JP2021192091A - Manufacturing method of polarization film - Google Patents

Abstract

To provide a manufacturing method of a polarization film capable of providing a polarization film with an excellent yellow discoloration suppression effect even under a high-temperature environment exceeding 95°C.SOLUTION: A method for manufacturing a polarization film from a polyvinyl alcohol-based resin film, comprises a first treatment step of bringing the polyvinyl alcohol-based resin film into contact with first treatment liquid. The first treatment liquid contains boric acid and an iodide compound, and has a pH of 5.0 or higher at 25°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a polarizing film, and further to a method for manufacturing a polarizing plate, a polarizing film, a polarizing plate, and an image display device.

In recent years, image display devices including polarizing plates have expanded their applications, such as being used as in-vehicle image display devices such as car navigation devices and back monitors in addition to mobile devices such as mobile phones and tablet terminals. There is. Along with this, the image display device is required to have higher durability in a harsher environment (for example, a high temperature environment) than conventionally required.

Patent Document 1 discloses that a polarizing plate having excellent optical properties and wet heat durability is provided by lowering the pH of a polarizing element. Patent Document 1 describes a method of adjusting the pH of the dural solution to 1.5 to 3.2 as a method of lowering the pH of the polarizing element.

Japanese Unexamined Patent Publication No. 2005-62458

When the polarizing film contained in the polarizing plate is exposed to a high temperature environment, the polyene formation of polyvinyl alcohol progresses, which causes a problem of yellowing. In particular, under severe temperature conditions exceeding 95 ° C. (for example, 105 ° C.), the progress of yellowing tends to be more remarkable.

An object of the present invention is to provide a method for producing a polarizing film, which can provide a polarizing film having an excellent yellowing suppressing effect even when exposed to a high temperature environment exceeding 95 ° C.

Another object of the present invention is a method for manufacturing a polarizing plate having a polarizing film having an excellent effect of suppressing yellowing even in a high temperature environment exceeding 95 ° C., the polarizing film, the polarizing plate, and an image display device provided with the polarizing plate. The purpose is to provide.

The present invention provides a method for manufacturing a polarizing film, a method for manufacturing a polarizing plate, a polarizing film, a polarizing plate, and an image display device shown below.

[1] A method for producing a polarizing film from a polyvinyl alcohol-based resin film.
The first treatment step of bringing the polyvinyl alcohol-based resin film into contact with the first treatment liquid is included.
A method for producing a polarizing film, wherein the first treatment liquid contains boric acid and an iodide compound and has a pH of 5.0 or higher at 25 ° C.
[2] A second treatment step of bringing the polyvinyl alcohol-based resin film into contact with the second treatment liquid is included.
The second treatment liquid contains boric acid and an iodide compound, and has a pH of less than 5.0 at 25 ° C.
The method for producing a polarizing film according to [1], wherein the second treatment step is performed before the first treatment step.
[3] The method for producing a polarizing film according to [1] or [2], wherein the first treatment liquid has a pH of 6.5 or less at 25 ° C.
^{[4] A test piece having an area of 1500 cm 2} obtained by cutting the polarizing film was immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes. The method for producing a polarizing film according to any one of [1] to [3], wherein the pH in the above is 5.3 or more.
[5] A step of manufacturing a polarizing film by the method for manufacturing a polarizing film according to any one of [1] to [4], and
A method for manufacturing a polarizing plate, comprising a bonding step of bonding a protective film to one or both sides of the polarizing film via a bonding layer.
[6] A polarizing film having an area of 1500 cm ² is immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes, and the pH of the immersion liquid after removing the polarizing film is 5.3 or more at 25 ° C. Polarizing film.
[7] The polarizing film according to [6], wherein the polyvinyl alcohol-based resin film is dyed with a dichroic dye.
[8] A polarizing plate having the polarizing film according to [6] or [7] and a protective film laminated on one side or both sides of the polarizing film via a bonding layer.
[9] An image display device in which the polarizing plate according to [8] and an image display element are laminated.
[10] A polarizing film with a bonding layer in which bonding layers are laminated on both sides of the polarizing film.
The polarizing film with a laminated layer having an area of 1500 cm ² was immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes, and the pH of the dipping solution after taking out the polarizing film with a bonded layer was 3. A polarizing film with a bonding layer, which is more than four.
[11] A polarizing plate in which a protective film is laminated on a bonded layer of the polarizing film with a bonded layer.
[12] An image display device in which the polarizing plate according to [11] and an image display element are laminated.

According to the present invention, a method for producing a polarizing film having an excellent effect of suppressing yellowing even in a high temperature environment exceeding 95 ° C., a method for producing a polarizing plate provided with the polarizing film, the polarizing film, the polarizing plate, and the present invention. An image display device including a polarizing plate can be provided.

It is sectional drawing which shows typically an example of the polarizing film manufacturing method which concerns on this invention, and the polarizing film manufacturing apparatus used for it.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In the drawings, the scales are appropriately adjusted and shown in order to make each component easier to understand, and the scale of each component shown in the drawing does not necessarily match the scale of the actual component.

<Manufacturing method of polarizing film>
In the present embodiment, the polarizing film is a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye (iodine or a dichroic dye) is adsorbed and oriented. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying the polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate-based resin can be, for example, a polyvinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids and the like. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000.

These polyvinyl alcohol-based resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes can also be used.

In the present embodiment, as a starting material for producing a polarizing film, an unstretched polyvinyl alcohol-based resin film having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less (raw material). Anti-film) is used. As a result, it is possible to obtain a thin-film polarizing film whose market demand is increasing more and more. The width of the raw film is not particularly limited and can be, for example, 400 to 6000 mm. The raw fabric film is prepared, for example, as a roll of a long unstretched polyvinyl alcohol-based resin film (raw fabric roll).

The polarizing film is a treatment liquid contained in a treatment tank by unwinding the above-mentioned long raw fabric film from the raw fabric roll and continuously transporting the polarizing film along the film transport path of the polarizing film manufacturing apparatus (hereinafter,). It can be continuously produced as a long polarizing film by carrying out a predetermined treatment step of immersing the film in a "treatment bath" and then drawing it out, and then carrying out a drying step. The treatment step is not limited to the method of immersing the film in the treatment bath as long as the treatment liquid is brought into contact with the film, and the treatment liquid adheres to the film surface by spraying, flowing down, dropping, or the like. It may be a method of processing the film. When the treatment step is performed by a method of immersing the film in a treatment bath, the treatment bath for performing one treatment step is not limited to one, and the film is sequentially immersed in two or more treatment baths. One processing step may be completed.

Examples of the treatment liquid include a swelling liquid, a staining liquid, a cross-linking liquid, a complementary color liquid, and a cleaning liquid. The treatment steps include a swelling step in which the swelling liquid is brought into contact with the raw film to perform a swelling treatment, a dyeing step in which the dyeing liquid is brought into contact with the film after the swelling treatment to perform a dyeing treatment, and a dyeing step after the dyeing treatment. A cross-linking step in which a cross-linking liquid is brought into contact with a film to carry out a cross-linking treatment, a complementary color step in which a complementary color liquid is brought into contact with the film after the cross-linking treatment to perform a complementary color treatment, and a cleaning treatment in which the cleaning liquid is brought into contact with the film after the complementary color treatment. An example is a cleaning step to be performed. In addition, uniaxial stretching treatment is performed wet or dry between these series of treatment steps (that is, before and after any one or more treatment steps and / or during any one or more treatment steps). Other processing steps may be added if necessary.

In the present specification, a treatment liquid containing boric acid and an iodide compound and having a pH of 5.0 or more at 25 ° C. is referred to as a first treatment liquid, and contains boric acid and an iodide compound and has a pH at 25 ° C. A treatment liquid having a pH of less than 5.0 is referred to as a second treatment liquid. Since both the first treatment liquid and the second treatment liquid contain boric acid and an iodide compound, they can be used for a cross-linking treatment for cross-linking the film after the dyeing treatment, and can also be used for a complementary color treatment for adjusting the hue of the film. can. Further, since both the first treatment liquid and the second treatment liquid have a limited numerical range of pH, they can also be used in the pH adjustment treatment for adjusting the pH of the film.

In the present embodiment, the first treatment step of bringing the film into contact with the first treatment liquid may be included, and the second treatment step of bringing the film into contact with the second treatment liquid may be included. When the second treatment step is included, it is preferably performed before the first treatment step, it is preferable that the treatment is performed in the order of the second treatment step and the first treatment step, and when the cleaning step is included, the first treatment step is included. It is preferable that the treatment is performed in the order of the two treatment steps, the first treatment step, and the cleaning step. The second treatment step and the first treatment step are, for example, a cross-linking step and a complementary color step, a first complementary color step and a second complementary color step, a first cross-linking step and a second cross-linking step, and the like. In the present embodiment, by including the first treatment step, it is possible to produce a polarizing film having an excellent yellowing suppressing effect even in a high temperature environment exceeding 95 ° C.

Hereinafter, an example of a method for manufacturing a polarizing film according to the present invention will be described in detail with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing method according to the present invention and a polarizing film manufacturing apparatus used thereof. The polarizing film manufacturing apparatus shown in FIG. 1 transports a raw fabric (unstretched) film 10 made of a polyvinyl alcohol-based resin along a film transport path while continuously unwinding the raw fabric (unstretched) film 10 from the raw fabric roll 11. A swelling bath (swelling liquid housed in the swelling tank) 13, a dyeing bath (staining liquid housed in the dyeing tank) 15, and a cross-linking bath (cross-linking liquid housed in the cross-linking tank) 17 provided on the transport path. , The complementary color bath (complementary color liquid contained in the complementary color tank) 18 and the washing bath (cleaning liquid housed in the washing tank) 19 are sequentially passed through, and finally passed through the drying furnace 21. The arrow in FIG. 1 indicates the transport direction of the film.

In the description of FIG. 1, "treatment tank" is a general term including a swelling tank, a dyeing tank, a cross-linking tank, a complementary color tank and a washing tank, and "treatment liquid" is a swelling liquid, a dyeing liquid, a cross-linking liquid, a complementary color liquid and It is a general term including a washing liquid, and "treatment bath" is a general term including a swelling bath, a dyeing bath, a cross-linking bath, a complementary color bath and a washing bath. The swelling bath, dyeing bath, cross-linking bath, complementary color bath, and washing bath each constitute a swelling part, a dyeing part, a cross-linking part, and a washing part in the manufacturing apparatus of the present embodiment.

In addition to the above-mentioned treatment bath, the film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 48, 60, 61 that can support the film to be transported or further change the film transport direction, and the film to be transported. Can be constructed by arranging nip rolls 50 to 55 capable of pressing and holding the film and applying a driving force due to its rotation to the film, or further changing the film transport direction, at appropriate positions. The guide roll and the nip roll can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced / immersed in the treatment bath and withdrawn from the treatment bath [see FIG. 1]. For example, by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls, the film can be immersed in each treatment bath.

In the polarizing film manufacturing apparatus shown in FIG. 1, nip rolls are arranged before and after each treatment bath (nip rolls 50 to 54), whereby the nip rolls are arranged before and after in any one or more of the treatment baths. It is possible to carry out inter-roll stretching in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between them. Hereinafter, each step will be described.

(Swelling process)
The swelling step is performed for the purpose of removing foreign matter on the surface of the raw fabric film 10, removing the plasticizer in the raw fabric film 10, imparting easy dyeability, and plasticizing the raw fabric film 10. The treatment conditions are determined within a range in which the object can be achieved and within a range in which defects such as extreme dissolution and devitrification of the raw film 10 do not occur.

In the swelling step, referring to FIG. 1, in the swelling step, the raw film 10 is continuously unwound from the raw fabric roll 11 and conveyed along the film transport path, and the raw fabric film 10 is immersed in the swelling bath 13 for a predetermined time. , Then can be carried out by pulling out. In the example of FIG. 1, from unwinding the raw film 10 to immersing it in the swelling bath 13, the raw film 10 is conveyed along the film conveying path constructed by the guide rolls 60 and 61 and the nip roll 50. Will be done. In the swelling treatment, the film is conveyed along the film transport path constructed by the guide rolls 30 to 32 and the nip roll 51.

The swelling liquid of the swelling bath 13 includes pure water, boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, and alcohols. It is also possible to use an aqueous solution to which the like is added in the range of about 0.01 to 10% by mass.

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

In the swelling treatment, the problem that the raw film 10 swells in the width direction and the film is wrinkled tends to occur. As one means for transporting the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used for the guide rolls 30, 31 and / or 32, or a cross guider or a bend bar is used. , Other widening devices such as tenter clips may be used. Another means for suppressing the occurrence of wrinkles is to apply a stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 by utilizing the difference in peripheral speed between the nip roll 50 and the nip roll 51.

In the swelling treatment, the film swells and expands in the transport direction of the film. Therefore, when the film is not actively stretched, it is arranged before and after the swelling bath 13, for example, in order to eliminate the slack of the film in the transport direction. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51. Further, for the purpose of stabilizing the film transfer in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, and the EPC device (Edge Position Control device: the edge of the film is detected to meander the film. It is also useful to use a device to prevent the problem.

In the example shown in FIG. 1, the film drawn from the swelling bath 13 passes through the guide roll 32, the nip roll 51, and the guide roll 33 in this order and is introduced into the dyeing bath 15.

(Dyeing process)
The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions are determined within a range in which the object can be achieved and within a range in which problems such as extreme dissolution and devitrification of the film do not occur. With reference to FIG. 1, in the dyeing step, the film is conveyed along the film transfer path constructed by the nip roll 51, the guide rolls 33 to 36, and the nip roll 52, and the film after the swelling treatment is housed in the dyeing bath 15 (dyeing tank). It can be carried out by immersing it in the treatment liquid) for a predetermined time and then withdrawing it. In order to improve the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film that has undergone at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or. 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 dye, the dyeing solution of the dyeing bath 15 has, for example, iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 / 10 / in terms of mass ratio. An aqueous solution of 100 can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from the cross-linking treatment and the complementary color treatment described later in that it contains iodine, and if the aqueous solution contains about 0.003 parts by mass or more of iodine with respect to 100 parts by mass of water. It can be regarded as a dyeing bath 15. The temperature of the dyeing bath 15 when immersing the film is usually 10 to 45 ° C, preferably 10 to 40 ° C, more preferably 20 to 35 ° C, and the immersing time of the film is usually 30 to 600 seconds. It is preferably 60 to 300 seconds.

When a water-soluble bicolor dye is used as the bicolor dye, the dyeing solution of the dyeing bath 15 has, for example, a concentration of the bicolor dye / water = about 0.001 to 0.1 / 100 in terms of mass ratio. An aqueous solution can be used. The dyeing bath 15 may be allowed to coexist with a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one kind of dichroic dye may be used alone, or two or more kinds of dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when immersing the film is, for example, 20 to 80 ° C., preferably 30 to 70 ° C., and the immersing time of the film is usually 30 to 600 seconds, preferably 60 to 300 seconds.

As described above, in the dyeing step, the film can be uniaxially stretched in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as providing a peripheral speed difference between the nip roll 51 and the nip roll 52 arranged before and after the dyeing bath 15.

In the dyeing treatment as well, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film as in the swelling treatment, the guide rolls 33, 34, 35 and / or 36 are provided with expander rolls, spiral rolls, crown rolls and the like. A roll having a widening function can be used, or other widening devices such as a cross guider, a bend bar, and a tenter clip can be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment as in the swelling treatment.

In the example shown in FIG. 1, the film drawn from the dyeing bath 15 passes through the guide roll 36, the nip roll 52, and the guide roll 37 in order and is introduced into the cross-linking bath 17.

(Crosslinking process)
The cross-linking step is a process of cross-linking the film in order to improve water resistance and the like. With reference to FIG. 1, in the cross-linking step, the cross-linking step is carried out along the film transport path constructed by the nip roll 52, the guide rolls 37 to 40 and the nip roll 53a, and the cross-linking bath 17 (the first cross-linking liquid contained in the cross-linking tank). It can be carried out by immersing the dyed film in a predetermined time and then pulling it out.

As the cross-linking solution, a solution in which a cross-linking agent is dissolved in a solvent can be used. Examples of the cross-linking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be one type or two or more types may be used in combination. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further contained. The concentration of the cross-linking agent in the cross-linking solution is not limited to this, but is preferably in the range of 1 to 20% by mass, more preferably 6 to 15% by mass.

The cross-linking liquid can be an aqueous solution containing, for example, about 1 to 10 parts by mass of boric acid with respect to 100 parts by mass of water. When the dichroic dye used in the dyeing treatment is iodine, the cross-linking solution preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by mass with respect to 100 parts by mass of water. Can be. Examples of the iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the crosslinking treatment, the concentrations of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. The cross-linking solution can be, for example, an aqueous solution having a concentration of boric acid / iodide / water = 3 to 10/1 to 20/100 in terms of mass ratio. If necessary, another cross-linking agent may be used instead of boric acid, or boric acid and another cross-linking agent may be used in combination. The temperature of the cross-linking bath 17 when immersing the film is usually 50 to 70 ° C., preferably 53 to 65 ° C., and the immersing time of the film is usually 10 to 600 seconds, preferably 20 to 300 seconds, more preferably. 20-200 seconds. When the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the crosslinking bath 17 is usually 50 to 85 ° C, preferably 55 to 80 ° C.

The cross-linking treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinked bath used may be the same or different as long as it is within the above range. Uniaxial stretching treatment can also be performed in the cross-linking bath 17 by utilizing the difference in peripheral speed between the nip roll 52 and the nip roll 53a.

In the cross-linking treatment as well, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film as in the swelling treatment, the guide rolls 37, 38, 39, and / or 40 are like an expander roll, a spiral roll, and a crown roll. It is possible to use a roll having a widening function, or to use other widening devices such as a cross guider, a bend bar, and a tenter clip. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment as in the swelling treatment.

(Complementary color process)
The complementary color step is a process of adjusting the hue of the film. With reference to FIG. 1, the complementary color step is carried along a film transport path constructed by the nip rolls 53a, guide rolls 41-44 and nip rolls 53b and crosslinked to the complementary color bath 18 (complementary color liquid contained in the complementary color tank). It can be carried out by immersing the film after the step for a predetermined time and then pulling it out.

The complementary color liquid can be an aqueous solution containing, for example, about 1 to 10 parts by mass of boric acid with respect to 100 parts by mass of water. When the dichroic dye used in the dyeing treatment is iodine, the complementary color solution preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by mass with respect to 100 parts by mass of water. Can be. Examples of the iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the supplementary color solution, for example, when iodine is used as the dichroic dye, boric acid / iodide / water = 1 to 5/3 to 30/100 can be used in terms of concentration by mass ratio. The temperature of the complementary color bath 18 when immersing the film is usually 10 to 45 ° C., and the immersing time of the film is usually 1 to 300 seconds, preferably 2 to 100 seconds.

The complementary color treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each complementary color bath used may be the same or different as long as it is within the above range. Further, the uniaxial stretching process can be performed in the complementary color bath 18 by utilizing the difference in peripheral speed between the nip roll 53a and the nip roll 53b.

In the complementary color treatment as well, in order to convey the polyvinyl alcohol-based resin film while removing the wrinkles of the film as in the swelling treatment, the guide rolls 41, 42, 43 and / or 44 are provided with expander rolls, spiral rolls, crown rolls, etc. A roll having a widening function can be used, or other widening devices such as a cross guider, a bend bar, and a tenter clip can be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment as in the swelling treatment.

In the example shown in FIG. 1, the film drawn from the complementary color bath 18 passes through the guide roll 44 and the nip roll 53b in this order and is introduced into the washing bath 19.

(Washing process)
The example shown in FIG. 1 includes a cleaning step after the complementary color step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film. The cleaning step is performed, for example, by immersing the complementary color-treated polyvinyl alcohol-based resin film in the cleaning bath 19. The cleaning step is performed by spraying the cleaning liquid on the film as a shower instead of immersing the film in the cleaning bath 19, or by using the immersion in the cleaning bath 19 and the spraying of the cleaning liquid in combination. You can also do it.

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

In the cleaning process, the guide rolls 45, 46, 47 and / or 48 have widening functions such as an expander roll, a spiral roll, and a crown roll for the purpose of transporting the polyvinyl alcohol-based resin film while removing wrinkles. Or other widening devices such as cross guiders, bend bars and tenter clips can be used. Further, in the film cleaning treatment, a stretching treatment may be performed in order to suppress the occurrence of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched wet or dry during the series of treatment steps (that is, before and after any one or more treatment steps and / or during any one or more treatment steps). It is processed. A specific method of uniaxial stretching treatment is, for example, between rolls for performing longitudinal uniaxial stretching with a peripheral speed difference between two nip rolls constituting a film transport path (for example, two nip rolls arranged before and after the treatment bath). Stretching, thermal roll stretching as described in Japanese Patent No. 2731813, tenter stretching and the like can be performed, and stretching between rolls is preferable. The uniaxial stretching step can be performed a plurality of times until the polarizing film 23 is obtained from the raw film 10. As described above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

The final cumulative draw ratio of the polarizing film 23 based on the raw film 10 is usually 4.5 to 7 times, preferably 5 to 6.5 times. The stretching step may be performed in any of the treatment steps, and even when the stretching treatment is performed in two or more treatment steps, the stretching treatment may be performed in any of the treatment steps.

(First processing step)
The first treatment step is a step of bringing the film into contact with the first treatment liquid, and the first treatment liquid contains boric acid and an iodide compound and has a pH of 5.0 or more at 25 ° C. The pH of the first treatment liquid at 25 ° C. is preferably 5.2 or higher, preferably 5.3 or higher, and even more preferably 5.5 or higher. The pH of the first treatment liquid at 25 ° C. is preferably 6.8 or less, more preferably 6.5 or less, and even more preferably 6.3 or less. The first processing step is, for example, the above-mentioned complementary color step. When the first treatment step is a complementary color step, the above description of the complementary color step can be directly applied to the description of the first treatment step. The first treatment liquid contains boric acid and an iodide compound, and has a pH of 5.0 or higher. As the first treatment liquid, an aqueous solution having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 in terms of mass ratio can be used. The first treatment liquid further contains a pH adjuster. Examples of the pH adjuster include potassium hydroxide and sodium hydroxide. The first treatment liquid is adjusted so that the pH at 25 ° C. is 5.0 or more by adjusting the amount of the pH adjusting agent added. In the present embodiment, by having the first treatment step, it is possible to provide a polarizing film having an excellent yellowing suppressing effect even in a high temperature environment exceeding 95 ° C.

(Second processing step)
The second treatment step is a step of bringing the film into contact with the second treatment liquid, and the second treatment liquid contains boric acid and an iodide compound, and the pH at 25 ° C. is less than 5.0. The second treatment step is, for example, the above-mentioned cross-linking step. When the second treatment step is a cross-linking step, the above description of the cross-linking step can be directly applied to the description of the second treatment step. The second treatment liquid contains boric acid and an iodide compound, and has a pH of less than 5.0 at 25 ° C. As the second treatment liquid, an aqueous solution having a concentration of boric acid / iodide / water = 3 to 10/1 to 20/100 in terms of mass ratio can be used. In the second treatment liquid, for example, the pH may be adjusted to less than 5.0 by adjusting the amount of boric acid or iodine compound added, or the pH at 25 ° C. may be adjusted to less than 5.0 by adding an acid pH adjuster. May be. The second treatment liquid is preferably adjusted so that the pH at 25 ° C. is less than 5.0 by adjusting the amount of boric acid added.

(Drying process)
It is preferable to perform a treatment for drying the polyvinyl alcohol-based resin film after the second treatment step or, if a washing step is included, after the washing step. The drying of the film is not particularly limited, but it can be performed using the drying oven 21 as in the example shown in FIG. The drying oven 21 may be equipped with, for example, a hot air dryer. The drying temperature is, for example, 30 to 100 ° C., and the drying time is, for example, 30 to 600 seconds. The process of drying the polyvinyl alcohol-based resin film can also be performed using a far-infrared heater.

(Other processing steps for polyvinyl alcohol-based resin film)
It is also possible to add a process other than the above process. Examples of the treatment that can be added include a dipping treatment in an aqueous iodide solution containing no boric acid and a dipping treatment (zinc treatment) in an aqueous solution containing zinc chloride or the like without boric acid.

The polarizing film obtained as described above may be sequentially wound on a winding roll to form a roll, or may be used as it is in a method for manufacturing a polarizing plate without being wound. The polarizing film in the form of a roll can also be subsequently used in a method for producing a polarizing plate. One aspect of the method for manufacturing a polarizing plate includes a bonding step of bonding a protective film to one side or both sides of a polarizing film via a bonding layer.

<Polarizing film>
The polarizing film according to the present embodiment is preferably a polyvinyl alcohol-based resin film dyed with a dichroic dye. The thickness of the polarizing film is preferably 5 μm or more and 60 μm or less, and more preferably 7 μm or more and 30 μm or less. ^{A test piece having an area of 1500 cm 2} obtained by cutting a polarizing film was immersed in 10 mL of pure water at 25 ° C. and left at a temperature of 25 ° C. for 10 minutes. The pH is preferably 5.3 or higher, more preferably 5.4 or higher, and even more preferably 5.6 or higher. The upper limit is preferably 6.8 or less, more preferably 6.5 or less, and even more preferably 6.2 or less. The details of the pH measurement of the immersion liquid of the polarizing film follow the method described in Examples described later. The visual sensitivity correction single transmittance Ty of the polarizing film is preferably 40 to 47%, more preferably 41 to 45%, in consideration of the balance with the visual sensitivity correction degree of polarization Py. The luminous efficiency correction degree of polarization Py is preferably 99.9% or more, and more preferably 99.95% or more. Such a polarizing film can be obtained by the above-mentioned manufacturing method.

<Polarizer>
The polarizing plate according to the present embodiment can be obtained by laminating a protective film on one side or both sides of the above-mentioned polarizing film via a bonding layer. Examples of the protective film include a film made of an acetyl cellulose resin such as triacetyl cellulose and diacetyl cellulose; a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin film and cyclo. Examples thereof include an olefin resin film; an acrylic resin film; and a film made of a chain olefin resin of a polypropylene resin.

In order to improve the adhesiveness between the polarizing film and the protective film, the surface to which the polarizing film and / or the protective film is bonded is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. It may be treated. The bonded layer interposed between the polarizing film and the protective film can be formed by using an adhesive or an adhesive. Examples of the adhesive include an active energy ray-curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, an aqueous solution containing a cross-linking agent, and a water-based adhesive such as a urethane-based emulsion adhesive. The agent can be mentioned. A zinc compound such as zinc nitrate may be added to the water-based adhesive. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, a mixture of an epoxy compound and a photocationic polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable 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.
The bonded layer is preferably a layer formed of a water-based adhesive, more preferably a layer formed of a water-based adhesive containing a zinc compound, and more preferably a water-based adhesive containing a zinc compound and a polyvinyl alcohol-based resin. It is more preferably a layer formed from the agent.

In the polarizing film with a bonding layer in which the bonding layers are laminated on both sides of the polarizing film, ^{a test piece having an area of 1500 cm 2} of the polarizing film with a bonding layer is immersed in 10 mL of pure water at 25 ° C. at a temperature of 25 ° C. The pH of the immersion liquid at 25 ° C. after taking out the test piece is preferably more than 3.4, more preferably 3.5 or more, and 4.0 or more. Is even more preferable, and 4.4 or more is even more preferable. The upper limit is preferably 6.8 or less, more preferably 6.5 or less, further preferably 6.2 or less, and particularly preferably less than 5.4. The details of the pH measurement of the immersion liquid of the polarizing film with the laminated layer follow the method described in Examples described later.
The thickness of the bonded layer in the polarizing film with the bonded layer is preferably 50 to 200 nm, more preferably 70 to 150 nm.

<Image display device>
The polarizing plate can be used in an image display device. Examples of the image display element used in the image display device include a liquid crystal display element, an organic EL display element, and the like. In constructing the liquid crystal display device, the polarizing plate according to the present invention may be arranged and used on the viewing side, may be arranged on the backlight side, and may be used on both the viewing side and the backlight side. It may be used for. The image display device of the present invention can be used for mobile devices such as televisions, personal computers, mobile phones and tablet terminals, and has a high inhibitory effect on yellowing in a high temperature environment, and is a stable image for a long period of time. Since it can exhibit a display function, it can be particularly preferably used for in-vehicle applications that are easily exposed to more severe temperature conditions. Examples of in-vehicle applications include image display devices used for car navigation devices, speedometers, touch panels for air conditioners, back monitors, rear monitors, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>
The polarizing film of Example 1 was manufactured from a polyvinyl alcohol-based resin film using the manufacturing apparatus shown in FIG. Specifically, a long polyvinyl alcohol (PVA) raw film with a thickness of 60 μm [trade name “Poval Film OPL Film M-6000” manufactured by Mitsubishi Chemical Corporation, degree of saponification of 99.9 mol% or more] is used. The film was continuously conveyed while being unwound from the roll, and was immersed in a swelling bath made of pure water at 28 ° C. with a swelling time of 140 seconds (swelling step). Then, the film pulled out from the swelling bath is subjected to a staining solution containing iodine having iodine / potassium iodide / boric acid / water of 0.03 / 1.3 / 0.3 / 100 (mass ratio) at 30 ° C. It was immersed in a dyeing bath with a soaking time of 130 seconds (dyeing step). Next, the film drawn from the dyeing bath was immersed in a cross-linking bath at 56 ° C. consisting of a cross-linking solution containing potassium iodide / boric acid / water at 13.9 / 3.0 / 100 (mass ratio) for a dipping time of 50 seconds. (Crosslinking step, second treatment step). The pH of the cross-linked bath at 25 ° C. was 3.8.

Subsequently, the film pulled out from the cross-linking bath was made up of a complementary color solution prepared by adding an aqueous potassium hydroxide solution to a solution having potassium iodide / boric acid / water of 9.0 / 3.0 / 100 (mass ratio). It was immersed in the complementary color bath of No. 1 with an immersion time of 10 seconds (complementary color step, first treatment step). Subsequently, the film drawn from the complementary color bath was immersed in a washing bath made of pure water at 7 ° C. for a dipping time of 10 seconds (cleaning step). Then, the film pulled out from the washing bath was allowed to stay in a drying oven at a temperature of 80 ° C. for 150 seconds to dry (drying step). The pH of the complementary color liquid (first treatment liquid) at 25 ° C. was 6.1.

The thickness of the obtained polarizing film was 23 μm. Further, the pH of the immersion liquid of the obtained polarizing film was measured by the method described later and found to be 6.14.

<Example 2>
Regarding the complementary color liquid used in the complementary color step, a polarizing film was produced in the same manner as in Example 1 except that potassium hydroxide was added to adjust the pH at 25 ° C. to 5.7.

The thickness of the obtained polarizing film was 23 μm. Further, the pH of the immersion liquid of the obtained polarizing film was measured by the method described later and found to be 5.92.

<Comparative Example 1>
Regarding the complementary color liquid used in the complementary color step, a polarizing film was produced in the same manner as in Example 1 except that sulfuric acid was added without adding potassium hydroxide. The pH of the complementary color solution at 25 ° C. was 3.8.

The thickness of the obtained polarizing film was 23 μm. Further, the pH of the immersion liquid of the obtained polarizing film was measured by the method described later and found to be 5.16.

<Example 3>
(Preparation of water-based adhesive composition)
Acetacetyl group-modified polyvinyl alcohol [trade name "Gosefimer Z-200", manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity of 4% aqueous solution = 12.4 mPa · sec, degree of saponification = 99.1 mol%] It was dissolved in pure water to prepare a 10% aqueous solution. This acetacetyl group-modified polyvinyl alcohol aqueous solution and sodium glyoxylate as a cross-linking agent are mixed so that the solid content mass ratio of the former: the latter is 1: 0.1, and further, nitrate is added to 100 parts by mass of water. An aqueous adhesive composition was prepared by diluting with pure water so that 1.5 parts by mass of zinc and 2.5 parts by mass of acetacetyl group-modified polyvinyl alcohol were added.

A 40 μm-thick triacetyl cellulose (TAC) film was saponified. Further, a low retardation TAC film having a thickness of 40 μm was saponified. Each of the polarizing films of Example 1 was laminated on both sides via the above-mentioned water-based adhesive to obtain a laminate having a layer structure of TAC / adhesive layer / polarizing film / adhesive layer / low retardation TAC film. The obtained laminated body is heat-treated at 80 ° C. for 140 seconds with a hot air dryer to obtain a polarized light having a layer structure of a TAC film / adhesive layer / polarizing film / adhesive layer / low retardation TAC film. A plate was made. The obtained polarizing plate was subjected to a yellowing evaluation test described later. The results are shown in Table 1.

<Example 4>
A polarizing plate was produced in the same manner as in Example 3 except that the polarizing film was the polarizing film produced in Example 2. The obtained polarizing plate was subjected to a yellowing evaluation test described later. The results are shown in Table 1.

<Comparative Example 2>
A polarizing plate was produced in the same manner as in Example 3 except that the polarizing film was the polarizing film produced in Comparative Example 1. The obtained polarizing plate was subjected to a yellowing evaluation test described later. The results are shown in Table 1.

[Measurement of pH of immersion liquid of polarizing film]
The polarizing films of Examples 1 and 2 and Comparative Example 1 ^{were cut into test pieces having an area of 1500 cm 2} (30 cm × 50 cm), respectively. The test piece was further cut into a size of 5 cm × 5 cm to obtain 60 polarizing films having a size of 5 cm × 5 cm. All 60 sheets of the obtained 5 cm × 5 cm size polarizing film were placed in a 500 mL beaker, and 10 mL of pure water having a temperature of 25 ° C. was added to the beaker using a pipette. After stirring by repeating the operation of sucking the added pure water into the pipette and the operation of discharging it from the pipette a plurality of times, the mixture was allowed to stand at a temperature of 25 ° C. for 10 minutes. Then, the pH of the immersion liquid after taking out the test piece at 25 ° C. was measured using a pH meter (HORIBA D-54). The results are shown in Table 1.

[Measurement of pH of immersion liquid of polarizing film with bonding layer]
40 μm thick TAC film / water-based adhesive layer / polarizing element of Example 1 / water-based adhesive in the same manner as in Example 3 except that the TAC film having a thickness of 40 μm and the low retardation TAC film having a thickness of 40 μm are not saponified. A polarizing plate having a laminated structure of a low retardation TAC film having a layer / thickness of 40 μm was obtained. A TAC film having a thickness of 40 μm and a low retardation TAC film having a thickness of 40 μm were peeled off from the obtained polarizing plate to obtain a polarizing film with an aqueous adhesive layer (polarizing film with a bonding layer). The obtained polarizing film with a water-based adhesive layer ^{was cut into 1500 cm 2} (30 cm × 50 cm) test pieces. The test pieces were further cut into a size of 5 cm × 5 cm, and 60 test pieces having a size of 5 cm × 5 cm were obtained. All the obtained test pieces were placed in a 500 mL beaker, and 10 mL of pure water having a temperature of 25 ° C. was added to the beaker using a pipette. After stirring by repeating the operation of sucking the added pure water into the pipette and the operation of discharging it from the pipette a plurality of times, the mixture was allowed to stand at a temperature of 25 ° C. for 10 minutes. Then, the pH of the immersion liquid after taking out the polarizing film with the laminated layer at 25 ° C. was measured using a pH meter (HORIBA D-54).
Further, the pH of each polarizing film immersion liquid with an aqueous adhesive layer was measured in the same manner as above except that the polarizing film of Example 2 or the polarizing film of Comparative Example 1 was used. The results are shown in Table 1.

[Yellowing evaluation (105 ° C)]
The polarizing plates of Examples 3 and 4 and Comparative Example 2 were cut to a size of 40 mm × 40 mm, respectively, and 40 mm × 40 mm non-alkali glass using an acrylic pressure-sensitive adhesive having a thickness of 25 μm on both sides thereof [“Corning Inc.” EAGLE XG "] was laminated to prepare an evaluation sample.

This evaluation sample was left for 20 minutes at a temperature of 50 ° C. and a pressure of 0.5 MPa (about 5 kg / cm ² ), and then left for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 55%. Further, it was then heat-treated at 95 ° C. for 3 hours. A heating test was conducted in which this sample was stored in a heating environment at a temperature of 105 ° C. for 50 hours, and the change in color before and after heating was visually confirmed. A is the one with almost no change, B is the one with slight color change but can be confirmed, C is the one where the color change can be confirmed in about half the area of the polarizing plate surface, and the color is almost entirely on the polarizing plate surface. The one that changed significantly was designated as D. When the evaluation result was A, the heating test of storing in a heating environment at a temperature of 105 ° C. for 50 hours was performed again, and the change in color before and after heating was visually confirmed. The heating test was terminated when the evaluation result was any of B to D. The total storage time in the heating test until the end is shown in Table 1 as the result of the yellowing evaluation test.

As shown in Table 1, in the polarizing plates of Examples 3 and 4, it was not possible to confirm the change in color before and after heating by the time the time reached 1000 hours. On the other hand, in the polarizing plate of Comparative Example 2, although the color change before and after heating could not be confirmed by the time it reached 300 hours, the total storage time in the heating test reached 300 hours. After that, after further storage for 50 hours, the change in color before and after heating was visually confirmed.

10 Raw fabric film made of polyvinyl alcohol resin, 11 Raw fabric roll, 13 Swelling bath, 15 Dyeing bath, 17 Cross-linking bath, 18 Complementary color bath, 19 Washing bath, 21 Drying furnace, 23 Polarizing film, 30-48, 60, 61 guide rolls, 50-52, 53a, 53b, 54, 55 nip rolls.

Claims (12)

A method for producing a polarizing film from a polyvinyl alcohol-based resin film.
The first treatment step of bringing the polyvinyl alcohol-based resin film into contact with the first treatment liquid is included.
A method for producing a polarizing film, wherein the first treatment liquid contains boric acid and an iodide compound and has a pH of 5.0 or higher at 25 ° C. A second treatment step of bringing the polyvinyl alcohol-based resin film into contact with the second treatment liquid is included.
The second treatment liquid contains boric acid and an iodide compound, and has a pH of less than 5.0 at 25 ° C.
The method for producing a polarizing film according to claim 1, wherein the second treatment step is performed before the first treatment step. The method for producing a polarizing film according to claim 1 or 2, wherein the first treatment liquid has a pH of 6.5 or less at 25 ° C. ^{A test piece having an area of 1500 cm 2} obtained by cutting the polarizing film was immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes. The method for producing a polarizing film according to any one of claims 1 to 3, which is 5.3 or more. A step of manufacturing a polarizing film by the method for manufacturing a polarizing film according to any one of claims 1 to 4.
A method for manufacturing a polarizing plate, comprising a bonding step of bonding a protective film to one or both sides of the polarizing film via a bonding layer. A polarizing film having an area of 1500 cm ² immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes, and the pH of the dipping solution after removing the polarizing film at 25 ° C. is 5.3 or higher. The polarizing film according to claim 6, wherein the polyvinyl alcohol-based resin film is dyed with a dichroic dye. A polarizing plate having the polarizing film according to claim 6 or 7, and a protective film laminated on one side or both sides of the polarizing film via a bonding layer. An image display device in which the polarizing plate according to claim 8 and an image display element are laminated. A polarizing film with a bonding layer in which bonding layers are laminated on both sides of the polarizing film.
The polarizing film with a laminated layer having an area of 1500 cm ² was immersed in 10 mL of pure water at 25 ° C. and left for 10 minutes, and the pH of the dipping solution after taking out the polarizing film with a bonded layer was 3. A polarizing film with a bonding layer, which is more than four. A polarizing plate in which a protective film is laminated on the bonded layer of the polarizing film with a bonded layer. An image display device in which the polarizing plate according to claim 11 and an image display element are laminated.

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