CN100388024C - Polarizing film, polarizing plate and method for producing optical laminate - Google Patents

Abstract

The subject of this invention is to provide the manufacturing method of the polarizing film which can display more neutral black, the manufacturing method of a polarizing plate, and the manufacturing method of an optical laminated body. The preparation method of the polarizing film comprises: after iodine is adsorbed and oriented on the polyvinyl alcohol film, multi-step dipping treatment is carried out in the aqueous solution containing boric acid, thereby making the polarizing film, it is characterized in that: the aqueous solution containing boric acid is (1) Relative to 100 parts by weight of water, containing 3-10 parts by weight of boric acid and 1-20 parts by weight of iodide, the temperature is an aqueous solution of 50-70 ° C, and (2) relative to 100 parts by weight of water, containing 1- 5 parts by weight of boric acid, 3-30 parts by weight of iodide, and an aqueous solution at a temperature of 10-45° C., after being treated with the boric acid-containing aqueous solution of (1), and then treated with the boric-acid aqueous solution of (2), and (1) Compared with the boric acid aqueous solution of (2), the iodide concentration of the boric acid aqueous solution is higher, and the concentration of boric acid is lower, in addition, the temperature is also lower.

Description

Polarizing film, polarizing plate and method for producing optical laminate

【Technical field】

The present invention relates to a method for preparing a polarizing film that can display a more neutral black color, and a method for preparing a polarizer that laminates a protective film on at least one surface of the polarizing film. In addition, it also relates to a retardation film, a brightness improvement film , A method for preparing an optical laminate by bonding any one of the field angle-improving film and the semi-reflective film alone or a plurality of them together.

【Background technique】

As a polarizing film, a polyvinyl alcohol-based film in which a dichroic dye is adsorbed and aligned has been conventionally 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. Usually, these polarizing films are made into polarizing plates by attaching a protective film such as triacetyl cellulose to one or both sides of the above-mentioned polarizing film with an adhesive consisting of an aqueous solution of polyvinyl alcohol resin.

In addition, after the immersion treatment in the aqueous solution containing boric acid, the immersion treatment in the aqueous solution of iodide may be performed again. For example, in Patent Document 1, a polyvinyl alcohol film is dyed with a dichroic dye, dipped in an aqueous solution containing boric acid, and then dipped in an aqueous solution of iodide at a predetermined concentration for a predetermined period of time. After drying, a polarizing film was prepared. According to Patent Document 1, the immersion treatment using an aqueous solution of iodide prevents the precipitation of boric acid from the thin film and overcomes defects such as spots and impurities.

In addition, in Example 1 of Patent Document 2, after the polyvinyl alcohol film is dyed, it is stretched in an aqueous solution having a boric acid concentration of 3.5% by weight and a potassium iodide concentration of 1.5% by weight, and then stretched in an aqueous solution having a boric acid concentration of 6% by weight and The polarizing film was prepared by dipping in an aqueous solution having a potassium iodide concentration of 1.5% by weight and drying. According to Patent Document 2, water resistance, heat and humidity resistance, durability, and optical properties are improved by using two or more treatment steps with different boric acid concentrations.

Yet, in the preparation method of the polarizing film so far, the polarizing film that can fully satisfy optical characteristic has not been obtained, for example, there are problems such as green or red in black, therefore, need a kind of can show more neutral black polarizing film.

[Patent Document 1] JP-A-2001-290027

[Patent Document 2] Japanese Patent Laid-Open Publication No. 07-198939

【Content of invention】

The subject of this invention is to provide the manufacturing method of the polarizing film which can display more neutral black, the manufacturing method of a polarizing plate, and the manufacturing method of an optical laminated body.

In order to solve the above-mentioned problems, the inventors of the present invention have repeatedly conducted intensive studies, and as a result, found the following new fact: after the polyvinyl alcohol-based film is subjected to multi-step immersion treatment in an aqueous solution containing boric acid after iodine is adsorbed orientated, when When using an aqueous solution with a higher concentration of iodide, a lower concentration of boric acid, containing boric acid and iodide, and a lower temperature than the treatment with the first aqueous solution containing boric acid, the second aqueous solution containing boric acid is used. , the obtained polarizing film can show a more neutral black color, and the present invention has been completed so far.

That is, the preparation method of the polarizing film of the present invention is a preparation method of forming a polarizing film by performing multi-step immersion treatment in an aqueous solution containing boric acid after adsorbing and orienting iodine on a polyvinyl alcohol film, characterized in that: The aqueous solution is the first aqueous solution containing boric acid and the second aqueous solution containing boric acid, wherein the first aqueous solution containing boric acid is: relative to 100 parts by weight of water, containing 3-10 parts by weight of boric acid and 1-20 parts by weight iodide, and the temperature is an aqueous solution of 50-70 ° C; the second aqueous solution containing boric acid is: relative to 100 parts by weight of water, containing 1-5 parts by weight of boric acid and 3-30 parts by weight of iodide, and Aqueous solution at a temperature of 10-45°C; treatment in the first aqueous solution containing boric acid, followed by treatment in the second aqueous solution containing boric acid, at this time, compared with the first aqueous solution containing boric acid, the second Aqueous solutions containing boric acid have higher concentrations of iodide and lower concentrations of boric acid, and are also cooler.

In the present invention, it is preferable to perform the treatment with the first boric acid-containing aqueous solution and/or the second boric acid-containing aqueous solution in multiple steps.

In addition, the method for producing a polarizing plate of the present invention is characterized in that a protective film is adhered to at least one surface of the above-mentioned polarizing film. The protective film may have any function of a phase difference film, a brightness improving film, a field angle improving film, and a semi-reflective film. Alternatively, an optical laminate may be prepared by bonding at least one film selected from a phase difference film, a brightness improving film, a field angle improving film, and a semi-reflective film on the above-mentioned polarizer having a protective film bonded on at least one surface. body.

According to the present invention, when multi-step immersion treatment is carried out in aqueous solution containing boric acid, when the iodide concentration is higher than the treatment with the first aqueous solution containing boric acid and the concentration of boric acid is lower than that of the first aqueous solution containing boric acid, and contains boric acid And the aqueous solution of iodide and lower temperature, the treatment with the second boric acid aqueous solution can improve the color complementary effect, so that a kind of polarizing film and polarizing plate that can display more neutral black can be obtained. A thin and high-quality liquid crystal display can be produced by applying the polarizing plate and optical laminate obtained by the present invention to a liquid crystal display device.

【Detailed ways】

The polyvinyl alcohol-based resin forming the polyvinyl alcohol-based film of the present invention generally includes resins obtained by saponifying polyvinyl acetate-based resins. The degree of saponification is above 85 mol%, preferably above 90 mol%, more preferably between 99 mol% and 100 mol%. As the polyvinyl acetate-based resin, in addition to polyvinyl acetate which is a vinyl acetate monomer, a copolymer of vinyl acetate and other monomers that can be copolymerized with it may be used, for example, ethylene-vinyl acetate copolymer, 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 resin is 1000-10000, preferably about 1500-5000.

These polyvinyl alcohol-based resins can also be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can also be used. Generally, as a starting material for producing a polarizing film, a polyvinyl alcohol-based resin film that has not been stretched and has a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm, is used. Industrially, films with a width of 1500mm-4000mm are practical.

The unstretched film is sequentially subjected to expansion treatment, dyeing treatment, boric acid treatment, washing treatment, and finally drying to obtain a polyvinyl alcohol-based polarizing film with a thickness of, for example, about 5-50 μm.

The polarizing film of the present invention is a polyvinyl alcohol-based uniaxially stretched film in which iodine is adsorbed and oriented, and its production method is roughly classified into two types. The first method is a method in which polyvinyl alcohol is uniaxially stretched in air or an inert gas, followed by expansion treatment, dyeing treatment, boric acid treatment, and water washing treatment in order, and finally drying. The second method is to sequentially perform expansion treatment, dyeing treatment, boric acid treatment and washing treatment on the unstretched polyvinyl alcohol film in an aqueous solution, and perform the boric acid treatment step and/or the step before the boric acid treatment step A method of wet uniaxial stretching followed by drying.

In either method, uniaxial stretching may be performed in one step, or may be performed in two or more steps, but it is preferable to perform uniaxial stretching in a plurality of steps. For the stretching method, a known method can be used, for example, the stretching between rollers that controls the peripheral speed difference between the two nip rollers that convey the film and stretches it, such as the hot roller described in the Japanese Patent No. 2731813 Cylinder stretching method, tenter stretching method, etc. In addition, the order of the steps is basically as described above, and there is no limitation on the number of treatment liquids and treatment conditions. In addition, it is of course possible to insert steps not described in the above steps for other purposes.

The swelling step is performed for the purpose of removing impurities on the surface of the film, removing plasticizers in the film, providing easy dyeability in subsequent steps, plasticizing the film, and the like. The processing conditions are set within a range in which these objects can be achieved and defects such as excessive dissolution and loss of transparency of the base material film do not occur. In the case of expanding the stretched film in a predetermined gas, for example, immersion is performed in an aqueous solution at 20°C to 70°C, preferably 30 to 60°C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 to 240 seconds. In the case of expanding an unstretched raw film from the beginning, for example, the film is dipped in an aqueous solution at 10°C to 50°C, preferably 20 to 40°C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 to 240 seconds.

In the expansion treatment process, since the expansion of the film along the width direction tends to cause problems such as creases on the film, it is preferable to use expander rolls, spiral rolls, crown rolls, and cloth guides. Guider), bending bar (bend bar), tenter clip and other well-known expansion devices to eliminate the creases of the film while conveying the film. In order to stably transport the film in the solution, it is useful to control the flow of water in the swelling solution with a spray pipe in water, or to use an EPC device (edge position control device: a device that detects the edge of the film to prevent the film from bending). In this step, the film also expands along the direction in which the film travels. In order to eliminate the sagging of the film in the conveying direction, for example, it is preferable to take methods such as controlling the speed of the conveying roller before and after the treatment. In addition, for the swelling treatment liquid used, in addition to pure water, boric acid (as described in JP-A-10-153709 ), chloride (as described in JP-A-06-281816 ) and 0.01% by weight to 10% by weight can also be used. mentioned), inorganic acid, inorganic salt, water-soluble organic solvent, alcohols, etc. aqueous solution.

The step of dyeing with iodine is carried out in order to adsorb iodine on the film and orient it. The processing conditions are set within a range in which these objects can be achieved without causing defects such as excessive dissolution and loss of transparency of the base material film. For example, at a temperature of 10°C-45°C, preferably 20°C-35°C, and in a weight ratio, at a concentration of iodine/KI/water=0.003-0.2/0.1-10/100, for 30 seconds- 600 seconds, preferably 60 seconds-300 seconds of dipping treatment. Other iodides can be used instead of potassium, such as zinc iodide and the like. In addition, other iodides and potassium iodide may be used simultaneously. In addition, compounds other than iodide, such as boric acid, leadous chloride, and cobalt chloride, may coexist. When boric acid is added, it differs from the boric acid treatment described below in that iodine is contained. If it contains 0.003 weight part or more of iodine with respect to 100 weight part of water, it can be regarded as a dyeing tank.

As mentioned above, it is also possible to stretch the film in the dye tank. Stretching is carried out by using a method such as providing a peripheral speed difference between the nip rolls before and after the dyeing tank. In addition, tenter rolls, helical rolls, nip rolls, fabric guides, bending rods, etc. may be provided in the dyeing solution and/or the solution inlet and outlet in the same manner as in the expansion step. In addition, after the expansion step, the polyvinyl alcohol-based film may be subjected to wet stretching treatment before dyeing treatment.

In the present invention, the immersion treatment with the boric acid-containing aqueous solution is performed in multiple steps. The first aqueous solution containing boric acid is (1) an aqueous solution containing 3-10 parts by weight of boric acid and 1-20 parts by weight of iodide relative to 100 parts by weight of water, and the temperature is 50-70°C. Borax, glyoxal, glutaraldehyde and other cross-linking agents can also be used together with boric acid. Potassium iodide, zinc iodide, etc. are mentioned as an iodide, Usually, potassium iodide is used. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, etc., may coexist.

The temperature of the first boric acid-containing aqueous solution is usually 50°C to 70°C, preferably 55°C to 65°C. The dipping time is generally about 30-600 seconds, preferably 60-420 seconds, more preferably 90-300 seconds. If the temperature is lower than 50°C, it is difficult to obtain the final optical properties, on the contrary, once it exceeds 70°C, the appearance of the film will be damaged, neither of which is ideal.

The treatment of the first aqueous solution containing boric acid can also be carried out in multiple steps by utilizing 2-4 such processes. The composition and temperature of the aqueous solution in each case may be the same or different within the above-mentioned range.

The second boric acid-containing aqueous solution is (1) an aqueous solution containing 1-5 parts by weight of boric acid and 3-30 parts by weight of iodide relative to 100 parts by weight of water, and at a temperature of 10-45°C. The dipping time is preferably about 2-120 seconds.

In the present invention, the first kind of boric acid-containing aqueous solution and the second kind of boric acid-containing aqueous solution are solutions that meet the above-mentioned concentration and temperature range, and the second kind of boric acid-containing aqueous solution must be higher than the iodide concentration of the first kind of boric acid-containing aqueous solution. High, the concentration of boric acid is lower, and the temperature is lower.

When the iodide concentration of the second boric acid-containing aqueous solution is lower than that of the first boric acid-containing aqueous solution, a neutral color tone cannot be obtained. When the boric acid concentration of the second boric-acid-containing aqueous solution is higher than that of the first boric-acid-containing aqueous solution, boric acid may precipitate to form foreign substances. In addition, when the temperature of the second boric-acid-containing aqueous solution is the same as or higher than the boric acid temperature of the first boric-acid-containing aqueous solution, a neutral color tone cannot be obtained.

The treatment of the 2nd kind of boric acid-containing aqueous solution can also be the same as the treatment of the 1st kind of boric-acid-containing aqueous solution, and it can be carried out in multiple steps through 2-4 such processes. Like this, in each step, the concentration of iodide and boric acid all must be in the above-mentioned concentration range, preferably make the iodide concentration of back step and the iodide concentration of front step identical or higher, and make the concentration of boric acid and temperature and front The steps are the same or lower.

The treatment with these boric acid-containing aqueous solutions is carried out for water repellency and color adjustment (prevention of greenish color etc.) by crosslinking. The treatment of the above-mentioned first type of boric acid-containing aqueous solution is mainly for waterproofing, and is also called waterproofing treatment, cross-linking treatment, positioning treatment and other names. In addition, the above-mentioned second type of boric acid-containing aqueous solution treatment is mainly for color adjustment, and is also called color adjustment treatment, color correction treatment, re-dyeing treatment and other names.

After treatment with an aqueous solution containing boric acid, the film is washed. The washing treatment is performed by, for example, immersing the boric acid-treated polyvinyl alcohol-based film in water, spraying water in the form of a shower, or performing both immersion and spraying. In the washing process, the water temperature can usually be about 2-40°C, and the immersion time is preferably about 2-120 seconds. After washing, a drying step is performed in a drying oven at a temperature of about 40-100° C. for about 60-600 seconds.

In the present invention, uniaxial stretching is performed before or during at least one of the steps of swelling treatment, dyeing treatment, and boric acid-containing aqueous solution. Alternatively, a wet stretching step for performing uniaxial stretching may be added in the middle of the above steps. Uniaxial stretching can be performed in one step, but is preferably performed in multiple steps. For the stretching method, a known method can be used, for example, stretching between rollers by controlling the peripheral speed difference between two nip rolls that convey the film, hot roller stretching as described in Japanese Patent No. 2731813. stretching method, stretching method, etc. In addition, the polyvinyl alcohol film may be uniaxially stretched in air or inert gas before the expansion step. The final cumulative stretch ratio is 4.5-7.0 times, preferably 5.0-6.5 times.

On at least one side of the polarizing film thus prepared, a protective film was adhered with an adhesive, thereby producing a polarizing plate.

Examples of protective films include films made of acetyl cellulose resins such as triacetyl cellulose and diacetyl cellulose, films made of polyethylene terephthalate, polyethylene naphthalate, polyethylene terephthalate, etc. Films made of polyester-based resins such as butylene formate, films made of polycarbonate-based resins, and films made of cycloolefin-based resins. As commercially available thermoplastic cycloolefin-based resins, for example, Topas (registered trademark) sold by Ticona Corporation of Germany, Arton (registered trademark) sold by JSR Corporation, Zeonor and Zeonnex (registered trademark) sold by Zeon Corporation of Japan, Apel (registered trademark) sold by Mitsui Chemicals Co., Ltd., etc. Then, a film obtained by forming such a cycloolefin-based resin into a film is used as a protective film, and a known method such as a solvent casting method or a melt extrusion method is suitably used for film forming. Cycloolefin-based resin films for film formation are also commercially available, for example, "Escina" and "SCA40" sold by Sekisui Chemical Co., Ltd., and the like.

The thickness of the protective film is preferably thin, but if the thickness is too thin, the strength decreases and the workability deteriorates. On the other hand, if the thickness is too thick, the transparency decreases, or the curing time required after lamination becomes longer, etc. question. Therefore, an appropriate thickness of the protective film is, for example, about 5-200 μm, preferably 10-150 μm, more preferably 20-100 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 bottom coating treatment can also be performed on the polarizing film and/or protective film , saponification treatment and other surface treatments.

On the protective film, surface treatments such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment may be performed alone or in combination. In addition, the protective film and/or the protective layer on the surface of the protective film may also contain ultraviolet absorbers such as benzophenone compounds and benzotriazole compounds and plasticizers such as phenylphosphate compounds and terephthalate compounds. .

The protective film can be bonded on one side or both sides of the polarizing film.

The polarizing film and protective film are laminated using adhesives such as water-solvent adhesives, organic solvent-based adhesives, hot-melt adhesives, and solvent-free adhesives. Examples of water-solvent-based adhesives include polyvinyl alcohol-based resin aqueous solutions, water-based two-component urethane-based latex adhesives, and organic solvent-based adhesives such as two-component urethane-based adhesives. Adhesive etc. As a solventless adhesive, a one-component type urethane adhesive etc. are mentioned, for example. In the case of using an acetylcellulose-based film that has been hydrophilically treated with a polarizing film by saponification or the like as the protective film, an aqueous solution of polyvinyl alcohol-based resin is suitably used as the binder. Among polyvinyl alcohol resins used as binders, in addition to vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate as a monomer of vinyl acetate, there are vinyl acetate and Vinyl alcohol copolymers obtained by saponifying copolymers of other monomers that have been copolymerized, and polyvinyl alcohol polymers that partially modify those hydroxyl groups. In this adhesive, polyaldehydes, water-soluble epoxy compounds, melamine compounds, etc. can also be used as additives.

For the method of bonding polarizing film and protective film, not particularly limited, for example, can enumerate on the surface of polarizing film or protective film and evenly coat adhesive, put another layer of film on the coated surface again, and Bonding with rolls, etc., drying methods, etc.

Usually, the adhesive is coated at a temperature of 15-40°C after preparation, and the bonding temperature is usually about 15-30°C. Drying is performed after bonding to remove solvents such as water contained in the adhesive, and the drying temperature at this time is usually 30-85°C, preferably 40-80°C. Then, it can also be cured in steps of 1-90 days at a temperature environment of 15-85°C, preferably 20-50°C, more preferably 35-45°C, to cure the adhesive. If the curing time is longer, the yield will decrease. Therefore, the curing time is about 1-30 days, preferably 1-7 days.

Therefore, a polarizing plate in which a protective film is adhered to one or both surfaces of a polarizing film via an adhesive layer can be produced.

In the present invention, the protective film may 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-reflective film, a function as a diffusion film, a function as an optical compensation film, etc. Function. Thus, for example, by laminating an optically functional film such as a retardation film, a brightness improvement film, a reflective film, a semi-reflective film, a diffusion film, or an optical compensation film on the surface of the protective film, such a function can be provided. In addition, such a function can also be brought to the protective film itself. In addition, the protective film itself may have various functions, such as a diffusion film having the function of a brightness improving film.

For example, by carrying out stretching treatment as described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or by performing the treatment described in Japanese Patent No. 3168850, it is possible to give the above-mentioned protective film the effect of being a retardation film. Function. In addition, by using the method described in Japanese Patent Application Laid-Open No. 2002-169025 and Japanese Patent Laid-Open No. 200329030 to form micropores, and then by overlapping two or more cholesteric liquid crystal layers having different selective reflection center wavelengths, the above-mentioned The protective film functions as a luminance improvement film. By forming a metal thin film on the protective film by steam or sputtering, it can function as a reflective film or a semi-reflective film. By coating the above-mentioned protective film with a resin solution containing fine particles, it can function as a diffusion film. In addition, by coating and aligning a liquid crystal compound such as a discotic liquid crystal compound on the protective film, a function as an optical compensation film can be brought about. In addition, brightness improvement films such as trade name: DBEF (manufactured by Suri-Em Co., Ltd.), and viewing angle improvement films such as trade name: WV film (manufactured by Fuji Photo Film Co., Ltd.) can be directly coated with an appropriate adhesive. Film, trade name: Sumikalight (registered trademark) (Sumitomo Chemical Industries Co., Ltd.) and other commercially available optical functional films such as phase difference films are directly bonded to the polarizing film.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

The following examples and comparative examples were carried out in accordance with the procedure of carrying out various treatments while conveying a long film of polyvinyl alcohol using a continuous conveying device combining nip rolls and free nip rolls. The uniaxial stretching is carried out by controlling the peripheral speed difference of the driven nip rolls before and after the treatment tank.

In addition, the optical performance refers to the measurement of the transmission direction and The ultraviolet-visible spectrum of the polarizer in the absorption direction, the color when two polarizers are arranged in a crossed Nicol prism, is calculated according to JIS-Z8729, and the orthogonal color, orthogonal L ^* , and orthogonal a ^* , orthogonal b ^* .

【Example 1】

Immerse a polyvinyl alcohol film with a thickness of 75 μm (Kurarebivinylon VF-PS#7500, a degree of polymerization of 2400, a degree of saponification of 99.9 mol% or more) in pure water at 30°C for about 130 seconds, and dry the film so that the film does not sag. Maintain tension to fully inflate the film. Next, the film was uniaxially stretched while being dipped in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.02/1.5/100 for dyeing treatment.

After that, the film was uniaxially stretched while dipping the film in a boric acid aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/5/100 and a temperature of 60°C until the accumulated stretching ratio was equal to the original value. 5.9 times. In addition, the film was dipped in a second boric acid aqueous solution at a weight ratio of potassium iodide/boric acid/water of 20/3/100 and a temperature of 30°C for about 30 seconds. Next, it was washed with pure water at 10° C. for about 10 seconds. Dry at a temperature of 60° C. for 2 minutes to prepare a polarizing film.

The optical performance of the polarizing film is cross a ^* =0.2, cross b ^* =-0.3, and it is a polarizing film with more neutral color.

[Example 2]

In addition to the treatment of the second boric acid-containing aqueous solution, the previous step uses potassium iodide/boric acid/water with a weight ratio of 15/3/100 and a temperature of 40°C, and the latter step uses potassium iodide/boric acid/water with a weight ratio of 20 /3/100, except that the aqueous solution at 30°C was used in two steps, a polarizing film was produced in the same manner as in Example 1.

The optical performance of the polarizing film is orthogonal a ^* =0.1, orthogonal b ^* =-0.1, and it is a polarizing film with more neutral color.

[Comparative Example 1]

A polarizing film was produced in the same manner as in Example 1, except that the second boric acid-containing aqueous solution was treated with an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 20/0.5/100 and a temperature of 30°C.

The optical properties of the polarizing film were cross a ^* = 0.6, cross b ^* = -1.8, and exhibited greenish black.

【Comparative example 2】

A polarizing film was produced in the same manner as in Example 1, except that the second boric acid-containing aqueous solution was treated with an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10/0/100 and a temperature of 30°C.

The optical properties of this polarizing film were cross a ^* = 1.3, cross b ^* = -4.1, and exhibited greenish black.

[Comparative Example 3]

Except that the weight ratio of potassium iodide/boric acid/water is 10/7.5/100, and the temperature is 30° C., except that the second kind of boric acid-containing aqueous solution is used, a polarizing film is obtained in the same manner as in Example 1, but in the solution Boric acid is precipitated on the exit roll, and after drying, foreign matter is produced.

[Comparative Example 4]

A polarizing film was produced in the same manner as in Example 1, except that the second boric acid-containing aqueous solution was treated with an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 1/5/100 and a temperature of 30°C.

The optical properties of the polarizing film were cross a ^* = 0.6, cross b ^* = -1.5, and showed greenish black.

【Comparative Example 5】

A polarizing film was produced in the same manner as in Example 1, except that the weight ratio of potassium iodide/boric acid/water was 20/3/100 and the temperature was 60° C., except that the second boric acid-containing aqueous solution was used.

The optical properties of the polarizing film were cross a ^* = 0.8, cross b ^* = -2.5, and showed greenish black.

Claims (5)

1. a kind of preparation method comprising the polarizing film of following steps, after iodine adsorption orientation is on the polyvinyl alcohol film, carry out multi-step dipping treatment in the aqueous solution containing boric acid, thereby make polarizing film, it is characterized in that: The aqueous solution containing boric acid is the first aqueous solution containing boric acid and the aqueous solution containing the second boric acid, and the aqueous solution containing boric acid of the first kind is: relative to 100 parts by weight of water, containing 3-10 parts by weight of boric acid and 1 -20 parts by weight of iodide and an aqueous solution at a temperature of 50-70°C; the second aqueous solution containing boric acid is: relative to 100 parts by weight of water, containing 1-5 parts by weight of boric acid and 3-30 parts by weight of iodine Compound, aqueous solution at a temperature of 10-45°C; after being treated with the first aqueous solution containing boric acid, and then treated with the second aqueous solution containing boric acid, compared with the first aqueous solution containing boric acid, the second aqueous solution contains The iodide concentration of the aqueous solution of boric acid is higher, and the concentration of boric acid is lower. In addition, the temperature is lower, wherein the time of immersion in the first aqueous solution containing boric acid is 30 to 600 seconds, and in the second aqueous solution containing boric acid. The time for immersion in the aqueous solution is 2 to 120 seconds. 2. The preparation method of polarizing film according to claim 1, characterized in that: the treatment with the 1st aqueous solution containing boric acid and/or the treatment with the 2nd aqueous solution containing boric acid is carried out in multiple steps. 3. A method for preparing a polarizer, characterized in that it includes the step of adhering a protective film on at least one side of the polarizing film produced by the method according to claim 1 or 2. 4. The method for preparing a polarizing plate according to claim 3, wherein the protective film has any function of a retardation film, a brightness improvement film, a field angle improvement film, and a semi-reflective film. 5. The preparation method of optical laminated body, it is characterized in that: on the polarizing plate that utilizes the method described in claim 3 to make, bonding is selected from retardation film, brightness improving film, field angle improving film and semireflection At least one film of film.