JP2020071241A - Polarizer and manufacturing method therefor - Google Patents

Abstract

To provide a highly heat-resistant polarizer.SOLUTION: A polarizer is provided, having a ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds in a range of 0.45 to 0.9, inclusive.SELECTED DRAWING: None

Description

  The present invention relates to a polarizer that can be used as a constituent member of a polarizing plate and a manufacturing method thereof.

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

JP, 2003-29042, A JP, 2004-61565, A JP, 2014-102353, A

  A polarizer may cause discoloration when used as a constituent member of a polarizing plate at a high temperature for a long time. Therefore, improvement in heat resistance of the polarizer is required.

  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 manufacturing the 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 of the polarizer, and a second thermoplastic resin film provided on the other surface thereof. A polarizing plate equipped with.
[5] The polarizing plate according to [4], wherein the second thermoplastic resin film is a retardation film.
[6] The polarizing plate according to [4] or [5], wherein the absolute value ΔTy of the difference in the transmittance Ty of the visibility-corrected single body before and after the durability test at 105 ° C. and 1000 hours is 4% or less.
[7] Any of [4] to [6], in which 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 a durability test at 105 ° C. and 1000 hours is 0.014 or less. A polarizing plate according to Crab.
[8] The polarizing plate according to any one of [4] to [7], wherein the absolute value Δa of the difference between orthogonal hue a values before and after the durability test at 105 ° C. and 1000 hours is 2.5 or less.
[9] The polarizing plate according to any one of [4] to [8], a translucent member arranged on the first thermoplastic resin film side of the polarizing plate, and a second thermoplastic resin of the polarizing plate. An in-vehicle display device including a display device disposed on the side in this order.
[10] The method for producing a polarizer according to any one of [1] to [3],
The polarizer includes a polyvinyl alcohol resin,
A method of manufacturing, comprising a step of treating a polyvinyl alcohol-based resin film with a treatment liquid containing a zinc salt.

  According to the present invention, a polarizer having good heat resistance can be provided.

It is a flow chart which shows the manufacturing method of the light polarizer concerning one mode of the present invention. It is a schematic cross section showing a polarizing plate concerning one mode of the present invention.

<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 absorption-type polarizer having. 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-based resin film, and such a polarizer is produced according to a method for producing a polarizer described below. be able to. The 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 having a thermoplastic resin film on at least one surface of a polarizer. The polyvinyl alcohol-based resin may be the same as that exemplified in the description of the method for manufacturing a polarizer described later.

  The 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 all yellowing, whitening, and redning when a durability test is performed using the polarizer as a constituent member of a polarizing plate. In the present invention, the term “durability test” means a durability test conducted according to the method described in the section of Examples below. Yellowing, whitening, and redning are described in later paragraphs.

  The polarizing plate of the in-vehicle display device is, for example, attached to the image display cell with an adhesive or an adhesive, and the surface opposite to the surface attached to the image display cell is a transparent plate such as a glass plate or a touch panel. The flexible member is attached with an adhesive or an adhesive. The polarizing plate of the in-vehicle display device may be used for a long time at a relatively high temperature, and discoloration tends to occur in such a case. As a result of the present inventor's research on discoloration, it was found that the discoloration that occurs in a polarizing plate that is used for a long time at a relatively high temperature is roughly classified into three types: yellowing, whitening, and redning. Hereinafter, yellowing, whitening, and redning may be collectively referred to as discoloration.

Yellowing is a change in color visually observed when the polarizing plate is observed through the light transmitted through the optical microscope before and after the durability test. As a result of a study on yellowing by the present inventor, the absolute value ΔTy (hereinafter, also simply referred to as “ΔTy”) of the difference in the luminosity correction single transmittance (Ty) before and after the durability test of the polarizing plate using the polarizer. Similarly, it was found that when the value of () was small, yellowing also tended to be small. Yellowing means that when the polarizing plate is heated to a temperature higher than 90 ° C., a part of the polyiodine complexes I ₃ ⁻ and I ₅ ⁻ that are oriented and adsorbed in the polyvinyl alcohol-based resin film is thermally decomposed to I ₂ , It is presumed that this is caused by the dehydration reaction on which I ₂ acts to release the hydroxyl group in the polyvinyl alcohol-based resin film and form a double bond. However, the present invention is not limited to this estimation. The visibility-corrected single transmittance (Ty) is measured according to the measuring method described in the section of Examples below.

Whitening means that when observing a polarizing plate through another polarizing plate with light transmitted through an optical microscope before and after the durability test, light leakage is observed in the state of the darkest field by rotating the polarizing plate. Say. As a result of the study on whitening by the present inventor, the absolute value ΔTD (hereinafter, also simply referred to as “ΔTD”) of the difference between the maximum values (TDmax) of the TD transmittance at the wavelength of 500 nm or more and 600 nm or less before and after the durability test is It was found that whitening also tended to be small when the size was small. Whitening, polyiodine complex I ₃ oriented adsorbed on a polyvinyl alcohol-based resin film in the polarizer ^- and I ₅ ^- is thermally decomposed in a durability test, polyiodine complex I ₃ in the polarizer ^- and I ₅ ^- It is presumed that this is caused by the decrease in the content of. However, the present invention is not limited to this estimation. The maximum value (TDmax) of the TD transmittance at a wavelength of 500 nm or more and 600 nm or less is measured according to the measuring method described in the section of Examples below.

The red discoloration is a color change visually recognized when the polarizing plate is observed through the light transmitted through the optical microscope before and after the durability test. As a result of a study 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 between the orthogonal hues a before and after the durability test of the polarizing plate using the polarizer is small. It was also found that there was a tendency for reddish to be small. The red discoloration shows that the polyiodine complex I ₅ ⁻ having an absorption maximum on the relatively long wavelength side of visible light, which is oriented and adsorbed in the polyvinyl alcohol-based resin film in the polarizer, is thermally decomposed in the durability test, and It is presumed that this is caused by the decrease in the content of the polyiodine complex I ₅ ⁻ of. However, the present invention is not limited to this estimation. The orthogonal hue a is measured according to the measuring method described in the section of Examples below.

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

  The I-Zn / I-I 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. Yes, and more preferably 0.55 or more and 0.75 or less.

  Examples of the method of setting the I-Zn / I-I bond ratio within the above range include adjustment of the content of zinc element in the polarizer and adjustment of the thickness of the polarizer. For example, when the content of zinc element is reduced, the I-Zn / I-I bond ratio tends to be low, and when the content of zinc element is increased, the I-Zn / I-I bond ratio tends to be high. Moreover, when the thickness of the film (for example, polyvinyl alcohol-based resin film) raw material used is made small, the ratio of the I-Zn / I-I bond ratio to the content of zinc element tends to become small.

  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, still more preferably 14 μm or less, particularly preferably 13 μm or less, more particularly preferably 12 μm or less. Is. When the thickness of the polarizer is 30 μm or less, whitening tends to be easily suppressed. 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 5 μm or more, for example.

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

The polarizer may contain elemental zinc in any content. When the I-Zn / I-I bond ratio is 0.48 or more, yellowing and red discoloration tend to be suppressed, and when the I-Zn / I-I bond ratio is 0.85 or less, whitening occurs. Since it tends to be 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 content of the zinc element is preferably 0.305 mass% or more, and more preferably 0.31% from the viewpoint of suppressing yellowing and redning. It is at least mass%. On the other hand, the content of the zinc element is preferably 0.75 mass% or less, more preferably 0.7 mass% or less, still more preferably 0.65 mass% or less, and more preferably 0.5 from the viewpoint of suppressing whitening. It is not more than mass%. The content of elemental zinc is measured according to the measuring method described in the section of Examples below.

  The content of the zinc element is, for example, the concentration of the zinc salt in the treatment liquid for treating the polyvinyl alcohol-based resin film, the immersion time of the polyvinyl alcohol-based resin film in the treatment liquid containing the zinc salt, the treatment liquid's By adjusting the temperature and the like, the content of the zinc element in the above range can be obtained.

When the polarizer contains the zinc element in the content within the above range, the thermal decomposition of the polyiodine complexes I ₃ ⁻ and I ₅ ^{− in} the polarizer and the production of I ₂ are suppressed, and as a result, yellowing or reddishing occurs. -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-corrected single transmittance (Ty) before the durability test of, for example, more than 40.5%, and the lower limit of the visibility-corrected single transmittance (Ty) is preferably 41.0%. Above, the upper limit is usually 50% or less, preferably 47% or less.

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

  The polarizer may have a visibility correction polarization degree (Py) of, for example, over 99.980 when the visibility correction single transmittance (Ty) before the durability test is 41.5%. The lower limit of the visibility-corrected polarization degree (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, and preferably 0.008 or less.

  The ΔTD of the polarizer may be, for example, 0.014 or less, and preferably 0.01 or less.

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

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

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

<Production method of 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 in which the polyvinyl alcohol resin film is dyed by immersing it 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 to perform cross-linking treatment
Can be included.

  The manufacturing method may further include other steps than the above, and a specific example thereof, as shown in FIG. 1, stores a treatment liquid containing water in the polyvinyl alcohol resin film before the dyeing step S20. These are a swelling step S10 of immersing in a swelling tank, a cleaning step S40 of immersing the film after the crosslinking step S30 in a cleaning tank, and a drying step S50 after the cleaning step S40. The polyvinyl alcohol-based resin film is uniaxially stretched in any one or more stages of the polarizer manufacturing process, more specifically, in any one or more stages from before the swelling process S10 to the crosslinking process S30. (Stretching step).

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

  Examples of the zinc salt contained in the treatment liquid include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Of these, zinc nitrate is preferred because it has a small change in tension. The zinc salt can be added to the treatment 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 mass or more and 4 parts by mass or less with respect to 100 parts by mass of the processing liquid contained in the processing tank.

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

  The various treatment steps included in the manufacturing method according to the present invention can be continuously performed by continuously transporting the polyvinyl alcohol-based resin film that is the raw film along the film transport path of the polarizer manufacturing apparatus. The film transport path is equipped with equipment (processing tank, furnace, etc.) for carrying out the various processing steps in the order in which they are carried out.

  The film transport path can be constructed by disposing guide rolls, nip rolls, and the like at appropriate positions in addition to the above facilities. For example, the guide rolls can be arranged before and after each treatment tank or in the treatment tank, whereby the film can be introduced into and dipped in the treatment tank and pulled out from the treatment tank. More specifically, two or more guide rolls are provided in each treatment tank, and the film is conveyed along these guide rolls, whereby the film can be immersed in each treatment tank.

  As the polyvinyl alcohol-based resin that constitutes the polyvinyl alcohol-based resin film that is the original film, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. In the present specification, “(meth) acrylic” means at least one selected from acrylic and methacrylic. The same applies to “(meth) acryloyl”.

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

  The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 or more and 10000 or less, more preferably 1500 or more and 8000 or less, and further 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 polarization performance, and if it exceeds 10,000, the film processability 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 is preferably 40 μm or less, more preferably 30 μm or less from the viewpoint of making the thickness of the polarizer 15 μm or less.

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

(1) Swelling step S10
The swelling treatment in this step is a treatment carried out as necessary for the purpose of removing foreign matter of the polyvinyl alcohol-based resin film which is the original film, removing the plasticizer, imparting easy dyeability, plasticizing the film, and the like. Specifically, the polyvinyl alcohol resin film can be immersed in a swelling tank containing a treatment liquid containing water. The film may be dipped in one swelling tank or sequentially dipped in two or more swelling tanks. 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 alcohols is added. As described above, the treatment liquid contained in the swelling tank can contain a zinc salt.

  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 It is about 20 to 300 seconds.

(2) Dyeing step S20
The dyeing treatment in this step is a treatment carried out for the purpose of adsorbing and orienting iodine to the polyvinyl alcohol-based resin film, and specifically, the polyvinyl alcohol-based resin film is placed in a dyeing tank containing a treatment liquid containing iodine. It can be a dipping process. The film may be dipped in one dyeing tank or may be sequentially dipped in two or more dyeing tanks. In order to improve the dyeability of iodine, the film used in the dyeing step 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.

  A dichroic organic dye can also be used together with iodine. When a dichroic organic dye is used, the dichroic organic dye can be used in combination with iodine in one dyeing tank, and when two or more dyeing tanks are used, the dyeing is different from that using iodine. It can also be used in a tank. Specific examples of the dichroic organic dye include red BR, red LR, red R, pink LB, rubin BL, Bordeaux GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy RY, green LG, violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Includes Sky Blue, Direct First Orange S and First Black. The dichroic dyes may be used alone or in combination of two or more.

  An aqueous solution containing iodine and potassium iodide can be used as the treatment liquid contained in the dyeing tank 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. Further, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described below in that it contains iodine. The content of iodine in the aqueous solution is usually 0.01 part by mass or more and 1 part by mass or less per 100 parts by mass of water. The content of iodide 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 described above, the treatment liquid contained in the dyeing tank can contain a zinc salt.

  The temperature of the treatment liquid accommodated 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, and the film The immersion time is usually 30 seconds or longer and 600 seconds or shorter, preferably 60 seconds or longer and 300 seconds or shorter.

When the 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. .. A dyeing aid and the like may coexist in the dyeing tank, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic organic dyes may be used alone or in combination of two or more. The temperature of the treatment liquid accommodated in the dyeing tank when the film is immersed is, for example, 20 ° C. or higher and 80 ° C., preferably 30 ° C. or higher and 70 ° C. or lower, and the film immersion time is usually 30 seconds or longer and 600 seconds or shorter, It is preferably 60 seconds or more and 300 seconds or less.

(3) Cross-linking step S30
The cross-linking treatment of the polyvinyl alcohol-based resin film after the dyeing step with a cross-linking agent is a treatment performed for the purpose of water resistance and hue adjustment by cross-linking, specifically, it is stored in a cross-linking tank containing a cross-linking agent. It may be a treatment of immersing the film after the dyeing step in the treatment liquid. The film may be dipped in one crosslinking tank or may be sequentially dipped in two or more crosslinking tanks. You may perform a uniaxial stretching process at the time of a crosslinking process.

  Examples of the cross-linking agent include boric acid, glyoxal, glutaraldehyde and the like, and boric acid is preferably used. It is also possible to use two or more crosslinking agents in combination. The content of boric acid in the treatment liquid housed in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less, per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the crosslinking tank preferably contains iodide in addition to boric acid. The content of iodide in the treatment liquid housed in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, preferably 5 parts by mass or more and 12 parts by mass or less, per 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Further, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may be allowed to coexist in the crosslinking tank. As described above, the treatment liquid contained in the crosslinking tank can contain zinc salt. When there are two or more crosslinking tanks, it is preferable that the treatment liquid contained in the last crosslinking tank contains a zinc salt.

  The temperature of the treatment liquid accommodated in the crosslinking tank 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 longer and 600 seconds or shorter. , And preferably 20 seconds or more and 300 seconds or less.

In the crosslinking step S30, there may be two or more crosslinking tanks. In this case, the composition and temperature of the treatment liquid contained in each crosslinking tank may be the same or different. The treatment liquid contained in the cross-linking tank may have a concentration of a cross-linking agent, an iodide or the like and a temperature depending on the purpose of immersing the polyvinyl alcohol resin film. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of tanks).
Generally, when both the crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for hue adjustment (complementary color) are performed, the tank for performing the crosslinking treatment for hue adjustment (complementary color) (complementary color tank) is at the latter stage. Will be 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, and preferably 20 ° C. or higher and 50 ° C. or lower. The content of the crosslinking agent in the treatment liquid contained in the complementary color tank is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The iodide content in the treatment liquid contained in the complementary color tank is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water. As described above, the treatment liquid contained in the complementary color bath can contain a zinc salt.

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

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

(4) Cleaning step S40
The cleaning treatment in this step is a treatment which is carried out as necessary for the purpose of removing extra cross-linking agents and dichroic dyes and other chemicals attached to the polyvinyl alcohol-based resin film, and a cleaning solution containing water is used. Is a treatment for washing the polyvinyl alcohol resin film after the crosslinking step. Specifically, it may be a treatment of immersing the polyvinyl alcohol-based resin film after the crosslinking step in a treatment liquid (washing liquid) contained in the washing tank. The film may be immersed in one cleaning tank, or may be sequentially immersed in two or more cleaning tanks. Alternatively, the cleaning treatment may be a treatment in which the cleaning liquid is sprayed as a shower onto the polyvinyl alcohol-based resin film after the crosslinking step, or the above immersion and spraying may be combined.

  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 alcohols is added. The temperature of the cleaning liquid can be, for example, about 5 ° C. or higher and 40 ° C. or lower.

  The washing step S40 is an optional step and may be omitted, or the washing process may be performed during the drying step S50 as described later. Preferably, the drying step S50 is performed on the film after the cleaning 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. While continuing to convey the polyvinyl alcohol-based resin film after the washing step S40, a drying process can be performed by introducing the film to the drying step S50, whereby a polarizer is obtained.

  The drying process is performed using a film drying means (heating means). A suitable example of the drying means is a drying oven. The drying furnace is preferably one capable of controlling the temperature inside the furnace. The drying oven is, for example, a hot air oven that can raise the temperature inside the oven by supplying hot air or the like. Further, the drying process by the drying means may be a process of bringing the polyvinyl alcohol resin film after the washing step S40 into close contact with one or more heating bodies having a convex curved surface, or a process of heating the film using a heater. Good.

  Examples of the heating body 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 an infrared heater, a halogen heater, a panel heater and the like.

  The temperature of the drying treatment (for example, the temperature inside the drying furnace, the surface temperature of the heat roll, etc.) is usually 30 ° C. or higher and 100 ° C. or lower, and preferably 50 ° C. or higher and 90 ° C. or lower. The drying time is not particularly limited, but 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-based resin film can be obtained.

  The obtained polarizer can be conveyed as it is, for example, to the next polarizing plate preparation step (the 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-mentioned polarizer, a first thermoplastic resin film provided on one surface thereof, and a second thermoplastic resin film provided on the other surface thereof. It is a polarizing plate provided. The polarizing plate will be described below with reference to the drawings. The polarizing plate 100 shown in FIG. 1 includes a first thermoplastic resin film 102 on one surface of a polarizer 101 and a second thermoplastic resin film 103 on the other surface. Hereinafter, the first thermoplastic resin film and the second thermoplastic resin film are collectively referred to as a thermoplastic resin film.

  The thermoplastic resin film may be a thermoplastic resin, for example, a polyolefin resin such as a chain polyolefin resin (such as polypropylene resin) or a cyclic polyolefin resin (such as norbornene resin); such as triacetyl cellulose or diacetyl cellulose. Cellulose ester resins; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate resins; (meth) acrylic resins such as polymethylmethacrylate resins; or mixtures or copolymers thereof It may be a transparent resin film made of a material or the like.

  One or both of the first thermoplastic resin film and the second thermoplastic resin film can be a protective film having an optical function as well, such as a retardation film or a brightness enhancement film. For example, a retardation film provided with an arbitrary retardation value by stretching (uniaxially stretching or biaxially stretching) a transparent resin film made of the above material or forming a liquid crystal layer or the like on the film. Can be

  Forming 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 on the surface of the thermoplastic resin film opposite to the polarizer 101. You can also

  The thickness of the thermoplastic resin film is preferably thin from the viewpoint of thinning the polarizing plate 100, but if it is too thin, the strength tends to decrease and the workability tends to be poor, so that it is preferably 5 to 150 μm, and more preferably. It is 5 to 100 μm, and more preferably 10 to 50 μm.

  The polarizing plate 100 can be obtained by laminating (laminating) thermoplastic resin films on both surfaces 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 is added thereto. Examples thereof include aqueous adhesives such as aqueous solutions and urethane emulsion adhesives. When laminating the thermoplastic resin films on both surfaces of the polarizer 101, the adhesives forming the two adhesive layers may be the same or different. For example, when laminating the thermoplastic resin films on both sides, one side may be laminated with an aqueous adhesive and the other side may be laminated with an active energy ray-curable adhesive. The UV-curable adhesive can be a mixture of a radically polymerizable (meth) acrylic compound and a photoradical polymerization initiator, a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator, and the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

  When an active energy ray-curable adhesive is used, 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 an active energy ray (ultraviolet ray) having a light emission distribution at a wavelength of 400 nm or less is preferable. A black light lamp, a microwave excited mercury lamp, a metal halide lamp 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 formed on 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, saponification treatment and the like may be performed.

  As described above, the polarizing plate 100 of the present invention can be produced by laminating a thermoplastic resin film on the polarizer 101 which is a single layer film, but the method is not limited to this. It can also be produced by a method using a base film, for example, 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.

After applying a coating liquid containing a polyvinyl alcohol-based resin on at least one surface of the substrate film, a resin layer forming step of forming a polyvinyl alcohol-based resin layer by drying to obtain a laminated film,
A stretching step of stretching 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 in which a thermoplastic resin film is laminated 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 contain the elemental zinc.

  When a thermoplastic resin film is laminated on both surfaces of the polarizer 101 layer (polarizer), a second thermoplastic resin film is further formed on the polarizer surface of the single-sided first polarizing plate with a thermoplastic resin film by using an adhesive. The second bonding step of bonding is included.

  In the above method utilizing a substrate film, a drying step can be included in the dyeing step for obtaining the polarizing laminated film (for example, after the crosslinking step or the washing step in the dyeing step for obtaining the polarizing laminated film). The polarizer contained in the polarizing laminate film, the polarizing plate with the one-sided thermoplastic resin film, and the polarizing plate with the double-sided thermoplastic resin film obtained through the second bonding step, or the polarizer isolated therefrom is also included. A polarizer belonging to the present invention.

  The I-Zn / II bond ratio, the zinc content, the thickness, the raw material, and the like of the polarizer 101 are the same as those exemplified in the above-mentioned section of the description of the polarizer.

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

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

  The polarizing plate may have a visibility correction polarization degree (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-corrected polarization degree (Py) when the transmittance (Ty) is 41.5% is preferably 99.985 or more. The visibility-corrected polarization degree (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, and preferably 0.008 or less.

  The ΔTD of the polarizing plate may be, for example, 0.014 or less, and preferably 0.01 or less.

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

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

  The polarizing plate can be used for a display device. The display device may be any one such as a liquid crystal display device and an organic EL display device, but is preferably a liquid crystal display device. The 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 a polarizing plate arranged on the viewing side, may be used for a polarizing plate arranged on the backlight side, or may be used on the viewing side and the backlight side. It may be used for both polarizing plates.

  The polarizing plate is equipped with 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 a display device. The translucent member may be a glass plate, a translucent resin film, or the like.

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

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

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

[Measurement of I-Zn / I-I bond ratio]
The X-ray absorption spectrum at the iodine-K absorption edge was measured by an XAFS (X-ray absorption fine structure) measuring device installed in the beam line NW-10A of Synchrotron Radiation Science Facility of High Energy Accelerator Research Organization.
In the measurement, a Si (311) dispersive crystal was used, the incident X-ray intensity was a 17 cm ion chamber using argon as a detection gas, and the transmitted X-ray intensity was a 31 cm ion chamber using krypton as a detection gas. It was measured by the method. The sample was measured by stacking 100 polarizers with their absorption axes aligned and then placing them so that the absorption axes of the polarizers were parallel to each other in the beam. The obtained absorption spectrum was Fourier-transformed with 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 I-I bond, and the ratio of the respective peak heights is the I-Zn / I-I bond ratio. And

[Maximum value of TD transmittance (TDmax) at wavelengths of 500 nm to 600 nm]
For the polarizing plate, the TD transmittance in the wavelength range of 380 to 780 nm was measured using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation), and the largest TD transmittance in the wavelength range of 500 nm to 600 nm. I asked.

[Emissive factor correction single transmittance (Ty) and luminosity factor correction polarization degree (Py)]
Regarding the polarizing plate, the MD transmittance and the TD transmittance in the wavelength range of 380 to 780 nm were measured using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation),
The following formula:
Single transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD-TD) / (MD + TD)} × 100
Based on the above, the simple substance transmittance and the polarization degree at each wavelength were calculated.
The “MD transmittance” is the transmittance when the direction of the polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing plate, and is represented by “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 orthogonal to the transmission axis of the polarizing plate, and is represented by "TD" in the above formula.
Regarding the obtained single transmittance and the degree of polarization, the visual sensitivity was corrected by the two-degree visual field (C light source) of JIS Z 8701: 1999 “Color display method-XYZ color system and X10Y10Z10 color system” to correct the visibility. The simple substance transmittance (Ty) and the visibility-corrected polarization degree (Py) were obtained.

[Orthogonal hue a]
The orthogonal hue a is an a value in the Lab color system, and standard light was measured using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation). The Lab color system is represented by Hunter's lightness index L and hues a and b as described in "5.5 Accelerated weathering test" of JIS K 5981: 2006 "Synthetic resin powder coating film". The values of the lightness index L and the hues a and b are calculated from the tristimulus values X, Y and Z defined in JIS Z 8722: 2009 “Measurement method of color-reflection and transmission object color” by the following formula. Calculated by
L = 10Y ^1/2
a = 17.5 (10.2 XY) / Y ^1/2
b = 7.0 (Y-0.847Z) / Y1 / ² .
In the Lab color system, the hue a value and the b value can indicate the position corresponding to the saturation, and when the hue a value increases, the hue becomes reddish, and when the hue b value increases, the hue becomes yellowish. Change. Further, the closer to 0, the closer to achromatic color.

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

  Next, after the film pulled out from the crosslinking tank is immersed in a cleaning tank containing pure water at 7 ° C. for 10 seconds for the immersion time (cleaning step), it is subsequently introduced into a heating furnace at 80 ° C. for an immersion time of 150 ° C. Drying treatment was performed for 2 seconds (drying step) to obtain a polarizer having a thickness of 12 μm. In the swelling step, the dyeing step, the crosslinking step, the complementary color step and the washing step, longitudinal uniaxial stretching was carried out at a magnification 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. The results are shown in Table 1.

<Example 2>
Other than changing the mass ratio of potassium iodide / boric acid / zinc nitrate hexahydrate / water to 9.0 / 3.0 / 3.0 / 100 in the treatment liquid stored in the complementary color tank in the complementary color process A 12 μm-thick polarizer was produced in the same manner as in Example 1.

<Example 3>
Other than changing the mass ratio of potassium iodide / boric acid / zinc nitrate hexahydrate / water to 9.0 / 3.0 / 4.0 / 100 in the treatment liquid stored in the complementary color tank in the complementary color process A 12 μm-thick polarizer was produced in the same manner as in Example 1.

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

<Comparative example 2>
Other than changing the mass ratio of potassium iodide / boric acid / zinc nitrate hexahydrate / water to 9.0 / 3.0 / 1.0 / 100 in the treatment liquid stored in the complementary color tank in the complementary color process A 12 μm-thick polarizer was produced in the same manner as in Example 1.

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

  Next, the film pulled out from the crosslinking tank is immersed in a cleaning tank containing pure water at 8 ° C. for 10 seconds for the immersion time (cleaning step), and subsequently introduced into a heating furnace at 80 ° C. for 300 seconds. Was dried (drying step) to obtain a polarizer having a thickness of 28 μm. In the swelling step, the dyeing step, the crosslinking step, the complementary color step and the washing step, longitudinal uniaxial stretching was carried out at a magnification 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>
Other than changing the mass ratio of potassium iodide / boric acid / zinc nitrate hexahydrate / water to 9.0 / 3.0 / 5.0 / 100 in the treatment liquid stored in the complementary color tank in the complementary color process In the same manner as in Comparative Example 3, a polarizer having a thickness of 28 μm was produced.

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

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

  Next, the film pulled out from the crosslinking tank is immersed in a cleaning tank containing pure water at 8 ° C. for 10 seconds for the immersion time (cleaning step), and then continuously introduced into a heating furnace at 80 ° C. for 300 minutes. Drying treatment was performed for 2 seconds (drying step) to obtain a polarizer having a thickness of 22 μm. In the swelling step, the dyeing step, the crosslinking step, the complementary color step and the washing step, longitudinal uniaxial stretching was carried out at a magnification 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 that the mass ratio of potassium iodide / boric acid / zinc nitrate hexahydrate / water in the treatment liquid stored in the complementary color tank in the complementary color process was changed to 9.0 / 3.0 / 5.0 / 100. A 22 μm thick polarizer was prepared in the same manner as in Comparative Example 6.

<Example 4>
An aqueous 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 saponified surface is coated with the water-based adhesive using a bar coater, and one side of a 40 μm thick low phase difference TAC film is applied. After saponification treatment, the water-based adhesive was applied to the saponification treated surface using a bar coater. A TAC film is laminated on one surface of the polarizer and a low retardation TAC film is laminated on the other surface so that the adhesive layer is on the polarizer side of Example 1, and the TAC film / adhesive layer / polarized light is laminated. A laminate having a layer structure of child / adhesive layer / low retardation TAC film was obtained. The obtained laminate is subjected to a heat treatment at 80 ° C. for 140 seconds with 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. The results are shown in Table 1.

<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. The results are shown in Table 1.

<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 as the polarizer. A durability test was performed on the obtained polarizing plate. The results are shown in Table 1.

<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. The results are shown in Table 1.

<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 as the polarizer. A durability test was performed on the obtained polarizing plate. The results are shown in Table 1.

<Comparative Example 10>
A TAC film / adhesive layer / polarizer / adhesive layer / TAC was obtained in the same manner as in Example 4 except that the polarizer prepared in Comparative Example 3 was used and the low retardation TAC film was changed to a TAC film having a thickness of 40 μm. A laminate having a film layer structure was obtained. The obtained laminate is subjected to heat treatment at 80 ° C. for 300 seconds with a hot air dryer to prepare a polarizing plate having a layer structure of TAC film / adhesive layer / polarizer / adhesive layer / low retardation TAC film. did. A durability test was performed on the obtained polarizing plate. The results are shown in Table 1.

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

<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. The results are shown in Table 1.

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

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

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

Claims (10)

  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.   The polarizer according to claim 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.   The polarizer according to claim 1, which has a thickness of 15 μm or less.   Polarized light comprising the polarizer according to any one of claims 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. Board.   The polarizing plate according to claim 4, wherein the second thermoplastic resin film is a retardation film.   The polarizing plate according to claim 4 or 5, wherein the absolute value ΔTy of the difference in the transmittance Ty of the visibility-corrected single body before and after the durability test at 105 ° C and 1000 hours is 4% or less.   7. 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 a durability test at 105 ° C. and 1000 hours is 0.014 or less. Polarizing plate.   The polarizing plate according to any one of claims 4 to 7, wherein an absolute value Δa of a difference between orthogonal hue a values before and after a durability test at 105 ° C and 1000 hours is 2.5 or less.   The polarizing plate according to any one of claims 4 to 8, a light-transmissive member arranged on the first thermoplastic resin film side of the polarizing plate, and a second thermoplastic resin side of the polarizing plate. In-vehicle display device including the above-described display device in this order. It is a manufacturing method of the polarizer as described in any one of Claims 1-3,
The polarizer includes a polyvinyl alcohol resin,
A manufacturing 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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