WO2013084924A1 - Method for producing polarizing film, method for producing polarizing plate, and polarizing plate - Google Patents

Abstract

This method for producing a polarizing film involves: a dyeing step of dyeing a polyvinyl alcohol-based film with a dichroic dye; a cross-linking step of cross-linking the dyed polyvinyl alcohol-based film by immersing same in a solution including a cross-linking agent; and a drying step of drying the cross-linked polyvinyl alcohol-based resin film. The drying step comprises a high-temperature drying step of performing drying at a drying temperature of 90°C or higher, and drying is performed such that the moisture content of the film becomes 8-15 wt%.

Description

Manufacturing method of polarizing film, manufacturing method of polarizing plate, and polarizing plate

The present invention relates to a polarizing film manufacturing method, a polarizing plate manufacturing method, and a polarizing plate.

Liquid crystal display devices are used in various display devices by taking advantage of features such as low power consumption, low voltage operation, light weight and thinness. The liquid crystal display device is 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.

On the other hand, liquid crystal display devices are required to have a product that can withstand severe durability conditions depending on the application. For example, a liquid crystal display device for a car navigation system may have a high temperature and humidity in a vehicle in which the liquid crystal display device is placed, and the temperature and humidity conditions are severe compared to a monitor for a normal television or personal computer. For such applications, polarizing plates that are highly durable are also required.

The polarizing plate usually has a configuration in which a transparent 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 with good hue and durability, a transparent film is applied to the surface of a polarizer prepared by iodine staining of a polyvinyl alcohol film and then uniaxially stretching in an aqueous boric acid solution. A provided polarizing plate is disclosed.

JP 2004-341503 A

In the liquid crystal display device, development has been progressed so far with the goal that the liquid crystal display screen is achromatic, but in recent years there is a need for chromatic color of the liquid crystal display screen. By using a chromatic color polarizing plate, it is easy to moderately color the liquid crystal display screen.

An object of the present invention is to provide a method for producing a chromatic color polarizing plate which has excellent polarization characteristics and is suitable for chromatic coloring of a liquid crystal display screen.

As a result of intensive studies, the present inventor has found that the dyed polarizing film can be colored by treating it at a temperature of 90 ° C. or higher. However, when the treatment is performed at a temperature of 90 ° C. or higher, the polarizing film may be curled or the polarization characteristics may be deteriorated. The present inventor has further intensively studied, found a method for producing a polarizing film having no inconvenience such as curling and has excellent polarization characteristics, and has reached the present invention.

In addition, the suitable degree of coloring of the polarizing plate here can be quantified by, for example, a single hue b value of the polarizing plate. The present inventor has found that the liquid crystal display screen can be suitably chromaticized when the hue b value of the single polarizer is, for example, 2.5 to 4.5.

The present invention relates to a dyeing process for dyeing a polyvinyl alcohol film with a dichroic dye, a crosslinking process for immersing the dyed polyvinyl alcohol film in a solution containing a crosslinking agent, and a crosslinked polyvinyl alcohol resin film. A drying process comprising: a drying step comprising: a high temperature drying step of drying at a drying temperature of 90 ° C. or higher, and a moisture content of the film of 8 to 15% by weight; Dry to be.

The above high-temperature drying step is preferably continued for 1 second to 60 seconds. The drying step preferably further includes a low temperature drying step in which drying is performed at a drying temperature of less than 90 ° C. for 30 seconds or longer. In one Embodiment of this invention, the said high temperature drying process is performed by making a polarizing film contact a heat roll.

Moreover, this invention is a manufacturing method of a polarizing plate provided with the process of manufacturing a polarizing film with the said manufacturing method, and the bonding process of bonding a transparent film to the at least one surface of a polarizing film. In the bonding step, the polarizing film and the transparent film are preferably bonded through an active energy ray-curable adhesive.

The present invention is also a polarizing plate comprising a polarizing film manufactured by the above-described manufacturing method and a transparent film bonded to at least one surface of the polarizing film, and the visibility corrected single transmittance is 42.5. % Or more, a visibility correction polarization degree of 99.99% or more, a single hue b value of 2.5 to 4.5, and an orthogonal hue b value of −1.5 to 0.1. Moreover, the polarizing plate of this invention can simplify the drying process after bonding, and can adjust a hue, when a polarizing film and a transparent film are bonded through an active energy ray hardening-type adhesive agent. Therefore, the effect is great when applied to a polarizing plate bonded through an active energy ray-curable adhesive.

According to the production method of the present invention, it is possible to obtain a polarizing plate that has excellent polarization characteristics and has a color that is suitable for chromatic coloration of a liquid crystal display screen.

Hereinafter, the present invention will be described in more detail.
[Production method of polarizing film]
The polarizing film produced by the production method of the present invention is a polyvinyl alcohol film that has been stretched and adsorbed and oriented with a dichroic dye. The method for producing a polarizing film 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. And a drying step of drying the polyvinyl alcohol-based resin film so that the moisture content is 8 to 15% by weight.

(Polyvinyl alcohol film)
The polyvinyl alcohol resin forming the polyvinyl alcohol film used in the production method of the present invention is usually obtained by saponifying a polyvinyl acetate resin. The saponification degree of the polyvinyl alcohol resin is usually 85 mol% or more, preferably 90 mol% or more, more preferably 99 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. In addition to the above ethylene, examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins other than ethylene, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol 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 resin having a thickness of 20 to 100 μm, preferably 30 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.

In the manufacturing method of the polarizing film of this embodiment, the process by a swelling process, a dyeing process, a bridge | crosslinking process, a water washing process, and a drying process is performed using an unstretched polyvinyl alcohol-type film. 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 drying process is, for example, 5 to 50 μm. Hereinafter, each step will be described in detail.

(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 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 a film previously stretched in a gas is swollen, for example, the film is immersed in an aqueous solution at 20 to 70 ° C., preferably 30 to 60 ° C. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds. When the unstretched raw film is swollen, for example, the film is immersed in an aqueous solution at 10 to 50 ° C., preferably 20 to 40 ° C. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling step, uniaxial stretching of the polyvinyl alcohol-based resin film may be performed. 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. For the purpose of stabilizing 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 bath can be used as a swelling bath. It is also possible to use an aqueous solution to which an organic solvent, alcohol or the like is added in an amount of 0.01 to 10% by weight.

(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 to 45 ° C., preferably 20 to 35 ° C., and in a weight ratio, iodine / potassium iodide / water = 0.003 to 0.2 / 0.1 to The immersion treatment is performed at a concentration of 10/100 for 30 to 600 seconds, preferably 60 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, at a temperature of 20 to 80 ° C., preferably 30 to 70 ° C., and by weight, the dichroic dye / water = 0.001 to 0.1 / The immersion treatment is performed at a concentration of 100 for 30 to 600 seconds, preferably 60 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 or a surfactant. 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 including 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 to 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 boric acid. The content of boric acid in this aqueous solution is usually about 1 to 10 parts by weight 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 with respect to 100 parts by weight of water. Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

The cross-linking step is performed for water resistance and hue adjustment (preventing bluishness, etc.) by cross-linking. In the case of water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used in addition to or together with boric acid, if 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 the unstretched film is used for the swelling step and then the dyeing step and the crosslinking step are performed, and the crosslinking step is aimed at water resistance, 3 to 10 boric acid is added to 100 parts by weight of water. A boric acid treatment bath containing 1 to 20 parts by weight of iodide and 1 to 20 parts by weight of iodide is used, and the reaction is usually performed at a temperature of 50 to 70 ° C, preferably 53 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. When the swelling process is performed using a pre-stretched film, and then the dyeing process and the crosslinking process are performed, the temperature of the boric acid treatment bath is usually 50 to 85 ° C., preferably 55 to 80 ° C.

After the crosslinking treatment for water resistance, a crosslinking treatment for adjusting the hue may be performed. 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. Usually, it is carried out 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.

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 usually 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 hue adjustment in water, spraying water as a shower, or combining immersion and spraying. The temperature of water in the washing step is usually about 2 to 40 ° C., and the immersion time is preferably 2 to 120 seconds.

(Drying process)
After the crosslinking step, the polyvinyl alcohol film is subjected to a drying step after passing through a water washing step as necessary. The drying process includes a high-temperature drying process in which drying is performed at a drying temperature of 90 ° C. or higher. In this way, by adopting a high-temperature drying process, the moisture content of the polarizing film obtained after the entire drying process is set to a high value of 8 to 15% by weight. Coloring is possible. The drying temperature in the high-temperature drying step is 90 ° C. or higher as described above, preferably 93 ° C. or higher, and preferably 110 ° C. or lower. As described above, the high-temperature drying step acts on the coloring of the polarizing plate produced using the obtained polarizing film. The high temperature drying step is preferably continued for 1 second to 60 seconds. If the high temperature drying process is less than 1 second, the polarizing plate alone may not be sufficiently colored. When the high temperature drying process exceeds 60 seconds, it becomes difficult to adjust the polarizing film to a predetermined moisture content, and the polarizing film tends to be curled. In the high temperature drying process, a plurality of zones having different temperatures may be passed.

It is preferable that the drying step further includes a low temperature drying step in which drying is performed at a drying temperature of less than 90 ° C. for 30 seconds or longer. The drying temperature in the low temperature drying step is preferably 30 ° C. or higher and lower than 90 ° C. The low temperature drying process may have a plurality of zones having different temperatures. By combining the high temperature drying step and the low temperature drying step, the polyvinyl alcohol film can be easily dried to a desired moisture content, and the polarizing plate can be appropriately colored. When combining a high-temperature drying step and a low-temperature drying step, it is preferable to place a high-temperature drying step after the low-temperature drying step because defects such as color unevenness, streaks, and wrinkles due to rapid drying of the film are less likely to occur. . In that case, a low temperature drying step can be further included after the high temperature drying step.

In the drying step, the polyvinyl alcohol film is finally dried so that the moisture content is 8 to 15% by weight. The moisture content is preferably 8.5% by weight or more, more preferably 9% by weight or more, and is preferably 14% by weight or less, more preferably 13.5% by weight or less. If the moisture content at this time is less than 8% by weight, curling is likely to occur in the polyvinyl alcohol film, and curling is also likely to occur in the polarizing plate produced therefrom. On the other hand, if the moisture content exceeds 15% by weight, the moisture content itself tends to fluctuate, and the optical performance of the polarizing film and thus the polarizing plate tends to fluctuate. If the moisture content at this time is large, the polarizing plate produced therefrom is likely to curl.

As described above, in the present invention, the moisture content of the polarizing film obtained by finishing the entire drying process is increased to 8 to 15% by weight while incorporating the high temperature drying process in which the drying process is performed at a drying temperature of 90 ° C. or higher. By setting this value, the polarizing plate produced from this polarizing film can be colored, and specifically, the single hue b value of the polarizing plate can be in the range of 2.5 to 4.5. . If the moisture content of the film when the drying process is finished is too small, the possibility that the hue b value of a single polarizing plate produced therefrom exceeds 4.5 is increased. On the other hand, if the moisture content is too large, there is a high possibility that the hue b value of a single polarizing plate produced therefrom is less than 2.5.

The moisture content here means the percentage of the amount of moisture obtained by the dry weight method with respect to the weight of the polyvinyl alcohol film, and when the polyvinyl alcohol film after the drying process is heat treated at 105 ° C. for 120 minutes, before and after the heat treatment. From the moisture content change at
Moisture content = (weight before heat treatment−weight after heat treatment) / weight before heat treatment × 100 (weight / weight%).

There are various methods for drying, 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, all of which can be suitably used. The method of drying by contacting with a heat roll is preferable in terms of improving the drying efficiency, making it easy to adjust the hue in a short time, and suppressing the shrinkage in the width direction of the film, thereby enabling widening. . The drying temperature in the high temperature drying step and the low temperature drying step 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. The drying temperature in the high-temperature drying step is preferably 90 ° C. or higher and 105 ° C. or lower, more preferably 93 ° C. or higher and 102 ° C. or lower. In this case, the treatment time is preferably 5 seconds or more and 50 seconds or less, more preferably 10 seconds or more and 40 seconds or less. On the other hand, in the case of a contact-type drying facility such as a heat roll, the drying temperature means the surface temperature of a heating medium (for example, a heat roll) that contacts the film. In this case, the drying temperature in the high-temperature drying step is Preferably they are 100 degreeC or more and 110 degrees C or less. Further, the processing time in this case is preferably 1 second or more and 20 seconds or less. Any of these methods is preferable because the polarizing plate alone can be colored while suppressing a decrease in moisture content in a shorter time as the temperature increases.

Through the above process, a polarizing film is manufactured. A polarizing film can be used as a component of a polarizing plate described below.

[Production method of polarizing plate]
The polarizing plate manufactured by the manufacturing method of the present invention includes a polarizing film and a transparent film bonded to at least one surface of the polarizing film. The manufacturing method of the polarizing plate of this invention is equipped with the process of producing a polarizing film with the above-mentioned manufacturing method, and the bonding process of bonding a transparent film on the at least one surface of a polarizing film after that.

In the method for producing a polarizing plate of the present embodiment, an unstretched polyvinyl alcohol-based resin film is used, and a polarizing film is produced by performing a swelling process, a dyeing process, a crosslinking process, a water washing process, and a drying process, and then polarizing. A bonding step of bonding a transparent film to at least one surface of the film is provided. Since each process of the swelling process, the dyeing process, the crosslinking process, the water washing process, and the drying process for producing the polarizing film is as described above, the description thereof is omitted. Hereinafter, the bonding process will be described.

(Bonding process)
A transparent film is bonded to one side or both sides of the polarizing film. The bonding method of a polarizing film and a transparent film is not specifically limited. For example, an adhesive layer or a pressure-sensitive adhesive layer is formed on the bonding surface of the polarizing film and / or the transparent film, and both are bonded via the adhesive layer or the pressure-sensitive adhesive layer.

<Transparent film>
Examples of the material constituting the transparent film include cycloolefin resins, cellulose acetate resins, polyethylene terephthalate, polyethylene naphthalate, polyester resins such as polybutylene terephthalate, polycarbonate resins, acrylic resins, and polypropylene. Examples thereof include film materials that have been widely used in the field. When a transparent film is bonded on both surfaces of a polarizing film, each transparent film may be the same or a different type of film.

The cycloolefin resin is a thermoplastic resin (also referred to as a thermoplastic cycloolefin resin) having a monomer unit made of a cyclic olefin (cycloolefin), such as norbornene or a polycyclic norbornene 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 unit of monomer composed of a chain olefin is usually 5 to 80 mol%, and the unit of monomer composed of an aromatic compound having a vinyl group is usually 5 to 80 mol%.

Cycloolefin-based resins are commercially available as appropriate, for example, TOPAS (made by TOPAS ADVANCED POLYMERS, sold by Polyplastics Co., Ltd. in the Asia-Pacific region including Japan), Arton (made by JSR Co., Ltd.), Zeonore ( ZEONOR (made by Nippon Zeon Co., Ltd.), ZEONEX (made by Nippon Zeon Co., Ltd.), Apel (made by Mitsui Chemicals), Oxis (OXIS) (made by Okura Kogyo Co., Ltd.), etc. Can be 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.), Zeonoa Film (manufactured by Nippon Zeon Co., Ltd.), Arton Film (manufactured by JSR 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 the film roll, and in a heating furnace, in 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 stretching 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, and therefore, the cycloolefin-based resin film is usually rolled after the protective film is bonded. In addition, since cycloolefin resin films generally have poor surface activity, surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment is performed on the surface to be bonded to the polarizing film. 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 part or a 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-based resin film, an appropriate commercially available product, for example, Fujitac TD80 (manufactured by Fuji Film Co., Ltd.), Fujitac TD80UF (manufactured by Fuji Film Co., Ltd.), Fujitac TD80UZ (manufactured by Fuji Film Co., Ltd.) KC8UX2M (manufactured by Konica Minolta Opto) KC8UY (manufactured by Konica Minolta Opto) Fujitac TD60UL (manufactured by FUJIFILM Corporation), KC4UYW (manufactured by Konica Minolta Opto), KC6UAW (Konica Minolta Opto) Etc.) can be used preferably.

Further, as the transparent film, a cellulose acetate-based resin film imparted with retardation characteristics is also preferably used. Commercially available cellulose acetate resin films with such retardation characteristics include WV BZ 438 (manufactured by FUJIFILM Corporation), KC4FR-1 (manufactured by Konica Minolta Opto), 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.

These cellulose acetate-based resin films are easy to absorb water, and the moisture content of the polarizing plate may affect the sagging at the end of the polarizing plate. The moisture content during the production of the polarizing plate is preferably closer to the equilibrium moisture content in the storage environment of the polarizing plate, for example, a clean room production line or a roll storage warehouse, and depends on the configuration of the laminated film. About 5% by weight, more preferably 2.5 to 3.0% by weight. The numerical value of the moisture content of this polarizing plate was measured by the dry weight method and is a change in weight after 105 ° C./120 minutes.

The thickness of the transparent film used in the method for producing a polarizing plate of the present invention is preferably thin, but if it is too thin, the strength is lowered and the workability is poor. On the other hand, if it is too thick, problems such as a decrease in transparency and a longer curing time after lamination are caused. Therefore, a suitable thickness of the transparent film is, for example, 5 to 200 μm, preferably 10 to 150 μm, more preferably 10 to 100 μm.

In order to improve the adhesion between the adhesive or pressure-sensitive adhesive and the polarizing film and / or transparent film, the polarizing film and / or transparent film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet treatment, primer coating treatment, saponification. Surface treatment such as treatment may be applied.

Further, the transparent film may be subjected to surface treatments such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment individually or in combination of two or more. The transparent film and / or the transparent 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.

Furthermore, optical functions such as functions as a retardation film, function as a brightness enhancement film, function as a reflection film, function as a transflective film, function as a diffusion film, 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 transparent film, such a function is achieved. In addition, the transparent film itself can be given such a function. Further, the transparent film may have a plurality of functions such as a diffusion film having the function of a brightness enhancement film.

For example, the above-described transparent 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, so that a retardation film is obtained. Functions can be added. The retardation characteristics of the retardation film can be appropriately selected, for example, such that the front retardation value is in the range of 5 to 100 nm and the thickness direction retardation value is in the range of 40 to 300 nm. Further, two or more layers having different central wavelengths of selective reflection are formed in the transparent film by forming micropores by a method as described in Japanese Patent Application Laid-Open Nos. 2002-169025 and 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 transparent film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. A function as a diffusion film can be imparted by coating the transparent film with a resin solution containing fine particles. A function as an optical compensation film can be imparted by coating and aligning a liquid crystal compound such as a discotic liquid crystal compound on the transparent film. Moreover, you may make the transparent 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 films (manufactured by Fuji Film Co., Ltd.). Film, Arton Film (manufactured by JSR Corporation), Zeonore Film (manufactured by ZEON Corporation), Essina (manufactured by Sekisui Chemical Co., Ltd.), VA-TAC (manufactured by Comic Minolta Opto), Sumikalite ( And a retardation film such as Sumitomo Chemical Co., Ltd.

<Adhesive layer>
Examples of the adhesive constituting the adhesive layer include an active energy ray-curable adhesive and a water-based adhesive. The active energy ray-curable adhesive is preferably used because it is not necessary to dry the adhesive and it is easy to prevent deterioration of the polarizing film due to drying.

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.

An epoxy resin means a compound having two or more epoxy groups in a molecule. From the viewpoint of weather resistance, refractive index, cationic polymerizability, etc., the epoxy resin contained in the curable epoxy resin composition as an adhesive is an epoxy resin containing no aromatic ring in the molecule (for example, JP-A-2004-245925). It is preferred that the Examples of such epoxy resins include hydrogenated epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins.

The hydrogenated epoxy resin is obtained by a method of glycidyl etherifying a nuclear hydrogenated polyhydroxy compound obtained by selectively subjecting a polyhydroxy compound, which is a raw material of an aromatic epoxy resin, to a nuclear hydrogenation reaction under pressure in the presence of a catalyst. Obtainable. Examples of aromatic epoxy resins include bisphenol-type epoxy resins such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol S diglycidyl ether; phenol novolac epoxy resins, cresol novolac epoxy resins, and hydroxy Examples include novolak-type epoxy resins such as benzaldehyde phenol novolac epoxy resins; glycidyl ethers of tetrahydroxyphenylmethane, glycidyl ethers of tetrahydroxybenzophenone, and polyfunctional epoxy resins such as epoxidized polyvinylphenol. Among the hydrogenated epoxy resins, hydrogenated glycidyl ether of bisphenol A is preferable.

The alicyclic epoxy resin means an epoxy resin having at least one epoxy group bonded to the alicyclic ring in the molecule. The “epoxy group bonded to an alicyclic ring” means a bridged oxygen atom —O— in the structure represented by the following formula. In the following formula, m is an integer of 2 to 5.

A compound in which a group in which one or more hydrogen atoms in (CH ₂ ) _m in the above formula are removed is bonded to another chemical structure can be an alicyclic epoxy resin. One or more hydrogen atoms in (CH ₂ ) _m may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among alicyclic epoxy resins, an epoxy resin having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula) exhibits excellent adhesion. Therefore, it is preferably used. Although the alicyclic epoxy resin used preferably below is specifically illustrated, it is not limited to these compounds.

(A) Epoxycyclohexylmethyl epoxycyclohexanecarboxylates represented by the following formula (I):

In the formula, R ¹ and R ² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(B) Epoxycyclohexanecarboxylates of alkanediol represented by the following formula (II):

In the formula, R ³ and R ⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and n represents an integer of 2 to 20.

(C) Epoxycyclohexyl methyl esters of dicarboxylic acid represented by the following formula (III):

In the formula, R ⁵ and R ⁶ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and p represents an integer of 2 to 20.

(D) Epoxycyclohexyl methyl ethers of polyethylene glycol represented by the following formula (IV):

In the formula, R ⁷ and R ⁸ independently of each other represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and q represents an integer of 2 to 10.

(E) Epoxycyclohexyl methyl ethers of alkanediols represented by the following formula (V):

In the formula, R ⁹ and R ¹⁰ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and r represents an integer of 2 to 20.

(F) Diepoxy trispiro compound represented by the following formula (VI):

In the formula, R ¹¹ and R ¹² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(G) Diepoxy monospiro compound represented by the following formula (VII):

In the formula, R ¹³ and R ¹⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(H) Vinylcyclohexene diepoxides represented by the following formula (VIII):

In the formula, R ¹⁵ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.
(I) Epoxycyclopentyl ethers represented by the following formula (IX):

In the formula, R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

(J) Diepoxytricyclodecanes represented by the following formula (X):

In the formula, R ¹⁸ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.
Among the alicyclic epoxy resins exemplified here, the following alicyclic epoxy resins are commercially available or similar, and are more preferably used because they are relatively easy to obtain.

(A) Esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and (7-oxa-bicyclo [4.1.0] hept-3-yl) methanol [formula (I) In which R ¹ = R ² = H],
(B) 4-methyl-7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and (4-methyl-7-oxa-bicyclo [4.1.0] hept-3-yl) methanol Ester compound of [In the formula (I), R ¹ = 4-CH ₃ , R ² = 4-CH ₃ compound],
(C) Esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and 1,2-ethanediol [in the formula (II), R ³ = R ⁴ = H, n = 2 Compound],
(D) (7-oxabicyclo [4.1.0] hept-3-yl) methanol and adipic acid ester compound [compound of formula (III) wherein R ⁵ = R ⁶ = H, p = 4] ,
(E) (4-Methyl-7-oxabicyclo [4.1.0] hept-3-yl) esterified product of methanol and adipic acid [in the formula (III), R ⁵ = 4-CH ₃ , R ⁶ = 4-CH ₃ , p = 4 compound]
(F) Etherified product of (7-oxabicyclo [4.1.0] hept-3-yl) methanol and 1,2-ethanediol [in the formula (V), R ⁹ = R ¹⁰ = H, r = Compound of 2].

In addition, examples of the aliphatic epoxy resin include polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof. More specifically, 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; glycerin triglycidyl ether; trimethylolpropane triglycidyl ether; polyethylene glycol diglycidyl ether; propylene Diglycidyl ether of glycol; Polyether of polyether polyol obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin A glycidyl ether etc. are mentioned.

The epoxy resin which comprises the adhesive agent which consists of an epoxy-type resin composition may be used individually by 1 type, and may use 2 or more types together. The epoxy equivalent of the epoxy resin used in this composition is usually in the range of 30 to 3,000 g / equivalent, preferably 50 to 1,500 g / equivalent. When the epoxy equivalent is less than 30 g / equivalent, the flexibility of the composite polarizing plate after curing may be reduced, or the adhesive strength may be reduced. On the other hand, if it exceeds 3,000 g / equivalent, the compatibility with other components contained in the adhesive may be lowered.

In this adhesive, cationic polymerization is preferably used as a curing reaction of the epoxy resin from the viewpoint of reactivity. Therefore, it is preferable to mix | blend a cationic polymerization initiator with the curable epoxy resin composition which is an active energy ray hardening-type adhesive agent. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and initiates an epoxy group polymerization reaction. Hereinafter, a cationic polymerization initiator that generates a cationic species or a Lewis acid by irradiation of active energy rays and initiates a polymerization reaction of an epoxy group is referred to as a “photo cationic polymerization initiator”.

The method of curing the adhesive by irradiating with active energy rays using a cationic photopolymerization initiator enables curing at room temperature, reducing the need to consider the distortion due to heat resistance or expansion of the polarizing film, and between the films Is advantageous in that it can be bonded well. In addition, since the photocationic polymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy resin.

Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-allene complexes.

Examples of the aromatic diazonium salt include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, benzenediazonium hexafluoroborate, and the like. Examples of the aromatic iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di (4-nonylphenyl) iodonium hexafluorophosphate, and the like.

Examples of the aromatic sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, 4,4′-bis (diphenylsulfonio) diphenyl sulfide bis ( Hexafluorophosphate), 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide, bis (hexafluoroantimonate), 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio ] Diphenyl sulfide bis (hexafluorophosphate), 7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate, 7 -[Di (p-toluyl) sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide hexafluorophosphate, 4- (p-tert-butylphenyl) Carbonyl) -4′-diphenylsulfonio-diphenyl sulfide, hexafluoroantimonate, 4- (p-tert-butylphenylcarbonyl) -4′-di (p-toluyl) sulfonio-diphenyl sulfide, tetrakis (pentafluorophenyl) borate, etc. Is mentioned.

Examples of the iron-allene complex include xylene-cyclopentadienyl iron (II) hexafluoroantimonate, cumene-cyclopentadienyl iron (II) hexafluorophosphate, xylene-cyclopentadienyl iron (II). -Tris (trifluoromethylsulfonyl) methanide and the like.

Commercial products of these photocationic polymerization initiators can be easily obtained. For example, “Kayarad PCI-220” and “Kayarad PCI-620” (Nippon Kayaku Co., Ltd. )), “UVI-6990” (manufactured by Union Carbide), “Adekaoptomer SP-150” and “Adekaoptomer SP-170” (manufactured by ADEKA Corporation), “CI-5102”, “ "CIT-1370", "CIT-1682", "CIP-1866S", "CIP-2048S" and "CIP-2064S" (above, Nippon Soda Co., Ltd.), "DPI-101", "DPI-102" , “DPI-103”, “DPI-105”, “MPI-103”, “MPI-105”, “BBI-101”, “BBI-1” 2 ”,“ BBI-103 ”,“ BBI-105 ”,“ TPS-101 ”,“ TPS-102 ”,“ TPS-103 ”,“ TPS-105 ”,“ MDS-103 ”,“ MDS-105 ” "DTS-102" and "DTS-103" (manufactured by Midori Chemical Co., Ltd.), "PI-2074" (manufactured by Rhodia), and the like.

The photocationic polymerization initiator may be used alone or in combination of two or more. Among these, aromatic sulfonium salts are preferably used because they have ultraviolet absorption characteristics even in a wavelength region of 300 nm or more, and thus can provide a cured product having excellent curability and good mechanical strength and adhesive strength.

The amount of the cationic photopolymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 part by weight or more, and preferably 15 parts by weight or less with respect to 100 parts by weight of the epoxy resin. When the blending amount of the cationic photopolymerization initiator is less than 0.5 parts by weight with respect to 100 parts by weight of the epoxy resin, curing becomes insufficient, and mechanical strength and adhesive strength tend to decrease. Moreover, when the compounding quantity of a photocationic polymerization initiator exceeds 20 weight part with respect to 100 weight part of epoxy resins, the hygroscopic property of hardened | cured material will become high because the ionic substance in hardened | cured material will increase, and durability performance. May be reduced.

When using a photocationic polymerization initiator, the curable epoxy resin composition may further contain a photosensitizer as necessary. By using a photosensitizer, the reactivity of cationic polymerization is improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, and photoreductive dyes.

More specific examples of photosensitizers include, for example, benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether, and α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, o Benzophenone derivatives such as methyl benzoylbenzoate, 4,4′-bis (dimethylamino) benzophenone, and 4,4′-bis (diethylamino) benzophenone; thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; 2 Anthraquinone derivatives such as chloroanthraquinone and 2-methylanthraquinone; acridone derivatives such as N-methylacridone and N-butylacridone; other α, α-diethoxyacetophenone, ben Examples include zil, fluorenone, xanthone, uranyl compounds, and halogen compounds. A photosensitizer may be used individually by 1 type and may use 2 or more types together. The photosensitizer is preferably contained within a range of 0.1 to 20 parts by weight in 100 parts by weight of the curable epoxy resin composition.

The epoxy resin contained in the adhesive is cured by photocationic polymerization, but may be cured by both photocationic polymerization and thermal cationic polymerization. In the latter case, it is preferable to use a photocationic polymerization initiator and a thermal cationic polymerization initiator in combination.

Examples of the thermal cationic polymerization initiator include benzylsulfonium salt, thiophenium salt, thioranium salt, benzylammonium, pyridinium salt, hydrazinium salt, carboxylic acid ester, sulfonic acid ester, and amine imide. These thermal cationic polymerization initiators can be easily obtained as commercial products. For example, “Adeka Opton CP77” and “Adeka Opton CP66” (manufactured by ADEKA Corporation), “ "CI-2639" and "CI-2624" (manufactured by Nippon Soda Co., Ltd.), "Sun-Aid SI-60L", "Sun-Aid SI-80L" and "Sun-Aid SI-100L" (Sanshin Chemical Co., Ltd.) ))).

The active energy ray-curable adhesive may further contain a compound that promotes cationic polymerization, such as oxetanes and polyols.

Oxetanes are compounds having a 4-membered ring ether in the molecule, such as 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, 3 -Ethyl-3- (phenoxymethyl) oxetane, di [(3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, phenol novolac oxetane and the like. These oxetanes can be easily obtained as commercial products. For example, all of them are trade names such as “Aron Oxetane OXT-101”, “Aron Oxetane OXT-121”, “Aron Oxetane OXT-211”. “Aron Oxetane OXT-221” and “Aron Oxetane OXT-212” (above, manufactured by Toagosei Co., Ltd.). These oxetanes are usually contained in the curable epoxy resin composition in a proportion of 5 to 95% by weight, preferably 30 to 70% by weight.

As the polyols, those having no acidic groups other than phenolic hydroxyl groups are preferable. For example, polyol compounds having no functional groups other than hydroxyl groups, polyester polyol compounds, polycaprolactone polyol compounds, polyol compounds having phenolic hydroxyl groups, polycarbonates A polyol etc. can be mentioned. The molecular weight of these polyols is usually 48 or more, preferably 62 or more, more preferably 100 or more, and preferably 1,000 or less. These polyols are contained in the curable epoxy resin composition in a proportion of usually 50% by weight or less, preferably 30% by weight or less.

Active energy ray-curable adhesives include ion trapping agents, antioxidants, chain transfer agents, tackifiers, thermoplastic resins, fillers, flow regulators, leveling agents, plasticizers, antifoaming agents, etc. Additives can be blended. Examples of the ion trapping agent include powdered bismuth-based, antimony-based, magnesium-based, aluminum-based, calcium-based, titanium-based, and mixed inorganic compounds. The antioxidant is a hindered phenol-based antioxidant. Etc.

Active energy ray-curable adhesives can be used as solventless adhesives that are substantially free of solvent components, but each coating method has an optimum viscosity range, A solvent may be included. It is preferable to use a solvent that dissolves the epoxy resin composition and the like well without degrading the optical performance of the polarizing film. For example, hydrocarbons represented by toluene, esters represented by ethyl acetate, and the like. And organic solvents such as The viscosity of the active energy ray-curable adhesive used in the present invention is, for example, in the range of about 5 to 1000 mPa · s, preferably 10 to 200 mPa · s, more preferably 20 to 100 mPa · s.

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 adhesive is usually applied at a temperature of 15 to 40 ° C. after its preparation, and the bonding temperature is usually in the range of 15 to 30 ° C. When using a water-system adhesive, after bonding a film, in order to remove the water contained in a water-system adhesive, it is made to dry. The temperature of the drying furnace is preferably 30 ° C. or higher and lower than 110 ° C. If it is less than 30 ° C., the adhesive surface tends to be peeled off. If it is 110 ° C. or higher, the optical performance of the polarizing film or the like may be deteriorated by heat. The drying time can be 1 to 1000 seconds.

After drying, it may be further cured at room temperature or slightly higher, for example, at a temperature of about 20 to 45 ° C. for about 12 to 600 hours. The temperature at the time of curing is generally set lower than the temperature adopted at the time of drying.

<Adhesive layer>
The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is usually a composition in which an acrylic resin, a styrene resin, a silicone resin, or the like is used as a base polymer and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. Become. Furthermore, a pressure-sensitive adhesive layer exhibiting light scattering properties can be formed by mixing fine particles in the pressure-sensitive adhesive.

The thickness of the pressure-sensitive adhesive layer is preferably 1 to 40 μm, but it is preferably applied thinly as long as the workability and durability characteristics are not impaired, and more preferably 3 to 25 μm. A thickness of 3 to 25 μm is suitable for giving good processability and suppressing dimensional change of the polarizing film. When the thickness of the pressure-sensitive adhesive layer is less than 1 μm, the tackiness is lowered. On the other hand, when the thickness exceeds 40 μm, problems such as the pressure-sensitive adhesive protruding easily occur.

The method of forming the pressure-sensitive adhesive layer on the transparent film or polarizing film is not particularly limited, and a solution containing each component including the above-mentioned base polymer is applied to the transparent film surface or the polarizing film surface, After drying to form a pressure-sensitive adhesive layer, it may be bonded to a separator or other types of film, or after forming a pressure-sensitive adhesive layer on the separator, it is laminated on a transparent film surface or a polarizing film surface. Also good.

[Polarizer]
The polarizing plate of the present invention includes a polarizing film and a transparent 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. The polarizing plate of the present invention is produced by the production method described above.

The polarizing plate of the present invention preferably has a single hue b value of 2.5 to 4.5. Here, the b value means a b value in Hunter's Lab color system. A single hue means a hue of light transmitted to the opposite surface when natural light is incident on one polarizing plate from one surface. A single hue b value is in such a numerical range, and the liquid crystal display device is configured using a polarizing plate appropriately colored, thereby facilitating the adjustment of the hue of the liquid crystal display screen. When the single hue b value of the polarizing plate is less than 2.5, since the polarizing plate is not sufficiently colored, it may be difficult to adjust the hue of the liquid crystal display screen when configuring a liquid crystal display device using the polarizing plate. is there. The polarizing plate of the present invention preferably has a hue b value of -1.5 to 0.1 when two sheets are arranged orthogonally. When the orthogonal hue b value is in such a numerical range, color unevenness in the display image is suppressed.

The polarizing plate of the present invention has optical properties such that the visibility corrected single transmittance is preferably 42.5% or more, and the visibility corrected polarization degree is preferably 99.99% or more. 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.

In general, in a polarizing plate having a high transmittance region of 42.5% or more, in order to adjust the hue b value of a single substance to 2.5 to 4.5, the drying in the drying process is strengthened or orthogonal Although it is necessary to adjust the hue b value, when the former is adopted, it becomes difficult to adjust the polarizing film to a predetermined moisture content, while when the latter is adopted, color unevenness and heat resistance are reduced. Problems such as deterioration are likely to occur. According to the present invention, by treating a dyed polarizing film at a temperature of 90 ° C. or higher, it is possible to obtain a polarizing plate having excellent characteristics that eliminates these problems.

Hereinafter, the present invention will be described more specifically with reference to examples. In the following examples, the optical performance of the obtained polarizing plate was set on a UV-visible spectrophotometer V-7100 manufactured by JASCO Corporation, and linearly polarized light in the transmission axis direction was incident on the polarizing plate. The UV-visible transmission spectrum was measured when the linearly polarized light in the absorption axis direction was incident, and was calculated based on the spectrum. The visibility corrected single transmittance, the visibility corrected polarization degree, the single hue b value, and the orthogonal hue b value were determined by software incorporated in the UV-visible spectrophotometer V-7100 used here. Moreover,% showing the moisture content in the following examples is based on weight.

[Example 1]
(Preparation of polarizing film)
A 75 μm-thick polyvinyl alcohol film (Kurarevinilon 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 sufficiently swell the film (swelling step). Next, after uniaxial stretching while being immersed in an aqueous solution containing iodine and potassium iodide (dyeing step and stretching step), potassium iodide / boric acid / water is 55 / C at a weight ratio of 12 / 4.4 / 100. While being immersed in an aqueous solution and subjected to water resistance treatment, uniaxial stretching was performed until the cumulative stretching ratio from the original fabric became 5.5 times (crosslinking step and stretching step). Subsequently, it was immersed in a 40 ° C. boric acid-containing aqueous solution having the same composition, and then washed with 6 ° C. pure water (cleaning step).

The polyvinyl alcohol film having been subjected to each of the above treatments is held for 90 seconds in a first drying furnace having an atmospheric temperature of 50 ° C. (low temperature drying step), and then in a second drying furnace having an atmospheric temperature of 95 ° C. For 30 seconds (high temperature drying step) to produce a polarizing film. The moisture content of the obtained polarizing film was 11.1%.

(Preparation of polarizing plate)
As a transparent film, a cellulose acetate-based resin film “KC4FR-1” (made by Konica Minolta Opto Co., Ltd.) having a retardation property of 40 μm thickness and a triacetyl cellulose film “KC8UX2MW” (Konica Minolta Co., Ltd.) having a thickness of 30 μm are used. The epoxy resin composition “KR-70T” (manufactured by ADEKA Corporation, viscosity: 44 mPa · s), which is an ultraviolet curable adhesive, is bonded to one side of these. Coating was performed using an agent coating apparatus so that the thickness after curing was 2.5 μm, and an adhesive layer was provided. Next, the adhesive layer of each transparent film was bonded to both surfaces of the polarizing film by a nip roll (bonding roll). In this way, the laminate of the cellulose acetate resin film “KC4FR-1”, the polarizing film, and the triacetyl cellulose film “KC8UX2MW” was irradiated with ultraviolet rays from the cellulose acetate resin film “KC4FR-1” side. The adhesive was cured. At this time, the total integrated light amount (integrated amount of light irradiation intensity in the wavelength region of wavelength 280 to 320 mm) measured by an ultraviolet ray measuring device (Power Pack II, manufactured by Fusion UV Systems) was 250 mJ / cm ² . .

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Example 1, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.996%, the single hue b value is 3.2, and the orthogonal hue b value is -0.5.

[Example 2]
(Preparation of polarizing film)
The polarizing film of Example 2 was produced in the same manner as the polarizing film of Example 1 except for the drying step. The drying process of Example 2 is held for 90 seconds in a first drying furnace having an atmospheric temperature of 50 ° C., and then for 30 seconds in a second drying furnace having an atmospheric temperature of 80 ° C. (Drying step), during this time, a hot roll having a surface temperature of 105 ° C. was brought into contact for 2 seconds (high temperature drying step). The moisture content of the obtained polarizing film was 13.0%.

(Preparation of polarizing plate)
Using the polarizing film of Example 2, the polarizing plate of Example 2 was produced in the same manner as Example 1.

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Example 2, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.996%, the single hue b value is 3.4, and the orthogonal hue b value is -0.5.

[Example 3]
(Preparation of polarizing film)
The polarizing film of Example 3 was produced in the same manner as the polarizing film of Example 1 except for the drying step. The drying process of Example 3 is held for 60 seconds in a first drying furnace having an atmospheric temperature of 50 ° C. (low temperature drying process), and subsequently held in a second drying furnace having an atmospheric temperature of 98 ° C. for 20 seconds. (High temperature drying step). The moisture content of the obtained polarizing film was 10.8%.

(Preparation of polarizing plate)
Using the polarizing film of Example 3, the polarizing plate of Example 3 was produced in the same manner as in Example 1.

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Example 3, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.996%, the single hue b value is 3.6, and the orthogonal hue b value is -0.5.

[Comparative Example 1]
(Preparation of polarizing film)
The polarizing film of Comparative Example 1 was produced in the same manner as the polarizing film of Example 1 except for the drying step. The drying process of Comparative Example 1 was only held for 3 minutes in a drying furnace having an atmospheric temperature of 70 ° C. The moisture content of the obtained polarizing film was 11.5%.

(Preparation of polarizing plate)
Using the polarizing film of Comparative Example 1, a polarizing plate of Comparative Example 1 was produced in the same manner as Example 1.

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Comparative Example 1, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.996%, the single hue b value is 2.1, and the orthogonal hue b value is -0.5.

[Comparative Example 2]
(Preparation of polarizing film)
The polarizing film of Comparative Example 2 was produced in the same manner as the polarizing film of Example 1 except for the drying step. The drying process of Comparative Example 2 was only held for 90 seconds in a drying furnace having an atmospheric temperature of 95 ° C. The moisture content of the obtained polarizing film was 6.7%.

(Preparation of polarizing plate)
Using the polarizing film of Comparative Example 2, a polarizing plate of Comparative Example 2 was produced in the same manner as Example 1.

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Comparative Example 2, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.995%, the single hue b value is 4.7, and the orthogonal hue b value is -0.2. Moreover, a large curl was seen in the obtained polarizing plate.

[Comparative Example 3]
(Preparation of polarizing film)
The polarizing film of Comparative Example 3 was produced in the same manner as the polarizing film of Example 1 except for the drying step. The drying process of Comparative Example 3 is held for 60 seconds in a first drying furnace having an atmospheric temperature of 50 ° C. (low temperature drying process), and then is held for 3 seconds in a second drying furnace having an atmospheric temperature of 90 ° C. (High temperature drying step). The moisture content of the obtained polarizing film was 17.1%.

(Preparation of polarizing plate)
Using the polarizing film of Comparative Example 3, a polarizing plate of Comparative Example 3 was produced in the same manner as Example 1.

(Optical properties of polarizing plate)
As for the optical characteristics of the polarizing plate of Comparative Example 3, the visibility corrected single transmittance is 42.8%, the visibility corrected polarization degree is 99.995%, the single hue b value is 2.2, and the orthogonal hue b value is -0.7. Moreover, a large curl was seen in the obtained polarizing plate.

As described above, a polarizing film is produced by incorporating a high-temperature drying step into the drying step as in Examples 1 to 3, and a polarizing plate is produced using this to maintain good polarization performance and a hue b value orthogonal to that. However, it was found that a single-piece hue b value was in the range of 2.5 to 4.5, and a polarizing plate having good optical characteristics was obtained.

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

Claims (8)

1. A dyeing step of dyeing a polyvinyl alcohol film with a dichroic dye;
   A crosslinking step in which the dyed polyvinyl alcohol film is immersed in a solution containing a crosslinking agent to be crosslinked;
   A drying step of drying the crosslinked polyvinyl alcohol-based resin film, and a method for producing a polarizing film comprising:
   The method for producing a polarizing film, wherein the drying step includes a high temperature drying step of drying at a drying temperature of 90 ° C. or more, and the film is dried so that the moisture content of the film is 8 to 15% by weight.
2. The method for producing a polarizing film according to claim 1, wherein the high-temperature drying step is continued for 1 second to 60 seconds.
3. The method for producing a polarizing film according to claim 1 or 2, wherein the drying step further includes a low temperature drying step of drying at a drying temperature of less than 90 ° C for 30 seconds or more.
4. The method for producing a polarizing film according to any one of claims 1 to 3, wherein the high-temperature drying step is performed by bringing the polarizing film into contact with a hot roll.
5. A step of producing a polarizing film by the method for producing a polarizing film according to any one of claims 1 to 4,
   The manufacturing method of a polarizing plate provided with the bonding process which bonds a transparent film to the at least one surface of the said polarizing film.
6. The manufacturing method of the polarizing plate of Claim 5 which bonds the said polarizing film and the said transparent film through an active energy ray hardening-type adhesive agent in the said bonding process.
7. A polarizing plate comprising a polarizing film produced by the method for producing a polarizing film according to any one of claims 1 to 4, and a transparent film bonded to at least one surface of the polarizing film,
   Visibility correction single transmittance is 42.5% or more, visibility correction polarization degree is 99.99% or more, single hue b value is 2.5 to 4.5, and orthogonal hue b value is -1.5 to A polarizing plate which is 0.1.
8. The polarizing plate according to claim 7, wherein the polarizing film and the transparent film are bonded via an active energy ray curable adhesive.