JP2023121757A - Polarizer and manufacturing method therefor - Google Patents

Abstract

To provide a highly heat-resistant polarizer.SOLUTION: A polarizer provided herein features a ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds in a range of 0.64 to 0.76, inclusive, in a direction parallel to a slow axis thereof, has a thickness of 15 μm or less, and is obtained by adsorbing and aligning a dichroic pigment in a polyvinyl alcohol resin film.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a polarizer that can be used as a constituent member of a polarizing plate and a method for producing the same.

As a polarizer, a polyvinyl alcohol-based resin film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented is known. Patent Documents 1 to 3 propose films containing zinc as such polyvinyl alcohol resin films.

Japanese Patent Application Laid-Open No. 2003-29042 JP 2004-61565 A JP 2014-102353 A

A polarizer may undergo discoloration when used for a long time at high temperature as a constituent member of a polarizing plate. Therefore, it is required to improve the heat resistance of the polarizer.

An object of the present invention is to provide a polarizer having good heat resistance.

The present invention provides the following polarizer, polarizing plate, and method for producing a polarizer.
[1] A polarizer having a ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds of more than 0.47 and less than 0.9.
[2] The polarizer according to [1], wherein the ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds in the direction parallel to the absorption axis of the polarizer is more than 0.47 and less than 0.9.
[3] The polarizer according to [1] or [2], which has a thickness of 15 μm or less.
[4] The polarizer according to any one of [1] to [3], a first thermoplastic resin film provided on one surface thereof, and a second thermoplastic resin film provided on the other surface thereof. A polarizing plate.
[5] The polarizing plate of [4], wherein the second thermoplastic resin film is a retardation film.
[6] The polarizing plate of [4] or [5], wherein the absolute value ΔTy of the difference in luminous efficiency-corrected single transmittance Ty before and after the durability test at 105° C. and 1000 hours is 4% or less.
[7] Any of [4] to [6], wherein the absolute value ΔTD of the difference between the maximum values of the TD transmittance at a wavelength of 500 nm or more and 600 nm or less before and after the durability test at 105 ° C. and 1000 hours is 0.014 or less. The polarizing plate according to 1.
[8] The polarizing plate according to any one of [4] to [7], wherein the absolute value Δa of the difference between the orthogonal hue a values before and after the durability test at 105° C. for 1000 hours is 2.5 or less.
[9] The polarizing plate according to any one of [4] to [8], a translucent member disposed on the first thermoplastic resin film side of the polarizing plate, and the second thermoplastic resin of the polarizing plate and a display device arranged on the side of the display device in this order.
[10] A method for producing a polarizer according to any one of [1] to [3],
The polarizer contains a polyvinyl alcohol-based resin,
A production method comprising the step of treating a polyvinyl alcohol resin film with a treatment liquid containing a zinc salt.

ADVANTAGE OF THE INVENTION According to this invention, the polarizer which has favorable heat resistance can be provided.

4 is a flow chart showing a method for manufacturing a polarizer according to one aspect of the present invention; 1 is a schematic cross-sectional view showing a polarizing plate according to one aspect of the present invention; FIG.

<Polarizer>
A polarizer according to one embodiment of the present invention has a property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). It is an absorptive polarizer. The polarizer may be, for example, a polarizer in which a dichroic dye such as iodine is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film, and such a polarizer is manufactured according to the method for manufacturing a polarizer described below. be able to. A polarizer can be used as a polarizing plate by laminating a protective film or the like on its surface with an adhesive or a pressure-sensitive adhesive. Hereinafter, unless otherwise specified, a polarizing plate means a polarizing plate comprising a polarizer and a thermoplastic resin film on at least one surface thereof. The polyvinyl alcohol-based resin may be the same as those exemplified in the description of the polarizer manufacturing method to be described later.

A polarizer according to one embodiment of the present invention can exhibit excellent heat resistance. The polarizer according to one embodiment of the present invention preferably suppresses yellowing, whitening, and red discoloration when a durability test is performed using the polarizer as a constituent member of the polarizing plate. The term "durability test" as used in the present invention means a durability test performed according to the method described in the Examples section below. Yellowing, whitening and reddening are discussed in later paragraphs.

A polarizing plate for an in-vehicle display device is, for example, bonded to an image display cell with an adhesive or an adhesive, and the surface opposite to the surface bonded to the image display cell is coated with a translucent glass plate, touch panel, or the like. A flexible member is laminated with a pressure-sensitive adhesive or an adhesive. A polarizing plate for a vehicle-mounted display device may be used at a relatively high temperature for a long time, and discoloration tends to occur easily in such a case. As a result of research on discoloration by the present inventors, it was found that discoloration occurring in polarizing plates used for a long time at relatively high temperatures is roughly classified into three types: yellowing, whitening and reddish. Hereinafter, yellowing, whitening and reddish are collectively referred to as discoloration.

Yellowing is a change in color visually observed when observing the polarizing plate through an optical microscope transmitted light before and after the durability test. As a result of research on yellowing by the present inventors, the absolute value ΔTy of the difference in luminosity correction single transmittance (Ty) before and after the durability test of a polarizing plate using a polarizer (hereinafter, simply referred to as “ΔTy” ) is small, yellowing also tends to be small. Yellowing occurs when the polarizing plate is heated to a temperature exceeding 90° C., and some of the polyiodine complexes I ₃ ⁻ and I ₅ ⁻ oriented and adsorbed in the polyvinyl alcohol resin film are thermally decomposed to form I ₂ . It is presumed that the dehydration reaction on which _I2 acts causes the hydroxyl groups in the polyvinyl alcohol-based resin film to be eliminated and the double bonds to be generated. However, the present invention is not limited to this estimation. The luminosity-correction single transmittance (Ty) is measured according to the measurement method described later in the section of Examples.

Whitening is observed before and after the durability test by observing the polarizing plate through another polarizing plate with transmitted light of an optical microscope, and when the polarizing plate is rotated and the darkest field is observed, light leakage is observed. say. As a result of research on whitening by the present inventor, the absolute value ΔTD (hereinafter also simply referred to as “ΔTD”) of the difference in the maximum value of TD transmittance (TDmax) at a wavelength of 500 nm or more and 600 nm or less before and after the durability test It was found that whitening also tends to be less when the size is small. Whitening is caused _by thermal decomposition ^of the polyiodine complexes I ₃ ^{- and} _{I 5} ^- oriented and adsorbed in the polyvinyl alcohol resin film in the polarizer in the durability test. It is presumed that this is caused by a decrease in the content of However, the present invention is not limited to this estimation. The maximum value of TD transmittance (TDmax) at a wavelength of 500 nm or more and 600 nm or less is measured according to the measurement method described later in Examples.

Red discoloration is a color change that is visually recognized when the polarizing plate is observed through an optical microscope transmitted light before and after the durability test. As a result of research on red discoloration by the present inventor, the same is true when the absolute value Δa (hereinafter also simply referred to as “Δa”) of the difference in the orthogonal hue a before and after the durability test of the polarizing plate using a polarizer is small. In addition, it was found that red discoloration tended to be less. Red discoloration is caused by thermal decomposition of the polyiodine complex I ₅ ^- , which has an absorption maximum on the relatively long wavelength side of visible light, which is oriented and adsorbed in the polyvinyl alcohol resin film in the polarizer in the durability test. is presumed to be caused by a decrease in the content of the polyiodine complex I ₅ ^- in . However, the present invention is not limited to this estimation. The orthogonal hue a is measured according to the measurement method described in the section of Examples below.

The polarizer has an iodine-zinc bond number ratio to the iodine bond number (hereinafter also referred to as I-Zn/II bond ratio) of more than 0.47 and less than 0.9, preferably the absorption of the polarizer Preferably, the I-Zn/II bond ratio in the direction parallel to the axis is greater than 0.47 and less than 0.9. An iodine-iodine bond (hereinafter also referred to as an II bond) is a bond between iodine atoms in an iodine compound adsorbed and oriented on a film (for example, a polyvinyl alcohol resin film). The iodine compound may be, for example, I ₃ ⁻ , I ₅ ⁻ , I ₂ and the like. An iodine-zinc bond (hereinafter also referred to as an I-Zn bond) is a bond between an iodine atom and a zinc atom in an iodine compound. If the I-Zn/II bond ratio exceeds 0.47, yellowing and reddish tend to be suppressed. Further, when the I--Zn/II bond ratio is less than 0.9, whitening tends to be suppressed. The I-Zn/II bond ratio is measured according to the measurement method described in the Examples section below.

The I-Zn/II bond ratio is preferably 0.48 or more and 0.85 or less, more preferably 0.5 or more and 0.8 or less from the viewpoint of suppressing discoloration when used at high temperature for a long time. and more preferably 0.55 or more and 0.75 or less.

Methods for adjusting the I—Zn/II bond ratio within the above range include, for example, adjusting the zinc element content in the polarizer and adjusting the thickness of the polarizer. For example, if the zinc element content is decreased, the I-Zn/II bond ratio tends to decrease, and if the zinc element content is increased, the I-Zn/II bond ratio tends to increase. Also, when the thickness of the film (eg, polyvinyl alcohol resin film) used is reduced, the ratio of the I—Zn/II bond ratio to the content of zinc element tends to decrease.

The thickness of the polarizer may be, for example, 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less, still more preferably 15 μm or less, even more preferably 14 μm or less, particularly preferably 13 μm or less, and even more preferably 12 μm or less. is. When the thickness of the polarizer is 30 μm or less, whitening tends to be suppressed easily. Further, reducing the thickness of the polarizer is advantageous for thinning the polarizing plate. The thickness of the polarizer is usually 2 μm or more, and may be, for example, 5 μm or more.

The thickness of the polarizer can be set within the above-described range by selecting a polyvinyl alcohol-based resin film, adjusting the draw ratio, and the like.

The polarizer can contain elemental zinc in any content. When the I-Zn/II bond ratio is 0.48 or more, yellowing and reddish tend to be suppressed, and when the I-Zn/II bond ratio is 0.85 or less, whitening tends to Since it tends to be easily suppressed, it is preferably adjusted within this range.
For example, when the thickness of the polarizer is 20 μm or less (preferably 15 μm or less), the zinc element content is preferably 0.305% by mass or more, more preferably 0.31% by mass, from the viewpoint of suppressing yellowing and reddishness. % by mass or more. On the other hand, the zinc element content is preferably 0.75% by mass or less, more preferably 0.7% by mass or less, still more preferably 0.65% by mass or less, and more preferably 0.5% by mass, from the viewpoint of suppressing whitening. % by mass or less. The content of elemental zinc is measured according to the measuring method described in the section of Examples described later.

The content of elemental zinc is determined by, for example, the concentration of zinc salt in the treatment solution for treating the polyvinyl alcohol resin film, the immersion time of the polyvinyl alcohol film in the treatment solution containing the zinc salt, and the amount of the treatment solution. By adjusting the temperature and the like, the zinc element content can be set within the range described above.

When the polarizer contains elemental zinc in a content within the above range, the thermal decomposition of the polyiodine complexes I ₃ ^- and I ₅ ^- in the polarizer and the formation of I ₂ are suppressed, resulting in yellowing and redning.・It is estimated that discoloration such as whitening tends to occur less easily. However, the present invention is not limited to this estimation.

The polarizer may have a visibility correction single transmittance (Ty) before the durability test of, for example, more than 40.5%, and the lower limit of the visibility correction single transmittance (Ty) is preferably 41.0%. Thus, the upper limit is usually 50% or less, preferably 47% or less.

The polarizer may have a ΔTy of, for example, 4% or less, preferably 3.5% or less.

The polarizer may have a visibility correction degree of polarization (Py) of, for example, more than 99.980 when the visibility correction single transmittance (Ty) before the durability test is 41.5%, and the visibility correction single The lower limit of the visibility correction degree of polarization (Py) when the transmittance (Ty) is 41.5% is preferably 99.985 or more.

The polarizer may have a maximum value (TDmax) of TD transmittance at a wavelength of 500 nm or more and 600 nm or less before the durability test, for example, 0.01 or less, preferably 0.008 or less.

The polarizer may have a ΔTD of, for example, 0.014 or less, preferably 0.01 or less.

The polarizer may have, for example, an orthogonal hue a of 2.6 or less, preferably 1 or less, before the durability test.

The polarizer may have Δa of, for example, 2.5 or less, preferably 2.45 or less.

The luminosity correction single transmittance (Ty), ΔTy, ΔTD, luminosity correction polarization degree (Py), orthogonal hue a and Δa of the polarizer were measured in the same manner as the polarizing plate according to the method described in the Examples section below. can be measured by

<Method for producing polarizer>
A method for manufacturing a polarizer according to another aspect of the present invention will be described with reference to the drawings.
The manufacturing method shown in FIG. 1 is a method for manufacturing a polarizer containing a polyvinyl alcohol-based resin, and includes the following steps:
A dyeing step S20 of immersing and dyeing the polyvinyl alcohol-based resin film in a dyeing tank containing a treatment liquid containing a dichroic dye;
A cross-linking step S30 in which the film after the dyeing step is immersed in a cross-linking tank containing a treatment liquid containing a cross-linking agent for cross-linking;
can include

The manufacturing method can further include other steps than the above, and a specific example thereof is, as shown in FIG. They are a swelling step S10 of immersing in a swelling tank, a washing step S40 of immersing the film after the cross-linking step S30 in a washing tank, and a drying step S50 after the washing step S40. In addition, the polyvinyl alcohol-based resin film is uniaxially stretched in any one or more steps of the polarizer manufacturing process, more specifically, any one or more steps from before the swelling step S10 to the cross-linking step S30. (stretching step).

In the production method, at least one of the treatment liquids for treating the polyvinyl alcohol-based resin film contains a zinc salt. Examples of the treatment tank containing the treatment liquid include a swelling tank, a dyeing tank, a cross-linking tank, a washing tank, a complementary color tank described later, and the like. The treatment tank containing the zinc salt-containing treatment solution is preferably a treatment tank located after the dyeing tank and before the washing tank, more preferably at least one tank selected from a bridging tank and a complementary color tank, and still more preferably. When there are two or more cross-linking tanks, it is at least one selected from the last cross-linking tank and complementary color tank. By immersing the polyvinyl alcohol-based resin film in a zinc salt-containing treatment liquid, the obtained polarizer can contain zinc element. The content of the zinc element in the polarizer can be adjusted by adjusting the concentration of the zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like. The content of zinc element can be in the range of

Examples of zinc salts contained in the treatment liquid include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferred because it causes little change in tension. The zinc salt can be added to the processing liquid as a zinc salt solution.

The concentration of the zinc salt in the treatment liquid may be different for each treatment tank, but may be, for example, 2 parts by weight or more and 4 parts by weight or less with respect to 100 parts by weight of the treatment liquid contained in the treatment tank.

The immersion time of the polyvinyl alcohol-based resin film in the treatment liquid and the temperature of the treatment liquid may differ for each treatment tank. The specific immersion time and temperature of the treatment liquid will be described for each step in subsequent paragraphs.

Various treatment steps included in the manufacturing method according to the present invention can be continuously performed by continuously transporting the polyvinyl alcohol resin film, which is the original film, along the film transport path of the polarizer manufacturing apparatus. The film transport path is provided with facilities (processing tanks, furnaces, etc.) for carrying out the various processing steps described above in order of implementation.

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, guide rolls can be placed before, after, or in each treatment tank, thereby allowing the film to be introduced into, immersed in, and pulled out of the treatment tank. More specifically, two or more guide rolls are provided in each treatment tank, and the film can be immersed in each treatment tank by transporting the film along these guide rolls.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film which is the raw film, a 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 polyvinyl alcohol resin is generally about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. As used herein, "(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, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like may be used.

The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 or more and 10000 or less, more preferably 1500 or more and 8000 or less, and still more preferably 2000 or more and 5000 or less. The average degree of polymerization of the polyvinyl alcohol-based 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 polarizing performance, and if it exceeds 10,000, film workability may be poor.

The thickness of the polyvinyl alcohol-based resin film is, for example, about 10 μm or more and 50 μm or less, and from the viewpoint of making the thickness of the polarizer 15 μm or less, it is preferably 40 μm or less, more preferably 30 μm or less.

The polyvinyl alcohol-based resin film, which is the raw film, can be prepared, for example, as a roll (wound product) of a long unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained as an elongated object. Each step will be described in detail below.

(1) Swelling step S10
The swelling treatment in this step is performed as necessary for the purpose of removing foreign matter from the polyvinyl alcohol resin film, which is the original film, removing the plasticizer, imparting easy dyeability, plasticizing the film, etc. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a swelling tank containing a treatment liquid containing water. The film may be immersed in one swelling bath, or may be immersed in two or more swelling baths sequentially. Before the swelling treatment, during the swelling treatment, or before and during the swelling treatment, the film may be uniaxially stretched.

The treatment liquid contained in the swelling tank 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. As noted above, the treatment liquid contained in the swelling bath may contain zinc salts.

The temperature of the treatment liquid contained in the swelling tank when the 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 about 10 to 600 seconds. It is about 20 to 300 seconds.

(2) Dyeing step S20
The dyeing treatment in this step is a treatment performed for the purpose of adsorbing and orienting iodine on the polyvinyl alcohol resin film. It can be an immersion treatment. The film may be immersed in one dyeing bath or sequentially immersed in two or more dyeing baths. In order to enhance the dyeability of iodine, the film subjected to the dyeing process may be uniaxially stretched to at least some extent. 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.

Dichroic organic dyes can also be used with iodine. When using a dichroic organic dye, the dichroic organic dye can be used in combination with iodine in one dyeing bath, and when using two or more dyeing baths, dyeing different from the dyeing bath using iodine It can also be used in tanks. Specific examples of 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, 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 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.

An aqueous solution containing iodine and potassium iodide can be used as the treatment liquid contained in the dyeing bath using iodine. 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 0.01 parts by mass or more and 1 part by mass or less per 100 parts by mass of water. Also, the content of iodides such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of water. As mentioned above, the treatment liquor contained in the dyeing bath may contain zinc salts.

The temperature of the treatment liquid contained in the dyeing tank when the film is immersed is usually 10° C. or higher and 45° C. or lower, preferably 10° C. or higher and 40° C. or lower, more preferably 20° C. or higher and 35° C. or lower. The immersion time is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

When a dichroic organic dye is used, an aqueous solution containing the dichroic organic dye can be used as the treatment liquid contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1×10 ⁻⁴ parts by mass or more and 10 parts by mass or less, preferably 1×10 ⁻³ parts by mass or more and 1 part by mass or less per 100 parts by mass of water. . Dyeing aids and the like may coexist in the dyeing bath, and for example, inorganic salts such as sodium sulfate, surfactants, and the like 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 treatment liquid contained in the dyeing tank when the film is immersed is, for example, 20° C. to 80° C., preferably 30° C. to 70° C., and the immersion time of the film is usually 30 seconds to 600 seconds. It is preferably 60 seconds or more and 300 seconds or less.

(3) Cross-linking step S30
The cross-linking treatment of treating the polyvinyl alcohol-based resin film after the dyeing process with a cross-linking agent is a treatment performed for the purpose of water resistance by cross-linking, color adjustment, etc. Specifically, it is stored in a cross-linking tank containing a cross-linking agent. It can be a treatment in which the film after the dyeing process is immersed in a treatment solution. The film may be immersed in one cross-linking bath, or may be immersed in two or more cross-linking baths sequentially. A uniaxial stretching treatment may be performed during the cross-linking treatment.

Examples of cross-linking agents include boric acid, glyoxal, glutaraldehyde, etc. Boric acid is preferably used. Two or more cross-linking agents can be used in combination. The content of boric acid in the treatment liquid contained in the cross-linking bath is usually 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the cross-linking tank preferably contains iodide in addition to boric acid. The content of iodide in the treatment liquid contained in the cross-linking bath is usually 0.1 to 15 parts by mass, preferably 5 to 12 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 tank. As noted above, the processing solution contained in the cross-linking bath may contain zinc salts. If there are two or more cross-linking vessels, it is preferred that the treatment liquid contained in the last cross-linking vessel contains a zinc salt.

The temperature of the treatment liquid contained in the cross-linking bath when the film is immersed is usually 50° C. or higher and 85° C. or lower, preferably 50° C. or higher and 70° C. or lower, and the film immersion time is usually 10 seconds or more and 600 seconds or less. , preferably 20 seconds or more and 300 seconds or less.

In the cross-linking step S30, there may be two or more cross-linking tanks. In this case, the composition and temperature of the treatment liquid contained in each cross-linking tank may be the same or different. The treatment liquid contained in the cross-linking tank may have the concentration and temperature of the cross-linking agent and iodide according to the purpose of immersing the polyvinyl alcohol-based resin film. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment (complementary color) may each be performed in a plurality of steps (for example, a plurality of tanks).
In general, when both the cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment (complementary color) are performed, the tank (complementary color tank) that performs the cross-linking treatment for hue adjustment (complementary color) is placed in the latter stage. placed. The temperature of the treatment liquid contained in the complementary color tank is, for example, 10° C. or higher and 55° C. or lower, preferably 20° C. or higher and 50° C. or lower. The content of the cross-linking agent in the treatment liquid contained in the complementary color bath is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the complementary color bath is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water. As noted above, the processing liquids contained in the complementary baths may contain zinc salts.

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

Uniaxial stretching may be either dry stretching in air or wet stretching in a tank, 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 draw ratio based on the original film (when the drawing treatment is performed in two or more stages, the cumulative draw ratio of those) is about 3 times or more and 8 times or less. In order to impart good polarizing properties, the draw ratio is preferably 4 times or more, more preferably 5 times or more.

(4) Washing step S40
The washing treatment in this step is a treatment that is performed as necessary for the purpose of removing excess cross-linking agents, dichroic dyes, and other chemicals adhering to the polyvinyl alcohol-based resin film, and a washing solution containing water is used. This is a treatment for washing the polyvinyl alcohol-based resin film after the cross-linking step. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film after the cross-linking step is immersed in a treatment liquid (washing liquid) contained in a washing tank. The film may be immersed in one washing tank, or may be immersed in two or more washing tanks sequentially. Alternatively, the washing treatment may be a treatment of spraying a washing solution as a shower onto the polyvinyl alcohol-based resin 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 5° C. or higher and 40° C. or lower.

The cleaning step S40 is an optional step and may be omitted, and as described later, the cleaning process may be performed during the drying step S50. Preferably, the drying step S50 is performed on the film after performing the washing step S40.

(5) Drying step S50
The drying step S50 is a zone for drying the polyvinyl alcohol resin film after the washing step S40. By introducing the film into the drying step S50 while continuing to transport the polyvinyl alcohol-based resin film after the washing step S40, a drying treatment can be performed, thereby obtaining a polarizer.

The drying treatment is performed using film drying means (heating means). A preferred example of drying means is a drying oven. The drying oven is preferably one capable of controlling the temperature inside the oven. The drying oven is, for example, a hot air oven capable of increasing the temperature inside the oven by supplying hot air or the like. Further, the drying treatment by the drying means may be a treatment of adhering the polyvinyl alcohol resin film after the washing step S40 to one or more heating bodies having a convex curved surface, or a treatment of heating the film using a heater. good.

Examples of the heating member include a roll (for example, a guide roll that also serves as a heat roll) that has a heat source (for example, a heat medium such as hot water or an infrared heater) inside and can increase the surface temperature. Examples of the heater include infrared heaters, halogen heaters, panel heaters, and the like.

The temperature of the drying treatment (for example, the temperature in the drying furnace, the surface temperature of the heat roll, etc.) is usually 30°C or higher and 100°C or lower, preferably 50°C or higher and 90°C or lower. Although the drying time is not particularly limited, it is, for example, 30 seconds or more and 600 seconds or less.

Through the above steps, a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film can be obtained.

The obtained polarizer can be conveyed as it is to the next polarizing plate manufacturing step (a step of laminating a thermoplastic resin film on one side or both sides of the polarizer).

<Polarizing plate>
A polarizing plate according to another aspect of the present invention includes the above-described polarizer, a first thermoplastic resin film provided on one surface thereof, and a second thermoplastic resin film provided on the other surface. It is a polarizing plate provided. The polarizing plate will be described below with reference to the drawings. A polarizing plate 100 shown in FIG. 1 includes a first thermoplastic resin film 102 on one side of a polarizer 101 and a second thermoplastic resin film 103 on the other side. Hereinafter, the first thermoplastic resin film and the second thermoplastic resin film are collectively referred to as thermoplastic resin films.

Thermoplastic resin films include thermoplastic resins such as linear polyolefin resins (polypropylene resins, etc.), polyolefin resins such as cyclic polyolefin resins (norbornene resins, etc.); cellulose ester-based resins; polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate-based resins; (meth) acrylic resins such as polymethyl methacrylate-based resins; It can be a transparent resin film made of a material or the like.

Either one or both of the first thermoplastic resin film and the second thermoplastic resin film may be a protective film having 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 thermoplastic resin film opposite to the polarizer 101. can also

The thickness of the thermoplastic resin film is preferably thin from the viewpoint of making the polarizing plate 100 thinner. 5 to 100 μm, more preferably 10 to 50 μm.

The polarizing plate 100 can be obtained by bonding (laminating) thermoplastic resin films on both sides of the polarizer 101 via an adhesive. As the adhesive used for laminating the polarizer 101 and the thermoplastic resin film, an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or a cross-linking agent mixed therein. Water-based adhesives such as aqueous solutions and urethane-based emulsion adhesives can be used. When the thermoplastic resin films are laminated on both sides of the polarizer 101, the adhesives forming the two adhesive layers may be of the same type or of different types. For example, when laminating thermoplastic resin 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 with an active energy ray after bonding. 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 adhesiveness between the polarizer 101 and the thermoplastic resin film, prior to bonding the polarizer 101 and the thermoplastic resin film, a corona is applied to the bonding surface of the polarizer 101 and/or the thermoplastic resin film. Surface treatment such as treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, and saponification treatment may be applied.

As described above, the polarizing plate 100 of the present invention can be produced by bonding a thermoplastic resin film to the polarizer 101, which is a single-layer film, but the method is not limited to this method. For example, it can also be produced by a method using a base film as described in JP-A-2009-98653. The latter method is advantageous for obtaining a polarizing plate having a thin film polarizer (polarizer layer), and can include, for example, the following steps.

A resin layer forming step of applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of the substrate film and then drying to form a polyvinyl alcohol-based resin layer to obtain a laminated film;
A stretching step of stretching the laminated film to obtain a stretched film,
A dyeing step of obtaining a polarizing laminated film by dyeing a polyvinyl alcohol-based resin layer of a stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizer);
A first laminating step of laminating a thermoplastic resin film on the polarizer layer of the polarizing laminated film using an adhesive to obtain a laminated film;
A peeling step of peeling and removing the base film from the laminated film to obtain a polarizing plate with a thermoplastic resin film on one side.
By adding a zinc salt to the treatment liquid containing the dichroic dye in the dyeing step, the polarizer can be made to contain zinc element.

When the thermoplastic resin film is laminated on both sides of the polarizer 101 layer (polarizer), the second thermoplastic resin film is further attached to the polarizer surface of the polarizing plate with the first thermoplastic resin film on one side using an adhesive. A second bonding step of bonding is included.

In the method using the substrate film, the dyeing step for obtaining the polarizing laminated film (for example, after the cross-linking step or after the washing step in the dyeing step for obtaining the polarizing laminated film) can include a drying step. The polarizer included in the polarizing laminated film, the polarizing plate with a single-sided thermoplastic resin film, and the polarizing plate with a double-sided thermoplastic resin film obtained through the second bonding step, or a polarizer isolated from these , are polarizers belonging to the present invention.

The I—Zn/II bond ratio, zinc content, thickness, raw material, etc. of the polarizer 101 are the same as those exemplified in the description of the polarizer above.

The polarizing plate may have, for example, a luminosity correction single transmittance (Ty) of more than 40.5% before the durability test, and the lower limit of the luminosity correction single transmittance (Ty) is preferably 41.0%. Thus, the upper limit is usually 50% or less, preferably 47% or less.

The polarizing plate may have a ΔTy of, for example, 4% or less, preferably 3.5% or less.

The polarizing plate may have a visibility correction degree of polarization (Py) of, for example, more than 99.980 when the visibility correction single transmittance (Ty) before the durability test is 41.5%. The lower limit of the visibility correction degree of polarization (Py) when the transmittance (Ty) is 41.5% is preferably 99.985 or more. The luminosity correction degree of polarization (Py) can be measured according to the method described in the Examples section below.

The polarizing plate may have a maximum value (TDmax) of TD transmittance at a wavelength of 500 nm or more and 600 nm or less before the durability test, for example, 0.01 or less, preferably 0.008 or less.

The polarizing plate may have a ΔTD of, for example, 0.014 or less, preferably 0.01 or less.

The polarizing plate may have, for example, an orthogonal hue a of 2.6 or less, preferably 1 or less, before the durability test.

The polarizing plate may have Δa of, for example, 2.5 or less, preferably 2.45 or less.

A polarizing plate can be used in a display device. The display device may be a liquid crystal display device, an organic EL display device, or the like, but is preferably a liquid crystal display device. A liquid crystal display device includes a liquid crystal panel including a liquid crystal cell as an image display element, and a backlight. In constructing the liquid crystal display device, the polarizing plate may be used as the polarizing plate arranged on the viewing side, may be used as the polarizing plate arranged on the backlight side, or may be used as the polarizing plate arranged on the viewing side and the backlight side. may be used for both polarizing plates.

The polarizing plate includes a polarizing plate, a translucent member arranged on the first thermoplastic resin film side of the polarizing plate, and a display device arranged on the second thermoplastic resin film side of the polarizing plate in this order. It is suitable for display devices for The translucent member may be a glass plate, a translucent resin film, or the like.

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

[Durability test]
A test piece of 40 mm×40 mm was cut out from the manufactured polarizing plate, and non-alkali glass of 40 mm×40 mm was pasted on both sides of the cut polarizing plate using an acrylic pressure-sensitive adhesive having a thickness of 25 μm. Using the obtained double-sided glass-laminated polarizing plate as a sample, the maximum value of TD transmittance (TDmax) at a wavelength of 500 nm or more and 600 nm or less, visibility correction single transmittance (Ty), visibility correction polarization degree (Py), and A measurement of the orthogonal hue a was performed. Next, the measured sample was heated in an oven at 105° C. for 1000 hours. The sample taken out of the oven was measured for the maximum value of TD transmittance (TDmax) at a wavelength of 500 nm or more and 600 nm or less, the luminosity correction single transmittance (Ty), and the optical characteristics of the orthogonal hue a.

[Measurement of zinc content]
The zinc content in the polarizer was measured as follows.
A solution obtained by adding nitric acid to a precisely weighed polarizer and performing acid decomposition with a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General was used as a measurement solution. The zinc concentration was determined by quantifying the zinc concentration of the measurement solution using an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies, and calculating the weight of zinc with respect to the weight of the polarizer.

[Measurement of I-Zn/II bond ratio]
The X-ray absorption spectrum of the iodine-K absorption edge was measured with an XAFS (X-ray absorption fine structure) measurement apparatus installed at the beamline NW-10A of the Synchrotron Radiation Science Facility of the High Energy Accelerator Research Organization.
In the measurement, a Si (311) analyzing crystal was used, the incident X-ray intensity was measured using a 17 cm ion chamber using argon as the detection gas, and the transmitted X-ray intensity was measured using a 31 cm ion chamber using krypton as the detection gas. measured by the method. The sample was measured by stacking 100 polarizers with their absorption axes aligned and placing them in the beam so that the absorption axes of the polarizers were parallel. The obtained absorption spectrum was subjected to Fourier transform using a data analysis program REX2000 (manufactured by Rigaku) to obtain a radial distribution function. In the radial distribution function, the peak near 2.1 Å is due to the I-Zn bond and the peak near 2.7 Å is due to the II bond, and the ratio of the peak heights is the I-Zn/II bond ratio. and

[Maximum value of TD transmittance (TDmax) at a wavelength of 500 nm or more and 600 nm or less]
For the polarizing plate, a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation] is used to measure the TD transmittance in the wavelength range of 380 to 780 nm, and the TD transmittance is the largest at a wavelength of 500 nm or more and 600 nm or less. asked for

[Visibility correction single transmittance (Ty) and visibility correction polarization degree (Py)]
For the polarizing plate, the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm are measured using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation],
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 plate, and is expressed as "MD" in the above formula. The "TD transmittance" is the transmittance when the direction of the polarized light emitted from the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing plate, and is expressed as "TD" in the above formula.
For the obtained single transmittance and degree of polarization, luminosity correction was performed using a 2-degree field of view (C light source) of JIS Z 8701: 1999 “Color display method-XYZ color system and X10Y10Z10 color system”. Single transmittance (Ty) and visibility correction polarization degree (Py) were determined.

[Orthogonal hue a]
The orthogonal hue a is the a value in the Lab colorimetric system, and was measured using standard light with a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation]. The Lab color system is JIS K
5981: 2006 "Synthetic resin powder coating film", "5.5 Accelerated weather resistance test", it is represented by Hunter's lightness index L and hues a and b, and lightness index L and The values of hues a and b are calculated from the tristimulus values X, Y and Z defined in JIS Z 8722:2009 "Methods for measuring colors-reflected and transmissive object colors" by the following equations.
L = 10Y ^1/2
a = 17.5 (10.2 XY) / Y ^1/2
b=7.0(Y−0.847Z)/Y ^1/2 .
In the Lab color system, the hue a value and the b value can indicate the position corresponding to the saturation. As the hue a value increases, the hue becomes reddish, and as the hue b value increases, the hue becomes yellowish. Change. Also, the closer to 0, the closer to an achromatic color.

<Example 1>
A long polyvinyl alcohol (PVA) raw film with a thickness of 30 μm [trade name “Kuraray Poval Film VF-PE #3000” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more]. While being unwound from the roll, it was continuously conveyed and immersed in a swelling layer containing pure water at 20° C. for 80 seconds (swelling step). After that, the film pulled out from the swelling tank is immersed in a dyeing tank containing an iodine-containing treatment solution of 1.3/0.3/100 (mass ratio) of potassium iodide/boric acid/water at 30°C. It was immersed for 130 seconds (dyeing process). Then, the film pulled out from the dyeing bath is immersed in a cross-linking bath containing a 56° C. treatment solution containing potassium iodide/boric acid/water of 13.9/3.0/100 (mass ratio) for 50 seconds. It was immersed (crosslinking step). Subsequently, the film withdrawn from the cross-linking bath was treated at 40° C. with a ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water of 9.0/3.0/2.0/100 (mass ratio). It was immersed in a complementary color bath containing a liquid for 10 seconds (complementary color process).

Next, the film pulled out from the cross-linking tank was immersed in a washing tank containing pure water at 7°C for an immersion time of 10 seconds (washing step), and then introduced into a heating furnace at 80°C for an immersion time of 150 seconds. A drying process was performed in seconds (drying process) to obtain a polarizer having a thickness of 12 μm. In the swelling process, the dyeing process, the cross-linking process, the complementary color process, and the washing process, longitudinal uniaxial stretching was performed at the ratio shown in Table 1 by stretching between rolls in a tank. The total draw ratio based on the original film was 6.0 times. The zinc content of the obtained polarizer was measured. Table 1 shows the results.

<Example 2>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color tank to 9.0/3.0/3.0/100 in the complementary color process. A polarizer having a thickness of 12 μm was produced in the same manner as in Example 1.

<Example 3>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color tank to 9.0/3.0/4.0/100 in the complementary color process. A polarizer having a thickness of 12 μm was produced in the same manner as in Example 1.

<Comparative Example 1>
Thickness 12 μm in the same manner as in Example 1 except that the mass ratio of potassium iodide/boric acid/water in the treatment liquid contained in the complementary color bath in the complementary color process was changed to 9.0/3.0/100. A polarizer was produced.

<Comparative Example 2>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color tank to 9.0/3.0/1.0/100 in the complementary color process. A polarizer having a thickness of 12 μm was produced in the same manner as in Example 1.

<Comparative Example 3>
A long polyvinyl alcohol (PVA) raw film with a thickness of 75 μm [trade name “Kuraray Poval Film VF-PS #7500” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more]. It was continuously transported while being unwound from the roll, and immersed in the treatment liquid contained in a swelling tank containing pure water at 25° C. for 150 seconds (swelling step). After that, the film pulled out from the swelling tank is immersed in a dyeing tank containing an iodine-containing treatment solution of 2.0/0.6/100 (mass ratio) of potassium iodide/boric acid/water at 30°C. It was immersed for 170 seconds (dyeing process). Then, the film pulled out from the dyeing tank was immersed in a cross-linking tank containing a 56° C. treatment solution containing potassium iodide/boric acid/water of 15.4/4.0/100 (mass ratio) for 80 seconds. After being immersed (crosslinking step), the film pulled out from the crosslinker was treated with potassium iodide/boric acid/zinc nitrate hexahydrate/water at a ratio of 15.4/4.0/0/100 (mass ratio). was immersed in a complementary color bath containing a treatment solution at 40° C. for an immersion time of 10 seconds (complementary color step).

Next, after the film pulled out from the cross-linking tank was immersed in a washing tank containing pure water at 8°C for 10 seconds (washing step), it was subsequently introduced into a heating furnace at 80°C for 300 seconds for immersion. (drying step) to obtain a polarizer having a thickness of 28 μm. In the swelling process, the dyeing process, the cross-linking process, the complementary color process, and the washing process, longitudinal uniaxial stretching was performed at the ratio shown in Table 1 by stretching between rolls in a tank. The total draw ratio based on the original film was 6.0 times.

<Comparative Example 4>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color tank to 9.0/3.0/5.0/100 in the complementary color process. A polarizer having a thickness of 28 μm was produced in the same manner as in Comparative Example 3.

<Comparative Example 5>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color tank to 9.0/3.0/7.0/100 in the complementary color process. A polarizer having a thickness of 28 μm was produced in the same manner as in Comparative Example 3.

<Comparative Example 6>
A long polyvinyl alcohol (PVA) raw film with a thickness of 60 μm [trade name “Kuraray Poval Film VF-PS#6000” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more]. It was continuously transported while being unwound from the roll, and immersed in the treatment liquid contained in a swelling tank containing pure water at 25° C. for 150 seconds (swelling step). After that, the film pulled out from the swelling tank is immersed in a dyeing tank containing an iodine-containing treatment solution of 1.3/0.6/100 (mass ratio) of potassium iodide/boric acid/water at 30°C. It was immersed for 170 seconds (dyeing process). Then, the film pulled out from the dyeing tank is immersed in a cross-linking tank containing a 56° C. treatment solution containing potassium iodide/boric acid/water of 13.9/4.0/100 (mass ratio) for 80 seconds. It was immersed (crosslinking step). Subsequently, the film pulled out from the cross-linking tank was treated with a 40° C. treatment solution containing potassium iodide/boric acid/zinc nitrate hexahydrate/water at a ratio of 15.4/5.0/0/100 (mass ratio). It was immersed in a complementary color bath for 10 seconds (complementary color step).

Next, the film pulled out from the cross-linking tank was immersed in a washing tank containing pure water at 8°C for 10 seconds (washing step), and then introduced into a heating furnace at 80°C for 300 immersion times. A drying process was performed in seconds (drying process) to obtain a polarizer having a thickness of 22 μm. In the swelling process, the dyeing process, the cross-linking process, the complementary color process, and the washing process, longitudinal uniaxial stretching was performed at the ratio shown in Table 1 by stretching between rolls in a tank. The total draw ratio based on the original film was 6.0 times.

<Comparative Example 7>
Except for changing the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the complementary color bath in the complementary color process to 9.0/3.0/5.0/100 A polarizer having a thickness of 22 μm was produced in the same manner as in Comparative Example 6.

<Example 4>
A water-based adhesive containing 3 parts by mass of polyvinyl alcohol per 100 parts by mass of water was prepared.
After saponifying one side of a 40 μm-thick triacetyl cellulose (TAC) film, the saponification-treated surface is coated with the water-based adhesive using a bar coater, and a 40 μm-thick low-retardation TAC film is coated on one side. After the saponification treatment, the water-based adhesive was applied to the saponification-treated surface using a bar coater. A TAC film is laminated on one side of the polarizer so that the adhesive layer is on the polarizer side of Example 1, and a low retardation TAC film is laminated on the other side to form a TAC film/adhesive layer/polarized light. A laminate having a layer structure of layer/adhesive layer/low retardation TAC film was obtained. The obtained laminate is subjected to heat treatment at 80 ° C. for 140 seconds in a hot air dryer to obtain a polarized light having a layer structure of TAC film / adhesive layer / polarizer / adhesive layer / low retardation TAC film. A plate was made. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Example 5>
A polarizing plate was produced in the same manner as in Example 4 except that the polarizer produced in Example 2 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Example 6>
A polarizing plate was produced in the same manner as in Example 4, except that the polarizer produced in Example 3 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 8>
A polarizing plate was produced in the same manner as in Example 4 except that the polarizer produced in Comparative Example 1 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 9>
A polarizing plate was produced in the same manner as in Example 4, except that the polarizer produced in Comparative Example 2 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 10>
TAC film/adhesive layer/polarizer/adhesive layer/TAC in the same manner as in Example 4 except that the polarizer was the polarizer produced in Comparative Example 3 and the low retardation TAC film was changed to a 40 μm thick TAC film. A laminate having a film layer structure was obtained. A polarizing plate having a layer structure of TAC film/adhesive layer/polarizer/adhesive layer/low retardation TAC film was produced by heat-treating the obtained laminate at 80° C. for 300 seconds in a hot air dryer. did. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 11>
A polarizing plate was obtained in the same manner as in Comparative Example 10, except that the polarizer produced in Comparative Example 4 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 12>
A polarizing plate was obtained in the same manner as in Comparative Example 10, except that the polarizer prepared in Comparative Example 5 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 13>
A polarizing plate was obtained in the same manner as in Comparative Example 10 except that the polarizer produced in Comparative Example 6 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

<Comparative Example 14>
A polarizing plate was obtained in the same manner as in Comparative Example 10 except that the polarizer produced in Comparative Example 7 was used. A durability test was performed on the obtained polarizing plate. Table 1 shows the results.

100 polarizing plate 101 polarizer 102 first thermoplastic resin film 103 second thermoplastic resin film

Claims (8)

A polarizer in which the ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds in the direction parallel to the absorption axis of the polarizer is 0.64 or more and 0.76 or less,
The thickness is 15 μm or less,
A polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film. A polarizing plate comprising the polarizer according to claim 1, a first thermoplastic resin film provided on one surface thereof, and a second thermoplastic resin film provided on the other surface thereof. The polarizing plate according to claim 2, wherein the second thermoplastic resin film is a retardation film. 4. The polarizing plate according to claim 2, wherein the absolute value ΔTy of the difference in luminous efficiency-corrected single transmittance Ty before and after the durability test at 105° C. and 1000 hours is 4% or less. The absolute value ΔTD of the difference between the maximum values of the TD transmittance at a wavelength of 500 nm or more and 600 nm or less before and after the durability test at 105 ° C. and 1000 hours is 0.014 or less. polarizer. 6. The polarizing plate according to any one of claims 2 to 5, wherein the absolute value Δa of the difference between the orthogonal hue a values before and after the durability test at 105°C for 1000 hours is 2.5 or less. The polarizing plate according to any one of claims 2 to 6, a translucent member arranged on the first thermoplastic resin film side of the polarizing plate, and the second thermoplastic resin side of the polarizing plate. and a display device arranged in this order. A method for manufacturing the polarizer according to claim 1,
The polarizer contains a polyvinyl alcohol-based resin,
A production method, wherein at least one of the treatment liquids for treating the polyvinyl alcohol-based resin film contains a zinc salt.

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