KR101760541B1 - Method for manufacturing polarizing film - Google Patents

Abstract

(1) is subjected to a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment in this order, and before or during the process of any of these steps, the difference between the two nip rolls (2, 2 ' A method of producing a polarizing film for performing uniaxial stretching using a main speed difference, comprising the step of providing at least one widening roll (3) between the two nip rolls (2, 2 ') to perform widening and uniaxial stretching, (In the case where there is no other drawing step up to the widening step, the drawing magnification in the widening step) to the widening step including the widening step is 1.6 or more, and in the widening step, the widening roll 3 The angle of the widening roll of the widened roll 3 with respect to the take-out direction of the film 1 is in the range of -40 ° to 70 ° (provided that the direction in which the film flows is from the left to the right, The carry-out direction is set to 0 °, The angle of the clockwise direction from - a counter-clockwise direction and the angle of a +).

Description

METHOD FOR MANUFACTURING POLARIZING FILM [0002]

This patent application claims the priority of the Paris Convention based on Japanese Patent Application No. 2010-141429 (filed on June 22, 2010), the entire contents of which are incorporated herein by reference .

The present invention relates to a method for producing a polarizing film used in the production of a polarizing plate used in a liquid crystal display device.

As the polarizing film, conventionally, a polyvinyl alcohol film in which a dichroic dye is adsorbed and oriented has been used. That is, an iodine-based polarizing film using iodine as a dichroic dye or a dye-based polarizing film using a dichroic dye as a dichroic dye are known. These polarizing films are usually formed by bonding a protective film such as triacetylcellulose through an adhesive made of an aqueous solution of a polyvinyl alcohol resin to at least one surface, preferably both surfaces, to form a polarizing plate. As a liquid crystal display (LCD) , A liquid crystal television, a monitor for a personal computer, a display screen of a cellular phone, and the like.

As a method for producing a polarizing film, nip rolls and guide rolls are used, and a polyvinyl alcohol film is dipped in water to swell, followed by dyeing with the dichroic dye, stretching it, and then fixing iodine to the film A method is known in which a polyvinyl alcohol film is subjected to a boric acid treatment (crosslinking treatment), followed by washing with water and then drying. At this time, the nip roll before and after the treatment bath is given a main speed difference to stretch the film, and the direction of transporting the film is changed by the guide roll to introduce and take out the film to the treatment liquid.

In recent years, along with the enlargement of the liquid crystal display device, the improvement of the function and the improvement of the luminance, the polarizing film used therefor is also required to be large-sized as well as to improve the optical characteristics and the in-plane uniformity. However, in order to obtain a large polarizing film, it is necessary to uniformly uniaxially stretch the wide original film. However, since the light absorption axis (hereinafter also referred to as absorption axis) of the obtained polarizing film fluctuates, . Further, when the optical characteristics in the plane are not uniform, display irregularity occurs in forming the image display device.

On the other hand, Patent Document 1 discloses a method for producing a polarizing film which is subjected to uniaxial stretching in a boric acid treatment step and / or a previous step. In order to obtain a polarizing film having less damage and wrinkles and no folding, A widening roll is used as a guide roll of a wiping roll. However, in the method described in Patent Document 1, for example, when stretching is performed 1.6 times or more at an integrated stretching magnification using a widening roll in a dyeing bath, fluctuation of the absorption axis occurs and optical properties of the obtained polarizing film are lowered There was a problem.

Patent Document 1: Japanese Patent Application Laid-Open No. 2005-227650

A problem to be solved by the present invention is to provide a method for producing a polarizing film excellent in optical characteristics.

As a result of diligent studies to solve the above problems, the inventors of the present invention have found that when the widening direction of the wider roll is set to a predetermined direction in performing uniaxial stretching of 1.6 times or more at an integrated stretching magnification while widening the wafers, And the polarizing film having good optical characteristics can be obtained. The present invention has been accomplished based on this finding.

That is, the method for producing a polarizing film of the present invention has the following constitution.

(1) A process for treating a polyvinyl alcohol film in the order of a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment, wherein the difference in speed between two nip rolls A method for producing a polarizing film for performing stretching, comprising a widening stretching step of performing widening and uniaxial stretching by providing at least one widening roll between the two nip rolls, In the widening stretching step, the stretching magnification (in the case where there is no other stretching step up to the widening stretching step, the stretching magnification in the widening stretching step) is 1.6 or more, and in the widening stretching step, In the direction of the widening direction of the film is -40 ° to 70 ° (note that when the direction in which the film flows is from left to right, And an angle in the clockwise direction from the take-out direction is -, and an angle in the counterclockwise direction is +).

(2) The method according to (1), which has two or more widening stretching processes.

(3) The method according to (1) or (2), wherein the wafers in the widening stretching step are arranged in the air.

(4) The widening roll in the widening stretching process is a sponge rubber roll. The sponge has a hardness of 20 to 60 degrees in JIS Shore C scale, a density of 0.4 to 0.6 g / cm3, and a surface roughness of 10 to 30 S To (3).

(5) The method according to any one of (1) to (4), wherein the stretching in the widening stretching step is carried out by wet stretching and the temperature of the liquid used is from 20 캜 to 40 캜.

(6) The method according to any one of (1) to (5), wherein an integrated stretching magnification ratio up to the widening stretching step (provided that the stretching magnification in the above step in the case where there is no other stretching step up to the above step) is two or more times.

According to the polarizing film producing method of the present invention, it is possible to suppress the fluctuation of the absorption axis of the obtained polarizing film and to produce a polarizing film excellent in optical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view showing one embodiment of a widening stretching process for widening the width and uniaxially stretching by providing a widening roll in the present invention. Fig.
2 is a front view showing an example of the widening roll in the present invention.
Fig. 3 is an explanatory view showing the relationship between the widening direction of the widened roll and the film take-out direction. The widening direction of the widened roll with respect to the film take-out direction is (a) and c represents a case of -40 °.

(Production method of polarizing film)

The polyvinyl alcohol resin forming the polyvinyl alcohol film in the present invention is usually one obtained by saponifying a polyvinyl acetate resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% to 100 mol%. Examples of the polyvinyl acetate resin include polyvinyl acetate as a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000 to 10000, and preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified, and examples thereof include polyvinylformal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like. Usually, an unoriented film of a polyvinyl alcohol-based resin film having a thickness of about 20 탆 to 100 탆, and preferably about 30 탆 to 80 탆 is used as a starting material for producing a polarizing film. In industry, the width of the film is practically about 1500 mm to 6000 mm.

The thickness of the polyvinyl alcohol polarizing film obtained by treating the undrawn film in the order of the swelling treatment, the dyeing treatment, the boric acid treatment (crosslinking treatment) and the water washing treatment, and finally drying is about 5 to 50 μm .

A polarizing film which is a polyvinyl alcohol uniaxially stretched film in which a dichroic dye is adsorbed and oriented is generally subjected to solution treatment in the order of a swelling treatment, a dyeing treatment, a boric acid treatment and a water washing treatment in an aqueous solution of an unstretched polyvinyl alcohol film, A boric acid treatment step and, if necessary, uniaxial drawing by wet or dry method in the previous step, and finally drying.

The uniaxial stretching in the present invention may be performed in only one widening stretching step or in two or more steps. In the case of carrying out in two or more steps, a known stretching method may be employed, except that at least one widening stretching step is employed. Examples of known stretching methods include inter-roll stretching in which stretching is performed with a main speed difference between two nip rolls for transporting the film, thermal roll stretching method and tenter stretching method as disclosed in Japanese Patent No. 2731813, and the like. Of course, the widening stretching process may be performed a plurality of times. Basically, the order of the steps is the same as described above, but there are no restrictions on the number of treatment baths and treatment conditions.

It goes without saying that it is also possible to insert a process without any description into the above process for other purposes. As an example of this step, an immersion treatment (iodide treatment) with an iodide aqueous solution containing no boric acid or an immersion treatment (zinc treatment) with an aqueous solution containing zinc chloride or the like not containing boric acid .

The swelling process is performed for the purpose of removing foreign substances on the film surface, removing the plasticizer in the film, imparting easiness of dyeing in the next process, plasticizing the film, and the like. The treatment conditions are determined within a range that can achieve such a purpose and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film stretched in advance in the gas is swelled, the film is immersed in an aqueous solution of, for example, about 20 ° C to 70 ° C, preferably about 30 ° C to 60 ° C. The immersion time of the film is preferably about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. When the undrawn original film is swollen from the beginning, the film is immersed in an aqueous solution of, for example, about 10 ° C to 50 ° C, preferably about 20 ° C to 40 ° C. The immersion time of the film is preferably about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

When the polyvinyl alcohol film is subjected to swelling, dyeing or boric acid treatment, uniaxial stretching may be performed in the swelling step. In this case, the stretching magnification is usually 1.2 to 3 times, preferably 1.3 to 2.5 times to be.

In the swelling process, the film tends to swell in the width direction to cause wrinkles in the film. Therefore, it is preferable to use a known widening width (width) such as a widened roll (expander roll), spiral roll, crown roll, cross guide, It is preferable to transport the film while removing wrinkles of the film with the apparatus. For the purpose of stabilizing the film transportation in the bath, the water stream in the swelling bath may be controlled by an underwater shower, or an EPC apparatus (edge position control apparatus: a device for detecting the film edge to prevent meandering of the film) useful. In this process, since the film swells and expands even in the running direction of the film, when the film is not actively stretched, in order to eliminate the relaxation of the film in the carrying direction, for example, the speed of the transport roll before and after the treatment tank is controlled It is desirable to take measures such as the following. In addition to the pure water, boric acid (described in Japanese Patent Application Laid-Open No. 10-153709), chloride (described in Japanese Patent Application Laid-Open No. 06-281816), inorganic acid, inorganic salt, , Alcohols and the like in the range of about 0.01 wt% to 10 wt% may be used.

The dyeing step with the dichroic dye is carried out for the purpose of adsorbing and orienting a dichroic dye on the film. The treatment conditions are determined within a range in which the above object can be achieved and within a range in which problems such as extreme dissolution of the base film and devitrification do not occur. When iodine is used as the dichroic dye, the iodine / KI / water = about 0.003 to 0.2 / about 0.1 to 10/100, for example, at a temperature of about 10 ° C to 45 ° C, preferably about 20 ° C to 35 ° C, Is carried out for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. In addition, other iodides may be used in combination with potassium iodide. Further, compounds other than iodide such as boric acid, zinc chloride, cobalt chloride, etc. may be coexistent. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. If it contains about 0.003 part by weight or more of iodine relative to 100 parts by weight of water, it can be regarded as a dyeing tank.

When a water-soluble dichroic dye is used as the dichroic dye, for example, at a temperature of about 20 ° C to 80 ° C, preferably about 30 ° C to 70 ° C, and at a weight ratio of dichroic dye / water of about 0.001 to 0.1 / 100 For about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may have a dyeing assistant and the like, and may contain an inorganic salt such as sodium sulfate, a surfactant, and the like. The dichroic dye may be used singly or two or more dichroic dyes may be used at the same time.

In the case of treating the polyvinyl alcohol film in the order of the swelling treatment, the dyeing treatment and the boric acid treatment, the film is usually stretched in a dyeing bath. The stretching magnification of the totalization up to the dyeing treatment (the stretching magnification in the above step when there is no stretching step up to the above step) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times. In addition, when the stretching magnification of the integration up to the dyeing treatment is less than 1.6 times, the frequency of breaking of the film is increased, and the yield tends to deteriorate.

Stretching is performed by a method such as imparting a main speed difference to the nip rolls before and after the dyeing bath. Also, as in the case of the swelling step, a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar and the like may be provided in a dyeing bath and / or a bath door. In addition, the uniaxial stretching in the present invention can be applied to any of the swelling step, the dyeing step, the boric acid treatment step and the cleaning step.

The boric acid treatment is carried out 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, iodide is preferably contained in an amount of about 1 to 30 parts by weight.

Examples of the iodide include potassium iodide and zinc iodide. Further, compounds other than iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may be coexistent.

This boric acid treatment is carried out for water resistance and color adjustment (such as prevention of blueness) by crosslinking and the like. In the case of water resistance by crosslinking, a crosslinking agent such as glyoxal, glutaraldehyde and the like may be used in addition to boric acid or boric acid, if necessary.

Further, the boric acid treatment for water resistance may be referred to as a water resistance treatment, a cross-link treatment or an immobilization treatment. The boric acid treatment for color adjustment may also be referred to as a complementary coloring treatment or a re-dyeing treatment.

This boric acid treatment is carried out by suitably changing the concentration of boric acid and iodide and the temperature of the treatment bath, depending on the purpose.

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

When the original film is subjected to swelling, dyeing or boric acid treatment, when the boric acid treatment is aimed at water resistance by cross-linking, about 3 to 10 parts by weight of boric acid and about 1 to 10 parts by weight of iodide, Is usually carried out at a temperature of about 50 캜 to 70 캜, preferably about 53 캜 to 65 캜, by using a boric acid treatment bath containing 20 parts by weight. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds.

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

After boric acid treatment for moisture resistance, boric acid treatment for color adjustment may be performed. 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 iodine is used, Lt; 0 > C to 45 < 0 > C. The immersing time is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

Such boric acid treatment may be carried out a plurality of times, usually in two to five times. In this case, the composition and temperature of the aqueous solution of each boric acid treatment tank to be used may be the same or different within the above range. The boric acid treatment for water resistance and the boric acid treatment for color adjustment may be performed in a plurality of steps, respectively.

The final integrated stretching magnification of the stretching of the polarizing film in the present invention is usually about 4.5 to 7 times, preferably about 5 to 6.5 times.

It is washed with water after treatment with boric acid. The water washing treatment is carried out, for example, by immersing a polyvinyl alcohol film treated with boric acid for water resistance and / or color tone adjustment in water, spraying water with a shower, or using immersion and spray in combination. The temperature of water in the water washing treatment is usually about 2 to 40 占 폚, and the immersion time is preferably about 2 to 120 seconds.

Thereafter, the polarizing film can be obtained by drying the polyvinyl alcohol film in a drying oven at a temperature of about 40 to 100 DEG C for about 60 to 600 seconds.

Also, in the boric acid treatment step and the cleaning treatment step, wafers can be used.

(Widening stretching process)

The film is uniaxially stretched between two nip rolls in any of the above-described processing steps, or in a separate drawing step from these steps. That is, the main speed of the nip roll on the downstream side in the transport direction of the film is made larger than the main speed of the nip roll on the upstream side, and the film is stretched by applying tension thereto.

At that time, in the present invention, in at least one step of the stretching process, at least one widening roll is provided between two nip rolls, and uniaxial stretching is performed while widening the film (widening stretching step).

(In the case where there is no drawing step up to the widening step, the drawing magnification in the widening drawing step is the same hereinafter) until the widening drawing step provided with the widening roll of the present invention is 1.6 times or more, And is usually not more than 7 times, preferably not more than 6.5 times, and thus the effect of suppressing the fluctuation of the absorption axis is sufficiently exhibited. If the total stretching magnification ratio up to the widening stretching process is less than 1.6 times, there is a possibility that the effect of suppressing a sufficient absorption axis variation can not be obtained. Further, as described above, , The frequency of breakage of the film tends to increase. The cumulative stretching magnification is a magnification obtained by adding the magnifications of the uniaxial stretching and the widening stretching, and when both the uniaxial stretching and the wavy stretching are performed a plurality of times, the multiplication factor becomes the multiplication factor obtained by integrating all of them.

The stretching may be either dry or wet, but it is preferable to perform the stretching by so-called wet stretching method in which the film is immersed in a predetermined solution while stretching. In this wet stretching method, since the film is not well broken and can be stretched sufficiently, necessary optical characteristics can be easily obtained, and the degree of polarization is higher than that of the dry stretching method.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of uniaxial stretching in the present invention will be described in detail with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view showing one embodiment of a widening stretching process in the present invention, and Fig. 2 is a front view showing an example of a widening roll in the present invention. Fig.

A treatment tank 10 shown in Fig. 1 is filled with a treatment liquid 4 (for example, iodine and potassium iodide aqueous solution), and on the upstream side of the polyvinyl alcohol film 1 passing through the treatment liquid 4, 2 and a nip roll 2 'on the downstream side, and a widening roll 3 and a guide roll 5 are provided between the two nip rolls. The widened roll 3 has a curved shape as shown in Fig.

In this widening stretching process, the polyvinyl alcohol film 1 is immersed in the treatment liquid 4 and is stretched through the widening roll 3, and stretched by the difference in peripheral speed between the two nip rolls 2, 2 ' do. In this case, a plurality of widening rolls 3 may be provided.

3 (a) to 3 (c) are explanatory diagrams showing the relationship between the widening direction M of the wider roll and the film take-out direction.

The widening direction M of the widening roll 3 is important in improving the optical characteristics of the polarizing film and the angle? Of the widening direction M with respect to the carrying-out direction of the film 1 is -40 to 70 Deg.], More preferably -30 [deg.] To 30 [deg.]. 3 (a) to 3 (c), when the direction in which the film 1 flows is from left to right, the direction in which the film 1 is taken out is 0 °, The angle in the clockwise direction is -, and the angle in the counterclockwise direction is +. In Fig. 3, (a), (b) and (c) indicate angles in the widening direction of the wider roll with respect to the film take-out direction of 70 °, 0 ° and -40 °, respectively. When the angle &thetas; is out of the above-mentioned range, the absorption axis of the polarizing film is not aligned in a certain direction (the transporting direction of the film), so that the optical characteristic of the film is deteriorated.

The radius of curvature of the widened roll 3 to be used is preferably 1000 to 50000 mm, more preferably 10000 to 40000 mm, the diameter d of the widened roll 3 is preferably 50 to 300 mm, Is 75 to 200 mm.

The widening roll 3 may be disposed either in the air (in the air) or in the liquid. However, as shown in Fig. 1, applying the present invention to the widened roll 3 installed in the air improves the optical characteristics .

Particularly, in the case where a plurality of rollers are provided in the swelling process or the dyeing process in which the width of the film is greatly changed by the swelling of the film, at least one roll 3 is provided in the air, The optical characteristics can be improved while suppressing the occurrence of the defects.

When a plurality of widening rolls 3 are provided, it is preferable that the widening rolls 3 to which the present invention is applied is large, and the present invention is applied to all widening rolls 3, It is highly desirable to install between the two nip rolls 2, 2 '.

As the material of the widening roll in the manufacturing process of the present invention, rubber, sponge and the like can be mentioned, but it is more preferable that it is a sponge rubber roll. The polyvinyl alcohol film is swollen in both length and width directions by the absorption of the bath liquid, but wrinkles and folding are likely to occur on the rolls if tension is applied without ending swelling in the width direction. When the sponge rubber roll is used as the wider roll, the high film gripping force based on the high surface roughness can exhibit a sufficient magnifying force, and the anti-skew prevention function, which is another role of the widening roll, And the folding is also eliminated.

As the sponge rubber roll used in the present invention, it is preferable that the hardness of the sponge is about 20 to 60 degrees, more preferably about 25 to 50 degrees, and the density is about 0.4 to 0.6 degrees in JIS Shore C scale measured by the test method of JIS K 6301 more preferably about 0.42 to 0.57 g / cm 3, and the surface roughness is about 10 to 30 S, more preferably about 10 to 30 S, expressed in terms of an average spacing S of local peaks of roughness curves of JIS B 0601 (surface roughness) Is preferably about 15 to 25 S.

When the stretching in the widening stretching process is a wet stretching process, the temperature of the solution in which the film is immersed may usually be 2 to 70 占 폚, but is preferably 20 to 40 占 폚, preferably 25 to 35 占 폚 In the case of stretching through a wider roll, it is possible to stretch without deteriorating the optical properties most.

The tension control may be performed so that the tensile force of the film is substantially constant in each step after the widening stretching process.

In the case where the iodide treatment or the zinc treatment is performed after the boric acid treatment, it is preferable to perform the tension control on these steps.

The tension in each process may be the same or different. The tension on the film in the tension control 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. If the tensile force is less than about 150 N / m, wrinkles and the like easily occur on the film. On the other hand, if the tensile strength exceeds about 2000 N / m, problems such as breakage of the film or wear of the bearing and water retention may occur. The tension per unit width is calculated from the film width in the vicinity of the entrance of the process and the tension value of the tension detector.

In addition, when tension control is performed, there is a case where it is inevitably stretched or shrunk to some extent, but in the present invention, this is not included in the stretching process.

A polarizing plate can be obtained by bonding a protective film to at least one surface of the thus prepared polarizing film with an adhesive.

As the protective film, for example, a film made of an acetylcellulose resin such as triacetylcellulose or diacetylcellulose, a film made of a polyester-based resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate, a film made of a polycarbonate- A film made of a resin, a film made of a cycloolefin-based resin, an acrylic resin film, and a polypropylene-based resin film.

A surface treatment such as a corona treatment, a flame treatment, a plasma treatment, an ultraviolet irradiation, a primer coating treatment, or a saponification treatment is applied to the polarizing film and / or the protective film in order to improve the adhesiveness between the adhesive and the polarizing film and / May be performed.

Example

EXAMPLES Next, the present invention will be described concretely with reference to Examples, but the present invention is not limited at all by these Examples.

≪ Measurement method of absorption axis >

With reference to the width direction of the film, a strip-shaped film piece was taken at a full width of 50 mm in the longitudinal direction with respect to the reference axis, and the width of the band-shaped film piece was measured using an automatic birefringence measuring device (trade name "RETS" manufactured by Otsuka Electronics Co., Ltd.) , And the angle of the absorption axis was measured at each position where the film piece was divided into nine parts in the width direction. A value obtained by subtracting the maximum value and the minimum value among the obtained shaft angles was adopted as the variation of the absorption axis.

[Example 1]

Uniaxial stretching was carried out at a stretching ratio of 1.30 while the film was sufficiently swollen by immersing the polyvinyl alcohol film (Kurarabinetron VF-PS # 7500, thickness: 2400, saponification degree: 99.9 mol% or more) having a thickness of 75 占 퐉 in pure water at 30 占 폚.

Next, uniaxial stretching as shown in Fig. 1 was carried out so as to be 2.80 times the total stretching magnification while immersing in a dyeing bath at 30 DEG C of iodine / potassium iodide / water at a weight ratio of 0.02 / 2.0 / 100. When the angle of the widening roll of the wafers with respect to the take-out direction of the film carried out from the widened roll at this time (when the direction in which the film flows is from left to right, (Hereinafter referred to as the holding angle of the wiping roll) was carried out at 0 DEG. Thereafter, uniaxial stretching was carried out until immersion in a 55 ° C aqueous solution of potassium iodide / boric acid / water at a weight ratio of 12 / 4.4 / 100 until the total draw ratio of the total from the master was 5.5 times, and potassium iodide / boric acid / And immersed in an aqueous solution of 40 DEG C having a weight ratio of 9 / 2.9 / 100. Subsequently, the film was washed with pure water at 5 캜 for 8 seconds and dried at 70 캜 for 3 minutes to obtain a polarizing film. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.04 °.

[Example 2]

A polarizing film was obtained in the same manner as in Example 1 except that the holding angle of the wiping roll in the dyeing bath was 30 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.08 °.

[Example 3]

A polarizing film was obtained in the same manner as in Example 1 except that the holding angle of the wiping roll in the dyeing bath was set to 60 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.12 °.

[Example 4]

A polarizing film was obtained in the same manner as in Example 1 except that the holding angle of the wider roll in the dyeing bath was set to -30 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.09 deg.

[Example 5]

Uniaxial stretching was carried out at a stretching ratio of 1.30 while the film was sufficiently swollen by immersing the polyvinyl alcohol film (Kurarabinetron VF-PS # 7500, thickness: 2400, saponification degree: 99.9 mol% or more) having a thickness of 75 占 퐉 in pure water at 30 占 폚.

Next, uniaxial stretching as shown in Fig. 1 was carried out so that the total amount of iodine / potassium iodide / water was 1.65 times as high as that of immersion in a dyeing bath at 30 DEG C at a weight ratio of 0.02 / 2.0 / 100. At this time, the carrying angle of the wafers was 0 °. Thereafter, uniaxial stretching was carried out until immersion in an aqueous solution at 53 DEG C in which potassium iodide / boric acid / water was 11 / 3.5 / 100 in weight ratio, until the cumulative stretching magnification from the disk was 5.8 times. Thereafter, potassium iodide / boric acid / Lt; 0 > C and 11 / 3.5 / 100. Subsequently, the film was washed with pure water at 5 캜 for 8 seconds and dried at 70 캜 for 3 minutes to obtain a polarizing film. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.10 °.

[Example 6]

A polarizing film was obtained in the same manner as in Example 5 except that the holding angle of the wiping roll in the dyeing bath was 30 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.13 °.

[Example 7]

A polarizing film was obtained in the same manner as in Example 5 except that the holding angle of the wiping roll in the dyeing tank was 60 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.15 °.

[Comparative Example 1]

A polarizing film was obtained in the same manner as in Example 1 except that the wiping roll in the dyeing bath had a holding angle of 90 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.23 deg.

[Comparative Example 2]

A polarizing film was obtained in the same manner as in Example 5 except that the holding angle of the wider roll in the dyeing bath was changed to 90 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.24 deg.

The results of Examples 1 to 4 and Comparative Example 1 are shown below.

From Table 1, it can be seen that in Examples 1 to 7, the fluctuation of the absorption axis (maximum-minimum difference) is smaller than that of Comparative Examples 1 and 2. [

[Example 8]

In the swelling tank, uniaxial stretching as shown in Fig. 1 was carried out with a stretching magnification of 2.20 times through a widening roll in a period of keeping the holding angle at 0 DEG, and then, as shown in Fig. 1 (The holding angle of the wiping roll in the dyeing bath was 0 DEG) as shown in Fig. 5A, and a polarizing film was obtained in the same manner as in Example 1. Fig. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.11 °.

[Comparative Example 3]

A polarizing film was obtained in the same manner as in Example 8 except that the holding angle of the wider roll in the swelling bath was changed to 90 °. The variation (maximum difference and minimum difference) of the absorption axis of the obtained polarizing film was 0.34 °.

The results of Example 8 and Comparative Example 3 are shown below.

From Table 2, it can be seen that the variation of the absorption axis (maximum-minimum difference) in Example 8 is lower than that of Comparative Example 3.

1: polyvinyl alcohol film 2, 2 ': nip roll
3: widening roll 4: treatment liquid
5: guide roll 10: boric acid treatment tank (stretching treatment)
M: widening direction d: diameter of widened roll 3

Claims (11)

A step of treating the polyvinyl alcohol film in the order of a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment, and the uniaxial stretching is carried out by using the peripheral speed difference between two nip rolls before or during any of these processes As a method for producing a polarizing film,
The uniaxial stretching includes a widening stretching step of performing widening and uniaxial stretching by providing at least one widening roll between two nip rolls. The stretching stretching step up to the widening stretching step including the widening stretching step , The stretching ratio in the widening stretching step in the case where there is no other stretching step up to the widening stretching step) is 1.6 times or more, and in the widening stretching step, in the widening direction of the widening roll Wherein the angle of the film is in the range of -40 ° to 70 ° (when the direction in which the film flows is from left to right, the direction of the film from the widening roll is 0 °, And the clockwise angle is +). The method according to claim 1, wherein two or more widening stretching processes are performed. The method according to claim 1, wherein the wider roll in the widening stretching step is disposed in the air. The method according to claim 2, wherein the widening roll in the widening stretching step is placed in the air. The method according to any one of claims 1 to 4, wherein the widening roll in the widening stretching step is a sponge rubber roll, the hardness of the sponge is 20 to 60 degrees in JIS Shore C scale, the density is 0.4 to 0.6 g / cm < And a surface roughness of 10 to 30 S. The method according to any one of claims 1 to 4, wherein the stretching in the widening stretching step is performed by wet stretching, and the temperature of the liquid used is 20 占 폚 to 40 占 폚. The method according to claim 5, wherein the stretching in the widening stretching step is performed by wet stretching, and the temperature of the liquid used is 20 占 폚 to 40 占 폚. The method according to any one of claims 1 to 4, wherein an integrated stretching magnification ratio up to the widening stretching step (in the case where there is no other stretching step up to the widening stretching step, the stretching magnification in the widening stretching step) is twice or more. 6. The method according to claim 5, wherein an integrated stretching magnification up to the widening stretching step (provided that the stretching magnification in the widening stretching step in the absence of another stretching step up to the widening stretching step) is two or more times. 7. The method according to claim 6, wherein an integrated stretching magnification ratio up to the widening stretching step (provided that the stretching magnification in the widening stretching step in the absence of another stretching step up to the widening stretching step) is two times or more. 8. The method according to claim 7, wherein an integrated stretching magnification up to the widening stretching step (provided that the stretching magnification in the widening stretching step when no other stretching step up to the widening stretching step) is two or more times.

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