the glass transition temperature + 100 ° C. is usually employed. The draw ratio 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 films tend to adhere to each other and easily cause blocking. Therefore, the cycloolefin-based resin film is usually rolled after the protective film is bonded. In addition, since the cycloolefin resin film generally has poor surface activity, the surface to be bonded to the polarizing film is subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment. Is preferred. Among these, plasma treatment that can be carried out relatively easily, particularly atmospheric pressure plasma treatment, and corona treatment are preferable.

  The cellulose acetate-based resin is a cellulose partial or completely esterified product, and examples thereof include a film made of cellulose acetate ester, propionate ester, butyrate ester, and mixed ester thereof. More specifically, a triacetyl cellulose film, a diacetyl cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, and the like can be given. As such a cellulose ester resin film, an appropriate commercially available product, for example, Fujitac TD80 (Fuji Film Co., Ltd.), Fujitac TD80UF (Fuji Film Co., Ltd.), Fujitac TD80UZ (Fuji Film Co., Ltd.) KC8UX2M (manufactured by Konica Minolta Opto), KC8UY (manufactured by Konica Minolta Opto) Fujitac TD60UL (manufactured by Fuji Film), KC4UYW (manufactured by Konica Minolta Opto), KC6UAW (Konica Minolta Opto) Etc.) can be used preferably.

  Moreover, the cellulose acetate type-resin film which provided the phase difference characteristic as a protective film is also used suitably. Commercially available cellulose acetate resin films to which such retardation characteristics are imparted include WV BZ 438 (manufactured by Fuji Film Co., Ltd.), KC4FR-1 (manufactured by Konica Minolta Opto), and KC4CR-1 (Konica Minolta). Opt Co., Ltd.), KC4AR-1 (Konica Minolta Opto Co., Ltd.) and the like. Cellulose acetate is also called acetyl cellulose 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 processability is poor. On the other hand, when it is too thick, problems such as a decrease in transparency and a longer curing time after lamination occur. Therefore, an appropriate thickness of the protective film is, for example, 5 to 200 μm, preferably 10 to 150 μm, and more preferably 10 to 100 μm.

  In order to improve the adhesion between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet treatment, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

  In addition, the protective film may be subjected to surface treatments such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment, either singly or in combination. 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.

  In addition, the protective film has a function as a retardation film, a function as a brightness enhancement film, a function as a reflection film, a function as a transflective film, a function as a diffusion film, a function as an optical compensation film, etc. Can have a function. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness enhancement film, a reflection film, a transflective film, a diffusion film, and an optical compensation film on the surface of the protective film, such a function is achieved. In addition, the protective film itself can be provided with such a function. In addition, a protective film may have a plurality of functions such as a diffusion film having a function of a brightness enhancement film.

  For example, the above-described protective film is subjected to a stretching process described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, or the like, or a process described in Japanese Patent No. 3168850 can be used as a retardation film. The function of can be provided. The retardation characteristics in the retardation film can be appropriately selected, for example, such that the front retardation value is 5 to 100 nm and the thickness direction retardation value is 40 to 300 nm. Further, two or more layers having different center wavelengths of selective reflection are formed in the protective film by forming micropores by a method as described in JP-A No. 2002-169025 and JP-A No. 2003-29030. By superimposing these cholesteric liquid crystal layers, a function as a brightness enhancement film can be imparted.

  If a metal thin film is formed on the above protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the protective film described above with a resin solution containing fine particles, a function as a diffusion film can be imparted. Moreover, the function as an optical compensation film can be provided by coating and aligning liquid crystalline compounds, such as a discotic liquid crystalline compound, on said protective film. Moreover, you may make the protective film contain the compound which expresses retardation. Further, various optical functional films may be directly bonded to the polarizing film using an appropriate adhesive. Examples of commercially available optical functional films include brightness enhancement films such as DBEF (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan), and viewing angle improvements such as WV film (manufactured by Fuji Film Co., Ltd.). Film, Arton Film (manufactured by JSR Corporation), Zeonoor Film (manufactured by Optes Corporation), Essina (manufactured by Sekisui Chemical Co., Ltd.), VA-TAC (manufactured by Comic Minolta Opto Corporation), Sumikalite (Sumitomo) (Chemical Co., Ltd.) etc. can be mentioned.

(Adhesive layer)
Examples of the adhesive constituting the adhesive layer include a water-based adhesive and an active energy ray-curable adhesive. When the water-based adhesive is used, the polarizing film and the adhesive can be dried at the same time in the second drying step, which is preferable.

  Examples of the water-based adhesive include a polyvinyl alcohol-based resin aqueous solution and a water-based two-component urethane emulsion adhesive. Polyvinyl alcohol resins used as adhesives include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. A polyhydric aldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound, or the like may be added as an additive to the water-based adhesive. When such a water-based adhesive is used, the adhesive layer obtained therefrom is usually much thinner than 1 μm. The aqueous adhesive is applied at a temperature of 15 to 40 ° C. after the preparation, and the bonding temperature is usually in the range of 15 to 30 ° C.

  Examples of the active energy ray-curable adhesive include an adhesive made of an epoxy resin composition containing an epoxy resin that is cured by irradiation with active energy rays from the viewpoint of weather resistance, refractive index, cationic polymerization, and the like. . However, the present invention is not limited to this, and various active energy ray-curable adhesives (organic solvent adhesives, hot melt adhesives, solventless adhesives) that have been used in the manufacture of polarizing plates. Etc.) can be adopted.

[Second drying step]
After the bonding step, the laminate composed of the polarizing film and the protective film is subjected to a second drying step to produce a polarizing plate. In the second drying step, the adhesive is dried and dried so that the polarizing plate has an appropriate moisture content. The thickness of the polyvinyl alcohol film is further reduced by the second drying step. In the present invention, an appropriate degree of drying is represented by a thickness ratio. That is, as described above, the ratio Ta / Tb of the polarizing film thickness Ta 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. The drying temperature and drying time of the second drying step are controlled so as to satisfy the relationship of ˜1.30.

  In the present invention, an appropriate degree of drying is also expressed by the width ratio. That is, 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 is 0.960. The drying temperature and the drying time in the second drying step are controlled so as to satisfy the relationship of above 1.000. The drying temperature in the second drying step can be, for example, 30 to 100 ° C., and the drying time can be, for example, 60 to 1200 seconds. The drying method in the second drying step is the same as that in the first drying step. It is preferable to provide a plurality of zones having different temperatures in the second drying step. By combining drying steps having different temperatures and times, the polarizing plate can be easily dried to a desired moisture content, and the hue and appearance of the polarizing plate Quality and curl can be adjusted moderately. 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. Moreover, it is preferable that a 2nd drying process includes the process performed at a drying temperature higher than the drying temperature at the time of a process start.

  The moisture content of the finally obtained polarizing plate is preferably 1.5 to 3.0%. If it is out of this range, the problem of curling or poor appearance tends to occur. In particular, when it is higher than 3.0%, the effect of reducing the thickness may be reduced.

  When the thickness ratio Ta / Tb is less than 1.02, most of the drying performed 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 more remarkable the shrinkage of the width of the polarizing film, which is not preferable. Therefore, in the present invention, in the second drying step, a part of the drying for obtaining an appropriate moisture content of the polarizing film by including a step of performing the treatment at a drying temperature higher than the maximum drying temperature of the first drying step. Only the first drying step is performed, and the second drying step performed after the protective film is bonded, the remaining drying is adjusted to an appropriate moisture content as the final product, thereby suppressing the width shrinkage of the polarizing film. This is preferable.

  Moreover, it is preferable that a 2nd drying process includes the process performed at a drying temperature higher than the drying temperature at the time of a process start. That is, in the second drying step in which a plurality of zones are provided, it is preferable to have a zone for processing at a temperature higher than that of the first zone after the second zone. For example, the temperature of the first zone is less than 60 ° C., and for the second zone and after, the temperature of at least one of the drying ovens is 60 ° C. or more, and the drying oven having this temperature of 60 ° C. or more is Preferably, it is set in the range of 60 ° C to 100 ° C. By doing so, after the adhesion between the polarizing film and the protective film is advanced, the thickness of the polarizing film can be sufficiently contracted.

  On the other hand, when the ratio Ta / Tb of the thickness exceeds 1.30, the degree of drying in the first drying step is not sufficient, and the drying conditions in the second drying step need to be strict. There may be a problem of process contamination such as generation of wrinkles and film breakage in the process, and deterioration of quality such as poor appearance of the polarizing plate.

  As described above, the polarizing plate can be manufactured so as to satisfy the relationship of the thickness ratio by controlling the degree of drying in the first drying step and the second drying step. And the degree of contraction of the width of the polarizing film can be suppressed. In the bonding of the protective film, when a water-based adhesive is used, the drying process performed for evaporating the solvent of the adhesive can be set as the second drying process.

  The polarizing plate produced as described above includes 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 for a liquid crystal display device. In addition, according to the manufacturing method of the present invention, for example, a polarizing plate having optical characteristics with a visibility corrected single transmittance of 41.5% or more and a visibility corrected polarization degree of 99.99% or more can be manufactured. Since the polarizing plate has such optical characteristics, when the polarizing plate is used as a polarizing plate of a liquid crystal display device, a display with a favorable contrast ratio can be obtained.

[Example 1]
(Preparation of polarizing film)
A 75-μm-thick polyvinyl alcohol film (Kurarevinylone VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) is kept in pure water at 30 ° C. so that the film does not loosen. The film was immersed as it was to swell the film sufficiently (swelling step). Next, after uniaxially stretching while immersing iodine and potassium iodide in a 30 ° C. aqueous solution having a weight ratio of 0.04 / 2.0 / 100 (dyeing step), potassium iodide / boric acid / water is weight. Uniaxial stretching was performed until the cumulative stretch ratio from the original film reached 5.7 times while being immersed in a 56 / ° C. aqueous solution having a ratio of 12 / 4.2 / 100 and crosslinking treatment (crosslinking step and stretching step). Next, after immersing in a 40 ° C. aqueous solution of 9 / 2.9 / 100 by weight of potassium iodide / boric acid / water, and subsequently washing with 5 ° C. pure water, a drying temperature of 30 ° C. and a drying time of 50 A polarizing film was obtained by performing a drying treatment under a second drying condition (first drying step). The obtained polarizing film had a thickness (Ta) of 33.1 μm, a width (Wa) of 225 mm, and a moisture content of 30%.

(Preparation of adhesive)
Pure acetoacetyl group-modified polyvinyl alcohol resin (trade name “Gosefimer Z-200”, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 4% aqueous solution viscosity 12.4 mPa · sec, saponification degree 99.1 mol%) A 10% strength aqueous solution was prepared by dissolving in water. This aqueous solution of acetoacetyl group-modified polyvinyl alcohol resin and sodium glyoxylate as a cross-linking agent are mixed so that the weight ratio of the former: latter solids is 1: 0.1, and further to 100 parts of water. The adhesive composition was prepared by diluting with pure water so that the acetoacetyl group-modified polyvinyl alcohol resin was 1 part.

(Preparation of polarizing plate)
A saponified triacetyl cellulose film 80 μm thick (KC8UX2MW, manufactured by Konica Minolta Opto Co., Ltd.) is pasted on both surfaces of the previously obtained polarizing film with a nip roll through the adhesive. The resultant was 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 in the obtained 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 was 1.23 and Wb / Wa was 0.982.

(Optical properties of polarizing plate)
In order to obtain the optical performance of the obtained polarizing plate, the polarizing plate was set in an ultraviolet-visible spectrophotometer V7100 manufactured by JASCO Corporation, and the UV-visible spectrum of the polarizing plate in the transmission direction and the absorption direction was measured. The single transmittance and the degree of polarization (visibility correction polarization degree) were obtained by calculation according to JIS-Z8729. Regarding the optical characteristics of the polarizing plate of Example 1, the visibility corrected single transmittance was 42.5%, and the visibility corrected polarization degree was 99.995%.

[Example 2]
(Preparation 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 a drying temperature of 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 moisture content of 16%.

(Preparation of polarizing plate)
A polarizing plate was obtained in the same manner as in Example 1. The polarizing film in the obtained 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. The optical characteristics of the polarizing plate of Example 2 were a visibility corrected single transmittance of 42.5% and a visibility corrected polarization degree of 99.997%.

[Example 3]
(Preparation of polarizing film)
A polarizing film was produced in the same manner as in Example 1. As in Example 1, the obtained polarizing film had a thickness (Ta) of 33.1 μm, a width (Wa) of 225 mm, and a moisture content of 30%.

(Preparation 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 a drying temperature of 90 ° C. and a drying time of 150 seconds. The polarizing film in the obtained 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. Regarding the optical characteristics of the polarizing plate of Example 3, the visibility corrected single transmittance was 42.5%, and the visibility corrected polarization degree was 99.996%.

[Example 4]
(Preparation 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 moisture content of 22%.

(Preparation of polarizing plate)
A polarizing plate was obtained in the same manner as in Example 2. The polarizing film in the obtained 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. Regarding the optical characteristics of the polarizing plate of Example 4, the visibility corrected single transmittance was 42.5%, and the visibility corrected polarization degree was 99.993%.

[Comparative Example 1]
(Preparation 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 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 moisture content of 9%.

(Preparation of polarizing plate)
A polarizing plate was obtained in the same manner as in Example 1. The polarizing film in the obtained 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 was 1.00 and Wb / Wa was 1.00. Regarding the optical characteristics of the polarizing plate of Comparative Example 1, the visibility corrected single transmittance was 42.5%, and the visibility corrected polarization degree was 99.996%.

[Comparative Example 2]
(Preparation of polarizing film)
A polarizing film was produced in the same manner as in Comparative Example 1 except that the cumulative draw ratio was 5.0. The obtained polarizing film had a thickness (Ta) of 34.4 μm, a width (Wa) of 227 mm, and a moisture content of 9.5%.

(Preparation of polarizing plate)
A polarizing plate was obtained in the same manner as in Example 1. The polarizing film in the obtained 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 was 1.01 and Wb / Wa was 1.00. The optical properties of the polarizing plate of Comparative Example 2 were a visibility corrected single transmittance of 42.5% and a visibility corrected polarization degree of 99.980%.

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

  As can be seen from Table 1, according to Examples 1-4 in which the drying conditions of the first drying step and the second drying step were adjusted so that Ta / Tb was 1.02-1.30, Comparative Example 1, 2 that the polarizing film in the polarizing plate was thin, wide, and a polarizing plate having a polarizing film with good optical performance was obtained.

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

Claims (7)

A dyeing step of dyeing a polyvinyl alcohol film with a dichroic dye;
A crosslinking step of immersing the dyed polyvinyl alcohol film in a solution containing a crosslinking agent to crosslink;
After the first drying step of drying the crosslinked polyvinyl alcohol-based film, and sequentially producing a polarizing film comprising a polyvinyl alcohol-based film,
A bonding step of forming a laminate by bonding a protective film to at least one surface of the polarizing film via an adhesive layer;
A production method for producing a polarizing plate comprising the laminate by sequentially performing a second drying step of drying the laminate.
The ratio Ta / Tb of the thickness Ta of the polarizing film after the first drying step and before the bonding step is 1.02 with respect to the thickness Tb of the polarizing film in the polarizing plate after the second drying step. The manufacturing method of a polarizing plate which is -1.30.   The ratio Wa / Wb 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 is 0.960. The manufacturing method of the polarizing plate of Claim 1 which is above 1.000.   The manufacturing method of the polarizing plate of Claim 1 or 2 whose moisture content of the said polarizing film after the said 1st drying process and before the said bonding process is 12 to 45%.   The manufacturing method of the polarizing plate in any one of Claims 1-3 whose boron content rate of the said polarizing film in the said polarizing plate after the said 2nd drying process is 2.5-4.5 wt%.   The said 2nd drying process is a manufacturing method of the polarizing plate in any one of Claims 1-4 including the process of processing at the drying temperature higher than the highest drying temperature of the said 1st drying process.   The said 2nd drying process is a manufacturing method of the polarizing plate in any one of Claims 1-5 including the process of performing a process with the drying temperature higher than the drying temperature at the time of the process start.   The manufacturing method of the polarizing plate in any one of Claims 1-6 which further has the removal process which cut | disconnects and removes the both ends of the said polyvinyl alcohol-type film before the said bonding process.