WO2016093278A1

WO2016093278A1 - Method for manufacturing polarizing film, and polarizing film

Info

Publication number: WO2016093278A1
Application number: PCT/JP2015/084534
Authority: WO
Inventors: 佑介北河; 勉古谷; 武藤　清; 浩濱松
Original assignee: 住友化学株式会社
Priority date: 2014-12-12
Filing date: 2015-12-09
Publication date: 2016-06-16
Also published as: CN107111035A; CN107111035B; KR20170095924A; JPWO2016093278A1; TW201629543A; JP6346307B2; KR102645999B1; JP2017219861A; TWI684032B

Abstract

Provided are a method for manufacturing a polarizing film, including a dyeing step for dyeing a polyvinyl alcohol-based resin film with a dichroic pigment, a crosslinking step for treating the film from the dyeing step with a crosslinking agent, and a high-temperature, high-humidity treatment step in which the film from the crosslinking step, in a wet state, is placed in an atmosphere having a temperature of 40-100°C and relative humidity of 40 g/m³ or above; a polarizing film having a dichroic pigment adsorption-oriented on a polyvinyl alcohol-based resin film, the polarizing film having a specific degree of orientation (%); and a polarizing plate including the same.

Description

Manufacturing method of polarizing film and polarizing film

The present invention relates to a method for producing a polarizing film that can be used as a constituent member of a polarizing plate. The present invention also relates to a polarizing film and a polarizing plate including the polarizing film.

Conventionally used is a polarizing film obtained by adsorbing and orienting a dichroic dye such as iodine or a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. In general, a polarizing film is produced by sequentially performing a dyeing treatment for dyeing a polyvinyl alcohol-based resin film with a dichroic dye, a crosslinking treatment with a crosslinking agent, and a uniaxial stretching treatment during the production process [for example, JP, 7-325218, A (patent documents 1)].

JP 7-325218 A

The polarizing film is used in an image display device typified by a liquid crystal display device. A polarizing film is usually a polarizing plate obtained by laminating a protective film on one side or both sides thereof, and is incorporated into an image display device. For example, a liquid crystal display device includes a liquid crystal panel in which polarizing plates are bonded to both surfaces of a liquid crystal cell as an image display element.

In recent years, there has been an increasing demand for thinner polarizing plates. However, especially when the polarizing plate is thin, warpage (curvature) is likely to occur in a high-temperature environment and a high-humidity environment. When a polarizing plate that causes warpage is bonded to a liquid crystal cell to construct a liquid crystal panel, the liquid crystal panel also warps in some cases. The warpage of the liquid crystal panel may adversely affect the visibility of the liquid crystal display device.

In order to suppress the warpage of the polarizing plate, and hence the warpage of the liquid crystal panel, it is effective to reduce the shrinkage force (hereinafter also referred to as “MD shrinkage force”) in the absorption axis direction of the polarizing film used for the polarizing plate. . As a method for reducing the MD shrinkage force, there is a method of lowering the stretching ratio at the time of producing the polarizing film, but in this case, the optical properties (for example, the degree of polarization) of the polarizing film become insufficient. .

An object of the present invention is to provide a method for producing a polarizing film having good optical properties and low MD shrinkage. Another object of the present invention is to provide a polarizing film having good optical properties and a small MD shrinkage force, and a polarizing plate including the polarizing film.

This invention provides the manufacturing method of a polarizing film, a polarizing film, and a polarizing plate shown below.
[1] A dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye;
A crosslinking step of treating the film after the dyeing step with a crosslinking agent;
A high-temperature and high-humidity treatment step in which a film after the crosslinking step and in a wet state is placed in an atmosphere having a temperature of 40 to 100 ° C. and an absolute humidity of 40 g / m ³ or more;
The manufacturing method of a polarizing film containing.

[2] The method further includes a washing step of washing the film after the crosslinking step using a washing solution containing water,
The manufacturing method according to [1], wherein the high-temperature and high-humidity treatment step is performed on the film after the washing step and in a wet state.

[3] The manufacturing method according to [1] or [2], wherein a processing time of the high-temperature and high-humidity processing step is 5 seconds to 60 minutes.

[4] The manufacturing method according to any one of [1] to [3], wherein the moisture content of the film is reduced by the high-temperature and high-humidity treatment step.

[5] The manufacturing method according to [4], wherein the difference in moisture content of the film before and after the high-temperature and high-humidity treatment step is less than 15% by weight.

[6] A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film,
Based on the azimuth distribution curve obtained by wide-angle X-ray diffraction measurement, the following formula:
Degree of orientation (%) = (360−W) / 360
[Wherein, W is the sum of all the peaks when the total width of the peak is 50% when the integrated value of the entire peak of the azimuth distribution curve is 100%. ]
The polarizing film has a degree of orientation determined in accordance with the following: 71% or less when the thickness of the polarizing film is 20 μm or more, and 74.0% or less when the thickness of the polarizing film is 10 μm or more and less than 20 μm.

[7] A polarizing plate comprising the polarizing film according to [6] and a protective film laminated on at least one surface thereof.

According to the present invention, it is possible to provide a polarizing film having good optical properties and a small MD shrinkage force and a method for producing the same. The polarizing plate and the liquid crystal panel using the polarizing film according to the present invention are less likely to warp in a high temperature environment or a high humidity environment.

It is a flowchart which shows an example of the manufacturing method of the polarizing film which concerns on this invention. It is a figure which shows an example of the azimuth distribution curve after background correction | amendment.

<Production method of polarizing film>
With reference to FIG. 1, the manufacturing method of the polarizing film which concerns on this invention is the following processes:
Dyeing step S20 for dyeing a polyvinyl alcohol resin film with a dichroic dye,
A cross-linking step S30 in which the film after the dyeing step is treated with a cross-linking agent, and the film after the cross-linking step and in a wet state is placed in an atmosphere having a temperature of 40 to 100 ° C. and an absolute humidity of 40 g / m ³ or more. Place high temperature and high humidity treatment process S50
including.

The manufacturing method of the polarizing film which concerns on this invention can further include other processes other than the above, The specific example is the swelling process S10 performed before dyeing process S20, and bridge | crosslinking, as FIG. 1 shows. This is a cleaning step S40 performed after step S30. In addition, the polyvinyl alcohol-based resin film is uniaxially stretched at any one or more stages of the polarizing film manufacturing process, more specifically, at any one or more stages from the swelling process S10 to the crosslinking process S30. (Extension process).

The various processing steps included in the production method according to the present invention can be carried out continuously by continuously conveying a polyvinyl alcohol-based resin film, which is a raw film, along the film conveyance path of the polarizing film production apparatus. The film transport path includes equipment (processing bath, furnace, etc.) for performing the various processing steps in the order of execution. The treatment bath refers to a bath containing a treatment liquid for treating a polyvinyl alcohol resin film, such as a swelling bath, a dyeing bath, a crosslinking bath, and a washing bath.

The film transport path can be constructed by arranging guide rolls, nip rolls and the like at appropriate positions in addition to the above equipment. For example, the guide roll can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath and pulled out from the treatment bath. More specifically, two or more guide rolls are provided in each treatment bath, and the film can be immersed in each treatment bath by transporting the film along these guide rolls.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film that is a raw fabric film, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers 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) acryl” means at least one selected from acryl and methacryl. The same applies to “(meth) acryloyl”.

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

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol resin can be determined according to JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain preferable polarization performance, and if it exceeds 10,000, 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 still more preferably 40 μm or less from the viewpoint of thinning the polarizing film. is there.

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

(1) Swelling step S10
The swelling treatment in this step is a treatment that is carried out as necessary for the purpose of removing foreign matter from the polyvinyl alcohol-based resin film that is the raw fabric film, removing the plasticizer, imparting easy dyeability, plasticizing the film, Specifically, it can be a treatment of immersing a polyvinyl alcohol-based resin film in a swelling bath containing water. The film may be immersed in one swelling bath or sequentially in two or more swelling baths. You may perform a uniaxial stretching process with respect to a film before a swelling process, a swelling process, or before a swelling process and a swelling process.

The swelling bath may be water (for example, pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added.

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

(2) Dyeing step S20
The dyeing process in this step is a process performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film, and specifically, the polyvinyl alcohol resin film in a dye bath containing the dichroic dye. It can be a process of immersing. The film may be immersed in one dyeing bath or sequentially in two or more dyeing baths. In order to improve the dyeability of the dichroic dye, the film subjected to the dyeing process may be subjected to at least some uniaxial stretching treatment. Instead of the uniaxial stretching process before the dyeing process, or in addition to the uniaxial stretching process before the dyeing process, the uniaxial stretching process may be performed during the dyeing process.

The dichroic dye can be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include: Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Includes Sky Blue, Direct First Orange S and First Black. A dichroic dye may be used individually by 1 type, and may use 2 or more types together.

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used for the dyeing bath. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described later in that it contains iodine. The iodine content in the aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of 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 dyeing bath when dipping the film is usually about 10 to 45 ° C., preferably about 10 to 40 ° C., more preferably about 20 to 35 ° C., and the dipping time for the film is usually 30 to 600 ° C. About 2 seconds, preferably about 60 to 300 seconds.

When a dichroic organic dye is used as the dichroic dye, an aqueous solution containing the dichroic organic dye can be used for the dyeing 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 this dyeing bath, a dyeing assistant or the like may coexist, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. A dichroic organic dye may be used individually by 1 type, and may use 2 or more types together. The temperature of the dyeing bath when dipping the film is, for example, about 20 to 80 ° C., preferably about 30 to 70 ° C., and the dipping time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. is there.

(3) Crosslinking step S30
The cross-linking treatment for treating the polyvinyl alcohol-based resin film after the dyeing step with a cross-linking agent is a treatment performed for the purpose of water resistance and hue adjustment by cross-linking, specifically, a dyeing step in a cross-linking bath containing a cross-linking agent. It can be a process of immersing the later film. The film may be immersed in one crosslinking bath or sequentially in two or more crosslinking baths. You may perform a uniaxial stretching process at the time of a crosslinking process.

Examples of the crosslinking agent include boric acid, glyoxal, and glutaraldehyde, and boric acid is preferably used. Two or more crosslinking agents can 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. When the dichroic dye is iodine, the crosslinking bath preferably contains iodide in addition to boric acid. The iodide content in the crosslinking bath is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like, may coexist in the crosslinking bath.

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

As described above, in the production of the polarizing film, the polyvinyl alcohol-based resin film is uniaxially stretched in any one or two or more stages from before the swelling step S10 to the crosslinking step S30 (stretching step, FIG. 1). . From the viewpoint of enhancing the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or In addition to the uniaxial stretching process before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

The uniaxial stretching treatment may be either dry stretching for stretching in the air or wet stretching for stretching in the bath, or both of them. The uniaxial stretching treatment may be inter-roll stretching, hot roll stretching, tenter stretching, or the like, in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between two nip rolls, and preferably includes inter-roll stretching. The draw ratio based on the raw film (the cumulative draw ratio in the case where the drawing process is performed in two or more stages) is about 3 to 8 times. In order to impart good polarization characteristics, the draw ratio is preferably 4 times or more, more preferably 5 times or more.

(4) Cleaning step S40
The cleaning process in this step is a process performed as necessary for the purpose of removing chemicals such as excess cross-linking agent and dichroic dye attached to the polyvinyl alcohol-based resin film, and uses a cleaning solution containing water. This is a treatment for washing the polyvinyl alcohol-based resin film after the crosslinking step. Specifically, it can be a treatment of immersing the polyvinyl alcohol-based resin film after the crosslinking step in a cleaning bath (cleaning liquid). The film may be immersed in one cleaning bath or sequentially in two or more cleaning baths. Alternatively, the cleaning process may be a process of spraying the cleaning liquid as a shower on the polyvinyl alcohol-based resin film after the crosslinking step, or a combination of the above immersion and spraying.

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

The cleaning step S40 is an optional step and may be omitted, and as will be described later, the cleaning process may be performed during the high-temperature and high-humidity processing step S50 (the high-temperature and high-humidity process may also serve as the cleaning process). ). Preferably, the high-temperature and high-humidity treatment step S50 is performed on the film after the washing step S40.

(5) High temperature and high humidity treatment step S50
The high temperature and high humidity treatment in this step is a treatment in which the film after the crosslinking step S30 or the washing step S40 is placed in an atmosphere having a temperature of 40 to 100 ° C. and an absolute humidity of 40 g / m ³ or more. Compared to the case of performing high temperature treatment (drying treatment) at an absolute humidity of less than 40 g / m ³ instead of high temperature high humidity treatment while suppressing deterioration of the optical properties of the polarizing film by performing high temperature high humidity treatment. MD contraction force can be reduced. It is considered that this is because the orientation of the molecular chain of the polyvinyl alcohol resin constituting the polarizing film is lowered without disturbing the orientation of the dichroic dye.

On the other hand, as in the method specifically described in Patent Document 1 above, conventional high-temperature treatment (drying treatment) at an absolute humidity of less than 40 g / m ^3, which is generally performed after the cleaning step, is performed as usual. Surprisingly, when the high temperature and high humidity treatment is performed, the MD shrinkage force is not decreased, but may even increase.

The high temperature and high humidity treatment is performed on the film after the crosslinking step S30 or the cleaning step S40 in a wet state. “In a wet state” means that a film having a high moisture content after the crosslinking step S30 or after the washing step S40 (without performing a conventional high-temperature treatment (drying treatment) at an absolute humidity of less than 40 g / m ³ ) This means that the film is subjected to a high-temperature and high-humidity treatment. More specifically, it means that the moisture content of the film is 13% by weight or more (preferably 15% by weight or more). The moisture content of the film is measured according to the method described in the Examples section described later.

The high-temperature and high-humidity treatment can be a treatment for introducing the film after the crosslinking step S30 or the cleaning step S40 into a furnace (heating furnace), a booth or a room where the temperature and humidity can be adjusted. In addition to treatment introduced into a furnace (heating furnace), booth or room, heating means such as a far-infrared heater or a heat roll may be used in combination. The high-temperature and high-humidity treatment is preferably performed after the cleaning step S40. However, the high-temperature and high-humidity treatment and the cleaning treatment may be performed at the same time, such as spraying a cleaning liquid in a predetermined high-temperature and high-humidity atmosphere. In the case where the film is substantially cleaned by being placed in a high-humidity atmosphere, the high-temperature and high-humidity process may also serve as the cleaning process.

The temperature of the high-temperature and high-humidity treatment is 40 ° C. or higher as described above, and preferably 55 ° C. or higher, more preferably 60 ° C. or higher, from the viewpoint of more effectively reducing the MD shrinkage force. Moreover, the temperature of the high temperature and high humidity treatment is 100 ° C. or lower as described above, and is preferably 90 ° C. or lower from the viewpoint of more effectively suppressing the deterioration of optical characteristics.

The absolute humidity in the high-temperature and high-humidity treatment is 40 g / m ³ or more as described above, and preferably 75 g / m ³ or more, more preferably 85 g / m ³ or more, from the viewpoint of more effectively reducing the MD shrinkage force. More preferably, it is 100 g / m ³ or more. On the other hand, if the absolute humidity is excessively high, there is concern about the occurrence of condensation in the treatment zone and the contamination of the film with condensed water. Therefore, the absolute humidity is preferably 550 g / m ³ or less, more preferably 400 g / m ^2. m ³ or less, more preferably 300 g / m ³ or less, and particularly preferably 160 g / m ³ or less.

The time for the high-temperature and high-humidity treatment is preferably 5 seconds or more, more preferably 10 seconds or more, from the viewpoint of effectively reducing the MD contraction force. Further, although the time depends on the temperature, if it is too long, there is a concern about deterioration of optical characteristics. Therefore, it is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 10 minutes or less. Especially preferably, it is 5 minutes or less.

The high-temperature and high-humidity treatment can be a treatment in which a long polyvinyl alcohol-based resin film is conveyed along the film conveyance path, and is continuously introduced and passed through the furnace or the like. The film tension is preferably 50 to 1000 N / m from the viewpoint of more effectively reducing the MD shrinkage force. From the viewpoint of suppressing wrinkling of the film, the film tension is more preferably 300 N / m or more.

The high-temperature and high-humidity treatment may also serve as a treatment for drying the polyvinyl alcohol-based resin film, i.e., a treatment for reducing the moisture content, and the drying treatment is usually performed at the same time unless extreme high-temperature and high-humidity conditions are adopted. The This eliminates the need for a separate drying process after the high-temperature and high-humidity treatment, so that it is compared with the conventional method in which the high-temperature and high-humidity process is performed after the high-temperature treatment (drying process) at an absolute humidity of less than 40 g / m ^3. Thus, this is advantageous in terms of simplification and efficiency of the manufacturing process.

The moisture content of the film subjected to the high temperature and high humidity treatment, that is, the film in the wet state after the crosslinking step S30 or the washing step S40 depends on the thickness of the film, but is usually about 13 to 50% by weight. The degree of reduction in moisture content due to high-temperature and high-humidity treatment, that is, the difference between the moisture content before high-temperature and high-humidity treatment and the moisture content after high-temperature and high-humidity treatment (moisture content difference ΔS) also depends on the thickness of the film. It is 5 to 45% by weight, preferably 8 to 35% by weight. For example, when the thickness of the raw film is about 40 μm or less, the moisture content difference ΔS can be less than 15% by weight.

The moisture content of the film after high-temperature and high-humidity treatment (or polarizing film when high-temperature and high-humidity treatment is the final process) is also 5 to 30% by weight, although it depends on the thickness of the film. From the viewpoint of properties, it is preferably 6 to 15% by weight. If the moisture content is too low, the film tends to tear during conveyance, and if the moisture content is too high, curling tends to occur at the film edge due to moisture release.

In general, the thinner the film, the more easily the moisture is dissipated. Therefore, the thinner the original film, the lower the moisture content before and during the high temperature and high humidity treatment. If the moisture content is too low, the film transportability tends to be lowered. Therefore, when the thickness of the raw film is about 40 μm or less, it is preferable to set the temperature of the high-temperature and high-humidity treatment to be low and to be 40 to 70 ° C.

Through the above steps, a polarizing film in which a dichroic dye is adsorbed and oriented on 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 as thin as 30 μm or less, and even 25 μm or less, the MD shrinkage is small, so that the warpage when used as a polarizing plate or a liquid crystal panel is effectively suppressed. can do.

For example, in order to adjust the moisture content, a drying process (a high temperature process at an absolute humidity of less than 40 g / m ³ ) may be performed after the high temperature and high humidity process step S50. However, since the moisture content can be adjusted by the high-temperature and high-humidity treatment step S50, this drying treatment is performed as necessary.

The obtained polarizing film can also be conveyed, for example, to the next polarizing plate production step (step of bonding a protective film on one or both sides of the polarizing film) as it is.

In one embodiment, the polarizing film according to the present invention is a film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, and wide angle X-ray diffraction (WAXD: Wide Angle X-ray Diffraction). ), The degree of orientation (%) representing the orientation of the polyvinyl alcohol resin constituting the polarizing film in the MD, measured by the through method. By having this characteristic, it is presumed that the polarizing film according to the present embodiment can exhibit the characteristics and effects that the MD contraction force is small while having good optical characteristics.

Specifically, when the thickness of the polarizing film according to this embodiment is 20 μm or more, the degree of orientation is preferably 71% or less, more preferably 70% or less, and 67% or less. More preferably. The degree of orientation of the polarizing film is usually 60% or more, preferably 65% or more when the thickness is 20 μm or more. The thickness of the polarizing film having a thickness of 20 μm or more is usually 30 μm or less, preferably 25 μm or less, and preferably 22 μm or more.

When the thickness of the polarizing film according to the present embodiment is 10 μm or more and less than 20 μm, the degree of orientation is preferably 74.0% or less, more preferably 73% or less, and 72% or less. More preferably it is. When the thickness is 10 μm or more and less than 20 μm, the orientation degree of the polarizing film is usually 65% or more, preferably 70% or more. The thickness of the polarizing film having a thickness of 10 μm or more and less than 20 μm is preferably 15 μm or less, more preferably 13 μm or less, and preferably 11 μm or more, more preferably 12 μm or more.

When the thickness of the polarizing film according to this embodiment is less than 10 μm, the degree of orientation is preferably 75% or less, and more preferably 74% or less. The degree of orientation of the polarizing film is usually 70% or more when the thickness 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 preferably 9 μm or less.

The polarizing film exhibiting the degree of orientation as described above can be preferably manufactured by the above-described manufacturing method of the polarizing film according to the present invention. The degree of orientation referred to here is measured according to the method described in the Examples section described later.

In another embodiment, the polarizing film according to the present invention is a film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, and the wave number representing a crosslinked state of the polarizing film by a crosslinking agent. It can be characterized by the ratio of the Raman scattered light intensity in the absorption axis direction and the Raman scattered light intensity in the transmission axis direction at 775 cm ⁻¹ (hereinafter also referred to as “Raman scattered light intensity ratio”). By having this characteristic, it is presumed that the polarizing film according to the present embodiment can exhibit the characteristics and effects that the MD contraction force is small while having good optical characteristics.

Specifically, in the polarizing film according to this embodiment, the Raman scattered light intensity ratio is preferably 0.86 or more, and more preferably 0.89 or more. The Raman scattered light intensity ratio is usually 1.00 or less, preferably 0.95 or less.

The polarizing film showing the Raman scattered light intensity ratio as described above can be preferably manufactured by the above-described manufacturing method of the polarizing film according to the present invention. The Raman scattered light intensity ratio here is measured according to the method described in the section of Examples described later.

In still another embodiment, the polarizing film according to the present invention is a film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, exhibits an orientation degree within the above range, and the above range. The Raman scattered light intensity ratio is shown. The degree of orientation within the above range and the Raman scattered light intensity ratio within the above range are advantageous for reducing the MD shrinkage force while having good optical properties.

<Polarizing plate>
Polarized light is produced by bonding (laminating) a protective film via an adhesive to at least one surface of a polarizing film produced as described above or exhibiting at least one of the degree of orientation and the Raman scattered light intensity ratio. A board can be obtained. As the protective film, thermoplastic resins, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.), cyclic polyolefin resins (norbornene resins, etc.); celluloses such as triacetyl cellulose and diacetyl cellulose Ester resins; Polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; Polycarbonate resins; (Meth) acrylic resins such as polymethyl methacrylate resins; or a mixture or copolymer thereof It can be a transparent resin film.

The protective film may be a protective film having both optical functions such as a retardation film and a brightness enhancement film. For example, a retardation film provided with an arbitrary retardation value by stretching a transparent resin film made of the above material (uniaxial stretching or biaxial stretching) or forming a liquid crystal layer or the like on the film. It can be.

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 can be formed on the surface of the protective film opposite to the polarizing film.

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

As an adhesive used for laminating a polarizing film and a protective film, an active energy ray curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or an aqueous solution in which a crosslinking agent is blended. And water-based adhesives such as urethane emulsion adhesives. When bonding a protective film on both surfaces of a polarizing film, the adhesive agent which forms two adhesive bond layers may be the same, and a different kind may be sufficient as it. For example, when a protective film is bonded to both surfaces, one surface may be bonded using a water-based adhesive, and the other surface may be bonded using an active energy ray-curable adhesive. The ultraviolet curable adhesive can be a mixture of a radical polymerizable (meth) acrylic compound and a photo radical polymerization initiator, a mixture of a cationic polymerizable epoxy compound and a photo cationic polymerization initiator, or the like. Further, a cationic polymerizable epoxy compound and a radical polymerizable (meth) acrylic compound may be used in combination, and a photo cationic polymerization initiator and a photo radical polymerization initiator may be used in combination as an initiator.

When using an active energy ray-curable adhesive, the adhesive is cured by irradiating active energy rays after bonding. The light source of the active energy ray is not particularly limited, but an active energy ray (ultraviolet ray) having a light emission distribution at a wavelength of 400 nm or less is preferable. A black light lamp, a microwave excitation mercury lamp, a metal halide lamp or the like is preferably used.

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

As described above, the polarizing plate of the present invention can also be produced by laminating a protective film on a polarizing film that is a single layer film, but is not limited to this method, and is described in, for example, JP-A-2009-98653. It can also be produced by a method using a base film. The latter method is advantageous for obtaining a polarizing plate having a thin polarizing film (polarizer layer), and can include, for example, the following steps.

After applying a coating liquid containing a polyvinyl alcohol-based resin on at least one surface of the base film, a resin layer forming step of forming a polyvinyl alcohol-based resin layer by drying to obtain a laminated film,
A stretching step of stretching a laminated film to obtain a stretched film;
A dyeing step of obtaining a polarizing laminated film by dyeing a polyvinyl alcohol resin layer of a stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizing film);
The 1st bonding process of bonding a protective film using the adhesive agent on the polarizer layer of a light-polarizing laminated film, and obtaining a bonding film,
The peeling process which peels and removes a base film from a bonding film, and obtains the polarizing plate with a single-sided protective film.

In the case where protective films are laminated on both sides of the polarizer layer (polarizing film), it further includes a second bonding step in which the protective film is bonded to the polarizer surface of the polarizing plate with a single-side protective film using an adhesive.

In the above method using a base film, a high-temperature and high-humidity treatment step is included in the dyeing step for obtaining a polarizing laminated film (for example, after the crosslinking step or the washing step in the dyeing step for obtaining the polarizing laminated film). Can do. A polarizing film contained in the polarizing laminate film, a polarizing plate with a single-sided protective film, and a polarizing plate with a double-sided protective film obtained through the second laminating step, or a polarizing film isolated therefrom are also included in the present invention. The polarizing film belongs, and preferably exhibits at least one of the orientation degree within the above range and the Raman scattered light intensity ratio within the above range.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

<Example 1>
A 60-μm long polyvinyl alcohol (PVA) raw film (trade name “Kuraray Poval Film VF-PE # 6000” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol% or more) It was continuously conveyed while being unwound from the roll, and immersed in a swelling bath made of pure water at 30 ° C. for a residence time of 81 seconds (swelling step). Thereafter, the film drawn out from the swelling bath was immersed in a dye bath at 30 ° C. containing iodine having a potassium iodide / water ratio of 2/100 (weight ratio) for a residence time of 143 seconds (dyeing step). Next, the film drawn from the dyeing bath was immersed in a 56 ° C. crosslinking bath having potassium iodide / boric acid / water of 12 / 4.1 / 100 (weight ratio) for a residence time of 67 seconds. It was immersed in a crosslinking bath at 40 ° C. in which potassium fluoride / boric acid / water was 9 / 2.9 / 100 (weight ratio) with a residence time of 11 seconds (crosslinking step). In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The total draw ratio based on the original film was 5.7 times.

Next, the film drawn from the crosslinking bath was immersed in a cleaning bath made of pure water at 5 ° C. for a residence time of 3 seconds (cleaning step), and subsequently introduced into the first heating furnace capable of adjusting the humidity. A high temperature and high humidity treatment was performed at a residence time of 161 seconds (high temperature and high humidity treatment step) to obtain a polarizing film having a thickness of 22.9 μm and a width of 207 mm. The temperature and absolute humidity in the first heating furnace were 80 ° C. and 88 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment was 565 N / m. The moisture content of the film immediately before and after the introduction of the first heating furnace (high temperature and high humidity treatment) was 33.3% by weight and 7.9% by weight, respectively, and the moisture content difference ΔS was 25.4% by weight.

<Example 2>
A thickness of 23.7 μm and a width of 200 mm were obtained in the same manner as in Example 1 except that the temperature and absolute humidity in the first heating furnace and the film tension during the treatment in the first heating furnace were changed as shown in Table 1. A polarizing film was prepared.

<Comparative Example 1>
Similar to Example 1, except that the temperature and absolute humidity in the first heating furnace and the film tension during the treatment in the first heating furnace were changed as shown in Table 1, the thickness was 23.2 μm and the width was 206 mm. A polarizing film was prepared. The temperature and absolute humidity in the first heating furnace were 76 ° C. and 8 g / m ³ , respectively. In the first heating furnace, only the heating (drying) process was performed instead of the high-temperature and high-humidity process.

<Comparative example 2>
Residence time is achieved by performing heating (drying) treatment in a first heating furnace having a temperature and an absolute humidity of 76 ° C. and 8 g / m ³ , respectively, and then introducing it into a second heating furnace capable of adjusting the humidity. A polarizing film having a thickness of 23.4 μm and a width of 208 mm was produced in the same manner as in Comparative Example 1 except that the high temperature and high humidity treatment was performed in 161 seconds. The temperature and absolute humidity in the second heating furnace were 80 ° C. and 88 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment in the second heating furnace was 2 N / m.

<Comparative Example 3>
A polarizing film having a thickness of 23.3 μm and a width of 207 mm was produced in the same manner as in Comparative Example 2 except that the temperature and absolute humidity in the second heating furnace were changed as shown in Table 1.

<Example 3>
A long polyvinyl alcohol (PVA) raw film having a thickness of 30 μm (trade name “Kuraray Poval Film VF-PE # 3000” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol% or more) It was continuously conveyed while being unwound from the roll, and immersed in a swelling bath made of pure water at 20 ° C. for a residence time of 31 seconds (swelling step). Thereafter, the film drawn out from the swelling bath was immersed in a dye bath at 30 ° C. containing iodine having a potassium iodide / water ratio of 2/100 (weight ratio) with a residence time of 122 seconds (dyeing step). Next, the film drawn from the dyeing bath was immersed in a 56 ° C. crosslinking bath having a potassium iodide / boric acid / water ratio of 12 / 4.1 / 100 (weight ratio) with a residence time of 70 seconds. It was immersed in a crosslinking bath at 40 ° C. in which potassium fluoride / boric acid / water was 9 / 2.9 / 100 (weight ratio) with a residence time of 13 seconds (crosslinking step). In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The total draw ratio based on the original film was 5.4 times.

Next, the film drawn from the crosslinking bath was immersed in a cleaning bath made of pure water at 5 ° C. for a residence time of 3 seconds (cleaning step), and subsequently introduced into the first heating furnace capable of adjusting the humidity. A high temperature and high humidity treatment was performed with a residence time of 190 seconds (high temperature and high humidity treatment step) to obtain a polarizing film having a thickness of 12.1 μm and a width of 208 mm. The temperature and absolute humidity in the first heating furnace were 73 ° C. and 89 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment was 601 N / m. The moisture content of the film immediately before and after the introduction of the first heating furnace (high temperature and high humidity treatment) was 19.4 wt% and 8.0 wt%, respectively, and the moisture content difference ΔS was 11.4 wt%.

<Examples 4 to 8>
A polarizing film was produced in the same manner as in Example 3 except that the temperature and absolute humidity in the first heating furnace and the film tension during the high-temperature and high-humidity treatment in the first heating furnace were changed as shown in Table 1. did.

<Comparative example 4>
Similar to Example 3, except that the temperature and absolute humidity in the first heating furnace and the film tension during the treatment in the first heating furnace were changed as shown in Table 1, the thickness was 12.5 μm and the width was 203 mm. A polarizing film was prepared. The temperature and absolute humidity in the first heating furnace were 60 ° C. and 12 g / m ³ , respectively. In the first heating furnace, only the heating (drying) process was performed instead of the high-temperature and high-humidity process.

<Comparative Example 5>
Residence time is achieved by performing heating (drying) treatment in a first heating furnace having a temperature and absolute humidity of 59 ° C. and 10 g / m ³ , respectively, and then introducing it into a second heating furnace in which further humidity control is possible. The thickness was 12.9 μm and the width was the same as in Comparative Example 4 except that the high-temperature and high-humidity treatment was performed in 161 seconds and the film tension during the treatment in the first heating furnace was changed as shown in Table 1. A polarizing film of 204 mm was produced. The temperature and absolute humidity in the second heating furnace were 73 ° C. and 89 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment in the second heating furnace was 1 N / m.

Table 1 summarizes the production conditions of the polarizing film in each example and comparative example, the moisture content of the film immediately before and after the introduction of the first heating furnace (high-temperature and high-humidity treatment), and the moisture content difference ΔS, which is the difference therebetween.

The absolute humidity in the heating furnace was calculated from the measured values of the furnace temperature and relative humidity. The thickness of the obtained polarizing film was measured using a digital micrometer “MH-15M” manufactured by Nikon Corporation. Moreover, the moisture content of the film (polarizing film) was calculated | required with the following method.

Using a plurality of polarizing film samples having different moisture percentages in advance, the correlation between the moisture percentage by the dry weight method and the measured value of an infrared absorption moisture meter (“IM 3SCV MODEL-1900L” manufactured by Fuji Work Co., Ltd.) Show the calibration curve (conversion formula):
In the case of a polarizing film using a thickness of 60 μm PVA: Moisture percentage (% by weight) by dry weight method = 0.0600 × (measured value of moisture meter) −50.0252
In the case of a polarizing film with a thickness of 30 μm PVA:
Moisture content by dry weight method (% by weight) = 0.0495 × (measured value of moisture meter) −38.8379. At this time, the moisture content by the dry weight method is expressed by the following formula when the weight of the polarizing film when dried at 105 ° C. for 2 hours is W1, and the weight of the polarizing film before drying is W0:
Moisture content by dry weight method (wt%) = {(W0−W1) ÷ W0} × 100
Sought according to. The moisture content shown in Table 1 is obtained by obtaining a measured value using the moisture meter and substituting it into the calibration curve (conversion formula) to convert the moisture content (% by weight) by the dry weight method. . The moisture content difference ΔS was calculated by subtracting the moisture content immediately after introduction from the moisture content immediately before introducing the first heating furnace.

[Evaluation of polarizing film]
About the following item, the characteristic of the polarizing film obtained by each Example and the comparative example was measured. The results are shown in Table 1.

(1) Visibility correction single transmittance (Ty) and visibility correction polarization degree (Py)
About the obtained polarizing film, MD transmittance and TD transmittance in a wavelength range of 380 to 780 nm were measured using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation), and the following formula:
Single transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD−TD) / (MD + TD)} × 100
Based on the above, the single transmittance and the degree of polarization at each wavelength were calculated.

“MD transmittance” is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing film sample, and is represented by “MD” in the above formula. The “TD transmittance” is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the polarizing film sample, and is represented by “TD” in the above formula. The obtained single transmittance and degree of polarization are corrected for visibility by JIS Z 8701: 1999 “color display method—XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system” with a two-degree field of view (C light source). The visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (Py) were obtained.

(2) MD shrinkage force From the obtained polarizing film, a measurement sample having a width of 2 mm and a length of 10 mm with the absorption axis direction (MD, stretching direction) as the long side was cut out. The long side generated when this sample is set on the thermomechanical analyzer (TMA) “EXSTAR-6000” manufactured by SII Nanotechnology, Inc. and kept at 80 ° C. for 4 hours while keeping the dimensions constant. The contraction force (MD contraction force) in the direction (absorption axis direction, MD) was measured.

(3) Degree of orientation The “degree of orientation” representing the orientation of the polyvinyl alcohol resin constituting the polarizing film in the MD was determined by a through method of wide angle X-ray diffraction (WAXD: Wide Angle X-ray Diffraction). First, a plurality of rectangular films having a long side in the absorption axis direction (MD, stretching direction) were cut out from the obtained polarizing film. A plurality of cut out films were fixed so that their MDs (long sides) were parallel, and this was used as a measurement sample. The thickness of the measurement sample was about 0.1 mm. Using the following X-ray diffractometer, irradiate one surface of the measurement sample with X-rays from the direction perpendicular to the surface of the measurement sample under the following X-ray output conditions, and obtain a diffraction image by the transmission method. I took an image.

X-ray diffractometer: “NANO-Viewer” manufactured by Rigaku Corporation,
X-ray output conditions: Cu target, 40 kV, 20 mA.

From the obtained diffraction image, an uncorrected azimuth distribution curve (azimuth angle (1) is first obtained by circular integration of the range of 2θ = 19.5 to 20.5 ° with respect to the peak near the diffraction angle 2θ = 20 °. β angle) -intensity distribution curve) was calculated. The uncorrected azimuth distribution curve refers to an azimuth distribution curve before performing background correction. Next, measurement was performed under the same conditions except that the measurement sample was removed from the X-ray optical axis, and the background of the azimuth distribution curve was calculated. After performing the transmittance correction, the background was removed from the above-mentioned uncorrected azimuth distribution curve to obtain an azimuth distribution curve after the background correction (hereinafter also simply referred to as “azimuth distribution curve”). . FIG. 2 shows an example of the azimuth distribution curve after background correction. The peak in this azimuth distribution curve is an orientation peak. In this measurement, the MD of the measurement sample was installed in the vertical direction, and the β angle at the maximum intensity of the orientation peak appearing in the horizontal direction was 0 °. The β angle (0 ° and 180 °) at the maximum intensity of the orientation peak is derived from the component oriented in the MD of the polarizing film. From the obtained azimuth distribution curve, the following formula:
Degree of orientation (%) = (360−W) / 360
The degree of orientation was determined according to W is the sum of these when the total peak width at which the integrated value is 50% when the integrated value of the entire peak of the azimuth distribution curve is 100% is obtained for all orientation peaks. The center position (°) in the full width of the peak coincides with the β angle (°) at which the peak shows the maximum intensity.

(4) Raman Scattered Light Intensity Ratio In order to obtain the Raman scattered light intensity ratio of the obtained polarizing film, an analytical film was prepared in the same manner as in each Example and each Comparative Example except that the dyeing bath did not contain iodine. did. It is recognized that the Raman scattered light intensity ratio of the obtained polarizing film is the same as the Raman scattered light intensity ratio of the analytical film.

About the obtained film for analysis, using a laser Raman spectrophotometer “NRS-5100” manufactured by JASCO Corporation, the Raman scattered light intensity in the absorption axis direction and the Raman scattered light intensity in the transmission axis direction at a wave number of 775 cm ⁻¹ . And the ratio (Raman scattered light intensity ratio) to the following formula:
Raman scattered light intensity ratio = (Raman scattered light intensity in the stretching direction of the analysis films in wavenumber 775cm ^-1) / (Raman scattered light intensity in the direction orthogonal to the stretching direction of the analysis films in wavenumber 775cm ^-1)
This was determined as the Raman scattered light intensity ratio of the obtained polarizing film.

Here, the Raman scattered light intensity in the stretching direction of the analytical film at a wave number of 775 cm ⁻¹ is such that the laser beam is perpendicular to the surface of the analytical film so that the polarization plane of the laser light is parallel to the stretching direction of the analytical film. Incidence was measured by making the plane of polarization of the analyzer parallel to the plane of polarization of the laser light. Similarly, the intensity of Raman scattered light in the direction orthogonal to the stretching direction of the analytical film at a wave number of 775 cm ⁻¹ is the surface of the analytical film so that the polarization plane of the laser light is perpendicular to the stretching direction of the analytical film. Measurement was performed such that the plane of incidence was more perpendicular and the plane of polarization of the analyzer was parallel to the plane of polarization of the laser light.

The conditions used for the above Raman spectroscopic measurement are as follows.
Excitation wavelength: 532 nm
・ Grating: 600 l / mm,
・ Slit width: 100 × 1000 μm,
・ Aperture: φ40μm
-Objective lens: 100 times.

<Example 9>
A long polyvinyl alcohol (PVA) raw film (trade name “Kuraray Poval Film VF-PE # 2000” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol% or more) having a thickness of 20 μm While being continuously unwound from the roll, it was uniaxially stretched 4.1 times in a dry manner, and further immersed in a swelling bath made of pure water at 30 ° C. with a residence time of 50 seconds while maintaining the tension state ( Swelling step). Thereafter, the film drawn out from the swelling bath was immersed in a dye bath at 30 ° C. containing iodine having a potassium iodide / water ratio of 5/100 (weight ratio) with a residence time of 88 seconds (dyeing step). Next, the film drawn out from the dyeing bath was immersed in a 65 ° C. crosslinking bath in which potassium iodide / boric acid / water was 18 / 5.6 / 100 (weight ratio) with a residence time of 115 seconds (crosslinking step). . In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was further performed by stretching between rolls in a bath. The total draw ratio based on the original film was 4.3 times.

Next, the film drawn from the crosslinking bath was immersed in a cleaning bath made of pure water at 4 ° C. for a residence time of 7 seconds (cleaning step), and subsequently introduced into the first heating furnace capable of adjusting the humidity. A high temperature and high humidity treatment was performed with a residence time of 97 seconds (high temperature and high humidity treatment step) to obtain a polarizing film having a thickness of 8.1 μm and a width of 216 mm. The temperature and absolute humidity in the first heating furnace were 71 ° C. and 135 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment was 208 N / m. The moisture content of the film immediately before and after the introduction of the first heating furnace (high temperature and high humidity treatment step) was 15.5 wt% and 9.7 wt%, respectively, and the moisture content difference ΔS was 5.8 wt%.

<Comparative Example 6>
A polarizing film was produced in the same manner as in Example 9 except that the temperature and absolute humidity in the first heating furnace and the film tension during the high-temperature and high-humidity treatment in the first heating furnace were changed as shown in Table 2. did.

Table 2 summarizes the production conditions of the polarizing film in Example 9 and Comparative Example 6, the moisture content of the film immediately before and after the introduction of the first heating furnace (high temperature and high humidity treatment), and the moisture content difference ΔS, which is the difference therebetween. . Moreover, about the said item, the characteristic of the polarizing film in Example 9 and Comparative Example 6 was measured. The results are shown in Table 2.

<Example 10>
(1) Production of base film Resin layer made of a random copolymer of propylene / ethylene containing about 5% by weight of ethylene unit (trade name “Sumitomo Noblen W151”, melting point Tm = 138 ° C., manufactured by Sumitomo Chemical Co., Ltd.) A base film having a three-layer structure in which a resin layer made of homopolypropylene (trade name “Sumitomo Nobrene FLX80E4” manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 163 ° C.), which is a homopolymer of propylene, is disposed on both sides of It was produced by coextrusion using a multilayer extruder. The total thickness of the obtained base film was 100 μm, and the thickness ratio (FLX80E4 / W151 / FLX80E4) of each layer was 3/4/3.

(2) Preparation of primer layer forming coating solution Polyvinyl alcohol powder (trade name “Z-200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100, saponification degree 99.5 mol%) is 95 ° C. Was dissolved in hot water to prepare an aqueous polyvinyl alcohol solution having a concentration of 3% by weight. The resulting aqueous solution was mixed with a crosslinking agent (trade name “Smiles Resin 650” manufactured by Taoka Chemical Co., Ltd.) at a ratio of 1 part by weight to 2 parts by weight of the polyvinyl alcohol powder to form a primer layer-forming coating. A working solution was obtained.

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

(4) Formation of polyvinyl alcohol-based resin layer While continuously transporting the substrate film prepared in (1) above, one surface thereof is subjected to corona treatment, and then a corona-treated surface is used with a small-diameter gravure coater. The primer layer-forming coating solution prepared in (2) above was continuously applied and dried at 60 ° C. for 3 minutes to form a primer layer having a thickness of 0.2 μm. Subsequently, while transporting the film, continuously apply the polyvinyl alcohol-based resin layer forming coating solution prepared in (3) above on the primer layer using a comma coater and dry at 90 ° C. for 4 minutes. Thus, a 9.5 μm-thick polyvinyl alcohol-based resin layer (hereinafter referred to as “first PVA layer”) was formed on the primer layer.

Subsequently, a primer layer having a thickness of 0.2 μm is formed on the surface of the base film opposite to the surface on which the first PVA layer is formed in the same manner as described above, and a polyvinyl alcohol resin layer is formed on the primer layer. A forming coating solution is applied and dried at 90 ° C. for 4 minutes to form a 9.4 μm-thick polyvinyl alcohol-based resin layer (hereinafter referred to as “second PVA layer”) on the primer layer. A laminated film having a PVA layer on both sides was obtained.

(5) Production of stretched film While continuously transporting the laminated film produced in (4) above, a magnification of 5.3 times in the longitudinal direction (film transport direction) at a stretching temperature of 160 ° C. by a stretching method between nip rolls. The film was uniaxially stretched to obtain a stretched film. In 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 Polarizing Laminated Film Containing Polarizing Film (Polarizer Layer) The stretched film produced in (5) above contains 30 iodine containing potassium iodide / water of 7.5 / 100 (weight ratio). It was immersed in a dyeing bath at 0 ° C. for a residence time of 230 seconds (dyeing step). Next, the film drawn from the dyeing bath was immersed in a 78 ° C. crosslinking bath having potassium iodide / boric acid / water of 10 / 9.5 / 100 (weight ratio) for a residence time of 240 seconds. It was immersed in a crosslinking bath at 70 ° C. in which potassium fluoride / boric acid / water was 4.5 / 5.0 / 100 (weight ratio) for a residence time of 77 seconds (crosslinking step).

Next, the film drawn from the crosslinking bath was immersed in a cleaning bath made of pure water at 4 ° C. for a residence time of 22 seconds (cleaning step), and subsequently introduced into the first heating furnace capable of adjusting the humidity. A polarizing laminate including a polarizing film (polarizer layer) having a thickness of 5.3 μm and a width of 210 mm formed from the second PVA layer by performing a high temperature and high humidity treatment at a residence time of 276 seconds (high temperature and high humidity treatment step). A film was obtained. The temperature and absolute humidity in the first heating furnace were 80 ° C. and 117 g / m ³ , respectively, and the film tension during the high temperature and high humidity treatment was 1290 N / m. The moisture content of the film immediately before and after the introduction of the first heating furnace (high temperature and high humidity treatment) was 18.2 wt% and 10.7 wt%, respectively, and the moisture content difference ΔS was 7.5 wt%.

<Comparative Example 7>
Similar to Example 10 except that the temperature and absolute humidity in the first heating furnace and the film tension during the treatment in the first heating furnace were changed as shown in Table 3, the thickness was 5.3 μm and the width was 210 mm. A polarizing laminated film including a polarizing film (polarizer layer) was prepared. The temperature and absolute humidity in the first heating furnace were 65 ° C. and 8 g / m ³ , respectively. In the first heating furnace, only the heating (drying) process was performed instead of the high-temperature and high-humidity process.

Table 3 shows the production conditions of the polarizing laminated film in Example 10 and Comparative Example 7, the moisture content of the polarizing film immediately before and after the introduction of the first heating furnace (high-temperature and high-humidity treatment), and the moisture content difference ΔS, which is the difference therebetween. Summarized in Moreover, about the said item (excluding orientation degree), the characteristic of the polarizing film in Example 10 and Comparative Example 7 was measured. The results are shown in Table 3. For the measurement of Ty and Py using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation), the polarized light formed from the first PVA layer was obtained from the obtained polarizing laminated film. A laminated film from which the film was peeled and removed was used as a measurement sample. At this time, measurement was performed by entering light from the side of the polarizing film (polarizing film formed from the second PVA layer). Moreover, MD contraction force took out only the polarizing film formed from the 2nd PVA layer from the obtained polarizing laminated film, and made this into the measurement sample.

Claims

A dyeing step of dyeing a polyvinyl alcohol resin film with a dichroic dye;
A crosslinking step of treating the film after the dyeing step with a crosslinking agent;
A high-temperature and high-humidity treatment step in which a film after the crosslinking step and in a wet state is placed in an atmosphere having a temperature of 40 to 100 ° C. and an absolute humidity of 40 g / m 3 or more;
The manufacturing method of a polarizing film containing.
The film after the cross-linking step further includes a cleaning step of cleaning with a cleaning liquid containing water,
The manufacturing method according to claim 1, wherein the high-temperature and high-humidity treatment step is performed on the film after the cleaning step and in a wet state.
The manufacturing method according to claim 1 or 2, wherein a processing time of the high-temperature and high-humidity processing step is 5 seconds to 60 minutes.
The production method according to any one of claims 1 to 3, wherein the moisture content of the film is reduced by the high-temperature and high-humidity treatment step.
The manufacturing method according to claim 4, wherein the difference in moisture content of the film before and after the high-temperature and high-humidity treatment step is less than 15% by weight.
A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film,
Based on the azimuth distribution curve obtained by wide-angle X-ray diffraction measurement, the following formula:
Degree of orientation (%) = (360−W) / 360
[Wherein, W is the sum of all the peaks when the total width of the peak is 50% when the integrated value of the entire peak of the azimuth distribution curve is 100%. ]
The polarizing film has a degree of orientation determined in accordance with the following: 71% or less when the thickness of the polarizing film is 20 μm or more, and 74.0% or less when the thickness of the polarizing film is 10 μm or more and less than 20 μm.
A polarizing plate comprising the polarizing film according to claim 6 and a protective film laminated on at least one surface thereof.