KR20230002830A - Polarizing plate and its manufacturing method - Google Patents

Abstract

[Problem] To provide a polarizing plate having good heat resistance.
[Solution] A polarizing plate comprising a polarizer, a first adhesive layer, and a first resin film in this order, wherein the polarizer and the first adhesive layer are in direct contact, the visibility correction single transmittance is 45.5% or more, and the polarizer and the first adhesive layer are in direct contact with each other. The content of the zinc element contained in the adhesive layer in direct contact with the polarizer is 0.15% by mass or more, and the polarizer has a thickness of 10 μm or more.

Description

Polarizing plate and its manufacturing method

The present invention relates to a polarizing plate and a manufacturing method thereof.

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

Patent Document 1: Japanese Unexamined Patent Publication No. 2003-29042 Patent Document 2: Japanese Unexamined Patent Publication No. 2004-61565 Patent Document 3: Japanese Unexamined Patent Publication No. 2014-102353

A polarizer is used in an image display device as a polarizing plate. When an image display device is used under high temperature for a long time, the optical properties of the polarizing plate may change. In particular, in a polarizing plate having high transmittance such as organic EL applications, the amount of circular dichroic dye in the polarizer is small, and it is difficult to satisfy durability tests such as heat resistance. Therefore, the improvement of the heat resistance of a polarizing plate is calculated|required.

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

This invention provides the following polarizing plate and the manufacturing method of a polarizing plate.

[1] A polarizing plate comprising a polarizer, a first adhesive layer, and a first resin film in this order,

The polarizer and the first adhesive layer are in direct contact,

Visibility correction single transmittance is 45.5% or more,

The content of the zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more,

The polarizer has a thickness of 10 μm or more, a polarizing plate.

[2] The polarizing plate according to [1], wherein the visibility correction polarization degree is 94.0% or more.

[3] The polarizing plate according to [1] or [2], wherein the content of elemental zinc contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.22% by mass or less.

[4] The polarizing plate according to any one of [1] to [3], wherein the first resin film has a water vapor transmission rate of 100 g/m 2 /24 h or more at a temperature of 40°C and a relative humidity of 90% RH.

[5] The polarizing plate according to any one of [1] to [4], wherein the first adhesive layer contains elemental zinc.

[6] Any one of [1] to [5] further comprising a second adhesive layer and a second resin film in this order from the side closer to the polarizer on the side opposite to the first resin film of the polarizer. The polarizing plate according to claim 1.

[7] The polarizing plate according to [6], wherein the second resin film has a water vapor transmission rate of 100 g/m 2 /24 h or more at a temperature of 40°C and a relative humidity of 90% RH.

[8] The polarizing plate according to [6] or [7], wherein the second adhesive layer contains elemental zinc.

[9] A method for producing the polarizing plate according to any one of [1] to [8],

The manufacturing method which has the process of manufacturing a polarizer by processing with the treatment liquid containing zinc salt with respect to a polyvinyl alcohol-type resin film.

According to the present invention, a polarizing plate having good high-temperature durability can be provided.

1 is a schematic cross-sectional view showing a polarizing plate according to an aspect of the present invention.
2 is a flowchart illustrating a method of manufacturing a polarizer according to an aspect of the present invention.

[Polarizer]

1 is a cross-sectional view schematically showing a polarizing plate according to an aspect of the present invention. The polarizing plate 1 includes a polarizer 10, a first adhesive layer 101, and a first resin film 102 in this order. The polarizer 10 and the first adhesive layer 101 are in direct contact. The polarizing plate has a visibility correction single transmittance (Ty) of 45.5% or more, and a zinc element content of 0.15% by mass or more. A polarizer is 10 micrometers or more in thickness. When the visibility corrected single transmittance (Ty) of the polarizing plate is 45.5% or more, a change in optical characteristics is easily recognized compared to a polarizing plate having a visibility corrected single transmittance (Ty) of less than 45.5%. According to the present invention, a polarizing plate having a visibility correction single transmittance (Ty) of 45.5% or more by setting the content of zinc element and the thickness of the polarizer contained in the polarizing plate to the above-mentioned range, has excellent heat resistance, even when subjected to a heat resistance test. , it is possible to provide a polarizing plate in which the change in optical properties is suppressed before and after the heat resistance test.

The polarizing plate has a visibility correction single transmittance (Ty) of preferably 46.0% or more, more preferably 47.0% or more. The visibility correction single transmittance (Ty) of the polarizing plate is usually 50% or less.

In this specification, a heat resistance test means a durability test of a heat resistance test performed according to the method described in the section of Examples described later. In the polarizing plate, as an optical characteristic whose change is suppressed before and after the durability test when subjected to the heat resistance test, the visibility correction polarization degree (Py) is exemplified. The rate of change (ΔPy) of the visibility correction polarization degree (Py) of the polarizing plate before and after the heat resistance test is, for example, 4.0% or less, preferably 3.5% or less, and more preferably 3.0% or less. According to the present invention, a polarizing plate exhibiting excellent heat resistance having a rate of change (ΔPy) within this range is obtained.

The visibility correction polarization degree (Py) of the polarizing plate is preferably 92.0% or more, more preferably 93.0% or more, still more preferably 94.0% or more. The visibility correction polarization degree (Py) of the polarizing plate may be 99.9% or less, and may be 99% or less in other forms, or may be 98% or less.

In the polarizing plate, the content of the zinc element in the polarizer and the adhesive layer directly in contact with the polarizer is 0.15% by mass or more. When the zinc element content of the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more, a polarizing plate having good high-temperature durability can be provided. The content of such elemental zinc is preferably 0.16% by mass or more, more preferably 0.17% by mass or more. The content of the zinc element is preferably 0.22% by mass or less, and more preferably 0.20% by mass or less, from the viewpoint of obtaining a polarizing plate having a desired color tone.

The content of the total zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is the content of the zinc element contained in the polarizer, the content of the zinc element in the first adhesive layer and/or the second adhesive layer in contact with the polarizer, and the like. You can control it by adjusting it. In addition, the measuring method of content of the zinc element contained in the polarizer and the adhesive bond layer which is in direct contact with the polarizer shall be based on the method described in the Example mentioned later.

The single color b value of the polarizing plate is, for example, -1.0 or more and 4.0 or less, preferably -0.5 or more and 3.0 or less, and more preferably 0 or more and 2.0 or less.

The absorbance A700 of the polarizing plate at a wavelength of 700 nm is, for example, 0.5 or more and 3.0 or less, preferably 0.7 or more and 2.0 or less, and more preferably 0.9 or more and 1.5 or less.

In the present specification, visibility corrected single transmittance (Ty), visibility corrected polarization (Py) and change rate (ΔPy) of visibility corrected polarization (Py), single color b value, absorbance A700 at a wavelength of 700 nm, and polarizer And content of the zinc element of the adhesive bond layer which is in direct contact with a polarizer is set as the value measured according to the measuring method demonstrated in the column of the Example mentioned later.

The 1st resin film is bonded to the surface of a polarizer via the 1st adhesive bond layer, for example.

The polarizing plate may further include a second adhesive layer and a second resin film in this order from the side closer to the polarizer on the side opposite to the first resin film. The 2nd resin film is bonded to the surface of a polarizer via the 2nd adhesive bond layer, for example. In the polarizing plate, when "the content of the total zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer" is obtained, the first adhesive layer corresponds to the adhesive layer in direct contact with the polarizer, and the second adhesive layer When formed in direct contact with the polarizer, the second adhesive layer also corresponds. Hereinafter, the first resin film and the second resin film are collectively referred to as a resin film, and the first adhesive layer and the second adhesive layer are collectively referred to as an adhesive layer.

<Polarizer>

A polarizer is an absorption type polarizer having a property of absorbing linearly polarized light having a vibration plane parallel to the absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). The polarizer may be, for example, a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, and such a polarizer can be manufactured according to a method for producing a polarizer described later.

The thickness of the polarizer is 10 μm or more. When the thickness of the polarizer is 10 μm or more, a polarizing plate having excellent resistance can be provided. The thickness of the polarizer is preferably 12 μm or more, and more preferably exceeds 15 μm. The thickness of the polarizer is preferably 50 μm or less, and more preferably 30 μm or less.

The thickness of the polarizer can be set to the thickness within the range described above by, for example, selection of a polyvinyl alcohol-based resin film, adjustment of a draw ratio, and the like.

It is preferable to perform adjustment of content of the zinc element contained in a polarizing plate by adjusting content of the zinc element contained in a polarizer. The polarizer contained in the polarizing plate of this invention contains zinc normally.

The content of the zinc element contained in the polarizer is, for example, the concentration of the zinc salt in the treatment liquid for processing the polyvinyl alcohol-based resin film, the immersion time of the polyvinyl alcohol-based resin film in the treatment liquid containing the zinc salt, and the treatment By adjusting the temperature of the liquid or the like, it is possible to set the zinc element content within the above-mentioned range.

<Method for manufacturing 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. 2 is a manufacturing method of a polarizer containing a polyvinyl alcohol-based resin, and the following steps:

A dyeing step (S20) of immersing and dyeing a polyvinyl alcohol-based resin film in a dyeing tank containing a treatment liquid containing a dichroic dye;

A crosslinking step of immersing the film after the dyeing step in a crosslinking tank containing a treatment liquid containing a crosslinking agent for crosslinking treatment (S30)

can include

The manufacturing method may further include steps other than the above, and the specific example is, as shown in FIG. 2, the polyvinyl alcohol-based resin film before the dyeing step (S20) is accommodated in a treatment liquid containing water. These are a swelling step (S10) of immersing in a swelling tank, 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). In addition, the polyvinyl alcohol-based resin film is uniaxially stretched at any one or more steps in the polarizer manufacturing process, more specifically, in any one or more steps from the beginning of the swelling step (S10) to the crosslinking step (S30) (stretching step) .

In the manufacturing method, at least one of the treatment liquids for treating the polyvinyl alcohol-based resin film contains zinc salt. Examples of the treatment tank for accommodating the treatment liquid include a swelling tank, a dyeing tank, a crosslinking tank, a washing tank, and a complementary coloring tank described later. The treatment tank for accommodating the treatment liquid containing 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 coloring tank, still more preferably two or more crosslinking tanks. When present, it is at least one selected from the last crosslinking tone and the complementary color tone. Zinc element can be made to contain the polarizer obtained by immersing a polyvinyl alcohol-type resin film in the treatment liquid containing zinc salt. The content of the zinc element in the polarizer is determined 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, so that the content of the zinc element is within the above range. can be done with

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. Among them, since it is inexpensive, zinc nitrate is preferred. 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 is preferably 2 parts by mass or more and 10 parts by mass or less, and more preferably 3 parts by mass or more and 6 parts by mass or less with respect to 100 parts by mass of the treatment liquid stored in the treatment tank. desirable.

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 are described for each step in the subsequent paragraphs.

The various processing steps included in the manufacturing method concerning this invention can be performed continuously by conveying the polyvinyl alcohol-type resin film which is a raw film continuously along the film conveyance path|route of a polarizer manufacturing apparatus. The film conveyance path is equipped with facilities (treatment tanks, furnaces, etc.) for performing the above-mentioned various treatment steps in order of implementation.

A film conveyance route can be constructed by arranging guide rolls, nip rolls, and the like at appropriate positions in addition to the above facilities. For example, guide rolls can be disposed before and after each treatment tank or inside the treatment tank, whereby the film can be introduced into and immersed in the treatment tank and taken out of the treatment tank. More specifically, the film can be immersed in each treatment tank by installing two or more guide rolls in each treatment tank and conveying the film along these guide rolls.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film, which is a raw film, what 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 with this. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group. The degree of saponification of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, "(meth)acryl" means at least one selected from acryl and methacryl. The same applies to "(meth)acryloyl".

The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can 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, still more preferably 2000 or more and 5000 or less. The average degree of polymerization of polyvinyl alcohol-based resin can be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain desirable polarization performance, and if the average degree of polymerization exceeds 10000, film workability may be poor.

The thickness of the polyvinyl alcohol-based resin film is preferably 20 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less, still more preferably 40 μm or more, from the viewpoint of setting the thickness of the polarizer to 10 μm or more. It is 65 micrometers or less.

The polyvinyl alcohol-based resin film, which is a raw film, can be prepared, for example, as a roll (winding product) of a long unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained as an elongated object. Hereinafter, each process is explained in detail.

(1) Swelling process (S10)

The swelling treatment in this step is a treatment performed as necessary for the purpose of removing foreign substances from the polyvinyl alcohol-based resin film, which is a raw film, removing plasticizers, imparting ease of dyeing, plasticizing the film, etc. Specifically, It may be a treatment in which the polyvinyl alcohol-based resin film is immersed in a swelling tank containing a treatment liquid containing water. The film may be immersed in one swelling tank or sequentially immersed in two or more swelling tanks. Before the swelling treatment, at the time of the swelling treatment, or before the swelling treatment and at the time of the swelling treatment, you may perform uniaxial stretching treatment with respect to the film.

The treatment liquid contained in the swelling tank may be water (for example, pure water) or may be an aqueous solution to which a water-soluble organic solvent such as alcohol is added. As described above, the treatment liquid contained in the swelling tank may contain zinc salt.

When the film is immersed, the temperature of the treatment liquid contained in the swelling tank is usually about 10 to 70 ° C, preferably about 15 to 50 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 ° C. It is about 300 seconds.

(2) Dyeing process (S20)

The dyeing treatment in this step is a treatment performed for the purpose of adsorbing and orienting a dichroic dye on a polyvinyl alcohol-based resin film. Specifically, polyvinyl It may be a treatment in which an alcohol-based resin film is immersed. The film may be immersed in one dyeing bath or sequentially immersed in two or more dyeing baths. In order to improve the dyeability of the dichroic dye, 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 during the dyeing treatment.

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

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used for the treatment liquid contained in the dye bath. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described later in that iodine is included. 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. In addition, content of iodides, such as potassium iodide, is 0.5 mass part or more and 20 mass parts or less per 100 mass parts of water normally. As described above, the treatment liquid contained in the dyeing bath may contain zinc salt.

The temperature of the treatment liquid accommodated in the dye bath when the film is immersed is usually 10 ° C or more and 45 ° C or less, preferably 10 ° C or more and 40 ° C or less, more preferably 20 ° C or more and 35 ° C or less. The time is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

When a dichroic organic dye is used as the dichroic dye, an aqueous solution containing the dichroic organic dye can be used for the treatment liquid contained in the dyeing bath. 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. The dyeing tank may coexist with a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. A dichroic organic dye may be used individually by 1 type, and may use 2 or more types together. When the film is immersed, the temperature of the treatment liquid accommodated in the dye bath is, for example, 20°C or more and 80°C, preferably 30°C or more and 70°C or less, and the film immersion time is usually 30 seconds or more and 600 seconds or less, preferably is 60 seconds or more and 300 seconds or less.

(3) Crosslinking process (S30)

The crosslinking treatment of treating the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent is a treatment performed for the purpose of water resistance or color adjustment by crosslinking, and specifically, a dyeing step in a treatment liquid contained in a crosslinking tank containing a crosslinking agent. It may be a treatment of immersing a later film.

The film may be immersed in one crosslinking tank or sequentially immersed in two or more crosslinking tanks. In the case of crosslinking treatment, you may perform uniaxial stretching treatment.

Examples of the crosslinking agent include boric acid, glyoxal, glutaraldehyde and the like, and boric acid is preferably used. Two or more types 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 per 100 parts by mass of water, preferably 1 part by mass or more and 10 parts by mass or less. 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 contained in the crosslinking tank is usually 0.1 parts 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. As iodide, potassium iodide, zinc iodide, etc. are mentioned. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may coexist in the crosslinking tank. As described above, the treatment liquid contained in the crosslinking tank may 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 zinc salt.

When the film is immersed, the temperature of the treatment liquid contained in the crosslinking tank is usually 50°C or more and 85°C or less, preferably 50°C or more and 70°C or less, and the immersion time of the film is usually 10 seconds or more and 600 seconds or less, preferably It is 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 crosslinking tank may have the concentrations of the crosslinking agent, iodide, etc., and the temperature according to the purpose of immersing the polyvinyl alcohol-based resin film. The crosslinking treatment for waterproofing by crosslinking and the crosslinking treatment for color adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of sets), respectively.

In general, when both the crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color adjustment (complementary color) are performed, a group (complementary color group) that performs the crosslinking process for color adjustment (complementary color) is disposed at the rear end. do. The temperature of the treatment liquid contained in the complementary color bath is, for example, 10°C or more and 55°C or less, and preferably 20°C or more and 50°C or less. The content of the crosslinking agent in the treatment liquid contained in the complementary color bath is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the complementary color bath is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water. As described above, the treatment liquid contained in the complementary color bath may contain a zinc salt.

As described above, during manufacture of the polarizer, the polyvinyl alcohol-based resin film is uniaxially stretched in any one or two or more steps from the beginning of the swelling step (S10) to the crosslinking step (S30) (stretching step, Fig. 2) . From the viewpoint of enhancing the dyeability of the dichroic dye, the film subjected to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or the uniaxial stretching treatment before the dyeing treatment. In addition, it is preferable to perform uniaxial stretching treatment at the time of dyeing treatment.

The uniaxial stretching treatment may be either dry stretching performed in air or wet stretching performed in a tank, or both of these may be performed. 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 circumferential speed between two nip rolls, but preferably includes inter-roll stretching. The stretch ratio (when performing the stretching process in two or more steps, these cumulative stretch ratios) based on the raw film is 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 process (S40)

The washing treatment in this step is a treatment performed as necessary for the purpose of removing excess crosslinking agent and chemicals such as dichroic dyes adhering to the polyvinyl alcohol-based resin film, and crosslinking using a washing liquid containing water. It is the process of washing|cleaning the polyvinyl alcohol-type resin film after a process. Specifically, it may be a treatment in which the polyvinyl alcohol-based resin film after the crosslinking step is immersed in a treatment liquid (washing liquid) contained in a washing tank. The film may be immersed in one washing tank or sequentially immersed in two or more washing tanks. Alternatively, the washing treatment may be a treatment of spraying a washing liquid as a shower on the polyvinyl alcohol-based resin film after the crosslinking step, or a combination of immersion and spraying described above.

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

The washing process (S40) is an arbitrary process and may be omitted, and as will be described later, the washing treatment may be performed during the drying process (S50). Preferably, a drying step (S50) is performed on the film after performing the washing step (S40).

(5) Drying process (S50)

The drying step (S50) is a zone for drying the polyvinyl alcohol-based resin film after the washing step (S40). A drying process can be performed by introduce|transducing the said film to a drying process (S50), continuing conveying the polyvinyl alcohol-type resin film after a washing|cleaning process (S40), and a polarizer is obtained by this.

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

Examples of the heating element include a roll (eg, a guide roll that also serves as a heat roll) having a heat source (for example, a heat source such as hot water or an infrared heater) inside to increase the surface temperature. As said heater, an infrared heater, a halogen heater, a panel heater, etc. are mentioned.

The temperature of the drying treatment (for example, the furnace temperature of the drying furnace, the surface temperature of the hot roll, etc.) is usually 30°C or higher and 100°C or lower, 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 polyvinyl alcohol-based resin film uniaxially stretched can be obtained.

The obtained polarizer can also be conveyed to the next polarizing plate manufacturing process (process of bonding a thermoplastic resin film to one side or both surfaces of a polarizer) as it is, for example.

<Resin film>

Examples of the resin film include thermoplastic resins such as polyolefin-based resins such as chain-shaped polyolefin-based resins (such as polypropylene-based resins) and cyclic polyolefin-based resins (such as norbornene-based resins); cellulose ester-based resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate-based resin; (meth)acrylic resins such as polymethyl methacrylate resins; Or it may be a transparent resin film made of mixtures or copolymers thereof.

Either one or preferably both of the first resin film and the second resin film has a water vapor transmission rate of 100 (g / m 2 / 24 h) or more, particularly 300 (g / m 2 / 24 h) at a temperature of 40 ° C. and a relative humidity of 90% RH ), it is particularly effective in the case of In such a film having high moisture permeability, high temperature durability is easily lowered due to moisture entering and exiting, but high temperature durability can be imparted by satisfying the invention requirements of the present patent. As a resin film satisfying such a moisture permeability, triacetyl cellulose etc. are mentioned. In addition, the resin film may have a surface treatment layer such as a hard coat layer or an antireflection layer on the surface of the resin film, as long as the water vapor transmission rate at a temperature of 40 ° C. and a relative humidity of 90% RH is 100 (g / m 2 / 24 h) or more. When a resin film having such a moisture permeability is used, the heat resistance of the polarizing plate tends to deteriorate, but the polarizing plate of the present invention has good durability.

Either one or both of the first resin film and the second resin film may be a protective film having both optical functions such as a retardation film or a brightness enhancing film. For example, a retardation film having an arbitrary retardation value can be obtained by stretching a transparent resin film made of the above material (eg, uniaxial stretching or biaxial stretching) or forming a liquid crystal layer or the like on the film.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, or an antifouling layer may be formed on the surface of the resin film on the opposite side to the polarizer.

The thickness of the resin film is preferably thin from the viewpoint of thinning the polarizing plate, but if it is too thin, the strength tends to decrease and workability tends to be poor, so it is preferably 5 to 150 μm, more preferably 5 to 100 μm More preferably, it is 10-60 micrometers.

(adhesive layer)

A polarizing plate can be obtained by bonding (laminating) a resin film to one side or both sides of a polarizer via an adhesive layer. Examples of the adhesive used for bonding the polarizer and the resin film include active energy ray curable adhesives such as ultraviolet curable adhesives, aqueous solutions of polyvinyl alcohol-based resins or aqueous solutions in which a crosslinking agent is blended, and water-based adhesives such as urethane emulsion adhesives. . As the adhesive, an adhesive containing a zinc element may be used.

By applying the adhesive containing elemental zinc to the surface of the polarizer, it is possible to suppress that the elemental zinc in the polarizer migrates from the polarizer to another layer, and it can suppress that the high-temperature durability is lowered. As a method of including elemental zinc in the adhesive, a method of adding zinc salt at the time of preparing the adhesive is exemplified. As the zinc salt, zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate and the like can be used. The zinc element content of the adhesive can be, for example, 0.1 part by mass or more and 5 parts by mass or less, in terms of solid content, when the total amount of the adhesive is 100 parts by mass.

When bonding a resin film on both surfaces of a polarizer, the adhesive which forms two adhesive bond layers may be of the same type, or may be of a different type. For example, when bonding a resin film on both sides, one side may be bonded using a water-based adhesive and the other side may be bonded using an active energy ray-curable adhesive. The ultraviolet curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a radical photopolymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. Moreover, a cationically polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound may be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used together as an initiator.

In the case of using an active energy ray-curable adhesive, the adhesive is cured by irradiating 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 luminous distribution at a wavelength of 400 nm or less is preferable, specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra high pressure mercury lamp, a chemical lamp, and a black light. A lamp, a microwave excited mercury lamp, a metal halide lamp or the like is preferably used.

In order to improve the adhesiveness between the polarizer and the resin film, corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, and saponification are applied to the bonding surface of the polarizer and/or the resin film prior to bonding of the polarizer and the resin film. You may perform surface treatment, such as treatment.

As described above, the polarizing plate of the present invention can also be produced by bonding a resin film to a polarizer that is a single-layer film through an adhesive layer, but is not limited to this method. For example, it can produce also by the method using a base film as described in Unexamined-Japanese-Patent No. 2009-98653. The latter method is advantageous for obtaining a polarizing plate having a thin film polarizer (polarizer layer), and may include, for example, the following steps.

A resin layer forming step of obtaining a laminated film by coating a coating solution containing a polyvinyl alcohol-based resin on at least one side of a base film and then drying it to form a polyvinyl alcohol-based resin layer;

A stretching step of obtaining a stretched film by stretching the laminated film;

A dyeing step of obtaining a polarizing laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form a polarizer layer (equivalent to a polarizer);

A first bonding step of bonding a resin film (first resin film) onto the polarizer layer of the polarizing laminated film using an adhesive (first adhesive layer) to obtain a bonded film;

The peeling process which peels and removes a base film from a bonding film, and obtains a polarizing plate with a single-sided resin film.

What is necessary is just to contain zinc in at least any one of the said dyeing process and a 1st bonding process. In the case of containing elemental zinc in the dyeing step, zinc can be contained in the polarizing plate by containing zinc salt in the treatment solution containing the dichroic dye. Moreover, when containing zinc element in a 1st bonding process, a polarizing plate can be made to contain zinc element by containing zinc element in an adhesive agent.

In the case of laminating the resin film on both sides of the polarizer layer (polarizer), a second bonding step of bonding the second resin film to the polarizer side of the polarizing plate with the single-sided first resin film using an adhesive (second adhesive layer) include Moreover, you may contain zinc element in the adhesive which bonds the 2nd resin film together.

In the above method using a base film, a drying step can be included in the dyeing step of obtaining the light-polarizing laminated film (for example, after a crosslinking step or after a washing step in the dyeing step of obtaining the light-polarizing laminated film). A polarizer included in the above polarizing laminated film, a polarizing plate with a single-sided thermoplastic resin film, and a polarizing plate with a double-sided thermoplastic resin film obtained through the second bonding step, or a polarizer isolated from them is also a polarizer belonging to the present invention.

A polarizing plate can be used for a display device. The display device may be anything such as a liquid crystal display device and an organic EL display device, but an organic EL display device is preferable. In the case of incorporating into a liquid crystal display device, it is preferably used on the viewing side of the liquid crystal light emitting element. In the case of incorporating into an organic EL display device, a circularly polarizing plate obtained by combining the retardation film and the polarizing plate of the present invention may be used as an antireflection film.

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

Hereinafter, the present invention will be described more specifically by showing examples, but the present invention is not limited by these examples.

Example

[Visibility correction single transmittance (Ty), visibility correction polarization degree (Py) and single color b value]

For the polarizing plate, MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm were measured using a spectrophotometer ["V7100" manufactured by Nippon Bunko Co., Ltd.] having an integrating sphere,

Eq.

Single transmittance (%)=(MD+TD)/2

Polarization degree (%) = {(MD-TD)/(MD+TD)} × 100

Based on this, the single transmittance and polarization degree at each wavelength were calculated.

The "MD transmittance" is the transmittance when the direction of polarized light emitted from the Glan Thomson prism and the transmission axis of the polarizing plate are parallel, and is represented by "MD" in the above formula. In addition, the "TD transmittance" is the transmittance when the direction of polarized light emitted from the Glan Thomson prism and the transmission axis of the polarizing plate are orthogonal, and is represented by "TD" in the above formula.

For the obtained single transmittance and polarization degree, visibility correction is performed by a 2-degree field of view (C light source) of JIS Z 8701: 1999 "Color display method-XYZ color system and X10Y10Z10 color system", and visibility correction single transmittance (Ty) and visibility correction are performed. The degree of polarization (Py) was obtained.

In addition, based on the method described in International Publication No. 2016/117659, the spectral transmittance τ (λ) of the polarizing plates prepared in Examples and Comparative Examples was measured with a spectrophotometer (V7100, Nippon Bunko Co., Ltd.), thereby An orthogonal spectral transmission spectrum was obtained, and a simple color b value and a value of A700 defined by the following formula were obtained.

A700=-Log ₁₀ {(T _MD,700 ×T _TD,700 )/10000}

In the above formula, T _MD,700 is the transmittance at a wavelength of 700 nm obtained when the polarizing plate is placed in a state in which the absorption axis of the polarizer is orthogonal to the linearly polarized light of the measurement light, and T _TD,700 is the polarizing plate, It is transmittance at a wavelength of 700 nm obtained when the absorption axis of the polarizer is arranged in a state in equilibrium with the linearly polarized light of the measurement light, and all of these units are %.

[Heat resistance test]

A 40 mm × 40 mm test piece was cut out from the prepared polarizing plate, and a 40 mm × 40 mm alkali-free glass was bonded to both surfaces of the cut polarizing plate using an acrylic pressure-sensitive adhesive having a thickness of 25 μm to prepare a sample. For each sample, before subjecting it to the heat resistance test, according to the method described above, based on the measured values, the visibility corrected single transmittance (Ty), the visibility corrected polarization degree (Py), the single color b value, and A700 were calculated. .

Each sample was subjected to a heat resistance test in which it was left in an oven at 80°C for 500 hours. For each sample, after subjecting it to the heat resistance test, the visibility correction polarization degree (Py) was measured according to the method described above, and the change rate ΔPy [%] of the visibility correction polarization degree was calculated according to the following method.

The change rate ΔPy [%] is the change rate of the visibility correction polarization (Py) before and after being subjected to the heat resistance test, and the visibility correction polarization (Py) before being subjected to the durability test is P1 and the visibility correction after being subjected to the heat resistance test. It is a value calculated by the following formula (1) when the degree of polarization (Py) is set to P2.

ΔPy={(P1-P2)/P1}×100 (One)

[Measurement of Zinc Elemental Content]

The polarizing plate was immersed in methylene chloride for 30 minutes, subjected to ultrasonic treatment, and the resin film (triacetyl cellulose film) on both sides of the polarizing plate was dissolved in methylene chloride, and a sample containing a polarizer and an adhesive layer in contact with the polarizer was taken out. 1 g of the sample taken out and 50 ml of mannitol solution were placed in a 100 ml container, and an electrode was inserted to perform titration with 0.1 N NaOH. The concentration was calculated from the following formula by recording the primary and secondary endpoints of the analytical instrument.

Zinc content (% by mass) contained in the polarizer and the adhesive layer in contact with the polarizer

= (Amount of 0.1 N NaOH at the second endpoint [mL]-Amount of 0.1 N NaOH at the first endpoint [mL]) × 0.29749 × 0.1 × 0.5 / Amount of sample [g]

Analytical instrument: Metrohom 736GP Titrino

Electrode: Combined pH electrode (Metrohm cat.#6.0258.000)

Titration solution: 0.1 N NaOH

Composition of mannitol solution: mannitol 500 g, pure water 3500 g

<Preparation of adhesive>

A polyvinyl alcohol-based resin adhesive A was prepared by dissolving 3.5 parts of Gosephamer Z-200 (manufactured by Nippon Kosei Chemical Industry Co., Ltd.), 0.12 parts of zinc chloride, and 0.89 parts of glyoxal with respect to 100 parts of water.

<Example 1>

(Manufacture of polarizer)

An unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray) having a saponification degree of 99.9% or more and a transparent thickness of 45 μm was immersed in 30 ° C. water (deionized water) for 2 minutes to swell, followed by iodine 0.45 mmol / L, iodination It dyed by immersing for 2 minutes in a 30 degreeC staining solution containing 2 mass parts of potassium and 0.35 mass part of boric acids. At this time, stretching was performed at a stretching ratio of 1.72 times and 1.54 times in the swelling and dyeing steps, respectively, and stretching was performed so that the cumulative stretching ratio to the dyeing tank was 2.64 times. Subsequently, stretching was performed at a draw ratio of 2.2 times while immersing a solution containing 7.9 parts by mass of potassium iodide and 4.3 parts by mass of boric acid in a crosslinking solution at 56°C for 30 seconds (crosslinking step) to crosslink. Further, the stretching treatment was performed while immersing in a 40°C crosslinking solution containing 10.6 parts by mass of potassium iodide, 5.0 parts by mass of zinc nitrate, and 3.9 parts by mass of boric acid for 5 seconds to crosslink (complementary coloring step). At this time, the total cumulative stretch ratio of the swelling, dyeing, crosslinking, and complementary color steps was set to be 5.9 times. After crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 100° C. to prepare a polarizer. The thickness of the polarizer was 18 μm.

(Manufacture of polarizer)

A protective film was bonded to both surfaces of the polarizer using the polyvinyl alcohol-based adhesive A prepared above. As a protective film, a triacetyl cellulose film (KC4UAW, manufactured by Konica Minolta Co., Ltd., thickness 40 μm, temperature 40 ° C. relative humidity 90% RH, moisture permeability 800 g / m / 24 h) is used on one side of the polarizer, and the other side An antireflection (LR) surface-treated triacetyl cellulose film (thickness: 60 μm, reflectance: 1%) was used. After bonding applied polyvinyl alcohol-type adhesive A to both surfaces of a polarizer, it bonded using a nip roll, and manufactured the polarizing plate of Example 1 by drying at 80 degreeC for 5 minutes.

<Example 2>

(Manufacture of polarizer)

In Example 1, a polarizer was prepared in the same manner as in Example 1, except that the temperature of the crosslinking liquid in the crosslinking step was 60 ° C instead of 56 ° C, and the boric acid concentration of the crosslinking liquid in the complementary step was 3.0 parts by mass. . The thickness of the polarizer was 18 μm.

(Manufacture of polarizer)

A polarizing plate of Example 2 was prepared in the same manner as in Example 1 using the polarizer prepared above.

<Example 3>

(Manufacture of polarizer)

In Example 1, except that the drying temperature of the polyvinyl alcohol film after crosslinking was completed was 90 ° C. instead of 100 ° C., and the boric acid concentration of the cross-linking solution in the complementary color step was 3.0 parts by mass, it was the same as in Example 1. A polarizer was prepared. The thickness of the polarizer was 18 μm.

(Manufacture of polarizer)

A polarizing plate of Example 3 was prepared in the same manner as in Example 1 using the polarizer prepared above.

<Example 4>

(Manufacture of polarizer)

In Example 1, instead of the unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray) having a saponification degree of 99.9% or more and a transparent thickness of 45 μm, an unstretched polyvinyl alcohol film having a saponification degree of 99.9% or more and a transparent thickness of 60 μm A polarizer was produced in the same manner as in Example 1 except that a film (PE-6000, manufactured by Kuraray) was used and the concentration of boric acid in the crosslinking liquid in the complementary color step was 3.0 parts by mass. The thickness of the polarizer was 23 μm.

(Manufacture of polarizer)

A polarizing plate of Example 4 was prepared in the same manner as in Example 1 using the polarizer prepared above.

<Comparative Example 1>

(Manufacture of polarizer)

In Example 1, a polarizer was manufactured in the same manner as in Example 1 except that the content of zinc nitrate in the crosslinking liquid in the complementary color step was 3.0 parts instead of 5.0 parts. The thickness of the polarizer was 18 μm.

(Manufacture of polarizer)

A polarizing plate of Comparative Example 1 was prepared in the same manner as in Example 1 using the polarizer prepared above.

<Comparative Example 2>

(Manufacture of polarizer)

In Example 1, a polarizer was manufactured in the same manner as in Example 1 except that the content of zinc nitrate in the crosslinking liquid in the complementary color step was 0 part instead of 5.0 parts. The thickness of the polarizer was 18 μm.

(Manufacture of polarizer)

A polarizing plate of Comparative Example 2 was prepared in the same manner as in Example 1 using the polarizer prepared above.

<Test>

For the polarizing plates of Examples 1 to 4 and Comparative Examples 1 to 2, visibility correction single transmittance (Ty), visibility correction polarization degree (Py), single color b value and A700 were measured as described above. Moreover, about the obtained polarizing plate, content of the zinc element of the polarizer was measured as mentioned above. Further, the obtained polarizing plate was subjected to a heat resistance test, and the change rate ΔPy of the visibility correction polarization degree was calculated. The results are shown in Table 1.

1: polarizer 10: polarizer
101: first adhesive layer 102: first resin film

Claims (9)

A polarizing plate comprising a polarizer, a first adhesive layer, and a first resin film in this order,
The polarizer and the first adhesive layer are in direct contact,
Visibility correction single transmittance is 45.5% or more,
The content of the total zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more,
The polarizer is a polarizing plate having a thickness of 10 μm or more. The polarizing plate according to claim 1, wherein the visibility correction polarization degree is 94.0% or more. The polarizing plate according to claim 1 or 2, wherein the total zinc element content contained in the polarizer and the adhesive layer directly in contact with the polarizer is 0.22% by mass or less. The polarizing plate according to any one of claims 1 to 3, wherein the first resin film has a water vapor transmission rate of 100 g/m 2 /24 h or more at a temperature of 40°C and a relative humidity of 90% RH. The polarizing plate according to any one of claims 1 to 4, wherein the first adhesive layer contains elemental zinc. The method according to any one of claims 1 to 5, wherein a second adhesive layer and a second resin film are further provided in this order on the side opposite to the first resin film of the polarizer, from the side close to the polarizer. polarizer to do. The polarizing plate according to claim 6 , wherein the second resin film has a water vapor transmission rate of 100 g/m 2 /24 h or more at a temperature of 40° C. and a relative humidity of 90% RH. The polarizing plate according to claim 6 or 7, wherein the second adhesive layer contains elemental zinc. As a manufacturing method of the polarizing plate according to any one of claims 1 to 8,
A manufacturing method comprising a step of processing a polyvinyl alcohol-based resin film with a treatment liquid containing zinc salt to manufacture a polarizer.

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