TW201738301A - Method for producing resin film and method for producing polarizing film - Google Patents

Abstract

The present invention aims at a method for producing a resin film exhibiting high polarizing property as a polarizing film, and a method for producing a polarizing film using the same. The present invention provides the method for producing a resin film, including a film-forming step of forming a belt-like unstretched film having a polyvinyl alcohol based resin as a forming material for reducing water by a coating film of a polyvinyl alcohol based resin solution; and an stretching step of obtaining a belt-like resin film which is stretched from the unstretched film while being delivered in the long direction. Between an end of the film forming step and the stretching step of stretching the unstrecthed film, a temperature T1, which the unstretched film is exposed at, and a glass transition temperature A1 of the unstrecthed film, which is represented by a formula (1), satisfy the following formula (2). T1(DEG C) < A1(DEG C)+4(DEG C) ...(2) (wherein a "moisture content of the unstretched film" is expressed as a mass fraction.).

Description

Method for producing resin film and method for producing polarizing film

The present invention relates to a method for producing a resin film and a method for producing a polarizing film.

The polarizing plate is widely used in an image display device such as a liquid crystal display device. The polarizing plate is generally formed by laminating a protective film on one surface or both surfaces of a polarizing film obtained by dyeing a resin film with a dichroic dye. A resin film which is a raw material of a polarizing film is produced by drying a water-soluble coating film containing a polyvinyl alcohol-based resin and then extending it (for example, JP-A-2014-059564 (Patent Document 1), Japanese Patent No. 5339053 No. (Patent Document 2)].

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2014-059564

[Patent Document 2] Japanese Patent No. 5395053

In the resin film for a polarizing film, it is required to exhibit high polarizing performance when the polarizing film is formed by stretching/dyeing. Therefore, it is desirable to form a crystal nucleus formed by a sufficient amount of a polyvinyl alcohol-based resin in the coating film when the water is dried by the above-mentioned coating film to form a dense crystal structure. However, between the drying of the coating film and the stretching of the resin film, or between the stretching of the resin film and the dyeing of the stretched resin film, the crystal grows and the dense crystal structure is disturbed. For this reason, in order to exhibit high polarizing performance when used as a polarizing film, it is necessary to suppress the growth of crystals during the period and maintain a dense crystal structure.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a method for producing a resin film which exhibits high polarization performance when used as a polarizing film, and a method for producing a polarizing film using the resin film.

According to an aspect of the invention, there is provided a method for producing a resin film, comprising: reducing water by a coating film of a polyvinyl alcohol-based resin solution, and forming a strip-shaped unstretched film formed of a polyvinyl alcohol-based resin; a film forming step; an extending step of extending the unstretched film while extending in the longitudinal direction to obtain a strip-shaped resin film extending from the unstretched film; and extending the unstretched film after the film forming step to the extending step The relationship between the temperature T1 exposed by the unstretched film and the glass transition temperature A1 of the unstretched film represented by the following formula (1) satisfies the following formula (2).

T1 (°C) <A1 (°C) + 4 (°C)...(2) (In the formula, "the moisture content of the unstretched film" is the mass fraction)

In one aspect of the invention, in the film forming step, it is preferred that the moisture content of the coating film before the water is reduced is more than 30% by mass, and the water content of the coating film in the process of reducing water is 30% by mass. The speed is 0.01 to 1.8% by mass/second.

In one aspect of the invention, in the film forming step, it is preferred that the moisture content of the coating film before the water is reduced is more than 30% by mass, and the water content of the coating film in the process of reducing water is 30 to 10% by mass, the water The average removal rate is 0.01 to 1.8% by mass/second.

According to an aspect of the invention, there is provided a method for producing a polarizing film, comprising: reducing water by a coating film of a polyvinyl alcohol-based resin solution, and forming a strip-shaped unstretched film formed of a polyvinyl alcohol-based resin; a film forming step; a step of extending the strip-shaped resin film formed by extending the unstretched film while extending the unstretched film in the longitudinal direction; and dyeing the resin film while transporting the dichroic substance while transporting the resin film in the longitudinal direction Thereafter, the resin film dyed with the dichroic substance is immersed in a dyeing step of a crosslinking bath containing a crosslinking agent; and the unstretched film is exposed between the end of the film forming step and the extension of the unstretched film in the extending step The relationship between the temperature T1 and the glass transition temperature A1 of the unstretched film represented by the following formula (1) satisfies the following formula (2).

T1 (°C) <A1 (°C) + 4 (°C) (2) (wherein, the "water content of the unstretched film" means the mass fraction).

In one aspect of the invention, it is preferred that the temperature T2 exposed by the resin film and the glass transition of the resin film represented by the following formula (3) are between the end of the stretching step and the dyed resin film in the dyeing step. The relationship of the temperature A2 satisfies the following formula (4).

T2 (°C) <A2 (°C) + 4 (°C) (4) (In the formula, "the water content of the resin film" means the mass fraction).

In one aspect of the present invention, in the film forming step, it is preferable to apply a polyvinyl alcohol-based resin solution to at least one surface of at least one surface of the base film while conveying the strip-shaped base film in the longitudinal direction. Unstretched film.

In one aspect of the invention, it is preferred that the thickness of the polarizing film is 10 μm or less.

In one aspect of the present invention, in the film forming step, it is preferred that the moisture content of the coating film before water is reduced is more than 30% by mass, and when the water content of the coating film in the process of reducing water is 30% by mass, the water removal rate is It is preferably from 0.01 to 1.8% by mass/second.

In one aspect of the present invention, in the film forming step, it is preferred that the moisture content of the coating film before the water is reduced is more than 30% by mass, and when the water content of the coating film in the process of reducing water is 30 to 10% by mass, the average The removal rate is 0.01 to 1.8% by mass/second.

According to an aspect of the invention, there is provided a method for producing a polarizing film, comprising: extending a strip-shaped unstretched film formed of a polyvinyl alcohol-based resin while being transported in a long direction; a step of extending the formed resin film; and dyeing the resin film dyed with the dichroic substance in a crosslinking bath containing a crosslinking agent after dyeing the resin film in the longitudinal direction; The relationship between the temperature T2 of the resin film exposed and the glass transition temperature A2 of the resin film represented by the following formula (3) after the completion of the stretching step and the dyeing resin film of the dyeing step is satisfied by the following formula (4) ).

T2 (°C) <A2 (°C) + 4 (°C) (4) (In the formula, "the water content of the resin film" means the mass fraction).

According to an aspect of the present invention, a method for producing a resin film exhibiting high polarizing performance as a polarizing film, and a method for producing a polarizing film using the resin film can be provided.

S11, S12, S13, S21, S22, S23, S24‧‧‧ Process

Fig. 1 is a flow chart showing a method of producing a polarizing film using a resin film according to the first embodiment of the present invention.

Fig. 2 is a flow chart showing a method of producing a polarizing film using a resin film according to a second embodiment of the present invention.

Fig. 3 is a graph obtained by plotting the relationship between the moisture content of the unstretched film obtained in the examples and the comparative examples of the present invention and the glass transition temperature.

<First embodiment>

In the following, a method for producing a resin film according to the first embodiment of the present invention and a method for producing a polarizing film using the resin film will be described with reference to the first embodiment. Fig. 1 is a flow chart showing a method of producing a polarizing film using a resin film according to the first embodiment of the present invention.

[Method for Producing Resin Film]

The method for producing a resin film of the present embodiment includes a film forming step including processes S11 and S12, and an extending step including a process S13.

(film formation step)

The film formation step of this embodiment includes a process S11 and a process S12.

In the preparation process of the process S11, a powder, a pulverized product, or a cut product of a polyvinyl alcohol-based resin (hereinafter referred to as a PVA-based resin) is swelled by a solvent, and then the swelled PVA-based resin is used. The mixture was heated and stirred to prepare a PVA resin solution. The concentration of the PVA-based resin in the PVA-based resin solution is preferably from 3 to 40% by mass, more preferably from 10 to 30% by mass.

As the PVA-based resin which is a material for forming the unstretched film, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include a polyvinyl acetate of a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable with vinyl acetate.

Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The PVA-based resin used in the present embodiment is preferably a completely saponified product. In the present embodiment, the degree of saponification of the PVA resin is preferably 80.0 mol% or more and 99.5 mol% or less, and preferably 90.0 mol% or more and 99.5 mol% or less, preferably 94.0 mol%. More than 99.0% of the above is better. When the degree of saponification of the PVA-based resin is less than 80.0 mol%, the water resistance/moisture resistance as a polarizing film is lowered. In addition, when the degree of saponification of the PVA-based resin is larger than 99.5 mol%, the dyeing speed is slowed in the production step of the polarizing film, and the polarizing film having sufficient polarizing properties cannot be obtained in the case where the productivity is lowered. .

In the present embodiment, the degree of saponification (unit: % by mole) of the PVA-based resin is a ratio at which the acetic acid group contained in the polyvinyl acetate-based resin of the PVA-based resin material is changed to a hydroxyl group by a saponification step. The unit ratio (unit: mole%) is a value defined by the following formula (S1). This value can be obtained by the method specified in JIS K 6726 (1994).

Degree of saponification = (number of hydroxyl groups) / (number of hydroxyl groups + number of acetate groups) × 100 (S1)

The higher the degree of saponification of the PVA-based resin, the higher the ratio of the hydroxyl group, that is, the ratio of the acetate group indicating that the crystallization is inhibited is low.

Further, the PVA-based resin used in the present embodiment may be a part of the modified PVA. For example, the PVA resin is an olefin such as ethylene or propylene; and acrylic acid, methacrylic acid, crotonic acid, etc. are not sufficient. And carboxylic acid; alkyl ester of unsaturated carboxylic acid, acrylamide and the like. The ratio of the modification is preferably less than 30 mol%, and more preferably less than 10 mol%. When the amount is more than 30 mol%, it becomes difficult to adsorb the dichroic dye, and the polarizing performance as a polarizing film becomes low.

In the present embodiment, the average degree of polymerization of the PVA-based resin is not particularly limited, but is preferably from 100 to 10,000, more preferably from 1,500 to 8,000, still more preferably from 2,000 to 5,000. The average degree of polymerization of the PVA-based resin can be determined by a method defined in accordance with JIS K 6726 (1994), similarly to the degree of saponification.

Examples of the PVA-based resin having such a property include PVA124 (saponification degree: 98.0 to 99.0 mol%) manufactured by Kuraray Co., Ltd., PVA117 (saponification degree: 98.0 to 99.0 mol%), and PVA624 (saponification degree: 95.0). To 96.0 mol%) and PVA617 (saponification degree: 94.5 to 95.5 mol%); for example, AH-26 (saponification degree: 97.0 to 98.8 mol%), AH-22 (saponification degree) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. : 97.5 to 98.5 mol%), NH-18 (saponification degree: 98.0 to 99.0 mol%), and N-300 (saponification degree: 98.0 to 99.0 mol%); for example, JC-33 of Japan VAM & POVAL Co., Ltd. (saponification) Degree: 99.0 mol% or more), JM-33 (saponification degree: 93.5 to 95.5 mol%), JM-26 (saponification degree: 95.5 to 97.5 mol%), JP-45 (saponification degree: 86.5 to 89.5 mo Ear %), JF-17 (saponification degree: 98.0 to 99.0% by mole), JF-17L (saponification degree: 98.0 to 99.0% by mole), and JF-20 (saponification degree: 98.0 to 99.0% by mole) and the like.

In the film forming step of the present embodiment, the first drying process of the process S12 is performed in accordance with the process of the process S11. In the first dry place In the meantime, water is reduced by the coating film of the PVA-based resin solution, and a band-shaped unstretched film made of a PVA-based resin is formed.

In the first drying process of the process S12, a conventionally known device can be used. The conventionally known device includes, for example, a device having a plurality of drying rolls whose rotation axes are parallel to each other. The PVA-based resin solution obtained in Process S11 was discharged onto one of the drying rolls of the apparatus to form a coating film. Next, using the drying roll and another drying roll on the downstream side of the drying roll, the coating film reduces water and forms an unstretched film made of a PVA-based resin.

The first drying treatment in the present embodiment can be carried out by heating, and can be carried out under reduced pressure as needed. The method of drying by heating the PVA-based resin solution may, for example, be warm air drying or the like.

In the film formation step of the present embodiment, the water content of the coating film of the PVA-based resin solution is preferably 30% by mass or more. At this time, in the first drying treatment, the water removal rate at a water content of the coating film of 30% by mass is preferably 0.01 to 1.8% by mass/second. Further, as conditions other than the above, the average removal rate of water at a water content of 30 to 10% by mass is preferably 0.01 to 1.8% by mass/second. Thereby, a sufficient amount of the crystal nucleus formed of the PVA-based resin can be formed in the coating film.

The drying temperature and the drying time in the first drying treatment may be determined depending on the water content of the coating film of the PVA resin solution, the water removal rate of the water content, or the average removal rate. The drying temperature is preferably, for example, 50 to 200 ° C, and more preferably 60 to 150 ° C.

By performing the first drying treatment under the above conditions, in the PVA In the coating film of the resin solution, the crystal nucleus formed by the PVA resin increases, and the density of the crystal nucleus increases. By doing so, a dense crystal structure is formed, whereby when the resin film is dyed with a dichroic material in the dyeing step, a dichroic substance and a PVA resin are formed in the vicinity of the crystal. Compound. This complex compound contributes to the improvement of the polarizing performance as a polarizing film because of its stability and high orientation.

Thus, by forming a dense crystal structure, the polarizing performance as a polarizing film can be improved. However, the crystal structure of the unstretched film may change between the end of the film formation step and the extension of the unstretched film in the stretching step described later.

In general, a thermoplastic resin having a crystallinity such as a PVA-based resin (hereinafter, abbreviated as "crystalline resin") has a crystal growth rate when it is at a temperature equal to or higher than the glass transition temperature. However, when the water content in the crystalline resin is increased, the water acts as a plasticizer, so that the crystalline resin is softened at a temperature lower than the original glass transition temperature, and the molecular chain in the crystalline resin is There will be more activities. Therefore, since the molecular chain is rearranged and crystallized at a temperature lower than the original glass transition temperature, the degree of crystallization becomes high. When the crystal in the crystalline resin grows, the ratio of the amorphous portion in the mass of the crystalline resin is reduced, so that the water content of the amorphous portion is relatively increased.

Therefore, the glass transition temperature of the crystallized crystalline resin becomes lower than the original glass transition temperature. Thereby, the crystal grows at a temperature lower than the original glass transition temperature, and the degree of crystallization becomes higher.

Here, in the present embodiment, in order to suppress such a The crystal growth of the unstretched film and the maintenance of the polarizing performance as a polarizing film are defined in the following manner. That is, the relationship between the temperature T1 exposed by the unstretched film and the glass transition temperature A1 obtained from the moisture content of the unstretched film is defined between the end of the film forming step and the extension of the unstretched film in the extending step described later. For the unstretched film that satisfies this regulation, an extension process is performed.

(extension step)

The extension step of this embodiment includes a process S13.

In the extension process of the process S13, the unstretched film obtained by the process S12 is extended while being conveyed in the longitudinal direction, and the strip-shaped resin film which extended the unstretched film is formed.

In the present embodiment, between the end of the film forming step and the extension of the unstretched film in the extending step, the temperature T1 (unit: ° C) exposed by the unstretched film and the unstretched film represented by the following formula (1) The relationship of the glass transition temperature A1 (unit: °C) satisfies the following formula (2). Further, the relationship between the temperature T1 and the glass transition temperature A1 of the unstretched film is preferably T1 < A1.

T1 (°C) <A1 (°C) + 4 (°C)...(2)

(In the formula, "the moisture content of the unstretched film" means the mass fraction).

By satisfying the above relationship, the crystal growth of the PVA-based resin in the unstretched film can be suppressed. Thereby, because it can be made in the unstretched film Since the crystal of the PVA-based resin is sufficiently small, a polarizing film having high polarizing performance as a polarizing film can be obtained. Further, the temperature T1 means the highest temperature at which the unstretched film is exposed between the end of the film forming step and the extension of the unstretched film in the extending step.

In the present embodiment, the time from the completion of the film formation step to the extension of the unstretched film in the stretching step is usually 1 second or longer, or may be one day or longer, and generally, from the viewpoint of suppressing the growth of crystal, It is less than 3 months. The time includes, for example, the time for the unstretched film to be transported from the film forming step to the extending step; and after the film forming step is finished, the unstretched film is temporarily taken up to the drum and then transported to the next step, and The time until the unstretched film is unwound from the drum.

The extension in the stretching process of the present embodiment is preferably a dry uniaxial stretching. The stretching ratio in the stretching step of the present embodiment is more than 5 times and 17 times or less, and more preferably more than 5 times and 8 times or less.

In the present embodiment, the humidity control treatment can be performed so as to have a desired moisture content before the elongation treatment. As a method of the humidity control treatment, for example, a method of placing an unstretched film in a room adjusted to a desired humidity and temperature, or a method of adjusting the unstretched film to a desired humidity and temperature can be cited. The method of the wet furnace, etc. In the humidity control treatment, depending on the state of the unstretched film before stretching, the moisture content of the unstretched film can be increased (humidification treatment), or the water content can be reduced (drying treatment).

According to the above configuration, it is possible to provide a method for producing a resin film capable of obtaining a polarizing film having high polarizing performance.

[Method of Manufacturing Polarizing Film]

Hereinafter, a method of manufacturing a polarizing film according to a first embodiment of the present invention will be described with reference to Fig. 1 and an appropriate symbol.

The method for producing a polarizing film using the resin film of the present embodiment includes a film forming step including a process S11 and a process S12, an extending step including a process S13, a dyeing step including a process S21 and a process S22, and a washing including a process S23. The net step, and the drying step including the process 24. In the first embodiment, in the method for producing a resin film of the present embodiment, the processes S11 to S13 are a common process. Therefore, the same symbols are denoted by the same reference numerals before the dyeing step, and the detailed description is omitted.

(staining step)

The dyeing step of the present embodiment includes a process S21 and a process S22.

In the dyeing process of the process S21, the resin film is dyed in a long direction while being dyed with a dichroic substance, and the dichroic substance is adsorbed to form a dyed film.

In the crosslinking treatment of the process S22, the resin film (hereinafter referred to as a dye film) dyed by the dichroic substance in the process S21 is crosslinked by a crosslinking agent to form a crosslinked film.

The dyeing treatment of the present embodiment is carried out by immersing a resin film in a liquid containing a dichroic substance (hereinafter referred to as a dye bath). As the dyeing bath, a solution in which the above-mentioned dichroic substance is dissolved in a solvent can be used. As the solvent of the dyeing bath, for example, water is preferred. In the dye bath, An organic solvent compatible with water may be further added. Specific examples of the organic solvent include methanol, ethanol, propanol or glycerin.

The dichroic substance used in the present embodiment may, for example, be iodine or a conventional dichroic organic dye as a pigment for a polarizing film. As the dichroic organic dye, for example, include: Red BR, Red LR, Red R, PINK LB, Rubin Red BL, Bordeaux GS, Skyblue LG, Lemon yellow, Blue BR, Blue 2R, Navy blue RY, Green LG, Violet LB , Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, ScarletRed GL, Scarlet Red KGL, CongoRed, Brilliant violet BK, SupraBlue G, Supra Blue GL, Supra orange GL, Direct skyblue , Direct Fast orange S, Fast black. The dichroic dye may be used alone or in combination of two or more.

The concentration of the dichroic substance in the dyeing bath is preferably from 0.01 to 10% by mass, more preferably from 0.02 to 7% by mass.

When iodine is used as the dichroic substance, it is preferred to further add the iodide to the dye bath containing iodine for the purpose of improving the dyeing efficiency. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, titanium iodide, and the like. It is preferred to add potassium iodide. Moreover, the dye bath may also contain a crosslinking agent.

The concentration of the iodide in the dyeing bath is preferably from 0.01 to 20% by mass. When potassium iodide is added to the dye bath containing iodine, the ratio of iodine to potassium iodide is preferably from 1:5 to 1:100 by mass ratio, from 1:6 to 1:80 is better.

The temperature of the dyeing bath is preferably from 10 to 60 ° C, more preferably from 20 to 40 ° C.

In the dyeing step of the present embodiment, the dyeing process is carried out by immersing the dyed film in a liquid containing a crosslinking agent (hereinafter referred to as a crosslinking bath) to carry out a crosslinking treatment of the crosslinked film.

The crosslinking agent used in the present embodiment is preferably a boron compound, glyoxal or glutaraldehyde, and more preferably a boron compound. Examples of the boron compound include boric acid, borax, and the like. The crosslinking agent may be used alone or in combination of two or more.

As the crosslinking bath of the present embodiment, a solution in which a crosslinking agent is dissolved in a solvent can be used. As the solvent, for example, water is preferred. The cross-linking bath may further contain an organic solvent compatible with water. Specific examples of the organic solvent are the same as described above. In the crosslinking bath, the concentration of the crosslinking agent is preferably from 1 to 20% by mass, more preferably from 6 to 15% by mass.

The crosslinking bath of the present embodiment may further contain an iodide. By adding an iodide to the crosslinking bath, the in-plane polarizing performance of the obtained polarizing film can be made uniform. Specific examples of the iodide are the same as described above.

The concentration of the iodide in the crosslinking bath is preferably from 0.05 to 15% by mass, more preferably from 0.5 to 8% by mass.

The temperature of the crosslinking bath is preferably from 10 to 90 °C.

In the present embodiment, the temperature T2 (unit: ° C) at which the resin film is exposed and the glass transition temperature A2 of the resin film represented by the following formula (3) between the dyeing resin film and the dyeing resin film after the completion of the stretching step are completed. The relationship (unit: °C) is preferably satisfied by the following formula (4). The reason is the same as the reason why the relationship between the temperature T1 at which the predetermined unstretched film is exposed and the glass transition temperature A1 of the unstretched film is determined between the end of the film forming step of the present embodiment and the extension of the unstretched film in the extending step. . Further, the relationship between the temperature T2 and the glass transition temperature A2 of the resin film is preferably T2 < A2.

T2 (°C) <A2 (°C) + 4 (°C) (4) (In the formula, "the water content of the resin film" means the mass fraction).

By satisfying the above relationship, the crystal growth of the PVA-based resin in the resin film can be suppressed between the end of the stretching step and the dyed resin film in the dyeing step. Thereby, the crystal of the PVA-based resin in the resin film can be made sufficiently small, and thus a polarizing film having high polarizing performance as a polarizing film can be obtained. Further, the temperature T2 is the highest temperature at which the resin film is exposed between the end of the stretching step and the dyed resin film in the dyeing step.

In the present embodiment, the time from the completion of the stretching step to the dyed resin film in the dyeing step is usually 1 second or longer, or may be one day or longer, and is generally from the viewpoint of suppressing the growth of crystals. In less than 3 months. The time includes, for example, the time from the stretching step to the resin film to the dyeing process or the cross-linking process; and after the end of the stretching step, the resin film is temporarily taken up to the drum and transported to the next step, and The time until the unstretched film is unwound from the drum.

(washing step)

The washing step of this embodiment includes a process S23.

In the cleaning process of the process S23, the crosslinked film obtained in the process S22 is washed.

The washing treatment of the present embodiment is carried out by immersing the crosslinked film in pure water (hereinafter referred to as a washing bath) such as ion-exchanged water or distilled water. Thereby, the agent remaining in the crosslinked film can be reduced, and for example, the remaining dichroic substance and the unreacted crosslinking agent can be reduced. In the washing bath, an organic solvent compatible with water may be further contained. Specific examples of the organic solvent are the same as described above.

The washing temperature is preferably from 3 to 50 ° C, more preferably from 4 to 20 ° C.

Further, the washing treatment of the present embodiment may be a washing treatment by an aqueous solution containing an iodide, or a washing treatment by an aqueous solution containing an iodide and a washing treatment by pure water. Specific examples of the iodide are the same as described above. The hue of the obtained polarizing film can be prepared by containing iodide in the washing bath. In addition, the cleaning bath may contain a crosslinking agent, and in order to prevent defects caused by the precipitation of the crosslinking agent on the surface of the film, the amount of addition is preferably 1 part by mass or less based on 100 parts by mass of water.

The concentration of the iodide in the washing bath is preferably from 1 to 15% by mass.

(drying step)

The drying step of this embodiment is provided with a process S24.

The second drying process of the process S24 is to dry the crosslinked film which has been washed in the process S23.

The second drying treatment of the present embodiment may be a conventionally known method, and examples thereof include natural drying, air drying, and heat drying. For example, in the case of heat drying, the drying temperature is preferably from 20 to 95 °C. If the drying temperature is too low, the drying time becomes long and the production efficiency is lowered.

On the other hand, when the drying temperature is too high, the obtained polarizing film is deteriorated, and the polarizing performance and the hue are deteriorated. Moreover, the drying time is preferably from 2 to 20 minutes. By doing so, a polarizing film can be obtained.

Further, in the method for producing a polarizing film of the present embodiment, the film forming step is the same as the method for producing the resin film of the present embodiment, and the film forming step can be omitted. In other words, in the method for producing a polarizing film of the present embodiment, a strip-shaped unstretched film made of a polyvinyl alcohol-based resin may be prepared by the following stretching step, and the unstretched film may be along the long side. The carrier is stretched to obtain a resin film formed by extending the unstretched film. In such a case, between the end of the stretching step and the dyed resin film in the dyeing step, the temperature T2 (unit: ° C) exposed by the resin film and the glass transition of the resin film represented by the above formula (3) The relationship of the temperature A2 (unit: °C) satisfies the above formula (4).

According to the above configuration, a method of producing a polarizing film capable of obtaining a polarizing film having high polarizing performance can be provided.

[Method of Manufacturing Polarizing Plate]

In the present embodiment, a polarizing film in which a polarizing film and a protective film are laminated can be obtained by bonding a protective film to at least one surface of the polarizing film produced by the above method using an adhesive.

(protective film)

The material of the protective film of the polarizing plate of the present embodiment is preferably a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropic properties. Examples of the thermoplastic resin include a cellulose acetate resin such as cellulose triacetate, a cycloolefin resin, a cycloolefin copolymer resin, polyethylene terephthalate, polyethylene naphthalate, and a polypair. A polyester resin such as butyl phthalate, an acrylic resin such as a polycarbonate resin or polymethyl methacrylate, a non-cyclic olefin resin such as polypropylene or polyethylene, or a mixture thereof.

The thickness of the above protective film is preferably from 1 to 200 μm, more preferably from 5 to 100 μm, still more preferably from 10 to 50 μm.

Further, in the present embodiment, when a protective film is provided on both surfaces of the polarizing film, a protective film made of the same resin material may be used for both surfaces, and a protective film made of a different resin material may be used.

(adhesive)

The adhesive for the polarizing plate of the present embodiment may, for example, be a water-based adhesive or an active energy ray-curable adhesive. The water-based adhesive agent may, for example, be an adhesive in which a polyvinyl alcohol-based resin is dissolved in water or a polyvinyl alcohol-based resin is dispersed. Active energy ray hardening adhesive can be listed For example, an adhesive containing a curable compound which is hardened by irradiation with active energy rays such as ultraviolet rays, visible rays, electron rays, and X rays.

The active energy ray-curable adhesive is preferably an active energy ray-curable property using either a cationically polymerizable curable compound or a radically polymerizable curable compound, since it exhibits good adhesion. The composition of the agent or the active energy ray-curable adhesive composition containing both of them is used. The active energy ray-curable adhesive may further contain a cationic polymerization initiator or a radical polymerization initiator for starting the curing reaction of the curable compound.

Examples of the cationically polymerizable curable compound include an epoxy compound (a compound having one or two or more epoxy groups in the molecule) and an oxetane compound (having 1 in the molecule). Or a compound of two or more oxetane rings), or a combination thereof.

Examples of the radically polymerizable curable compound include a (meth)acrylic compound (a compound having one or two or more (meth)acryloxy groups in the molecule), and a radical. Another vinyl compound of a polymerizable double bond or a combination of these.

The active energy ray-curable adhesive may contain a cationic polymerization accelerator, an ion replenishing agent, an antioxidant, a chain transfer agent, a tackifier, a thermoplastic resin, a filler, a flow regulator, a plasticizer, or a consumer, as needed. Additives such as foaming agents, antistatic agents, leveling agents, and solvents.

Hereinafter, a method of manufacturing the polarizing plate of the embodiment will be described. When the protective film is bonded by using an active energy ray-curable adhesive, the protective film is laminated on the polarizing film via an active energy ray-curable adhesive. its Then, an active energy ray such as ultraviolet rays, visible light, electron rays, or X-rays is irradiated to cure the adhesive layer formed of the active energy ray-curable adhesive. As the active energy ray, ultraviolet light is preferred. In this case, as the light source, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a fluorescent lamp, a black light lamp, a microwave excited mercury lamp, a metal halide lamp, or the like can be used.

On the other hand, when a protective film is bonded using a water-based adhesive, the protective film may be laminated on the polarizing film via a water-based adhesive, and then heated and dried.

The polarizing plate of the present embodiment can be surface-treated with a polarizing film, a protective film, or both for the purpose of improving adhesion to an adhesive. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet treatment, primer treatment, saponification treatment, solvent application, and solvent treatment by drying.

Further, a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, or an antifouling layer may be formed on the surface of the protective film on the opposite side to the polarizing film.

According to the configuration as described above, it is possible to provide a polarizing plate which exhibits high polarization performance by providing the polarizing film of the embodiment.

<Second embodiment>

Hereinafter, a method for producing a resin film and a method for producing a polarizing film using the resin film according to the second embodiment of the present invention will be described with reference to FIG. 2 and using appropriate symbols. Fig. 2 is a view showing the use of the second embodiment of the present invention A flowchart of a method of producing a polarizing film of a resin film of a form.

As shown in Fig. 2, the method for producing a resin film of the present embodiment, and the method for producing a polarizing film using the resin film, and the processes S11 to S13 and the processes S21 to S24 of the first embodiment shown in Fig. 1 For common. The first embodiment differs from the second embodiment in that, in the film forming step of the first embodiment, the process S31 is included between the process S11 and the process S12. Therefore, in the present embodiment, the steps after the dyeing step common to the first embodiment are denoted by the same reference numerals, and the detailed description thereof will be omitted.

(film formation step)

The film formation step of this embodiment includes a process S11, a process S31, and a process S12.

In the coating process of the process S31, the P-based resin solution prepared by the process S11 is applied to at least one surface of the base film while conveying the strip-shaped base film in the longitudinal direction. Thereby, a coating layer is formed on at least one surface of the base film.

In the first drying process of the process S12, the coating layer obtained in the process S31 is reduced in water, and a laminate having an unstretched film in at least one area of the base film is formed.

In the base film used in the present embodiment, a material which is conventionally used as a protective film for a polarizing film can be used. For example, transparency, mechanical strength, thermal stability, moisture barrier property, and the like can be used as a material for forming the base film. Excellent thermoplastic resin such as properties and extensibility.

Examples of the thermoplastic resin include a polyolefin resin such as a chain polyolefin resin or a cyclic polyolefin resin (norbornene resin), a polyester resin, a (meth)acrylic resin, and the like. a cellulose ester resin such as cellulose acetate or diacetate cellulose, a polycarbonate resin, a polyvinyl alcohol resin, a polyvinyl acetate resin, a polyarylate resin, or a polystyrene resin. A polyether oxime resin, a polyfluorene-based resin, a polyamine-based resin, a polyimide-based resin, or a mixture thereof. Further, a copolymer obtained by copolymerizing a monomer of the above resin may be used as a material for forming a base film. Among these, a polyester resin such as a polyolefin resin such as polypropylene or a polyester resin such as amorphous polyethylene terephthalate is preferable.

The base film in the present embodiment is formed of one or two or more thermoplastic resins. The base film may have a single layer structure composed of a resin layer of one layer, or may have a multilayer structure in which a plurality of resin layers are laminated. The resin constituting the substrate film is preferably one which extends the suitable extension temperature of the unstretched film in the stretching step performed after the film forming step.

The base film may further contain: an ultraviolet absorber, an antioxidant, a smoothing agent, a plasticizer, a mold release agent, a color preventive agent, a flame retardant, a nucleating agent, and an anti-wear agent, within a range not impairing the effects of the present invention. Additives such as electrostatic agents, pigments or colorants.

In the present embodiment, the thickness of the base film is preferably from 1 to 500 μm, preferably from 1 to 300 μm, more preferably from 5 to 200 μm, and from 5 to 150 μm in terms of strength, handleability, and the like. Very good.

In the present embodiment, as a method of applying the PVA-based resin solution, a conventionally known method can be employed. Conventional methods can be listed For example, wire bar coating, reverse coating, gravure coating, etc., roll coating, die coating, dot coating, lip coating, screen coating, spray coating, impregnation Method, spraying method, etc. The PVA resin solution may be applied only to one side of the substrate film or may be applied to both surfaces.

In order to improve the adhesion between the substrate film of the obtained laminate and the unstretched film between the process S11 and the process S31, the surface of the substrate film on the side on which the coating layer is formed may be subjected to a surface treatment. Such surface treatment may, for example, be corona treatment, plasma treatment or flame treatment. Further, for the same purpose, a coating layer may be formed on the base film via an undercoat layer or the like.

As a material for forming the undercoat layer, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropic property, and elongation can be used. Examples of such a thermoplastic resin include a (meth)acrylic resin and a polyvinyl alcohol-based resin.

As a material for forming the undercoat layer, since the base film of the obtained laminate can exhibit good adhesion to both of the unstretched films, a polyvinyl alcohol resin is preferable, and a polyvinyl alcohol resin is more preferable. .

As a method of forming the undercoat layer, for example, a method in which the mixed solution of the above resin and a solvent is applied to the surface of the substrate film and then dried is exemplified. The solvent is not particularly limited as long as it can dissolve the above resin, but water is preferred. The coating method of the undercoat layer is the same as the coating method of the PVA-based resin solution. The drying temperature at the time of forming the undercoat layer is preferably from 50 to 200 ° C, more preferably from 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C or higher.

The undercoat layer may contain a crosslinking agent in order to increase its strength. Specific examples of the crosslinking agent include an epoxy-based, isocyanate-based, dialdehyde-based, metal-based or polymer-based crosslinking agent. Examples of the metal-based crosslinking agent include metal salts, metal oxides, metal hydroxides, and organometallic compounds. When a polyvinyl alcohol-based resin is used as the material for forming the undercoat layer, a polyamide solvent, a methylolated melamine resin, a dialdehyde-based crosslinking agent, a metal chelate-based crosslinking agent, or the like is preferably used.

The thickness of the undercoat layer is preferably from about 0.05 to 1 μm, more preferably from 0.1 to 0.4 μm. When the thickness of the undercoat layer is thinner than 0.05 μm, there is a case where the substrate film and the unstretched film are not sufficiently adhered.

In the film formation step of the present embodiment, the first drying treatment is performed by reducing the water from the coating layer in the laminate to form the unstretched film.

The first drying treatment in the present embodiment can be carried out by the same heating as in the first embodiment, and can be carried out under reduced pressure as needed. The method of drying by heating the PVA-based resin solution may, for example, be drying by a hot roll or drying by warm air.

In the film formation step of the present embodiment, the water content of the coating layer in the laminate is preferably 30% by mass or more. In this case, in the first drying treatment, the water removal rate when the water content of the coating film is 30% by mass is preferably 0.01 to 1.8% by mass/second. Further, as conditions other than the above, it is preferred that the water removal rate at a water content of 30 to 10% by mass is preferably 0.01 to 1.8% by mass/second. Thereby, a sufficient amount of the crystal nucleus formed of the PVA-based resin can be generated in the coating layer.

(extension step)

The extension step of this embodiment includes a process S13.

In the extension process of the process S13, the layered body obtained in the process S12 is extended to form a laminated film which is an extended base film extending from the laminated base film and a resin formed on at least one side of the extended base film. The film is formed.

In the extending step of the embodiment, the temperature T1 (unit: ° C) exposed by the unstretched film and the not expressed by the above formula (1) are from the end of the film forming step to the extension of the extending step to the unstretched film. The relationship of the glass transition temperature A1 (unit: °C) of the stretched film is the same as that of the first embodiment. Thereby, the crystal growth of the PVA-based resin in the unstretched film can be suppressed. Thereby, since the crystal of the PVA-based resin in the unstretched film can be made sufficiently small, a polarizing film having high polarization performance as a polarizing film can be obtained.

In the present embodiment, the time from the end of the film formation step to the extension of the unstretched film in the stretching step is usually 1 second or longer, or may be one day or longer, and from the viewpoint of suppressing crystal growth. Usually it is under 3 months. The time includes, for example, a time during which the unstretched film is transported from the film forming step web to the production line; and after the film forming step is finished, the unstretched film is temporarily taken up to the drum and then transported to the next step, and The time until the unstretched film is unwound from the drum.

The stretching ratio of the stretching treatment of the present embodiment may be appropriately selected depending on the desired polarizing performance, and is preferably more than 5 times and 17 times or less with respect to the original length of the laminated body, and more than 5 times and 8 times. The next is better. When the stretching ratio is 5 times or less, the orientation of the PVA-based resin may be insufficient, and there is a concern that sufficient polarizing performance cannot be obtained as a polarizing film. On the other hand, when the stretching ratio exceeds 17 times, the breakage of the laminated film is likely to occur, and the thickness of the laminated film is thinner than the desired thickness, and the workability and handleability in the subsequent step are lowered.

If the stretching ratio is within the above range, the stretching treatment can be carried out in multiple stages. In this case, all of the multi-stage stretching treatment may be continuously performed before the dyeing step, or the stretching treatment after the second stage may be performed in the dyeing step or the cross-linking treatment of the dyeing step or both. In such a case, for example, the first stage of stretching may be performed in a dry manner, and the stretching ratio may be more than 1.1 times and not more than 3.0 times, and the second stage of stretching may be performed in water, and the stretching ratio may be twice or more. And less than 5 times.

The stretching treatment may be a longitudinal extension extending in the longitudinal direction of the laminate (the direction in which the laminate is conveyed), a lateral extension extending in the width direction of the laminate, or an oblique extension or the like. Examples of the longitudinal stretching method include stretching between rolls using a roll extension, compression stretching, extension using a jig (clip), and the like. As a lateral extension method, a tenter method etc. are mentioned. For the stretching treatment, any of the wet stretching method and the dry stretching method may be employed, but it is preferable that the stretching temperature of the dry stretching method can be selected from a wide range.

The extension temperature is preferably 80 to 160 ° C, more preferably 90 to 150 ° C, and more preferably 100 to 130 ° C, as long as it is set to a temperature at which the laminate is extensible to exhibit fluidity.

The thickness of the resin film in the laminated film is preferably 3 to 30 μm, more preferably 5 to 20 μm. In the present embodiment, the thickness of the resin film is easily stained by a dichroic material in the dyeing step within the above range, and excellent polarizing performance is obtained when a polarizing film is formed.

In the present embodiment, the continuous stretching treatment may be performed to insolubilize the resin film in the laminated film. The insolubilization treatment can be carried out by immersing the laminated film in a solution containing a crosslinking agent (hereinafter, an insoluble bath). The crosslinking agent contained in the insoluble bath is the same as the crosslinking agent used in the crosslinking treatment of the first embodiment. As the solvent of the insolubilizing bath, for example, water is preferred. The insoluble bath may further contain an organic solvent compatible with water. Specific examples of the organic solvent are the same as described above.

The concentration of the crosslinking agent in the insolubilizing bath is preferably from 1 to 4% by mass. Further, the temperature of the insolubilizing bath is preferably 25 ° C or more, more preferably 30 to 85 ° C, and still more preferably 30 to 60 ° C. The time for immersing the laminated film in the insolubilizing bath is preferably from 5 to 800 seconds, more preferably from 8 to 500 seconds.

The dyeing step, the washing step, and the drying step which are carried out after the stretching step of the present embodiment are the same as in the first embodiment. In this way, a polarizing laminated film having a polarizing film on the surface layer of the base film can be obtained.

According to the present embodiment, as in the first embodiment, a method of producing a polarizing film which exhibits high polarization performance when used as a polarizing film can be provided. Moreover, in the present embodiment, the base film and the unstretched film can be simultaneously extended Since the film is formed as a resin film, it is easier to obtain a thin polarizing film than the method for producing a conventional resin film in which the film made of the PVA resin is separately stretched and the method for producing the polarizing film. In other words, the thickness of the polarizing film obtained by the method for producing a polarizing film of the present embodiment is preferably 10 μm or less, and may be 7 μm or less.

In particular, a polarizing film having a thickness of 10 μm or less is more likely to be neglected by polarized light than a polarizing film having a thickness of more than 10 μm because of a large amount of a complex formed by a dichroic substance and a PVA-based resin present on the surface of the polarizing film. The impact of performance. In the present embodiment, after drying the coating layer, between extending the unstretched film on the substrate film or between extending to the dyed resin film, the temperature exposed by the film is managed and The relationship between the glass transition temperatures of the above films suppresses the crystal growth in the film, and the high polarizing performance as a polarizing film can be maintained continuously.

[Method of Manufacturing Polarizing Plate]

In the present embodiment, the polarizing film of the polarizing laminated film produced by the above method, that is, the surface of the polarizing film opposite to the base film, can be bonded to the surface by using an adhesive. A polarizing laminated film having a protective film applied to one side was obtained. The protective film and the adhesive used in the present embodiment are the same as those in the first embodiment.

Further, when the polarizing film is provided on both surfaces of the base film, the protective film can be bonded to the polarizing film on both surfaces. In this case, a protective film made of the same resin material may be used, or a protective film made of a different resin material may be used.

In the present embodiment, the base film is peeled off from the polarizing laminate film having the protective film applied to one surface, whereby a polarizing plate having a protective film applied to one side can be obtained.

Moreover, such a polarizing laminated film is provided with a polarizing film on both surfaces of the base film, and when a protective film is bonded to the two polarizing films, a protective film is applied to one surface of each of the polarizing laminated films. 2 pieces of polarizing plate.

The method of peeling a base film can employ the same method as the peeling process of the separator (release film) by the polarizing plate which has the conventional adhesive.

On the polarizing film of the polarizing plate on which the protective film is applied on one side, that is, on the surface opposite to the bonded protective film, a protective film can be applied on both sides by bonding the protective film with an adhesive. Polarized plate. Specific examples of the protective film and the adhesive used in this case are the same as described above.

According to the configuration described above, since the polarizing film of the present embodiment is provided, a polarizing plate exhibiting high polarization performance can be provided.

<Modification>

Further, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be added without departing from the effects of the present invention.

In the first embodiment and the second embodiment, the first drying process uses a device having a plurality of drying rolls whose rotation axes are parallel to each other. At this time, a heat treatment roll may be provided on the downstream side of the plurality of drying rolls. Thereby, before the stretching step of the present embodiment, the crystal nucleus formed of the PVA-based resin can be increased, and the elongation of the film in the extended film can be improved.

In the first embodiment and the second embodiment, the dyeing step is performed after the stretching step, but the steps may be performed before the stretching step or simultaneously.

Further, in the dyeing step of the first embodiment and the second embodiment, the crosslinking treatment is performed before the dyeing treatment, but the crosslinking agent may be blended in the dyeing bath to perform the dyeing treatment. Further, two or more types of crosslinking baths having different compositions may be used, and the crosslinking treatment may be carried out twice or more.

In the first embodiment and the second embodiment, either the polarizing film of the polarizing plate on which the protective film is applied on one side or the protective film of the polarizing plate on which the protective film is applied on both sides may be laminated to laminate The polarizer is bonded to an adhesive layer of another member (for example, a liquid crystal cell used in a liquid crystal display device). The adhesive forming the adhesive layer is formed of an adhesive composition in which a crosslinking agent is added to the matrix polymer. Examples of the matrix polymer include a (meth)acrylic resin, a styrene resin, and a polyfluorene-based resin. Examples of the crosslinking agent include an isocyanate compound, an epoxy compound, and an aziridine compound. The adhesive composition may further contain fine particles to form a light-scattering adhesive layer. The thickness of the adhesive layer is preferably from 1 to 40 μm, more preferably from 3 to 25 μm.

Further, another optical layer may be laminated on the polarizing film of the polarizing plate on which the protective film is applied on one side or on any of the polarizing plates on which the protective film is applied. Examples of the other optical layer include a reflective polarizing film, a film having a surface antireflection function, a reflective film having a reflective function on the surface, and a transflective reflection having both a reflecting function and a penetrating function. Film, viewing angle compensation film, and the like. The polarizing plate having the polarizing film obtained by the production method of the present embodiment can be suitably applied to the viewing side and the back side of the display device.

[Examples]

The invention is illustrated by the following examples, but the invention is not limited to the examples.

<Manufacturing example (manufacturing of laminated body)>

[Substrate film]

A three-layer structure in which a resin layer made of a homopolymer of propylene homopolymer is disposed on both sides of a resin layer made of a propylene/ethylene random copolymer containing about 5% by weight of ethylene units. A film is used as a substrate film. The base film was produced by co-extrusion molding using a multilayer extrusion molding machine.

As the propylene/ethylene random copolymer and the homogeneous polypropylene, the following materials were used.

Propylene/ethylene random copolymer: Sumitomo (registered trademark) NOBLEN (registered trademark) W151, manufactured by Sumitomo Chemical Co., Ltd., melting point = 138 ° C

Homogeneous Polypropylene: Sumitomo (registered trademark) NOBLEN (registered trademark) FLX80E4, manufactured by Sumitomo Chemical Co., Ltd., melting point = 163 ° C

The total thickness of the obtained base film was 90 μm, and the thickness ratio of each layer (FLX80E4/W151/FLX80E4) was 3/4/3.

[Undercoat layer forming step]

PVA powder (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Z-200, average polymerization degree 1100, saponification degree: 99.5 mol%) was dissolved in hot water at 95 ° C to prepare an aqueous solution of 3 mass% PVA. In the obtained PVA aqueous solution, 5 parts by weight of a crosslinking agent (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumirez Resin (registered trademark) 650) was mixed as a binder with respect to 6 parts by weight of the PVA powder.

The obtained adhesive was applied to the surface of the substrate film subjected to corona treatment using a micro gravure coater. The coated substrate film was dried at 80 ° C for 10 minutes, thereby forming an undercoat layer having a thickness of 0.2 μm.

[film forming step]

PVA powder (manufactured by Kuraray Co., Ltd., trade name: PVA124, average polymerization degree 2400, saponification degree: 98.0 to 99.0 mol%) was dissolved in hot water at 95 ° C to prepare a 7.5% by mass aqueous PVA solution. The obtained PVA aqueous solution was applied to the surface of the base film on which the undercoat layer was formed using a die coater. The coated base film was dried at 80 ° C, thereby forming a resin layer made of polyvinyl alcohol having a thickness of 9.2 μm. The water removal rate at a water content of 30% by mass was 1.20% by mass/second, and the average removal rate of water at a water content of 30 to 10% by mass was 1.21% by mass/second.

By doing so, a laminate having a three-layer structure in which a base film, an undercoat layer, and a resin layer are laminated in the following order is produced.

<Storage test of laminated body>

[Examples 1 to 9, Comparative Examples 1 to 6]

The laminate produced in the production example was stored for 2 weeks in a hot and humid environment managed by the temperature (unit: ° C) shown in Table 1 and the moisture content (unit: mass fraction) of the unstretched film in the laminate. .

For the unstretched film of the laminate of each of the examples and the comparative examples, the crystallization index (peak ratio) X at the start of storage and the end of storage was obtained, and the crystallization index after storage was subtracted from the storage. The crystallization index of the crystallization index is ΔX. At this time, the larger the crystallization index difference ΔX is, the more the crystal grows in the unstretched film during storage. Further, the crystallization index (spectral peak ratio) X of the resin layer was obtained by the following method.

[Method for Calculating Crystallization Index (Spectrum Ratio) X]

First, the infrared spectroscopy spectrum of the resin layer contained in the laminated body before and after storage was measured by a penetration method using a Fourier transform infrared spectrophotometer (Varian 640-IR, manufactured by Varian Inc.). At this time, the decomposition energy is set at 0.5 cm ^-1 and the cumulative number of times is 16 times.

Next, the absorbance at 1141 cm ^-1 and 1440 cm ^-1 was obtained from the obtained infrared spectroscopy spectrum, and the crystallization index (spectral peak ratio) X was calculated from the following formula (S2). Further, the peak 1141cm ^-1 wavenumber spectrum of the PVA-based resin is should be formed by crystallization, peak wavenumber 1440cm ^-1 corresponding to the reference (reference) value.

Crystallization index (spectral peak ratio) X = A ₁₁₄₁ / A ₁₄₄₀ (S2) (In the formula (S2), A ₁₁₄₁ and A ₁₄₄₀ mean absorbances in wave numbers of 1141 cm ^-1 and 1440 cm ^-1 , respectively).

The storage test results of the laminates of the respective examples and the comparative examples were evaluated by the following criteria. To satisfy the following formula (2) "○" is "X" if the following formula (2) is not satisfied.

T1 (°C) <A1 (°C) + 4 (°C)...(2)

Table 1 shows the crystallization index X at the start of storage and the end of storage of the laminate of each of the examples and the comparative examples, and the crystallization index difference ΔX. Further, Fig. 3 is a graph showing the relationship between the water content of the unstretched film obtained in the examples and the comparative examples and the glass transition temperature. The graph in Fig. 3 shows the relationship between the water content in the unstretched film and the glass transition temperature when the degree of crystallization is 0%. Further, "○" and "×" shown in Fig. 3 correspond to "○" and "×" shown in Table 1.

As shown in Table 1, it is known that the relationship between the glass transition temperature A1 (unit: °C) and the storage temperature T1 (unit: °C) obtained from the water content in the unstretched film of the laminate is satisfied. The above formula (2). The crystallization index difference ΔX at this time was less than 0.053. On the other hand, it is known that the relationship between the glass transition temperature A1 obtained from the moisture content of the unstretched film of the laminate and the storage temperature T1 in each comparative example does not satisfy the above formula (2).

The crystallization index difference ΔX at this time is 0.053 or more.

<Manufacture of polarizing film>

[Extension step]

The laminates stored in the respective examples and the comparative examples were uniaxially stretched at 5.3 times the free end at 150 ° C using a floating vertical uniaxial stretching device to obtain a laminated film. The thickness of the resin film in the laminated film was 5.1 μm.

[staining step]

An iodine aqueous solution (dyeing bath) containing 0.6 parts by mass of iodine and 10.0 parts by mass of potassium iodide was prepared in an amount of 100 parts by mass of water. In a dyeing bath adjusted to a liquid temperature of 30 ° C, a laminated film was impregnated for 180 seconds to be dyed with iodine to prepare a dyed film.

Next, a boric acid aqueous solution containing 10.4 parts by mass of boric acid was prepared in an amount of 100 parts by mass based on the water. The mixture was immersed in an aqueous boric acid solution adjusted to a liquid temperature of 78 ° C for 120 seconds. Furthermore, an aqueous solution (crosslinking bath) of 5.0 parts by mass of boric acid and 12.0 parts by mass of potassium iodide was prepared in an amount of 100 parts by mass of water. In the crosslinking bath adjusted to a liquid temperature of 65 ° C, a crosslinking treatment was carried out by immersing for 60 seconds to form a crosslinked film.

[Washing step and drying step]

The obtained crosslinked film was immersed in pure water adjusted to a liquid temperature of 10 ° C for 10 seconds, and washed. Immediately after washing, the air blower attached to the surface was removed by a blower to dry it. By doing so, a polarizing laminated film having a polarizing film on the surface of the base film is obtained.

<Evaluation of Polarization Performance of Polarizing Film>

A polarizing film was produced from the laminate of each of the examples and the comparative examples, and the polarizing performance was evaluated. In Table 1, the laminate having a crystallization index difference ΔX of less than 0.053, that is, the polarizing film produced by using the laminate of the example, is known as compared with the polarizing film produced by using the laminate of the comparative example. The system shows higher polarization performance. This is because it can inhibit unstretched film during storage. The crystal grows to maintain a dense crystalline structure.

From the above, the present invention is indeed useful.

S11, S12, S13, S21, S22, S23, S24‧‧‧ Process

Claims (10)

A method for producing a resin film, comprising: a film forming step of reducing water by a coating film of a polyvinyl alcohol-based resin solution to form a strip-shaped unstretched film using a polyvinyl alcohol-based resin as a material for forming, and an extending step; And extending the unstretched film in the longitudinal direction to obtain a strip-shaped resin film extending from the unstretched film; and after extending the film forming step to the unstretched film in the extending step, The relationship between the temperature T1 exposed by the unstretched film and the glass transition temperature A1 of the unstretched film represented by the following formula (1) satisfies the following formula (2). T1 (°C) <A1 (°C) + 4 (°C) (2) In the formula, "the moisture content of the unstretched film" is the mass fraction. The method for producing a resin film according to the first aspect of the invention, wherein, in the film forming step, the water content of the coating film before the water is reduced is larger than 30% by mass, and the water is reduced. The water removal rate when the water content of the coating film is 30% by mass is 0.01 to 1.8% by mass/second. The method for producing a resin film according to the first aspect of the invention, wherein, in the film forming step, the water content of the coating film before the water is reduced is larger than 30% by mass, and the water is reduced. , the average removal rate of water when the moisture content of the coating film is 30 to 10% by mass It is 0.01 to 1.8% by mass/second. A method for producing a polarizing film, comprising: a film forming step of reducing water by a coating film of a polyvinyl alcohol-based resin solution, forming a strip-shaped unstretched film formed of a polyvinyl alcohol-based resin, and extending the step The unstretched film is stretched in the longitudinal direction to obtain a strip-shaped resin film extending from the unstretched film, and the dyeing step is carried out by dyeing the resin film while transporting the dichroic material in the longitudinal direction. Thereafter, the resin film dyed with the dichroic substance is immersed in a crosslinking bath containing a crosslinking agent; between the end of the film forming step and the extension of the unstretched film in the extending step, the aforementioned unstretched The relationship between the temperature T1 exposed by the film and the glass transition temperature A1 of the unstretched film represented by the following formula (1) satisfies the following formula (2). T1 (°C) <A1 (°C) + 4 (°C) (2) In the formula, "the moisture content of the unstretched film" is the mass fraction. The method for producing a polarizing film according to claim 4, wherein a temperature T2 at which the resin film is exposed between the end of the stretching step and the dyeing of the resin film in the dyeing step is as follows (3) The relationship between the glass transition temperature A2 of the resin film shown is such that the following formula (4) is satisfied. T2 (°C) <A2 (°C) + 4 (°C) In the formula (4), the "water content of the resin film" is a mass fraction. The method for producing a polarizing film according to the fourth aspect of the invention, wherein, in the film forming step, the strip-shaped base film is conveyed in the longitudinal direction while being coated on at least one side of the base film. The polyvinyl alcohol-based resin solution is coated with the unstretched film in at least one of the area layers. The method for producing a polarizing film according to any one of claims 4 to 6, wherein the polarizing film has a thickness of 10 μm or less. The method for producing a polarizing film according to any one of claims 4 to 7, wherein in the film forming step, the water content of the coating film before the water is reduced is larger than 30% by mass. In the process of reducing water, the water removal rate when the water content of the coating film is 30% by mass is 0.01 to 1.8% by mass/second. The method for producing a polarizing film according to any one of the fourth aspect of the present invention, wherein, in the film forming step, the water content of the coating film before the water is reduced is larger than 30% by mass, and the water is In the reduction process, the water removal rate at the water content of the coating film of 30 to 10% by mass is 0.01 to 1.8% by mass/second. A method for producing a polarizing film, comprising: an extending step of extending a strip-shaped unstretched film having a polyvinyl alcohol-based resin as a material for forming in a longitudinal direction, and obtaining a resin extending from the unstretched film a film, a dyeing step of immersing the resin film dyed with the dichroic substance in a cross-linking bath containing a crosslinking agent, after dyeing the resin film in the longitudinal direction by a dichroic substance; When the resin film is dyed in the dyeing step, the temperature T2 exposed by the resin film and the glass transition temperature A2 of the resin film represented by the following formula (3) are satisfied. a method for producing a polarizing film of the above formula (4), T2 (°C) <A2 (°C) + 4 (°C) In the formula (4), the "water content of the resin film" is a mass fraction.