JP6734745B2 - Polarizer and manufacturing method thereof - Google Patents

Description

The present invention relates to a polarizer and a method for manufacturing the same.

A method has been proposed in which a polyvinyl alcohol aqueous solution is applied on a resin substrate to form a resin layer, and the laminate is stretched and dyed to obtain a polarizer (for example, Patent Document 1). According to such a method, a polarizer having a small thickness (for example, 8 μm or less) can be obtained, and therefore, it has been noted that it can contribute to a reduction in the thickness of an image display device, for example.

JP, 2000-338329, A

However, in the above method, since a resin base material is used, there is a problem that the manufacturing process is easily restricted. For example, the coating temperature of the solution is limited according to the glass transition temperature Tg of the resin base material, and thus coating at high temperature is difficult. On the other hand, when the coating temperature is lowered, gelation of polyvinyl alcohol is promoted, and foreign matter is likely to be generated in the coating film. Moreover, since the viscosity of the solution increases, the occurrence of coating defects such as streaks increases. As described above, there is a problem that the quality (for example, reliability of humidification) of the obtained polarizer is insufficient because the manufacturing process is easily restricted.

The present invention has been made to solve the above problems, and a main object thereof is to provide a polarizer having excellent quality while being thin.

The polarizer of the present invention is composed of a resin film containing a polyvinyl alcohol resin. The saponification degree of the polyvinyl alcohol resin is 99.5 mol% or more, and the thickness of the resin film is 8 μm or less.
According to another aspect of the present invention, a method for manufacturing a polarizer is provided. This manufacturing method comprises a step of forming a resin layer by applying a coating liquid containing a polyvinyl alcohol-based resin on a resin base material to form a laminate, and a saponification degree of the polyvinyl alcohol-based resin contained in the resin layer. The step of increasing and the step of dyeing the resin layer are included in this order.
In one embodiment, the saponification degree of the polyvinyl alcohol-based resin contained in the coating liquid is less than 99.5 mol%.
In one embodiment, saponification increases the saponification degree of the polyvinyl alcohol-based resin contained in the resin layer.
In one embodiment, the saponification increases the saponification degree of the polyvinyl alcohol resin by 0.1 mol% or more.
In one embodiment, the saponification is performed by contacting the resin layer with a basic solution.
In one embodiment, the above-mentioned manufacturing method further includes a process of extending the above-mentioned layered product.
In one embodiment, the stretching comprises underwater stretching.
In one embodiment, the underwater stretching is performed after the dyeing step.

According to the present invention, a thin polarizer having excellent quality can be obtained.

FIG. 3 is a partial cross-sectional view of a laminated body according to one embodiment of the present invention.

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

A. Polarizer The polarizer of the present invention is composed of a resin film containing a polyvinyl alcohol-based resin (hereinafter, referred to as “PVA-based resin”). Examples of the PVA-based resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer.

The saponification degree of the PVA-based resin is 99.5 mol% or more, preferably 99.8 mol% or more. The upper limit of the saponification degree is 100 mol %. When the PVA-based resin contained in the polarizer satisfies such a saponification degree, excellent humidification reliability can be achieved. The degree of saponification can be determined according to JIS K 6726-1994.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 6000, and more preferably 2000 to 5000. The average degree of polymerization can be determined according to JIS K 6726-1994.

The thickness of the polarizer (resin film) of the present invention is 8 μm or less, preferably 5 μm or less. On the other hand, the thickness of the polarizer is preferably 1.0 μm or more, more preferably 2.0 μm or more.

The polarizer typically includes a dichroic material. Specific examples of the dichroic substance include iodine and organic dyes. These may be used alone or in combination of two or more. Iodine is preferably used as the dichroic substance.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 42.0% or more, further preferably 42.5% or more, particularly preferably 43.0% or more. The degree of polarization of the polarizer is preferably 99.8% or more, more preferably 99.9% or more, still more preferably 99.95% or more. The degree of polarization (P) is calculated by the following equation by measuring the simple substance transmittance (Ts), the parallel transmittance (Tp) and the orthogonal transmittance (Tc). Here, Ts, Tp, and Tc are Y values measured by a 2 degree visual field (C light source) of JIS Z 8701 and subjected to luminosity correction.
Polarization degree (P)(%)={(Tp−Tc)/(Tp+Tc)} ^1/2 ×100

B. Method for Producing Polarizer The method for producing a polarizer of the present invention comprises a step of forming a resin layer containing a PVA-based resin on a resin substrate to produce a laminate, and a saponification of the PVA-based resin contained in the resin layer. And a step of increasing the degree. Specifically, a step of increasing the saponification degree of the PVA-based resin is performed after the step of producing the laminate. Accordingly, it is possible to manufacture a polarizer having excellent quality (for example, humidification reliability) while ensuring film-forming properties of the PVA-based resin layer (for example, preventing generation of foreign matter and streaks).

B-1. Fabrication of Laminate FIG. 1 is a partial cross-sectional view of a laminate according to one embodiment of the present invention. The laminated body 10 includes a resin base material 11 and a resin layer 12. The laminated body 10 is typically manufactured by forming a resin layer 12 on a long resin base material 11. The resin layer 12 is formed by applying a coating liquid containing a PVA-based resin on the resin base material 11 and drying it as necessary.

Any appropriate material can be adopted as the material for forming the resin base material. Examples thereof include ester resins such as polyethylene terephthalate resin, cycloolefin resins, olefin resins such as polypropylene, (meth)acrylic resins, polyamide resins, polycarbonate resins, and copolymer resins thereof.

The glass transition temperature (Tg) of the resin substrate is preferably 120°C or lower, more preferably 100°C or lower. This is because when the laminate is stretched, the stretchability can be sufficiently ensured while suppressing the crystallization of the resin layer (PVA-based resin). As a result, a polarizer having excellent polarization characteristics can be manufactured. On the other hand, the glass transition temperature of the resin base material is preferably 60° C. or higher. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

The thickness of the resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. The surface of the resin base material may be subjected to surface modification treatment (for example, corona treatment), or an easily adhesive layer may be formed. By such a treatment, a laminate having excellent adhesion between the resin base material and the resin layer can be obtained.

As described above, the coating liquid contains the PVA resin. The degree of saponification of the PVA-based resin contained in the coating liquid is preferably less than 99.5 mol%, more preferably 99.0 mol% or less. By using the PVA-based resin having such a saponification degree, it is possible to sufficiently secure the film forming property on the resin base material. Specifically, when the coating liquid is applied to the resin base material, problems such as deformation of the resin base material may occur if the coating temperature is too high. However, by lowering the saponification degree of the PVA-based resin, The viscosity of the coating liquid can be lowered without raising the temperature of, and gelation of the PVA-based resin can be prevented.

The coating liquid is typically a solution in which the PVA resin is dissolved in a solvent. Examples of the solvent used for the coating liquid include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. To be These may be used alone or in combination of two or more. Of these, water is preferable. The PVA-based resin concentration of the solution can be set to any appropriate value. For example, it is set according to the degree of polymerization or the degree of saponification of the PVA resin. The PVA-based resin concentration of the solution is, for example, 3 to 20 parts by weight with respect to 100 parts by weight of the solvent.

The coating liquid may contain additives. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained resin layer. Further, examples of the additive include an easily adhesive component. By using the easy-adhesion component, the adhesiveness between the resin base material and the resin layer can be improved. As a result, for example, it is possible to suppress defects such as peeling of the resin layer from the resin base material, and to perform the dyeing described below in a good manner. As the easy-adhesion component, for example, modified PVA such as acetoacetyl-modified PVA is used.

Any appropriate method can be adopted as a method for applying the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (a comma coating method, etc.) and the like can be mentioned.

The application temperature (for example, the temperature of the application liquid when applying the application liquid) can be set to any appropriate value depending on the resin substrate used. The coating temperature is, for example, 20° C. or higher, preferably 50° C. or higher. On the other hand, the coating temperature is, for example, less than Tg, preferably Tg(°C)-20°C or less, and more preferably Tg(°C)-30°C or less with respect to the glass transition temperature (Tg) of the resin substrate.

When the applied coating film is dried, the drying temperature is, for example, 20° C. or higher, preferably 50° C. or higher. On the other hand, the drying temperature is preferably lower than the glass transition temperature (Tg) of the resin substrate, and more preferably Tg(°C)-10°C or lower.

The thickness of the resin layer (before stretching) is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm, and particularly preferably 3 μm to 15 μm.

B-2. Adjustment of Saponification Degree Any appropriate method can be adopted as a method for increasing the saponification degree of the PVA-based resin. Preferably, a method of performing saponification treatment on the PVA-based resin contained in the resin layer formed on the resin substrate is adopted. By the saponification treatment, unsaponifiable groups of the PVA-based resin may be saponified and the saponification degree may be increased. As a result, the obtained polarizer can be excellent in humidification reliability while being thin.

The saponification treatment preferably increases the saponification degree of the PVA-based resin contained in the resin layer by 0.1 mol% or more, more preferably 0.5 mol% or more, and particularly preferably 1.0 mol% or more. Let The saponification degree of the PVA-based resin after saponification treatment is typically over 99.0 mol%, for example, 99.3 mol% or more, preferably 99.5 mol% or more, more preferably 99.8 mol%. % Or more.

In one embodiment, saponification treatment is performed by contacting the resin layer with a basic solution. Any appropriate method can be adopted as the method of contacting the basic solution. For example, a method of dropping, coating and spraying a basic solution on the resin layer, and a method of immersing the resin layer (laminate) in the basic solution can be mentioned.

Any appropriate basic compound can be used as the basic compound contained in the basic solution. Examples of the basic compound include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, and inorganic alkali metal salts such as sodium carbonate. , Organic alkali metal salts such as sodium acetate, aqueous ammonia and the like. These may be used alone or in combination of two or more. Among these, alkali metal hydroxides are preferable, sodium hydroxide, potassium hydroxide and lithium hydroxide are more preferable, and sodium hydroxide is particularly preferable.

Examples of the solvent used for the basic solution include water, alcohols such as ethanol and methanol, ether, benzene, chloroform, and mixed solvents thereof. Among these, water and alcohol are preferably used.

The concentration of the basic solution is, for example, 0.01N to 5N, preferably 0.05N to 3N, and more preferably 0.1N to 2.5N. When the basic solution is an aqueous sodium hydroxide solution, its concentration is preferably 1.0 w% or more, more preferably 2 w% to 8 w%.

The liquid temperature of the basic solution is, for example, 20° C. or higher, and preferably 25° C. to 50° C. The contact time of the basic solution is set, for example, according to the thickness of the resin layer and the type and concentration of the basic compound contained in the basic solution. The contact time is, for example, 5 seconds to 30 minutes, preferably 5 seconds to 5 minutes.

The basic solution can be removed from the resin layer by any suitable method after contacting with the resin layer. Examples of the method for removing the basic solution include washing, wiping, suction, and drying. Preferably, removal by washing is adopted. As the cleaning liquid used for cleaning, for example, water, alcohol such as methanol or ethanol is used.

B-3. Dyeing The resin layer may be dyed. Examples of the dyeing method include a method of immersing a resin layer (laminate) in a dyeing solution containing the dichroic substance, a method of applying the dyeing solution to the resin layer, and a method of spraying the dyeing solution onto the resin layer. There is a method. A method of immersing the resin layer in the dyeing solution is preferably used.

The dyeing solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.1 part by weight to 0.5 part 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. 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, titanium iodide. Etc. Among these, potassium iodide is preferable. The iodide content is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of water.

The temperature of the dyeing solution during dyeing is preferably 20°C to 50°C. The immersion time is preferably 5 seconds to 5 minutes. The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or single transmittance of the finally obtained polarizer falls within a predetermined range.

Preferably, the saponification is performed before dyeing the resin layer. This is to impart sufficient polarization characteristics to the obtained polarizer.

B-4. Stretching The laminate can be stretched. Any appropriate method can be adopted as a method for stretching the laminate. Specifically, it may be fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, a method of uniaxially stretching by passing a laminate between rolls having different peripheral speeds). Further, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) may be used, or sequential biaxial stretching may be used. Stretching of the laminate may be performed in one stage or in multiple stages. When carrying out in multiple stages, the stretching ratio of the laminate to be described later is the product of the stretching ratio of each stage.

Any appropriate direction can be selected as the stretching direction of the laminate. In one embodiment, the long laminate is stretched in the longitudinal direction. Specifically, it is the transport direction (MD) of transporting the laminate in the longitudinal direction. In another embodiment, the long laminate is stretched in the width direction. Specifically, it is a direction (TD) in which the laminate is transported in the longitudinal direction and is orthogonal to the transport direction (MD).

The laminate is preferably stretched 4.0 times or more from the original length, and more preferably 5.0 times or more.

The stretching method is not particularly limited and may be, for example, an in-air stretching method or an underwater stretching method in which the laminate is immersed in a stretching bath.

The stretching temperature of the laminate can be set to any appropriate value depending on the resin base material, the stretching method, and the like. When the in-air stretching method is adopted, the stretching temperature is preferably the glass transition temperature (Tg) of the resin substrate or more, more preferably the glass transition temperature (Tg) of the resin substrate+10° C. or more, particularly preferably Tg+15° C. That is all. On the other hand, the stretching temperature of the laminate is preferably 170° C. or lower. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, and defects due to the crystallization (for example, hindering orientation of the PVA-based resin due to stretching) can be suppressed. ..

When the underwater stretching method is adopted as the stretching method, the liquid temperature of the stretching bath is preferably 40°C to 85°C, more preferably 50°C to 85°C. At such a temperature, the PVA resin can be stretched at a high magnification while suppressing the dissolution thereof. Specifically, as described above, the glass transition temperature (Tg) of the resin base material is preferably 60° C. or higher in relation to the formation of the resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the resin substrate by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin, and there is a possibility that excellent polarization characteristics may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

When the underwater stretching method is adopted, it is preferable that the laminate is immersed in a boric acid aqueous solution and stretched (boric acid underwater stretching). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin can be provided with rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight with respect to 100 parts by weight of water. When the boric acid concentration is 1 part by weight or more, the dissolution of the PVA-based resin can be effectively suppressed.

Preferably, the underwater stretching is performed after dyeing the resin layer. This is because the stretchability can be more excellent. In this case, it is preferable to add iodide to the boric acid aqueous solution. This is because the elution of iodine contained in the resin layer can be suppressed. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of water.

Preferably, the underwater stretching is performed at least once. By adopting the underwater stretching, the dyeability can be secured while the PVA-based resin contained in the resin layer has a high saponification degree (for example, 99.0 mol% or more). Specifically, when a PVA-based resin having a high degree of saponification is stretched at a high temperature (for example, 120° C. or higher), sufficient dyeability may not be secured after stretching. In one embodiment, the laminate is subjected to a dyeing step after being stretched in air at, for example, 95°C to 150°C, and then stretched by underwater stretching. In this case, the draw ratio of the laminate in the air is, for example, 1.5 times to 3.5 times, preferably 2.0 times to 3.0 times. Further, the draw ratio of the laminate in water is preferably 2.0 times or more.

The saponification may be performed before the stretching step or after the stretching step. Preferably, saponification is performed after the in-air stretching. This is to ensure sufficient stretchability and dyeability.

B-5. Others The resin layer (laminate) may be subjected to any appropriate treatment other than the above. For example, insolubilization treatment, crosslinking treatment, washing treatment, and drying treatment can be mentioned.

(Insolubilization treatment)
The insolubilization treatment is typically performed by immersing the resin layer in an aqueous boric acid solution. Especially when the underwater stretching method is adopted, water resistance can be imparted to the PVA-based resin by performing insolubilization treatment. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 40°C. Preferably, the insolubilization treatment is performed before dyeing or drawing in water.

(Crosslinking treatment)
The cross-linking treatment is typically performed by immersing the resin layer in an aqueous boric acid solution. Water resistance can be imparted to the PVA-based resin by performing the crosslinking treatment. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. Further, when the crosslinking treatment is performed after the dyeing, it is preferable to further add iodide. By blending iodide, elution of iodine adsorbed on the resin layer can be suppressed. The iodide content is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the crosslinking treatment is performed before the underwater stretching. In one embodiment, dyeing, crosslinking and drawing in water are performed in this order.

(Washing process)
The washing treatment is typically performed by immersing the resin layer in an aqueous potassium iodide solution.

(Drying process)
The drying temperature of the drying process is, for example, 30°C to 100°C.

C. Polarizing Plate The polarizing plate of the present invention has the above polarizer. The polarizing plate typically has a polarizer and a protective film arranged on at least one side of the polarizer. As the protective film, the resin base material may be used as it is, or a film different from the resin base material may be used. Examples of the material for forming the protective film include cellulosic resins such as diacetyl cellulose and triacetyl cellulose (TAC), cyclomethacrylate resins such as (meth)acrylic resins and norbornene resins, and olefin resins such as polyethylene and polypropylene. Examples thereof include ester resins such as polyethylene terephthalate resin, polyamide resins, polycarbonate resins, and copolymer resins thereof. The "(meth)acrylic resin" means an acrylic resin and/or a methacrylic resin.

The thickness of the protective film is typically 10 μm to 100 μm. Various surface treatments may be applied to the protective film. The protective film can function not only as a protective film for the polarizer but also as a retardation film or the like.

The protective film is typically laminated on the polarizer via an adhesive layer (specifically, an adhesive layer or a pressure-sensitive adhesive layer). The adhesive layer is typically formed of a PVA-based adhesive or an activated energy ray-curable adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive.

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.
1. The thickness was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").
2. Glass transition temperature (Tg)
It was measured according to JIS K 7121.

[Example 1]
(Preparation of laminated body)
An amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a Tg of 75° C. was used as a resin substrate.
Corona treatment was applied to one surface of the resin substrate, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, saponification degree 99.0 mol) were applied to the corona-treated surface. % Or more, manufactured by Nippon Gohsei Kagaku Kogyo Co., Ltd., trade name “Gosephimmer Z200”) at a ratio of 9:1 is applied and dried at 23° C. to form a PVA-based resin layer having a thickness of 12 μm and laminated. The body was made. The degree of saponification of the PVA-based resin contained in the aqueous solution is 99.3 mol%.

(Production of polarizing plate)
The obtained laminated body was uniaxially stretched at 2.0 times in the longitudinal direction between rolls having different peripheral speeds in an oven at 120° C. (in-air auxiliary stretching).
Next, the laminate was immersed in a 1 mol/L (1N, 4w%) sodium hydroxide aqueous solution for 10 seconds (saponification treatment).
Next, the laminated body was immersed in an insolubilizing bath having a liquid temperature of 30° C. (boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Then, it was immersed in a dyeing bath having a liquid temperature of 30° C. while adjusting the iodine concentration and the immersion time so that the resulting polarizing plate had a predetermined transmittance. In this example, 0.2 part by weight of iodine was added to 100 parts by weight of water, and 1.5 parts by weight of potassium iodide was added, and the resultant was immersed for 60 seconds in an aqueous iodine solution (dyeing treatment). ..
Then, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 30° C. (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water). (Crosslinking treatment).
Then, the laminate was immersed in an aqueous boric acid solution having a liquid temperature of 70° C. (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with 100 parts by weight of water). On the other hand, uniaxial stretching was performed between rolls having different peripheral speeds such that the total stretching ratio was 5.5 times in the machine direction (stretching in water).
After that, the laminate was immersed in a cleaning bath having a liquid temperature of 30° C. (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).

After washing, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosephimmer (registered trademark) Z-200”, resin concentration: 3% by weight) was applied to the surface of the PVA-based resin layer of the laminate. , An acrylic film (thickness 40 μm, water vapor transmission rate 80 g/m ² /24H) were stuck together, and this was heated in an oven maintained at 60° C. for 5 minutes to prepare a polarizing plate having a polarizer with a thickness of 5 μm.

[Example 2]
(Preparation of laminated body)
As the resin base material, a cycloolefin resin film having a Tg of about 135° C. (manufactured by JSR, ARTON) was used.
An aqueous solution of polyvinyl alcohol having a degree of polymerization of 2400 and a degree of saponification of 98.0% was applied to one surface of the resin substrate at 80° C. and dried to form a PVA-based resin layer having a thickness of 12 μm, and a laminate was prepared.

(Production of polarizing plate)
The obtained laminated body was stretched to a draw ratio of 5.0 times by free-end uniaxial stretching under heating at 160°C. The thickness of the PVA-based resin layer after the stretching treatment was 5 μm (in-air stretching).
Next, the laminate was immersed in a 1 mol/L (1N, 4w%) sodium hydroxide aqueous solution for 10 seconds (saponification treatment).
Next, the laminate is dyed at a liquid temperature of 30° C. (an iodine aqueous solution obtained by adding 0.5 parts by weight of iodine and 3.5 parts by weight of potassium iodide to 100 parts by weight of water). It was dipped in the glass for 60 seconds (dyeing treatment).
Then, the laminated body was placed in a crosslinking bath at a liquid temperature of 60° C. (an aqueous boric acid solution obtained by mixing 5 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) for 60 seconds. It was immersed (crosslinking treatment).
Then, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 3 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).

After washing, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosephimmer (registered trademark) Z-200”, resin concentration: 3% by weight) was applied to the surface of the PVA-based resin layer of the laminate. , An acrylic film (thickness 40 μm, moisture vapor transmission rate 80 g/m ² /24H) were stuck together, and this was heated in an oven maintained at 80° C. for 5 minutes to prepare a polarizing plate having a polarizer with a thickness of 5 μm.

[Comparative Example 1]
A polarizing plate was obtained in the same manner as in Example 1 except that the laminate was not saponified.

[Comparative example 2]
A polarizing plate was obtained in the same manner as in Example 2 except that the laminate was not saponified.

[Comparative Example 3]
When forming the PVA-based resin layer, polyvinyl alcohol having a polymerization degree of 4200 and a saponification degree of 99.9 mol% was used instead of polyvinyl alcohol having a polymerization degree of 4200 and a saponification degree of 99.2 mol% (included in the aqueous solution. The production of a polarizing plate was tried in the same manner as in Example 1 except that the saponification degree of the PVA-based resin used was 99.9 mol %).

[Comparative Example 4]
Example 2 except that polyvinyl alcohol having a polymerization degree of 4200 and a saponification degree of 99.9 mol% was used instead of polyvinyl alcohol having a polymerization degree of 2400 and a saponification degree of 98.0% when forming the PVA-based resin layer. An attempt was made to prepare a polarizing plate in the same manner as in.

(Reference example 1)
Polyvinyl alcohol (polymerization degree: 4200, saponification degree: 99.9 mol%) and acetoacetyl-modified PVA (polymerization degree: 1200, saponification degree: 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gose Fimmer Z200” )) in a ratio of 9:1 (80° C.) is applied on a metal plate heated to 80° C. under an atmosphere of 80° C. so that the thickness after drying is 12 μm. A film was obtained.
An attempt was made to prepare a polarizer by subjecting the obtained PVA-based resin film to various treatments, but the resin film broke during stretching in water.

The saponification degree and humidification reliability of the polarizers of Examples and Comparative Examples were evaluated. The evaluation results are shown in Table 1 together with the production conditions.
1. Method for measuring saponification degree A cut piece obtained by cutting out a predetermined portion of the obtained polarizer (PVA) is immersed in heavy water and heated to dissolve the cut piece, and the measurement sample obtained is subjected to ¹ H-NMR measurement. I served. The measurement conditions are as follows.
Equipment: ¹ H-NMR (Bruker Biospin, AVANCE III-400)
・Observation frequency: 400 MHz
・Chemical shift standard: TSP-d ₄ (0.00 ppm)
・Measuring solvent: heavy water ・Measuring temperature: 80°C
Using each peak area was assigned identification, seeking unsaponified groups strength [VAc] and Ken groups strength [VOH], was determined more saponification degree in the following equation.
100: (Saponification degree)=[VOH]+[VAc]:[VOH ]
2. Method for evaluating humidification reliability The resin substrate was peeled from the obtained polarizer, and the peeled surface of the resin substrate was attached to a glass plate via an adhesive to obtain a sample. The transmittance (Ts) immediately after bonding was 42.5%. This sample was left to stand in an environment of a temperature of 85° C. and a humidity of 85% for 240 hours, and the change amount (ΔP) of the polarization degree of the polarizer before and after being left in a humidified environment was measured. A spectral transmittance meter (manufactured by Murakami Color Research Laboratory, product name “DOT-3C”) was used as a measuring machine.

Comparing Example 1 with Comparative Example 1 and Example 2 with Comparative Example 2, the polarizers of Examples are thin and have excellent humidification reliability.
In Comparative Examples 3 and 4, gelation occurred when the aqueous solution containing the PVA-based resin was applied to the resin base material, and many defects such as breakage occurred in the subsequent stretching step, and the resin layer was well formed. Could not be formed.
The "dyeability" in the table means the single transmittance (Ts) of the obtained polarizer when the iodine concentration in the dyeing bath is 0.5% by weight and the immersion time in the dyeing bath is 60 seconds. ) Was 42.0% or less, it was judged as "good".

The polarizer of the present invention is a liquid crystal panel of 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 copier, a printer, a fax machine, a clock, a microwave oven, or the reflection of an organic EL device. It is suitable for use as a protective film.

10 Laminated body 11 Resin base material 12 Resin layer (polarizer)

Claims (8)

A step of applying a coating liquid containing a polyvinyl alcohol-based resin on a resin base material to form a resin layer, and producing a laminate,
A step of increasing the saponification degree of the polyvinyl alcohol-based resin contained in the resin layer,
And a step of dyeing the resin layer in this order. The production method according to claim 1, wherein the saponification degree of the polyvinyl alcohol-based resin contained in the coating liquid is less than 99.5 mol %. The production method according to claim 1, wherein the saponification enhances the degree of saponification of the polyvinyl alcohol-based resin contained in the resin layer. The production method according to claim 3, wherein the saponification increases the saponification degree of the polyvinyl alcohol-based resin by 0.1 mol% or more. The production method according to claim 3 or 4, wherein the saponification is performed by bringing the resin layer into contact with a basic solution. The manufacturing method according to claim 1, further comprising a step of stretching the laminate. The manufacturing method according to claim 6, wherein the stretching includes underwater stretching. The manufacturing method according to claim 7, wherein the underwater stretching is performed after the dyeing step.

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