TWI443389B - Process for producing polarizer - Google Patents

Description

Method for manufacturing polarizing plate

The present invention relates to a method for producing a polarizing plate, which comprises laminating a protective film on one side of a polarizing film made of a polyvinyl alcohol resin via an adhesive layer, thereby producing a polarizing plate.

A polarizing plate is widely used as a polarizing supply element in a liquid crystal display device or a polarizing detecting element. In the past, such a polarizing plate has been formed by using a protective film made of cellulose triacetate followed by a polarizing film made of polyvinyl alcohol, but in recent years, liquid crystal display devices have become more and more popular for notebook computers and mobile phones. Such as portable devices, and even extended to use in large TVs, etc., and required thin and lightweight. In addition, since it becomes portable and the use place becomes wider, it is also required to improve durability.

In order to achieve a thin and light weight, a polarizing plate in which only a protective film is laminated on one side of a polarizing film is proposed in order to achieve a reduction in thickness and weight. Japanese Laid-Open Patent Publication No. 2007-193333 (Patent Document 2) proposes a method of producing a polarizing plate in which only a protective film is laminated on one side of a polarizing film to form a polarizing plate. However, as described in the above-mentioned Patent Documents 1 and 2, when only a protective film is laminated on one side of the polarizing film to produce a polarizing plate, in the drying step of drying the polarizing film and the protective film, When the polarizing film side of the polarizing plate is disposed below and the protective film side is placed upward, curling of the protective film side into a convex shape (thus causing the polarizing film side to be convex) is likely to occur (referred to as reverse curling). )problem.

When the reverse curl is large, when the polarizing film is bonded to the liquid crystal panel via the adhesive layer or the like in a direction in which the surface of the liquid crystal panel is aligned with the liquid crystal panel (that is, the protective film is positioned outside from the liquid crystal panel), It is known that air bubbles are easily generated between the pressure-sensitive adhesive layer and the liquid crystal panel (for example, refer to Japanese Laid-Open Patent Publication No. 2004-184809 (Patent Document 3)).

This reverse curl is considered to be caused by shrinkage of the polarizing film in the drying step after the polarizing film and the protective film are laminated, and can be suppressed by drying at a temperature at which the polarizing film is less likely to shrink at 40 ° C or lower. On the other hand, when the drying temperature is low, in order to sufficiently dry the polarizing plate, it takes a long time to dry, and there is a problem in production. If drying is desired for a limited period of time, the polarizing plate may be uneven due to insufficient drying. This unevenness causes the image of the fluorescent lamp to be significantly deformed when the fluorescent lamp is reflected on the surface of the polarizing plate. Fig. 1 shows a state in which the fluorescent lamp is reflected on the surface of the polarizing plate where unevenness occurs, and it is understood that the image of the fluorescent lamp is significantly deformed.

Accordingly, an object of the present invention is to provide a method for efficiently producing a polarizing plate by laminating a protective film on one side of a polarizing film composed of a polyvinyl alcohol resin via an adhesive layer, thereby producing a small curling condition. Polarized plate.

In order to achieve the above object, the inventors of the present invention have found that when a protective film is laminated on one side of a polarizing film made of a polyvinyl alcohol resin via a water-based adhesive layer to produce a polarizing plate, a water-based adhesive is used. After the polarizing film and the protective film are laminated in a layer, the polarizing plate having a small curling condition can be effectively obtained by drying under specific drying conditions. That is, the present invention is as follows.

The present invention provides a method for producing a polarizing plate, comprising the steps of: bonding a protective film to one side of a polarizing film made of a polyvinyl alcohol resin via a water-based adhesive layer, and polarizing A drying step of drying the film and the protective film. Wherein, the drying step comprises the steps of: retaining in a drying oven maintained at a temperature of less than 50 ° C until the total residence time is 150 seconds or more, and retaining in a drying oven maintained at a temperature of 50 ° C or higher. The high-temperature drying step until the total residence time is 150 seconds or less.

In the method for producing a polarizing plate of the present invention, the drying step is preferably carried out in the order of a low temperature drying step, a high temperature drying step, and a low temperature drying step.

The protective film in the method for producing a polarizing plate of the present invention is preferably a film composed of a cellulose acetate resin.

In the method for producing a polarizing plate of the present invention, the drying furnace temperature in the high-temperature drying step is preferably maintained at 60 ° C or lower.

According to the present invention, since the protective film is laminated on one side of the polarizing film composed of polyvinyl alcohol, the thickness of the polarizing plate can be made thinner and more effective than the polarizing plate in which the protective film is laminated on both sides. A polarizing plate having a small amount of curl is produced.

The method for producing a polarizing plate of the present invention basically comprises the steps of: bonding a protective film to one side of a polarizing film made of a polyvinyl alcohol resin via a water-based adhesive layer, and subjecting the polarizing film to A drying step in which the cover of the protective film is dried under specific conditions. According to the method for producing a polarizing plate of the present invention, since the protective film is laminated on one side of the polarizing film composed of polyvinyl alcohol, the thickness of the polarizing plate can be made thicker than the polarizing plate in which the protective film is laminated on both sides. It is thinned and can effectively produce a polarizing plate having a small amount of curl.

In the method for producing a polarizing plate of the present invention, the polarizing film of the bonding step is supplied, specifically, the uniaxial stretching is applied to the polyvinyl alcohol resin film, and the dyeing treatment is performed by the dichroic dye, and the dichroic dye is adsorbed and aligned. Founder. The polyvinyl alcohol resin constituting the polarizing film can be usually obtained by saponifying a polyvinyl acetate resin. The degree of saponification of the polyvinyl alcohol resin is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. In the case of the polyvinyl acetate-based resin, in addition to the polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer such as vinyl acetate and other monomers copolymerizable therewith, such as ethylene-acetic acid, may also be mentioned. Vinyl ester copolymer and the like. Examples of the other monomer copolymerizable with vinyl acetate include an unsaturated carboxylic acid, an olefin, a vinyl ether, an unsaturated sulfonic acid, and the like. The degree of polymerization of the polyvinyl alcohol resin is usually from about 1,000 to 10,000, preferably from about 1,500 to 5,000.

These polyvinyl alcohol resins may also be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral may be used. Wait. In general, in the case of producing a raw material of a polarizing film, an unstretched film of a polyvinyl alcohol resin film having a thickness of 20 to 100 μm (preferably 30 to 80 μm) is used. Industrially, the film width is 1500 to 4000 nm. The unstretched film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, and uniaxially stretched in the step up to the boric acid treatment, and finally the thickness of the polarizing film obtained by drying is, for example, 5 Up to 50 μm.

The manufacturing method of the polarizing film is roughly divided into two manufacturing methods. In the first method, after the polyvinyl alcohol resin film is uniaxially stretched in air or an inert gas, the solution treatment is carried out in the order of the swelling treatment step, the dyeing treatment step, the boric acid treatment step, and the water washing treatment step, and finally the drying method is performed. . In the second method, the unstretched polyvinyl alcohol resin film is subjected to solution treatment in the order of the aqueous solution swelling treatment step, the dyeing treatment step, the boric acid treatment step and the water washing treatment step, and in the boric acid treatment step and/or the previous step. The method of uniaxially stretching in a wet manner and finally drying.

In either method, the uniaxial stretching can be carried out in one step or in two or more steps, but it is preferably carried out in a plurality of steps. The stretching method may be a well-known method, for example, a method of stretching between rolls of a nip between rolls of a film having a peripheral speed difference, and a heat roll stretching method as described in Japanese Patent No. 2731813. The tenter extension method and the like. Further, the order of the basic steps is as described above, but the number of processing baths, processing conditions, and the like are not limited. Further, steps not described in the first and second methods may be added for other purposes. Examples of such steps include, for example, immersion treatment (iodide treatment) with a boric acid-free iodide solution after boric acid treatment or immersion treatment with an aqueous solution containing boric acid or the like without boric acid (zinc) Processing) and so on.

The swelling treatment 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 to the next step, plasticizing the film, and the like. The treatment conditions are determined within the range in which such a purpose can be achieved, and in a range in which the substrate film is not extremely dissolved and no devitrification occurs. When the film which has been previously stretched 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 from 30 to 300 seconds, preferably from 60 to 240 seconds. On the other hand, when the original film which has not been stretched first is swelled, for example, the film is immersed in an aqueous solution of 10 to 50 ° C, preferably 20 to 40 ° C. The immersion time of the film is from 30 to 300 seconds, preferably from 60 to 240 seconds.

In the swelling treatment step, the film is likely to swell in the width direction to cause wrinkles and the like in the film. Therefore, it is preferable to use a widening roller (expansion roller), a spiral roller, a crown roll, a cloth guider, a bend bar, a tenter clip, and the like. The expansion device removes wrinkles from the film and simultaneously transports the film. For the purpose of stabilizing the transport of the film in the bath, the water in the swelling bath is controlled by a shower in the water, or EPC (Edge Position Control device: a device for detecting the end of the film and preventing the meandering of the film) is used in combination. The method is also useful. In this step, since the film is swollen and expanded in the direction in which the film is conveyed, it is preferable to remove the speed of the film in the transport direction, for example, to control the speed of the transport roller before and after the treatment tank. In addition, as for the swelling treatment bath to be used, in addition to pure water, boric acid (described in JP-A-10-153709) and chloride (described in JP-A-H06-153709) can be used in the range of 0.01 to 0.1% by weight. An aqueous solution of inorganic acid, inorganic salt, water-soluble organic solvent, alcohol, or the like.

A dyeing treatment step using a dichroic dye, the purpose of which is to adsorb and align a dichroic dye in a film. The processing conditions are within the range in which such effects can be attained, and are determined within a range in which the substrate film is not extremely dissolved and no devitrification occurs. When iodine is used as the dichroic dye, for example, at a temperature of 10 to 45 ° C (preferably 20 to 35 ° C), the weight ratio is iodine / potassium iodide / water = (0.003 to 0.2) / (0.1 to An aqueous solution having a concentration of 10)/100 is subjected to an immersion treatment for 30 to 600 seconds (preferably 60 to 300 seconds). Other iodides (such as zinc iodide, etc.) can also be used in place of potassium iodide. Further, other iodides may be used together with potassium iodide. Further, a compound other than the iodide such as boric acid, zinc chloride, cobalt chloride or the like may be coexisted. When boric acid is added, it contains iodine and is distinguished from the following boric acid treatment. It is considered to be a dyeing tank as long as it contains 0.003 parts by weight or more of iodine per 100 parts by weight of water.

When a dichroic dye is used as the water-soluble dichroic dye, for example, at a temperature of 20 to 80 ° C (preferably 30 to 70 ° C), the weight ratio is dichroic dye/water = (0.001 to The aqueous solution having a concentration of 0.1)/100 is subjected to an immersion treatment for 30 to 600 seconds (preferably 60 to 300 seconds). The aqueous solution of the dichroic dye to be used may contain a dyeing assistant 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.

As described above, the film can also be stretched in the dyeing bath. The stretching is performed by a method in which the nip rolls before and after the dyeing tank have a peripheral speed difference. Further, similarly to the swelling treatment step, a widening roller (expansion roller), a spiral roller, a crown roller, a cloth guide, a bending bar, or the like may be provided in the dye bath and/or the dye bath inlet and outlet.

The boric acid treatment is carried out by immersing the polyvinyl alcohol-based resin 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 is preferably 1 to 30 parts by weight based on 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 coexisted.

The boric acid treatment is carried out in order to achieve hydration resistance and hue adjustment (prevention of blue color tone, etc.) by crosslinking. When the boric acid treatment is carried out in order to achieve hydration 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 boric acid treatment for achieving water resistance is sometimes referred to as a water resistance treatment, a crosslinking treatment, and an immobilization treatment. In addition, the boric acid treatment for achieving the hue adjustment may be referred to as a complementary color treatment or a re-dye treatment.

This boric acid treatment appropriately changes the concentration of boric acid and iodide and the temperature of the treatment bath depending on the purpose. The boric acid treatment for achieving the hydration resistance and the boric acid treatment for achieving the hue adjustment are not particularly distinguished, and can be carried out under the following conditions. When the original film is subjected to swelling treatment, dyeing treatment, boric acid treatment, and boric acid treatment for the purpose of achieving water resistance by crosslinking, 3 to 10 parts by weight of boric acid, iodide is used with respect to 100 parts by weight of water. The 1 to 20 parts by weight of the boric acid treatment bath is usually carried out at a temperature of 50 to 70 ° C, preferably 55 to 65 ° C. The immersion time is 90 to 300 seconds. Further, in the case of dyeing the boric acid treatment and boric acid treatment, the temperature of the boric acid treatment bath is usually 50 to 85 ° C, preferably 55 to 80 ° C.

After the boric acid treatment for achieving water resistance, a boric acid treatment for achieving hue adjustment can also be performed. For example, when the dichroic dye is iodine, in order to achieve the above object, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide with respect to 100 parts by weight of water is used, usually at 10 to 45 ° C. The temperature is carried out. The immersion time is usually from 3 to 300 seconds, preferably from 10 to 240 seconds. Subsequent boric acid treatment to achieve hue adjustment is generally carried out at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the boric acid treatment used to achieve hydration resistance.

These boric acid treatments can be carried out in a plurality of steps, usually in two to five steps. In this case, the aqueous solution composition and temperature of each of the boric acid treatment tanks used may be the same or different. The above-described boric acid treatment for achieving a hydration-resistant boric acid treatment to achieve hue adjustment can be carried out in a plurality of steps.

Further, in the boric acid treatment step, the stretching of the film may be carried out in the same manner as the dyeing treatment step. The final cumulative stretching ratio is 4 to 7 times, preferably 4.5 to 6.5 times. Here, the "cumulative stretching ratio" means the length of the reference length in the longitudinal direction of the original film in the film after the end of all the stretching processes, for example, the portion which is originally 1 m in the original film, and ends at all the stretching processes. When the film is 5 m in the subsequent film, the cumulative stretching ratio at this time is 5 times.

After the boric acid treatment, a water washing treatment is performed. The water washing treatment is performed by immersing the boric acid-treated polyvinyl alcohol resin film in water in order to achieve water resistance and/or hue adjustment, by spraying with water as a shower, or by using both immersion and spraying. The temperature of the water in the water washing treatment is usually 2 to 40 ° C, and the immersion time is 2 to 120 seconds.

Here, in each step after the stretching process, the tension control can be performed so that the tension of the film is substantially constant. Specifically, when the stretching is ended in the dyeing treatment step, the tension control is performed in the subsequent boric acid treatment step and the water washing treatment step. When the stretching is ended in the step before the dyeing treatment step, the tension control is performed in the subsequent step including the dyeing treatment step and the boric acid treatment step. When the boric acid treatment step is constituted by a plurality of boric acid treatment steps, it is preferred to extend the film in the boric acid treatment step initially or from the beginning to the second stage, and in the boric acid treatment step from which the elongation treatment has been carried out. Tension control is performed in each step from the next boric acid treatment step to the water washing step, or the boric acid treatment step is extended from the initial to the third stage, and under the boric acid treatment step from which the elongation treatment has been carried out The tension control is performed in each step from the boric acid treatment step to the water washing step, but in terms of industrial properties, it is more preferable to extend the film in the boric acid treatment step initially or from the beginning to the second stage, and The tension control is performed in each step up to the boric acid treatment step to the water washing step in the boric acid treatment step of the elongation treatment. Further, after the boric acid treatment, when the iodide treatment or the zinc treatment as described above is carried out, the tension control may be performed in these steps.

The tension in each step from the swelling treatment to the water washing treatment may be the same or different. The tension of the film in the tension control is not particularly limited, and may be appropriately set in the range of 150 to 2000 N/m, preferably 600 to 1500 N/m per unit width. When the tension is less than 150 N/m, the film is liable to cause wrinkles and the like. On the other hand, when the tension exceeds 2000 N/m, problems such as cracking of the film and wear of the bearing are caused. In addition, the tension per unit width is calculated from the film width near the entrance of the step and the tension value of the tension detector. In addition, when tension control is performed, although there are inevitably a number of extensions and contractions, these are generally not included in the extension process.

At the end of the polarizing film production step, a drying treatment is performed. The drying treatment is preferably carried out by gradually changing the tension and performing in multiple stages, but in terms of equipment limitations, it is usually carried out in 2 to 3 stages. When it is carried out in two stages, the tension of the front stage is preferably set in the range of 600 to 1500 N/m, and the tension in the rear stage is preferably set in the range of 300 to 1200 N/m. When the tension is too large, the crack of the film becomes large, and when the tension is too small, the wrinkles become large, which is not preferable. Further, the drying temperature in the preceding stage is preferably set in the range of 30 to 90 ° C, and the drying temperature in the subsequent stage is preferably set in the range of 50 to 100 ° C. When the temperature is too high, the cracking of the film becomes large and the optical characteristics are degraded. When the temperature is too low, the streaks become large, which is not preferable. The drying treatment time may be, for example, 60 to 600 seconds, and the drying time of each stage may be the same or different. If the time is too long, it is not good in terms of productivity. If the time is too short, the drying is not sufficient.

Further, the moisture ratio of the polarizing film used in the method for producing a polarizing plate of the present invention is not particularly limited, but is preferably in the range of 3 to 14% by weight, more preferably 3 to 10% by weight. It is particularly preferably in the range of 3 to 8% by weight. When the moisture content of the polarizing film is less than 3% by weight, the polarizing film becomes brittle, and it becomes easy to be cleaved along the extending direction and is difficult to handle. Further, when the moisture content of the polarizing film exceeds 14% by weight, the polarizing film is It is easy to shrink under dry heat. Further, the moisture content of the polarizing film can be calculated from the change in weight after holding for 1 hour under dry heat of 105 °C. The polarizing film having the moisture content within the above preferred range can be obtained, for example, by controlling the drying temperature and drying time of the polarizing film.

In this manner, the polyvinyl alcohol resin film was subjected to uniaxial stretching, dyeing treatment with a dichroic dye, and boric acid treatment to obtain a polarizing film. The thickness of this polarizing film is usually in the range of 5 to 40 μm.

In the method for producing a polarizing plate of the present invention, on one side of the polarizing film, a protective film is laminated via an adhesive layer to form a polarizing plate. Examples of the protective film include a cellulose acetate resin film such as a cycloolefin resin film, cellulose triacetate or cellulose diacetate, polyethylene terephthalate, polyethylene naphthalate, and polyparaphenylene. A polyester resin film such as butylene dicarboxylate; a film which has been widely used in the field from the past, such as a polycarbonate resin film, an acrylic resin film, and a polypropylene resin film.

For the cycloolefin resin to be used as the protective film of the present invention, a commercially available product such as Topas (manufactured by Ticona Co., Ltd.), ARTON (manufactured by JSR Co., Ltd.), and ZEONOR (manufactured by Nippon Zeon Co., Ltd.) can be suitably used. ZEONEX (made by Japan ZEON Co., Ltd.), APEL (made by Mitsui Chemicals Co., Ltd.), etc. When the cycloolefin resin is formed into a film to form a film, a known method such as a solvent casting method or a melt extrusion method is suitably used. In addition, it is also possible to use, for example, a film of a cycloolefin resin film which has been previously formed into a film, such as an Escena (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), or a ZEONOR film (manufactured by Optes Co., Ltd.). Sale.

The cycloolefin resin film may be a uniaxially stretched or biaxially stretched one. By stretching, any phase difference can be imparted to the cycloolefin resin film. The stretching is usually performed by continuously winding the film roll while continuing in the heating furnace in the direction in which the roll is proceeding, in the direction perpendicular to the direction of progress, or in both directions. The temperature of the furnace is usually in the range of from the glass transition temperature of the cycloolefin resin to the glass transition temperature + 100 °C. The stretching ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

Since the cycloolefin resin film generally has a poor surface activity, it is preferably subjected to 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, plasma treatment and corona treatment which are relatively easy to implement are preferred.

In addition, in the cellulose acetate resin film which can be used as a protective film in the present invention, a commercially available product such as Fujitac TD80 (manufactured by Fuji Film Co., Ltd.) and Fujitac TD80UF (manufactured by Fuji Film Co., Ltd.) can be suitably used. Fujitac TD80UZ (manufactured by Fuji Film Co., Ltd.), Fujitac TD40UZ (manufactured by Fuji Film Co., Ltd.), KC8CX2M (manufactured by Konica Minolta Opto Co., Ltd.), KC4UY (manufactured by Konica Minolta Opto Co., Ltd.), and the like.

The surface of the cellulose acetate resin film may be subjected to surface treatment such as antiglare treatment, hard coating treatment, antistatic treatment, and antireflection treatment depending on the application. Further, in order to improve the viewing angle characteristics, a liquid crystal layer or the like may be formed. Further, in order to impart a phase difference, the cellulose resin film may be extended. Further, in order to improve the adhesion to the polarizing film, the cellulose acetate resin film is usually subjected to a saponification treatment. The saponification treatment may be carried out by immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

When the above-mentioned protective film is in a roll state, since the film tends to adhere to each other and tends to adhere to each other, the end portion of the roll is subjected to uneven processing, or a ribbon is inserted at the end portion, or a protective film is attached. And made into a roll.

The thickness of the protective film is preferably thin, but if it is too thin, the strength is lowered and the workability is deteriorated. On the other hand, if it is too thick, there arises a problem that the transparency is lowered or the hardening time required after lamination is lengthened. Therefore, the appropriate thickness of the protective film is, for example, about 5 to 100 μm, preferably 10 to 80 μm, more preferably 20 to 40 μm.

In the method for producing a polarizing plate of the present invention, the polarizing film and the protective film are bonded together via a water-based adhesive layer such as a polyvinyl alcohol resin aqueous solution or an aqueous two-liquid amine ester emulsion adhesive.

When a cellulose acetate film produced by hydrophilizing a contact surface with a polarizing film or the like is used as a protective film, the polyvinyl alcohol resin aqueous solution can be suitably used as an adhesive. In the polyvinyl alcohol 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, it is also possible to exemplify, for example, vinyl acetate A copolymer of a copolymer of another monomer, a vinyl alcohol copolymer obtained by saponification treatment, and a modified polyvinyl alcohol polymer obtained by partially modifying the hydroxyl groups. Additives such as a polyvalent aldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, and a zinc compound may be added to the aqueous binder. When such a water-based adhesive is used, the adhesive layer obtained therefrom is usually 1 μm or less, and the adhesive layer is not actually observed even when the cross section is observed by a usual optical microscope.

The method of bonding the polarizing film and the protective film is not particularly limited, and examples thereof include a method in which an adhesive is uniformly applied to the surface of the polarizing film and/or the protective film, and the other film is superposed on the coated surface. It is bonded by a roller and dried. Usually, the 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.

When the polarizing film is bonded to the protective film, the peelable protective film may be bonded to protect the surface of the polarizing film on the opposite side of the protective film from damage. For example, in the case where an adhesive layer is formed on the surface of the polarizing film of the polarizing plate, the protective film can be peeled off at a stage where it is unnecessary.

The peeling force between the pellicle film and the polarizing film is from 0.01 to 5 N/25 mm, preferably from 0.01 to 2 N/25 mm, more preferably from 0.01 to 0.5 N/25 mm. If the peeling force is less than 0.01 N/25 mm, the protective film may be partially peeled off due to the small adhesion force between the polarizing film and the protective film. Further, when the peeling force exceeds 5 N/25 mm, it is difficult to peel off the pellicle film from the polarizing film, which is not preferable.

The material of the pellicle film can be a polyethylene resin, a polypropylene resin, a polystyrene resin, a polyethylene terephthalate resin or the like which is easy to handle and can ensure a certain degree of transparency, and one or the like can be used. Two or more films formed into a single layer or a plurality of layers are used as a protective film.

For the protective film, for example, Sunytect (sold by San-A Chemical Research Co., Ltd.) having an adhesive layer formed on the surface of the polyethylene resin film, and formed on the surface of the ethylene terephthalate resin film can be cited. E-Mask (manufactured by Nitto Denko Corporation) having an adhesive layer, and a commercial product of Mastack (manufactured by Fujimori Industrial Co., Ltd.) having an adhesive layer formed on the surface of the ethylene terephthalate resin film.

Among them, the self-adhesive protective film which is adhesive to the polarizing film alone is more suitable because it does not need to protect the adhesive layer on the surface of the protective film. The commercially available product of the self-adhesive resin film which exhibits a preferable peeling force to the polarizing film is, for example, Toretec (manufactured by Toray Co., Ltd.) made of a polyethylene resin.

Further, the protective film is preferably a defect such as a fish eye. If there is a defect, the shape is transferred to the polarizing film, which may become a defect of the polarizing film.

In the method for producing a polarizing plate of the present invention, after the polarizing film and the protective film are bonded together, the laminated film is dried in order to remove water contained in the aqueous adhesive. Drying can be carried out by continuously passing through a drying furnace maintained at an appropriate temperature. For example, it can be carried out by continuously passing through a drying furnace and winding the dried polarizing plate into a roll shape, but is not limited thereto. The method for producing a polarizing plate of the present invention is characterized in that the drying step comprises the steps of: retaining in a drying oven maintained at a temperature of not up to 50 ° C to a low temperature drying step in which the total residence time is 150 seconds or more; and maintaining at a temperature The high temperature drying step is carried out in a drying oven at 50 ° C or higher until the total residence time is 150 seconds or less.

The low-temperature drying step in the present invention is a step of drying in a drying oven maintained at a temperature of not more than 50 ° C until the total residence time is 150 seconds or longer. When the drying temperature in the low-temperature drying step exceeds 50 ° C, since the low-temperature drying step does not exist (this drying step is equivalent to the high-temperature drying step), significant reverse curl is observed on the manufactured polarizing plate, depending on the conditions. In some cases, the polarizing plate cannot be kept in a plate shape and becomes a cylindrical shape. If the reverse curl is to be effectively suppressed, the drying temperature in the low-temperature drying step is preferably 49 ° C or lower. Further, from the viewpoint of preventing the polarizing film and the protective film from being easily peeled off, the drying temperature in the low-temperature drying step is preferably 30 ° C or higher, more preferably 40 ° C or higher.

The drying time in the low-temperature drying step may be 150 seconds or longer, and is usually 1200 seconds or less from the viewpoint of productivity. When the drying time is less than 150 seconds, there is a tendency that the reverse curling state becomes large at the time of the high-temperature drying step.

Further, the high-temperature drying step in the present invention is carried out in a drying furnace maintained at a temperature of 50 ° C or higher until the total residence time is 150 seconds or less. When the drying temperature in the high-temperature drying step is less than 50 ° C, since the high-temperature drying step does not exist (this drying step is equivalent to the low-temperature drying step), if the drying of the polarizing plate is sufficiently performed, it takes a long time to dry, and There are production problems. Further, from the viewpoint of preventing significant bending due to shrinkage of the polarizing film, the drying temperature in the high-temperature drying step is preferably 60 ° C or lower.

The drying time in the high-temperature drying step may be 150 seconds or less. However, if drying is performed for a limited period of time, the polarizing plate tends to be uneven due to insufficient drying, and therefore it is usually 20 seconds or longer. When the drying time in the high-temperature drying step exceeds 150 seconds, there is a tendency that the reverse curling state becomes large. In addition, when the drying time in the high-temperature drying step is 0 seconds (that is, when the high-temperature drying step is not present), although the reverse curl does not occur, since the drying temperature is low, it takes a long time to sufficiently dry the polarizing plate. It is dry and has problems in production.

In the method for producing a polarizing plate of the present invention, the low-temperature drying step and the high-temperature drying step may be carried out in this order, or may be carried out in the reverse order, or a plurality of low-temperature drying steps and high-temperature drying steps may be sequentially combined. If the high-temperature drying step is performed first, the optical characteristics of the polarizing plate, especially the vertical hue, tend to become blue, so the drying step is advanced in the low-temperature drying step, especially the low-temperature drying step, the high-temperature drying step, The sequence of the low temperature drying step is preferably carried out. Further, when a plurality of low-temperature drying steps and high-temperature drying steps are performed, the drying time is the total time of each low-temperature drying step and the total time of each high-temperature drying step. That is, as described above, when the drying step is performed in the order of the low temperature drying step, the high temperature drying step, and the low temperature drying step, the drying time of the low temperature drying step is equivalent to the drying time of the initial low temperature drying step and the final low temperature drying step. The total time of drying time.

In the method for producing a polarizing plate of the present invention, as described above, since the drying step includes a low-temperature drying step and a high-temperature drying step, a polarizing plate having less curl can be produced than in the related art. Here, the "curl of the polarizing plate" means a state in which the polarizing plate is convex or concave when a polarizing plate is provided on a plane. The term "reverse curling" means that a convex shape is formed when the polarizing film side is placed on the lower surface and the protective film side is placed on the surface; and the "positive curling" indicating the opposite state is set on the plane. When the protective film side is placed underneath and the polarizing film side is placed on top, a convex curl is exhibited.

The curl of the polarizing plate can be measured, for example, as follows. First, from the manufactured polarizing plate, a rectangular measurement sample of 250 mm × 300 mm is cut at an angle of 45° with respect to the absorption axis (MD direction), and is managed to a temperature of 23 ° C ± 2 ° C and a relative humidity of 50%. In an environment of ±5%, it is placed on the plane for 1 hour. Then, the curled and convex surface is placed on the plane, and the distance between the polarizing plate and the plane is measured at a corner located on a diagonal line close to the TD direction of the rectangular sample (the direction perpendicular to the absorption axis). Since there are two corners, the average value is used as the curl measurement value. Since the curl measurement value is the distance between the corner portion of the polarizing plate and the plane, it is difficult to measure the polarizing plate without being concave with respect to the plane, and the curl value itself is measured to be zero or a positive value. When the polarizing plate exhibited reverse curl, the curl value when the protective film side was on the lower polarizing film side and placed on a flat surface was determined. On the other hand, the state in which the polarizing film side is convex and the protective film side is concave is called "smooth curl". In the case of the smooth curl, the curl value when the polarizing film having a convex shape was formed on the lower surface and the protective film side was placed on the flat plate was determined. In the present specification, the curl value at the time of reverse curl is represented by a negative value, and the curl value at the time of curling is represented by a positive value, but the magnitude of "when the curl is large" is based on the absolute value of the curl value.

In the case of reverse curling and a large absolute value, the polarizing film is placed in a direction in which the surface of the liquid crystal panel is aligned with the surface of the liquid crystal panel (that is, the protective film is positioned outside from the liquid crystal panel), and the polarizing plate is applied via an adhesive layer or the like. When bonded to a liquid crystal panel, there is a tendency for air bubbles to easily occur between the adhesive layer and the liquid crystal panel. Since the curl value of the reverse curl which is likely to generate bubbles is usually about -5 mm, when the polarizing plate produced by the present invention is reversely curled, the curl value is preferably in the range of 0 to -5 mm. In addition, when the film is bonded to the liquid crystal panel or the like via the adhesive layer or the like, the film can be bonded to the periphery without being mixed with air bubbles or the like. A large curl value does not cause a big problem, but can be sufficiently tolerated to about +20 mm. However, the state of the polarizing plate produced by the present invention is a state in which the protective film is adhered only to one side of the polarizing film composed of the polyvinyl alcohol resin, and the polarizing film composed of the polyvinyl alcohol resin is easily contracted. Therefore, almost no big curl value is displayed.

In the drying furnace used in the drying step in the method for producing a polarizing plate of the present invention, the drying temperature can be set to 30 to 60 ° C from the viewpoint of suitably performing the low-temperature drying step and the high-temperature drying step (more preferably A range of 40 to 60 ° C) is preferred. That is, a drying furnace which can be set to be dried in a range of 30 ° C below the preferred drying temperature of the low-temperature drying step and 60 ° C above the preferred drying temperature of the high-temperature drying step can be used. As described above, since the polarizing film and the protective film tend to be easily peeled off when the temperature is less than 30 ° C, and when it exceeds 60 ° C, there is a possibility of significant bending due to shrinkage of the polarizing film. . The total residence time of the laminated film in the drying furnace may be, for example, more than 150 seconds and less than 1200 seconds, and particularly preferably from 170 to 600 seconds from the viewpoint of productivity.

In the method for producing a polarizing plate of the present invention, after the drying step, the curing may be carried out at a temperature of about room temperature or slightly higher than room temperature, for example, at a temperature of about 20 to 45 ° C for about 12 to 600 hours. . The temperature at the time of ripening is generally set to be lower than the temperature used for drying.

The polarizing plate thus obtained usually has an adhesive layer formed on at least one side thereof. When an adhesive layer is formed on the surface of the polarizing film of the polarizing plate, the adhesive used for the purpose is a storage elastic modulus having a storage elastic modulus of 0.15 to 1 MPa in a temperature range of 23 to 80 °C. good. In general, an adhesive used for an optical film has a storage elastic modulus of only about 0.1 MPa, and an adhesive having a storage elastic modulus higher than this value is suitable for use in a polarizing film surface. By setting the storage elastic modulus of the adhesive within the above range, dimensional change due to shrinkage of the polarizing film in a high-temperature environment can be suppressed to be small, and good durability can be obtained. The storage elastic modulus of the adhesive can be determined by using a DYNAMIC ANALYZER RDA II (manufactured by REOMETRIC Co., Ltd.) as a cylinder of 8 mmφ × 1 mm thick and by making a frequency of 1 Hz.

On the other hand, in the adhesive formed on the protective film surface of the polarizing plate, in addition to the above-described storage elastic modulus, the storage elastic modulus lower than the above may be used without any particular limitation, for example, usually An adhesive for displaying an elastic modulus of 0.1 MPa or less for an optical film.

The adhesive used in the present invention may, for example, be an acrylic resin, a rubber, an amine ester, a silicone, a polyvinyl ether resin or the like. Further, an adhesive such as an energy ray-curing type or a thermosetting type can be used particularly as an adhesive having a high storage modulus. Among these, an adhesive which is excellent in transparency, weather resistance, heat resistance, and the like as a base polymer is preferable.

The acrylic adhesive is not particularly limited, and butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, or the like can be suitably used ( A methylated acrylate polymer or a copolymerized polymer of two or more kinds of (meth) acrylates. Further, polar polymers are copolymerized in these polymers. Examples of the polar monomer include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, and N,N-di(meth)acrylate. A monomer having a functional group such as a carboxyl group, a hydroxyl group, a decylamino group, an amine group or an epoxy group, such as methylaminoethyl ester or glycidyl (meth)acrylate.

These acrylic adhesives can of course be used singly, but usually in combination with a crosslinking agent. The crosslinking agent may, for example, be a metal salt which is a divalent or polyvalent group and forms a metal carboxylate with a carboxyl group; a polyamine compound which forms a guanamine bond with a carboxyl group; and a polyepoxy compound or a polyalcohol compound And forming an ester bond with a carboxyl group; belonging to a polyisocyanate compound, and forming a guanamine bond with a carboxyl group. Among them, a polyisocyanate compound is widely used as an organic crosslinking agent.

The "energy-hardening type adhesive" refers to a property of being cured by irradiation with an energy ray such as an ultraviolet ray or an electron beam, and is also adhesive to the film before being irradiated with an energy ray, and is adhered to an object such as a film. An adhesive that hardens and has the property of being able to adjust the adhesion. The energy ray-curable adhesive is preferably an ultraviolet curable adhesive. The energy ray-curable adhesive generally contains an acrylic adhesive and an energy ray polymerizable compound as a main component. The crosslinking agent is usually further formulated, and a photopolymerization initiator or a photosensitizer may be formulated as needed.

In the adhesive composition, in addition to the above polymer and cross-linking agent, in order to adjust the adhesive adhesion, cohesive force, viscosity, elastic modulus, glass transition temperature, etc., it may be formulated as natural or synthetic as needed. Suitable additives such as resins, adhesives, antioxidants, ultraviolet absorbers, dyes, pigments, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and the like. Further, fine particles may be further contained to form an adhesive layer which exhibits light scattering properties.

The thickness of the adhesive layer is preferably from 1 to 40 μm, but the thin polarizing plate for the purpose of obtaining the present invention can be coated to be thinner and well maintained from the viewpoint of not impairing the properties of workability and durability. From the viewpoint of workability and suppression of dimensional change of the polarizer, it is more preferably 3 to 25 μm. If the adhesive layer is too thin, the adhesiveness is lowered, and if it is too thick, the adhesiveness is likely to be out of range.

Further, in the method for producing a polarizing plate of the present invention, the method of forming the adhesive layer is not particularly limited, and it may be applied to one side or both sides of the polarizing plate (polarizing film surface, protective film surface, or both). The cloth contains a solution comprising the components of the above-mentioned base polymer, and after drying to form an adhesive layer, it is obtained by laminating a spacer which is subjected to release treatment such as polyfluorene or the like; and an adhesive may be formed on the spacer. After the layer is transferred to the polarizing film surface of the polarizing plate, the protective film surface, or both, and laminated. Further, when the adhesive layer is formed on the polarizing plate, at least one of the adhesive layer forming surface and the adhesive layer of the polarizing plate may be subjected to an adhesion treatment such as corona treatment or the like as necessary. Further, the surface of the formed adhesive layer is usually protected by a spacer film which is subjected to a release treatment, and the spacer film is peeled off before the polarizing plate is attached to a liquid crystal cell or other optical film or the like. .

The polarizing plate manufactured by the manufacturing method of the present invention usually has a large roll material or a sheet material type, and is obtained by a cutting tool having a sharp blade in order to obtain a polarizing plate having a desired shape and a transmission axis. Tip cut. Therefore, in the polarizing plate tip obtained by cutting, the polarizing film is exposed to the outside in the outer peripheral end portion.

When the polarizing plate of this state is subjected to a durability test such as a thermal shock test, it is easier than a polarizing plate which is generally used, that is, a polarizing plate which protects both sides of the polarizing film with a cellulose resin film or the like. There is a tendency to cause problems such as peeling or cracking. In order to avoid such a problem, the polarizing plate piece obtained by the present invention is preferably such that the outer peripheral end face is continuously cut by a fly cut method or the like.

(Example)

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. In the examples, "%" and "parts" indicating the content or the amount used are based on weight unless otherwise specified.

<Example 1>

A polyvinyl alcohol film having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more and a thickness of 75 μm was uniaxially stretched to about 5 times in a dry manner, and then kept in a tight state, and immersed in pure water at 60 ° C. After a minute, it was immersed in an aqueous solution of iodine/potassium iodide/water in a weight ratio of 0.1/5/100 at 28 ° C for 60 seconds. Then, it was immersed at 72 ° C for 300 seconds in an aqueous solution of potassium iodide / boric acid / water in a weight ratio of 10.5 / 7.5 / 100. Then, it was washed with pure water of 10 ° C for 5 seconds, and then dried at 90 ° C for 180 seconds to obtain a polarizing film obtained by adsorbing iodine to polyvinyl alcohol.

In addition, in 100 parts of water, 3 parts of fully saponified polyvinyl alcohol (Kuraray Poval 117H, manufactured by Kuraray Co., Ltd.) and polyvinyl alcohol modified by acetamidine (Gohsefimer 200, Japan Synthetic Chemical Industry) 3 parts of zinc chloride, 0.18 parts of zinc chloride (sold by Nacalai Tesque Co., Ltd.), and 1.4 parts of glyoxal (sold by Nacalai Tesque Co., Ltd.) were dissolved, and a polyvinyl alcohol resin adhesive was prepared.

On one side of the previously obtained polarizing film, a film of a thickness of 40 μm (KC4UY, manufactured by Konica Minolta Opto Co., Ltd.) composed of cellulose triacetate which was saponified was attached to the surface of the polarizing film obtained by the above-mentioned adhesive. While maintaining the tension of the composition at 430 N/m, the film was dried at 40 ° C for 14 seconds, dried at 45 ° C for 61 seconds, dried at 55 ° C for 117 seconds, and dried at 45 ° C for 118 seconds to obtain a polarizing plate. In short, it was dried at a temperature of less than 50 ° C for 193 seconds (low temperature drying step), and dried at a temperature of 50 ° C or higher for 117 seconds (high temperature drying step).

The obtained polarizing plate was evaluated to have a crimp value of 0.5 mm (smooth curl), and a polarizing plate having a small curl amount was produced. In addition, there is no unevenness on the surface of the polarizing plate.

<Examples 2 to 5 and Comparative Examples 1 to 5>

Hereinafter, as shown in Table 1, a polarizing plate was prepared by combining a low-temperature drying step and a high-temperature drying step, and the curl value and the appearance of the polarizing plate were evaluated. The results (including the results of Example 1) are shown in Table 1. In the table, "TD curl" is a curl value measured at a corner near the diagonal line in the TD direction by the above method, and the minus sign is as described above as an inverse curl, and no negative sign (that is, a positive value) ) means a smooth curl. In Comparative Examples 4 and 5, the term "tubular" means that the curling is performed in the form of a reverse curl, that is, a state in which the side of the polarizing film is inside.

[Table 1]

As is clear from Table 1, in the drying step after bonding the protective film, if the residence time at 50 ° C or higher becomes longer, the reverse curl becomes larger, especially as shown in Comparative Examples 4 and 5, when the drying step is 50 ° C as a whole. In the above case, the polarizing plate cut into a size of 250 mm × 300 mm will exhibit a cylindrical reverse curl. In contrast, according to the present invention, a low-temperature dry bathing step of less than 50 ° C is used and a high temperature of 50 ° C or higher is simultaneously combined. In the dry bathing step, a polarizing plate having a small curling condition can be produced.

Fig. 1 is a view showing a state in which a fluorescent lamp is reflected on a surface of a polarizing plate which is uneven.

Since the picture in this case is an experimental photograph, it is not a representative figure of this case.

Therefore, there is no designated representative map in this case.

Claims (3)

A method for producing a polarizing plate, comprising the steps of: bonding a protective film to one side of a polarizing film made of a polyvinyl alcohol resin via a water-based adhesive layer, and attaching the polarizing film to the protective film a drying step of drying; wherein the drying step comprises the steps of: retaining in a drying oven maintained at a temperature of less than 50 ° C to a low temperature drying step in which the total residence time is 150 seconds or more, and maintaining the temperature at 50 In a drying oven of ° C or more and 60 ° C or less, the high temperature drying step is carried out until the total residence time is 150 seconds or less. The method for producing a polarizing plate according to the first aspect of the invention, wherein the drying step is performed in the order of a low temperature drying step, a high temperature drying step, and a low temperature drying step. The method for producing a polarizing plate according to the first or second aspect of the invention, wherein the protective film is a film composed of a cellulose acetate resin.