CN111103649A

CN111103649A - Polarizing plate and method for producing same

Info

Publication number: CN111103649A
Application number: CN201911023449.9A
Authority: CN
Inventors: 住田幸司; 武藤清; 宇田幸弘
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2018-10-29
Filing date: 2019-10-25
Publication date: 2020-05-05
Anticipated expiration: 2039-10-25
Also published as: JP2020071241A; TWI835886B; JP2023121757A; CN111103649B; JP7474896B2; KR20200049602A; TW202028785A

Abstract

Polarizing plate and method for manufacturing the same. The invention provides a polarizing plate with excellent heat resistance. The present invention is a polarizing plate in which the ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds is 0.45 to 0.9.

Description

Polarizing plate and method for producing same

Technical Field

The present invention relates to a polarizing plate that can be used as a constituent member of a polarizing plate, and a method for manufacturing the same.

Background

As a polarizing plate, a polyvinyl alcohol 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 a zinc-containing polyvinyl alcohol resin film as such a polyvinyl alcohol resin film.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-29042

Patent document 2: japanese patent laid-open publication No. 2004-61565

Patent document 3: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

When a polarizing plate is used at high temperature for a long time as a constituent member of the polarizing plate, the polarizing plate may be discolored. Therefore, the heat resistance of the polarizing plate is required to be improved.

The invention aims to provide a polarizing plate with good heat resistance.

Means for solving the problems

The invention provides a polarizing plate, a polarizing plate and a method for manufacturing the polarizing plate.

[1] A polarizing plate 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 polarizing plate according to [1], wherein a ratio of the number of iodine-zinc bonds to the number of iodine-iodine bonds in a direction parallel to an absorption axis of the polarizing plate is more than 0.47 and less than 0.9.

[3] The polarizing plate according to [1] or [2], which has a thickness of 15 μm or less.

[4] A polarizing plate comprising the polarizing plate 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.

[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 an absolute value Δ Ty of a difference between the visibility-corrected monomer transmittances Ty before and after the durability test at 105 ℃ for 1000 hours is 4% or less.

[7] The polarizing plate according to any one of [4] to [6], wherein an absolute value Δ TD of a difference between maximum values of TD transmittance at a wavelength of 500nm or more and 600nm or less before and after a durability test at 105 ℃ for 1000 hours is 0.014 or less.

[8] The polarizing plate according to any one of [4] to [7], wherein an absolute value Δ a of a difference between orthorhombic a-values before and after a durability test at 105 ℃ for 1000 hours is 2.5 or less.

[9] An in-vehicle display device comprising the polarizing plate according to any one of [4] to [8], a light-transmitting member disposed on a first thermoplastic resin film side of the polarizing plate, and a display device disposed on a second thermoplastic resin film side of the polarizing plate in this order.

[10] A method for producing the polarizing plate according to any one of [1] to [3],

the polarizer comprises a polyvinyl alcohol resin,

the method comprises a step of treating a polyvinyl alcohol resin film with a treatment liquid containing a zinc salt.

Effects of the invention

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

Drawings

Fig. 1 is a flowchart showing a method for manufacturing a polarizing plate according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing a polarizing plate according to an embodiment of the present invention.

Description of the symbols

100 polarizing plates, 101 polarizing plates, 102 a first thermoplastic resin film, 103 a second thermoplastic resin film.

Detailed Description

< polarizing plate >

A polarizing plate according to one embodiment of the present invention is an absorption-type polarizing plate that absorbs linearly polarized light having a vibration plane parallel to its absorption axis and transmits linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to its transmission axis). The polarizing plate may be, for example, a polarizing plate in which a uniaxially stretched polyvinyl alcohol resin film is adsorbed and oriented with a dichroic dye such as iodine, and such a polarizing plate may be produced by a method for producing a polarizing plate described later. The polarizing plate can be used as a polarizing plate by attaching a protective film or the like to the surface thereof with an adhesive or an adhesive. Hereinafter, unless otherwise specified, the polarizing plate refers to a polarizing plate having a thermoplastic resin film on at least one surface of a polarizer. The polyvinyl alcohol resin may be the same as the polyvinyl alcohol resin exemplified in the description of the method for producing a polarizing plate to be described later.

The polarizing plate according to one embodiment of the present invention can exhibit excellent heat resistance. In the polarizing plate according to one embodiment of the present invention, yellowing, whitening, and reddening are preferably suppressed when the polarizing plate is used as a constituent member of a polarizing plate and subjected to a durability test. In the present invention, the term "durability test" refers to a durability test conducted according to the method described in the section of examples described later.

The yellowing, whitening and reddening will be described in the following paragraphs.

A polarizing plate of an in-vehicle display device is bonded to, for example, an image display unit with an adhesive or bonding agent, and a light-transmitting member such as a glass plate or a touch panel is bonded to a surface opposite to the surface bonded to the image display unit with an adhesive or bonding agent. Polarizing plates for in-vehicle display devices are sometimes used at relatively high temperatures for a long period of time, and in such cases, discoloration tends to occur easily. As a result of research on discoloration, the present inventors have found that discoloration of polarizing plates used at relatively high temperatures for a long period of time is roughly classified into 3 types, i.e., yellowing, whitening, and reddening. Hereinafter, yellowing, whitening, and reddening may be collectively referred to as discoloration.

Yellowing is the change in color observed when a polarizing plate is observed through transmission light of an optical microscope before and after a durability test. As a result of investigation on yellowing, the present inventors have found that when the absolute value Δ Ty of the difference in the visibility-correcting monomer transmittance (Ty) between before and after the durability test of a polarizing plate using a polarizing plate (hereinafter, also simply referred to as "Δ Ty") is small, yellowing tends to be small as well. It is presumed that the yellowing occurs due to the polyiodide complex I which is adsorbed in the polyvinyl alcohol resin film while being oriented when the polarizing plate is heated to a temperature higher than 90 ℃₃ ^－And I₅ ^－Is thermally decomposed to become I₂Due to I₂The dehydration reaction proceeds by the formation of double bonds after hydroxyl groups in the polyvinyl alcohol resin film are eliminated. However, the present invention is not limited to this estimation. Visibility correction monomer transmittance (Ty) according toThe measurement was carried out by the measurement method described in the section of example.

The whitening is a phenomenon in which light leakage is observed in a state where the polarizing plate is rotated to reach the darkest field of view when the polarizing plate is observed through another polarizing plate by light transmitted through an optical microscope before and after the durability test. As a result of studies on whitening, the present inventors have found that when the absolute value Δ TD (hereinafter, also simply referred to as "Δ TD") of the difference between the maximum TD transmittance values (TDmax) at wavelengths of 500nm to 600nm before and after the durability test is small, whitening tends to be small as well. It is presumed that whitening is caused by the polyiodide complex I having been adsorbed in the polyvinyl alcohol resin film in the orientation of the polarizing plate₃ ^－And I₅ ^－Is thermally decomposed in a durability test, and a polyiodide complex I in a polarizing plate₃ ^－And I₅ ^－The content of (B) becomes small. However, the present invention is not limited to this estimation. The maximum TD transmittance (TDmax) at a wavelength of 500nm to 600nm was measured by the measurement method described in the section of example.

The red change is a change in color observed when the polarizing plate is observed by passing light transmitted through the polarizing plate by an optical microscope before and after the durability test. As a result of investigation on the red discoloration, the present inventors have found that, when the absolute value Δ a of the difference in cross-tone a between before and after the durability test of a polarizing plate using a polarizing plate (hereinafter, also simply referred to as "Δ a") is small, the red discoloration tends to be small as well. It is presumed that the reddening was caused by the polyiodide complex I having the orientation in the polarizing plate adsorbed on the polyvinyl alcohol resin film and having the maximum absorption at the longer wavelength side of visible light₅ ^－Is thermally decomposed in a durability test, and a polyiodide complex I in a polarizing plate₅ ^－The content of (B) becomes small. However, the present invention is not limited to this estimation. The cross-color tone a was measured according to the measurement method described in the column of examples described later.

The 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 the polarizing plate is more than 0.47 and less than 0.9, and preferably parallel to the polarizing plateThe I-Zn/I-I bond ratio in the direction of the absorption axis of the vibrating plate is greater than 0.47 and less than 0.9. The iodine-iodine bond (hereinafter also referred to as an I-I bond) is a bond between iodine atoms in an iodine compound which is oriented and adsorbed in a film (for example, a polyvinyl alcohol resin film). The iodine compound may be, for example, I₃－、I₅ ^－、I₂And 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. When the I-Zn/I-I bond ratio is more than 0.47, yellowing and reddening tend to be easily suppressed. In addition, when the I-Zn/I-I bond ratio is less than 0.9, whitening tends to be suppressed easily. The I-Zn/I-I bond ratio was measured according to the measurement method described in the following section of examples.

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, and still more preferably 0.55 or more and 0.75 or less, from the viewpoint of suppressing discoloration when used at high temperatures for a long time.

Examples of the method for adjusting the I-Zn/I-I bond ratio to fall within the above range include adjustment of the content of zinc element in the polarizing plate, adjustment of the thickness of the polarizing plate, and the like. For example, when the content of zinc element is decreased, 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. Further, when the thickness of the film material (for example, a polyvinyl alcohol resin film) to be used is reduced, the ratio of the I-Zn/I-I bond to the content of zinc element tends to be reduced.

The thickness of the polarizing plate 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, yet more preferably 14 μm or less, particularly preferably 13 μm or less, and still more preferably 12 μm or less. When the thickness of the polarizing plate is 30 μm or less, whitening tends to be suppressed easily. In addition, the reduction of the thickness of the polarizer is advantageous for the thinning of the polarizing plate. The thickness of the polarizing plate is usually 2 μm or more, and may be 5 μm or more, for example.

The thickness of the polarizing plate can be set to the above range by, for example, selecting a polyvinyl alcohol resin film, adjusting the stretching ratio, or the like.

The polarizing plate may contain zinc element at an arbitrary content. The ratio of I-Zn/I-I bond is preferably adjusted to be within the above range because yellowing and reddening tend to be easily suppressed when the ratio is 0.48 or more, and whitening tends to be easily suppressed when the ratio is 0.85 or less.

For example, when the thickness of the polarizing plate 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 mass% or more, from the viewpoint of suppressing yellowing and reddening. On the other hand, from the viewpoint of suppressing whitening, the content of the zinc element 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 still more preferably 0.5% by mass or less. The content of zinc element was measured by the measurement method described in the following section of examples.

For example, the content of zinc element can be set to the content of zinc element in the above range by adjusting the concentration of zinc salt in the treatment liquid for treating the polyvinyl alcohol resin film, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing zinc salt, the temperature of the treatment liquid, and the like.

It is presumed that the polyiodide complex I in the polarizing plate is obtained by including zinc element in the polarizing plate in the above-mentioned range₃ ^－And I₅ ^－Thermal decomposition of and I₂The formation of (b) is suppressed, and as a result, discoloration such as yellowing, reddening, or whitening tends to be less likely to occur. However, the present invention is not limited to this estimation.

The visibility-correcting monomer transmittance (Ty) before the durability test of the polarizing plate may be, for example, more than 40.5%, and the lower limit value of the visibility-correcting monomer transmittance (Ty) is preferably 41.0% or more, and the upper limit value is usually 50% or less, preferably 47% or less.

The Δ Ty of the polarizing plate may be, for example, 4% or less, preferably 3.5% or less.

The visibility correction polarization degree (Py) of the polarizing plate before the durability test may be, for example, more than 99.980 when the visibility correction monomer transmittance (Ty) is 41.5%, and the lower limit value of the visibility correction polarization degree (Py) when the visibility correction monomer transmittance (Ty) is 41.5% is preferably 99.985 or more.

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

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

The cross-color tone a before the durability test of the polarizing plate may be, for example, 2.6 or less, and preferably 1 or less.

The Δ a of the polarizing plate may be, for example, 2.5 or less, preferably 2.45 or less.

The visibility-correcting monomer transmittance (Ty), Δ Ty, Δ TD, visibility-correcting polarization degree (Py), and cross-color tone a and Δ a of the polarizing plate can be measured in the same manner as the measurement of the polarizing plate in accordance with the method described in the section of example.

< method for producing polarizing plate >

A method for manufacturing a polarizing plate according to another embodiment 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 polarizing plate including a polyvinyl alcohol resin, and may include the steps of:

a dyeing step S20 of immersing and dyeing the polyvinyl alcohol resin film in a dyeing bath containing a treatment liquid containing a dichroic dye; and

the crosslinking step S30 is a step of immersing the film after the dyeing step in a crosslinking tank containing a treatment liquid containing a crosslinking agent to perform crosslinking treatment.

The production method may further include other steps than those described above, and specifically, for example, as shown in fig. 1, the steps include a swelling step S10 of immersing the polyvinyl alcohol resin film before the dyeing step S20 in a swelling tank containing a treatment liquid containing water, a washing step S40 of immersing the film after the crosslinking step S30 in a washing tank, and a drying step S50 after the washing step S40. The polyvinyl alcohol resin film is subjected to uniaxial stretching treatment (stretching step) at any one or more stages of the polarizing plate production step, more specifically, at any one or more stages from the swelling step S10 to the crosslinking step S30.

At least 1 of the treatment liquids for treating the polyvinyl alcohol resin film in the production method contains a zinc salt. Examples of the treatment tank for storing the treatment liquid include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, and a color correction tank described later. The treatment tank containing the treatment solution containing the zinc salt is preferably a treatment tank located after the dyeing tank and before the washing tank, more preferably at least 1 selected from the crosslinking tank and the color correction tank, and when there are 2 or more crosslinking tanks, more preferably at least 1 selected from the last crosslinking tank and the color correction tank. The polyvinyl alcohol resin film can be impregnated with a treatment liquid containing a zinc salt to make the polarizing plate contain zinc. The content of zinc element in the polarizing plate can be set to the content of zinc element in the above range by adjusting the concentration of zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing zinc salt, the temperature of the treatment liquid, and the like.

Examples of the zinc salt contained in the treatment solution include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferable because the change in tension is small. The zinc salt may be added to the treatment solution as a zinc salt solution.

The concentration of the zinc salt in the treatment liquid may vary from treatment tank to treatment tank, and 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 treatment liquid contained in the treatment tank.

The immersion time of the polyvinyl alcohol 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 solution will be described in the following paragraphs for each step.

The various processing steps included in the production method of the present invention can be continuously performed by continuously conveying a polyvinyl alcohol resin film as a raw material film along a film conveying path of a polarizing plate production apparatus. The film transport path includes devices (a processing tank, a furnace, and the like) for performing the various processing steps described above in order of their implementation.

The film transport path can be constructed by arranging guide rollers, nip rollers, and the like at appropriate positions in addition to the above-described apparatus. For example, the guide rollers may be disposed before and after each treatment tank and in the treatment tank, whereby the film can be introduced into, immersed in, and pulled out of the treatment tank. More specifically, 2 or more guide rollers are provided in each processing bath, and the film is transported along these guide rollers, whereby the film can be immersed in each processing bath.

As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film used as the raw material film, a resin obtained by saponifying a polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. The saponification degree of the polyvinyl alcohol resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The term "(meth) acrylic" as used herein means at least one member selected from the group consisting of acrylic and methacrylic. The same applies to "(meth) acryloyl group".

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

The polyvinyl alcohol resin preferably has an average degree of polymerization of 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 polymerization degree of the polyvinyl alcohol resin can be determined in accordance with JISK 6726 (1994). If the average polymerization degree is less than 100, it is difficult to obtain preferable polarization performance, and if it exceeds 10000, film processability may be poor.

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

The polyvinyl alcohol resin film used as the raw material film can be prepared, for example, as a long roll (wound product) of an unstretched or stretched polyvinyl alcohol resin film. In this case, the polarizing plate can be obtained as a long object. Hereinafter, each step will be described in detail.

(1) Swelling step S10

The swelling treatment in this step is carried out as needed for the purpose of removing foreign matter from the polyvinyl alcohol resin film used as a raw material film, removing a plasticizer, imparting easy dyeability, plasticizing the film, and the like, and specifically, may be a treatment in which the polyvinyl alcohol resin film is immersed in a swelling tank containing a treatment liquid containing water. The film may be immersed in 1 swelling bath, or may be successively immersed in 2 or more swelling baths. The membrane may be uniaxially stretched before, during, or both the swelling treatment and the swelling treatment.

The treatment liquid contained in the swelling tank may be water (for example, pure water) or an aqueous solution to which a water-soluble organic solvent such as an alcohol is added. As described above, the treatment liquid contained in the swelling bath may 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 ℃, preferably about 15 to 50 ℃, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(2) Dyeing step S20

The dyeing treatment in this step is a treatment for adsorbing iodine to the polyvinyl alcohol resin film and orienting the same, and specifically, may be a treatment in which the polyvinyl alcohol resin film is immersed in a dyeing bath containing a treatment solution containing iodine. The membrane can be immersed in 1 staining tank, also can be sequentially immersed in more than 2 staining tanks. In order to improve the iodine dyeability, the film subjected to the dyeing step may be subjected to at least a certain degree of 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 at the time of the dyeing treatment.

In addition, a dichroic organic dye may also be used together with iodine. In the case of using the dichroic organic dye, the dichroic organic dye may be used in combination with iodine in 1 dyeing bath, and in the case of using 2 or more dyeing baths, it may be used in a dyeing bath different from the dyeing bath using iodine. Specific examples of dichroic organic dyes include Red BR (RedBR), Red LR (Red LR), Red R (Red R), pink LB (Pink LB), ruby Red BL (Rubine BL), Red GS (Bordeaux GS), sky Blue LG (sky Blue LG), lemon Yellow, Blue BR (Blue BR), Blue 2R (Blue 2R), Tibetan Blue RY (Navy RY), green LG (Green), purple LB (Violet LB), purple B (Violet B), black H (Black), black B (Black B), black GSP (Black GSP), Yellow 3G (Yellow 3G), Yellow R (Yellow R), Orange LR (Orange LR), Orange LG 3R (Orange 3R), scarlet (scarlet), Brillid Red LR (Red GL), Blue BK (Red GL), Blue GL (Red GL), Blue GL), Blue LG (sky Blue LG), lemon Yellow B (lemon Yellow BR), Blue BR (Blue BR), Blue BR (Blue 2R), Blue 2R (Blue 2R), Blue RY 3R), Blue RY (Black GL), Blue GL (Black GL), Orange GL (R (Red GL), Orange GL (R) and, Direct Fast orange S, Fast Black (Fast Black). The dichroic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

As the treatment liquid to be contained in the dyeing vessel using iodine, an aqueous solution containing iodine and potassium iodide may be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. Further, a compound other than iodide, for example, boric acid, zinc chloride, cobalt chloride, or the like may be coexistent. The addition of boric acid is different from the crosslinking treatment described later in that iodine is contained. 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. 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 solution contained in the dyeing bath may contain a zinc salt.

The temperature of the treatment liquid contained in the dyeing bath when the membrane is immersed is usually 10 ℃ to 45 ℃, preferably 10 ℃ to 40 ℃, more preferably 20 ℃ to 35 ℃, and the immersion time of the membrane is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

In the case of using a dichroic organic dye, an aqueous solution containing the dichroic organic dye may be used as the treatment liquid contained in the dyeing bath. The content of the dichroic organic dye in the aqueous solution is usually 1X 10 per 100 parts by mass of water^-4Not less than 10 parts by mass, preferably 1X 10^-3The amount of the organic solvent is not less than 1 part by mass. The dyeing vessel may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. The dichroic organic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The temperature of the treatment liquid contained in the dyeing vessel when the membrane is immersed is, for example, 20 ℃ to 80 ℃, preferably 30 ℃ to 70 ℃, and the immersion time of the membrane is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

(3) Cross-linking step S30

The crosslinking treatment of the polyvinyl alcohol resin film after the dyeing step with the crosslinking agent is carried out for the purpose of utilizing the resistance to hydration of crosslinking, adjusting the color tone, and the like, and specifically, may be a treatment of immersing the film after the dyeing step in a treatment liquid contained in a crosslinking tank containing the crosslinking agent. The membrane may be immersed in 1 crosslinking bath, or may be successively immersed in 2 or more crosslinking baths. The uniaxial stretching treatment may be performed at the time of the crosslinking treatment.

Examples of the crosslinking agent include boric acid, glyoxal, and glutaraldehyde, and boric acid is preferably used. More than 2 kinds of crosslinking agents may be used in combination. The content of boric acid in the treatment liquid contained 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 an iodide in addition to boric acid. The content of the iodide in the treatment liquid contained 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 the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may be present in the crosslinking tank. As described above, the treatment liquid contained in the crosslinking tank may contain a zinc salt. When there are 2 or more crosslinking chambers, the treatment liquid contained in the last crosslinking chamber preferably contains a zinc salt.

The temperature of the treatment liquid contained in the crosslinking tank when the membrane is immersed is usually 50 ℃ to 85 ℃, preferably 50 ℃ to 70 ℃, and the immersion time of the membrane is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds.

In the crosslinking step S30, there may be 2 or more crosslinking grooves. 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 crosslinking tank may have a concentration and a temperature of a crosslinking agent, an iodide, and the like corresponding to the purpose of impregnating the polyvinyl alcohol resin film. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color tone adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of tanks).

In general, when both the crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color tone adjustment (color compensation) are performed, a groove (color compensation groove) for performing the crosslinking treatment for color tone adjustment (color compensation) is disposed at the subsequent stage. The temperature of the treatment liquid contained in the color correction tank is, for example, 10 ℃ to 55 ℃, preferably 20 ℃ to 50 ℃. The content of the crosslinking agent in the treatment liquid contained in the color replenishment 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 content of the iodide in the treatment liquid contained in the color replenishment 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 color correction tank may contain a zinc salt.

As described above, in the production of the polarizing plate, the polyvinyl alcohol resin film is uniaxially stretched (stretching step, fig. 1) at any 1 or 2 or more stages from the swelling step S10 to the crosslinking step S30. From the viewpoint of improving the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or is preferably subjected to uniaxial stretching treatment at the time of dyeing treatment in place of or in addition to the uniaxial stretching treatment before dyeing treatment.

The uniaxial stretching treatment may be either dry stretching in which stretching is performed in air or wet stretching in which stretching is performed in a tank, or both of them. The uniaxial stretching treatment may be inter-roll stretching, hot-roll stretching, tenter stretching or the like in which longitudinal uniaxial stretching is performed with a difference in peripheral speed applied between 2 nip rolls, but preferably includes inter-roll stretching. The stretching ratio based on the raw material film (cumulative stretching ratio in the case of stretching treatment in 2 or more stages) is about 3 to 8 times. In order to provide good polarization characteristics, the stretching magnification is preferably 4 times or more, and more preferably 5 times or more.

(4) Cleaning step S40

The cleaning treatment in this step is carried out as needed for the purpose of removing an excessive crosslinking agent, dichroic dye, or other chemical agent attached to the polyvinyl alcohol resin film, and is a treatment of cleaning the polyvinyl alcohol resin film after the crosslinking step with a cleaning solution containing water. Specifically, the polyvinyl alcohol resin film after the crosslinking step may be immersed in a treatment liquid (cleaning liquid) contained in a cleaning tank. The membrane can be immersed in 1 cleaning tank, or can be sequentially immersed in more than 2 cleaning tanks. Alternatively, the cleaning treatment may be a treatment of spraying the polyvinyl alcohol resin film after the crosslinking step with a cleaning liquid as a spray liquid, or a combination of the above-mentioned dipping and spraying.

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

The cleaning step S40 is an optional step, and may be omitted, or the cleaning treatment may be performed in the drying step S50 as described later. The film after the cleaning step S40 is preferably subjected to a drying step S50.

(5) Drying step S50

The drying step S50 is a region for drying the polyvinyl alcohol resin film after the washing step S40. The polyvinyl alcohol resin film after the washing step S40 can be continuously conveyed and subjected to a drying treatment by introducing the film into the drying step S50, thereby obtaining a polarizing plate.

The drying process is performed using a drying mechanism (heating mechanism) for the film. A suitable example of the drying means is a drying oven. The drying oven is preferably capable of controlling the temperature within the oven. The drying furnace is, for example, a hot air oven capable of raising the temperature in the furnace by supplying hot air or the like. The drying process by the drying means may be a process of adhering the polyvinyl alcohol resin film after the washing step S40 to 1 or 2 or more heating bodies having a convex curved surface, or a process of heating the film by a heater.

Examples of the heating body include a roller (e.g., a guide roller serving also as a heat roller) having a heat source (e.g., a heat medium such as warm water or an infrared heater) therein and capable of increasing the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a plate heater.

The temperature of the drying treatment (for example, the temperature in the drying furnace, the surface temperature of the hot roll, etc.) is usually 30 ℃ to 100 ℃, and preferably 50 ℃ to 90 ℃. The drying time is not particularly limited, and is, for example, 30 seconds or more and 600 seconds or less.

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

The obtained polarizer may be directly transported to, for example, the following polarizing plate production step (step of bonding a thermoplastic resin film to one or both surfaces of the polarizer).

< polarizing plate >

A polarizing plate according to another embodiment of the present invention is a polarizing plate including the above-described polarizer, a first thermoplastic resin film provided on one surface of the polarizer, and a second thermoplastic resin film provided on the other surface of the polarizer. Hereinafter, the polarizing plate will be described 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 also collectively referred to as thermoplastic resin films.

The thermoplastic resin film may include thermoplastic resins, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylic resins such as polymethyl methacrylate resins; or a mixture or copolymer thereof.

One or both of the first thermoplastic resin film and the second thermoplastic resin film may be a protective film having an optical function, such as a retardation film or a brightness enhancement film. For example, a retardation film to which an optional retardation value is added can be produced by stretching (uniaxial stretching, biaxial stretching, or the like) a transparent resin film containing the above-mentioned material, or forming a liquid crystal layer on the film.

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 on the side opposite to the polarizing plate 101.

From the viewpoint of thinning the polarizing plate 100, the thickness of the thermoplastic resin film is preferably small, but if it is too thin, the strength tends to be lowered and the processability tends to be poor, and therefore, it is preferably 5 to 150 μm, more preferably 5 to 100 μm, and further preferably 10 to 50 μm.

The polarizing plate 100 can be obtained by bonding (laminating) thermoplastic resin films on both surfaces of the polarizer 101 with an adhesive interposed therebetween. Examples of the adhesive used for bonding the polarizing plate 101 and the thermoplastic resin film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous adhesive such as an aqueous solution of a polyvinyl alcohol resin, an aqueous solution in which a crosslinking agent is mixed in the aqueous solution, and a urethane emulsion adhesive. When the thermoplastic resin films are bonded to both surfaces of the polarizing plate 101, the adhesives forming the 2 adhesive layers may be the same type or different types. For example, when the thermoplastic resin film is bonded to both surfaces, one surface may be bonded with an aqueous adhesive and the other surface may be bonded with an active energy ray-curable adhesive. The ultraviolet-curable adhesive may be a mixture of a radical-polymerizable (meth) acrylic compound and a photo-radical polymerization initiator, a mixture of a cation-polymerizable epoxy compound and a photo-cation polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used in combination as an initiator, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

In the case of using an active energy ray-curable adhesive, after bonding, the adhesive is cured by irradiation with an active energy ray. The light source of the active energy ray is not particularly limited, but active energy rays (ultraviolet rays) having a light emission distribution at a wavelength of 400nm or less are preferable, and specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, or the like is preferably used.

In order to improve the adhesiveness between the polarizing plate 101 and the thermoplastic resin film, the surface of the polarizing plate 101 and/or the surface of the thermoplastic resin film to be bonded may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, or saponification treatment before the polarizing plate 101 and the thermoplastic resin film are bonded.

As described above, the polarizing plate 100 of the present invention may be manufactured by laminating a thermoplastic resin film to the polarizer 101, which is a single-layer film, but is not limited to this method. For example, the film can be produced by a method using a base film as described in Japanese patent application laid-open No. 2009-98653. The latter method is advantageous for obtaining a polarizing plate having a thin polarizer (polarizer layer), and may include the following process, for example.

A resin layer forming step of forming a polyvinyl alcohol resin layer by applying a coating liquid containing a polyvinyl alcohol resin to at least one surface of a base film and then drying the coating liquid to obtain a laminated film;

a stretching step of stretching the laminated film to obtain a stretched film;

a dyeing step of dyeing the polyvinyl alcohol resin layer of the stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizing plate) and thereby obtain a polarizing laminated film;

a first bonding step of bonding a thermoplastic resin film to a polarizer layer of a polarizing laminate film using an adhesive to obtain a bonded film;

and a peeling step of peeling and removing the base film from the adhesive film to obtain a polarizing plate having a thermoplastic resin film on one surface.

The polarizing plate may contain zinc element by adding zinc salt to the treatment liquid containing the dichroic dye in the dyeing step.

When the thermoplastic resin films are laminated on both surfaces of the polarizer 101 layer (polarizer), the second bonding step of bonding the second thermoplastic resin film to the polarizer surface of the polarizer having the first thermoplastic resin film on one surface thereof with an adhesive is further included.

In the above method using a base film, the dyeing step for obtaining the polarizing laminate film (for example, after the crosslinking step or after the washing step in the dyeing step for obtaining the polarizing laminate film) may include a drying step. The polarizing film of the present invention is not particularly limited as long as it is a polarizing film having a polarizing function and a polarizing plate having a thermoplastic resin film on one side thereof, and a polarizing plate having a thermoplastic resin film on both sides thereof obtained by the second bonding step.

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

The Δ Ty of the polarizing plate may be, for example, 4% or less, and preferably 3.5% or less.

The visibility correction polarization degree (Py) of the polarizing plate before the durability test may be, for example, greater than 99.980 when the visibility correction monomer transmittance (Ty) is 41.5%, and the lower limit value of the visibility correction polarization degree (Py) when the visibility correction monomer transmittance (Ty) is 41.5% is preferably 99.985 or more. The visibility correction polarization degree (Py) can be measured by the method described in the section of example.

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

Polarizing plates may be used for the display device. The display device may be any display device such as a liquid crystal display device, an organic EL display device, or the like, but is preferably a liquid crystal display device. The liquid crystal display device includes a liquid crystal panel having a liquid crystal cell as an image display element, and a backlight. When constructing a liquid crystal display device, the polarizing plate may be used as a polarizing plate disposed on the viewing side, a polarizing plate disposed on the backlight side, or both the viewing side and the backlight side.

The polarizing plate is suitable for an in-vehicle display device including a polarizing plate, a light-transmitting member disposed on the first thermoplastic resin film side of the polarizing plate, and a display device disposed on the second thermoplastic resin film side of the polarizing plate in this order. The light-transmitting member may be a glass plate, a resin film having light-transmitting properties, or the like.

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

[ examples ]

[ durability test ]

A40 mm × 40mm test piece was cut out from the produced polarizing plate, and 40mm × 40mm alkali-free glass was bonded to both sides of the cut-out polarizing plate using an acrylic adhesive having a thickness of 25 μm. The polarizing plate with glass bonded on both sides obtained was used as a sample, and the maximum TD transmittance (TDmax), the visibility-corrected monomer transmittance (Ty), the visibility-corrected polarization degree (Py), and the cross-tone a at a wavelength of 500nm to 600nm were measured. Then, the sample subjected to the measurement was heated in an oven at 105 ℃ for 1000 hours. The sample taken out of the oven was subjected to measurement of the maximum TD transmittance (TDmax) at a wavelength of 500nm or more and 600nm or less, the visibility-corrected monomer transmittance (Ty), and the optical characteristics of the orthotone a.

[ measurement of Zinc content ]

The measurement of the zinc content in the polarizing plate was performed as follows.

Nitric acid was added to a precisely weighed polarizing plate, and the solution was subjected to acid decomposition using a microwave sample pretreatment apparatus (ETHOS D) made by Milestone General (マイルストーンゼネラル) to obtain a measurement solution. The zinc concentration was determined by an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technology, and the zinc concentration of the measurement solution was calculated from the mass of zinc relative to the mass of the polarizing plate.

[ measurement of I-Zn/I-I bond ratio ]

The X-ray absorption spectrum of the iodine-K absorption edge was measured by an XAFS (X-ray absorption Fine Structure) measuring apparatus provided in Beam Line NW-10A, a radiology science facility of high-energy Accelerator research organization.

In the measurement, using a Si (311) spectroscopic crystal, the incident X-ray intensity was measured by a transmission method using a 17cm ion chamber using argon as a detection gas, and the transmitted X-ray intensity was measured by a transmission method using a 31cm ion chamber using krypton as a detection gas. After overlapping 100 polarizers aligned with the absorption axis so that the absorption axis of the polarizers is flat in the beamThe samples were placed and measured in a row format. 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 radial distribution function

The nearby peaks are due to the I-Zn bond,

the adjacent peaks are caused by I-I bonds, and the ratio of the height of each peak is defined as the ratio of I-Zn/I-I bonds.

[ maximum value of TD transmittance (TDmax) at a wavelength of 500nm to 600nm ]

The polarizing plate was measured for TD transmittance at a wavelength of 380 to 780nm using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO corporation), and the maximum TD transmittance was determined at a wavelength of 500nm to 600 nm.

[ visibility-correcting monomer transmittance (Ty) and visibility-correcting polarization degree (Py) ]

For the polarizing plate, the MD transmittance and TD transmittance in the wavelength range of 380 to 780nm were measured using a spectrophotometer with an integrating sphere ("V7100" manufactured by japan spectro corporation), and the monomer transmittance and degree of polarization at each wavelength were calculated based on the following formulas:

monomer transmittance (%) - (MD + TD)/2

Degree of polarization (%) { (MD-TD)/(MD + TD) } × 100

The "MD transmittance" is a transmittance when the direction of polarized light emitted from the glan thomson prism is parallel to the transmission axis of the polarizing plate, and is expressed as "MD" in the above formula. The "TD transmittance" is a transmittance when the direction of polarized light emitted from the grazing tomson prism is perpendicular to the transmission axis of the polarizing plate, and is represented by "TD" in the above formula.

The obtained monomer transmittance and polarization degree were measured according to JIS Z8701: 1999 "color expression method-XYZ color system and X10Y10Z10 color system" the visibility was corrected by a 2-degree field of view (C light source), and the visibility-corrected individual transmittance (Ty) and the visibility-corrected polarization degree (Py) were obtained.

[ Cross tone a ]

The orthogonal hue a is a value a in the Lab color system, and the standard light is measured using a spectrophotometer with an integrating sphere ("V7100" manufactured by Nippon Kagaku corporation). The Lab color system is like JIS K5981: a color system represented by brightness index L and hues a and b of Hunter as described in "5.5 accelerated weather resistance test" of 2006 "synthetic resin powder coating film", values of brightness index L and hues a and b being in accordance with JIS Z8722: 2009 "method of measuring color-tristimulus values X, Y and Z specified in reflection and transmission object color" were calculated by the following equation.

L＝10Y^1/2

a＝17.5(10.2X－Y)/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 may indicate positions corresponding to chroma, and when the hue a value increases, the hue changes to the red color system, and when the hue b value increases, the hue changes to the yellow color system. Further, the closer to 0, the closer to achromatic color is.

< example 1 >

A long polyvinyl alcohol (PVA) Film having a thickness of 30 μm (trade name "Kuraray Poval Film VF-PE # 3000" manufactured by Kuraray Co., Ltd.), an average polymerization degree of 2400 and a saponification degree of 99.9 mol% or more was continuously transported while being wound from a roll, and the Film was immersed in a swelling tank containing pure water at 20 ℃ for an immersion time of 80 seconds (swelling step). Thereafter, the film drawn out of the swelling tank was immersed for 130 seconds in a staining tank containing a treatment solution containing iodine at 30 ℃ and having a potassium iodide/boric acid/water ratio of 1.3/0.3/100 (mass ratio) (staining step). Then, the membrane drawn out of the dyeing vessel was immersed for 50 seconds in a crosslinking vessel containing a treatment solution of 56 ℃ with potassium iodide/boric acid/water at a mass ratio of 13.9/3.0/100 (crosslinking step). Next, the film drawn out of the crosslinking tank was immersed for 10 seconds in a color correction tank containing a treatment liquid at 40 ℃ in which potassium iodide/boric acid/zinc nitrate hexahydrate/water was 9.0/3.0/2.0/100 (mass ratio) (color correction step).

Then, the film drawn out of the crosslinking tank was immersed for 10 seconds in a cleaning tank containing pure water at 7 ℃ (cleaning step), and then introduced into a heating furnace at 80 ℃ (drying step), whereby drying treatment was performed for 150 seconds, and a polarizing plate having a thickness of 12 μm was obtained. In the swelling step, dyeing step, crosslinking step, color correction step, and washing step, longitudinal uniaxial stretching was performed at a magnification shown in table 1 by inter-roll stretching in a tank. The total stretching ratio based on the raw material film was 6.0 times. The obtained polarizing plate was measured for zinc content. The results are shown in table 1.

< example 2 >

A polarizing plate having a thickness of 12 μm was produced in the same manner as in example 1, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/3.0/100.

< example 3 >

A polarizing plate having a thickness of 12 μm was produced in the same manner as in example 1, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/4.0/100.

< comparative example 1 >

A polarizing plate having a thickness of 12 μm was produced 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 color compensation tank in the color compensation step was changed to 9.0/3.0/100.

< comparative example 2 >

A polarizing plate having a thickness of 12 μm was produced in the same manner as in example 1, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/1.0/100.

< comparative example 3 >

A long polyvinyl alcohol (PVA) Film having a thickness of 75 μm (trade name "Kuraray Poval Film VF-PS # 7500", manufactured by Kuraray Co., Ltd.), an average polymerization degree of 2400 and a saponification degree of 99.9 mol% or more was continuously transported while being wound from a roll, and immersed in a treatment liquid contained in a swelling tank containing pure water at 25 ℃ for 150 seconds (swelling step). Thereafter, the film drawn out of the swelling tank was immersed for 170 seconds in a staining tank containing a treatment solution containing iodine at 30 ℃ and having a potassium iodide/boric acid/water ratio of 2.0/0.6/100 (mass ratio) (staining step). Then, the film drawn out of the dyeing bath was immersed for 80 seconds in a crosslinking bath containing a treatment solution of 56 ℃ with a potassium iodide/boric acid/water ratio of 15.4/4.0/100 (mass ratio) (crosslinking step), and then immersed for 10 seconds in a color replenishment bath containing a treatment solution of 40 ℃ with a potassium iodide/boric acid/zinc nitrate hexahydrate/water ratio of 15.4/4.0/0/100 (mass ratio) (color replenishment step).

Then, the film drawn out of the crosslinking tank was immersed for 10 seconds in a cleaning tank containing pure water at 8 ℃ (cleaning step), and then introduced into a heating furnace at 80 ℃ (drying step) to be dried for 300 seconds, thereby obtaining a polarizing plate having a thickness of 28 μm. In the swelling step, dyeing step, crosslinking step, color correction step, and washing step, longitudinal uniaxial stretching was performed at a magnification shown in table 1 by inter-roll stretching in a tank. The total stretching ratio based on the raw material film was 6.0 times.

< comparative example 4 >

A polarizing plate having a thickness of 28 μm was produced in the same manner as in comparative example 3, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/5.0/100.

< comparative example 5 >

A polarizing plate having a thickness of 28 μm was produced in the same manner as in comparative example 3, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/7.0/100.

< comparative example 6 >

A60 μm-thick long polyvinyl alcohol (PVA) raw Film (trade name "Kuraray Poval Film VF-PS # 6000" manufactured by Kuraray, Ltd.), having an average polymerization degree of 2400 and a saponification degree of 99.9 mol% or more) was continuously transported while being wound from a roll, and immersed in a treatment liquid contained in a swelling tank containing pure water at 25 ℃ for 150 seconds (swelling step). Thereafter, the film drawn out of the swelling tank was immersed for 170 seconds in a staining tank containing a treatment solution containing iodine at 30 ℃ and having a potassium iodide/boric acid/water ratio of 1.3/0.6/100 (mass ratio) (staining step). Then, the membrane drawn out of the dyeing vessel was immersed for 80 seconds in a crosslinking vessel containing a treatment solution of 56 ℃ and potassium iodide/boric acid/water at a mass ratio of 13.9/4.0/100 (crosslinking step). Next, the film drawn out of the crosslinking tank was immersed for 10 seconds in a color correction tank containing a treatment liquid at 40 ℃ containing potassium iodide/boric acid/zinc nitrate hexahydrate/water at 15.4/5.0/0/100 (mass ratio) (color correction step).

Then, the film drawn out of the crosslinking tank was immersed for 10 seconds in a cleaning tank containing pure water at 8 ℃ (cleaning step), and then introduced into a heating furnace at 80 ℃ (drying step) to be dried for 300 seconds, thereby obtaining a polarizing plate having a thickness of 22 μm. In the swelling step, dyeing step, crosslinking step, color correction step, and washing step, longitudinal uniaxial stretching was performed at a magnification shown in table 1 by inter-roll stretching in a tank. The total stretching ratio based on the raw material film was 6.0 times.

< comparative example 7 >

A polarizing plate having a thickness of 22 μm was produced in the same manner as in comparative example 6, except that the mass ratio of potassium iodide/boric acid/zinc nitrate hexahydrate/water in the treatment liquid contained in the color correction tank in the color correction step was changed to 9.0/3.0/5.0/100.

< example 4 >

An aqueous adhesive containing 3 parts by mass of polyvinyl alcohol per 100 parts by mass of water was prepared.

After one surface of a triacetyl cellulose (TAC) film having a thickness of 40 μm was subjected to saponification, the water-based adhesive was applied to the saponification-treated surface using a bar coater, and after one surface of a TAC film having a thickness of 40 μm was subjected to saponification, the water-based adhesive was applied to the saponification-treated surface using a bar coater. A laminate having layers of TAC film/adhesive layer/polarizing plate/adhesive layer/low retardation TAC film was obtained by laminating a TAC film on one surface of a polarizing plate and a low retardation TAC film on the other surface so that the adhesive layer was on the polarizing plate side in example 1. The obtained laminate was subjected to heat treatment at 80 ℃ for 140 seconds by a hot air dryer, thereby producing a polarizing plate having a layer of TAC film/adhesive layer/polarizer/adhesive layer/low-phase difference TAC film. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in example 2. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in example 3. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 1. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 2. The obtained polarizing plate was subjected to a durability test. The results are shown in table 1.

< comparative example 10 >

A laminate having layers of TAC film/adhesive layer/polarizer/adhesive layer/TAC film was obtained in the same manner as in example 4, except that the polarizer was the polarizer produced in comparative example 3 and the low-phase TAC film was changed to a TAC film having a thickness of 40 μm. The laminate thus obtained was subjected to heat treatment at 80 ℃ for 300 seconds by a hot air dryer, thereby producing a polarizing plate having a layer of TAC film/adhesive layer/polarizer/adhesive layer/TAC film. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 4. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 5. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 6. The obtained polarizing plate was subjected to a durability test. 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 polarizing plate was the one produced in comparative example 7. The obtained polarizing plate was subjected to a durability test. The results are shown in table 1.

[ Table 1]

Claims

1. A polarizing plate 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 polarizing plate according to claim 1,

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 polarizing plate is more than 0.47 and less than 0.9.

3. The polarizing plate according to claim 1 or 2, which has a thickness of 15 μm or less.

4. A polarizing plate is provided with: the polarizing plate 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.

5. The polarizing plate of claim 4,

the second thermoplastic resin film is a retardation film.

6. The polarizing plate of claim 4 or 5,

the absolute value Δ Ty of the difference between the visibility-corrected monomer transmittance Ty before and after the durability test at 105 ℃ for 1000 hours is 4% or less.

7. The polarizing plate according to any one of claims 4 to 6,

the absolute value DeltaTD of the difference between the maximum values of TD transmittance at wavelengths of 500nm to 600nm before and after a durability test at 105 ℃ for 1000 hours is 0.014 or less.

8. The polarizing plate according to any one of claims 4 to 7,

the absolute value Deltaa of the difference between the orthorhombic color tone a values before and after the durability test at 105 ℃ for 1000 hours is 2.5 or less.

9. An in-vehicle display device is provided with: the polarizing plate according to any one of claims 4 to 8, a light-transmitting member disposed on the first thermoplastic resin film side of the polarizing plate, and a display device disposed on the second thermoplastic resin film side of the polarizing plate.

10. A method for producing the polarizing plate according to any one of claims 1 to 3,

the polarizer comprises a polyvinyl alcohol resin,

at least 1 of the treatment liquids for treating the polyvinyl alcohol resin film contains a zinc salt.