JPWO2020090197A1 - Polarizer manufacturing method - Google Patents

Abstract

To provide a method capable of easily and inexpensively producing a polarizer having excellent reliability in a high temperature environment. The method for producing a polarizer of the present invention includes at least stretching and dyeing a polyvinyl alcohol-based resin film, and after the dyeing, a treatment containing citric acid and lithium hydroxide in the polyvinyl alcohol-based resin film. Includes applying or spraying liquid. The pH of this treatment liquid is in the range of 2.5 to 6.0, and has a buffering action in the pH range.

Description

The present invention relates to a method for producing a polarizer.

A liquid crystal display device, which is a typical image display device, has polarizing plates (substantially, polarizing plates including the polarizing elements) arranged on both sides of the liquid crystal cell due to the image forming method. The polarizer is typically produced by dyeing a polyvinyl alcohol (PVA) -based resin film with a dichroic substance such as iodine (for example, Patent Documents 1 and 2). In recent years, there has been an increasing demand for thinner image display devices. Therefore, the polarizer is also required to be further thinned. However, there is a problem that the thinner the polarizer, the lower the reliability in a high temperature and high humidity environment.

Japanese Patent No. 5048120 Japanese Unexamined Patent Publication No. 2013-156391

The present invention has been made to solve the above problems, and a main object thereof is to provide a method capable of producing a highly reliable polarizer easily and inexpensively even in a high temperature environment. It is in.

The method for producing a polarizer of the present invention includes at least stretching and dyeing a polyvinyl alcohol-based resin film, and after the dyeing, a treatment containing citric acid and lithium hydroxide in the polyvinyl alcohol-based resin film. Includes applying or spraying liquid. The pH of this treatment liquid is in the range of 2.5 to 6.0, and has a buffering action in the pH range.
In one embodiment, the polyvinyl alcohol-based resin film is a polyvinyl alcohol-based resin layer formed by applying a coating liquid containing a polyvinyl alcohol-based resin to a base material, and the base material and the polyvinyl alcohol-based resin film. The laminate with the resin layer is subjected to stretching and dyeing.
In another aspect of the present invention, a method for producing a polarizing plate with an adhesive layer is provided. This manufacturing method is a method for manufacturing a polarizing plate with an adhesive layer having a polarizing element, a protective film arranged on one side of the polarizing element, and an adhesive layer arranged on the other side of the polarizer. The polarizer is produced by the above method, a protective film is attached to one side of the polarizer obtained by the production method, and a lithium salt is contained in the other side of the polarizer. Includes forming a pressure-sensitive adhesive layer.

According to the manufacturing method of the present invention, it is possible to provide a highly reliable polarizer in a high temperature and high humidity environment even if it is thin. In the production method of the present invention, after dyeing a polyvinyl alcohol-based resin, a treatment liquid containing citric acid and lithium hydroxide is applied or sprayed onto a polyvinyl alcohol-based resin film. As a result, a highly reliable polarizer can be obtained in a high temperature environment. Moreover, since this manufacturing method does not require any special equipment or complicated operation, the above-mentioned polarizer can be manufactured easily and inexpensively.

Further, in a polarizing plate with a pressure-sensitive adhesive layer having a pressure-sensitive adhesive layer containing a lithium salt as a conductive agent, there may be a problem that the desired conductive performance of the pressure-sensitive adhesive layer is impaired. Specifically, it is considered that the lithium ion contained in the pressure-sensitive adhesive layer can make the iodine complex more stable than the other cation (for example, potassium ion) contained in the polarizer. By exchanging lithium ions in the pressure-sensitive adhesive layer with other cations (for example, potassium ions) contained in the polarizer, the lithium ions contained in the pressure-sensitive adhesive layer are reduced, and the pressure-sensitive adhesive layer becomes aging. The desired conductive performance may be impaired. In the present invention, a polarizing plate is produced using a polarizing element that has been treated with a treatment liquid containing citric acid and lithium hydroxide. As a result, the lithium ions contained in the treatment liquid are first taken into the polarizer, so that the excessive exchange reaction between the lithium ions contained in the pressure-sensitive adhesive layer and other cations contained in the polarizer is suppressed, and the pressure-sensitive adhesive layer The desired properties can be maintained.

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

A. Method for manufacturing a polarizer A-1. Outline of Method for Producing Polarizer The method for producing a polarizer according to the embodiment of the present invention includes at least stretching and dyeing a polyvinyl alcohol (PVA) -based resin film. Typically, the production method includes a step of preparing a PVA-based resin film, a stretching step, a swelling step, a dyeing step, a cross-linking step, a washing step, and a drying step. Each step in which the PVA-based resin film is provided can be performed in any suitable order and timing. Therefore, each step may be performed in the above order, or may be performed in a different order from the above. If necessary, one step may be performed a plurality of times. Further, a step other than the above (for example, an insolubilization step) may be performed at an arbitrary appropriate timing, and a step other than the dyeing step may be omitted.

A-1-2. PVA-based resin film Examples of the PVA-based resin forming the PVA-based resin film include polyvinyl alcohol and an ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponification of polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the 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%, and more preferably 99.0 mol% to 99.93 mol%. be. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, 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-based resin can be appropriately selected depending on the intended 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.

The thickness of the PVA-based resin film is not particularly limited and can be set according to the desired thickness of the polarizer. The thickness of the PVA-based resin film is, for example, 10 μm to 200 μm.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on a substrate. The laminate of the base material and the PVA-based resin layer can be obtained, for example, by 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. In these cases, 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 cross-linking step, a cleaning step, and the like.

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

A-2. Coating or spraying of treatment liquid The production method of the present invention includes coating or spraying a treatment liquid containing citric acid and lithium hydroxide on a PVA-based resin film after dyeing. The treatment liquid may be applied or sprayed after dyeing, and may be performed at any appropriate timing. Specifically, the coating or spraying of the treatment liquid may be performed before or after the cross-linking step, may be performed before the cleaning step, or may be performed after the cleaning step. When the stretching step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before or after the stretching step. When the swelling step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before or after the swelling step. When the insolubilization step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before or after the insolubilization step. Typically, the application or spraying of the treatment liquid can be performed after the cleaning 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 treatment liquid used in the present invention is an aqueous solution containing citric acid and lithium hydroxide. The treatment liquid containing citric acid, for example, has a buffering action in a wider pH range as compared with other materials having a buffering action, and as a result, can have a better anti-discoloration effect in a high temperature environment. Further, the pH of the treatment liquid can be adjusted to a desired range by containing lithium hydroxide. The treatment liquid has a pH in the range of 2.5 to 6.0, and the treatment liquid has a buffering action 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% by weight to 5% by weight, more preferably 0.1% by weight to 0.5% by weight.

In the production method of the present invention, discoloration of the polarizer in a high temperature environment can be remarkably suppressed by applying or spraying such a treatment liquid on a PVA-based resin film. This can suppress the generation of protons in the PVA-based resin by the buffering action in the predetermined pH range of the treatment liquid, and as a result, the generation of a large number of double bonds in the PVA-based resin under a high temperature environment (polyene). It is considered that this is because it was possible to suppress the change in color and the discoloration. Considering the production efficiency, such contact with the treatment liquid can usually be performed by immersing the PVA-based resin film in the treatment liquid. However, in the polarizer obtained by the manufacturing method including immersion in the treatment liquid, the PVA-based resin film swells during immersion, so that the state of the iodine complex in the PVA-based resin film is likely to change, and the polarizer before and after immersion. There is a problem that the absorption spectrum of iodine is easily changed. On the other hand, by applying or spraying the treatment liquid on the PVA-based resin film, it is possible to prevent a problem of change in the absorption spectrum of the polarizer before and after immersion in immersion, and as a result, polyene formation of PVA can be further prevented.

The treatment liquid is applied or sprayed on the PVA-based resin film by any suitable method. Examples of the coating means include a reverse coater, a gravure coater (direct, reverse and 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, pressure nozzle type, rotary disc type) can be mentioned.

A-3. Stretching Step In the stretching step, the PVA-based resin film is typically uniaxially stretched or biaxially stretched 3 to 7 times. The stretching direction may be the longitudinal direction of the film (MD direction), the width direction of the film (TD direction), or both the longitudinal direction and the width direction. The stretching method may be dry stretching, wet stretching, or a combination of these. Further, the PVA-based resin film may be stretched when performing 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 polarizer.

A-4. Swelling step The swelling step is usually performed before the dyeing step. The swelling step is performed, for example, by immersing a 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 contain any suitable other ingredients other than water. Examples of other components include solvents such as alcohol, additives such as surfactants, and iodides. Examples of 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. And so on. 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.

A-5. Dyeing step The dyeing step is a step of dyeing a PVA-based resin film with a dichroic substance. 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 bicolor substance, a method of applying the dyeing solution to the PVA-based resin film, and a method of spraying the dyeing solution onto the PVA-based resin film. The method of doing this can be mentioned. A method of immersing the PVA-based resin film in the dyeing solution is preferable. This is because the dichroic substance can be adsorbed well.

Examples of the dichroic substance include iodine and a dichroic dye. Iodine is preferred. When iodine is used as the dichroic substance, an aqueous iodine solution is preferably used as the staining solution. The iodine content of the iodine aqueous solution is preferably 0.04 parts by weight 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 content of iodide is preferably 0.3 to 15 parts by weight with respect to 100 parts by weight of water.

The liquid temperature at the time of dyeing the dyeing liquid can be set to an arbitrary 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.

A-6. Cross-linking step In the cross-linking step, a boron compound is usually used as a cross-linking agent. Examples of the boron compound include boric acid and borax. Preferably, it is boric acid. In the cross-linking 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% 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 suitable 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 can be mentioned. Be done. It is preferable to immerse in an aqueous solution containing a boron compound.

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

A-7. Cleaning Step The cleaning step can typically be performed after the crosslinking step. The cleaning step is typically performed by immersing a PVA-based resin film in a cleaning liquid. Pure water is a typical example of the cleaning liquid. Potassium iodide may be added 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.

A-8. Drying Step The drying step can be carried out by any suitable method. Examples of the drying method include natural drying, blast drying, vacuum drying, heat drying and the like. 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.

B. Polarizer The thickness of the polarizer obtained by the production method of the present invention is preferably 80 μm or less in one embodiment, preferably 20 μm or less in another embodiment, and in yet another embodiment. Is preferably 10 μm or less, preferably 5 μm or less in still another embodiment, preferably 3 μm or less in yet 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 preferably 0.8 μm or more in yet another embodiment. That is all. According to the production method of the present invention, it is possible to realize a desired single transmittance as described later even with a polarizing element having a thin thickness, and further, the amount of change in the single transmittance in a high temperature environment is remarkably suppressed. be able to.

The polarizer obtained by the production method of the present invention may contain lithium. The lithium content (Li _POL ) of the polarizer is preferably 0.3% by weight or more, and more preferably 0.35% by weight or more. When the lithium content (Li _POL ) is in such a range, it can be suitably used in the method for producing a polarizing plate with an adhesive layer, which will be described later. Specifically, by using a polarizer having such a lithium content, even when a polarizing plate having a pressure-sensitive adhesive layer containing a lithium salt as a conductive agent is formed, the pressure-sensitive adhesive layer has desired characteristics. It can be preferably maintained. The lithium content (Li _POL ) of the polarizer is, for example, 10% by weight or less. The lithium content of the polarizer can be measured by ICP-MS.

The iodine content of the polarizer obtained by the production method of the present invention can be appropriately set according to the thickness of the polarizer from the viewpoint of imparting sufficient polarization performance and optimum transmittance. For example, if the thickness of the polarizer is more than 5 μm and less than 10 μm, the iodine content is preferably 3.5% to 8.0% by weight; the thickness of the polarizer is more than 3 μm and less than 5 μm. When the iodine content is preferably 5.0% by weight to 13.0% by weight; when the thickness of the polarizer is 3 μm or less, the iodine content is preferably 10.0% by weight. ~ 25.0% by weight. As used herein, the term "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, in the polarizer ^{, iodine exists in the form of iodine ion (I −} ), iodine molecule (I ₂ ), polyiodine ion (I ₃ ⁻ , I ₅ ⁻ ), etc., as used herein. Iodine content means the amount of iodine that includes all of these forms. The iodine content can be calculated, for example, by the calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, a complex of PVA and tri-iodide ion (PVA · _{I 3} ^-) has a light absorption peak around 470 nm, a complex of PVA and five iodide ion (PVA · _{I 5} ^-) is 600nm near Has an absorptive peak. As a result, polyiodine ions can absorb light in a wide range of visible light, depending on their morphology. On the other hand, iodide ion (I ⁻ ) has an absorption peak near 230 nm and is not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in the form of a complex with PVA may be mainly involved in the absorption performance of the polarizer.

The simple substance transmittance (Ts) of the polarizer obtained by the production method of the present invention is preferably 30.0% to 43.0%, more preferably 35.0% to 41.0%. The degree of polarization 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 degree of polarization to be high, the contrast can be increased and the black display can be displayed in black, so that an image display device having 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 two-degree field of view (C light source) of JIS Z 8701 and corrected for luminosity factor. For example, a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, product name: V7100). ) Can be used for measurement.

In the polarizer obtained by the production method of the present invention, the absolute value of the amount of change in simple substance transmittance ΔTsa after being left in an environment of 85 ° C. for 500 hours is preferably 5.0% or less, more preferably 3.0. % Or less. The polarizer obtained by the production method of the present invention realizes the above-mentioned desired single transmittance and degree of polarization, and the amount of change in the single transmittance in a high temperature environment is remarkably suppressed. Therefore, it is possible to realize a polarizer in which discoloration is suppressed in a high temperature environment. As a result, the polarizer can be suitably used for applications that require heat resistance. Such an excellent effect can be obtained by applying or spraying a treatment liquid having a predetermined pH and a buffering action on a polyvinyl alcohol-based resin film in the step after dyeing in the method for producing a polarizer as described above. It is considered to be realized by preventing polyene formation of the child in a high temperature environment. This solves a new problem found by actually producing a very thin (for example, 7 μm or less) polarizer, which was difficult to produce in the past, and is unexpectedly excellent. It is an effect. Further, the simple substance transmittance change amount ΔTsa is preferably negative (that is, smaller than 0.0%). The amount of change in single transmittance ΔTsa is expressed by the following equation:
ΔTsa (%) = Tsa ₅₀₀ −Ts ₀
Here, Ts ₀ is the simple substance transmittance before the heating test, and Tsa ₅₀₀ is the simple substance transmittance after being left in an environment of 85 ° C. for 500 hours. Further, when the simple substance transmittance is simply described as Ts in the present specification, it means _{the simple substance transmittance Ts 0 before heating.}

The polarizer obtained by the production method of the present invention has a simple substance transmittance change amount ΔTsb of preferably 3.5% or less after being left in an environment of 60 ° C. and 90% RH for 500 hours, which is more preferable. Is 3.0% or less. The polarizer obtained by the production method of the present invention realizes the above-mentioned desired single transmittance and degree of polarization, and the amount of change in the single transmittance is remarkably suppressed even in a high humidity environment. Therefore, it is possible to realize a polarizer in which discoloration is suppressed even in a high humidity environment. Further, the simple substance transmittance change amount ΔTsb is preferably positive (that is, larger than 0.0%). The amount of change in single transmittance ΔTsb is expressed by the following equation:
ΔTsb (%) = Tsb ₅₀₀ −Ts ₀
Here, Ts ₀ is the single transmittance before the heating test as described above, and Tsb ₅₀₀ is the single transmittance after being left in an environment of 60 ° C. and 90% RH for 500 hours.

C. Method for manufacturing a polarizing plate with a pressure-sensitive adhesive layer In one embodiment of the present invention, a method for manufacturing a polarizing plate with a pressure-sensitive adhesive layer is provided. The method for producing a polarizing plate with an adhesive layer of the present invention has a polarizer, a protective film arranged on one side of the polarizer, and an adhesive layer arranged on the other side of the polarizer. This is a method for manufacturing a polarizing plate. In this production method, a polarizer is produced by the method according to the above item A, a protective film is attached to one side of the polarizer obtained by the production method, and the other side of the polarizer is used. Includes forming a pressure-sensitive adhesive layer containing a lithium salt.

C-1. Fabrication of Polarizer The polarizer can be produced by the method according to the above item A. As described above, the polarizer produced by the method according to item A may contain lithium. By forming a pressure-sensitive adhesive layer containing a lithium salt on such a polarizer, it is possible to reduce the change in the characteristics of the pressure-sensitive adhesive layer with time. As a result, excellent moisture resistance can be realized.

C-2. Adhesion of Protective Film Next, a protective film is attached to one side of the polarizer. As the protective film, any suitable resin film is used. Examples of the resin film forming material include (meth) acrylic resin, cellulose resin such as diacetyl cellulose and triacetyl cellulose, cycloolefin resin such as norbornene resin, olefin resin such as polypropylene, and polyethylene terephthalate resin. Etc., ester-based resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. The "(meth) acrylic resin" refers to an acrylic resin and / or a methacrylic resin.

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

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

When a polarizer is produced using a laminate of a base material and a PVA-based resin layer, the base material may be used as it is as a protective film without peeling. Further, depending on the purpose, any suitable optical functional film may be used as a protective film (and another protective film, if present). Examples of the optical functional film include a retardation film and a reflective polarizer (luminance improving film).

C-3. Formation of Adhesive Layer Any suitable method can be adopted as the method for forming the adhesive layer. As a typical example of the forming method, a method of applying the pressure-sensitive adhesive composition to a separator or the like which has been peeled off, drying and removing a polymerization solvent or the like to form a pressure-sensitive adhesive layer, and then transferring the pressure-sensitive adhesive composition to a polarizer, or the above-mentioned Examples thereof include a method in which a pressure-sensitive adhesive composition is applied and a polymerization solvent or the like is dried and removed to form a pressure-sensitive adhesive layer on a polarizer. When applying the pressure-sensitive adhesive, one or more solvents other than the polymerization solvent may be newly added, if necessary.

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 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 and decyl. Examples thereof include a group, an isodecyl group, a dodecyl group, an isomyristyl group, a lauryl group, a tridecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group and an 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 to 9.

The base polymer may contain monomer units derived from any suitable copolymerization component, depending on the intended 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, a (N-substituted) amide-based monomer, and (meth) acrylic. Alkylaminoalkyl acid-based monomer, alkoxyalkyl-based (meth) acrylate-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-based (meth) acrylic ester monomer, silane-based monomer, and polyfunctional monomer. By adjusting the type, number, combination, and copolymerization ratio (weight ratio) of the copolymerization components, a base polymer (finally, a pressure-sensitive adhesive layer) having desired properties can be obtained. The ratio of the copolymerization component to all the monomer components is preferably 0% by weight to 20% by weight, more preferably 0.1% by weight to 15% by weight, still more preferably 0.1% by weight, based on 100% by weight of all the monomer components. % 10% by weight.

The weight average molecular weight of the base polymer is typically 500,000 to 3,000,000, preferably 700,000 to 2.7 million, and more preferably 800,000 to 2.5 million. 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.

C-3-3. Lithium salt The pressure-sensitive adhesive composition contains a lithium salt (lithium-anionic salt). As mentioned above, the lithium salt can function 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 ⁻ , and 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 _{2 m} 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, q are integers of 1 to 10),
Anion represented by. 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 an imide anion having a perfluoroalkyl group. Specific examples include the above (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ and the 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 _{2 m} 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, q are integers of 1 to 10),
Anion represented by. It is preferably a (perfluoroalkylsulfonyl) imide represented by the general formula (1) such as _{(CF 3} SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ _{, and more preferably (CF 3} SO _2). ) It is a bis (trifluoromethanesulfonyl) imide represented by ₂ N ^−. Therefore, a preferred lithium salt that can 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 parts by weight to 5 parts by weight, more preferably 0.5 parts by weight, based on 100 parts by weight of the base polymer. It is ~ 3 parts by weight, more preferably 0.7 parts by weight to 1.5 parts by weight. When the content of the lithium salt is in such a range, the moisture resistance of a thin and high iodine content polarizing element (as a result, a polarizing plate containing such a polarizing element) can be remarkably improved.

C-3-4. The organic cationic salt pressure-sensitive adhesive composition may further contain an organic cationic salt, if necessary. By using the lithium salt and the organic cationic salt in combination, the surface resistance value can be further lowered without bleeding out the lithium salt.

The organic cation salt is specifically an organic cation-anion salt. Typical examples of the cation constituting the cation portion of the organic cation salt include organic onium in which onium ions are formed by substitution with an organic group. Examples of onium in organic onium include nitrogen-containing onium, sulfur-containing onium, and phosphorus-containing onium. Nitrogen-containing onium and sulfur-containing onium are preferable. The nitrogen-containing onium includes ammonium cation, piperidinium cation, pyrrolidinium cation, pyridinium cation, pyrrolin skeleton cation, pyrrole skeleton cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, Examples thereof include pyrazolium cation and pyrazolinium cation. Ammonium cations, piperidinium cations, and pyrrolidinium cations are preferable, and pyrrolidinium cations are more preferable. Examples of sulfur-containing onium include sulfonium cations. Examples of the phosphonium-containing cation include a phosphonium cation. Examples of the organic group in organic onium include an alkyl group, an alkoxyl group, and an alkenyl group. Specific examples of preferable organic onium include tetraalkylammonium cations, alkylpiperidinium cations, and alkylpyrrolidinium cations. More preferably, it is an ethylmethylpyrrolidinium cation. The anions constituting the anion portion of the organic cation salt are as described with respect to the anions constituting the anion portion of the lithium salt. Therefore, 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 cationic salt in the pressure-sensitive adhesive composition (as a result, the pressure-sensitive adhesive layer) is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.3 parts by weight, based on 100 parts by weight of the base polymer. It is 3 parts by weight, more preferably 0.5 parts by weight 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.

C-3-5. Silane Coupling Agent The pressure-sensitive adhesive composition may further contain a silane coupling agent. Durability can be improved by using a silane coupling agent. As the silane coupling agent, those having any suitable 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) acryloxy group, an acetoacetyl group, an isocyanate group, a styryl group, a polysulfide group and the like. Specifically, for example, a vinyl group-containing silane coupling agent such as vinyl triethoxysilane, vinyl tripropoxysilane, vinyl triisopropoxysilane, vinyl tributoxysilane; γ-glycidoxypropyltrimethoxysilane, γ-gly. Epyl group-containing silane coupling agents such as sidoxylpropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane; γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, γ-triethoxysilyl-N- (1,3-dimethylbutylidene) Amino group-containing silane coupling agents such as propylamine and N-phenyl-γ-aminopropyltrimethoxysilane; mercapto group-containing silane coupling agents such as γ-mercaptopropylmethyldimethoxysilane; styryl such as p-styryltrimethoxysilane Group-containing silane coupling agent; (meth) acrylic group-containing silane coupling agent such as γ-acryloxypropyltrimethoxysilane and γ-methacryloxypropyltriethoxylane; Coupling agent; Examples thereof include a polysulfide group-containing silane coupling agent such as bis (triethoxysilylpropyl) tetrasulfide.

C-3-6. The other pressure-sensitive adhesive composition (as a result, the pressure-sensitive adhesive layer) may further contain any suitable additive. Specific examples of additives include cross-linking agents, silane coupling agents, rework improvers, antioxidants, antistatic agents, cross-linking retarders, emulsifiers, colorants, powders such as pigments, dyes, surfactants, and plastics. Agents, tackifiers, surface lubricants, leveling agents, softeners, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, inorganic fillers, organic fillers, metal powders, particles, foils Can be mentioned. The number, type, amount and combination of additives can be appropriately set according to the purpose.

Any suitable method can be adopted as the method for forming the pressure-sensitive adhesive layer. As a typical example of the forming method, a method of applying the above-mentioned pressure-sensitive adhesive composition to a separator or the like which has been peeled off, drying and removing a polymerization solvent or the like to form a pressure-sensitive adhesive layer, and then transferring the pressure-sensitive adhesive composition to a polarizer, or to a polarizer. Examples thereof include a method in which the pressure-sensitive adhesive composition is applied and a polymerization solvent or the like is dried and removed to form a pressure-sensitive adhesive layer on a polarizer. 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, Japanese Patent Application Laid-Open No. 2014-488497. The description of this gazette is incorporated herein by reference.

Hereinafter, the present invention will be specifically described with reference to 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 copolymer polyethylene terephthalate (IPA copolymer PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75 ° C. was used. One side of the base material is corona-treated, 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. %, Degree of polymerization of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z200") in a ratio of 9: 1 is applied and dried at 25 ° C. to a thickness of 11 μm. A PVA-based resin layer was formed to prepare a laminate.
The obtained laminate was stretched 4.5 times in the air at 140 ° C. in a direction orthogonal to the longitudinal direction of the laminate using a tenter stretching machine (stretching treatment).
Next, the laminate was immersed in a dyeing bath at 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 washing bath (pure water) having a liquid temperature of 25 ° C. for 6 seconds (first washing treatment).
Then, it was immersed in a cross-linking bath (an 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. for 16 seconds (crosslinking treatment).
Next, the laminate was immersed in a washing bath (an aqueous solution having a potassium iodide concentration of 1% by weight) at a liquid temperature of 25 ° C. for 3 seconds (second washing treatment).
The laminate was then dried in an oven at 60 ° C. for 21 seconds (first drying process).
Next, a treatment liquid (0.15 parts by weight of citric acid and 0.01 parts by weight of lithium hydroxide was added to 50 parts by weight of water using a bar coater to the PVA-based resin layer of the laminate, and the mixture was stirred for 10 minutes. , The pH was measured, and then 50 parts by weight of ethanol was added to prepare a treatment solution. pH = 2.9) was applied so that the film thickness was 7 μm (wet state).
Finally, the laminate was dried in an oven at 60 ° C. for 60 seconds to obtain a laminate having a PVA-based resin layer (polarizer) having a thickness of 1.2 μm.

[Example 2]
As the treatment liquid, the same as in Example 1 except that the treatment liquid (pH = 4.2) obtained in the same manner as in Example 1 was used except that the amount of lithium hydroxide added was 0.04 parts by weight. Similarly, a laminate having a polarizer was obtained.

[Example 3]
As the treatment liquid, the same as in Example 1 except that the treatment liquid (pH = 5.8) obtained in the same manner as in Example 1 was used except that the amount of lithium hydroxide added was 0.08 parts by weight. Similarly, a laminate having a polarizer was obtained.

(Comparative Example 1)
As the treatment liquid, the polarizer was prepared 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 except that lithium hydroxide was not added. A laminate having was obtained.

(Comparative Example 2)
The treatment liquid (pH = 13.0) obtained in the same manner as in Example 1 except that citric acid was not added and the amount of lithium hydroxide added was 0.2 parts by weight. ) Was used, and a laminate having a polarizer was obtained in the same manner as in Example 1.

(Comparative Example 3)
As the treatment liquid, the same as in Example 1 except that the treatment liquid (pH = 11.0) obtained in the same manner as in Example 1 was used except that the amount of lithium hydroxide added was 0.2 parts by weight. Similarly, a laminate having a polarizer was obtained.

The pressure-sensitive adhesive composition obtained by the following method is uniformly coated on the surface of a polyethylene terephthalate film (separator) treated with a silicone-based release agent with a fountain coater, and dried in an air circulation type constant temperature oven at 155 ° C. for 2 minutes. Then, a pressure-sensitive adhesive layer having a thickness of 20 μm was formed on the surface of the separator. Next, this pressure-sensitive adhesive layer was transferred to the polarizer surface of the laminate obtained in each Example and Comparative Example to obtain a polarizing plate with a pressure-sensitive 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)
A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas introduction tube, and a cooler was charged with a monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate. Further, 0.1 part of 2,2'-azobisisobutyronitrile was charged together with ethyl acetate as a polymerization initiator with respect to 100 parts of the above-mentioned monomer mixture (solid content), and nitrogen gas was introduced while gently stirring. After substituting with nitrogen, the liquid temperature in the flask was maintained at around 60 ° C. and the polymerization reaction was carried out for 7 hours. Then, ethyl acetate was added to the obtained reaction solution to adjust the solid content concentration to 30%. In this way, a solution of an acrylic polymer (A-1) (base polymer) having a weight average molecular weight of 1.4 million was prepared.

(Preparation of adhesive composition)
For 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.) and ethylmethylpyrrolidinium bis (manufactured by Mitsubishi Materials Electronics Co., Ltd.) as conductive agents. Trifluoromethanesulfonyl) imide (manufactured by Tokyo Kasei Kogyo Co., Ltd.) 0.7 parts, trimethyl propanoxylylene diisocyanate (manufactured by Mitsui Chemicals, Inc .: Takenate D110N) 0.095 parts and dibenzoyl peroxide 0.3 parts, silane cup 0.2 parts of organosilane (manufactured by Soken Kagaku Co., Ltd .: A100) and 0.2 parts of thiol group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd .: X41-1810) as ring agents, rework improver (manufactured by Kaneka Co., Ltd., Cyril) A pressure-sensitive adhesive composition (solution) was prepared by blending 0.03 part of SAT10) and 0.3 part of an antioxidant (Irganox1010 manufactured by BASF).

(1) Heating reliability test The polarizing plate with the pressure-sensitive adhesive layer obtained in each example and comparative example was bonded to non-alkali glass having a thickness of 1.3 mm, and an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product). _{The single transmittance (Ts 0} ) of the thin polarizing film was measured using the name “V7100”). The sample was then placed in an oven at 85 ° C. for 500 hours. Using the taken-out sample, the simple substance transmittance (Tsa ₅₀₀ ) was similarly measured with an ultraviolet-visible spectrophotometer, and ΔTsa was determined by the following formula.
ΔTsa (%) = Tsa ₅₀₀ −Ts ₀
In addition, Examples and Comparative Examples were evaluated according to the following criteria.
◯: Absolute value of ΔTsa is within 3.0% Δ: Absolute value of ΔTsa is within 5.0% ×: Absolute value of ΔTsa exceeds 5.0% (2) Humidification reliability evaluation Each Example and Comparative Example The polarizing plate with the pressure-sensitive adhesive layer obtained in the above method was bonded to non-alkali glass having a thickness of 1.3 mm. _{Then, the single transmittance (Ts 0} ) of the thin polarizing film was measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). Then, the sample was put into a constant temperature and humidity chamber at 60 ° C. and 90% Rh for 500 hours. Using the taken-out sample, the simple substance transmittance (Tsb ₅₀₀ ) was similarly measured with an ultraviolet-visible spectrophotometer, and ΔTsb was determined by the following formula.
ΔTsb (%) = Tsb ₅₀₀ −Ts ₀
In addition, Examples and Comparative Examples were evaluated according to the following criteria.
◯: Absolute value of ΔTsb is within 3.0% Δ: Absolute value of ΔTsb is within 3.5% ×: Absolute value of ΔTsb exceeds 3.5% (3) Appearance of polarizer Each Example and Comparative Example The polarizing plate with the pressure-sensitive adhesive layer obtained in the above method was bonded to non-alkali glass having a thickness of 1.3 mm. Then, it was put into a constant temperature and humidity chamber at 20 ° C. and 98% RH for 120 hours, and the appearance was evaluated. The polarizing plates before and after loading were visually compared and observed, and evaluated according to the following criteria.
◯: No change in appearance was observed Δ: Slight change in appearance was observed, but the change in appearance recovered after being left at room temperature for 6 hours ×: The change in appearance (discoloration, unevenness) was remarkable. .. The change in appearance did not completely recover even after being left at room temperature for 6 hours.

As is clear from Table 1, the polarizer obtained by the production method of the examples of the present invention is excellent in heating and humidifying even when a polarizing plate with an adhesive layer having an adhesive layer containing a conductive agent is used. It was reliable. Furthermore, the appearance was excellent even after being placed in a humid environment.

The production method of the present invention can easily and inexpensively produce a polarizer in which discoloration is suppressed in a high temperature environment. The polarizer obtained by the manufacturing method of the present invention is a liquid crystal panel for a liquid crystal television, a liquid crystal display, a mobile phone, a digital camera, a video camera, a portable game machine, a car navigation system, a copy machine, a printer, a fax machine, a clock, a microwave oven, or the like. Can be widely applied to.

Claims (3)

A method for producing a polarizer, which comprises at least stretching and dyeing a polyvinyl alcohol-based resin film.
After the dyeing, the polyvinyl alcohol-based resin film is coated with or sprayed with a treatment liquid containing citric acid and lithium hydroxide.
A method for producing a polarizer, wherein 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. The polyvinyl alcohol-based resin film is a polyvinyl alcohol-based resin layer formed by applying a coating liquid containing a polyvinyl alcohol-based resin to a base material, and a laminate of the base material and the polyvinyl alcohol-based resin layer is formed. The production method according to claim 1, which is used for stretching and dyeing. A method for manufacturing a polarizing plate with an adhesive layer, which comprises a polarizing element, a protective film arranged on one side of the polarizing element, and an adhesive layer arranged on the other side of the polarizer.
Producing a polarizer by the method according to claim 1 or 2.
A protective film is attached to one side of the polarizer obtained by the manufacturing method, and
A method for producing a polarizing plate with a pressure-sensitive adhesive layer, which comprises forming a pressure-sensitive adhesive layer containing a lithium salt on the other side of the polarizer.