CN1800881B - Manufacturing method of polarizing film, polarizing plate, and optical laminate - Google Patents

Abstract

To provide a method for manufacturing a polarizing film having less color unevenness and a uniform thickness. In the method for manufacturing the polarizing film in which a polyvinyl alcohol-based film is sequentially subjected to swelling, dyeing, boric acid treatment, washing and drying, and in at least two steps of the treatment steps, a peripheral speed difference is provided between two nip rolls for carrying the film to stretch the film, when the film is immersed in a boric acid solution in the boric acid treatment step, the film is immersed in noncontact with a roll and the time from the immersion to first contact with a roll in the boric acid solution is 0.4-5s.

Description

Manufacturing method of polarizing film, polarizing plate, and optical laminate

technical field

The present invention relates to a method for producing a polarizing film with less color unevenness and uniform film thickness, a polarizing plate in which a protective film is laminated on at least one side of the obtained polarizing film, and a retardation film, brightness improvement An optical laminate obtained by laminating one or more of a film, a viewing angle improving film, and a transflective film.

Background technique

As a polarizing film, a film in which a dichroic dye is adsorbed and aligned on a polyvinyl alcohol-based film has conventionally been used. That is, an iodine-based polarizing film using iodine as a dichroic dye, a dye-based polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually bonded with a protective film such as triacetyl cellulose to at least one surface, preferably both surfaces thereof, with an adhesive containing an aqueous solution of a polyvinyl alcohol-based resin to form a polarizing plate.

As a method for producing a polarizing film, there is known a method of dipping a polyvinyl alcohol-based film in water to swell it using nip rolls or guide rolls, dyeing it with the above-mentioned dichroic dye, and stretching it. Next, in order to immobilize iodine on the film, the polyvinyl alcohol-based film was treated with boric acid, washed with water, and dried. At this time, the nip rolls before and after the treatment bath are provided with a peripheral speed difference to stretch the film, and the transport direction of the film is changed by guide rolls to introduce and export the film into the treatment liquid (for example, refer to Patent Document 1).

In recent years, along with the improvement of the quality of liquid crystal display devices using polarizing films, it is desired to obtain polarizing films with less color unevenness and uniform film thickness than polarizing films obtained by conventional methods.

[Patent Document 1] Japanese Unexamined Patent Publication No. 10-170721

Contents of the invention

The main problem to be solved by the present invention is to provide a method for producing a polarizing film with less color unevenness and uniform film thickness.

The inventors of the present invention have worked hard to produce a polarizing film with less color unevenness and uniform film thickness. As a result, it has been found that when the film is immersed in a boric acid solution in the boric acid treatment step, the film is dipped without contacting the roll. When the time from immersion of the film to the first contact with the roll in the boric acid solution is 0.4 to 5 seconds, a polarizing film with less color unevenness and uniform film thickness can be obtained, thereby completing the present invention.

That is, the manufacturing method of the polarizing film of the present invention is to treat the polyvinyl alcohol-based film in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment, and at least two treatments in the treatment steps In the process, a method of producing a polarizing film by stretching the film by giving a peripheral speed difference between two nip rollers for conveying the film is characterized in that when the film is immersed in a boric acid solution in the boric acid treatment process, The immersion in a state not in contact with the roll is such that the time from immersion of the membrane to the first contact with the roll in the boric acid solution is 0.4 to 5 seconds.

The time from immersion of the membrane to the first contact with the roll in the boric acid solution is preferably 0.5 to 3 seconds.

In addition, the temperature of the boric acid solution is preferably 50 to 85°C.

Furthermore, in the polarizing plate of the present invention, a protective film is bonded to at least one surface of the polarizing film obtained as described above. This protective film may have any one function of a retardation film, a brightness improvement film, a viewing angle improvement film, and a transflective film. In addition, the optical laminate of the present invention has at least one member selected from the group consisting of a retardation film, a brightness improvement film, a viewing angle improvement film, and a transflective film bonded to the polarizer having a protective film bonded to at least one side thereof.

According to the method of the present invention, a polarizing film with less color unevenness and uniform film thickness can be manufactured, and by using the polarizing plate and optical laminate made of the polarizing film in a liquid crystal display device, a thin, high Classy LCD display.

Detailed ways

The present invention will be described in detail below.

The polyvinyl alcohol-type resin which forms a polyvinyl-alcohol-type film in this invention generally exemplifies what saponified polyvinyl acetate-type resin. The degree of saponification is about 85 mol % or more, preferably about 90 mol % or more, and more preferably about 99 mol % to 100 mol %. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, there are also copolymers of vinyl acetate and other monomers that can be copolymerized with it, such as ethylene-vinyl acetate copolymer things etc. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like. The degree of polymerization of the polyvinyl alcohol-based resin is about 1,000 to 10,000, preferably about 1,500 to 5,000.

These polyvinyl alcohol-based resins may also be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes can also be used. Generally, as a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of about 20 μm to 100 μm, preferably about 30 μm to 80 μm is used. The industrially practical film width is about 1500 mm to 4000 mm.

The polyvinyl alcohol-based polarizing film obtained by treating the unstretched film in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment and finally drying is, for example, about 5 μm to 50 μm.

The polarizing film of the present invention is a polyvinyl alcohol-based uniaxially stretched film in which a dichroic dye is adsorbed and oriented, and its production method is roughly classified into two types. One method is a method in which a polyvinyl alcohol-based film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, and finally drying.

The second method is to carry out solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment in the aqueous solution of the unstretched polyvinyl alcohol-based film, and in the boric acid treatment process and/or in the previous process. A method in which uniaxial stretching is carried out in a wet process, followed by drying.

In the present invention, in any method, uniaxial stretching is performed in a plurality of steps. As the stretching method, a known method can be used, for example, stretching between rolls in which a circumferential speed difference is applied between two nip rolls that transport the film, and stretching with heated rolls as described in Japanese Patent No. 2731813. method, tenter stretching method, etc. In addition, basically the sequence of steps is as described above, but the number of treatment baths, treatment conditions and the like are not limited.

In addition, of course, steps not described in the above-mentioned steps are also freely inserted for other purposes. As an example of this step, immersion treatment (iodide treatment) performed with an iodide aqueous solution not containing boric acid after boric acid treatment, or immersion treatment performed with an aqueous solution containing zinc chloride or the like not containing boric acid (zinc chloride, etc.) processing) procedures, etc.

The swelling step is performed for the purpose of removing foreign substances on the surface of the film, removing the plasticizer in the film, imparting easy dyeability in the next process, and plasticizing the film. The treatment conditions are determined within the range in which these objects can be achieved, and in the range in which disadvantages such as extreme dissolution and devitrification of the base film do not occur. To swell a film previously stretched in air, it is performed by immersing the film in an aqueous solution at, for example, about 20°C to 70°C, preferably about 30°C to 60°C. The immersion time of the membrane is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. When the unstretched roll (raw) film is initially swelled, it is performed by immersing the film in an aqueous solution at, for example, about 10°C to 50°C, preferably about 20°C to 40°C. The immersion time of the membrane is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

In the swelling treatment process, since the film swells in the transverse direction, it is easy to cause problems such as wrinkles on the film, so it is preferable to use a flat roll (expanding roll), a spiral roll, a convex roll, a cloth guide (cross guide), The film is conveyed by a known open-width device such as a bender roll and tenter clips while removing wrinkles of the film. For the purpose of stabilizing the transport of the membrane in the bath, control the flow of water in the swelling bath with a water sprinkler, or use an EPC device (EdgePosition Control device: a device that detects the end of the membrane and prevents the membrane from bending), etc. Also useful. In this step, since the film swells and expands in the moving direction of the film, in order to eliminate the slack of the film in the conveying direction, for example, a method such as controlling the speed of conveying rollers before and after the treatment tank is preferably employed. In addition, the swelling treatment bath used, in addition to pure water, can also use boric acid (described in JP-A-10-153709 A) and chloride (described in JP-A-10-153709 ) in the range of about 0.01% by weight to 10% by weight. 06-281816), aqueous solutions of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

The dyeing step of the dichroic dye is performed for the purpose of adsorbing the dichroic dye to the film, orienting it, and the like. The treatment conditions are determined within the range in which these objects can be achieved, and in the range in which disadvantages such as extreme dissolution and devitrification of the base film do not occur. When using iodine as a dichroic dye, for example, at a temperature of about 10°C to 45°C, preferably about 20°C to 35°C, and in a weight ratio of iodine/KI/water=about 0.003 to 0.2/about 0.1 to 10/ The immersion treatment is performed at a concentration of 100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide or the like may also be used. In addition, other iodides may be used in combination with potassium iodide. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, and the like may coexist. When boric acid is added, it is distinguished from the boric acid treatment described below in that iodine is contained. If it contains about 0.003 weight part or more of iodine with respect to 100 weight part of water, it can be regarded as a dyeing tank.

When using a water-soluble dichroic dye as the dichroic dye, for example, at a temperature of about 20°C to 80°C, preferably about 30°C to 70°C, and in a weight ratio of dichroic dye/water = about 0.001 to 0.1 The immersion treatment is performed for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds at a concentration of 1/100. The aqueous solution of the dichroic dye to be used may contain dyeing auxiliaries and the like, and may contain, for example, inorganic salts such as sodium sulfate, surfactants and the like. The dichroic dyes may be used alone, or two or more dichroic dyes may be used in combination.

It is also possible to stretch the film in a dye tank as described above. Stretching is performed by a method such as providing a peripheral speed difference between the nip rolls in the front and back of the dyeing tank. In addition, as in the swelling process, it is also possible to install open rolls (spreading rolls), spiral rolls, crowned rolls, cloth guides, variable rolls, etc. in the dyeing bath and/or at the entrance and exit of the bath.

The boric acid treatment is performed by immersing a polyvinyl alcohol-based film dyed with a dichroic dye in an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by weight of iodide.

Potassium iodide, zinc iodide, etc. are mentioned as an iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may coexist.

This boric acid treatment is performed for water resistance due to crosslinking, color tone adjustment (prevention of bluishness, etc.), and the like. When used for water resistance by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde can be used in addition to boric acid or together with boric acid as needed.

Boric acid treatment for water resistance is also sometimes called water resistance treatment, crosslinking treatment, immobilization treatment, and the like. In addition, the boric acid treatment used for color tone adjustment is sometimes referred to by names such as color correction treatment, recoloring treatment, and the like.

This boric acid treatment can be performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose.

The boric acid treatment for water resistance and the boric acid treatment for color tone adjustment are not particularly distinguished, and are carried out under the following conditions.

When the roll film is subjected to swelling, dyeing, and boric acid treatment, when the boric acid treatment is aimed at water resistance caused by crosslinking, use a product containing about 3 to 10 parts by weight of boric acid and about 1 to 10 parts by weight of iodide relative to 100 parts by weight of water. The 20 parts by weight boric acid treatment bath is usually carried out at a temperature of about 50°C to 70°C, preferably about 55°C to 65°C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, and more preferably about 90 to 300 seconds.

When dyeing and boric-acid-treating the pre-stretched film, the temperature of the boric-acid treatment bath is usually about 50°C to 85°C, preferably about 55°C to 80°C.

Boric acid treatment for color tone adjustment may be performed after boric acid treatment for water resistance. For example, when the dichroic dye is iodine, for this purpose, a boric acid treatment bath containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide relative to 100 parts by weight of water is used, usually at about 10° C. to 45° C. at temperature. The immersion time is usually about 3 to 300 seconds, preferably about 10 to 240 seconds.

The boric acid treatment for color tone adjustment is generally performed at a lower boric acid concentration, higher iodide concentration, and lower temperature than the boric acid treatment for water resistance.

These boric acid treatments can also be performed in a plurality of steps, and are usually performed in 2 to 5 steps in many cases. At this time, the composition and temperature of the aqueous solution of the boric acid treatment tank used may be the same or different within the above-mentioned range. The above-mentioned boric acid treatment for water resistance and boric acid treatment for color tone adjustment may be performed in a plurality of steps, respectively.

In the boric acid treatment step, the stretching of the film can also be performed in the same manner as in the dyeing step. The final cumulative draw ratio is about 4.5 to 7.0 times, preferably about 5.0 to 6.5 times.

After the boric acid treatment, a water washing treatment is performed. The water washing treatment is performed, for example, by immersing a polyvinyl alcohol-based film treated with boric acid for the purpose of water resistance and/or color tone adjustment in water, spraying water with a water jet, or combining immersion and spraying. The water temperature at the time of washing with water is usually about 2 to 40° C., and the immersion time may be about 2 to 120 seconds.

Drying after washing with water is performed at a temperature of about 40 to 100° C. for about 60 to 600 seconds in a drying oven.

In each step after the stretching treatment, tension control may be performed so that the tension of the film is substantially constant.

When stretching is completed in the dyeing treatment process, tension control is performed in the subsequent boric acid treatment process and water washing treatment process. When stretching is completed in the preceding process of the dyeing process, tension control is performed in subsequent processes including the dyeing process and the boric acid treatment process.

When the boric acid treatment process includes a plurality of boric acid treatment processes, it is preferable to stretch the above-mentioned film in the boric acid treatment process from the first stage or from the first stage to the second stage, and to wash the film after the boric acid treatment process following the stretched boric acid treatment process. Tension control is carried out in each step of the process; or the above-mentioned film is stretched in the boric acid treatment step from the first to the third stage, and in each step from the boric acid treatment step following the stretched boric acid treatment step to the water washing step However, it is industrially more preferable to stretch the above-mentioned film in the boric acid treatment step from the first stage or from the first stage to the second stage, and to stretch the film from the boric acid treatment step following the stretched boric acid treatment step to the water washing step. Tension control is performed in each process.

When performing the above-mentioned iodide treatment or zinc treatment after the boric acid treatment, tension control is also performed in these steps.

The tension in each step may be the same or different.

In tension control, the tension of the film is not particularly limited, and is appropriately set within a range of about 150 N/m to 2000 N/m, preferably about 600 N/m to 1500 N/m per unit width. When the tension is less than about 150 N/m, wrinkles and the like tend to occur on the film. On the other hand, when the tension exceeds about 2000 N/m, problems such as film breakage and reduced life due to abrasion of the bearing surface occur. In addition, the tension per unit width is calculated from the film width near the entrance of the process and the tension value of the tension detector.

When tension control is performed, some stretching/shrinking is unavoidable in some cases, but this is not included in the stretching treatment in the present invention.

In the present invention, when the film is immersed in the boric acid solution in the boric acid treatment step, the film is immersed in a state not in contact with the roll. When it is carried out in contact with a roll, color unevenness occurs, and the film thickness in the transverse direction of the film becomes uneven. In addition, the time from immersion of the film to the first contact with the roll in the boric acid solution is 0.4 to 5 seconds, preferably 0.5 seconds to 3 seconds. This time is adjusted in consideration of the arrangement positions of the rollers and the transport speed of the film.

When the time until the contact with the roll is too short, color unevenness occurs and the film thickness in the lateral direction of the film becomes uneven. When it is too long, wrinkles occur and the film thickness becomes uneven.

When a protective film is bonded to a polarizing film having color unevenness to form a polarizing plate, color unevenness is also seen, which is not preferable. When a polarizing film with uneven film thickness or wrinkles is used as a polarizing plate, it is not preferable because it is easily cracked and has poor durability.

As the nip rolls and guide rolls used in the present invention including the rolls that are first contacted in the boric acid solution, rubber rolls, stainless steel buff rolls, and sponge-like rubber rolls are used.

As a rubber roller, it is preferable that it contains NBR, etc., and its hardness is about 60 to 90 degrees, preferably about 70 to 80 degrees, under the JIS Shore C grade measured by the test method of JIS K 6301, and the surface roughness is measured by JIS The average interval S of the local peaks of the roughness curve of B 0601 (surface roughness) is about 0.1-5S, preferably about 0.5-1.

As a polishing roller made of stainless steel, it contains SUS304, SUS316, etc., and its surface roughness is represented by the average interval S of the local peaks of the roughness curve of JIS B 0601 (surface roughness), preferably It is about 0.2 to 1.0S, and the coefficient of dynamic friction is about 0.1 to 0.4, preferably about 0.15 to 0.35. The coefficient of dynamic friction in the present invention is represented by a value measured with a polyvinyl alcohol film and water according to the test method of JIS K 7125.

As a sponge-like rubber roller, the hardness of the sponge body is about 20 to 60 degrees, preferably about 25 to 50 degrees, and the density is about 0.4 to 0.6 g/ ^cm3 under the JIS Shore C grade measured by the test method of JIS K 6301 , preferably about 0.42-0.57 g/cm ³ , and the surface roughness is about 10-30S, preferably about 15-25S, expressed by the average interval S of local peak tops of the roughness curve of JIS B 0601 (surface roughness).

When the guide roll in the treatment liquid is a web roll, it is preferably a sponge-like rubber web roll. In particular, it is preferable to use a sponge-like rubber open-width roll in the swelling treatment step. In the swelling treatment process, the polyvinyl alcohol-based film is swelled in both the longitudinal direction and the lateral direction by the absorbent bath, but especially when tension is applied while the lateral swelling is not completed, wrinkles or folds will occur on the roll . When using a sponge-like rubber open width roller, the tension applied to the film can be greatly reduced due to its light weight, and at the same time, due to its high film holding force based on its high surface roughness, sufficient tension can be exerted even at low tension Open width force, and the other function of the open width roller to prevent bending is also maximized, the wrinkles are reduced, and the folds are eliminated. The use of the sponge-like squeegee is not limited to swelling treatment, and can be used in other treatments.

A protective film is bonded to at least one surface of the polarizing film produced in this way with an adhesive to obtain a polarizing plate.

Examples of protective films include films containing acetyl cellulose-based resins such as triacetyl cellulose and diacetyl cellulose, films containing polyethylene terephthalate or polyethylene naphthalate, polyethylene terephthalate Films of polyester-based resins such as butylene dicarboxylate, films containing polycarbonate-based resins, and films containing cycloolefin-based resins. Commercially available thermoplastic cycloolefin-based resins include, for example, "Topas" (registered trademark) sold by Ticona Corporation of Germany, "A-TON" (registered trademark) sold by Jieiyesua-ru Co., Ltd. "Zionoa" and "Zeonex" (both are registered trademarks), "Apel" (registered trademark) sold by Mitsui Chemicals Co., Ltd., etc. A film made of such a cycloolefin-based resin is used as a protective film, and well-known methods such as a solvent casting method and a melt extrusion method are suitably used for film formation. Cycloolefin-based resin films to be formed into films are also commercially available, for example, "Escina" and "SCA40" sold by SEKISUI CHEMICAL CO., LTD.

The thickness of the protective film is preferably thin, but if it is too thin, the strength will decrease and the workability will be poor. On the other hand, if it is too thick, there will be problems such as lowered transparency and longer curing time after lamination. Therefore, an appropriate thickness of the protective film is, for example, about 5 to 200 μm, preferably about 10 to 150 μm, and more preferably about 20 to 100 μm.

In order to improve the adhesion between the adhesive and the polarizing film and/or protective film, corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, and primer coating can also be performed on the polarizing film and/or protective film. , saponification treatment and other surface treatments.

Surface treatments such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment can also be performed on the protective film alone or in combination. In addition, the protective film and/or the surface protective layer of the protective film may have ultraviolet absorbers such as benzophenone-based compounds and benzotriazole-based compounds, or enhancers such as phenyl phosphate-based compounds and phthalate compounds. plasticizer.

Such a protective film can be attached to one side or both sides of the polarizing film.

The polarizing film and the protective film are laminated using adhesives such as water solvent adhesives, organic solvent adhesives, hot melt adhesives, and non-solvent adhesives. Examples of water-solvent-based adhesives include polyvinyl alcohol-based resin aqueous solutions, water-based two-component urethane-based emulsion adhesives, and the like; examples of organic solvent-based adhesives include two-component urethane-based adhesives. and the like; as the non-solvent-based adhesive, for example, one-component urethane-based adhesive and the like are mentioned. When an acetylcellulose-based film whose bonding surface with the polarizing film has been hydrophilized by saponification or the like is used as a protective film, a polyvinyl alcohol-based resin aqueous solution is preferably used as an adhesive.

Polyvinyl alcohol-based resins used as adhesives include, in addition to vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate as a homopolymer of vinyl acetate, vinyl acetate and Vinyl alcohol-based copolymers obtained by saponifying copolymers of other monomers that have been copolymerized, modified polyvinyl alcohol-based polymers obtained by partially modifying their hydroxyl groups, and the like. Polyhydric aldehydes, water-soluble epoxy compounds, melamine-based compounds, and the like can also be used as additives in this adhesive.

The method of laminating polarizing film and protective film is not particularly limited, for example enumerates: on the surface of polarizing film or protective film uniform coating adhesive agent, overlaps another film on coated surface, adopts roller etc. to bond, and drying method etc.

Usually, after the adhesive is prepared, it is applied at a temperature of about 15 to 40°C, and the bonding temperature is usually in the range of about 15 to 30°C. After bonding, drying treatment is performed to remove solvents such as water contained in the adhesive, but the drying temperature at this time is usually about 30 to 85°C, preferably about 40 to 80°C. Then, the adhesive may be cured by curing usually for about 1 to 90 days in a temperature environment of about 15 to 85°C, preferably about 20 to 50°C, more preferably about 35 to 45°C. When this curing time is long, the productivity is poor, so the curing period is about 1 to 30 days, preferably about 1 to 7 days.

In this way, a polarizing plate is obtained in which a protective film is bonded to one or both surfaces of the polarizing film via an adhesive layer.

In the present invention, the protective film can also have a function as a retardation film, a function as a brightness improving film, a function as a reflective film, a function as a semi-transmissive reflective film, a function as a dipping film, a function as an optical compensation film functions and other optical functions. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness improvement film, a reflective film, a semi-transmissive reflective film, a dipping film, and an optical compensation film on the surface of the protective film to provide such a function, Such a function can also be imparted to the protective film itself. In addition, the protective film itself may have various functions, such as a dipping film having a function of a brightness improving film.

For example, by performing the stretching treatment described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or implementing the treatment described in Japanese Patent No. 3168850, etc., to the above-mentioned protective film, it is possible to impart a phase Poor membrane functionality. In addition, by forming micropores on the above-mentioned protective film by the method described in JP-A-2002-169025 or JP-A-2003-29030, or by superimposing two or more layers of cholesteric materials having different central wavelengths of selective reflection. The liquid crystal layer can be provided with a function as a brightness improving film.

By forming a metal thin film on the protective film by vapor deposition, sputtering, etc., it is possible to impart a function as a reflective film or a semi-transmissive reflective film. By coating the resin solution containing fine particles on the protective film, it is possible to impart a function as an impregnated film. In addition, 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 protective film. In addition, a brightness-improving film such as a product name: DBEF (manufactured by Three-Em Co., Ltd.), a product name: WV film (Fuji Photo Film) Co., Ltd. Commercially available optical functional films such as viewing angle improving films such as those manufactured by Sumitomo Chemical Industry Co., Ltd., and retardation films such as product name: Sumikalite (registered trademark) (Sumitomo Chemical Industries, Ltd.).

Example

Examples are shown below and the present invention will be specifically described, but the present invention is not limited by these examples.

Example 1

A polyvinyl alcohol film with a thickness of 75 μm (Kurarevinylon VF-PS#7500, a degree of polymerization of 2400, and a degree of saponification of 99.9 mol% or more) was immersed in pure water at 30°C for approximately 130°C while keeping the film in a tense state without loosening. seconds to fully swell the membrane. Next, uniaxial stretching was carried out while dipping in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.02/1.5/100 for dyeing treatment (total stretching ratio so far: 3.2 times). Then, it is immersed in an aqueous solution at about 55°C with a weight ratio of potassium iodide/boric acid/water of 10/5/100 in a state where it is not in contact with the roller, and the boric acid treatment is performed so that the time from immersion to contact with the first guide roller 1.8 seconds, and uniaxially stretched until the cumulative stretching ratio from the roll reaches 5.9 times. After the boric acid treatment, it was washed with pure water at about 10°C for about 10 seconds. After washing with water, it was dried at about 80° C. for 2 minutes to obtain an iodine-based polarizing film with a thickness of about 28 μm. The first submerged guide roller of the boric acid treatment tank used an NBR rubber roller with a surface roughness of 0.6S and a rubber hardness (JIS Shore A grade) of 80 degrees. Stretching is performed by making the nip rollers arranged before and after the treatment tank have a peripheral speed difference.

In the obtained polarizing film, color unevenness due to stretching was not observed, and the film thickness in the film transverse direction was uniform.

Apply a polyvinyl alcohol-based adhesive to both sides of the obtained polarizing film, and stick a protective film on both sides [triacetyl cellulose film with saponification treatment on the surface, "Fujitaku (registered trademark) T80UNL", Fuji Photo Film Co., Ltd., thickness 80 μm], and dried at about 60° C. for about 5 minutes to prepare a polarizing plate. Color unevenness was not seen on the polarizer.

Example 2

After dipping in the boric acid solution, the first roller that comes into contact is a nip roller made of NBR rubber with a surface roughness of 0.6S and a rubber hardness (JIS Shore A grade) of 80 degrees. A polarizing film was obtained in the same manner as in Example 1 except that the time was 0.6 second.

In the obtained polarizing film, color unevenness due to stretching was not observed, and the film thickness in the film transverse direction was uniform.

Using the obtained polarizing film, it carried out similarly to Example 1, and produced the polarizing plate. Color unevenness was not seen on the polarizer.

Example 3

A polarizing film was obtained in the same manner as in Example 1 except that a stainless steel polishing roll with a surface roughness of 0.2S and a dynamic friction coefficient of 0.24 was used as the first submerged guide roll of the boric acid treatment tank.

In the obtained polarizing film, color unevenness due to stretching was not observed, and the film thickness in the film transverse direction was uniform.

Using the obtained polarizing film, it carried out similarly to Example 1, and produced the polarizing plate. Color unevenness was not seen on the polarizer.

Example 4

The first submerged guide roller of the boric acid treatment tank uses a sponge-like rubber roller with a sponge body hardness of JIS Shore C grade 25 degrees, a density of 0.42g/cm ³ , and a surface roughness of 20S. In Example 1, a polarizing film was obtained in the same manner.

In the obtained polarizing film, color unevenness due to stretching was not observed, and the film thickness in the film transverse direction was uniform.

Using the obtained polarizing film, it carried out similarly to Example 1, and produced the polarizing plate. Color unevenness was not seen on the polarizer.

Comparative example 1

A polarizing plate was obtained in the same manner as in Example 1 except that it was immersed in a boric acid solution while contacting a nip roller made of NBR rubber with a surface roughness of 0.6S and a rubber hardness (JIS Shore A grade) of 80 degrees. .

Twelve color unevenness due to stretching was observed on the obtained polarizing film. In addition, it is a film in which the film thickness in the film lateral direction is not uniform.

Comparative example 2

After immersion in the boric acid solution, the first contact roller is a nip roller made of NBR rubber with a surface roughness of 0.6S and a rubber hardness (JIS Shore A grade) of 80 degrees. A polarizing film was obtained in the same manner as in Example 1 except that the time was 0.2 seconds.

Five spots of color unevenness due to stretching were observed on the obtained polarizing film. In addition, it is a film in which the film thickness in the film lateral direction is not uniform.

Claims (2)

1. A manufacturing method of a polarizing film is to process the polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, washing treatment and drying treatment, and at least two treatment procedures in the treatment procedures Among them, a method of producing a polarizing film by stretching the film by giving a peripheral speed difference between two nip rollers for conveying the film, is characterized in that when the film is immersed in a boric acid solution in the boric acid treatment step, the The roll was immersed in a state where the roll was not in contact, so that the time from the dipping of the film to the first contact with the roll in the boric acid solution was 0.4 to 1.8 seconds. 2. The method for producing a polarizing film according to claim 1, wherein the temperature of the boric acid solution is 50-85°C.