TW201626004A - Method for producing polarizing film, and polarizing film - Google Patents

Abstract

Provided is a method for producing a polarizing film, which comprises: a dyeing step for dyeing a polyvinyl alcohol resin film with a dichroic dye; a crosslinking step for treating the film after the dyeing step with a crosslinking agent; a first stretching step for uniaxially stretching the polyvinyl alcohol resin film during and/or before the crosslinking step; and a second stretching step for uniaxially stretching the film after the crosslinking step in a high-temperature high-humidity atmosphere wherein the temperature is 40-100 DEG C and the absolute humidity is 40 g/m3 or more. Also provided are: a polarizing film which is obtained by having a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin film, and which has a specific TD/MD ratio; and a polarizing plate which comprises this polarizing film.

Description

Polarizing film manufacturing method and polarizing film

The present invention relates to a method of producing a polarizing film which can be used as a constituent member of a polarizing plate. Further, the present invention relates to a polarizing film and a polarizing plate comprising the same.

Regarding the polarizing film, a divalent coloring matter such as iodine or a dichroic dye is adsorbed to a uniaxially stretched polyvinyl alcohol-based resin film. In general, the polarizing film is subjected to a dyeing treatment for dyeing a polyvinyl alcohol-based resin film by a dichroic dye, a crosslinking treatment by a crosslinking agent, and a uniaxial stretching treatment between the production steps. For example, Japanese Patent Laid-Open Publication No. Hei 07-325218 (Patent Document 1).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 07-325218

The polarizing film is used for an image display device represented by a liquid crystal display device. Regarding the polarizing film, a protective film is usually bonded to one surface or both surfaces thereof to form a polarizing plate, and is incorporated in an image display device. For example, a liquid crystal display device is provided with a liquid crystal panel in which a polarizing plate is bonded to both sides of a liquid crystal cell as an image display element.

In order to improve the visibility of the liquid crystal display device, it is advantageous to increase the optical characteristics (for example, the degree of polarization) of the polarizing film. In order to improve the optical characteristics, it is effective to increase the magnification of the uniaxial stretching treatment, and if the stretching ratio is increased, the contraction force in the absorption axis direction of the polarizing film (hereinafter also referred to as "MD shrinkage force") becomes large, and it is easy to cause warpage (bending) of the polarizing plate in a high-temperature environment and a high-humidity environment. The thinner the polarizer, the more significant the problem of warpage.

When the polarizing plate that has warped is bonded to the liquid crystal cell to construct a liquid crystal panel, the liquid crystal panel also warps depending on the situation. The warpage of the liquid crystal panel has a bad influence on the visibility of the liquid crystal display device.

An object of the present invention is to provide a method for producing a polarizing film which suppresses an increase in MD shrinkage force but has excellent optical characteristics. Further, another object of the present invention is to provide a polarizing film which is suppressed in the increase in MD shrinkage force and which has excellent optical characteristics, and a polarizing plate including the same.

The present invention provides a polarizing film, a polarizing film, and a method of producing a polarizing plate described below.

[1] A method for producing a polarizing film, comprising: a dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye; and a crosslinking step of treating a film after the dyeing step with a crosslinking agent; a step of uniaxially stretching the polyvinyl alcohol resin film in the crosslinking step and/or before; and a second stretching step of subjecting the film after the crosslinking step to a temperature of 40 to 100 ° C and an absolute humidity of 40 g Further uniaxial extension in a high temperature and high humidity environment of /m ³ or more.

[2] The production method according to [1], wherein the uniaxial stretching ratio in the second stretching step is 1.01 to 1.4 times.

[3] The production method according to [1] or [2], wherein the moisture content of the film is lowered by the second stretching step.

[4] The production method according to [3], wherein a difference in moisture content of the film before and after the second stretching step is less than 15% by weight.

[5] The production method according to any one of [1] to [4] wherein after the crosslinking step, Further, a washing step of washing the polyvinyl alcohol-based resin film with a washing liquid containing water is carried out, and after the washing step, the second extending step is carried out.

[6] The production method according to any one of [1] to [5] wherein the uniaxial extension of the second extension step is a dry extension.

[7] A polarizing film obtained by adsorbing a dichroic dye to a polyvinyl alcohol-based resin film, and based on an azimuthal distribution curve obtained by wide-angle X-ray diffraction measurement, according to the following formula: TD/MD ratio = (intensity of TD) / (peak intensity of MD) [In the formula, the peak intensity of MD is the average of the peak angles of the above-mentioned azimuthal distribution curves at 0° and 180°, and the intensity of TD The TD/MD ratio obtained by the average value of the intensity at the β angle of 90° and 270° is 0.142 or less when the thickness of the polarizing film is 10 μm or more, and 0.160 or less when the thickness of the polarizing film is less than 10 μm. .

[8] A polarizing plate comprising the polarizing film of [7] and a protective film laminated on at least one side thereof.

According to the present invention, it is possible to provide a polarizing film which suppresses an increase in MD shrinkage force but exhibits excellent optical characteristics, and a method for producing the same. The polarizing plate and the liquid crystal panel using the polarizing film of the present invention exhibit good visibility.

Fig. 1 is a flow chart showing an example of a method for producing a polarizing film of the present invention.

<Method of Manufacturing Polarized Film>

Referring to Fig. 1, a method for producing a polarizing film of the present invention comprises the following steps: a dyeing step S20 of dyeing a polyvinyl alcohol-based resin film with a dichroic dye; and a crosslinking step S30 of treating the dyeing step with a crosslinking agent a film; a first stretching step S40, wherein the polyvinyl alcohol resin film is uniaxially stretched in the crosslinking step and/or before; and a second stretching step S60, wherein the film after the crosslinking step is at a temperature of 40~ Further uniaxial stretching in a high temperature and high humidity environment of 100 ° C and an absolute humidity of 40 g/m ³ or more.

The method for producing a polarizing film of the present invention may further include a step other than the above, and specifically, for example, as shown in FIG. 1, a swelling step S10 performed before the dyeing step S20 and a cleaning step S50 performed after the crosslinking step S30.

The various processing steps included in the production method of the present invention can be continuously carried out by continuously transporting a polyvinyl alcohol-based resin film as a green film along the film transport path of the polarizing film production apparatus. The film transport path is provided with equipment (treatment bath, furnace, etc.) for carrying out the various processing steps described above in the order of the execution. The treatment bath means a bath containing a treatment liquid for treating a polyvinyl alcohol-based resin film, such as a swelling bath, a dye bath, a cross-linking bath, and a cleaning bath.

The film transport path can be constructed by disposing a guide roller or a nip roller or the like in an appropriate position in addition to the above-described equipment. For example, the guide rolls can be disposed before or after the respective treatment baths, whereby the introduction of the film into the treatment bath, the immersion, and the extraction from the treatment bath can be performed. More specifically, by providing two or more guide rolls in each treatment bath, the film can be conveyed along the guide rolls, and the film can be immersed in each treatment bath.

A polyvinyl alcohol-based resin constituting a polyvinyl alcohol-based resin film which is a green film can be obtained by saponifying a polyvinyl acetate-based resin. As the polyvinyl acetate-based resin, a copolymer of vinyl acetate and another monomer copolymerizable therewith is exemplified as a polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. The degree of saponification of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. In the present specification, "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. The same is true for "(meth)acrylonitrile".

The polyvinyl alcohol-based resin may be modified, and for example, an aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral or the like may be used.

The average degree of polymerization of the polyvinyl alcohol-based resin 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 polyvinyl alcohol-based resin can be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain a preferable polarizing performance, and if it exceeds 10,000, the film processability may be inferior.

The thickness of the polyvinyl alcohol-based resin film is, for example, about 10 to 150 μm, and is preferably 100 μm or less, more preferably 70 μm or less, further preferably 50 μm or less, and further preferably 40 μm from the viewpoint of thinning of the polarizing film. the following.

The polyvinyl alcohol-based resin film as the green film can be prepared, for example, in the form of a roll (rolled product) of a long stretched polyvinyl alcohol-based resin film. In this case, the polarizing film is also obtained in the form of a long strip. Hereinafter, each step will be described in detail.

(1) Swelling step S10

The swelling treatment in this step is carried out as needed for the purpose of removing foreign matter, plasticizer removal, dyeing property, plasticization of the film, etc. of the polyvinyl alcohol-based resin film as a green film, specifically, The treatment may be carried out by immersing the polyvinyl alcohol-based resin film in a swelling bath containing water. The film may be immersed in a swelling bath or sequentially immersed in two or more swelling baths. The film may also be subjected to uniaxial stretching treatment before swelling treatment, swelling treatment, or before swelling treatment and swelling treatment.

The swelling bath may be water (for example, pure water), or may be an aqueous solution containing an alcohol-like water-soluble organic solvent.

The temperature of the swelling bath when immersing the film is usually about 10 to 70 ° C, preferably about 15 to 50 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(2) Dyeing step S20

The dyeing treatment in this step is to align the dichroic dye to the polyvinyl alcohol tree. The lipid film is treated for the purpose, and specifically, the polyvinyl alcohol-based resin film may be immersed in a dye bath containing a dichroic dye. The film may be immersed in a dye bath or sequentially immersed in more than two dye baths. In order to improve the dyeability of the dichroic dye, the film for the dyeing step may also be subjected to at least some degree of uniaxial stretching treatment. The uniaxial stretching treatment may be performed at the time of the dyeing treatment instead of the uniaxial stretching treatment before the dyeing treatment, or the uniaxial stretching treatment may be performed in the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

The dichroic dye can be an iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include red BR, red LR, red R, pink LB, deep red BL, jujube GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy RY, green LG, purple LB, purple B , Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Bright Purple BK, Super Blue G, Super Blue GL, Super Orange GL, Direct Sky Blue, Directly resistant to orange S, fast tan. The dichroic dye may be used alone or in combination of two or more.

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used as the dye bath. Instead of other iodides such as zinc iodide, potassium iodide may be used, and potassium iodide may be used in combination with other iodides. Further, a compound other than the iodide such as boric acid, zinc chloride, cobalt chloride or the like may be allowed to coexist. In the case of adding boric acid, the aspect containing iodine is distinguished from the cross-linking treatment described below. The content of iodine in the above aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. Further, the content of the iodide such as potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water.

The temperature of the dye bath when immersing the film is usually about 10 to 45 ° C, preferably about 10 to 40 ° C, more preferably about 20 to 35 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably 60. ~300 seconds or so.

In the case where a dichroic organic dye is used as the dichroic dye, an aqueous solution containing a dichroic organic dye can be used as the dye bath. The content of the dichroic organic dye in the aqueous solution is usually about 1 × 10 ^-4 to 10 parts by weight, preferably about 1 × 10 ^-3 to 1 part by weight, per 100 parts by weight of water. In the dyeing bath, a dyeing aid or the like may be allowed to coexist, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic organic dye may be used alone or in combination of two or more. The temperature of the dye bath when immersing the film is, for example, about 20 to 80 ° C, preferably about 30 to 70 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

(3) Cross-linking step S30

The crosslinking treatment of the polyvinyl alcohol-based resin film after the dyeing step is treated by the crosslinking agent for the purpose of water resistance or hue adjustment based on crosslinking, and specifically, the film after the dyeing step can be used. The treatment is immersed in a crosslinking bath containing a crosslinking agent. The film may be immersed in a crosslinking bath or sequentially immersed in two or more crosslinking baths. Uniaxial stretching treatment can also be performed during the crosslinking treatment.

Examples of the crosslinking agent include boric acid, glyoxal, and glutaraldehyde, and boric acid is preferably used. Two or more kinds of crosslinking agents may also be used in combination. The content of boric acid in the crosslinking bath is usually about 0.1 to 15 parts by weight, preferably about 1 to 10 parts by weight, per 100 parts by weight of water. In the case where the dichroic dye is iodine, it is preferred that the crosslinking bath contains an iodide in addition to boric acid. The content of the iodide in the crosslinking bath is usually from about 0.1 to 15 parts by weight, preferably from about 5 to 12 parts by weight, per 100 parts by weight of water. Examples of the iodide include potassium iodide, zinc iodide, and the like. Further, a compound other than the iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate or the like may be coexisted in the crosslinking bath.

The temperature of the crosslinking bath when immersing the film is usually about 50 to 85 ° C, preferably about 50 to 70 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(4) First extension step S40

As described above, in the production of the polarizing film, the polyvinyl alcohol-based resin film is subjected to a single step in the crosslinking step S30 and/or before, that is, at any one or two stages from the self-swelling step S10 to the crosslinking step S30. Axis extension processing. From the viewpoint of improving the dyeability of the dichroic dye, the film for the dyeing step is preferably subjected to at least some degree of uniaxial stretching treatment. The film is preferably uniaxially stretched in place of the uniaxial stretching treatment before the dyeing treatment or in addition to the uniaxial stretching treatment before the dyeing treatment.

The uniaxial stretching treatment of the first extending step S40 may be either a dry extension extending in the air or a wet stretching extending in the bath, or both. The uniaxial stretching treatment may be a roll-to-roll extension, a heat roll extension, a tenter stretching, or the like which imparts a longitudinal uniaxial extension between the two nip rolls, and preferably includes an inter-roller extension. The blank film is used as a reference stretching ratio (the cumulative stretching ratio when the film is stretched in two or more stages) is about 3 to 8 times. In order to impart good polarizing characteristics, the stretching ratio is preferably 4 times or more, more preferably 4.5 times or more. Further, since the manufacturing method of the present invention includes the second extending step S60, the stretching ratio of the first extending step S40 may be 7 times or less, further 6 times or less, and further 5 times or less.

(5) Cleaning step S50

The cleaning treatment in this step is carried out as needed for the purpose of removing a chemical agent such as an excess cross-linking agent or a dichroic dye attached to the polyvinyl alcohol-based resin film, and is a step of washing and crosslinking using a washing liquid containing water. The subsequent treatment with a polyvinyl alcohol-based resin film. Specifically, it can be a process of immersing the polyvinyl alcohol-based resin film after the crosslinking step in a cleaning bath (cleaning liquid). The film may be immersed in a clear bath or may be immersed in two or more cleaning baths in sequence. Alternatively, the cleaning treatment may be a treatment in which the cleaning liquid is sprayed in the form of a shower to the polyvinyl alcohol-based resin film after the crosslinking step, or may be a combination of the above-mentioned immersion and spraying.

The washing liquid may be water (for example, pure water), or may be an aqueous solution to which an alcohol-like water-soluble organic solvent is added. The temperature of the cleaning liquid can be, for example, about 5 to 40 °C.

The cleaning step S50 is an arbitrary step, and may be omitted. The cleaning process may be performed in the second extending step S60 as follows (the high-temperature and high-humidity treatment in the second extending step S60 may also serve as a cleaning process). It is preferable that the film after the cleaning step S50 is subjected to the second stretching step S60.

(6) Second extension step S60

In the second extension treatment of the step, the film after the crosslinking step S30 is further uniaxially stretched in a high-temperature and high-humidity environment having a temperature of 40 to 100 ° C and an absolute humidity of 40 g/m ³ or more, in other words, it is high in temperature and high temperature. The wet processing is performed simultaneously with the uniaxial stretching process. In the case where the washing step S50 is carried out, it is preferred to carry out the second stretching treatment on the film after the washing step. In the case where the drying treatment (high temperature treatment when the absolute humidity is less than 40 g/m ^{3 )} is performed after the cleaning step S50, it is preferred to carry out the second stretching treatment on the film after the drying treatment.

By performing the second stretching process, even when the stretching ratio of the first stretching step S40 is controlled to be low, it is possible to ensure a sufficient stretching ratio as the total stretching magnification, and it is possible to impart excellent optical characteristics to the polarizing film. Further, since the stretching treatment is performed in a high-temperature and high-humidity environment, the increase in the MD contraction force can be effectively suppressed. The reason why the improvement of the optical characteristics and the increase in the MD shrinkage force can be simultaneously suppressed is that the alignment treatment in a high-temperature and high-humidity environment can improve the alignment of the dichroic dye, and on the other hand, the polarizing film can be formed. The alignment of the molecular chain of the polyvinyl alcohol-based resin is lowered, whereby the increase in the residual stress in the film can be suppressed. In summary, the thinner the film becomes, the more difficult it is to exhibit excellent optical properties. Therefore, the present invention is particularly effective in the case where the film used is thin, for example, in the case of using a green film having a thickness of 40 μm or less.

On the other hand, when the second stretching step S60 is not provided and only the stretching ratio of the first extending step S40 is increased to obtain good optical characteristics, the MD shrinkage force rises, causing a problem of warpage of the polarizing plate or even the liquid crystal panel. .

By providing the second extending step S60 and performing the stretching treatment in a high-temperature and high-humidity environment, it is possible to prevent the film from being broken and to effectively increase the total stretching ratio (plus the cumulative stretching ratio of the stretching in the first extending step S40). It is also advantageous, and it is also advantageous in terms of an increase in the area of acquisition of the polarizing film which increases the total stretch ratio and a decrease in the production unit.

The uniaxial stretching process in the second extending step S60 is usually a dry stretching because it needs to be extended in a high-temperature and high-humidity environment. Uniaxial extension treatment can be between 2 nip rolls The inter-roller extension, the heat roll extension, the tenter extension, and the like which impart a longitudinal uniaxial extension to the circumferential speed difference are preferably extended between the rolls. The stretching ratio in this step is usually 1.01 to 1.4 times, and from the viewpoint of improvement in optical characteristics, it is preferably 1.1 to 1.4 times. It is advantageous to set the stretching ratio to 1.4 times or less in terms of suppressing an increase in MD shrinkage force or film breakage.

The stretching treatment in a high-temperature and high-humidity environment may be performed by, for example, introducing a film after the crosslinking step S30 into a furnace (heating furnace) or a shed or a room in which temperature and humidity can be adjusted, and performing high-temperature and high-humidity treatment. . Regarding the high-temperature and high-humidity treatment, in addition to the treatment introduced into the furnace (heating furnace) or the shed or the room, a heating mechanism such as a far-infrared heater or a heat roller may be used in combination. The second extending step S60 is preferably performed after the cleaning step S50, and the stretching treatment and the cleaning treatment in a high-temperature and high-humidity environment are simultaneously performed, for example, the cleaning liquid is sprayed while being extended in a specific high-temperature and high-humidity environment, and The second extending step S60 may also serve as a cleaning process, and for example, a film cleaning may be performed substantially by placing it in a high-temperature and high-humidity environment.

When the ambient temperature of the second stretching treatment is 40° C. or higher as described above, the viewpoint of more effectively suppressing the increase in the MD shrinkage force and maintaining the transportability of the film to be good are preferably 55° C. or more. Good is above 60 °C. Further, the ambient temperature is 100 ° C or less as described above, and from the viewpoint of obtaining excellent optical characteristics, it is preferably 90 ° C or lower.

The absolute humidity of the environment in which the second stretching treatment is performed is 40 g/m ³ or more as described above, and is preferably 75 g/m ³ or more, and more preferably 85 g/m from the viewpoint of more effectively suppressing an increase in MD shrinkage force. ³ or more, further preferably 100 g/m ³ or more. On the other hand, if the absolute humidity is too high, there is a fear of occurrence of condensation in the treatment area or contamination of the film by the condensed water, so the absolute humidity is preferably 550 g/m ³ or less, more preferably 400 g/m ³ or less. Further, it is preferably 300 g/m ³ or less, and particularly preferably 160 g/m ³ or less.

The time for the second stretching treatment, that is, the time for the high-temperature and high-humidity treatment, is more preferably 5 seconds or more, and even more preferably 10, from the viewpoint of more effectively suppressing the increase in the MD shrinkage force and obtaining excellent optical characteristics. More than two seconds. Again, this time also depends on the temperature, if If it is long, the optical characteristics are deteriorated. Therefore, it is preferably 60 minutes or shorter, more preferably 30 minutes or shorter, further preferably 10 minutes or shorter, and particularly preferably 5 minutes or shorter.

In the second extension treatment, the long-length polyvinyl alcohol-based resin film is conveyed along the film transport path, and is continuously introduced into the furnace or the like to be passed through and extended, and the elongation treatment in such a high-temperature and high-humidity environment is performed. The tension of the film is preferably from 50 to 5,000 N/m from the viewpoint of more effectively suppressing an increase in MD shrinkage force. The film tension is more preferably from 300 to 1,500 N/m from the viewpoint of suppressing generation of wrinkles of the film.

The second stretching treatment may also serve as a treatment for drying the polyvinyl alcohol-based resin film, that is, a treatment for lowering the water content, and the drying treatment is usually carried out at the same time as long as the extreme high-temperature and high-humidity conditions are not employed. Thereby, it is not necessary to separately perform a drying process before or after the 2nd extension process.

The moisture content of the film for the second extension treatment depends on the thickness of the film, and is usually about 13 to 50% by weight. Further, the degree of reduction in the moisture content obtained by the second stretching treatment, that is, the difference between the moisture content before the second stretching treatment and the moisture ratio after the second stretching treatment (the moisture ratio difference ΔS) also depends on the thickness of the film. For example, it is 5 to 45% by weight, preferably 8 to 35% by weight. For example, when the thickness of the green film is about 40 μm or less, the moisture content difference ΔS may be less than 15% by weight.

Further, the moisture content of the film after the second stretching treatment (the polarizing film in the case where the second stretching treatment is the final step) depends on the thickness of the film, and is usually 5 to 30% by weight, and the film is transported thereafter. From the viewpoint of sex, it is preferably from 6 to 15% by weight. When the water content is too low, the film is likely to be broken during transportation, and if the moisture content is too high, it is likely to cause curling at the end portion of the film due to moisture release.

In short, the thinner the film, the more easily the water is dissipated. Therefore, the thinner the green film, the easier the water content in the second stretching treatment and the second stretching treatment is. When the moisture content is too low, the transportability of the film is liable to lower. Therefore, when the thickness of the green film is about 40 μm or less, the temperature of the second stretching treatment is set to be low, preferably 40 to 70 °C.

The second extending step S60 may be performed immediately after the crosslinking step S30 or the washing step S50, or may be performed after performing the other steps after the crosslinking step S30 or the washing step S50. As another step, a drying treatment (high temperature treatment when the absolute humidity is less than 40 g/m ³ ) may be mentioned. However, from the viewpoint of more effectively suppressing an increase in MD shrinkage force, it is preferred to directly supply the film of the crosslinking step S30 or the cleaning step S50 to the second stretching step S60.

Through the above steps, a polarizing film obtained by adsorbing a dichroic dye to a uniaxially stretched polyvinyl alcohol-based resin film can be obtained. The thickness of the polarizing film is usually 5 to 40 μm, preferably 30 μm or less. According to the polarizing film obtained by the present invention, even when the thickness is 30 μm or less and further 25 μm or less, excellent optical characteristics can be obtained, and an increase in MD shrinkage force can be suppressed.

For example, in order to adjust the water content, the drying treatment (high temperature treatment when the absolute humidity is less than 40 g/m ³ ) may be performed after the second stretching step S60. However, since the moisture content can be adjusted by the second extending step S60, the drying process is performed as needed.

The obtained polarizing film can be directly transferred, for example, to the subsequent polarizing plate producing step (step of bonding the protective film to one side or both sides of the polarizing film).

In one embodiment, the polarizing film of the present invention is a film obtained by adsorbing a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film, and is capable of diffraction by wide-angle X-ray (WAXD: Wide Angle X) - ray Diffraction) The TD/MD ratio of the alignment of the polyvinyl alcohol-based resin constituting the polarizing film on the MD is characteristic. By having such a feature, it is estimated that the polarizing film of the present embodiment can exhibit the following characteristics and effects, that is, the increase in the MD shrinkage force is suppressed, and the optical characteristics are excellent.

Specifically, when the thickness of the polarizing film of the present embodiment is 10 μm or more, the TD/MD is preferably 0.142 or less, more preferably 0.14 or less, still more preferably 0.13 or less, still more preferably 0.11 or less. The TD/MD ratio of the polarizing film is usually 0.02 or more, preferably 0.08 or more, when the thickness thereof is 10 μm or more. The thickness of the polarizing film having a thickness of 10 μm or more is usually 30 μm or less, preferably 15 μm or less, and more preferably 14 or less. Below μm, further preferably, it is 11 μm or more, and more preferably 12 μm or more.

In the polarizing film of the present embodiment, when the thickness is less than 10 μm, the TD/MD is preferably 0.160 or less, more preferably 0.155 or less, still more preferably 0.148 or less. The TD/MD ratio of the polarizing film is usually 0.02 or more, preferably 0.13 or more, when the thickness thereof is less than 10 μm. The thickness of the polarizing film having a thickness of less than 10 μm is usually 3 μm or more, preferably 7 μm or more, and more preferably 9 μm or less.

The polarizing film showing the above TD/MD ratio can be preferably produced by the above-described method for producing a polarizing film of the present invention. The TD/MD ratio described herein is determined in accordance with the method described in the following examples.

Further, in another embodiment, the polarizing film of the present invention is a film obtained by adsorbing a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film, and may be a crosslinking agent based on a polarizing film. The ratio of the Raman scattered light intensity in the absorption axis direction to the Raman scattered light intensity in the transmission axis direction (hereinafter also referred to as "Raman scattered light intensity ratio") in the cross-linked state wave number of 775 cm ^-1 is characteristic. By having such a feature, it is estimated that the polarizing film of the present embodiment can exhibit the following characteristics and effects, that is, the increase in the MD shrinkage force is suppressed, and the optical characteristics are excellent.

Specifically, in the polarizing film of the present embodiment, the intensity of the Raman scattered light is preferably 0.81 or more, more preferably 0.87 or more. The Raman scattered light intensity ratio is usually 1.00 or less, preferably 0.95 or less.

The polarizing film which exhibits the above-described Raman scattered light intensity ratio can be preferably produced by the above-described method for producing a polarizing film of the present invention. The Raman scattered light intensity ratio described herein was measured in accordance with the method described in the following examples.

In still another embodiment, the polarizing film of the present invention is a film obtained by adsorbing a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film, and exhibiting a TD/MD ratio within the above range, and displaying the above Raman scattered light intensity ratio in the range. It is advantageous to display the above in terms of achieving excellent optical characteristics while suppressing an increase in MD shrinkage force. The TD/MD ratio within the range and shows the Raman scattered light intensity ratio within the above range.

<Polarizing plate>

The protective film can be obtained by laminating (layering) the protective film on at least one side of the polarizing film manufactured as above or displaying at least one of the above TD/MD ratio and the Raman scattered light intensity ratio. Polarizer. The protective film may be a transparent resin film containing a thermoplastic resin, for example, a chain polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin. a polyolefin resin such as an olefin resin; a cellulose ester resin such as triethylene fluorene cellulose or diethyl phthalocyanine; polyethylene terephthalate, polyethylene naphthalate, poly pair A polyester resin such as butyl phthalate; a polycarbonate resin; a (meth)acrylic resin such as a polymethyl methacrylate resin; or a mixture or a copolymer thereof.

The protective film may be one of a retardation film and a brightness enhancement film and has an optical function protective film. For example, a retardation film to which an arbitrary retardation value is imparted can be produced by stretching a transparent resin film containing the above material (uniaxial stretching or biaxial stretching or the like) or forming a liquid crystal layer or the like on the film.

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 opposite to the polarizing film.

The thickness of the protective film is preferably thinner from the viewpoint of thinning of the polarizing plate, but if it is too thin, the strength is lowered and the workability is poor, so it is preferably 5 to 150 μm, more preferably 5 to 100 μm. It is preferably 10 to 50 μm.

Examples of the adhesive for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet curable adhesive, or an aqueous solution of a polyvinyl alcohol-based resin, or a crosslinking agent thereof. It is an aqueous solution, a urethane-based emulsion adhesive like a water-based adhesive. When the protective film is bonded to both surfaces of the polarizing film, the adhesives forming the two adhesive layers may be of the same kind or different types. For example, when the protective film is attached to both sides, it is also possible to use a water-based adhesive on one side and a single-sided use on the other side. The performance amount line hardenable adhesive is applied. The ultraviolet curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as a starting agent.

In the case of using an active energy ray-curable adhesive, the adhesive is hardened by irradiation of the active energy ray after bonding. The light source of the active energy ray is not particularly limited, and is preferably an active energy ray (ultraviolet light) having a light-emitting distribution at a wavelength of 400 nm or less. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, or the like is preferably used. Chemical lamps, black lamps, microwave-excited mercury lamps, metal halide lamps, etc.

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing film and/or the protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation before bonding between the polarizing film and the protective film. Surface treatment such as treatment, primer coating treatment, saponification treatment, and the like.

As described above, the polarizing plate of the present invention can be produced by laminating a protective film on a polarizing film as a single layer film, but is not limited to this method, and can be, for example, Japanese Patent Laid-Open Publication No. 2009-98653 It is produced by the method of using a base film. The latter method is advantageous for obtaining a polarizing plate having a film polarizing film (polarizing element layer), and for example, may include the following steps.

a resin layer forming step of applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of a base film, followed by drying to form a polyvinyl alcohol-based resin layer to obtain a laminated film, and an extending step of The laminated film is stretched to obtain a stretched film, and the dyeing step is performed by dyeing a polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form a polarizing element layer (corresponding to a polarizing film), thereby obtaining a polarizing laminated film; a bonding step of bonding a protective film to a polarizing laminated film using an adhesive A bonding film is obtained on the optical element layer, and a peeling step of peeling off the base film from the bonding film to obtain a polarizing plate with a single-sided protective film.

In the case of the double-layer protective film of the polarizing element layer (polarizing film), the second bonding step is further included, and the protective film is bonded to the polarizing element surface of the polarizing plate with the single-sided protective film using an adhesive. .

Regarding the above method of using the substrate film, the second stretching step can be included in the dyeing step of obtaining the polarizing laminated film (for example, after the crosslinking step in the dyeing step of obtaining the polarizing laminated film or after the washing step). The polarizing laminated film, the polarizing plate with the single-sided protective film, and the polarizing film included in the polarizing plate with the double-sided protective film obtained by the second bonding step or the polarizing film from the single-sided polarizing film In the polarizing film of the present invention, it is preferred to exhibit at least one of a TD/MD ratio within the above range and a Raman scattered light intensity ratio within the above range.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples.

<Example 1>

A polyvinyl alcohol (PVA) green film having a thickness of 30 μm [trade name "Keleli polyvinyl alcohol film VF-PE #3000" manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol% The above was continuously carried out while being rolled off from the roll, and was immersed in a swelling bath containing pure water at 20 ° C for 31 seconds (swelling step). Thereafter, the film taken out from the swelling bath was immersed in a dye bath containing iodine at 30 ° C (dyeing step) with a potassium iodide/water ratio of 2/100 (weight ratio) for a residence time of 122 seconds. Next, the film drawn from the dyeing bath was immersed in a crosslinking bath of potassium iodide/boric acid/water of 12/4.1/100 (weight ratio) at 56 ° C for 70 seconds, and then immersed in potassium iodide at a residence time of 13 seconds. The boric acid/water is a cross-linking bath of 40° C. of 9/2.9/100 (weight ratio) (crosslinking step). In the dyeing step and the crosslinking step, by the roller in the bath The extension is performed in a longitudinal uniaxial extension (first extension step). The total stretching ratio D1 based on the green film was set to 5.36 times.

Next, the film taken out from the cross-linking bath was immersed in a cleaning bath containing pure water at 5 ° C for 3 seconds (washing step). Then, the high-temperature and high-humidity treatment was carried out by introducing into a heating furnace capable of adjusting humidity with a residence time of 189 seconds, and the vertical uniaxial stretching treatment (second stretching step) was carried out by stretching between rolls in the air to obtain a thickness of 12.6 μm. A polarizing film with a width of 208 mm. The temperature and absolute humidity in the heating furnace were set to 60 ° C and 78 g/m ³ , respectively, and the film tension in the second extension step was set to 755 N/m. Immediately before the introduction of the heating furnace (second stretching step), the moisture content of the film immediately after the introduction of the heating furnace (second stretching step) was 19.0% by weight and 9.2% by weight, respectively, and the moisture content difference ΔS was 9.8% by weight. Further, in the second extending step, the stretching ratio D2 based on the film immediately before introduction into the heating furnace was set to 1.01 times.

<Examples 2 to 10, Comparative Examples 1 to 2>

The total stretching ratio D1 in the first stretching step, the temperature and absolute humidity in the heating furnace, the stretching ratio D2 in the second stretching step, the residence time in the heating furnace, and the film tension in the second stretching step are as shown in Table 1. A polarizing film was produced in the same manner as in Example 1 except for the above.

In Comparative Examples 1 and 2, the temperature and absolute humidity in the heating furnace were 60 ° C and 12 g/m ³ , respectively, and the heating (drying) treatment was performed without performing high-temperature and high-humidity treatment in the heating furnace. Further, the stretching treatment is not performed in the heat treatment. In Examples 6 to 8, the total stretching ratio D1 in the first stretching step was set to be 4.81 times lower than 5.36 times in Example 1, by reducing the magnification of the stretching in the crosslinking step.

The production conditions of the polarizing film in each of the examples and the comparative examples, the moisture content of the film immediately after the introduction of the heating furnace (the second stretching step) and immediately after the introduction of the heating furnace (the second stretching step) are used as the The poor moisture content difference ΔS and the thickness and width of the obtained polarizing film are summarized in Table 1.

Furthermore, the absolute humidity in the furnace is determined according to the temperature and relative humidity in the furnace. The value is calculated. The thickness of the obtained polarizing film was measured using a digital micrometer "MH-15M" manufactured by Nikon Co., Ltd. Further, the moisture content of the film (polarizing film) was determined by the following method.

A plurality of polarizing film samples having different moisture contents were used in advance, and the moisture content obtained by the dry weight method was correlated with the measured value of the infrared absorption type moisture meter ("IM 3SCV MODEL-1900L" manufactured by Fujiwork Co., Ltd.). The calibration curve (converted formula) was obtained by the following formula: the water content (% by weight) obtained by the dry weight method = 0.0495 × (measured value of moisture meter) - 38.8379. In this case, the moisture content obtained by the dry weight method is set to W1 when the weight of the polarizing film is dried at 105 ° C for 2 hours, and the weight of the polarizing film before drying is set to W0, according to the following formula: The water content (% by weight) obtained by the dry weight method was determined by {(W0 - W1) ÷ W0} × 100. The water content shown in Table 1 was obtained by using the above-described moisture meter, and was substituted into the above calibration curve (converted formula), and converted into a water content (% by weight) obtained by a dry weight method. The water content difference ΔS is calculated by subtracting the water content immediately after introduction from the moisture rate immediately before introduction into the heating furnace.

[Evaluation of polarizing film]

The characteristics of the polarizing film obtained by each of the examples and the comparative examples were measured for the following items. The results are shown in Table 1.

(1) Optical properties

For the obtained polarizing film, the MD transmittance and the TD transmittance in the range of 380 to 780 nm are measured using a spectrophotometer with an integrating sphere [V7100 manufactured by JASCO Corporation], based on the following formula: Volume transmittance (%) = (MD + TD) / 2 degree of polarization (%) = {(MD-TD) / (MD + TD)} × 100 The monomer transmittance and the degree of polarization at each wavelength were calculated. Further, based on the following formula: A400 = LOG [100 / {TD transmittance (%) at a wavelength of 400 nm}] A700 = LOG [100 / {TD transmittance (%) at a wavelength of 700 nm}] Calculated at a wavelength of 400 nm Absorbance (A400) and absorbance at a wavelength of 700 nm (A700).

The "MD transmittance" is a transmittance when the orientation of the polarized light emitted from the Glan-Thompson is parallel to the transmission axis of the polarizing film sample, and is expressed as "MD" in the above formula. In addition, the "TD transmittance" is a transmittance when the orientation of the polarized light emitted from the Glan-Thompson is orthogonal to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula. The transmittance and the degree of polarization of the obtained monomer are based on a 2 degree field of view (C light source) of JIS Z 8701:1999 "Color expression method - XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system". Correction, obtain the visibility correction monomer transmittance (Ty) and the visibility correction polarization (Py).

(2) MD contraction force

A measurement sample having a width of 2 mm in length and a length of 10 mm in the absorption axis direction (MD, extending direction) was cut out from the obtained polarizing film. The sample was placed in a thermomechanical analyzer (TMA) "EXSTAR-6000" manufactured by SII NanoTechnology Co., Ltd., and the size was kept constant, and the long-side direction generated at 80 ° C for 4 hours was measured ( The contraction force (MD contraction force) of the absorption axis direction, MD).

(3) TD/MD ratio

The "TD/MD ratio" indicating the orientation of the polyvinyl alcohol-based resin constituting the polarizing film on the MD was determined by a pass method of Wide Angle X-ray Diffraction (WAXD). First, a plurality of sheets are cut out from the obtained polarizing film, and the absorption axis direction (MD, extending direction) is a rectangular film of the long side. The cut film was superposed and fixed in such a manner that the MDs (long sides) were parallel, and this was used as a sample for measurement. The thickness of the sample for measurement was set to about 0.1 mm. X-rays were irradiated onto the surface of one of the measurement samples by the following X-ray output conditions in the direction perpendicular to the surface of the measurement sample by the following X-ray diffraction apparatus, and a diffraction image by the transmission method was taken.

X-ray diffraction device: "NANO-Viewer" manufactured by Rigaku Co., Ltd., X-ray output conditions: Cu target, 40 kV, 20 mA.

According to the obtained diffraction image, with respect to the peak near the diffraction angle 2θ=20°, the uncorrected azimuth distribution curve (the azimuth angle (β angle) is first calculated by circularly integrating the range of 2θ=19.5 to 20.5°. ) - intensity distribution curve). The uncorrected azimuth distribution curve means an azimuthal distribution curve before the background correction is performed. Next, the measurement sample was taken out from the optical axis of the X-ray, and the measurement was performed under the same conditions to calculate the base of the azimuthal distribution curve. After the transmittance correction is performed, the base is removed from the uncorrected azimuth distribution curve, and the azimuth distribution curve after the base correction (hereinafter also referred to as "azimuth distribution curve") is obtained. The peak of the azimuthal distribution curve is an orientation peak. In the present measurement, the MD of the measurement sample was set to the vertical direction, and the β angle at the maximum intensity of the alignment peak appearing in the horizontal direction was set to 0°. The β angle (0° and 180°) at the maximum intensity of the alignment peak is derived from the composition of the MD that is aligned to the polarizing film. Based on the obtained azimuth distribution curve, the TD/MD ratio is obtained according to the following formula: TD/MD ratio = (intensity of TD) / (peak intensity of MD). The peak intensity of MD means the average of the peak intensities at a β angle of 0° and 180°. The intensity of TD means the intensity at a β angle of 0° from the β angle and 90° from the 180°, that is, the average of the intensity at a β angle of 90° and the intensity at a β angle of 270°. Regarding all the orientation peaks existing in the azimuthal distribution curve, the average value of the TD/MD ratio obtained by the above equation is set to "TD/MD ratio" in the present specification.

(4) Raman scattered light intensity ratio

In order to obtain the Raman scattered light intensity ratio of the obtained polarizing film, and the dye bath did not contain iodine, a film for analysis was produced in the same manner as in each of the examples and the comparative examples. It was confirmed that the obtained Raman scattered light intensity ratio of the polarizing film was the same as the Raman scattered light intensity ratio of the film for analysis.

For the obtained analysis film, a laser Raman spectrophotometer "NRS-5100" manufactured by JASCO Corporation was used according to the following formula: Raman scattered light intensity ratio = (analysis at wave number 775 cm ^-1 ) Raman scattered light intensity of Raman scattered light intensity) / (wave number of 775cm extending direction of the film orthogonal to the direction of analysis of the film under the extending direction of ^-1) to obtain a wavenumber of 775cm ^-1 absorption axis The ratio of the Raman scattered light intensity in the direction to the Raman scattered light intensity in the transmission axis direction (Raman scattered light intensity ratio) is taken as the Raman scattered light intensity ratio of the obtained polarizing film.

Here, the Raman scattered light intensity in the extending direction of the analysis film at a wave number of 775 cm ^-1 is such that the laser light is perpendicular to the surface of the analysis film in such a manner that the polarizing surface of the laser light and the extending direction of the analysis film are parallel. The incidence was measured such that the polarizing surface of the phosphor beam and the polarizing surface of the laser beam were parallel. Similarly, the Raman scattered light intensity in the direction orthogonal to the extending direction of the analysis film at a wave number of 775 cm ^-1 is such that the laser light is self-analyzed in such a manner that the polarizing surface of the laser light is orthogonal to the extending direction of the analysis film. The surface of the film was incident perpendicularly, and the polarizing surface of the phosphor beam was measured in parallel with the polarizing surface of the laser light.

The conditions for the above Raman spectrometry are as follows.

‧Excitation wavelength: 532 nm, ‧Grating: 600 l/mm, ‧Slit width: 100×1000 μm, ‧Aperture: 40μm, ‧ objective lens: 100 times.

<Example 11>

A polyvinyl alcohol (PVA) green film having a thickness of 20 μm [trade name "Keleli polyvinyl alcohol film VF-PE#2000" manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol% The above-mentioned one side was continuously conveyed from the roll, and the dry uniaxially stretched 4.1 times, and kept in a stretched state, and immersed in a swelling bath containing pure water of 30 ° C for a residence time of 50 seconds (swelling step) ). Thereafter, the film taken out from the swelling bath was immersed in a dye bath containing iodine at 30 ° C in a potassium iodide/water ratio of 5/100 (weight ratio) for a residence time of 88 seconds (dyeing step). Next, the film taken out from the dyeing bath was immersed in a cross-linking bath of 65 ° C of potassium iodide/boric acid/water of 18/5.6/100 (weight ratio) for a residence time of 115 seconds (crosslinking step). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching is further carried out by stretching between rolls in the bath. The total stretching ratio D1 based on the green film was set to 4.26 times.

Next, the film extracted from the self-crosslinking bath was immersed in a cleaning bath containing pure water at 4 ° C for 7 seconds (washing step), and then introduced into a furnace with adjustable humidity for a residence time of 95 seconds. In the high-temperature and high-humidity treatment, a longitudinal uniaxial stretching treatment (second stretching step) was carried out by stretching between rolls in the air to obtain a polarizing film having a thickness of 8.0 μm and a width of 218 mm. The temperature and absolute humidity in the heating furnace were respectively set to 70 ° C and 133 g/m ³ , and the film tension in the second extension step was set to 280 N/m. Immediately before the introduction of the heating furnace (the second stretching step), the moisture content of the film immediately after the introduction of the heating furnace (second stretching step) was 15.1% by weight and 11.4% by weight, respectively, and the moisture content difference ΔS was 3.7% by weight. Further, in the second stretching step, the stretching ratio D2 based on the film immediately before introduction into the heating furnace was set to 1.05 times.

<Example 12, Comparative Examples 3 to 4>

The temperature and absolute humidity in the heating furnace, the stretching ratio D2 in the second stretching step, the residence time in the heating furnace, and the film tension in the second stretching step are as shown in Table 2, and the examples and examples are given. 11 A polarizing film was produced in the same manner.

The production conditions of the polarizing films of Examples 11 to 12 and Comparative Examples 3 to 4, immediately before the introduction of the heating furnace (the second stretching step), and immediately after the introduction of the heating furnace (the second stretching step) The moisture content of the film, the moisture content difference ΔS as the difference, and the thickness and width of the obtained polarizing film are summarized in Table 2. Further, regarding the above items, the characteristics of the polarizing films of Examples 11 to 12 and Comparative Examples 3 to 4 were measured. The results are shown in Table 2.

<Example 13>

(1) Fabrication of substrate film

By a co-extrusion molding using a multilayer extrusion molding machine, a random copolymer containing propylene/ethylene containing about 5% by weight of an ethylene unit (Sumitomo Noblen W151, manufactured by Sumitomo Chemical Co., Ltd.), melting point Tm, was produced. A resin layer containing a homopolymer of propylene as a homopolymer of propylene (trade name "Sumitomo Noblen FLX80E4" manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 163 ° C) is disposed on both sides of the resin layer of 138 ° C) A substrate film of a layer structure. The total thickness of the obtained base film is 100 μm, and the thickness ratio of each layer (FLX80E4/W151/FLX80E4) is 3/4/3.

(2) Preparation of coating liquid for forming an undercoat layer

Polyvinyl alcohol powder (trade name "Z-200" manufactured by Nippon Synthetic Chemical Co., Ltd., average polymerization degree 1100, saponification degree 99.5 mol%) was dissolved in hot water at 95 ° C to prepare a concentration of 3% by weight. Aqueous vinyl alcohol solution. A cross-linking agent (trade name "Sumirez Resin 650" manufactured by Tajika Chemical Industry Co., Ltd.) was mixed with the obtained aqueous solution in a ratio of 1 part by weight based on 2 parts by weight of the polyvinyl alcohol powder to obtain an undercoat layer. Coating solution.

(3) Preparation of coating liquid for forming polyvinyl alcohol-based resin layer

Polyvinyl alcohol powder (trade name "PVA124" manufactured by Kuraray Co., Ltd., average polymerization degree 2400, average saponification degree 98.0-99.0 mol%) was dissolved in hot water at 95 ° C to prepare polyethylene having a concentration of 8 wt%. An aqueous alcohol solution was used to prepare a coating liquid for forming a polyvinyl alcohol-based resin layer.

(4) Formation of a polyvinyl alcohol-based resin layer

The substrate film produced in the above (1) is continuously conveyed, and one surface thereof is subjected to corona treatment, and then the corona-treated surface is continuously coated with the above-mentioned (2) using a small-diameter gravure coater. The coating liquid for forming an undercoat layer prepared in the above was dried at 60 ° C for 3 minutes, thereby forming an undercoat layer having a thickness of 0.2 μm. Then, the coating liquid for forming a polyvinyl alcohol-based resin layer prepared in the above (3) was continuously applied onto the undercoat layer by a Kama coater, and dried at 90 ° C for 4 minutes. A polyvinyl alcohol-based resin layer (hereinafter referred to as "first PVA layer") having a thickness of 9.5 μm was formed on the undercoat layer.

Then, on the surface opposite to the surface on which the first PVA layer was formed, a primer layer having a thickness of 0.2 μm was formed in the same manner as described above, and a polyvinyl alcohol resin was coated on the undercoat layer. The coating liquid for layer formation was dried at 90 ° C for 4 minutes to form a polyvinyl alcohol-based resin layer (hereinafter referred to as "second PVA layer") having a thickness of 9.4 μm on the undercoat layer, and was obtained on both sides. A laminate film of the PVA layer.

(5) Production of stretch film

The laminated film produced in the above (4) was continuously conveyed, and uniaxially stretched in the longitudinal direction (film transport direction) at a stretching temperature of 160 ° C at a stretching temperature of 160 ° C to obtain a laminated film produced in the above (4). Stretch film (first extension step). Regarding the stretched film, the thickness of the first PVA layer was 5.0 μm, and the thickness of the second PVA layer was 4.9 μm.

(6) Production of a polarizing laminated film including a polarizing film (polarizing element layer)

The stretched film produced in the above (5) was immersed in a dye bath containing iodine at 30 ° C in a 7.5/100 (by weight) potassium iodide/water retention time for 230 seconds (dyeing step). Next, the film extracted from the dyeing bath was immersed in a crosslinking bath of 78 ° C of potassium iodide/boric acid/water of 10/9.5/100 (weight ratio) for 240 seconds, and then immersed in potassium iodide with a residence time of 77 seconds. / Boric acid / water is 4.5 / 5.0 / 100 (by weight) in a 70 ° C cross-linking bath (crosslinking step).

Next, the film extracted from the self-crosslinking bath was immersed in a cleaning bath containing pure water at 4 ° C for a residence time of 22 seconds (cleaning step), and then, by introducing into a heating furnace capable of adjusting humidity, the residence time was obtained. The high-temperature and high-humidity treatment was performed for 276 seconds, and the vertical uniaxial stretching treatment (second stretching step) was performed by stretching between the rolls in the air to obtain a polarizing film (polarizing element layer) including the first and second PVA layers. A polarizing laminated film. The temperature and absolute humidity in the heating furnace were set to 80 ° C and 117 g/m ³ , respectively, and the film tension in the second stretching step was set to 1338 N/m. The moisture content of the film immediately after the introduction of the heating furnace (the second stretching step) and immediately after the introduction of the heating furnace (second stretching step) was 18.2% by weight and 10.6% by weight, respectively, and the moisture content difference ΔS was 7.6% by weight. Further, in the second stretching step, the stretching ratio D2 based on the film immediately before introduction into the heating furnace was set to 1.05 times.

<Comparative Example 5>

The polarizing film was produced in the same manner as in Example 13 except that the temperature and the absolute humidity in the heating furnace, the stretching ratio D2 in the second stretching step, and the film tension in the second stretching step were as shown in Table 3. . In Comparative Example 5, the temperature and the absolute humidity in the heating furnace were 65 ° C and 8 g/m ³ , respectively, and the heating and drying treatment was not performed in the heating furnace, and only the heating (drying) treatment was performed, and the elongation was not performed (D2). = 1.00 times).

The production conditions of the polarizing laminated film of Example 13 and Comparative Example 5, the moisture content of the polarizing film immediately before the introduction of the heating furnace (the second stretching step) and immediately after the introduction of the heating furnace (the second stretching step), and The moisture content difference ΔS as the difference is summarized in Table 3. Further, regarding the above items (excluding the TD/MD ratio), the characteristics of the polarizing films of Example 13 and Comparative Example 5 were measured. The results are shown in Table 3. Furthermore, in the measurement of the optical characteristics of the spectrophotometer ("V7100" manufactured by JASCO Corporation] using an integrating sphere, the obtained polarizing laminated film is peeled off and removed by the first PVA layer. A laminated film of a polarizing film was used as a measurement sample. At this time, light was incident from the side of the polarizing film (the polarizing film formed of the second PVA layer). Further, the MD contraction force is obtained by taking only the polarizing film formed of the second PVA layer from the obtained polarizing laminated film, and using this as a measurement sample.

Claims (8)

A method for producing a polarizing film, comprising: a dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye; a crosslinking step of treating a film after the dyeing step with a crosslinking agent; and a first stretching step The polyvinyl alcohol-based resin film is uniaxially stretched in the above-mentioned crosslinking step and/or before, and the second stretching step is such that the film after the crosslinking step is at a temperature of 40 to 100 ° C and an absolute humidity of 40 g/m ³ Further uniaxial stretching in the above high temperature and high humidity environment. The manufacturing method of claim 1, wherein the uniaxial stretching ratio in the second extending step is 1.01 to 1.4 times. The manufacturing method of claim 1 or 2, wherein the moisture content of the film is lowered by the second stretching step. The method of claim 3, wherein the moisture content difference of the film before and after the second stretching step is less than 15% by weight. The manufacturing method according to any one of claims 1 to 4, wherein after the crosslinking step, further comprising a washing step of washing the polyvinyl alcohol-based resin film with a washing liquid containing water, after the washing step, performing the above 2 extension steps. The manufacturing method according to any one of claims 1 to 5, wherein the uniaxial extension of the second extending step is a dry extension. A polarizing film obtained by adsorbing a dichroic dye to a polyvinyl alcohol-based resin film and based on azimuth distribution curve obtained by wide-angle X-ray diffraction measurement according to the following formula: TD/MD Ratio = (intensity of TD) / (peak intensity of MD) [In the formula, the peak intensity of MD is the average of the peak angles of 0° and 180° of the above azimuth distribution curve, and the average of the intensity of TD is the average of the intensity of the β angle of 90° and 270°] The TD/MD ratio is 0.142 or less when the thickness of the polarizing film is 10 μm or more, and 0.160 or less when the thickness of the polarizing film is less than 10 μm. A polarizing plate comprising the polarizing film of claim 7 and a protective film laminated on at least one side thereof.