CN1595211A - Polarizing film, method for producing same, polarizing plate, and optical laminate - Google Patents

Abstract

The present invention provides a polarizing film with less color unevenness. A polarizing film, prepared by a method comprising the following operations: sequentially performing expansion treatment, dyeing treatment, boric acid treatment and water washing treatment on a polyvinyl alcohol film, performing a single Axial stretching, and further, in each process after the stretching treatment, the tension applied to the above-mentioned film is kept substantially constant. A method for manufacturing a polarizing film, the method comprising continuously and sequentially performing expansion treatment, dyeing treatment, boric acid treatment and water washing treatment on a polyvinyl alcohol film, performing a single step in the boric acid treatment process and/or the process before the boric acid treatment process Axial stretching is to control the tension of the above-mentioned film in each process after the stretching treatment. As a result, film operation can be stabilized and staining can be reduced.

Description

Polarizing film, manufacturing method thereof, polarizing plate, and optical laminate

【Technical field】

The present invention relates to a polarizing film with less color unevenness, a method for producing the same, a polarizer having a protective film laminated on at least one side of the polarizing film, a phase difference film, a brightness improving film, a viewing angle improving film, and a semi-polarizing film. An optical laminate composed of any one of the transflective films alone or bonded together.

【Background technique】

As a polarizing film, a polyvinyl alcohol-based film in which a dichroic dye is oriented and adsorbed 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. These polarizing films are generally made into polarizers by bonding protective films such as triacetyl cellulose to at least one side, preferably both sides thereof, with an adhesive composed of an aqueous solution of polyvinyl alcohol resin.

As a method for producing a polarizing film, for example, Patent Document 1 describes a method in which a polyvinyl alcohol-based film is immersed in water and swelled, dyed with the above-mentioned dichroic dye, and stretched. Next, in order to immobilize iodine on the film, the polyvinyl alcohol film was treated with boric acid, washed with water, and then dried.

In addition, Patent Document 2 describes a method of dyeing and relaxing a dry uniaxially stretched polyvinyl alcohol film with the aforementioned dichroic dye aqueous solution, and stretching the film in a boric acid aqueous solution. , to prepare a polarizing film.

To obtain a polarizing film with a high degree of polarization, uniaxial stretching of the polyvinyl alcohol film is important. Wet stretching in stretching can generally be carried out by changing the rotation speed of the nip roll before and after dipping the film in the treatment liquid, specifically, by making the rotation speed of the nip roll after dipping higher than that before dipping. Stretching at rotational speed. At this time, in order to perform stretching with high precision, the ratio of the rotational speeds of the nip rolls before and after immersion in the treatment liquid is controlled, that is, ratio control is performed.

However, even if such ratio control is accurately performed, color spots are generated on the prepared polarizing film. Such color spots degrade the quality of the polarizing film.

[Patent Document 1] Japanese Unexamined Patent Publication No. 10-153709

[Patent Document 2] Japanese Unexamined Publication No. 2002-182035

【Content of invention】

【Problems to be solved by the invention】

The main problem to be solved by the present invention is to provide a polarizing film with less color unevenness.

【How to solve the problem】

In order to thoroughly investigate the cause of the above-mentioned color spots, the inventors of the present invention have repeatedly conducted intensive research. As a result, it has been considered whether the tension of the polyvinyl alcohol-based film will be changed due to the change of the tension of the film after the stretching treatment. The operation of the machine was unstable, which led to the occurrence of color spots, and further research was repeated, and the following new facts were found: By using the tension control in the process after the stretching process instead of the ratio control used in the entire process before, so that Changes in the tension applied to the polyvinyl alcohol-based film can be suppressed, and as a result, the running of the film becomes stable, and color unevenness can be reduced. Thus, the present invention has been accomplished.

That is, the polarizing film of the present invention is obtained by performing expansion treatment, dyeing treatment, boric acid treatment, and water washing treatment on the polyvinyl alcohol film in sequence, and performing a single step in the boric acid treatment process and/or the process before the boric acid treatment process. Axial stretching, and in each process after the stretching treatment, the tension applied to the above-mentioned film is kept substantially constant.

In addition, the manufacturing method of the polarizing film of the present invention is a method as follows: continuously and sequentially perform expansion treatment, dyeing treatment, boric acid treatment and water washing treatment on the polyvinyl alcohol film, and in the boric acid treatment step and/or boric acid treatment The method of performing uniaxial stretching in a step before the step is characterized in that the tension of the film is controlled in each step after the stretching treatment.

In each step after the stretching treatment, the tension per unit width of the film is preferably 150 N/m to 2000 N/m.

In the present invention, the above-mentioned boric acid treatment process may also include a plurality of boric acid treatment processes. In this case, the above-mentioned film may be stretched at the initial or from the initial boric acid treatment process to the second step. Tension control is performed in each step from the boric acid treatment step after the stretched boric acid treatment step to the water washing step, and the tension of each of the above-mentioned films is kept substantially constant.

In addition, the polarizing plate of the present invention is a polarizing plate in which a protective film is adhered to at least one surface of the above-mentioned polarizing film. The protective film may function as any one of a retardation film, a brightness improvement film, a viewing angle improvement film, and a transflective film. Alternatively, the polarizer of the present invention may also be on the above-mentioned polarizer bonded with a protective film on at least one side, and bonded with at least one selected from the retardation film, the brightness improvement film, the viewing angle improvement film and the semi-transmissive reflection sheet. The optical laminate obtained by this kind.

【Effect of invention】

According to the present invention, since the tension applied to the above-mentioned film is substantially kept constant by carrying out tension control in each process after the stretching treatment, thereby suppressing changes in the tension, the running of the film is stabilized, and it is possible to reduce the color of the film. spots effect. By applying the polarizing plate and the optical laminate of the present invention to a liquid crystal display device, a thin high-quality liquid crystal display can be obtained.

【The best way to implement the invention】

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol-based resin forming the polyvinyl alcohol-based film of the present invention generally includes a resin obtained by saponifying polyvinyl acetate-based resin. The degree of saponification is 85 mol% or more, preferably 90 mol% or more, more preferably 99 mol% to 100 mol%. Examples of polyvinyl acetate-based resins include, in addition to polyvinyl acetate monomers of vinyl acetate, copolymers of vinyl acetate and monomers that can be copolymerized therewith, for example, ethylene-vinyl acetate copolymers, and the like. 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 can also be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can be used. Generally, as a starting material of a polarizing film, an unstretched film such as a polyvinyl alcohol-based resin film having a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm is used. Industrially, a film width of 1500 mm to 4000 mm is practical.

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

The polarizing film of the present invention is a polyvinyl alcohol-based uniaxially stretched film in which a dichroic dye is fixedly adsorbed, and its production method is roughly divided into two types. The first method is to uniaxially stretch a polyvinyl alcohol film in air or an inert gas, then sequentially perform expansion treatment, dyeing treatment, boric acid treatment, and water washing treatment, and finally dry it. The second method is to sequentially perform expansion treatment, dyeing treatment, boric acid treatment and water washing treatment on the unstretched polyvinyl alcohol film in an aqueous solution, and perform wet processing in the boric acid treatment process and/or the process before the boric acid treatment process. A method of 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, and is preferably performed in a plurality of steps. The stretching method can be a known method, for example, stretching between rolls that stretches by producing a peripheral speed difference between two nip rolls that convey the film, such as hot roll stretching as described in Patent No. 2731813 method, tenter stretching method, etc. In addition, the order of the steps is basically as described above, and there are no restrictions on the amount of treatment liquid, treatment conditions, and the like.

In addition, of course, steps not described in the above-mentioned steps may be inserted for other purposes. As an example of such a process, after boric acid treatment, immersion treatment with an iodide aqueous solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment) ) process, etc.

The expansion process is performed for the purpose of removing foreign matter on the surface of the film, removing the plasticizer in the film, providing easy dyeing in subsequent processes, plasticizing the film, and the like. 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. When expanding the stretched film in a preset gas, the film is dipped in an aqueous solution at, for example, 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 original film from the beginning, the film is dipped in an aqueous solution at, for example, 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 it is easy to cause problems such as expansion of the film in the width direction and creases on the film, it is preferable to use a tenter roll (expander roll), a spiral roll (spiral roll), a crown roll (crown roll), and a cloth guide. Known wide-width devices such as cross guider, bend bar, and tenter clip eliminate creases of the film while conveying the film. In order to achieve the purpose of stably transporting the film in the solution, it is very important to use the spray pipe in the water to control the water flow in the swelling solution, or to use the EPC device (edge position control device: a device that detects the edge of the film and prevents the film from bending) at the same time. useful. In this step, since the film also expands along the film running direction, in order to eliminate the sagging of the film in the conveying direction, for example, it is preferable to adopt methods such as controlling the speed of the conveying rollers before and after the treatment. In addition, the expansion treatment liquid used, in addition to pure water, can also be used to add 0.01% by weight to 10% by weight of boric acid (as described in JP-A-10-153709), chloride (as described in JP-A-06-281816 No. Gazette), aqueous solutions of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

The process of dyeing with a dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The processing conditions are set within a range in which these objects can be achieved without causing defects such as excessive dissolution of the base material film, loss of transparency, and the like. When using iodine as a dichroic dye, for example, at a temperature of 10°C to 45°C, preferably at a temperature of 20°C to 35°C, and in terms of weight ratio, iodine/KI/water=0.003～0.2/0.1～10/ At a concentration of 100, immersion treatment is performed for 30 seconds to 600 seconds, preferably 60 to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide and the like can be used. In addition, other iodides can be used simultaneously with potassium iodide. In addition, it can also coexist with compounds other than iodide such as boric acid, zinc chloride, cobalt chloride, and the like. When boric acid is added, it differs from the boric acid treatment described below in that iodine is contained. As long as it contains 0.003 parts by weight or more of iodine relative to 100 parts by weight 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 20°C to 80°C, preferably 30°C to 70°C, and in terms of weight ratio, dichroic dye/water = 0.001 to At a concentration of 0.1/100, the immersion treatment is performed for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. The dichroic dye aqueous solution to be used may contain dyeing auxiliaries and the like, for example, inorganic salts such as sodium sulfate, surfactants and the like. Dichroic dyes may be used alone, or two or more dichroic dyes may be used in combination.

As mentioned above, it is also possible to stretch the film in the dye tank. Stretching is carried out by using a method in which there is a peripheral speed difference between nip rolls before and after the dyeing tank. In addition, tenter rolls, spiral rolls, nip rolls, fabric guides, bending rods, etc. may be provided in the dyeing solution and/or at the inlet and outlet of the solution in the same manner as in the expansion step.

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

Potassium iodide, zinc iodide, etc. are mentioned as an iodide. In addition, it can also coexist with compounds other than iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate.

This boric acid treatment is performed for the purpose of water repellency through crosslinking, color adjustment (prevention of greenish tint, etc.), and the like. When the purpose is to achieve water repellency by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde may be used in addition to boric acid, or the above crosslinking agent may be used together with boric acid as needed.

In addition, boric acid treatment for the purpose of waterproofing is sometimes called waterproofing treatment, cross-linking treatment, positioning treatment and other names. In addition, boric acid treatment for the purpose of color adjustment is sometimes referred to as complementary color treatment, re-dyeing treatment and other names.

This boric acid treatment is carried out by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment liquid according to the purpose of the treatment.

The boric acid treatment for the purpose of waterproofing is not particularly different from the boric acid treatment for the purpose of color adjustment, and is carried out under the following conditions.

In the case of swelling, dyeing, and boric acid treatment of the original film, when the boric acid treatment is for the purpose of cross-linking and water repellency, use about 3 to 10 parts by weight of boric acid and about 1 to 20 parts by weight of iodine per 100 parts by weight. The boric acid treatment solution of the compound is generally carried out at a temperature of 50°C to 70°C, preferably at a temperature of 55°C to 65°C. The immersion time is generally about 30 to 600 seconds, preferably 60 to 420 seconds, more preferably 90 to 300 seconds.

In addition, when performing dyeing and boric acid treatment on the pre-stretched film, the temperature of the boric acid treatment liquid is generally 50-85°C, preferably 55°C-80°C.

After the boric acid treatment for the purpose of waterproofing, the boric acid treatment for the purpose of color adjustment may be performed. For example, when the dichroic dye is iodine, for this purpose, a boric acid treatment solution containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide is used for this purpose, generally at 10° C. to 45 at a temperature of °C. The immersion time is generally about 3 to 300 seconds, preferably 10 to 240 seconds.

Compared with the boric acid treatment for the purpose of waterproofing, the boric acid treatment for the purpose of color adjustment is generally carried out at a lower boric acid concentration, a higher iodide concentration and a lower temperature.

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 each boric acid treatment tank used may be the same as or different from the above-mentioned range. The above-mentioned boric acid treatment for the purpose of waterproofing and the boric acid treatment for the purpose of color adjustment may be performed in a plurality of steps, respectively.

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

After the boric acid treatment, a water washing treatment is performed. For example, the water washing treatment is carried out by immersing a polyvinyl alcohol-based film treated with boric acid for water repellency and/or color adjustment in water, spraying water in a shower, or performing both dipping and spraying. The water temperature in the water washing process is usually about 2 to 40° C., and the immersion time may be about 2 to 120 seconds. After washing with water, drying is performed for about 60 to 600 seconds at a temperature of about 40 to 100° C. in a drying oven.

In the present invention, in each step after the stretching treatment, tension control is performed so that the tension of the film is kept 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 a process preceding 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 at the beginning or from the very beginning to the second boric acid treatment process, and from the boric acid treatment after the boric acid treatment process for stretching treatment In each process from the process to the water washing process, tension control is carried out; or preferably, the above-mentioned film is stretched from the beginning to the boric acid treatment process of the third step, and the film is stretched from the boric acid treatment process after the boric acid treatment process to water washing. In each process of the process, tension control is carried out, but industrially, it is more preferable to stretch the above-mentioned film at the beginning or from the beginning to the boric acid treatment process of the second step, and from the boric acid treatment process after the stretching treatment. Tension control is performed in each process from the boric acid treatment process to the water washing process.

After performing the boric acid treatment, when performing the above-mentioned iodide treatment or zinc treatment, tension control may also be performed in these steps.

The tension in each process may be the same or different. In tension control, the tension of the film is not particularly limited, and is appropriately set in the range of 150 N/m to 2000 N/m, preferably 600 N/m to 1500 N/m, per unit width. If the tension is lower than 150 N/m, creases and the like are likely to be generated on the film. On the other hand, if the tension exceeds 2000 N/m, there arises a problem that the lifetime is reduced due to film breakage and bearing wear. In addition, the tension per unit width is calculated from the width of the film in the vicinity of the process entrance and the tension value of the tension detector.

In addition, when performing tension control, there are unavoidably a few cases of stretching and shrinkage, but in the present invention, these cases are not included in the stretching treatment.

Figure 1 shows an example of such tension control. That is, as shown in FIG. 1 , nip rollers 2 and 3 are respectively provided at the entrance and exit of the treatment tank 1 , and the polyvinyl alcohol film 4 is conveyed in the direction of the arrow by these nip rollers 2 and 3 . Inside and outside the treatment tank 1, a plurality of guide rolls are arranged. Wherein, on the free roll 5 that is arranged behind the nip roll 2 adjacent to the entrance, a tension detector is equipped.

Generally, a commercially available detector can be used as the tension detector, and the tension can be detected using a principle such as a differential transformer method or a strain gauge. The tension monitoring is carried out continuously in this way. For example, the detected tension value is transmitted to the control system 6 . In the control system 6, when the detected tension value deviates from the set value, its value is measured, and the signal is transmitted to the driving device (for example, a servo motor, etc.) that drives the nip roller 3 at the exit, and the drive is controlled, so that The tension value is kept constant.

In the boric acid treatment process or the previous treatment process, ratio control is performed by controlling the ratio of the rotational speeds of the nip rolls installed before and after the treatment tank in accordance with the relationship of performing uniaxial stretching. Therefore, in the present invention, by combining ratio control and tension control, stretching and running of the film are stabilized, thereby producing a polarizing film free of color spots.

A protective film is adhered on at least one side of the polarizing film thus manufactured with an adhesive to obtain a polarizing plate.

Examples of protective films include films made of acetylcellulose-based resins such as triacetyl cellulose and diacetyl cellulose, films made of polyethylene terephthalate, polyethylene naphthalate, polyethylene terephthalate, etc. A film made of polyester resin such as butylene dicarboxylate, a film made of polycarbonate resin, and a film made of cycloolefin resin. Commercially available thermoplastic cycloolefin-based resins include, for example, "Topas" (registered trademark) sold by Ticona Corporation of Germany, "Arion" (registered trademark) sold by JSR Corporation, and "Zeonor" sold by Zeon Corporation of Japan. and "Zeonex" (registered trademark), "Apel" (registered trademark) sold by Mitsui Chemicals Co., Ltd., and the like. A film obtained by forming a film from such a cycloolefin resin is used as a protective film, and a known method such as a solvent casting method or a melt extrusion method is appropriately used for film formation. Cycloolefin-based resin films for film formation are also commercially available, for example, "Essh-na" and "SCA40" sold by Sekisui Chemical Co., Ltd.

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

This protective film can also be bonded to one side or both sides of the polarizing film.

Polarizing films and protective films are laminated with 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, in which an adhesive surface with a polarizing film is hydrophilically treated by saponification treatment or the like, as the protective film, an aqueous solution of a polyvinyl alcohol-based resin is suitably used as a binder. For the polyvinyl alcohol resin used as a binder, in addition to the vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate as a vinyl acetate monomer, there are also vinyl acetate and Polyvinyl alcohol copolymers prepared by saponifying copolymers of other monomers, modified polyvinyl alcohol polymers that further partially modify those hydroxyl groups, etc. 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 coating adhesive uniformly, on the coated surface again stack another layer of film, and a method of bonding with rolls or the like, followed by drying, and the like.

Usually, the adhesive is coated at a temperature of 15-40°C after preparation, and the bonding temperature is usually about 15-30°C. After bonding, solvents such as water contained in the adhesive are removed by drying treatment, but the drying temperature at this time is usually 30 to 85°C, preferably 40 to 80°C. Then, the adhesive may be cured by generally curing for about 1 to 90 days in a temperature environment of 15 to 85°C, preferably 20 to 50°C, more preferably 35 to 45°C. If the curing time is long, the productivity will deteriorate, so the curing time is about 1 to 30 days, preferably 1 to 7 days.

In this way, a polarizing plate having a protective film bonded to one or both surfaces of a polarizing film can be obtained via an adhesive layer.

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-transmissive reflective film, a function as a diffusion film, and a function as an optical compensation film. and other optical functions. In this case, for example, by laminating an optically functional film such as a retardation film, a brightness improvement film, a reflective film, a semi-transmissive reflective film, a diffusion film, or an optical compensation film on the surface of the protective film, such a Functionality, among other things, 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 utilizing the method described in JP-A-2002-169025 or JP-A-2003-29030 to form micropores, and then laminating two or more cholesteric liquid crystal layers having different selective reflection center wavelengths, it is possible The function of a brightness improving film is given to the above-mentioned protective film. By forming a metal thin film on the above-mentioned protective film by deposition, sputtering, etc., it is possible to bring about a function as a reflective film or a transflective 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, the function as an optical compensation film can be brought about by coating and aligning a liquid crystal compound such as a DISCOTECH liquid crystal compound on the protective film. In addition, a brightness improving film such as trade name: DBEF (manufactured by Suli-Em Co., Ltd.), and a viewing angle improving film such as trade name: WV film (manufactured by Fuji Photo Film Co., Ltd.) can also be prepared using an appropriate adhesive. , trade name: Sumikalight (registered trademark) (Sumitomo Chemical Industries, 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 more specifically by way of examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, % and parts indicating content or usage-amount are based on weight.

In addition, the optical performance refers to: In the ultraviolet-visible spectrophotometer UV2450 manufactured by Shimadzu Corporation, the "film holder equipped with a polarizer" is installed as an optional auxiliary part, and the transmission direction and the absorption direction are measured. The ultraviolet-visible spectrum of the polarizer, the color when two polarizers are arranged on a crossed Nicol prism, is calculated according to JIS-Z8729, and the orthogonal color, orthogonal L ^* , orthogonal a ^* , Orthogonal b ^* .

【Example 1】

A polyvinyl alcohol film with a thickness of 75 μm (Kurarevinylon VF-PS#7500, a degree of polymerization of 2400, a degree of saponification of 99.9 mol% or more) was placed in pure water at 30°C, and the film was kept in a tense state so that the film would not sag , Dip for about 130 seconds to fully expand 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. Then, while immersing the film in a 60°C aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/5/100 for boric acid treatment, it was uniaxially stretched until the accumulated stretch ratio was 5.9 times the original. Further, at 40° C., the film was immersed in an aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/3/100 for about 30 seconds to perform the second boric acid treatment. After performing the second boric acid treatment, it was washed with pure water at 10°C for about 10 seconds.

In the second boric acid treatment and water washing process, while detecting the respective tensions, the tensions were controlled (tension control), and the tensions of both tanks were maintained at 1250 N/m. After washing with water, it was dried at 60° C. for 2 minutes to obtain an iodine-based polarizing film with a thickness of 28 μm.

A polyvinyl alcohol-based adhesive was applied to both sides of the polarizing film, and a protective film [triacetyl cellulose film saponified on the surface, "Fujitaku (registered trademark) T80UNL" produced by Fuji Photo Film Co., Ltd. , thickness 80 μm] were bonded on both sides, and dried at 60° C. for 5 minutes to prepare a polarizer.

Measure the 31 points at the off-line where the orthogonal color and luster of the polarizer is equal on the flow direction of the film, and obtain the standard deviation of the orthogonal b' value. As a result, the standard deviation was 0.2, and the obtained polarizer had few color spots.

[Example 2]

The procedure was carried out in the same manner as in Example 1, except that the second-step boric acid treatment and tension control were performed as described below.

While immersing the film in a 60°C aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/5/100 for boric acid treatment, it was uniaxially stretched until the cumulative stretching ratio was 5.9 times the original. Further, at 60° C., the film was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10/5/100 for about 30 seconds to perform a second boric acid treatment.

In the second boric acid treatment and water washing process, the tension is controlled while detecting each tension.

The result of obtaining the standard deviation of the orthogonal b' value is as follows: the standard deviation is 0.2, and the obtained polarizer has few color spots.

[Example 3]

Except for carrying out the third step of boric acid treatment and tension control as described below, the same operation as in Example 1 must be carried out.

The film was uniaxially stretched while being immersed in a 55°C aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/5/100, and further immersed in a film with a weight ratio of potassium iodide/boric acid/water of 10/5. /100 in a 60°C aqueous solution for the second waterproofing treatment while performing uniaxial stretching until the cumulative stretching ratio is 5.9 times the original. Further, at 40° C., the film was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10/3/100 for about 30 seconds to perform the third boric acid treatment. In the third boric acid treatment and water washing process, the tension is controlled while detecting each tension.

The result of obtaining the standard deviation of the orthogonal b' value is as follows: the standard deviation is 0.2, and the obtained polarizer has few color spots.

【Example 4】

Except for carrying out the third step of boric acid treatment and tension control as described below, the same operation as in Example 1 must be carried out.

The film was uniaxially stretched while being immersed in a 45° C. aqueous solution having a weight ratio of potassium iodide/boric acid/water of 1.5/2/100 to perform a boric acid treatment. Then, while immersing the film in a 60°C aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10/5/100, performing a second boric acid treatment, uniaxial stretching was carried out until the cumulative stretching ratio was the original 5.9 times. Further, at 40° C., the film was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10/3/100 for about 30 seconds to perform the third boric acid treatment. In the third boric acid treatment and water washing process, the tension is controlled while detecting each tension.

The result of obtaining the standard deviation of the orthogonal b' value is as follows: the standard deviation is 0.2, and the obtained polarizer has few color spots.

[Comparative Example 1]

In addition to the ratio control in the second boric acid treatment process and water washing process, the pull-out ratio of the nip roller at the inlet and outlet of each solution is set to 1, that is, the setting will not cause stretching and relaxation A polarizing film was produced in the same manner as in Example 1 except for the conditions above. However, during processing, the tension of the film varies irregularly. The standard deviation of the orthogonal b' value of the polarizing plate made by using the above-mentioned polarizing film is 0.7, and the color spots are more than those in Examples 1-4.

【Brief description of the drawings】

[ Fig. 1 ] An explanatory diagram showing an example of tension control of the present invention.

【Symbol Description】

1. Treatment tank

2. Nip roller

3. Nip roller

4. Polyvinyl alcohol film

5. Free Roll

6. Control system

Claims (7)

1. polarization film, make by following operation: successively the polyvinyl alcohol film is advanced expansion process, dyeing processing, boric acid processing and washing and handle, carry out uniaxial tension in the operation before boric acid treatment process and/or boric acid treatment process, and further in the operation of each after stretch processing, tension force on the above-mentioned film is basic respectively to keep constant with being applied to.

2. the manufacture method of a polarization film that comprises the steps, continuously, successively the polyvinyl alcohol film being carried out expansion process, dyeing processing, boric acid processing and washing handles, carry out uniaxial tension in the operation before boric acid treatment process and/or boric acid treatment process, it is characterized in that: in each operation after stretch processing, the tension force of above-mentioned film is controlled.

3. the manufacture method of polarization film as claimed in claim 2, it is characterized in that: in each operation after above-mentioned stretch processing, the tension force of the per unit width of above-mentioned film is 150N/m～2000N/m.

4. as the manufacture method of each described polarization film of claim 2～3, it is characterized in that: above-mentioned boric acid treatment process comprises a plurality of boric acid treatment process, initial or from initial up to the 2nd the step the boric acid treatment process, above-mentioned film stretches, in the boric acid treatment process after the boric acid treatment process of carrying out stretching process up to each operation of washing step, carry out Tension Control, make basic respectively the maintenance necessarily of tension force of above-mentioned film.

5. polaroid, its by at least on the single face of the described polarization film of claim 1 bonding protective film make.

6. polaroid as claimed in claim 5, wherein above-mentioned protective film possess and are selected from phase-contrast film, brightness improving film, field angle and improve any one function in film and the Transflective film.

7. optical laminate, its by with the described polaroid of claim 5 be selected from phase-contrast film, brightness improving film, field angle and improve bonding the making of at least a film in film and the Transflective film.

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