CN112912776B

CN112912776B - Method for manufacturing polarizing element

Info

Publication number: CN112912776B
Application number: CN201980070512.6A
Authority: CN
Inventors: 三田聪司
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2018-11-01
Filing date: 2019-08-23
Publication date: 2023-06-06
Anticipated expiration: 2039-08-23
Also published as: TWI826513B; CN112912776A; TW202017994A; WO2020090197A1; JP7126797B2; JP2022121752A; JPWO2020090197A1; KR20210086624A

Abstract

Provided is a method for manufacturing a polarizing material having excellent reliability in a high-temperature environment, simply and inexpensively. The method for manufacturing the polarizing element comprises the following steps: the method for producing a polyvinyl alcohol resin film comprises at least stretching and dyeing the film, and comprises the steps of: after the dyeing, the polyvinyl alcohol resin film is coated or sprayed with a treatment liquid containing citric acid and lithium hydroxide. The pH of the treatment liquid is in the range of 2.5 to 6.0, and the treatment liquid has a buffering effect in the pH range.

Description

Method for manufacturing polarizing element

Technical Field

The present invention relates to a method for manufacturing a polarizing element.

Background

In a liquid crystal display device, which is a typical image display device, polarizers (substantially polarizing plates including polarizers) are disposed on both sides of a liquid crystal cell due to an image forming method. The polarizing material is typically produced by dyeing a polyvinyl alcohol (PVA) resin film with a dichroic material such as iodine (for example, patent documents 1 and 2). In recent years, demand for thinning of image display devices has increased. Therefore, further thinning of the polarizer is also required. But has the following problems: the thinner the polarizer is, the lower the reliability in a high-temperature and high-humidity environment is.

Prior art literature

Patent literature

Patent document 1: japanese patent No. 5048120

Patent document 2: japanese patent laid-open publication No. 2013-156391

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described problems, and a main object of the present invention is to provide a method for manufacturing a highly reliable polarizing element simply and inexpensively even in a high-temperature environment.

Solution for solving the problem

The method for manufacturing the polarizing element comprises the following steps: a method for producing a polyvinyl alcohol resin film, which comprises stretching and dyeing at least a polyvinyl alcohol resin film, comprising: after the dyeing, the polyvinyl alcohol resin film is coated or sprayed with a treatment liquid containing citric acid and lithium hydroxide. The pH of the treatment liquid is in the range of 2.5 to 6.0, and the treatment liquid has a buffering effect in the pH range.

In one embodiment, the polyvinyl alcohol resin film is a polyvinyl alcohol resin layer formed by applying a coating liquid containing a polyvinyl alcohol resin to a substrate, and a laminate of the substrate and the polyvinyl alcohol resin layer is stretched and dyed.

In another aspect of the present invention, a method for manufacturing a polarizing plate with an adhesive layer is provided. The method for manufacturing a polarizing plate with an adhesive layer, the polarizing plate having a polarizing material, a protective film disposed on one side of the polarizing material, and an adhesive layer disposed on the other side of the polarizing material, the method comprising: manufacturing a polarizing element by the above method; attaching a protective film to one side of the polarizing material obtained by the manufacturing method; and forming an adhesive layer containing lithium salt on the other side of the polarizer.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the manufacturing method of the present invention, a polarizing material having high reliability in a high-temperature and high-humidity environment can be provided even if the polarizing material is thin. In the production method of the present invention, after the polyvinyl alcohol resin is dyed, a treatment liquid containing citric acid and lithium hydroxide is applied or sprayed to the polyvinyl alcohol resin film. As a result, a highly reliable polarizing material in a high-temperature environment can be obtained. Further, since this manufacturing method requires neither a special apparatus nor a complicated operation, the polarizing material described above can be manufactured simply and inexpensively.

In addition, the polarizing plate with an adhesive layer having an adhesive layer containing a lithium salt as a conductive agent may cause a problem that desired conductive performance of the adhesive layer is impaired. Specifically, it is considered that lithium ions contained in the adhesive layer can make the iodine complex more stable than other cations (for example, potassium ions) contained in the polarizer. An exchange reaction of lithium ions in the adhesive layer with other cations (for example, potassium ions) contained in the polarizer occurs, and thus, lithium ions contained in the adhesive layer may be reduced, and desired conductive performance of the adhesive layer may be deteriorated with time. In the present invention, a polarizing plate is produced using a polarizing material treated with a treatment liquid containing citric acid and lithium hydroxide. Accordingly, since lithium ions contained in the treatment liquid are first taken into the polarizer, excessive exchange reaction between lithium ions contained in the adhesive layer and other cations contained in the polarizer can be suppressed, and desired characteristics of the adhesive layer can be maintained.

Detailed Description

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Method for manufacturing polarizing element

A-1. Outline of method for manufacturing polarizing element

The method for manufacturing a polarizing element according to an embodiment of the present invention includes at least stretching and dyeing a polyvinyl alcohol (PVA) resin film. Typically, the manufacturing method includes: a step of preparing a PVA-based resin film, a stretching step, a swelling step, a dyeing step, a crosslinking step, a cleaning step, and a drying step. The steps for supplying the PVA-based resin film may be performed in any appropriate order and timing. Accordingly, the steps may be performed in the above-described order, or may be performed in a different order from the above-described order. If necessary, 1 step may be performed a plurality of times. Further, the steps other than the above (for example, the insolubilization step) may be performed at any appropriate timing, or the steps other than the dyeing step may be omitted.

A-1-2.PVA resin film

Examples of the PVA-based resin forming the PVA-based resin film include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% or more and less than 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing element excellent in durability can be obtained. If the saponification degree is too high, gelation may occur.

The average polymerization degree of the PVA-based resin may be appropriately selected according to purposes. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. The average polymerization degree can be determined according to JIS K6726-1994.

The thickness of the PVA-based resin film is not particularly limited, and may be set according to the desired thickness of the polarizing material. The thickness of the PVA resin film is, for example, 10 μm to 200. Mu.m.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on a substrate. The laminate of the substrate and the PVA-based resin layer can be obtained, for example, by a method of applying a coating liquid containing the PVA-based resin to the substrate, a method of laminating a PVA-based resin film on the substrate, or the like. In this case, the laminate of the base material and the PVA-based resin layer is subjected to a stretching step, a swelling step, a dyeing step, a crosslinking step, a cleaning step, and the like.

The steps are described below, and as described above, the steps may be performed in any appropriate order, and are not limited to the order described.

A-2 coating or spraying of the treatment liquid

The production method of the present invention comprises applying or spraying a treatment liquid containing citric acid and lithium hydroxide to the PVA-based resin film after dyeing. The application or spraying of the treatment liquid may be performed at any appropriate timing as long as the treatment liquid is applied after dyeing. Specifically, the application or spraying of the treatment liquid may be performed before the crosslinking step, may be performed after the crosslinking step, may be performed before the cleaning step, or may be performed after the cleaning step. In the case where the stretching step is performed after the dyeing step, the coating or spraying of the treatment liquid may be performed before the stretching step or after the stretching step. In the case where the swelling step is performed after the dyeing step, the treatment liquid may be applied or sprayed before the swelling step or after the swelling step. In the case of performing the insolubilizing step after the dyeing step, the treatment liquid may be applied or sprayed before or after the insolubilizing step. Typically, the treatment liquid may be applied or sprayed after the cleaning step and before the drying step, or between the 1 st drying step and the 2 nd drying step when the drying step is performed in 2 stages.

The treatment liquid used in the present invention is an aqueous solution containing citric acid and lithium hydroxide. The treatment liquid containing citric acid has a buffer effect in a wider pH region than other materials having a buffer effect, for example, and as a result, can have a more excellent discoloration preventing effect in a high-temperature environment. In addition, the pH of the treatment liquid may be adjusted to a desired range by including lithium hydroxide. The pH of the treatment liquid is in the range of 2.5 to 6.0, and the treatment liquid has a buffer function in this range. The pH of the treatment liquid is preferably 3.0 to 5.7, more preferably 3.5 to 4.8.

The concentration of citric acid in the treatment liquid is preferably 0.05 to 5 wt%, more preferably 0.1 to 0.5 wt%.

The production method of the present invention can significantly suppress discoloration of the polarizing material in a high-temperature environment by applying or spraying such a treatment liquid to the PVA-based resin film. This is thought to be because: the buffer action of the treatment liquid in a predetermined pH range can suppress the generation of protons in the PVA-based resin, and as a result, the generation of many double bonds (polyeneization) in the PVA-based resin in a high-temperature environment can be suppressed, and discoloration can be suppressed. In view of the production efficiency, the contact with such a treatment liquid can be usually performed by immersing the PVA-based resin film in the treatment liquid. However, the polarizing material obtained by the manufacturing method including immersion in the processing liquid has the following problems: since the PVA-based resin film swells during impregnation, the state of the iodine complex in the PVA-based resin film is easily changed, and the absorption spectrum of the polarizing element is easily changed before and after impregnation. On the other hand, by applying or spraying the treatment liquid to the PVA-based resin film, it is possible to prevent defects such as changes in absorption spectrum of the polarizing material before and after impregnation at the time of impregnation, and as a result, it is possible to more favorably prevent the multiolefin of PVA.

The treatment liquid is applied or sprayed to the PVA-based resin film by any suitable method. Examples of the coating means include reverse coaters, gravure coaters (direct, reverse, offset), bar reverse coaters, roll coaters, die coaters, bar coaters, and bar coaters. Examples of the spraying means include any suitable spraying device (for example, a pressurized nozzle type and a rotary disk type).

A-3 stretching step

In the stretching step, the PVA-based resin film is typically uniaxially or biaxially stretched to 3 to 7 times. The stretching direction may be the longitudinal direction (MD direction) of the film, the width direction (TD direction) of the film, or both the longitudinal direction and the width direction. The stretching method may be dry stretching, wet stretching, or a combination thereof. The PVA-based resin film may be stretched in a crosslinking step, a swelling step, a dyeing step, or the like. The stretching direction may correspond to the absorption axis direction of the obtained polarizing element.

A-4 swelling procedure

The swelling process is usually performed before the dyeing process. The swelling step may be performed by immersing the PVA-based resin film in a swelling bath, for example. As the swelling bath, water such as distilled water and pure water is generally used. The swelling bath may also contain any suitable other ingredients besides water. Examples of the other component include solvents such as alcohols, additives such as surfactants, and iodides. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Preferably potassium iodide is used. The temperature of the swelling bath is, for example, 20℃to 45 ℃. The immersion time is, for example, 10 seconds to 300 seconds.

A-5 dyeing Process

The dyeing step is a step of dyeing the PVA-based resin film with a dichroic material. Preferably by adsorption of the dichroic substance. Examples of the adsorption method include a method of immersing the PVA-based resin film in a dyeing liquid containing a dichroic material, a method of applying the dyeing liquid to the PVA-based resin film, and a method of spraying the dyeing liquid to the PVA-based resin film. The PVA-based resin film is preferably immersed in a dyeing liquid. This is because the dichromatic substance can be adsorbed well.

Examples of the dichroic material include iodine and dichroic dyes. Iodine is preferred. When iodine is used as the dichroic material, an aqueous iodine solution is preferably used as the dyeing liquid. The iodine content of the aqueous iodine solution is preferably 0.04 to 5.0 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to compound iodide in an aqueous iodine solution. As iodide, potassium iodide is preferably used. The content of iodide is preferably 0.3 to 15 parts by weight relative to 100 parts by weight of water.

The liquid temperature at the time of dyeing of the dyeing liquid can be set to any appropriate value, for example, 20 to 50 ℃. When the PVA-based resin film is immersed in the dyeing liquid, the immersing time is, for example, 5 seconds to 5 minutes.

A-6 Cross-linking step

In the crosslinking step, a boron compound is generally used as a crosslinking agent. Examples of the boron compound include boric acid and borax. Boric acid is preferred. In the crosslinking step, the boron compound is usually used in the form of an aqueous solution.

When an aqueous boric acid solution is used, the boric acid concentration of the aqueous boric acid solution is, for example, 1 to 15% by weight, preferably 1 to 10% by weight. The aqueous boric acid solution may further contain an iodide such as potassium iodide, a zinc compound such as zinc sulfate or zinc chloride.

The crosslinking process may be carried out by any suitable method. Examples include: a method of immersing the PVA-based resin film in an aqueous solution containing a boron compound, a method of applying an aqueous solution containing a boron compound to the PVA-based resin film, or a method of spraying an aqueous solution containing a boron compound to the PVA-based resin film. Preferably in an aqueous solution comprising a boron compound.

The temperature of the solution used for crosslinking is, for example, 25℃or higher, preferably 30℃to 85℃and more preferably 40℃to 70 ℃. The dipping time is, for example, 5 seconds to 800 seconds, preferably 8 seconds to 500 seconds.

A-7 cleaning procedure

The cleaning process may typically be performed after the crosslinking process. The cleaning step is typically performed by immersing the PVA-based resin film in a cleaning solution. As a representative example of the cleaning liquid, pure water is given. Potassium iodide may be added to the pure water.

The temperature of the cleaning liquid is, for example, 5 to 50 ℃. The immersion time is, for example, 1 to 300 seconds.

A-8 drying step

The drying process may be performed by any suitable method. Examples of the drying method include natural drying, air drying, reduced pressure drying, and heat drying. Preferably, heat drying is used. In the case of heat drying, the heating temperature is, for example, 30 to 100 ℃. The drying time is, for example, 20 seconds to 10 minutes.

B. Polarizing element

The thickness of the polarizing material obtained by the production method of the present invention is preferably 80 μm or less in 1 embodiment, preferably 20 μm or less in another embodiment, preferably 10 μm or less in yet another embodiment, preferably 5 μm or less in yet another embodiment, preferably 3 μm or less in yet another embodiment, preferably 2 μm or less. The thickness of the polarizing material is preferably 0.5 μm or more in 1 embodiment, preferably 0.6 μm or more in another embodiment, and preferably 0.8 μm or more in yet another embodiment. According to the manufacturing method of the present invention, even in the case of a thin polarizer, a desired monomer transmittance as described below can be achieved, and further, the amount of variation in the monomer transmittance in a high-temperature environment can be significantly suppressed.

The polarizing material obtained by the production method of the present invention may contain lithium. Lithium content of polarizerQuantity (Li) _POL ) Preferably 0.3 wt% or more, more preferably 0.35 wt% or more. By making the lithium content (Li _POL ) Such a range can be suitably used for a method for producing a polarizing plate with an adhesive layer, which will be described later. Specifically, by using such a lithium-containing polarizing material, even in the case of producing a polarizing plate in which an adhesive layer containing a lithium salt as a conductive agent is formed, the adhesive layer can appropriately maintain desired characteristics. Lithium content of polarizing element (Li _POL ) For example, 10 wt% or less. The lithium content of the polarizer can be determined by ICP-MS.

The iodine content of the polarizing material obtained by the production method of the present invention can be appropriately set according to the thickness of the polarizing material from the viewpoint of imparting sufficient polarizing performance and optimal transmittance. For example, when the thickness of the polarizer exceeds 5 μm and is 10 μm or less, the iodine content is preferably 3.5 to 8.0 wt%; when the thickness of the polarizer exceeds 3 μm and is 5 μm or less, the iodine content is preferably 5.0 to 13.0 wt%; when the thickness of the polarizer is 3 μm or less, the iodine content is preferably 10.0 to 25.0 wt%. The "iodine content" in the present specification means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine is detected as iodine ions (I ^- ) Iodine molecule (I) ₂ ) Polyiodide (I) ₃ ^- 、I ₅ ^- ) When the forms of the present invention exist, the iodine content in the present specification means the amount of iodine containing all of these forms. The iodine content can be calculated by, for example, standard curve method of fluorescent X-ray analysis. The polyiodide is present in the polarizer in a state where a PVA-iodine complex is formed. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, a complex of PVA and triiodide ion (PVA. I) ₃ ^- ) Has a light absorption peak around 470nm, and a complex of PVA and pentaiodide ion (PVA. I) ₅ ^- ) Has a light absorption peak around 600 nm. As a result, the polyiodide ions can absorb light in a wide range of visible light according to the form thereof. On the other hand, iodide (I) ^- ) At 2The light absorption peak is near 30nm, and the light absorption peak does not substantially participate in the absorption of visible light. Therefore, the polyiodide ion present in a state of a complex with PVA is mainly related to the absorption performance of the polarizer.

The monomer transmittance (Ts) of the polarizing material obtained by the production method of the present invention is preferably 30.0% to 43.0%, more preferably 35.0% to 41.0%. The polarization degree of the polarizer is preferably 99.9% or more, more preferably 99.95% or more, and still more preferably 99.98% or more. By setting the individual transmittance to be low and increasing the polarization degree, the contrast can be increased, and the black display can be displayed darker, so that an image display device with excellent image quality can be realized. The monomer transmittance is a value measured by a spectrophotometer with an integrating sphere. The transmittance of the monomer is a Y value obtained by measuring the transmittance in a 2-degree visual field (C light source) of JIS Z8701 and correcting the sensitivity, and can be measured, for example, by using a spectrophotometer with an integrating sphere (product name: V7100, manufactured by Japanese Spectroscopy Co., ltd.).

The absolute value of the monomer transmittance change amount Δtsa of the polarizing material obtained by the production method of the present invention after being left at 85 ℃ for 500 hours is preferably 5.0% or less, more preferably 3.0% or less. The polarizing material obtained by the method of the present invention can achieve the desired monomer transmittance and polarization degree and significantly suppress the variation in the monomer transmittance in a high-temperature environment. Therefore, a polarizing element in which discoloration in a high-temperature environment is suppressed can be realized. As a result, the polarizing material can be suitably used in applications requiring heat resistance. Such excellent effects are considered to be achieved as follows: as described above, the polyvinyl alcohol resin film is coated or sprayed with a treatment liquid having a predetermined pH and a buffer function in the step after dyeing in the method for producing a polarizing material, thereby preventing the resultant polarizing material from being multi-functionalized in a high-temperature environment. This solves the problem newly found by actually producing a very thin (for example, a thickness of 7 μm or less) polarizer which has been difficult to produce in the past, and is an unexpected excellent effect. The amount of change in the transmittance Δtsa of the monomer is preferably negative (i.e., less than 0.0%). The monomer transmittance change amount Δtsa is represented by the following formula:

ΔTsa(％)＝Tsa ₅₀₀ -Ts ₀

here, ts ₀ Tsa for monomer transmittance before heating test ₅₀₀ The transmittance of the monomer after 500 hours of standing at 85 ℃. In the present specification, when the monomer transmittance is merely expressed as Ts, the monomer transmittance Ts before heating is referred to as ₀ 。

The absolute value of the monomer transmittance change amount Δtsb after the polarizing material obtained by the production method of the present invention is left for 500 hours at 60 ℃ in an environment of 90% rh is preferably 3.5% or less, more preferably 3.0% or less. The polarizing material obtained by the method of the present invention can achieve the desired monomer transmittance and the desired polarization degree, and can significantly suppress the variation in the monomer transmittance even in a high-humidity environment. Therefore, a polarizing element that can suppress discoloration even in a high-humidity environment can be realized. Further, the amount of change in the transmittance Δtsb of the monomer is preferably positive (that is, greater than 0.0%). The monomer transmittance change amount Δtsb is represented by the following formula:

ΔTsb(％)＝Tsb ₅₀₀ -Ts ₀

here, ts ₀ As described above, the transmittance of the monomer before the heat test, tsb ₅₀₀ The monomer transmittance after 500 hours at 60℃and 90% RH.

C. Method for manufacturing polarizing plate with adhesive layer

In one embodiment of the present invention, a method for producing a polarizing plate with an adhesive layer is provided. The method for producing a polarizing plate with an adhesive layer of the present invention is a method for producing a polarizing plate comprising a polarizer, a protective film disposed on one side of the polarizer, and an adhesive layer disposed on the other side of the polarizer. The manufacturing method comprises the following steps: manufacturing a polarizer by the method described in item A above; attaching a protective film to one side of the polarizing material obtained by the manufacturing method; and forming an adhesive layer containing a lithium salt on the other side of the polarizer.

C-1. Manufacture of polarizing element

The polarizing plate can be produced by the method described in item A above. As described above, the polarizer produced by the method described in item a may contain lithium. By forming the adhesive layer containing a lithium salt on such a polarizer, the change with time of the characteristics of the adhesive layer can be reduced. As a result, excellent moisture resistance can be achieved.

C-2. Laminating of protective film

Next, a protective film is attached to one side of the polarizer. As the protective film, any appropriate resin film is used. Examples of the material for forming the resin film include (meth) acrylic resins, cellulose resins such as cellulose diacetate and cellulose triacetate, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The "(meth) acrylic resin" refers to an acrylic resin and/or a methacrylic resin.

In one embodiment, the (meth) acrylic resin having a glutarimide structure is used as the (meth) acrylic resin. (meth) acrylic resins having a glutarimide structure (hereinafter, also referred to as glutarimide resins) are described in, for example, japanese patent application laid-open No. 2006-309033, japanese patent application laid-open No. 2006-317560, japanese patent application laid-open No. 2006-328329, japanese patent application laid-open No. 2006-328334, japanese patent application laid-open No. 2006-337491, japanese patent application laid-open No. 2006-337492, japanese patent application laid-open No. 2006-337493, japanese patent application laid-open No. 2006-337569, japanese patent application laid-open No. 2007-009182, japanese patent application laid-open No. 2009-161744, and Japanese patent application laid-open No. 2010-284840. These descriptions are incorporated by reference into this specification.

The protective film is attached to the polarizer by any suitable adhesive layer.

In the case of manufacturing a polarizing element using a laminate of a base material and a PVA-based resin layer, the polarizing element can be used as a protective film without peeling the base material. In addition, any appropriate optical functional film may be used as the protective film (and other protective films in the case where present) depending on the purpose. Examples of the optical functional film include a retardation film and a reflective polarizer (light enhancement film).

C-3 formation of adhesive layer

As a method for forming the adhesive layer, any suitable method may be employed. Typical examples of the formation method include: a method in which the adhesive composition is applied to a separator or the like subjected to a peeling treatment, and a polymerization solvent or the like is dried and removed to form an adhesive layer, which is then transferred to a polarizing element; alternatively, a method of forming an adhesive layer on a polarizing plate by applying the adhesive composition to the polarizing plate and drying and removing a polymerization solvent or the like. When the adhesive is applied, one or more solvents other than the polymerization solvent may be newly added as needed.

C-3-1 adhesive composition

The adhesive composition constituting the adhesive layer contains a base polymer and a lithium salt.

C-3-2 base Polymer

As a representative example of the base polymer, (meth) acrylic polymer ((meth) acrylic resin) is given. The (meth) acrylic polymer typically contains a monomer unit derived from an alkyl (meth) acrylate as a main component. The alkyl (meth) acrylate is an alkyl (meth) acrylate. Examples of the alkyl group forming the alkyl ester include straight-chain or branched-chain alkyl groups having 1 to 18 carbon atoms. Specific examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, decyl, isodecyl, dodecyl, isomyristyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl. These may be used alone or in combination. The average carbon number of the alkyl group contained in the (meth) acrylic polymer is preferably 3 to 9.

The base polymer may comprise monomer units derived from any suitable co-component, depending on the purpose. Examples of the comonomer include hydroxyl group-containing monomers, carboxyl group-containing monomers, anhydride group-containing monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, (N-substituted) amide-based monomers, alkylaminoalkyl (meth) acrylate-based monomers, alkoxyalkyl (meth) acrylate-based monomers, succinimide-based monomers, maleimide-based monomers, itaconimide-based monomers, vinyl-based monomers, cyano (meth) acrylate-based monomers, epoxy group-containing (meth) acrylic monomers, glycol (meth) acrylate-based monomers, silane-based monomers, and polyfunctional monomers. By adjusting the type, number, combination, and copolymerization ratio (weight ratio) of the copolymerization components, a base polymer (eventually an adhesive layer) having desired characteristics can be obtained. The proportion of the copolymerized component in the whole monomer component is preferably 0 to 20% by weight, more preferably 0.1 to 15% by weight, and still more preferably 0.1 to 10% by weight, based on 100% by weight of the whole monomer component.

The weight average molecular weight of the base polymer is typically 50 to 300 tens of thousands, preferably 70 to 270 tens of thousands, more preferably 80 to 250 tens of thousands. If the weight average molecular weight is too small, heat resistance may be insufficient. If the weight average molecular weight is too large, the handleability may be deteriorated. In addition, a large amount of a diluting solvent is required for viscosity adjustment in order to apply the coating, and the cost may be increased. The weight average molecular weight is a value measured by GPC (gel permeation chromatography) and calculated by conversion to polystyrene.

C-3-3 lithium salt

The binder composition comprises a lithium salt (lithium-anion salt). As described above, the lithium salt functions as a conductive agent. Examples of the anions constituting the anion portion include Cl ^- 、Br ^- 、I ^- 、AlCl ₄ ^- 、Al ₂ Cl ₇ ^- 、BF ₄ ^- 、PF ₆ ^- 、ClO ₄ ^- 、NO ₃ ^- 、CH ₃ COO ^- 、CF ₃ COO ^- 、CH ₃ SO ₃ ^- 、CF ₃ SO ₃ ^- 、(CF ₃ SO ₂ ) ₃ C ^- 、AsF ₆ ^- 、SbF ₆ ^- 、NbF ₆ ^- 、TaF ₆ ^- 、(CN) ₂ N ^- 、C ₄ F ₉ SO ₃ ^- 、C ₃ F ₇ COO ^- 、(CF ₃ SO ₂ )(CF ₃ CO)N ^- 、 ^- O ₃ S(CF ₂ ) ₃ SO ₃ ^- And anions represented by the following general formulae (1) to (4).

(1)：(C _n F _2n+1 SO ₂ ) ₂ N ^- (n is an integer of 1 to 10),

(2)：CF ₂ (C _m F _2m SO ₂ ) ₂ N ^- (m is an integer of 1 to 10),

(3)： ^- O ₃ S(CF ₂ ) _l SO ₃ ^- (l is an integer of 1 to 10),

(4)：(C _p F _2p+1 SO ₂ )N ^- (C _q F _2q+1 SO ₂ ) (p and q are integers of 1 to 10).

As the anion, a fluorine-containing anion is preferable, and a fluorine-containing imide anion is more preferable.

Examples of the fluorine-containing imide anion include imide anions having a perfluoroalkyl group. Specific examples include the above (CF ₃ SO ₂ )(CF ₃ CO)N ^- And anions represented by the general formulae (1), (2) and (4).

(1)：(C _n F _2n+1 SO ₂ ) ₂ N ^- (n is an integer of 1 to 10),

(2)：CF ₂ (C _m F _2m SO ₂ ) ₂ N ^- (m is an integer of 1 to 10),

Preferably (CF) ₃ SO ₂ ) ₂ N ^- 、(C ₂ F ₅ SO ₂ ) ₂ N ^- (perfluoroalkyl sulfonyl) imides of the general formula (1) are more preferred(CF ₃ SO ₂ ) ₂ N ^- The bis (trifluoromethanesulfonyl) imide shown. Thus, a preferred lithium salt that may be used in embodiments of the present invention is lithium bis (trifluoromethanesulfonyl) imide.

The content of the lithium salt in the adhesive composition (resulting in the adhesive layer) is preferably 0.01 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and still more preferably 0.7 to 1.5 parts by weight relative to 100 parts by weight of the base polymer. When the content of the lithium salt is in such a range, the moisture resistance of a thin polarizing material having a high iodine content (as a result, a polarizing plate including such a polarizing material) can be remarkably improved.

C-3-4 organic cation salt

The adhesive composition may further comprise an organic cationic salt as needed. By using a lithium salt and an organic cation salt in combination, the surface resistance value can be further reduced without exuding the lithium salt.

The organic cation salt is specifically an organic cation-anion salt. As the cations constituting the cation portion of the organic cation salt, there are typically exemplified organic onium ions in which onium ions are formed by substitution with an organic group. Examples of the onium in the organic onium include a nitrogen-containing onium, a sulfur-containing onium, and a phosphonium-containing onium. Preferred are nitrogen-containing onium and sulfur-containing onium. Examples of the nitrogen-containing onium include ammonium cation, piperidinium cation, pyrrolidinium cation, pyridinium cation, cation having pyrroline skeleton, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, and pyrazolinium cation. Ammonium cations, piperidinium cations, pyrrolidinium cations are preferred, and pyrrolidinium cations are more preferred. Examples of the sulfonium salt include sulfonium cations. Examples of the phosphonium include phosphonium cations. Examples of the organic group in the organic onium include an alkyl group, an alkoxy group, and an alkenyl group. Specific examples of the preferable organic onium include a tetraalkylammonium cation, an alkylpiperidinium cation, and an alkylpyrrolidinium cation. More preferably an ethylmethylpyrrolidinium cation. The anions constituting the anion portion of the organic cation salt are as described in the description of the anions constituting the anion portion of the lithium salt. Thus, a preferred organic cation salt that can be used in embodiments of the present invention is a pyrrolidinium salt, more preferably ethyl methyl pyrrolidinium bis (trifluoromethanesulfonyl) imide.

The content of the organic cation salt in the adhesive composition (resulting in the adhesive layer) is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 3 parts by weight, and still more preferably 0.5 to 1.5 parts by weight relative to 100 parts by weight of the base polymer. When the content of the organic cation salt is within such a range, the effect of the combination of the organic cation salt and the lithium salt becomes remarkable.

C-3-5 silane coupling agent

The adhesive composition may further comprise a silane coupling agent. By using a silane coupling agent, durability can be improved. As the silane coupling agent, a silane coupling agent having any appropriate functional group can be used. Specifically, examples of the functional group include a vinyl group, an epoxy group, an amino group, a mercapto group, a (meth) acryloyloxy group, an acetoacetyl group, an isocyanate group, a styryl group, and a polysulfide group. Specifically, examples thereof include vinyl-containing silane coupling agents such as vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, and vinyltributoxysilane; epoxy group-containing silane coupling agents such as gamma-glycidoxypropyl trimethoxysilane, gamma-glycidoxypropyl triethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, and 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane; amino silane coupling agents such as gamma-aminopropyl trimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropyl methyl dimethoxysilane, N- (2-aminoethyl) 3-aminopropyl methyl dimethoxysilane, gamma-triethoxysilyl-N- (1, 3-dimethylbutylidene) propylamine, and N-phenyl-gamma-aminopropyl trimethoxysilane; mercapto silane coupling agents such as gamma-mercaptopropyl methyl dimethoxy silane; styrene-containing silane coupling agents such as p-styrene trimethoxysilane; (meth) acrylic acid group-containing silane coupling agents such as gamma-acryloxypropyl trimethoxysilane and gamma-methacryloxypropyl triethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatopropyl triethoxysilane; polysulfide-based silane coupling agents such as bis (triethoxysilylpropyl) tetrasulfide.

C-3-6. Others

The adhesive composition (and consequently the adhesive layer) may also contain any suitable additives. Specific examples of the additives include crosslinking agents, silane coupling agents, reprocessing improvers, antioxidants, antistatic agents, crosslinking retarders, emulsifiers, colorants, powders such as pigments, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, light stabilizers, ultraviolet absorbers, polymerization inhibitors, inorganic fillers, organic fillers, metal powders, particulates, and foils. The amount, kind, amount, combination, etc. of the additives may be appropriately set according to the purpose.

As a method for forming the adhesive layer, any suitable method may be employed. Typical examples of the formation method include: a method of applying the adhesive composition to a separator or the like subjected to a peeling treatment, drying and removing a polymerization solvent or the like to form an adhesive layer, and transferring the adhesive layer to a polarizing material; alternatively, the adhesive composition is applied to a polarizer, and a polymerization solvent or the like is dried and removed to form an adhesive layer on the polarizer. In the application of the adhesive, one or more solvents other than the polymerization solvent may be newly added as needed.

Details of the adhesive composition are described in, for example, japanese patent application laid-open No. 2014-48497. The disclosure of this publication is incorporated by reference into this specification.

Examples

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows.

Example 1

As the thermoplastic resin base material, an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75℃was used. A single side of the substrate was corona treated and coated with a coating of 9:1 (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification degree 4.6%, saponification degree 99.0 mol% or more, trade name "gossfimer Z200" manufactured by japan chemical industries, ltd.) were dried to form a PVA-based resin layer having a thickness of 11 μm, and a laminate was produced.

The obtained laminate was subjected to 4.5-fold air stretching (stretching treatment) at 140℃in a direction perpendicular to the longitudinal direction of the laminate using a tenter.

Subsequently, the laminate was immersed in a dyeing bath (aqueous solution having an iodine concentration of 1.4 wt% and a potassium iodide concentration of 9.8 wt%) at a liquid temperature of 25℃for 12 seconds, and dyed (dyeing treatment).

Subsequently, the laminate was immersed in a washing bath (pure water) having a liquid temperature of 25℃for 6 seconds (1 st washing treatment).

Then, the resultant was immersed in a crosslinking bath (aqueous solution having a boron concentration of 1% by weight and a potassium iodide concentration of 1% by weight) at a liquid temperature of 60℃for 16 seconds (crosslinking treatment).

Subsequently, the laminate was immersed in a washing bath (aqueous solution having a potassium iodide concentration of 1 wt%) at a liquid temperature of 25℃for 3 seconds (washing treatment 2).

Subsequently, the laminate was dried in an oven at 60 ℃ for 21 seconds (1 st drying treatment).

Next, a treatment liquid (treatment liquid prepared by adding 0.15 parts by weight of citric acid and 0.01 parts by weight of lithium hydroxide to 50 parts by weight of water, stirring for 10 minutes, measuring pH, and then adding 50 parts by weight of ethanol, ph=2.9) was applied to the PVA-based resin layer of the laminate by a bar coater so that the film thickness became 7 μm (wet state).

Finally, the laminate was dried in an oven at 60℃for 60 seconds to obtain a laminate having a PVA-based resin layer (polarizing element) with a thickness of 1.2. Mu.m.

Example 2

A laminate having a polarizing plate was obtained in the same manner as in example 1, except that the treatment liquid (ph=4.2) obtained in the same manner as in example 1 was used as the treatment liquid except that the addition amount of lithium hydroxide was 0.04 parts by weight.

Example 3

A laminate having a polarizing plate was obtained in the same manner as in example 1, except that the treatment liquid (ph=5.8) obtained in the same manner as in example 1 was used as the treatment liquid except that the addition amount of lithium hydroxide was 0.08 parts by weight.

Comparative example 1

A laminate having a polarizing plate was obtained in the same manner as in example 1, except that the treatment liquid (ph=2.0) obtained in the same manner as in example 1 was used as the treatment liquid without adding lithium hydroxide.

Comparative example 2

A laminate having a polarizing plate was obtained in the same manner as in example 1, except that the treatment liquid (ph=13.0) obtained in the same manner as in example 1 was used, except that citric acid was not added and the amount of lithium hydroxide added was 0.2 parts by weight.

Comparative example 3

A laminate having a polarizing plate was obtained in the same manner as in example 1, except that the treatment liquid (ph=11.0) obtained in the same manner as in example 1 was used as the treatment liquid except that the addition amount of lithium hydroxide was 0.2 parts by weight.

The adhesive composition obtained by the following method was uniformly applied to the surface of a polyethylene terephthalate film (separator) treated with a silicone-based release agent by a spray coater (fountain coater), and dried in an air-circulating type constant temperature oven at 155℃for 2 minutes, to form an adhesive layer having a thickness of 20. Mu.m. Next, the adhesive layer was transferred onto the surface of the polarizing plate of the laminate obtained in each of examples and comparative examples, to obtain a polarizing plate with an adhesive layer. The following evaluation was performed using the obtained polarizing plate with an adhesive layer. The results are shown in Table 1.

(preparation of base Polymer of adhesive composition)

Into a 4-neck flask equipped with a stirring blade, a thermometer, a nitrogen inlet pipe, and a condenser, a monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate was charged. Further, 0.1 part of 2,2' -azobisisobutyronitrile as a polymerization initiator was charged together with ethyl acetate to 100 parts of the above-mentioned monomer mixture (solid content), nitrogen was introduced while stirring slowly to replace nitrogen, and then the liquid temperature in the flask was kept at around 60℃to carry out polymerization for 7 hours. Thereafter, ethyl acetate was added to the obtained reaction solution to adjust the solid content to 30%. Thus, a solution of the acrylic polymer (A-1) (base polymer) having a weight average molecular weight of 140 ten thousand was prepared.

(preparation of adhesive composition)

1.0 part of lithium bis (trifluoromethanesulfonyl) imide (Mitsubishi Materials Electronic Chemicals Co., ltd.) and 0.7 part of ethyl methyl pyrrolidinium bis (trifluoromethanesulfonyl) imide (Tokyo chemical Co., ltd.) as a conductive agent, 0.095 part of trimethylolpropane xylylene diisocyanate (TAKENATE D N, sanjing chemical Co., ltd.) and 0.3 part of dibenzoyl peroxide as a crosslinking agent, 0.2 part of organosilane (A100, sanko chemical Co., ltd.: X41-1810) and 0.2 part of thiol-containing silane coupling agent (SILYL SAT10, manufactured by BASF corporation, irganox 1010) as a crosslinking agent, 0.03 part of a reworking improver (Kaneka Corporation, SILYL SAT 10) and 0.3 part of an antioxidant (BASF corporation, irganox 1010) were blended with 100 parts of the solid content of the solution of the acrylic polymer (A-1) to prepare an adhesive composition (solution).

(1) Reliability test of heating

The polarizing plates with the adhesive layers obtained in examples and comparative examples were bonded to alkali-free glass having a thickness of 1.3mm, and the monomer transmittance (Ts) of the thin polarizing film was measured using an ultraviolet-visible spectrophotometer (product name "V7100" manufactured by Japanese Specification Co., ltd.) ₀ ). The sample was then placed in an oven at 85 ℃ for 500 hours.The monomer transmittance (Tsa) was measured using the removed sample in the same manner using an ultraviolet-visible spectrophotometer ₅₀₀ ) Δtsa is obtained by the following equation.

ΔTsa(％)＝Tsa ₅₀₀ -Ts ₀

The examples and comparative examples were evaluated according to the following criteria.

O: the absolute value of DeltaTsa is within 3.0%

Delta: absolute value of ΔTsa is within 5.0%

X: the absolute value of ΔTsa exceeds 5.0%

(2) Humidification reliability evaluation

The polarizing plates with the adhesive layers obtained in examples and comparative examples were bonded to alkali-free glass having a thickness of 1.3 mm. Then, the monomer transmittance (Ts) of the thin polarizing film was measured by using an ultraviolet-visible spectrophotometer (product name "V7100", manufactured by Japanese Specification Co., ltd.) ₀ ). Then, the sample was put into a constant temperature and humidity tank of 90% Rh at 60℃for 500 hours. The monomer transmittance (Tsb) was measured using the removed sample in the same manner using an ultraviolet-visible spectrophotometer ₅₀₀ ) Δtsb is obtained by the following equation.

ΔTsb(％)＝Tsb ₅₀₀ -Ts ₀

O: the absolute value of DeltaTsb is within 3.0%

Delta: the absolute value of DeltaTsb is within 3.5%

X: the absolute value of ΔTsb exceeds 3.5%

(3) Appearance of polarizing element

The polarizing plates with the adhesive layers obtained in examples and comparative examples were bonded to alkali-free glass having a thickness of 1.3 mm. Then, the mixture was put into a constant temperature and humidity tank at 98% RH at 20℃for 120 hours, and the appearance was evaluated. The polarizing plates before and after the loading were visually compared and evaluated according to the following criteria.

O: no change in appearance was observed

Delta: a slight change in appearance was observed, but the change in appearance was recovered when left at room temperature for 6 hours

X: the change in appearance (discoloration, unevenness) was remarkable. Even when left at room temperature for 6 hours, the change in appearance was not completely recovered

TABLE 1

As apparent from table 1, the polarizing material obtained by the manufacturing method of the example of the present invention has excellent reliability of heating and humidifying even when the polarizing plate with the adhesive layer having the adhesive layer containing the conductive agent is manufactured. Further, the appearance was excellent even after being left under a humidified environment.

Industrial applicability

The method of the present invention can easily and inexpensively manufacture a polarizing element in which discoloration under a high-temperature environment is suppressed. The polarizing material obtained by the manufacturing method of the present invention can be widely used in liquid crystal panels of liquid crystal televisions, liquid crystal displays, cellular phones, digital cameras, video cameras, portable game machines, car navigation, copiers, printers, facsimile machines, watches, microwave ovens, and the like.

Claims

1. A method for producing a polarizing element, which comprises stretching and dyeing at least a polyvinyl alcohol resin film,

the manufacturing method comprises the following steps: after the dyeing, coating or spraying a treatment liquid on the polyvinyl alcohol resin film, wherein the treatment liquid comprises citric acid and lithium hydroxide,

the pH of the treatment liquid is in the range of 2.5 to 6.0, and the treatment liquid has a buffering action in the pH range.

2. The method according to claim 1, wherein the polyvinyl alcohol resin film is a polyvinyl alcohol resin layer formed by applying a coating liquid containing a polyvinyl alcohol resin to a substrate, and a laminate of the substrate and the polyvinyl alcohol resin layer is subjected to stretching and dyeing.

3. A method for manufacturing a polarizing plate with an adhesive layer, the polarizing plate with an adhesive layer comprising: a polarizer, a protective film disposed on one side of the polarizer, and an adhesive layer disposed on the other side of the polarizer,

the manufacturing method comprises the following steps:

manufacturing a polarizing element by the method of claim 1 or 2;

attaching a protective film to one side of the polarizing material obtained by the manufacturing method; the method comprises the steps of,

an adhesive layer containing a lithium salt is formed on the other side of the polarizer.