TWI671181B - Method for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a manufacturing method in which a polyvinyl alcohol-based resin film having a thickness of 65 μm or less is subjected to at least a dyeing treatment, and the polyvinyl alcohol-based resin film is sequentially immersed in a container containing a crosslinking agent. A method for producing a polarizing film by crosslinking treatment in two or more liquid baths, wherein in at least one of the two or more baths, a polyvinyl alcohol-based resin film is disposed along the bath in the bath. Two or more guide rollers are transported, and the final guide roller that passes last among the two or more guide rollers is passed so that the wrap angle becomes 100 ° or more and less than 180 °. Final guide roller.

Description

Manufacturing method of polarizing film

This invention relates to the manufacturing method of the polarizing film which can be used as a structural member of a polarizing plate.

The polarizing film has conventionally used an iodine or a dichroic dye-like dichroic dye to adsorb and align it to a uniaxially stretched polyvinyl alcohol-based resin film. A polarizing film is usually formed by bonding a protective film to one or both sides with an adhesive to form a polarizing plate, and is used in an image display device including a liquid crystal display device such as a liquid crystal television, a personal computer monitor, and a mobile phone.

In general, a polarizing film is treated by sequentially immersing a long polyvinyl alcohol-based resin film that is continuously transported in a processing bath such as a swelling bath, a dyeing bath, or a crosslinking bath. Stretch processing is performed between processes [for example, Japanese Patent Application Laid-Open No. 2004-070104 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2008-250326 (Patent Document 2)]. Patent Documents 1 and 2 disclose that the wet drawing is performed in order to suppress film breakage (stretch cut) caused when the polyvinyl alcohol-based resin film is wet-drawn at a high magnification of 1.2 times or more. The wrapping angle of the film in the guide roller that the initial film set in the stretching bath contacts is set within a predetermined range.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2004-070104

[Patent Document 2] Japanese Patent Laid-Open No. 2008-250326

In recent years, a thin film of a polarizing film has been required. With this, when a thinner film is used as a raw material film of a polyvinyl alcohol-based resin film, in the step of manufacturing a polarizing film, both ends of the film in the width direction are likely to occur Warping that is gently bent toward the inside, or that the part that is strongly bent and warped toward the inside forms an inward bend that is stuck to the inside of the film. When the warped or inwardly folded film is generated, a crease may be formed when it passes through a roll or a stretching treatment is performed, or the film may be cracked or broken at the crease.

Defects such as warpage or inward folding may occur in any treatment in which the film is immersed in a liquid and then pulled out. However, the present invention specifically aims to suppress the above-mentioned defects when immersed in a crosslinking bath. That is, an object of the present invention is to provide a method for manufacturing a polarizing film from a thin polyvinyl alcohol resin film, which can suppress warping or inward folding of both ends in the width direction of the film caused by immersion in a crosslinking bath. Of manufacturing method.

This invention provides the manufacturing method of the polarizing film shown below.

[1] A manufacturing method in which at least a dyeing treatment is performed while a polyvinyl alcohol-based resin film having a thickness of 65 μm or less is transported, and the polyethylene is A method for producing a polarizing film by sequentially immersing an alcohol-based resin film in a cross-linking treatment in two or more baths containing a liquid containing a cross-linking agent, wherein: In at least one of the two or more baths, the polyvinyl alcohol-based resin film is transported along two or more guide rollers arranged in the bath, and in the two or more guide rollers. Among the final guide rollers that pass last, the final guide roller is passed so that the wrap angle becomes 100 ° or more and less than 180 °.

[2] The manufacturing method according to [1], wherein the at least one bath having the final guide roller arranged so that a wrap angle is 100 ° or more and less than 180 ° is The stretching treatment is performed, and the stretching ratio of the stretching treatment in each bath is 1.14 times or less.

[3] The production method according to [1] or [2], wherein the polyvinyl alcohol-based resin film supplied to the crosslinking treatment is a stretched film.

[4] The manufacturing method according to [3], wherein the cumulative stretching ratio of the polarizing film based on the polyvinyl alcohol-based resin film having a thickness of 65 μm or less is 5.9 times or less.

[5] The manufacturing method according to any one of [1] to [4], wherein the final guide roller is an expansion roller.

According to the method of the present invention, In the method of producing a polarizing film with a lipid film, warping or inward folding at both ends in the width direction of the film caused by immersion in a crosslinking bath can be effectively suppressed in the past.

10‧‧‧ embryonic membrane made of polyvinyl alcohol resin

11‧‧‧ Pull out the roller

13‧‧‧Swelling bath

15‧‧‧ Dyeing bath

17a‧‧‧The first cross-linking bath

17b‧‧‧ 2nd Crosslinking Bath

17c‧‧‧3rd Crosslinking Bath

19‧‧‧washing bath

21‧‧‧ drying furnace

23‧‧‧Polarizing Film

30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47‧‧‧ guide rollers

50, 51, 52, 53, 54, 55, 56, 57‧‧‧ rolls

FIG. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and an apparatus for producing a polarizing film used in the method.

<Manufacturing method of polarizing film>

In the present invention, the polarizing film is a polarizing film in which a dichroic pigment (iodine or dichroic dye) is adsorbed and aligned on a uniaxially stretched polyvinyl alcohol resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The saponification degree is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. Examples of the polyvinyl acetate-based resin include, in addition to polyvinyl acetate, a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable with the vinyl acetate. 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 1,000 to 10,000, and preferably about 1500 to 5,000.

These polyvinyl alcohol-based resins can be modified, and for example, polyvinyl aldehyde modified by polyvinyl aldehyde, polyvinyl acetal, polyvinyl butyral, etc. can also be used.

In the present invention, a starting material for manufacturing a polarizing film is an unstretched polyvinyl alcohol-based resin film (embryonic film) having a thickness of 65 μm or less, preferably about 10 to 50 μm, and more preferably about 10 to 35 μm. . Thereby, a thin film polarizing film can be obtained. When the thickness of the embryonic membrane is thicker than 65 μm, since the mechanical strength of the film is quite high, there is almost no problem of warping or inward folding of both ends in the width direction of the film caused by immersing the film in a crosslinking bath.

The width of the embryonic membrane is not particularly limited, and may be, for example, about 400 to 6000 mm, but the larger the film width, the more likely it is to warp or fold in. Therefore, the production method of the present invention is particularly effective when the width of the embryonic membrane is large, and specifically, when the width of the embryonic membrane is 1000 mm or more.

The germ film is generally prepared by using a long roll (wound product) of an unstretched polyvinyl alcohol-based resin film.

The polarizing film can continuously produce a long polarizing film by continuously transporting the embryonic film along a film transport path of a polarizing film manufacturing apparatus and performing a predetermined processing step. The predetermined treatment steps may include a swelling treatment step in which the embryo membrane is immersed in a swelling bath, a dyeing treatment step in which the film after the swelling treatment step is immersed in a dyeing bath, and a cross-linking in which the film after dyeing treatment is immersed in a crosslinking bath Processing steps. In addition, between these series of processing steps (that is, before and / or during any one or more processing steps and / or during any one or more processing steps), uniaxial stretching is applied by wet or dry processing. Additional processing steps can be added as needed.

Each of the above treatment steps may be a treatment in which the film is immersed in one bath or a treatment in which two or more baths are immersed. In the polarizing film of the present invention, at least the cross-linking treatment step causes the film after the dyeing treatment step to Sequentially immersed in two or more crosslinking baths. This is because when a cross-linking treatment is performed using two or more cross-linking baths, defects such as warpage or inward folding are particularly likely to occur.

Hereinafter, a method for manufacturing a polarizing film of the present invention will be described in more detail with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and an apparatus for producing a polarizing film used in the method. The polarizing film manufacturing apparatus shown in FIG. 1 is configured to continuously roll an embryo (unstretched) film 10 made of a polyvinyl alcohol resin from a take-out roller 11 while conveying it along a film conveying path, thereby It passes sequentially through the swelling bath 13, the dyeing bath 15, the first cross-linking bath 17a, the second cross-linking bath 17b, the third cross-linking bath 17c, and the washing bath 19 provided on the film transport path, and finally passes through the drying furnace 21 constructs. The obtained polarizing film 23 can be directly transported, for example, to the next polarizing plate manufacturing step (the step of bonding the protective film to one or both sides of the polarizing film 23). The arrows in FIG. 1 indicate the transport direction of the film.

The example shown in FIG. 1 uses three cross-linking baths in the cross-linking treatment step, but is not limited to this, as long as two or more cross-linking baths are provided as described above. In addition, the invention is not limited to the example shown in FIG. 1, and there may be two or more of a swelling bath, a dyeing bath, and a washing bath. In this specification, a bath for accommodating a treatment solution for a polyvinyl alcohol-based resin film, such as a swelling bath, a dyeing bath, a crosslinking bath, and a washing bath, is also referred to as a "treatment bath".

In addition to the above-mentioned processing bath, the film transport path of the polarizing film manufacturing device can also be arranged at an appropriate position: a guide roller 30 to support the film to be transported or further change the film transport direction 47; It is constructed by pressing / holding the film being transported, and giving driving force generated by its rotation to the film, or rollers 50 to 57 which can further change the direction of film transport. For example, the guide rollers can be arranged before and after each processing bath or in the processing baths, whereby the film can be introduced and immersed in the processing bath, and the film can be pulled out from the processing bath [refer to FIG. 1]. Specifically, two or more guide rollers (not limited to the example in FIG. 1, but three or more) are provided in each treatment bath, and the film is conveyed along these guide rollers, so that the film can be dipped. In each treatment bath.

In addition, the polarizing film manufacturing apparatus shown in FIG. 1 is provided with rolls (rollers 50 to 56) before and after each processing bath, so that in any one or more processing baths, it can be placed between the rollers arranged before and after it. A rotational speed difference is formed, and roll-to-roll stretching is carried out by performing uniaxial stretching in the longitudinal direction. Each processing step is described below.

(Swelling treatment)

The swelling treatment is performed for the purpose of removing impurities on the surface of the embryonic membrane 10, removing plasticizers from the embryonic membrane 10, imparting easy dyeability, and achieving plasticization of the embryonic membrane 10. The processing conditions are determined within a range in which this purpose can be achieved without causing defects such as extreme dissolution or devitrification of the embryonic membrane 10.

Referring to FIG. 1, the swelling process can be carried along a film conveying path constructed by the guide rollers 30 to 32 and the roll 50, and the embryonic film 10 is immersed in the swelling bath 13 (the processing solution contained in the swelling tank). Set the time, and then pull out to implement. It is also possible to apply a uniaxial stretching treatment to the swelling bath 13 by utilizing the difference in the rotational speed between the roll 50 and the roll 51.

When the embryonic membrane 10 is first subjected to a swelling treatment, the swelling bath 13 The temperature is, for example, about 10 to 50 ° C, preferably about 10 to 40 ° C, and more preferably about 15 to 30 ° C. The immersion time of the embryonic membrane 10 is preferably about 10 to 300 seconds, and more preferably about 20 to 200 seconds. When the stretched polyvinyl alcohol-based resin film is swelled in a gas in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70 ° C, preferably about 30 to 60 ° C. The immersion time of the film is preferably about 30 to 300 seconds, and more preferably about 60 to 240 seconds.

In the swelling bath 13, in addition to pure water, boric acid (Japanese Patent Application Laid-Open No. 10-153709), chloride (Japanese Patent Application Laid-Open No. 06-281816) can be used in the range of about 0.01 to 10% by weight, An aqueous solution of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

In the swelling treatment, a problem that the germ membrane 10 swells in the width direction and wrinkles are formed in the film easily occurs. One of the means for removing the wrinkles and transporting the film at the same time may include a roller having a widening function such as an expansion roller, a spiral roller, or a crown crown roller in the guide rollers 30, 31, and / or 32, or Use cloth guides, bend bars, other tentering devices such as tenter clamps. Another method to suppress the occurrence of wrinkles is to apply a stretching treatment.

In the swelling process, since the film will still swell and expand in the transport direction of the film, when the film is not actively stretched, in order to eliminate the slack of the film in the transport direction, it is preferable to use a control placed in the swelling bath 13 The speed of the front and rear rolls 50, 51 and other means. In addition, in order to stabilize the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by rinsing in water, or an EPC device (Edge Position Control device is used to detect the end of the film and prevent the film from hunting) Device) Etc. are also valid.

In the example shown in FIG. 1, the film drawn from the swelling bath 13 is introduced into the dyeing bath 15 through the guide roll 32 and the roll 51 in this order.

(Dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing a dichroic dye and orienting the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which this purpose can be achieved without causing defects such as extreme dissolution or devitrification of the film. Referring to FIG. 1, the dyeing process can be carried along the film conveying path constructed by the guide rollers 33 to 35 and the roll 51, and the swelling-treated film is immersed in the dyeing bath 15 (the process stored in the dyeing tank) Liquid) for a predetermined time, and then pulled out to implement. In order to improve the dyeability of the dichroic pigment, the film provided to the dyeing treatment step is preferably a film subjected to at least some uniaxial stretching treatment, or used to replace the uniaxial stretching treatment before the dyeing treatment. In addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

When iodine is used as the dichroic pigment, for example, an aqueous solution having a concentration in a weight ratio of iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 can be used in the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. When boric acid is added, the point where boron is included is distinguished from the crosslinking treatment described later, and the aqueous solution needs to contain about 0.003 with respect to 100 parts by weight of water. Iodine by weight or more can be regarded as the dyeing bath 15. The temperature of the dyeing bath 15 when the film is immersed is usually about 10 to 45 ° C, preferably 10 to 40 ° C, more preferably 20 to 35 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye / water = about 0.001 to 0.1 / 100 in a weight ratio can be used in the dyeing bath 15. The dyeing bath 15 may coexist with a dyeing auxiliary agent and the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. A dichroic dye may be used individually by 1 type, or may use 2 or more types of dichroic dyes in combination. The temperature of the dyeing bath 15 when the film is immersed is, for example, about 20 to 80 ° C, preferably 30 to 70 ° C. The immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

As described above, in the dyeing process step, the film can be uniaxially stretched in the dyeing bath 15. Uniaxial stretching of the film can be performed by a method such as a rotation speed difference between the rolls 51 and the rolls 52 disposed before and after the dyeing bath 15.

The dyeing process is also the same as the swelling process. In order to remove the wrinkles of the film and transport the polyvinyl alcohol-based resin film at the same time, an extension roller, a spiral roller, and a crown roller can be used for the guide rollers 33, 34, and / or 35 Rollers with expansion function, or other expansion devices such as cloth guides, bending rods, and tenter clamps. Another method to suppress the occurrence of wrinkles is the same as the swelling treatment, which is a stretching treatment.

In the example shown in Fig. 1, the film pulled out from the dyeing bath 15 is introduced to the first pass through the guide roll 35 and the roll 52 in this order. Joint bath 17a.

(Cross-linking treatment)

The cross-linking treatment is performed for the purpose of water resistance, hue adjustment (to prevent the film from being blue, etc.), and the like achieved by cross-linking. Referring to FIG. 1, the cross-linking treatment using the first cross-linking bath 17a can be carried along the film transport path constructed by the guide rollers 36 to 38 and the roll 52, and the film after the dyeing treatment is dipped in The first cross-linking bath 17a (the treatment liquid contained in the cross-linking tank) containing the liquid containing the cross-linking agent is carried out for a predetermined period of time and then pulled out. The same applies to the crosslinking treatment using the second crosslinking bath 17b and the third crosslinking bath 17c.

The liquid containing the cross-linking agent contained in the first cross-linking bath 17a, the second cross-linking bath 17b, and the third cross-linking bath 17c may contain, for example, about 1 to 10 parts by weight of the liquid relative to 100 parts by weight of water. Aqueous solution of boric acid. In these crosslinking baths, when the dichroic pigment used in the dyeing treatment is iodine, it is preferable to contain iodide in addition to boric acid, and the amount may be 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like can coexist.

In the crosslinking treatment, the concentrations of the crosslinking agent (boric acid) and iodide, and the temperature of the crosslinking bath may be appropriately changed according to the purpose. For example, when the purpose of the crosslinking treatment is to achieve water resistance by crosslinking, and the polyvinyl alcohol resin film is sequentially subjected to swelling treatment, dyeing treatment, and crosslinking treatment, the crosslinking bath contains a crosslinking agent. Liquid, concentration can be by weight Calculated as boric acid / iodide / water = 3 to 10/1 to 20/100 aqueous solution. According to needs, other cross-linking agents such as Glyoxal or Glutaraldehyde can be used instead of boric acid, or boric acid can be used in combination with other cross-linking agents. The temperature of the crosslinking bath when dipping the film is usually about 50 to 70 ° C, preferably 53 to 65 ° C. The dipping time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds. On the other hand, when the stretched polyvinyl alcohol-based resin film is sequentially subjected to a dyeing treatment and a crosslinking treatment, the temperature of the crosslinking bath is usually about 50 to 85 ° C, preferably 55 to 80 ° C. .

In the cross-linking treatment for the purpose of hue adjustment, when using iodine as a dichroic pigment, for example, a concentration containing boric acid / iodide / water = 1 to 5/3 to 30/100 can be used in a weight ratio. Agent liquid. The temperature of the crosslinking bath when dipping the film is usually about 10 to 45 ° C, and the dipping time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

When both the cross-linking treatment for the purpose of water resistance and the cross-linking treatment for the purpose of hue adjustment are performed, the cross-linking treatment for the purpose of hue adjustment may be performed after the cross-linking treatment for the purpose of water resistance. For example, in the example shown in Fig. 1, the cross-linked structure using the first cross-linking bath 17a can be used for water resistance, and the cross-linked structure using the second cross-link bath 17b can be used for water resistance. For the hue adjustment purpose, the cross-linking treatment using the third crosslinking bath 17c is used as the hue adjustment purpose. However, the cross-linking treatment for the purpose of hue adjustment is arbitrary, so it can be omitted.

After the dyeing treatment of the polyvinyl alcohol-based resin film is immersed in the cross-linking bath, it can be guided along two or more guides arranged in the cross-linking bath. The film is carried by a guide roller. The film is transported by successive films, and then the film is pulled out of the cross-linking bath by the last (downstreammost) guide roller (final guide roller) arranged in the cross-linking bath. At this time, in the present invention, the In at least one of the two or more cross-linking baths, pass the final guide roll so that the wrapping angle in the final guide roll becomes 100 ° or more and less than 180 °, and pass through the final guide roll. Pull out in the bath. In this way, the wrapping angle in the final guide roller is adjusted to be shallower (larger), and the film restraint caused by the final guide roller is reduced, thereby suppressing or preventing the film from being pulled out of the crosslinking bath. Warping or inward folding of the film at both ends in the width direction may occur.

Here, the so-called wrap angle in the final guide roller means the angle θ shown in FIG. 1, which is a film before (immediately before) passing through the final guide roller and a film after (just after) passing through. The angle formed, and finally the angle of the side where the guide roller is present. The wrap angle can take a value from 0 to 180 °, but in the present invention, this is set to be 100 ° or more and less than 180 °. When the angle θ is 180 ° or more, the film is no longer suspended from the final guide roller, so a wrap angle of 180 ° or more is not conceptually stored.

From the viewpoint of more effectively suppressing or preventing warpage or inward folding, the wrapping angle in the final guide roller is preferably 135 to 178 °, and more preferably 145 to 175 °.

At least one of the two or more cross-linking baths may be a cross-linking bath having a final guide roller arranged so that the wrapping angle becomes 100 ° or more and less than 180 °, and can be more effectively suppressed. From the viewpoint of preventing warpage or inward folding, in a crosslinking bath in which such defects are particularly likely to occur when the wrap angle is not adjusted, it is preferable to adjust the wrap angle to the above-mentioned predetermined range.

Examples of the cross-linking baths that are prone to warping or internal folding defects include the following cross-linking baths.

(1) The tension of the film in the crosslinking bath is smaller than that of other crosslinking baths. When the tension of the film is relatively small, the above-mentioned defects are likely to occur because both ends in the width direction of the film are loosened.

(2) The concentration of the cross-linking agent (boric acid) in the cross-linking bath (liquid containing the cross-linking agent) is smaller than other cross-linking baths. When the film is immersed in a bath having a relatively small concentration of the crosslinking agent, the concentration of the crosslinking agent in the film also decreases. It is considered that the width direction both ends of a film tend to become loose easily by this.

(3) The temperature of the crosslinking bath is higher than that of other crosslinking baths. When the temperature of the cross-linking bath is relatively high, the above-mentioned defects are likely to occur because both ends in the width direction of the film are loosened.

(4) A cross-linking bath in which the stretching magnification performed in the cross-linking bath is smaller than that in other cross-linking baths. In order to impart a desired cumulative stretching ratio to the obtained polarizing film to improve the polarization characteristic, uniaxial stretching treatment may be performed in a plurality of crosslinking baths in two or more crosslinking baths, but when the stretching ratio is relatively When it is small (for example, when the stretching ratio in the crosslinking bath is 1.14 times or less, further 1.1 times or less, and further 1.05 times or less), the width of the film may be loosened at both ends in the width direction, which may easily cause the above. defect. Referring to Figure 1, the uniaxial stretching treatment in the crosslinking bath is, for example, the third crosslinking In the bath 17c, the rotation speed difference between the roll 54 and the roll 55 can be used (the same applies to other crosslinking baths). The uniaxial stretching treatment may be performed in one of the two or more crosslinking baths, or the uniaxial stretching treatment may not be performed in the crosslinking treatment. The stretching ratio performed in the crosslinking bath is usually more than 1 times, and typically more than 1 times in each crosslinking bath.

The time from when the film is immersed in a crosslinking bath (a liquid containing a crosslinking agent) to when it reaches the final guide roller (almost equivalent to the immersion time) is 5 seconds or longer, or it is longer than other crosslinking baths. bath. When the immersion time is long, the concentration change of the crosslinking agent and the like contained in the film tends to become large. It is considered that the width direction both ends of a film tend to become loose easily by this.

When two or more cross-linking baths are used for the cross-linking treatment, the cross-linking baths after the second stage (including the second stage) are more suitable for the above-mentioned (1) to ( At least any one of 5), and the final crosslinking bath is most suitable for at least any one of (1) to (5) above. For example, when the final cross-linking bath configuration is used as a cross-linking bath for the purpose of hue adjustment, the boric acid concentration is usually smaller than that of other cross-linking baths. Therefore, in the present invention, the cross-linking bath whose envelope angle is adjusted to the above-mentioned predetermined range preferably includes the cross-linking bath after the second stage, and more preferably includes the final cross-linking bath. FIG. 1 shows an example of adjusting the wrap angle to the predetermined range in the final third crosslinking bath 17c among the three crosslinking baths. However, it is also possible to adjust the wrapping angle to the above-mentioned predetermined range by using a plurality of cross-linking baths or all cross-linking baths which are in two or more cross-linking baths.

In the cross-linking process, in order to remove the wrinkles of the film and transport the polyvinyl alcohol-based resin film at the same time, or to more effectively suppress or prevent warpage or inward folding, an extension roller, a spiral roller, Crown roller Rollers with expansion function, or other expansion devices such as cloth guides, bending rods, and tenter clamps. In order to more effectively suppress or prevent warping or inward folding, especially the final guide roller (the guide roller 43 in the first figure) arranged so that the wrapping angle is 100 ° or more and less than 180 ° It is preferable to use the above-mentioned rolls having a widening function. Among them, it is preferable to use an expanding roll. Performing a stretching treatment during the crosslinking treatment is also effective for suppressing wrinkles, warping, and inward folding.

In the example shown in FIG. 1, the film pulled out from the third crosslinking bath 17 c is introduced into the cleaning bath 19 through the guide roller 44 and the roll 55 in this order.

(Washing treatment)

The manufacturing method of the present invention may include a washing treatment step after the crosslinking treatment step. The cleaning treatment is performed for the purpose of removing excess boric acid or iodine from the polyvinyl alcohol resin film. The washing treatment can be performed, for example, by immersing the polyvinyl alcohol-based resin film after the cross-linking treatment in the washing bath 19 (water), spraying the film with shower water, or using these methods in combination.

FIG. 1 shows an example when a polyvinyl alcohol-based resin film is immersed in a washing bath 19 to perform a washing treatment. The temperature of the washing bath 19 in the washing treatment is usually about 2 to 40 ° C, and the immersion time of the film is usually about 2 to 120 seconds.

In the cleaning process, for the purpose of removing wrinkles of the film and transporting the polyvinyl alcohol-based resin film at the same time, the guide rollers 45, 46, and / or 47 can be used. In the use of expansion rollers, spiral rollers, crown rollers with a widening function, or using cloth guides, bending rods, tenter clamp-like other widening devices. In addition, in the washing treatment, a stretching treatment may be applied in order to suppress the occurrence of wrinkles.

(Stretching treatment)

As mentioned above, the embryonic membrane 10 is uniaxially performed by wet or dry application between the above-mentioned series of processing steps (ie, before and after any one or more processing steps and / or any one or more processing steps). Stretch processing. A specific method of uniaxial stretching may be, for example, forming a rotational speed difference between two rolls constituting a film conveying path (for example, two rolls arranged before and after a processing bath), and performing roll uniaxial stretching between rolls. Stretching; hot-roll stretching described in Japanese Patent No. 2731813; tenter stretching and the like, stretching between rolls is preferred. The uniaxial stretching process is repeated several times from the embryonic membrane 10 to the polarizing film 23.

The final cumulative stretching ratio of the polarizing film 23 based on the embryonic film 10 (polyvinyl alcohol-based resin unstretched film having a thickness of 65 μm or less) is based on the thickness of the embryonic film 10, but the polarized light from the obtained polarizing film 23 From the viewpoint of characteristics, it is usually 4.5 times or more, and preferably 5.0 times or more. On the other hand, when the cumulative stretching ratio is too high, the film may be too thin to reduce handling properties, or the film may be easily cracked or broken during the stretching process. Therefore, when the thickness of the embryonic membrane 10 is less than 35 μm, It is preferably 5.9 times or less, more preferably 5.7 times or less, and still more preferably 5.5 times or less. When the thickness of the embryonic membrane 10 is 35 μm or more and 65 μm or less, it is preferably 6.3 times or less, and more preferably 6.1. Times or less, and more preferably 5.9 times or less.

The stretching step can be performed in any processing step. When the stretching processing is performed in two or more processing steps, the stretching step can also be performed in any processing step, but it can improve the dyeability of the dichroic pigment. From the viewpoint, the film provided to the dyeing treatment step is preferably a film subjected to at least some uniaxial stretching treatment, or used to replace the uniaxial stretching treatment before the dyeing treatment, and it is preferably other than the dyeing treatment. In addition to the previous uniaxial stretching process, the uniaxial stretching process is also performed during the dyeing process. Thereby, the stretched film can be provided to the cross-linking treatment step. According to the present invention, even when the film that is easily warped or inwardly folded due to stretching and thinning is crosslinked, it can effectively suppress or Prevent warping or inward folding. In a preferred embodiment, the stretching treatment is performed in a swelling treatment step and / or a dyeing treatment step and a crosslinking treatment step.

As described above, the stretching treatment helps suppress wrinkles of the film being transported, especially the warpage and inward folding generated during the crosslinking treatment. When the stretching ratio in the cross-linking treatment is low, the effect becomes small and warpage or inward folding is easily caused. According to the present invention, even if the stretching ratio in each cross-linking bath is 1.14 times or less When it is further lower than 1.1 times and further lower than 1.05 times, it can also effectively suppress or prevent warping or inward folding.

(Drying)

After the washing treatment, a treatment for drying the polyvinyl alcohol-based resin film is preferably performed. The drying of the film is not particularly limited, as in the example shown in Figure 1, This can be performed using the drying furnace 21. The drying temperature is, for example, about 30 to 100 ° C, and the drying time is, for example, about 30 to 600 seconds. The thickness of the polarizing film 23 obtained in the above manner is, for example, about 5 to 30 μm.

(Other processing steps)

Processing other than the above processing may be added. Examples of the additional treatment include: an immersion treatment (color correction treatment) in which an iodide aqueous solution containing no boric acid is immersed after a crosslinking treatment; and an immersion treatment in an aqueous solution containing no boric acid and containing zinc chloride. Dipping treatment (zinc treatment).

In addition, in order to suppress or prevent the film pulled out from the swelling bath 13 and / or the dyeing bath 15 from being warped or folded inward, the film pulled out with the treatment liquid adhered on both sides can be made Treatment for reducing the amount of liquid adhered at both ends in the width direction of the surface. It is also possible to apply the treatment for reducing the amount of liquid adhesion in a cross-linking bath, for example, in at least one cross-linking bath, and use the treatment for reducing the amount of liquid adhesion and the treatment of adjusting the enclosing angle within the predetermined range. Herein, the both ends of the film in the width direction are preferably 2 to 20% of the entire width of the film when the both ends are combined. The treatment for reducing the amount of liquid adhered at both ends in the width direction can be performed, for example, by the following methods a) to c).

a) A method in which a gas is blown to both sides of the polyvinyl alcohol-based resin film pulled out from the processing bath, thereby removing the liquid adhering to at least the surfaces at both end portions in the width direction of the film to reduce the amount of liquid adhesion. This gas blowing process can be used: a duct (with one Tube) or hose, or use a gas blowing device like an air knife.

There is no particular limitation on the type of gas used in the gas blowing device, but generally it is air, nitrogen, argon, or the like which is inert to the film, and preferably air. The ejection pressure of the gas is also not particularly limited as long as the attached liquid can be blown away.

In order to suppress the warpage or inward folding of the film pulled out from the processing bath, it is sufficient to perform gas blowing treatment only on both ends in the width direction of both sides of the film, but other films can be used in addition to the ends in the width direction. The surface area is subjected to a gas blowing treatment together. For example, the entire surface of both sides of the film may be subjected to a gas blowing process.

For example, referring to FIG. 1, when performing a gas blowing process on the film pulled out from the swelling bath 13, a gas blowing device may be provided between the guide roller 32 and the roll 51, and after the film is pulled out from the swelling bath 13 to reach Between the guide rollers 32, or both. The gas blowing treatment is preferably performed on at least the film immediately after being pulled out from the liquid surface of the processing bath.

b) A roller or a rod is brought into contact with (pressed against) both sides of the polyvinyl alcohol-based resin film pulled out from the processing bath, whereby the roller or the rod is used to drip the liquid adhered to at least the surfaces of both ends in the width direction of the film Fall and reduce the amount of liquid adhesion.

The rollers contacting the surfaces at both ends in the width direction of the film may be, for example, a pair of rollers of a polyvinyl alcohol-based resin film pulled out from the processing bath from both sides by a double-sided clamp like a cloth guide device. Through the film between the pair of rollers, the adhered liquid is squeezed out in the area of the surface in contact with the rollers. On the other hand, the rods that come into contact with the surfaces at both ends in the width direction of the film are not themselves like rollers. Those who can rotate, but hold the polyvinyl alcohol-based resin film pulled out from the processing bath from both sides, or one pair of rods in order to contact the film sequentially on each side. When the rod is used, the liquid adhered to it will be squeezed out through the film between the rods in the area of the surface where it contacts the rod.

The surfaces of the rollers and rods that are in contact with the film may be made of, for example, a metal such as stainless steel, or rubber, sponge, or the like. The shapes of the rollers and rods may be curved surfaces as long as they are in contact with the film, but they are preferably cylindrical. When a cylindrical roller or rod is used, its diameter is about 5 to 100 mm, preferably 10 to 50 mm. When the diameter is within this range, the film can be smoothly transported.

In order to suppress the warpage or inward folding of the film pulled out from the processing bath, it is sufficient to perform a treatment in which a roller or a rod is only in contact with both ends in the width direction of both sides of the film, except for the ends in the width direction. The contact treatment may be performed on other film surface regions together. This contact treatment can be performed on the whole of both sides of the film, for example. The installation angle of the rollers and rods is not particularly limited, and the length direction of the rollers and rods may be parallel to the film width direction or inclined to the film width direction.

For example, referring to FIG. 1, when the film pulled out from the swelling bath 13 is subjected to a contact treatment with the roller or rod, the contact treatment may be between the guide roller 32 and the roll 51 and the film pulled from the swelling bath 13 It is carried out between the time when it exits and when it reaches the guide roller 32, or both. The contact treatment with the roller or rod is preferably performed at least on the film immediately after being pulled out from the liquid surface of the processing bath.

c) A method of introducing a polyvinyl alcohol-based resin film drawn from the processing bath into a roll, and dropping the liquid adhered to the film surface by the roll to reduce the amount of liquid adhered. In this method, the entire liquid adhering to both sides of the film is usually dropped.

When using the method a) or b) above to perform the treatment of reducing the amount of liquid adhesion only on the two ends in the width direction of the film, the film drawn from the treatment bath and subjected to the treatment of reducing the amount of liquid adhesion is usually a diameter It is transported by flat rolls covering a certain width of a cylindrical guide roll. That is, when the film pulled out from the processing bath and subjected to a treatment for reducing the amount of liquid adhesion first passes through the guide roller and then passes through the roller, the one or more guide rollers are preferably flat rollers. . It is more effective to use a flat roll arranged horizontally with respect to the floor to transport the film that has been treated to reduce the amount of liquid adhesion. This prevents the liquid in the center of the width direction of the film from flowing into both ends during the transportation of the film, so it is more effective. In order to suppress warpage or inward folding of both ends of the film.

<Polarizer>

A polarizing plate can be obtained by bonding a protective film on at least one side of the polarizing film manufactured by the above method via an intermediary agent. Examples of the protective film include: a thin film made of cellulose triacetate or cellulose diacetate resin like cellulose diacetate; polyethylene terephthalate, polyethylene naphthalate, and polyethylene terephthalate. Films made of polyester resins like butyl phthalate; polycarbonate resin films, cycloolefin resin films; (meth) acrylic resin films; chain polyolefin resins made of polypropylene resin Thin film made of resin.

In the present specification, the "(meth) acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing film and / or the protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, and the like. Surface treatment. Examples of the adhesive used for the bonding of the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or an aqueous solution prepared with a crosslinking agent. Water-based adhesives like urethane-based emulsification adhesives. The ultraviolet curable adhesive may be a mixture of a (meth) acrylic compound and a photoradical polymerization initiator, or a mixture of an epoxy compound and a photocationic polymerization initiator. In addition, a cationic polymerizable epoxy compound and a radical polymerizable (meth) acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

(Example)

Hereinafter, the present invention will be described more specifically by showing examples, but the present invention is not limited to these examples.

<Example 1>

The polarizing film 23 was manufactured using the same apparatus as the polarizing film manufacturing apparatus shown in FIG. 1. Each of the guide rollers 30 to 41 uses a flat roller.

(1) Swelling treatment steps

Continuously transport 30 μm thick polyvinyl alcohol film [Kuraray Co., Ltd. has The product name is "Kuraray Poval Film VF-PE # 3000", the degree of polymerization is 2400, and the degree of saponification is 99.9 mole% or more], and immersed in a swelling bath 13 containing pure water at 20 ° C for 30 seconds. In this swelling treatment, a roll speed is formed between the rolls 50 and 51 to perform roll-to-roll stretching (longitudinal uniaxial stretching) so that the film width immediately after being pulled out of the swelling bath 13 is immersed in the swelling bath 13 The film width is below. The stretching ratio based on the embryonic membrane 10 was set to 2.5 times.

For the film pulled out from the swelling bath 13, a gas blowing device (air jet nozzle) provided in front of the guide roller 32 and a gas blowing device (air jet nozzle) provided between the guide roller 32 and the roll 51 are used. Air is sprayed on both ends in the width direction on both sides of the film to remove the liquid attached to it.

(2) Dyeing process steps

Next, the film passing through the roller 51 was immersed in a dyeing bath 15 at 30 ° C. having an iodine / potassium iodide / water (weight ratio) of 0.05 / 2/100 for 120 seconds. In this dyeing process, a peripheral speed difference is also formed between the rolls 51 and 52 to perform roll-to-roll stretching (longitudinal uniaxial stretching) so that the film width immediately after being pulled out from the dyeing bath 15 is immersed in the dyeing bath 15 Before the film width. The cumulative stretching ratio in the swelling treatment and the dyeing treatment based on the embryonic membrane 10 was 2.7 times (the stretching ratio in the dyeing treatment was 1.08 times).

(3) Cross-linking processing steps

In order to perform the first crosslinking treatment for the purpose of water resistance, The film of the roll 52 was immersed in the first crosslinking bath 17a at 55 ° C at potassium iodide / boric acid / water (weight ratio) of 12 / 4.4 / 100 for 30 seconds. In this first cross-linking treatment, a roll speed is also formed between the roll 52 and the roll 53 provided between the first cross-linking bath 17a and the second cross-linking bath 17b to perform roll-to-roll stretching (longitudinal uniaxial stretching). Stretching) so that the film width immediately after being pulled out from the first crosslinking bath 17a is equal to or less than the film width before being immersed in the first crosslinking bath 17a. The cumulative stretching ratio in the swelling treatment, the dyeing treatment, and the first crosslinking treatment based on the embryonic membrane 10 was set to 4.3 times (the stretching ratio in the first crosslinking treatment was 1.6 times).

Next, the film after the first cross-linking treatment was immersed in a second cross-linking bath 17b at 59 ° C having the same composition as the first cross-linking bath 17a for 30 seconds (second cross-linking treatment), and the second cross-linking treatment In addition, a roll speed is formed between the roll 53 and the roll 54 provided between the second cross-linking bath 17b and the third cross-linking bath 17c to perform roll-to-roll stretching (longitudinal uniaxial stretching) so that The film width after being pulled out from the second crosslinking bath 17b is equal to or less than the film width before being immersed in the second crosslinking bath 17b. The cumulative stretching ratio in the swelling treatment, the dyeing treatment, the first crosslinking treatment, and the second crosslinking treatment based on the embryonic membrane 10 was set to 5.4 times (the stretching ratio in the second crosslinking treatment was 1.25 times).

Next, in order to perform a cross-linking treatment for the purpose of hue adjustment, it was immersed in a third cross-linking bath 17c at 40 ° C. of potassium iodide / boric acid / water (weight ratio) of 9 / 2.9 / 100 for 15 seconds (third cross-linking). deal with). At this time, the wrapping angle of the film in the final guide roller 43 disposed in the third cross-linking bath 17c was formed at 160 ° to carry the film. In this third crosslinking treatment, a rotation speed difference is also formed between the roll 54 and the roll 55 to perform roll-to-roll stretching (longitudinal uniaxial stretching) so that the film width immediately after being pulled out from the third crosslinking bath 17c Become impregnated in 3 Film width before the crosslinking bath 17c. The cumulative stretching ratio in the swelling treatment, the dyeing treatment, the first crosslinking treatment, the second crosslinking treatment, and the third crosslinking treatment based on the embryonic membrane 10 was set to 5.5 times (the stretching in the third crosslinking treatment). Magnification is 1.02 times).

Then, the film after the third cross-linking treatment was immersed in a washing bath 19 containing pure water at 5 ° C., and then passed through a drying furnace 21 to be dried at 70 ° C. for 3 minutes to produce a polarizing film 23.

The above-mentioned production of the polarizing film was continuously performed for 24 hours. During the 24-hour operation, no warpage or inward folding was observed at both ends in the width direction of the film in any of the processing steps, and no possible concomitant observation was observed. Creases or breaks in the resulting film.

<Example 2>

Except for the swelling treatment, dyeing treatment, first crosslinking treatment, second crosslinking treatment, and third crosslinking treatment based on the embryonic membrane 10, the cumulative stretching ratio was set to 6.0 times (in the third crosslinking treatment). Except for the stretching ratio (1.11 times), the production of a polarizing film was continuously performed for 24 hours in the same manner as in Example 1. In the 24-hour operation, although no warpage or inward folds were observed at both ends in the width direction of the film and no creases of the film were observed in any of the processing steps, as the cumulative stretching ratio was set It is 6.0 times larger, and the film breaks once during 24 hours of operation.

<Example 3>

Except for the final guide roller 43 to be arranged in the third crosslinking bath 17c The wrap angle of the film was set to other than 135 °, and other than that in Example 1, the production of a polarizing film was continuously performed for 24 hours. During the 24-hour operation, no warpage or inward folding was observed on both ends of the film in the width direction in any of the processing steps, and no creases or breakage of the film which may be caused by these were observed.

<Example 4>

A polarizing film was continuously produced for 24 hours in the same manner as in Example 1 except that the wrapping angle of the film in the final guide roller 43 disposed in the third crosslinking bath 17c was set to 110 °. At a position immediately after being pulled out from the third cross-linking bath 17c, about 5 hours, a 1 mm wide inward fold was generated at both ends in the width direction of the film. However, during the 24-hour operation, no film breakage caused by this was observed.

<Comparative Example 1>

A polarizing film was continuously produced for 24 hours in the same manner as in Example 1 except that the wrapping angle of the film in the final guide roller 43 disposed in the third crosslinking bath 17c was set to 80 °. At the position immediately after being pulled out from the third cross-linking bath 17c, once every 2 hours, a 1 mm wide inward fold will be generated on both ends in the width direction of the film. A crease is formed at the end of the film, and the film is broken. The film was broken twice during 24 hours of operation.

<Comparative Example 2>

Except for the final guide roller 43 to be arranged in the third crosslinking bath 17c The wrapping angle of the film was set to be 30 ° or less. Other than that, the polarizing film was continuously produced for 24 hours in the same manner as in Example 1. In the position immediately after being pulled out from the third cross-linking bath 17c, a 2 mm wide inner fold is often generated on both ends in the width direction of the film. Since the roller 55 is passed in this state, a crease is formed on the end of the film. , And the film breaks. The film was broken five times during 24 hours of operation.

Claims (4)

A manufacturing method in which a polyvinyl alcohol-based resin film having a thickness of 65 μm or less is conveyed, at least a dyeing treatment is performed, and the polyvinyl alcohol-based resin film is sequentially immersed in two or more liquids containing a crosslinking agent-containing liquid. A method for producing a polarizing film by a crosslinking treatment in a bath, wherein in at least one of the two or more baths described above, the polyvinyl alcohol-based resin film is arranged along two or more guides arranged in the bath. The guide roller is transported, and the final guide roller that passes last among the two or more guide rollers passes the final guide roller so that the wrap angle becomes 100 ° or more and less than 180 °. In the aforementioned at least one bath having the aforementioned final guide rollers arranged such that the wrapping angle is 100 ° or more and less than 180 °, a stretching treatment is applied, and the stretching in each bath is performed. The stretch ratio of the treatment is 1.14 times or less. The manufacturing method as described in claim 1, wherein the polyvinyl alcohol-based resin film supplied to the aforementioned crosslinking treatment is a stretched film. The manufacturing method according to item 2 of the scope of patent application, wherein the cumulative stretching ratio of the polarizing film based on the polyvinyl alcohol-based resin film having a thickness of 65 μm or less is 5.9 times or less. The manufacturing method according to item 1 or 2 of the scope of patent application, wherein the final guide roller is an expansion roller.