WO2020090196A1

WO2020090196A1 - Polarizing plate having adhesive layer

Info

Publication number: WO2020090196A1
Application number: PCT/JP2019/032973
Authority: WO
Inventors: 聡司三田
Original assignee: 日東電工株式会社
Priority date: 2018-11-01
Filing date: 2019-08-23
Publication date: 2020-05-07
Also published as: CN112955791A; JPWO2020090196A1; JP7126796B2; JP2022121751A; KR20210084464A; CN112955791B; TW202018341A; TWI813752B

Abstract

In order to provide a thin polarizing plate having an adhesive layer and having extremely excellent thermal resistance, this polarizing plate having an adhesive layer has: a polarizer; a protective film arranged on one side of the polarizer; and an adhesive layer including lithium salt and arranged on the other side of the polarizer. The lithium content (LiPOL) in the polarizer is at least 0.3% by mass and the lithium content (LiPSA) in the adhesive layer is at least 0.0035% by mass.

Description

Polarizing plate with adhesive layer

The present invention relates to a polarizing plate with an adhesive layer.

A liquid crystal display device, which is a typical image display device, has a polarizer (substantially a polarizing plate including a polarizer) arranged on both sides of a liquid crystal cell due to its image forming method. The polarizer is typically manufactured by dyeing a polyvinyl alcohol (PVA) resin film with a dichroic material such as iodine. In recent years, there is an increasing demand for thinner image display devices. Therefore, further thinning of the polarizer is also required. However, there is a problem that the thinner the polarizer is, the more the optical characteristics are likely to deteriorate in a high temperature environment.

Also, the polarizer is usually attached to another component (for example, a protective film) via an adhesive layer. Various materials may be used for the composition forming the pressure-sensitive adhesive layer (pressure-sensitive adhesive composition) in order to impart desired properties. However, there is a problem that the composition contained in the pressure-sensitive adhesive composition is impaired by the migration of the material to the polarizer, and desired characteristics cannot be maintained.

JP 2012-247574 A JP, 2017-102476, A JP, 2005-094906, A JP, 2005-094907, A

The present invention has been made to solve the above problems, its main purpose is to have a very excellent heat resistance, and a pressure-sensitive adhesive layer-attached polarizing plate with little change over time in the properties of the pressure-sensitive adhesive layer. To provide.

The pressure-sensitive adhesive layer-attached polarizing plate of the present invention comprises a polarizer, a protective film arranged on one side of the polarizer, and a pressure-sensitive adhesive layer containing a lithium salt arranged on the other side of the polarizer. Have. In this pressure-sensitive adhesive layer-attached polarizing plate, the lithium content (Li _POL ) of the polarizer is 0.3% by weight or more, and the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is 0.0035% by weight or more. Is.
In one embodiment, the ratio (Li _POL / Li _PSA ) of the lithium content (Li _POL ) of the polarizer and the lithium content (Li _PSA ) of the adhesive layer is 100 or less.
In one embodiment, the iodine content of the polarizer is 10% to 25% by weight.
In one embodiment, the polarizer contains at least one selected from the group consisting of citric acid and citrate ions.
In one embodiment, the thickness of the polarizer is 3 μm or less.

According to the present invention, it is possible to provide a polarizing plate with a pressure-sensitive adhesive layer that realizes very excellent heat resistance even if it is thin. The pressure-sensitive adhesive layer-attached polarizing plate of the present invention comprises a polarizer, a protective film arranged on one side of the polarizer, and a pressure-sensitive adhesive layer containing a lithium salt arranged on the other side of the polarizer. Including. When the lithium content (Li _POL ) of the polarizer of this polarizing plate is 0.3% by weight or more and the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is 0.0035% by weight or more, heat resistance is improved. A polarizing plate with an adhesive layer having excellent properties can be provided. Furthermore, when the polarizer and the pressure-sensitive adhesive layer contain lithium in a specific content, it is possible to reduce changes over time in the characteristics (specifically, conductivity) of the pressure-sensitive adhesive layer.

It is a schematic sectional drawing explaining the polarizing plate with a pressure sensitive adhesive layer by one embodiment of the present invention.

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

A. Outline of Polarizing Plate with Adhesive Layer FIG. 1 is a schematic cross-sectional view of a polarizing plate with an adhesive layer according to one embodiment of the present invention. The pressure-sensitive adhesive layer-attached polarizing plate 100 of the illustrated example is a pressure-sensitive adhesive layer including a polarizer 10, a protective film 20 arranged on one side of the polarizer 10, and a lithium salt arranged on the other side of the polarizer. 30 and. The adhesive layer 30 is typically the outermost layer on the image display device side. Practically, a separator (not shown) is detachably temporarily attached to the pressure-sensitive adhesive layer 30 to protect the pressure-sensitive adhesive layer until actual use and enable roll formation.

The pressure-sensitive adhesive layer-attached polarizing plate of the present invention is used in combination with a pressure-sensitive adhesive layer containing a lithium salt that functions as a conductive agent, and a polarizer having a lithium content (Li _POL ) of 0.3% by weight or more. It is considered that lithium ions contained in the pressure-sensitive adhesive layer can stabilize the iodine complex more than other cations (eg potassium ions) contained in the polarizer. Therefore, the lithium ions contained in the pressure-sensitive adhesive layer and the iodine complex in the polarizer are bonded to each other to form a more stable iodine complex, and the lithium ions in the pressure-sensitive adhesive layer and other ions contained in the polarizer ( Exchange reactions with, for example, potassium ions) can occur. By forming a more stable iodine complex, it is possible to suppress the reduction of iodine (particularly, polyiodine ions such as I ₃ ⁻ and I ₅ ⁻ ) in the polarizer under a high temperature environment. On the other hand, when lithium contained in the pressure-sensitive adhesive layer excessively shifts to the polarizer, the lithium content (Li _POL ) of the pressure-sensitive adhesive layer itself is lowered, and desired characteristics (for example, surface resistance value) are deteriorated with time. obtain. As a result, this may also result in deterioration of the characteristics of the polarizing plate with time.

The polarizer used in the present invention is treated with a treatment liquid containing lithium ions as described later. Therefore, first, it is considered that an exchange reaction between lithium ions contained in the treatment liquid and other ions (for example, potassium ions) of the polarizer occurs. Due to this exchange reaction, the polarizer itself contains lithium. Therefore, an excessive exchange reaction with lithium ions contained in the pressure-sensitive adhesive layer is suppressed, and it is possible to reduce the change over time in the characteristics (for example, conductivity) of the pressure-sensitive adhesive layer.

The lithium content (Li _POL ) of the polarizer is 0.3% by weight or more, preferably 0.35% by weight or more. When the lithium content (Li _POL ) is in the above range, an excessive exchange reaction between lithium ions contained in the pressure-sensitive adhesive layer and other ions (for example, potassium ions) of the polarizer is suppressed, and as a result, It has excellent heat resistance and can reduce the change over time in the properties of the pressure-sensitive adhesive layer. The lithium content (Li _POL ) of the polarizer is, for example, 10% by weight or less. The lithium content (Li _POL ) can be measured, for example, by ICP-MS.

The lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is 0.0035% by weight or more, preferably 0.0040% by weight or more, and more preferably 0.0050% by weight or more. When the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is within the above range, the pressure-sensitive adhesive layer can exhibit desired conductive performance. The lithium content (Li _PSA ) of the pressure-sensitive adhesive layer can be measured by ICP-MS.

The pressure-sensitive adhesive layer-attached polarizing plate of the present invention has a ratio (Li _POL / Li _PSA ) between the lithium content (Li _POL ) of the polarizer and the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer, which is hereinafter referred to as “lithium content ratio”. (Also referred to as)) is preferably 100 or less, and more preferably 85 or less. Since the lithium content ratio (Li _POL / Li _PSA ) of the polarizing plate is within the above range, excellent heat resistance can be achieved even when the thickness is thin, and the characteristics of the pressure-sensitive adhesive layer can be changed with time. Can be made smaller. The lithium content ratio is, for example, 30 or more, preferably 60 or more.

Hereinafter, the polarizer, the protective film, and the pressure-sensitive adhesive layer that compose the polarizing plate with the pressure-sensitive adhesive layer will be specifically described.

B. Polarizer B-1. Configuration and Properties of Polarizer The polarizer is typically composed of a polyvinyl alcohol (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 can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% or more and less than 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. is there. The saponification degree can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizer having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on the base material. The laminate of the base material and the PVA-based resin layer can be obtained by, for example, a method of applying the coating liquid containing the PVA-based resin to the base material, a method of laminating a PVA-based resin film on the base material, or the like.

The lithium content (Li _POL ) of the polarizer is 0.3% by weight or more, preferably 0.35% by weight or more. The polarizer may include lithium during its manufacturing process. For example, the polarizer obtained by treating the PVA-based resin film with a treatment liquid containing lithium may contain lithium. When the polarizer contains lithium, it is possible to suppress changes in characteristics of the pressure-sensitive adhesive layer with time due to excessive migration of lithium contained in the pressure-sensitive adhesive layer to the polarizer. The lithium content (Li _POL ) of the polarizer is, for example, 10% by weight or less.

The iodine content of the polarizer can be appropriately set so as to achieve both sufficient polarization performance and optimum single transmittance. The iodine content is preferably 10% by weight to 25% by weight, more preferably 15% by weight to 25% by weight. According to the pressure-sensitive adhesive layer-attached polarizing plate of the present invention, even if it is a polarizing plate including a polarizer having such an extremely high iodine content, it is difficult in the past by adopting a specific pressure-sensitive adhesive layer described below. It is possible to realize the very excellent heat resistance that was present. In the present specification, the “iodine content” means the total amount of iodine contained in the polarizer (PVA-based resin film). More specifically, iodine is present in the polarizer in the form of iodine ion (I ⁻ ), iodine molecule (I ₂ ), polyiodine ion (I ₃ ⁻ , I ₅ ⁻ ), etc. The iodine content means the amount of iodine including all these forms. The iodine content can be calculated, for example, by a calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in a state of forming a PVA-iodine complex in the polarizer. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ion (PVA · I ₃ ⁻ ) has an absorption peak near 470 nm, and the complex of PVA and pentaiodide ion (PVA · I ₅ ⁻ ) is around 600 nm. Has an absorption peak at. As a result, polyiodine ions can absorb light in a wide range of visible light, depending on their morphology. On the other hand, iodine ion (I ⁻ ) has an absorption peak near 230 nm and does not substantially participate in absorption of visible light. Therefore, the polyiodine ion existing in the form of a complex with PVA may be mainly involved in the absorption performance of the polarizer.

The thickness of the polarizer is preferably 5 μm or less in one embodiment, preferably 3 μm or less in another embodiment, and preferably 2 μm or less in yet another embodiment. The thickness of the polarizer is preferably 0.5 μm or more in one embodiment, preferably 0.6 μm or more in another embodiment, and 0.8 μm in still another embodiment. Above, in another embodiment, it is preferably 1 μm or more, and in yet another embodiment, preferably 2 μm or more. According to the embodiments of the present invention, it is possible to achieve desired single transmittance and degree of polarization even with a thin polarizer.

The single transmittance (Ts) of the polarizer 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 further preferably 99.98% or more. By setting the single transmittance to be low and the polarization degree to be high, the contrast can be increased and the black display can be displayed more black. Therefore, an image display device with excellent image quality can be realized. The single transmittance is a value measured by a spectrophotometer with an integrating sphere. The single transmittance is a Y value measured by a JIS Z 8701 2 degree visual field (C light source) and subjected to luminosity correction. For example, an ultraviolet-visible spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, product name : V7100).

In the pressure-sensitive adhesive layer-attached polarizing plate of the present invention, although the iodine content of the polarizer is extremely high as described above, changes in optical properties under a high temperature environment can be significantly suppressed. Further, the hue change under the high temperature environment is also suppressed. As described above, such an excellent effect can be realized by using a pressure-sensitive adhesive layer containing a lithium salt functioning as a conductive agent in combination with the above-mentioned polarizer.

The polarizer may preferably contain citric acid and / or citrate ions. The polarizer may more preferably include citrate ions. This is due to the treatment (B-2-2) with the treatment liquid in the production method (B) described later. When the polarizer contains such a compound (in other words, by manufacturing the polarizer by the manufacturing method including the treatment described in the paragraph B-2-2), the discoloration of the polarizer in a high temperature environment becomes remarkable. Can be suppressed to. This can suppress the generation of protons in the PVA-based resin by the buffering action of the treatment liquid in a predetermined pH region, and as a result, the generation of a large number of double bonds (polyene) in the PVA-based resin under a high temperature environment. It is considered that this is because it is possible to suppress discoloration and suppress discoloration. Furthermore, cracking and warping can be suppressed by suppressing polyene formation. This is considered as follows: When a double bond is formed in the PVA-based resin molecule by polyene formation, the distance between the monomer units near the double bond becomes small. As a result, PVA-based resin molecules (chains) may partially contract, and such partial contraction may cause warpage or cracks. By suppressing polyene formation, formation of such double bonds is suppressed, and as a result, warpage and cracks can be suppressed.

B-2. Method for manufacturing polarizer B-2-1. Outline of Manufacturing Method A polarizer can be manufactured by a manufacturing method including at least stretching and dyeing a PVA-based 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 washing step, and a drying step. The steps of providing the PVA-based resin film can be performed in any suitable order and timing. Therefore, the steps may be performed in the above order or may be performed in a different order from the above. You may perform one process several times as needed. Furthermore, steps other than the above (eg, insolubilization step) may be performed at any appropriate timing, and steps other than the dyeing step may be omitted. When the PVA-based resin film is the PVA-based resin layer formed on the base material, the laminate of the base material and the PVA-based resin layer is subjected to the above steps.

As described above, the polarizer of the polarizing plate of the present invention contains lithium. Therefore, it is preferable that the method for manufacturing the polarizer includes a treatment step with a treatment liquid containing lithium. As the treatment liquid containing lithium, specifically, a treatment liquid containing lithium iodide and / or lithium hydroxide in water or an appropriate solvent other than water is used. The polarizer may contain lithium by undergoing a treatment process with a treatment liquid containing lithium. The treatment process with the treatment liquid can be performed at any appropriate timing after the above-mentioned staining.

Each step will be described below, but as described above, each step can be performed in any appropriate order and is not limited to the order described.

B-2-2. Treatment with Treatment Liquid As described above, the method for producing the polarizer used in the present invention includes treating the PVA-based resin film with a treatment liquid containing lithium after dyeing. The treatment with the treatment liquid may be performed at any appropriate timing after dyeing. Specifically, the treatment with the treatment liquid may be performed before or after the crosslinking step, or may be performed before or after the washing step. When the stretching step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the stretching step. When the swelling step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the swelling step. When the insolubilization step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the insolubilization step. Typically, the treatment with the treatment liquid can be performed after the washing step and before the drying step, or between the first drying step and the second drying step when the drying step is performed in two steps.

The pH of the treatment liquid is preferably 2.5 to 6.0, more preferably 3.0 to 5.7, and further preferably 3.5 to 4.8. Furthermore, the treatment liquid preferably has a buffering action in the pH range (that is, in the pH range of 2.5 to 6.0). Such a treatment liquid may be, for example, an aqueous solution containing sodium hydrogen carbonate, potassium hydrogen carbonate, disodium hydrogen phosphate, potassium carbonate, sodium carbonate, and citric acid. The treatment liquid containing these compounds has a buffering action in a high pH region as compared with the treatment liquid containing an acetic acid compound, and as a result, it may have a better discoloration preventing effect in a high temperature environment. The aqueous solution may contain these compounds individually and may contain 2 or more types. The treatment liquid is preferably an aqueous solution of citric acid. Therefore, the polarizer used in the present invention may include citrate and / or citrate ions. The concentration of the aqueous solution can be set appropriately depending on the desired pH and buffering effect. For example, the concentration of the aqueous citric acid solution may preferably be 0.10% by weight to 3.0% by weight. Further, the aqueous solution preferably contains a pH adjuster. Examples of the pH adjuster include lithium hydroxide. By using the treatment liquid containing lithium hydroxide as the pH adjuster, the obtained polarizer may contain lithium.

The treatment with the treatment liquid typically includes contacting the treatment liquid with a PVA-based resin film. The contact method includes any appropriate method. Specific examples include immersion of the PVA-based resin film in the treatment liquid and application or spraying of the treatment liquid on the PVA-based resin film. Application or spraying of the treatment liquid is preferred. This is because it is possible to prevent a defect that the absorption spectrum of the polarizer changes before and after the immersion, and as a result, it is possible to more favorably prevent polyeneization of PVA. Any appropriate method (means) can be adopted as a method (means) for applying or spraying the treatment liquid onto the PVA-based resin film. Examples of the coating means include a reverse coater, a gravure coater (direct, reverse or offset), a bar reverse coater, a roll coater, a die coater, a bar coater, and a rod coater. As the spraying means, any suitable spraying device (for example, a pressure nozzle type, a rotating disk type) can be mentioned.

B-2-3. Stretching Step In the stretching step, the PVA-based resin film is typically uniaxially or biaxially stretched 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. Further, the PVA-based resin film may be stretched when performing the crosslinking step, the swelling step, the dyeing step, and the like. The stretching direction may correspond to the absorption axis direction of the obtained polarizer.

B-2-4. Swelling step The swelling step is usually performed before the dyeing step. The swelling step is performed, for example, by immersing the PVA-based resin film in a swelling bath. As the swelling bath, water such as distilled water or pure water is usually used. The swelling bath may include any suitable other component than water. Other components include solvents such as alcohols, additives such as surfactants, iodides and the like. 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. Etc. Preferably potassium iodide is used. The temperature of the swelling bath is, for example, 20 ° C to 45 ° C. The immersion time is, for example, 10 seconds to 300 seconds.

B-2-5. Dyeing step The dyeing step is a step of dyeing the PVA-based resin film with a dichroic material. It is preferably carried out by adsorbing a dichroic substance. Examples of the adsorption method include a method of immersing a PVA-based resin film in a dyeing solution containing a dichroic substance, a method of applying the dyeing solution to the PVA-based resin film, and a spraying of the dyeing solution onto the PVA-based resin film. And the like. The preferred method is to immerse the PVA resin film in the dyeing solution. This is because the dichroic substance can be favorably adsorbed.

Examples of the above dichroic substances include iodine and dichroic dyes. Preferred is iodine. When iodine is used as the dichroic substance, an iodine aqueous solution is preferably used as the dyeing solution. The iodine content of the aqueous iodine solution is preferably 0.04 to 5.0 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Potassium iodide is preferably used as the iodide. The iodide content is preferably 0.3 to 15 parts by weight with respect to 100 parts by weight of water.

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

B-2-6. Crosslinking Step In the crosslinking step, a boron compound is usually 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 a boric acid aqueous solution is used, the boric acid concentration of the boric acid aqueous solution is, for example, 1% by weight to 15% by weight, preferably 1% by weight to 10% by weight. The boric acid aqueous solution may further contain an iodide such as potassium iodide and a zinc compound such as zinc sulfate and zinc chloride.

The cross-linking step can be performed by any appropriate method. For example, a method of immersing a PVA-based resin film in an aqueous solution containing a boron compound, a method of applying an aqueous solution containing a boron compound to a PVA-based resin film, or a method of spraying an aqueous solution containing a boron compound onto a PVA-based resin film is mentioned. Be done. Immersion in an aqueous solution containing a boron compound is preferred.

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

B-2-7. Washing Step The washing step can be typically performed after the crosslinking step. The cleaning step is typically performed by immersing the PVA-based resin film in a cleaning liquid. Pure water is a typical example of the cleaning liquid. You may add potassium iodide to pure water.

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

B-2-8. Drying Step The drying step can be performed by any appropriate method. Examples of the drying method include natural drying, blast drying, reduced pressure drying, and heat drying. Heat drying is preferably used. When heat drying is performed, the heating temperature is, for example, 30 ° C. to 100 ° C. The drying time is, for example, 20 seconds to 10 minutes.

C. Protective film Any suitable resin film is used as the protective film (and another protective film when present). Examples of the material for forming the resin film include (meth) acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, and polyethylene terephthalate resins. And the like, ester-based resins, polyamide-based resins, polycarbonate-based resins, copolymer resins thereof, and the like. The “(meth) acrylic resin” means an acrylic resin and / or a methacrylic resin.

In one embodiment, a (meth) acrylic resin having a glutarimide structure is used as the (meth) acrylic resin. The (meth) acrylic resin having a glutarimide structure (hereinafter, also referred to as glutarimide resin) is disclosed in, for example, JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, and JP-A-2006-328329. No. 2006-328334, No. 2006-337491, No. 2006-337492, No. 2006-337493, No. 2006-337569, No. 2007-009182, No. 2009- It is described in Japanese Patent Application No. 161744 and Japanese Patent Application Laid-Open No. 2010-284840. These descriptions are incorporated herein by reference.

When a polarizer is manufactured using a laminate of a base material and a PVA-based resin layer, the base material may be directly used as a protective film without being peeled off. Alternatively, the base material may be peeled off and the polarizer may be attached to the protective film.

Depending on the purpose, any suitable optical functional film may be used as the protective film (and another protective film if present). Examples of the optical functional film include a retardation film and a reflective polarizer (brightness improving film).

D. Adhesive Layer A polarizing plate with an adhesive layer according to an embodiment of the present invention typically has a protective film disposed on one side of the polarizer and an adhesive layer disposed on the other side of the polarizer, as described above. Has been done. That is, in this embodiment, the pressure-sensitive adhesive layer is directly arranged on the polarizer without disposing the protective film on the other side of the polarizer.

As described above, the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is 0.0035% by weight or more, preferably 0.0040% by weight or more, and more preferably 0.0050% by weight or more. When the lithium content (Li _PSA ) of the pressure-sensitive adhesive layer is within the above range, the pressure-sensitive adhesive layer can exhibit desired conductive performance.

D-1. Pressure-sensitive adhesive composition The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer contains a base polymer and a lithium salt.

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

The base polymer may include monomer units derived from any appropriate copolymerization component depending on the purpose. Examples of the copolymerization component include a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, an (N-substituted) amide monomer, and a (meth) acryl. Acid alkylaminoalkyl-based monomer, (meth) acrylic acid alkoxyalkyl-based monomer, succinimide-based monomer, maleimide-based monomer, itaconimide-based monomer, vinyl-based monomer, cyano (meth) acrylate-based monomer, epoxy group-containing (meth) acrylic-based monomer , Glycol (meth) acrylic ester monomers, silane monomers, and polyfunctional monomers. By adjusting the type, number, combination, and copolymerization ratio (weight ratio) of the copolymerization components, a base polymer (finally, pressure-sensitive adhesive layer) having desired properties can be obtained. The proportion of the copolymerization component in all the monomer components is preferably 0% to 20% by weight, more preferably 0.1% to 15% by weight, further preferably 0.1% by weight, based on 100% by weight of the total monomer components. % To 10% by weight.

The weight average molecular weight of the base polymer is typically 500,000 to 3,000,000, preferably 700,000 to 270,000, and more preferably 800,000 to 2,500,000. If the weight average molecular weight is too small, the heat resistance may be insufficient. If the weight average molecular weight is too large, the handleability may deteriorate. In addition, a large amount of diluting solvent is required for viscosity adjustment for coating, which may increase the cost. The weight average molecular weight is a value measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene.

D-1-2. Lithium Salt The pressure-sensitive adhesive layer contains a lithium salt (lithium-anion salt). As mentioned above, the lithium salt can function as a conductive agent. Examples of anions constituting the anion part 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 the following general formula (1 ) ~ (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 from 1 to 10),
(4): (C _p F _{2p + 1} SO ₂ ) N ⁻ (C _q F _{2q + 1} SO ₂ ), (p and q are integers from 1 to 10),
An anion represented by Fluorine-containing anions are preferable, and fluorine-containing imide anions are more preferable.

Examples of the fluorine-containing imide anion include imide anions having a perfluoroalkyl group. Specific examples thereof include the above (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , and general formulas (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),
(4): (C _p F _{2p + 1} SO ₂ ) N ⁻ (C _q F _{2q + 1} SO ₂ ), (p and q are integers from 1 to 10),
An anion represented by Preferred are (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{−, and} other (perfluoroalkylsulfonyl) imides represented by general formula (1), and more preferred are (CF ₃ SO ₂₎ ₂ N ^- bis represented by (trifluoromethanesulfonyl) imide. Therefore, 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 pressure-sensitive adhesive composition (as a result, the pressure-sensitive adhesive layer) is preferably 0.01 to 5 parts by weight, more preferably 0.5 parts by weight, based on 100 parts by weight of the base polymer. To 3 parts by weight, more preferably 0.7 to 1.5 parts by weight. When the content of the lithium salt is in such a range, the heat resistance of the thin polarizer having a high iodine content (as a result, the polarizing plate including such a polarizer) can be significantly improved.

D-1-3. Organic Cationic Salt The pressure-sensitive adhesive composition may further contain an organic cationic salt, if necessary. By using the lithium salt and the organic cation salt in combination, the surface resistance value can be further reduced without causing the lithium salt to bleed out.

The organic cation salt is specifically an organic cation-anion salt. As the cation constituting the cation portion of the organic cation salt, typically, an organic onium having an onium ion formed by substitution with an organic group can be mentioned. Examples of onium in the organic onium include nitrogen-containing onium, sulfur-containing onium, and phosphorus-containing onium. Of these, nitrogen-containing onium and sulfur-containing onium are preferred. As the nitrogen-containing onium, an ammonium cation, a piperidinium cation, a pyrrolidinium cation, a pyridinium cation, a cation having a pyrroline skeleton, a cation having a pyrrole skeleton, an imidazolium cation, a tetrahydropyrimidinium cation, a dihydropyrimidinium cation, Examples thereof include a pyrazolium cation and a pyrazolinium cation. Of these, an ammonium cation, a piperidinium cation and a pyrrolidinium cation are preferable, and a pyrrolidinium cation is more preferable. Examples of the sulfur-containing onium include a sulfonium cation. Examples of the phosphorus-containing onium include a phosphonium cation. Examples of the organic group in the organic onium include an alkyl group, an alkoxyl group, and an alkenyl group. Specific examples of preferable organic onium include a tetraalkylammonium cation, an alkylpiperidinium cation, and an alkylpyrrolidinium cation. More preferably, it is an ethylmethylpyrrolidinium cation. The anion forming the anion part of the organic cation salt is as described for the anion forming the anion part of the lithium salt. Thus, the preferred organic cation salt that can be used in the embodiments of the present invention is a pyrrolidinium salt, more preferably ethylmethylpyrrolidinium bis (trifluoromethanesulfonyl) imide.

The content of the organic cation salt in the pressure-sensitive adhesive composition (as a result, the pressure-sensitive adhesive layer) is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.3 part by weight, relative to 100 parts by weight of the base polymer. Parts to 3 parts by weight, more preferably 0.5 to 1.5 parts by weight. When the content of the organic cation salt is in such a range, the effect of the combination of the above organic cation salt and the lithium salt becomes remarkable.

D-1-4. Silane Coupling Agent The pressure-sensitive adhesive composition may further contain a silane coupling agent. The durability can be improved by using the silane coupling agent. As the silane coupling agent, one having any appropriate functional group can be used. Specific examples of the functional group include a vinyl group, an epoxy group, an amino group, a mercapto group, a (meth) acryloxy group, an acetoacetyl group, an isocyanate group, a styryl group, and a polysulfide group. Specifically, for example, vinyl group-containing silane coupling agents such as vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, and vinyltributoxysilane; γ-glycidoxypropyltrimethoxysilane, γ-glycine Epoxy group-containing silane coupling agents such as cidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane; γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, γ-triethoxysilyl-N- (1,3-dimethylbutylidene) Propylamine, N-phenyl-γ Amino group-containing silane coupling agents such as aminopropyltrimethoxysilane; γ-mercaptopropylmethyldimethoxysilane and other mercapto group-containing silane coupling agents; styryl group-containing silane coupling agents such as p-styryltrimethoxysilane; γ- (Meth) acrylic group-containing silane coupling agents such as acryloxypropyltrimethoxysilane and γ-methacryloxypropyltriethoxylane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane; bis (triethoxysilyl) Examples thereof include polysulfide group-containing silane coupling agents such as propyl) tetrasulfide.

D-1-5. Others The pressure-sensitive adhesive composition (as a result, the pressure-sensitive adhesive layer) may further contain any appropriate additive. Specific examples of additives include cross-linking agents, silane coupling agents, rework improving agents, antioxidants, antistatic agents, cross-linking retarders, emulsifiers, colorants, powders such as pigments, dyes, surfactants, plasticizers. Agents, tackifiers, surface lubricants, leveling agents, softeners, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, inorganic fillers, organic fillers, metal powders, particles, foils Is mentioned. The number, type, amount and combination of additives can be appropriately set according to the purpose.

Any appropriate method can be adopted as a method for forming the adhesive layer. As a typical example of the forming method, the pressure-sensitive adhesive composition is applied to a release-treated separator or the like, and a method of transferring to a polarizer after forming a pressure-sensitive adhesive layer by drying and removing a polymerization solvent, or a polarizer A method of applying the above-mentioned pressure-sensitive adhesive composition and drying and removing a polymerization solvent and the like to form a pressure-sensitive adhesive layer on the polarizer is mentioned. When applying the pressure-sensitive adhesive, one or more solvents other than the polymerization solvent may be newly added, if necessary.

Details of the pressure-sensitive adhesive composition are described in, for example, JP-A-2014-48497. The description of the publication is incorporated herein by reference.

D-2. Structure and Properties of Adhesive Layer The thickness of the adhesive layer is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm. When the thickness of the pressure-sensitive adhesive layer is in such a range, the effect of improving the heat resistance by the lithium salt can be remarkable.

The surface resistance value (initial) of the pressure-sensitive adhesive layer is preferably 1.0 × 10 ¹¹ Ω · □ or less, more preferably 8.0 × 10 ¹⁰ Ω · □ or less, and further preferably 5.0 ×. It is 10 ¹⁰ Ω · □ or less. The surface resistance value of the adhesive layer may be, for example, 5.0 × 10 ⁹ Ω · □ or more. When the surface resistance value of the pressure-sensitive adhesive layer is in such a range, there is an advantage that it is easy to suppress static electricity unevenness.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measuring method of each characteristic is as follows. In the examples, “parts” and “%” are based on weight unless otherwise specified.

(1) Iodine Content Regarding the polarizers of the pressure-sensitive adhesive layer-attached polarizing plates obtained in Examples and Comparative Examples, a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, trade name “ZSX-PRIMUS II”, measurement diameter: ψ20 mm) Was used to measure the fluorescent X-ray intensity (kcps). On the other hand, the thickness (μm) of the polarizer was measured using a spectroscopic film thickness meter (trade name “MCPD-3000” manufactured by Otsuka Electronics Co., Ltd.). The iodine content (% by weight) was determined from the obtained fluorescent X-ray intensity and thickness using the following formula.
(Iodine content) = 20.5 × (fluorescent X-ray intensity) / (polarizer thickness)
The coefficient for calculating the iodine content varies depending on the measuring device, but the coefficient can be obtained using an appropriate calibration curve.

(2) Lithium Content The separator was peeled off from the pressure-sensitive adhesive layer-attached polarizing plates obtained in Examples and Comparative Examples, and 20 mg of a sample was sampled and weighed in a Teflon (registered trademark) container. Next, an acid was added and the mixture was sealed, and microwaves were irradiated using a collective microwave irradiation system (manufactured by CEM, product name: MARS5), and acid decomposition under pressure was performed at a maximum of 220 ° C. After acid decomposition, ultrapure water was added to adjust the volume to 25 mL, and the mixture was appropriately diluted, and Li quantitative analysis by ICP-MS was performed using ELAN DRC II (manufactured by PerkinElmer). The measurement conditions are as follows.
Nebulizer: Teflon (registered trademark) coaxial nebulizer m / z: Li (7)
DRC mode: OFF
Separately, a polarizing plate with a pressure-sensitive adhesive layer from which the pressure-sensitive adhesive composition was removed was prepared and measured in the same manner as above to obtain the lithium content in the polarizer. The lithium content of the pressure-sensitive adhesive layer was calculated by subtracting the lithium content of the polarizer from the lithium content of the polarizing plate with the pressure-sensitive adhesive layer (the following formula).
(Lithium content of pressure-sensitive adhesive layer) = (Lithium content of polarizing plate with pressure-sensitive adhesive layer)-(Lithium content of polarizer)

(3) Surface Resistance The polarizing plates with pressure-sensitive adhesive layers obtained in Examples and Comparative Examples were left for 30 days or more in an environment of 23 ° C. and 55% RH. After that, the separator film was peeled off, and the surface resistance value (Ω · □) of the pressure-sensitive adhesive surface was measured using a resistivity meter (Mitsubishi Chemical Analytech, product name: Hiresta-UP MCP-HT450).

(4) Heating reliability The separator was peeled off from the pressure-sensitive adhesive layer-attached polarizing plate obtained in each of the examples and comparative examples, and laminated on a non-alkali glass having a thickness of 1.3 mm. After that, it was placed in an oven at 105 ° C. for 60 hours, and the heating reliability was evaluated. The polarizing plates before and after the addition were visually compared to confirm the presence or absence of red color change of the polarizing plate due to occurrence of polyene.

[Example 1]
(Preparation of Base Polymer for Adhesive Composition)
A monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate was charged into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas introduction tube, and a condenser. Further, to 100 parts of the above monomer mixture (solid content), 0.1 part of 2,2′-azobisisobutyronitrile as a polymerization initiator was charged together with ethyl acetate, and nitrogen gas was introduced while gently stirring. After purging with nitrogen, the liquid temperature in the flask was kept at around 60 ° C. to carry out a polymerization reaction for 7 hours. Then, ethyl acetate was added to the obtained reaction solution to adjust the solid content concentration to 30%. Thus, a solution of the acrylic polymer (A-1) (base polymer) having a weight average molecular weight of 1.4 million was prepared.

(Preparation of adhesive composition)
With respect to 100 parts of the solid content of the acrylic polymer (A-1) solution, 1.0 part of lithium bis (trifluoromethanesulfonyl) imide (manufactured by Mitsubishi Materials Electronics Co., Ltd.) as a conductive agent and ethylmethylpyrrolidinium bis ( 0.7 parts of trifluoromethanesulfonyl) imide (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.095 parts of trimethylolpropane xylylene diisocyanate (manufactured by Mitsui Chemicals: Takenate D110N) as a cross-linking agent, and 0.3 parts of dibenzoyl peroxide, silane cup As a ring agent, 0.2 parts of organosilane (A100, manufactured by Soken Chemical Industry Co., Ltd.) and 0.2 part of a silane coupling agent containing a thiol group (X41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.), a rework improving agent (Kaneka Corporation, Cyryl) SAT10) 0.03 part, and antioxidant (BASF Ltd., Irganox1010) 0.3 parts by blending, pressure-sensitive adhesive composition (solution) was prepared.

(Production of polarizing plate)
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 ° C. was used as a thermoplastic resin substrate. One side of the base material is subjected to corona treatment, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl modification degree 4.6) are applied to the corona-treated surface. %, Saponification degree 99.0 mol% or more, Nippon Gohsei Kagaku Kogyo Co., Ltd., trade name “Gosephimmer Z200”) at a ratio of 9: 1 was applied and dried at 25 ° C. to a thickness of 11 μm. A PVA-based resin layer was formed to produce a laminate.
The obtained laminate was stretched in the air in a direction orthogonal to the longitudinal direction of the laminate at 140 ° C. by a factor of 4.5 using a tenter stretching machine (stretching treatment).
Then, the laminate was immersed in a dyeing bath having a liquid temperature of 25 ° C. (an aqueous solution having an iodine concentration of 1.4% by weight and a potassium iodide concentration of 9.8% by weight) for 12 seconds for dyeing (dyeing treatment).
Next, the laminate was immersed in a cleaning bath (pure water) having a liquid temperature of 25 ° C. for 6 seconds (first cleaning treatment).
Then, it was immersed for 16 seconds 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 ° C. (crosslinking treatment).
Next, the laminated body was immersed in a cleaning bath having a liquid temperature of 25 ° C. (aqueous solution having a potassium iodide concentration of 1% by weight) for 3 seconds (second cleaning treatment).
Then, the laminate was dried in an oven at 60 ° C. for 21 seconds (drying treatment).
Next, a treatment liquid (0.15 parts by weight of citric acid and 0.04 parts by weight of lithium hydroxide was added to 50 parts by weight of water) was added to the PVA-based resin layer of the laminate using a bar coater and stirred for 10 minutes. After that, the pH was measured, and then, 50 parts by weight of ethanol was added to prepare the solution, and pH = 4.2) was applied so that the film thickness in the wet state was 8 μm.
Finally, the laminate was dried in an oven at 60 ° C. for 60 seconds to obtain a laminate (polarizing plate) having a PVA-based resin layer (polarizer) having a thickness of 1.2 μm. In the obtained polarizing plate, the iodine content of the polarizer was 20.9% by weight, and the single transmittance was 40.3%.

(Preparation of polarizing plate with adhesive layer)
The pressure-sensitive adhesive composition is uniformly applied to the surface of a polyethylene terephthalate film (separator) treated with a silicone-based release agent with a fountain coater, and dried for 2 minutes in a constant temperature air-circulation oven at 155 ° C. to form a separator surface. An adhesive layer having a thickness of 20 μm was formed. Next, this pressure-sensitive adhesive layer was transferred onto the surface of the polarizer of the above polarizing plate to obtain a polarizing plate with a pressure-sensitive adhesive layer.

The obtained polarizing plate with the pressure-sensitive adhesive layer was subjected to the above evaluations (3) to (4). The results are shown in Table 1.

[Example 2]
A polarizing plate with a pressure-sensitive adhesive layer was obtained in the same manner as in Example 1 except that the treatment liquid was applied so that the film thickness in the wet state was 5 μm. The obtained polarizing plate with an adhesive layer was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
A polarizing plate with a pressure-sensitive adhesive layer was obtained in the same manner as in Example 1 except that the treatment liquid was not applied. The obtained polarizing plate with an adhesive layer was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

(Comparative example 2)
Examples except that a treatment liquid whose pH was adjusted by using sodium hydroxide in place of lithium hydroxide was used as the treatment liquid, and the treatment liquid was applied so that the film thickness in the wet state was 7 μm. A polarizing plate with a pressure-sensitive adhesive layer was obtained in the same manner as in 1. The obtained polarizing plate with an adhesive layer was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

As is apparent from Table 1, the pressure-sensitive adhesive layer-attached polarizing plates of the examples of the present invention were suppressed in the increase in the surface resistance value of the pressure-sensitive adhesive layer and had excellent humidification reliability.

The polarizing plate with an adhesive layer of the present invention is widely used for liquid crystal panels such as liquid crystal televisions, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigations, copiers, printers, fax machines, watches and microwave ovens. Can be applied.

10 Polarizer 20 Protective Film 30 Adhesive Layer 100 Polarizing Plate with Adhesive Layer

Claims

A polarizer, a protective film arranged on one side of the polarizer, and a pressure-sensitive adhesive layer containing a lithium salt arranged on the other side of the polarizer,
Polarization with pressure-sensitive adhesive layer, wherein the lithium content (Li POL ) of the polarizer is 0.3% by weight or more, and the lithium content (Li PSA ) of the pressure-sensitive adhesive layer is 0.0035% by weight or more. Board.
The pressure-sensitive adhesive layer according to claim 1, wherein a ratio (Li POL / Li PSA ) between the lithium content (Li POL ) of the polarizer and the lithium content (Li PSA ) of the pressure-sensitive adhesive layer is 100 or less. Polarizer.
The pressure-sensitive adhesive layer-attached polarizing plate according to claim 1 or 2, wherein the iodine content of the polarizer is 10% by weight to 25% by weight.
The pressure-sensitive adhesive layer-attached polarizing plate according to any one of claims 1 to 3, wherein the polarizer contains at least one selected from the group consisting of citric acid and citrate ions.
The pressure-sensitive adhesive layer-attached polarizing plate according to claim 1, wherein the thickness of the polarizer is 3 μm or less.