WO2023038076A1

WO2023038076A1 - Polarizing film and polarizing plate

Info

Publication number: WO2023038076A1
Application number: PCT/JP2022/033656
Authority: WO
Inventors: 幸司住田; 泰紀丹羽; 智康竹内
Original assignee: 住友化学株式会社
Priority date: 2021-09-13
Filing date: 2022-09-08
Publication date: 2023-03-16
Also published as: TW202328306A

Abstract

A polarizing film is provided that has excellent uniformity of contraction force in the direction of the absorption axis in the transmission axis direction while having excellent optical characteristics. The polarizing film comprises a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin film. In the polarizing film, the luminosity factor-corrected unit transmittance Ty is greater than or equal to 43.20% and the luminosity factor-corrected polarization degree Py is greater than or equal to 99.9970%. In the transmission axis direction of the polarizing film, the difference between the maximum value and the minimum value of the film thickness is less than or equal to 2.1 μm.

Description

Polarizing film and polarizing plate

The present invention relates to polarizing films and polarizing plates.

Polarizing films are used in display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices. As a polarizing film, it is known to use a stretched polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented (for example, Patent Document 1).

JP 2013-148806 A

In order to improve the optical properties of the polarizing film, the stretch ratio of the polyvinyl alcohol resin film may be increased. In the polarizing film with a high draw ratio, the shrinkage force in the direction of the absorption axis tended to differ greatly between the central portion and the end portions in the direction of the transmission axis. Here, the transmission axis direction is the direction perpendicular to the stretching direction of the polarizing film, and the absorption axis direction is the stretching direction of the polarizing film.

A polarizing film is usually used in a display device or the like as a polarizing plate with a protective film laminated on one or both sides thereof. As a polarizing plate applied to a display device, from the viewpoint of production efficiency, etc., a polarizing plate cut out so that one or more products can be obtained from a polarizing plate as a material, a polarizing plate obtained by so-called picking (hereinafter referred to as It is sometimes called a "picked-up polarizing plate.") may be used. For example, when a cut polarizing plate is obtained by performing multi-cutting so that two or more polarizing plates are obtained in the transmission axis direction from a polarizing plate before cutting, the side of the cutting polarizing plate has a cut A side formed from or near the center in the transmission axis direction of the polarizing film of the previous polarizing plate and a side formed from or near the end may be included. Therefore, if the contraction force in the absorption axis direction of the polarizing plate before trimming is different in the transmission axis direction, the contraction force in the absorption axis direction is different on each side of the trimmed polarizing plate. In such a trimmed polarizing plate, for example, the shrinkage force on each side of the trimmed polarizing plate is distributed, such that the shrinkage force increases only on one side of the trimmed polarizing plate. Such a shrinkage force distribution is not limited to the case of obtaining a trimmed polarizing plate by multiple trimming. The same can occur when obtaining a polarizing plate.

When a display device in which a polarizing plate is attached to a display panel is exposed to high temperature conditions, heat unevenness may occur in the polarizing plate. When the trimmed polarizing plate having the distribution of the shrinkage force is applied to a display device, the heat unevenness described above does not occur uniformly over the entire trimmed polarizing plate, but occurs non-uniformly. Non-uniform heat unevenness is conspicuous, and may cause deterioration in appearance quality of the display device. In addition, the distribution of the shrinkage force as described above causes a distribution of warpage occurring on each side of the polarizing plate for picking, for example, the warp of only one side of the polarizing plate for picking increases. It can also be a cause of lowering the handleability of the polarizing plate.

An object of the present invention is to provide a polarizing film having excellent uniformity of contraction force in the direction of the absorption axis in the direction of the transmission axis while having excellent optical properties, and a polarizing plate including the same.

The present invention provides the following polarizing film and polarizing plate.
[1] A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin film,
The visibility correction single transmittance Ty is 43.20% or more,
Visibility correction polarization degree Py is 99.9970% or more,
A polarizing film, wherein the difference between the maximum value and the minimum value of film thickness in the transmission axis direction is 2.1 μm or less.
[2] The polarizing film according to [1], wherein the difference between the maximum film thickness in the end regions in the transmission axis direction and the maximum film thickness in the central region in the transmission axis direction is 2.1 μm or less.
[3] The polarizing film according to [1] or [2], wherein the length in the transmission axis direction is 800 mm or more and 2500 mm or less.
[4] The polarizing film according to any one of [1] to [3], wherein the average film thickness in the central region in the transmission axis direction is 5 μm or more and 30 μm or less.
[5] The polarizing film according to any one of [1] to [4], wherein the average film thickness in the central region in the transmission axis direction is 16 μm or more and 29 μm or less.
[6] A polarizing plate in which a protective film is laminated on one or both sides of the polarizing film according to any one of [1] to [5].

According to the present invention, it is possible to provide a polarizing film and a polarizing plate including the same, which have excellent optical properties and excellent uniformity of contraction force in the direction of the absorption axis in the direction of the transmission axis.

The polarizing film and polarizing plate of the present invention are described below.
(polarizing film)
The polarizing film of the present embodiment is a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film (hereinafter sometimes referred to as "PVA-based film"). The luminosity correction single transmittance Ty of the polarizing film is 43.20% or more, and the luminosity correction polarization degree Py of the polarizing film is 99.9970% or more. In the transmission axis direction of the polarizing film, the difference Δt1 between the maximum value and the minimum value of the film thickness is 2.1 μm or less.

The transmission axis direction of the polarizing film is a direction perpendicular to the stretching direction of the PVA-based film. The later-described absorption axis direction of the polarizing film is the stretching direction of the PVA-based film.

The luminosity correction single transmittance Ty of the polarizing film is 43.20% or more, may be 43.25% or more, may be 43.30% or more, and may be 43.32% or more. good too. The luminosity correction single transmittance Ty of the polarizing film is usually 43.80% or less, may be 43.70 or less, or may be 43.60% or less. Visibility correction polarization degree Py of the polarizing film is 99.9970% or more, may be 99.9975% or more, may be 99.9980% or more, or may be 99.9985% or more good. The visibility correction polarization degree Py of the polarizing film is usually 99.9999% or less, may be 99.9990% or less, or may be 99.9987% or less. A polarizing film in which the visibility-corrected single transmittance Ty and the visibility-corrected degree of polarization Py are within the above ranges has excellent optical properties. The luminosity-corrected single transmittance Ty and the luminosity-corrected polarization degree Py are values measured at the center (middle) position in the transmission axis direction of the polarizing film, and can be measured by the method described in the examples below. .

A polarizing film having a luminosity-corrected single transmittance Ty and a luminosity-corrected polarization degree Py within the above ranges can be obtained, for example, in the method for producing a polarizing film described later, by stretching the PVA-based film, and in each step of producing the polarizing film. It can be obtained by adjusting the processing conditions and the like.

The difference Δt1 (maximum value−minimum value) between the maximum value and the minimum value of the film thickness in the transmission axis direction of the polarizing film is 2.1 μm or less, may be 2.0 μm or less, or is 1.9 μm or less. may be, usually 0 μm or more, 0.1 μm or more, 1.0 μm or more, 1.5 μm or more, or 1.8 μm or more good. The difference Δt1 is obtained by measuring the film thickness of the polarizing film in each of 26 regions divided by dividing the polarizing film into 26 equal parts in the direction of the transmission axis, and measuring the maximum value and This value is calculated based on the minimum value. The difference Δt1 can be measured by the method described in Examples below.

In the polarizing film in which the difference Δt1 is within the above range, the contraction force in the direction of the absorption axis is suppressed from being distributed in the direction of the transmission axis. Excellent uniformity. Therefore, even when a polarizing film or a polarizing plate containing a polarizing film is used as a material and one or more products are obtained from this material by so-called picking, the polarizing film or polarizing plate obtained by picking (hereinafter each referred to as It is sometimes referred to as a "pick-up polarizing film" or "pick-up polarizing plate"), the shrinkage force in the direction of the absorption axis in the direction of the transmission axis can be made uniform. As a result, it is possible to prevent non-uniform heat unevenness, which may occur when the polarizing film or polarizing plate is exposed to high temperature conditions after being applied to a display device. Therefore, it is possible to prevent heat unevenness from becoming conspicuous in the display device, and it becomes easy to provide a display device having excellent appearance quality.

By using a polarizing film in which the difference Δt1 is within the above range, the occurrence of warpage in the cut polarizing film or the cut polarizing plate is suppressed, and the cut polarizing film or the cut polarizing plate is made flat. Easy to use. If the cut-off polarizing film or the cut-off polarizing plate is warped, it interferes with the production equipment of the display device and falls off the production line. Cheap. On the other hand, a flat cut-off polarizing film or cut-off polarizing plate is less likely to cause the above problems and is excellent in handleability.

In the polarizing film, the region having the maximum film thickness is usually located at the end of the polarizing film in the transmission axis direction, and among the above 26 regions, from one or both ends of the polarizing film in the transmission axis direction Each may be in the range of 1 region or more and 8 regions or less, each may be in the range of 1 region or more and 6 regions or less, or each may be in the range of 1 region or more and 4 regions or less.

In the polarizing film, the region having the minimum film thickness is usually located in the center of the polarizing film in the transmission axis direction, and among the 26 regions, the center (middle) in the transmission axis direction Towards both ends, each may be in the range of 1 to 5 regions (2 to 10 regions in total), and the range of 1 to 4 regions (2 to 8 regions in total). may be within the range of 1 to 3 regions (total of 2 to 6 regions), respectively, and may be within the range of 1 to 2 regions (total of 2 to 4 regions) may be inside.

In the polarizing film, the difference Δt2 between the maximum film thickness in the end regions in the transmission axis direction and the maximum film thickness in the central region in the transmission axis direction (maximum film thickness in the end regions - film thickness in the central region) maximum value) is preferably 2.1 μm or less, may be 2.0 μm or less, may be 1.8 μm or less, may be 1.7 μm or less, and is usually 0.5 μm 1.0 μm or more, or 1.2 μm or more.

The difference Δt2 is obtained by measuring the film thickness of the polarizing film in each of the 26 regions described above divided by dividing the polarizing film into 26 equal parts in the direction of the transmission axis, and dividing the regions included in the 26 regions according to their positions. It is a value calculated based on the maximum film thickness of the polarizing film in each of the edge region and the central region, classified into the edge region and the central region. The difference Δt2 can be measured by the method described in Examples below. Out of the 26 regions, the end region is a range of 8 regions from both ends in the transmission axis direction of the polarizing film, and the central region is out of the 26 regions described above, in the direction of the transmission axis of the polarizing film. 5 areas (10 areas in total) from the center (middle) to both ends in the transmission axis direction.

A polarizing film in which the difference Δt2 is within the above range can suppress the occurrence of distribution in the contraction force in the direction of the absorption axis in the transmission axis direction of the polarizing film, and the contraction force in the direction of the absorption axis in the direction of the transmission axis can be uniform. Excellent in nature. By using a polarizing film in which the difference Δt2 is within the above range, the shrinkage force of the cut-off polarizing film or the cut-off polarizing plate, particularly in the direction of the transmission axis and in the direction of the absorption axis, can be made uniform. This makes it easier to provide a display device with excellent appearance quality using the cut-off polarizing film or cut-off polarizing plate, and to improve the handleability of the cut-off polarizing film or the pick-up polarizing plate.

A polarizing film in which the difference Δt1 and the difference Δt2 are within the above ranges can be obtained by adjusting the processing conditions and the like in the process of manufacturing the polarizing film in the method for manufacturing the polarizing film described later. In order to adjust the difference Δt1 and the difference Δt2 of the polarizing film, for example, the temperature of the crosslinking step, the temperature of the high-temperature, high-humidity step, the absolute humidity, the cumulative draw ratio up to the crosslinking step, and the high-temperature, high-humidity The draw ratio and the like in the process may be adjusted. Here, "until the cross-linking step" refers to a step until the cross-linking treatment is completed.

The average thickness of the polarizing film in the central region in the transmission axis direction is preferably 5 μm or more, may be 7 μm or more, may be 9 μm or more, may be 10 μm or more, or may be 16 μm or more. 18 μm or more, preferably 30 μm or less, 29 μm or less, 25 μm or less, 22 μm or less, or 21 μm or less. may be 20 μm or less. The central region in the transmission axis direction of the polarizing film is within the range described above. The average film thickness in the central region is the average value of film thicknesses measured in each of the regions included in the central region among the 26 regions. The average film thickness can be measured by the method described in Examples below.
The average film thickness in the end regions of the polarizing film in the transmission axis direction is preferably within the range described for the average film thickness in the central region. The average thickness of the edge regions of the polarizing film may be the same as or different from the average thickness of the central region, or may be greater than the average thickness of the central region. The end region of the polarizing film in the transmission axis direction is the region within the range described above, and the average film thickness of the end region is the average value of the film thicknesses measured in each of the regions included in the end region among the 26 regions. be.

The polarizing film of the present embodiment can be suitably used as a polarizing film as a material for obtaining a cut polarizing film or a cut polarizing plate as described above. Therefore, the length of the polarizing film in the transaxial direction is preferably 800 mm or more, more preferably 1000 mm or more, and more preferably 1200 mm or more, so as to enable cutting, preferably multiple cutting. Also, it is preferably 2500 mm or less, more preferably 2300 mm or less, may be 2000 mm or less, or may be 1500 mm or less.

(Method for producing polarizing film)
The method for producing the polarizing film of this embodiment includes, for example,
A dyeing step of dyeing the PVA-based film with a dichroic dye,
A cross-linking step of treating the film after the dyeing step with a cross-linking bath containing a cross-linking agent,
A high-temperature and high-humidity process of subjecting the film after the cross-linking process to a high-temperature and high-humidity treatment, and
a stretching step of uniaxially stretching the PVA-based film.

In the above method for producing a polarizing film,
The cross-linking step includes a step of treating with a cross-linking bath having a temperature of 58.0 ° C. or higher,
The high temperature and high humidity step includes a step of exposing to an atmosphere with a temperature of 70.0 ° C or higher and an absolute humidity of 40.0 g / m ³ or higher,
The cumulative draw ratio of the PVA-based film up to the cross-linking step is 5.50 times or more and 5.90 times or less,
The stretch ratio of the PVA-based film in the high temperature and high humidity process is 1.02 times or more and 1.20 times or less,
The total draw ratio of the PVA-based film is 5.60 times or more.

The manufacturing method of the polarizing film can further include other steps than the above. Other processes include a swelling process performed before the dyeing process, a washing process performed after the cross-linking process, and a drying process performed during or after the high-temperature and high-humidity process.

Various processing steps included in the manufacturing method of the polarizing film can be continuously performed by continuously transporting the PVA-based film, which is the original film, along the film transport path of the polarizing film manufacturing apparatus. The film transport path is provided with facilities (processing baths, furnaces, etc.) for performing the various processing steps described above in order of implementation. The term "treatment bath" refers to a bath containing a treatment liquid for treating the PVA-based film, such as a swelling bath, a dyeing bath, a cross-linking bath, and a washing bath.

In addition to the above equipment, the film transport route can be constructed by arranging guide rolls, nip rolls, etc. at appropriate positions. For example, guide rolls can be placed before, after, and within each treatment bath to allow introduction, immersion, and withdrawal of the film into and out of the treatment bath. More specifically, the film can be immersed in each treatment bath by providing two or more guide rolls in each treatment bath and conveying the film along these guide rolls.

As the polyvinyl alcohol-based resin (hereinafter sometimes referred to as "PVA-based resin") that constitutes the PVA-based film, which is the original film, saponified polyvinyl acetate-based resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group. The degree of saponification of the PVA-based resin is generally about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. "(Meth)acryl" means at least one selected from acryl and methacryl. The same applies to "(meth)acryloyl".

The PVA-based resin may be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. may be used.

The average degree of polymerization of the PVA-based resin is preferably 100-10000, more preferably 1500-8000, still more preferably 2000-5000. The average degree of polymerization of the PVA-based resin can be obtained according to JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain preferable polarizing performance, and if it exceeds 10,000, film workability may be poor.

The thickness of the PVA-based film as the original film is, for example, about 10 μm or more and 150 μm or less, and from the viewpoint of thinning the polarizing film, it is preferably 100 μm or less, more preferably 70 μm or less, still more preferably 50 μm or less, and even more preferably 50 μm or less. is 40 μm or less.

A PVA-based film, which is a raw film, can be prepared, for example, as a roll (wound product) of a long unstretched PVA-based film. In this case, the polarizing film is also obtained as an elongated product. Each step of the method for producing a polarizing film will be described in detail below.

(Swelling process)
The swelling treatment in the swelling step is performed as necessary for the purpose of removing foreign substances from the original PVA-based film, removing the plasticizer, imparting easy dyeability, plasticizing the film, and the like. Specifically, it can be a treatment in which the PVA-based film is immersed in a swelling bath containing water. The PVA-based film may be immersed in one swelling bath or sequentially immersed in two or more swelling baths. Before the swelling treatment, during the swelling treatment, or before and during the swelling treatment, the film may or may not be uniaxially stretched.

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

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

(Dyeing process)
The dyeing process in the dyeing process is a process performed for the purpose of adsorbing and orienting the dichroic dye on the PVA-based film, and specifically, a process of immersing the PVA-based film in a dyeing bath containing the dichroic dye. can be The PVA-based film may be immersed in one dyeing bath, or may be immersed in two or more dyeing baths sequentially. In order to enhance the dyeability of the dichroic dye, the PVA-based film subjected to the dyeing process may be subjected to at least some uniaxial stretching treatment. Instead 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 may be performed during the dyeing treatment.

The dichroic dye can be iodine or a dichroic organic dye. Dichroic organic dyes 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, and 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, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue , Direct Fast Orange S, Fast Black, and the like. A dichroic dye may be used individually by 1 type, and may use 2 or more types together.

When using iodine as a 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. Compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. The addition of boric acid is distinguished from the cross-linking treatment described later in that it contains iodine. The content of iodine in the aqueous solution is usually about 0.003 to 1 part by mass per 100 parts by mass of water. The content of iodides such as potassium iodide is usually about 0.1 to 20 parts by mass per 100 parts by mass of water.

The temperature of the dyeing bath when the PVA-based film is immersed 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 30°C. It is about 600 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. This dyeing bath may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. 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 the film is immersed is, for example, about 20 to 80° C., preferably about 30 to 70° C., and the immersion time of the film is usually about 20 to 600 seconds, preferably about 30 to 300 seconds. be.

(Crosslinking step)
In the cross-linking step, a cross-linking treatment is performed by treating the PVA-based film after the dyeing step with a cross-linking agent. The cross-linking treatment is performed for the purpose of water resistance by cross-linking, color adjustment, etc. Specifically, it can be a treatment of immersing the film after the dyeing step in a cross-linking bath containing a cross-linking agent. The film may be immersed in one cross-linking bath or sequentially immersed in two or more cross-linking baths. A uniaxial stretching treatment may be performed during the cross-linking treatment.

The cross-linking agent includes boric acid, and may further include other cross-linking agents such as glyoxal and glutaraldehyde. The content of boric acid in the cross-linking bath is usually about 0.1 to 15 parts by mass, preferably about 1 to 10 parts by mass, per 100 parts by mass of water.
When the dichroic dye is iodine, the cross-linking bath preferably contains iodide in addition to boric acid. The content of iodide in the cross-linking bath is usually about 0.1 to 20 parts by mass, preferably about 5 to 15 parts by mass, per 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist in the cross-linking bath.

In the cross-linking step, when the PVA-based film is sequentially immersed in two or more cross-linking baths, the composition and content of the components contained in the cross-linking baths may be the same, but preferably different.

The temperature of the cross-linking bath when the PVA-based film is immersed has the luminosity correction single transmittance Ty and the luminosity correction degree of polarization Py in the above ranges, and the film thickness difference Δt1 in the above ranges. From the viewpoint of obtaining a film, the temperature is preferably 58.0°C or higher, more preferably 58.3°C or higher, and may be 58.5°C or higher, usually 85.0°C or lower, preferably 70°C. 0° C. or lower, may be 65.0° C. or lower, may be 63.0° C. or lower, or may be 61.0° C. or lower. The immersion time in the cross-linking bath at this temperature is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

When the PVA-based film is sequentially immersed in two or more cross-linking baths, the temperature and cross-linking time in at least one cross-linking bath may be within the above ranges, and the temperature and cross-linking time in the other cross-linking baths may be within the above-described temperatures and cross-linking baths. It may be within the range of the cross-linking time or may be outside the range. When the PVA-based film is immersed in two or more cross-linking baths in sequence, it is preferable to use a cross-linking bath having a temperature of 58.0° C. or higher as the first cross-linking bath. The temperature in other cross-linking baths may be, for example, about 50 to 85° C., or about 50 to 70° C., and the film immersion time may be, for example, about 10 to 600 seconds, or about 20 to 300 seconds.

(Washing process)
The washing treatment in the washing step is a treatment carried out as necessary for the purpose of removing excess crosslinking agents and dichroic dyes adhering to the PVA-based film, and crosslinking is performed using a washing solution containing water. This is a treatment for washing the PVA-based film after the process. Specifically, it can be a treatment in which the PVA-based film after the cross-linking step is immersed in a cleaning bath (cleaning liquid). The PVA-based film may be immersed in one cleaning bath, or may be immersed in two or more cleaning baths sequentially.
Alternatively, the washing treatment may be a treatment of spraying a washing solution as a shower onto the PVA-based film after the cross-linking step, or a combination of the above immersion and spraying.

The cleaning liquid may be water (for example, pure water), or may be an aqueous solution to which a water-soluble organic solvent such as alcohol is added. The temperature of the cleaning liquid can be, for example, about 1 to 40° C., and the cleaning time can be, for example, about 1 to 60 seconds.

The cleaning step is an optional step and may be omitted, or the cleaning treatment may be performed during the high temperature and high humidity step (the high temperature and high humidity treatment may also serve as the cleaning treatment). Preferably, the film after the washing step is subjected to a high-temperature and high-humidity treatment.
Further, in the washing process, a stretching treatment may be applied within a range that does not affect the performance of the film.

(High temperature and high humidity process)
The high-temperature, high-humidity treatment in the high-temperature, high-humidity process is a treatment in which the PVA-based film after the cross-linking process or after the washing process is exposed to an atmosphere with a temperature of 70.0° C. or higher and an absolute humidity of 40.0 g/m ³ or higher. Compared to the case of performing high temperature treatment (drying treatment) at an absolute humidity of less than 40.0 g/m ³ instead of high temperature and high humidity treatment, while suppressing deterioration of the optical properties of the polarizing film by performing high temperature and high humidity treatment. It is possible to obtain a polarizing film having excellent uniformity of shrinkage force in the direction of the absorption axis in the direction of the transmission axis while having excellent optical properties.

The high-temperature and high-humidity treatment is preferably applied to the PVA-based film after the cross-linking step or after the washing step in a wet state. "In a wet state" means that the PVA-based film with a high moisture content after the cross-linking step or after the washing step is left as it is (without performing a high-temperature treatment (drying treatment) at an absolute humidity of less than 40.0 g/m ³ ). It means subjecting to high temperature and high humidity treatment.

The high-temperature and high-humidity treatment can be a treatment in which the PVA-based film after the cross-linking process or after the washing process is introduced into a furnace (heating furnace), booth, or room in which temperature and humidity can be adjusted. In addition to the treatment introduced into the furnace (heating furnace), booth, or room, a 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 carried out after the washing step, but the high-temperature and high-humidity treatment and the washing treatment may be performed at the same time, such as by spraying a washing solution in a predetermined high-temperature and high-humidity atmosphere. The high-temperature and high-humidity treatment may also serve as the cleaning treatment, as in the case where the PVA-based film is substantially cleaned by exposing it to a moist atmosphere.

The temperature of the high-temperature and high-humidity treatment has the visibility-corrected single transmittance Ty and the visibility-corrected degree of polarization Py in the above ranges, and from the viewpoint of obtaining a polarizing film having the film thickness difference Δt1 in the above ranges, 70.0° C. or higher, preferably 75.0° C. or higher, more preferably 78.0° C. or higher, still more preferably 80.0° C. or higher, usually 100.0° C. or lower, preferably 95.0° C. or higher 0°C or less, more preferably 90.0°C or less.

The absolute humidity in the high-temperature and high-humidity treatment has the luminosity-corrected single transmittance Ty and the luminosity-corrected degree of polarization Py in the above ranges, and from the viewpoint of obtaining a polarizing film having the film thickness difference Δt1 in the above ranges. , 40.0 g/m ³ or more, preferably 75.0 g/m ³ or more, more preferably 80.0 g/m ³ or more, and still more preferably 85.0 g/m ³ or more. ^On the other hand, if the absolute humidity is excessively high, there is a concern that dew condensation will occur in the treatment zone and the PVA-based film will be contaminated by the condensed water. Preferably 400.0 g/m ³ or less, more preferably 300.0 g/m ³ or less, 250.0 g/m ³ or less, or 180.0 g/m ³ or less, particularly preferably It is 160.0 g/m ³ or less, and may be 100.0 g/m ³ or less.

The time for the high-temperature and high-humidity treatment is, from the viewpoint of obtaining a polarizing film having the visibility-corrected single transmittance Ty and the visibility-corrected degree of polarization Py in the above ranges and the film thickness difference Δt1 in the above ranges, It is preferably 5 seconds or longer, more preferably 10 seconds or longer. Although the time depends on the temperature, if it is too long, the optical properties may deteriorate, so it is preferably 60 minutes or less, more preferably 30 minutes or less, and still more preferably 10 minutes or less. , particularly preferably 5 minutes or less.

The high-temperature and high-humidity treatment can be a treatment in which a long PVA-based film is conveyed along the film conveying route and continuously introduced into and passed through the furnace or the like. The tension of the film in such a high-temperature and high-humidity treatment has the luminosity-correction single transmittance Ty and the luminosity-correction polarization degree Py in the above ranges, and a polarizing film having a film thickness difference Δt1 in the above ranges. is preferably from 50 to 3000 N/m, more preferably from 200 to 2000 N/m, and more preferably from 300 to 2000 N/m. From the viewpoint of suppressing the occurrence of wrinkles in the film, the film tension is preferably 200 N/m or more, more preferably 500 N/m or more.

The high-temperature, high-humidity treatment may also serve as a treatment for drying the PVA-based film, that is, a treatment for lowering its moisture content, and unless extreme high-temperature, high-humidity conditions are employed, the drying treatment is usually performed at the same time. As a result, it is not always necessary to perform a separate drying treatment after the high-temperature and high-humidity treatment, so compared to the method of performing the high-temperature and high-humidity treatment after the high-temperature treatment (drying treatment) at an absolute humidity of less than 40 g / m ³ , which is advantageous in terms of simplification and efficiency of the manufacturing process.

(Drying process)
In the drying step, a drying process for drying the PVA-based film is performed. The drying treatment may be performed during the high-temperature and high-humidity process as described above, but may be performed after the high-temperature and high-humidity process. When the drying treatment is performed after the high temperature and high humidity process, the high temperature treatment may be performed at an absolute humidity of less than 40 g/m ³ . The drying treatment may be performed as necessary, and the drying treatment may not be performed.

(Stretching process)
The stretching step is a step of stretching the PVA-based film, and the PVA-based film is preferably uniaxially stretched. A PVA-based film is uniaxially stretched in one or more steps of a swelling process, a dyeing process, a cross-linking process, a washing process, a high-temperature high-humidity process, and a drying process. From the viewpoint of obtaining a polarizing film having the luminosity-corrected single transmittance Ty and the luminosity-corrected degree of polarization Py in the above ranges and having the film thickness difference Δt1 in the above ranges, the uniaxial stretching includes the dyeing step, the cross-linking It is preferable to perform a uniaxial stretching treatment in the process and the high-temperature, high-humidity process.

The uniaxial stretching treatment may be either dry stretching in air or wet stretching in a bath, or both. The uniaxial stretching treatment can be inter-roll stretching, hot roll stretching, tenter stretching, etc., in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between two nip rolls, but preferably includes roll-to-roll stretching.

The cumulative stretch ratio up to the cross-linking step when the raw film is used as a reference has the luminosity correction single transmittance Ty and the luminosity correction polarization degree Py in the above range, and the film thickness difference in the above range. From the viewpoint of obtaining a polarizing film having Δt1, it is preferably 5.50 times or more and 5.90 times or less, and may be 5.50 times or more and 5.80 times or less.
The total draw ratio including the cumulative draw ratio up to the cross-linking process when based on the raw film and the subsequent treatment process (mainly the high temperature and high humidity process) Cumulative draw ratio) is preferable from the viewpoint of obtaining a polarizing film having the luminosity correction single transmittance Ty and the luminosity correction degree of polarization Py in the above range and having the film thickness difference Δt1 in the above range. is 5.60 times or more, may be 5.70 times or more, may be 5.80 times or more, may be 5.90 times or more, and is usually 7 times or less.
In particular, from the viewpoint of obtaining a polarizing film having the visibility-corrected single transmittance Ty and the visibility-corrected polarization degree Py in the above ranges and having the film thickness difference Δt1 in the above ranges, the draw ratio in the above step and In addition, the draw ratio in the high-temperature and high-humidity process is preferably 1.02 times or more and 1.20 times or less, and may be 1.02 times or more and 1.17 times or less.

The cumulative draw ratio up to the cross-linking step and the total draw ratio including the subsequent treatment steps are within a certain range or more in order to increase the optical performance of the polarizing film, such as the visibility correction single transmittance Ty and the visibility correction polarization degree Py. However, stretching more than necessary may cause breakage of the PVA-based film or poor appearance. In particular, if the cumulative draw ratio up to the cross-linking step exceeds 5.90 times, the room for stretching the PVA-based film in the subsequent processing steps (especially the high-temperature and high-humidity step) becomes small, and the optical performance is rather reduced. If the PVA-based film is forcibly stretched in subsequent processing steps such as high-temperature and high-humidity processing, the film thickness distribution in the PVA-based film may become large, and the difference in shrinkage force of the polarizing film may become large.
In addition, even if the cumulative draw ratio up to the cross-linking step is in the above range (5.50 times or more and 5.90 times or less), excessive stretching in the high-temperature and high-humidity step (stretching at a draw ratio exceeding 1.20 times) On the contrary, the film thickness distribution in the PVA-based film becomes large, and there is a possibility that the difference in shrinkage force of the polarizing film becomes large.

The stretching process in the high-temperature and high-humidity process is performed by, for example, introducing the PVA-based film after the cross-linking process into a furnace (heating furnace), booth, or room in which the temperature and humidity can be adjusted, while performing the high-temperature and high-humidity process. It can be a process to In the high-temperature and high-humidity treatment, heating means such as a far-infrared heater and heat rolls may be used in combination with the treatment introduced into a furnace (heating furnace), booth, or room. The stretching treatment in the high-temperature and high-humidity process may be carried out simultaneously in a high-temperature and high-humidity atmosphere, such as by spraying a cleaning solution while stretching the PVA-based film in a predetermined high-temperature and high-humidity atmosphere. Also, when the PVA-based film is substantially washed by being placed in a high-temperature and high-humidity atmosphere, the high-temperature and high-humidity treatment and the stretching treatment may also serve as the washing treatment.

(Polarizer)
The polarizing plate of this embodiment is obtained by laminating a protective film on one side or both sides of the polarizing film described above. The protective film may be laminated on the polarizing film via a bonding layer, or may be laminated so as to be in direct contact with the polarizing film. The lamination layer is a pressure-sensitive adhesive layer or an adhesive layer.

Protective films include thermoplastic resins such as linear polyolefin resins (polypropylene resins, etc.), polyolefin resins such as cyclic polyolefin resins (norbornene resins, etc.); cellulose esters such as triacetyl cellulose and diacetyl cellulose. Resin; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resins; (meth)acrylic resins such as polymethyl methacrylate resins; Can be film.

The protective film can also be a protective film that has 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 (uniaxially or biaxially stretching, etc.) a transparent resin film made of the above materials, or by forming a liquid crystal layer or the like on the film. can be

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and 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 thin from the viewpoint of thinning the polarizing plate. 10 to 50 μm.

Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or an aqueous solution containing a cross-linking agent. Water-based adhesives such as urethane-based emulsion adhesives can be used. When the protective films are attached to both sides of the polarizing film, the adhesives forming the two adhesive layers may be of the same type or of different types. For example, when laminating protective films on both sides, one side may be laminated using a water-based adhesive, and the other side may be laminated using an active energy ray-curable adhesive. The UV-curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, a mixture of a cationic polymerizable epoxy compound and a photocationic polymerization initiator, or the like. Moreover, a cationic polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound can be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator can also be used together as initiators.

When using an active energy ray-curable adhesive, the adhesive is cured by irradiating it with an active energy ray after lamination. The light source of the active energy ray is not particularly limited, but the active energy ray (ultraviolet rays) having an emission distribution at a wavelength of 400 nm or less is preferable. Black light lamps, microwave excited mercury lamps, metal halide lamps and the like are preferably used.

In order to improve the adhesion between the polarizing film and the protective film, prior to laminating the polarizing film and the protective film, corona treatment, flame treatment, plasma treatment, ultraviolet Surface treatments such as irradiation treatment, primer coating treatment, and saponification treatment may be applied.

As the adhesive used for bonding the polarizing film and the protective film, conventionally known adhesives having excellent optical transparency can be used without particular limitation. Examples include acrylic polymers, urethane polymers, silicone polymers, and polyvinyl ethers. A pressure-sensitive adhesive containing a base polymer such as can be used. Adhesives using acrylic resin as a base polymer, which are excellent in transparency, adhesive strength, removability (reworkability), weather resistance, heat resistance, etc., are suitable. The pressure-sensitive adhesive layer preferably comprises a reaction product of a pressure-sensitive adhesive composition containing a (meth)acrylic resin, a cross-linking agent and a silane compound, and may contain other components.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" and "parts" in Examples and Comparative Examples are % by mass and parts by mass.

[Example 1]
A long polyvinyl alcohol (PVA) resin film with a thickness of 45 μm and a width of 2900 mm as a raw film [degree of saponification of 99.9 mol% or more] is continuously conveyed while being unwound from a roll, and a pure film at a temperature of 30 ° C. It was immersed in a swelling bath made of water for a residence time of 81 seconds (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath containing iodine with a potassium iodide/water ratio of 2/100 (mass ratio) at a temperature of 30°C for a residence time of 143 seconds (dyeing step). Then, the film pulled out from the dyeing bath is immersed in a crosslinking bath with a potassium iodide/boric acid/water ratio of 12/3.8/100 (mass ratio) at a temperature of 58.5°C for a residence time of 67 seconds, followed by Then, it was immersed in a crosslinking bath containing potassium iodide/boric acid/water at a ratio of 9/2.4/100 (mass ratio) at a temperature of 40°C for a residence time of 11 seconds (crosslinking step). In the dyeing process and the cross-linking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The cumulative draw ratio up to the cross-linking step was 5.74 times based on the raw film.

Next, the film pulled out from the cross-linking bath is immersed in a cleaning bath made of pure water at a temperature of 4° C. for a retention time of 3 seconds (cleaning step), and then introduced into a heating furnace capable of controlling humidity for retention. A high-temperature and high-humidity treatment was performed for 161 seconds (high-temperature and high-humidity process) to obtain a polarizing film. The temperature and absolute humidity in the heating furnace were set to 80.0° C. and 88.0 g/m ³ respectively, and the film tension during high temperature and high humidity treatment was set to 1300 N/m. The absolute humidity in the heating furnace was calculated from the measured values of the temperature and relative humidity in the furnace. As a result of further longitudinal uniaxial stretching (stretch ratio: 1.02 times) by introduction into a heating furnace (high temperature and high humidity treatment), the total stretch ratio based on the original film of the polarizing film was 5.83 times. rice field.

The length (width) in the transmission axis direction of the polarizing film obtained above was 1242 mm. This polarizing film was evaluated as described later. Table 1 shows the results.

[Comparative Example 1]
Example 1 except that the temperature and absolute humidity of the heating furnace used in the high temperature and high humidity treatment of Example 1 were 40.0 ° C. and 1.5 g / m ³ , respectively, and the stretching treatment in the heating furnace was not performed. A polarizing film was obtained in the same manner as in 1. The treatment in the heating furnace is heat treatment (dry treatment) rather than high temperature and high humidity treatment. The final total draw ratio based on the raw film of the polarizing film was 5.74 times (the draw ratio in the high temperature and high humidity process was 1.00 times).

The length (width) in the transmission axis direction of the polarizing film obtained above was 1270 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 1 shows the results.

[Comparative Example 2]
A polarizing film was obtained in the same manner as in Comparative Example 1, except that the longitudinal uniaxial stretching ratio in the inter-roll stretching in the bath was increased in the crosslinking step (cumulative stretching ratio up to the crosslinking step: 5.81 times). The final total draw ratio based on the raw film of the polarizing film was also 5.81 times (the draw ratio in the high temperature and high humidity process was 1.00 times).

The length (width) of the polarizing film obtained above in the transmission axis direction was 1280 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 1 shows the results.

[Example 2]
A long polyvinyl alcohol (PVA) resin film with a thickness of 45 μm and a width of 450 mm as a raw film [degree of saponification of 99.9 mol% or more] is continuously conveyed while being unwound from a roll, and a pure film at a temperature of 30 ° C. It was immersed in a swelling bath made of water for a residence time of 45 seconds (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a dyeing bath containing iodine with a potassium iodide/water ratio of 2/100 (mass ratio) at a temperature of 30°C for a residence time of 57 seconds (dyeing step). Then, the film pulled out from the dyeing bath is immersed in a crosslinking bath containing potassium iodide/boric acid/water at a ratio of 12/4.1/100 (mass ratio) at a temperature of 59°C for a residence time of 40 seconds, followed by It was immersed in a cross-linking bath at a temperature of 60° C. in which potassium iodide/boric acid/water were 11.7/4.1/100 (mass ratio) for a residence time of 6 seconds (cross-linking step). In the dyeing process and the cross-linking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The cumulative draw ratio up to the cross-linking step was 5.54 times based on the original film.

Next, the film pulled out from the cross-linking bath is immersed in a cleaning bath made of pure water at a temperature of 5° C. for a residence time of 1 second (washing step), and subsequently introduced into a heating furnace capable of controlling humidity for residence. A high temperature and high humidity treatment was performed for 93 seconds (high temperature and high humidity process) to obtain a polarizing film. The temperature and absolute humidity in the heating furnace were set to 80.0° C. and 175 g/m ³ respectively, and the film tension during high temperature and high humidity treatment was set to 200 N/m. The absolute humidity in the heating furnace was calculated from the measured values of the temperature and relative humidity in the furnace. As a result of further longitudinal uniaxial stretching by introduction into a heating furnace (high-temperature and high-humidity treatment), the total draw ratio based on the original film of the polarizing film was 6.50 times (stretch ratio in the high-temperature and high-humidity process was 1.15 times).

The length (width) in the transmission axis direction of the polarizing film obtained above was 188 mm. This polarizing film was evaluated as described later. Table 2 shows the results.

[Example 3]
The temperature and absolute humidity of the heating furnace used in the high-temperature and high-humidity treatment of Example 2 were set to 70.0° C. and 120 g/m ³ respectively, and the path of the film in the heating furnace was made shorter than in Example 2 to reduce the residence time. A polarizing film was obtained in the same manner as in Example 2, except that the time was set to 31 seconds and the draw ratio in the high-temperature and high-humidity process was set to 1.02 times. The final total draw ratio based on the raw film of the polarizing film was 5.77 times.

The length (width) in the transmission axis direction of the polarizing film obtained above was 205 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 2 shows the results.

[Example 4]
Based on the original film, the cumulative draw ratio until the cross-linking step was 5.70 times, and the temperature and absolute humidity of the heating furnace used in the high temperature and high humidity treatment of Example 2 were 80.0 ° C. and 203 g / m ³ respectively. A polarizing film was obtained in the same manner as in Example 2, except that the draw ratio in the high-temperature, high-humidity process was 1.16 times. The final total draw ratio based on the raw film of the polarizing film was 6.75 times.

The length (width) in the transmission axis direction of the polarizing film obtained above was 186 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 2 shows the results.

[Comparative Example 3]
Based on the original film, the cumulative draw ratio until the cross-linking step was 5.92 times, and the temperature and absolute humidity of the heating furnace used in the high temperature and high humidity treatment in Example 2 were 80.0 ° C. and 120 g / m ³ respectively. A polarizing film was obtained in the same manner as in Example 2, except that the residence time was 99 seconds and the draw ratio in the high-temperature and high-humidity process was 1.03 times. The final total draw ratio based on the raw film of the polarizing film was 6.24 times.

The length (width) in the transmission axis direction of the polarizing film obtained above was 199 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 3 shows the results.

[Comparative Example 4]
Based on the original film, the cumulative draw ratio up to the cross-linking step was 6.35 times, and the temperature and absolute humidity of the heating furnace used in the high temperature and high humidity treatment of Example 2 were 80.0 ° C. and 10.4 g / m ³ , the residence time was 103 seconds, the film tension during the high-temperature and high-humidity treatment was 40 N/m, the draw ratio in the high-temperature and high-humidity treatment was 0.94 times, and the drawing treatment in the heating furnace was not performed. A polarizing film was obtained in the same manner as in Example 2 except for the above. The final total draw ratio based on the raw film of the polarizing film was 6.10 times.

The length (width) in the transmission axis direction of the polarizing film obtained above was 207 mm. Evaluation mentioned later was performed about the polarizing film obtained above. Table 3 shows the results.

[Visibility correction single transmittance (Ty) and visibility correction polarization degree (Py)]
Using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation], MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm are measured at the center (middle) position of the transmission axis direction of the polarizing film. was measured. The formula below:
Single transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD-TD) / (MD + TD)} x 100
, 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 perpendicular to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula.

Regarding the obtained single transmittance and degree of polarization, visibility correction was performed with a 2-degree field of view (C light source) of JIS Z 8701: 1999 “Color display method-XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system”. Then, the luminosity-corrected single transmittance Ty and the luminosity-corrected polarization degree Py were obtained.

[Differences in film thickness Δt1 and Δt2, and average film thickness]
The thickness of each of the 26 regions divided by dividing the polarizing film into 26 equal parts in the direction of the transmission axis was measured using a digital micrometer ["MH-15M" manufactured by Nikon Corporation].

(Calculation of difference Δt1)
The maximum and minimum values of the 26 film thicknesses obtained by the above measurements were calculated, and the difference between the two was calculated as the difference Δt1 between the maximum and minimum film thicknesses in the transmission axis direction of the polarizing film. . In any polarizing film, the region where the film thickness is the minimum value is one or more regions from the center (middle) in the transmission axis direction toward both ends in the transmission axis direction among the 26 regions described above. It is a region within the range of 5 regions or less (a total of 2 regions or more and 10 regions or less), and regions other than these regions include regions where the film thickness reaches the maximum value.

(Calculation of difference Δt2)
8 regions from both ends of the polarizing film in the transmission axis direction of the 26 regions are defined as end regions, and from the center (middle) in the transmission axis direction of the polarizing film toward both ends in the transmission axis direction A range of 5 regions (total of 10 regions) was defined as the central region. The difference between the maximum film thickness of the regions included in the edge regions and the maximum film thickness of the regions included in the central region (maximum film thickness of the edge regions - film thickness of the central region) ) was calculated as Δt2.

(Calculation of average film thickness)
Of the 26 regions, the average value of the film thickness of the region included in the central region and the average value of the film thickness of the regions included in the end region are calculated as the average film thickness in the central region in the transmission axis direction of the polarizing film. It was calculated as an average value in the thickness and the end region in the transmission axis direction of the polarizing film.

[MD shrinkage force of polarizing film]
From each of the 26 regions obtained by dividing the polarizing film into 26 equal parts in the transmission axis direction, a measurement sample of 2 mm in width and 10 mm in length was cut out with the long side in the absorption axis direction (MD direction, stretching direction). This sample for measurement was set in a thermomechanical analyzer (TMA) ["EXSTAR-6000" manufactured by SII Nanotechnology Co., Ltd.] and held at a temperature of 80° C. for 4 hours while keeping the dimensions constant. The MD contractile force, which is the contractile force in the longitudinal direction (MD direction, absorption axis direction) that sometimes occurs, was measured. The difference between the maximum and minimum MD contractile forces of the measurement samples prepared for each of the 26 regions was determined. In any polarizing film, the measurement sample with the minimum MD shrinkage force was oriented from the center (middle) in the transmission axis direction to both ends in the transmission axis direction in the 26 regions described above. A measurement sample made from a region within the range of 1 region or more and 5 regions or less (a total of 2 regions or more and 10 regions or less). It contained a different measurement sample.

As shown in Tables 1 to 3, the polarizing films of Examples have large luminosity-correction single transmittance Ty and luminosity-correction polarization degree Py and are excellent in optical properties. Excellent uniformity of shrinkage force in the absorption axis direction of the polarizing film in the transmission axis direction.

Claims

A polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film,
The visibility correction single transmittance Ty is 43.20% or more,
Visibility correction polarization degree Py is 99.9970% or more,
A polarizing film, wherein the difference between the maximum thickness and the minimum thickness in the transmission axis direction is 2.1 μm or less.
The polarizing film according to claim 1, wherein the difference between the maximum film thickness in the end regions in the transmission axis direction and the maximum film thickness in the central region in the transmission axis direction is 2.1 µm or less.
The polarizing film according to claim 1, wherein the length in the transmission axis direction is 800 mm or more and 2500 mm or less.
The polarizing film according to claim 1, wherein the average film thickness in the central region in the transmission axis direction is 5 µm or more and 30 µm or less.
The polarizing film according to claim 1, wherein the average film thickness in the central region in the transmission axis direction is 16 µm or more and 29 µm or less.
A polarizing plate comprising a protective film laminated on one or both sides of the polarizing film according to any one of claims 1 to 5.