JP7240090B2 - Polarizing plate, image display device, and method for manufacturing polarizing plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polarizing plate, an image display device, and a method for manufacturing a polarizing plate.

A method for obtaining a thin polarizer by forming a polyvinyl alcohol-based resin layer on a polyester-based resin substrate, stretching and dyeing the laminate has been proposed (for example, Patent Document 1). Such a method for manufacturing a polarizer is attracting attention as it can contribute to, for example, thinning of an image display device.

The polarizer can be used as it is laminated on the polyester-based resin substrate, and in this case, the polyester-based resin substrate is used as a protective layer of the polarizer (Patent Document 2). Thereby, the laminate of the polyester-based resin base material and the polarizer can be used as the polarizing plate without attaching a protective film to the polarizer, which can contribute to cost reduction of the image display device, for example.

JP-A-2000-338329 Japanese Patent No. 4979833

However, when the polarizer-side surface of the polarizing plate is adhered to another optical member such as a display cell or a retardation plate via an adhesive, the thermal shrinkage behavior of the polyester-based resin substrate is large. , peeling of the polarizing plate may occur in a high-temperature and high-humidity environment.

The present invention has been made to solve the above-mentioned conventional problems, and the main purpose thereof is to provide a polarizing plate with small thermal shrinkage behavior and suppressed peeling, an image display device comprising the above polarizing plate, and a polarizing plate To provide a manufacturing method of

The polarizing plate of the present invention includes a polyester resin base material and a polarizer laminated on one side of the polyester resin base material, the thickness of the polarizer being 10 μm or less, and the polyester resin base material. has an elastic modulus of 2.70 GPa or more.
In one embodiment, the polarizer is laminated on one side of the polyester-based resin base without an adhesive layer interposed therebetween.
In one embodiment, an easy-adhesion layer is provided between the polyester-based resin base material and the polarizer.
In one embodiment, the polyester-based resin substrate functions as a protective layer of the polarizer.
According to another aspect of the present invention, an image display device is provided. This image display device has the above polarizing plate.
According to another aspect of the present invention, there is provided a method for manufacturing the polarizing plate. The production method comprises forming a polyvinyl alcohol-based resin layer on one side of the polyester-based resin base material to form a laminate, and dyeing and stretching the laminate to form the polyvinyl alcohol-based resin layer as a polarizer. and heat-treating the laminate of the polyester resin base material and the polarizer after the stretching, wherein the temperature of the stretching bath in the stretching is 67 ° C. or less, and in the heat treatment The maximum heating temperature is 102° C. or higher, or the temperature of the drawing bath in the drawing is 69° C. or lower and the maximum heating temperature in the heat treatment is 105° C. or higher.

ADVANTAGE OF THE INVENTION According to this invention, the thermal contraction behavior is small and the polarizing plate by which peeling was suppressed, the image display apparatus provided with the said polarizing plate, and the manufacturing method of a polarizing plate can be provided.

1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention; FIG. It is the schematic which shows the manufacturing process of the polarizing plate which concerns on one embodiment.

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

A. Overall Configuration of Polarizing Plate FIG. 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention. As shown in FIG. 1 , the polarizing plate 10 has a polyester-based resin base material 11 and a polarizer 12 laminated on one side of the polyester-based resin base material 11 . The thickness of the polarizer 12 is 10 μm or less. The elastic modulus of the polyester-based resin base material 11 is 2.70 GPa or more. The elastic modulus of the polyester-based resin base material 11 is typically measured by a nanoindentation method using an indentation tester (typically a nanoindenter). More specifically, the elastic modulus (E) of the polyester resin base material 11 is obtained from a displacement-load hysteresis curve obtained by pressing a probe (indenter) against the surface of the polyester resin base material to be measured. It is calculated by the following formula from the obtained contact stiffness S and the contact projection area A between the indenter and the polyester-based resin base material.
E=S×π ^1/2 /2A ^1/2
The polarizer 12 is preferably laminated on one surface of the polyester-based resin base material 11 (in other words, without an adhesive layer interposed therebetween). The polarizing plate 10 preferably has an easy-adhesion layer (not shown) between the polyester-based resin substrate 11 and the polarizer 12 . The polarizing plate 10 may have a protective film (not shown) on the side of the polarizer 12 opposite to the polyester-based resin substrate 11 . The polyester-based resin base material 11 typically functions as a protective layer for the polarizer 12 . When a conventional polarizing plate is placed in a high-temperature and high-humidity environment with the polarizer-side surface attached to another optical member, the polarizing plate may peel off from the optical member at both ends in the stretching direction. On the other hand, in the polarizing plate 10 of the present embodiment, the thermal shrinkage behavior of the polyester-based resin base material 11 when the surface on the polarizer 12 side is attached to another optical member is small, and the heat shrinkage behavior of the polyester resin base material 11 is small. Peeling can be suppressed.

B. Polarizer The polarizer is substantially a polyvinyl alcohol-based resin layer (PVA-based resin layer) in which iodine is adsorbed and oriented. As described above, the thickness of the polarizer is 10 μm or less, preferably 7.5 μm or less, and more preferably 5 μm or less. On the other hand, the thickness of the polarizer is preferably 0.5 μm or more, more preferably 1.5 μm or more. If the thickness is too thin, the resulting polarizer may have poor optical properties. 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 41.0% or more, still more preferably 42.0% or more. The degree of polarization of the polarizer is preferably 99.8% or higher, more preferably 99.9% or higher, still more preferably 99.95% or higher.

Any appropriate resin may be employed as the PVA-based resin forming the PVA-based resin layer. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . 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 with 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 purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

C. Polyester Resin Base Material The polyester resin base material has an elastic modulus of 2.70 GPa or more as described above. The elastic modulus is preferably 2.70 GPa to 4.50 GPa, more preferably 2.80 GPa to 3.90 GPa. This makes it possible to suppress shrinkage of the polyester-based resin base material in a high-temperature and high-humidity environment, and as a result, when the polarizing plate is attached to the optical member, it is possible to suppress the separation of the polyester-based resin base material from the optical member. obtain. In the method for manufacturing a polarizing plate described later, the elastic modulus is the temperature of the stretching bath when stretching the laminate of the polyester resin substrate and the polyvinyl alcohol resin layer in water, and the maximum when heat treatment is performed after stretching in water. By appropriately setting the heating temperature, it can be controlled within a desired numerical range.

Materials for forming the polyester-based resin base material include, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), isophthalic acid, alicyclic dicarboxylic acid containing cyclohexane ring, or alicyclic dicarboxylic acid or alicyclic ring. Copolymerized PET (PET-G) containing diols of the formula (PET-G), other polyesters, and copolymers and blends thereof can be used. Among them, it is preferable to use amorphous (non-crystallized) PET or copolymerized PET. These resins are amorphous in an unstretched state and have excellent stretchability suitable for high-ratio stretching, and can impart heat resistance and dimensional stability by being crystallized by stretching and heating. Furthermore, heat resistance to the extent that the PVA-based resin can be applied and dried in an unstretched state can be ensured.

The glass transition temperature (Tg) of the polyester-based resin substrate is preferably 170° C. or lower. By using such a polyester-based resin base material, it is possible to sufficiently ensure stretchability while suppressing crystallization of the PVA-based resin layer. Considering the plasticization of the polyester-based resin substrate with water and the excellent stretching in water, the temperature is more preferably 120° C. or less. In one embodiment, the glass transition temperature of the polyester-based resin substrate is preferably 60° C. or higher. By using such a polyester-based resin base material, the polyester-based resin base material is deformed (for example, irregularities, sagging, wrinkles, etc. occur) when applying and drying a coating liquid containing a PVA-based resin, which will be described later. Such troubles can be prevented. Also, the laminate can be stretched at a suitable temperature (for example, about 60° C. to 70° C.). In another embodiment, the glass transition temperature may be lower than 60° C. as long as the polyester-based resin substrate is not deformed when the coating liquid containing the PVA-based resin is applied and dried. The glass transition temperature (Tg) is a value determined according to JIS K7121.

In one embodiment, the polyester-based resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. Such a polyester-based resin base material absorbs water, and the water acts like a plasticizer to plasticize the base material. As a result, the drawing stress can be greatly reduced in water drawing, and the drawability can be excellent. On the other hand, the water absorption rate of the polyester-based resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a polyester-based resin base material, it is possible to prevent problems such as a deterioration in the appearance of the obtained laminate due to a marked decrease in the dimensional stability of the polyester-based resin base material during production. Moreover, it is possible to prevent breakage during stretching in water and separation of the PVA-based resin layer from the polyester-based resin substrate. Incidentally, the water absorption is a value determined according to JIS K7209.

The thickness of the polyester resin substrate is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm.

D. Protective Film The polarizing plate 10 may have a protective film on the side of the polarizer 12 opposite to the polyester-based resin substrate 11, as described above. Examples of materials for forming the protective film include (meth)acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins, olefin resins such as polypropylene, and ester resins such as polyethylene terephthalate resins. Resins, polyamide-based resins, polycarbonate-based resins, copolymer resins thereof, and the like are included. The thickness of the protective film is preferably 10 μm to 100 μm.

E. Easy-Adhesion Layer The polarizing plate 10 may have an easy-adhesion layer between the polyester-based resin base material 11 and the polarizer 12 as described above. The easy-adhesion layer may be a layer formed substantially only from the easy-adhesion layer-forming composition, and the easy-adhesion layer-forming composition and the polarizer-forming material are mixed (including compatible). It may be a layer or region. Excellent adhesion can be obtained by forming the easy-adhesion layer. The thickness of the easy-adhesion layer is preferably about 0.05 μm to 1 μm. The easy-adhesion layer can be confirmed, for example, by observing a cross section of the polarizing plate with a scanning electron microscope (SEM).

The easy-adhesion layer-forming composition preferably contains a polyvinyl alcohol-based component. Any appropriate PVA-based resin may be used as the polyvinyl alcohol-based component. Specific examples include polyvinyl alcohol and modified polyvinyl alcohol. Modified polyvinyl alcohols include, for example, polyvinyl alcohols modified with acetoacetyl groups, carboxylic acid groups, acrylic groups and/or urethane groups. Among these, acetoacetyl-modified PVA is preferably used. A polymer having at least a repeating unit represented by the following general formula (I) is preferably used as the acetoacetyl-modified PVA.

In the above formula (I), the ratio of n to l+m+n is preferably 1% to 10%.

The average degree of polymerization of the acetoacetyl-modified PVA is preferably 1000-10000, preferably 1200-5000. The degree of saponification of acetoacetyl-modified PVA is preferably 97 mol % or more. The pH of the 4% by weight aqueous solution of acetoacetyl-modified PVA is preferably 3.5-5.5.

The easy-adhesion layer-forming composition may further contain polyolefin-based components, polyester-based components, polyacrylic-based components, and the like, depending on the purpose and the like. Preferably, the easily adhesive layer-forming composition further contains a polyolefin component.

Any appropriate polyolefin-based resin may be used as the polyolefin-based component. Examples of the olefin component, which is the main component of the polyolefin resin, include olefin hydrocarbons having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene and 1-hexene. These can be used alone or in combination of two or more. Among these, olefinic hydrocarbons having 2 to 4 carbon atoms such as ethylene, propylene, isobutylene and 1-butene are preferred, and ethylene is more preferred.

Among the monomer components constituting the polyolefin resin, the ratio of the olefin component is preferably 50% by weight to 95% by weight.

The polyolefin resin preferably has a carboxyl group and/or an anhydride group thereof. Such a polyolefin-based resin can be dispersed in water, and an easy-adhesion layer can be satisfactorily formed. Monomer components having such functional groups include, for example, unsaturated carboxylic acids and their anhydrides, and half esters and half amides of unsaturated dicarboxylic acids. Specific examples of these include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid and crotonic acid. The polyolefin resin has a molecular weight of, for example, 5,000 to 80,000.

In the easily adhesive layer-forming composition, the blending ratio of the polyvinyl alcohol-based component and the polyolefin-based component (former: latter (solid content)) is preferably 5:95 to 60:40, more preferably 20:80 to 50. :50. If the polyvinyl alcohol-based component is too large, there is a risk that sufficient adhesion cannot be obtained. Specifically, the peeling force required for peeling the polarizer from the polyester-based resin base material may decrease, and sufficient adhesion may not be obtained. On the other hand, if the polyvinyl alcohol-based component is too small, the appearance of the obtained polarizing plate may be impaired. Specifically, problems such as clouding of the coating film may occur during the formation of the easy-adhesion layer, making it difficult to obtain a polarizing plate with excellent appearance.

The easily adhesive layer-forming composition is preferably water-based. The easy-adhesion layer-forming composition may contain an organic solvent. Examples of organic solvents include ethanol and isopropanol. The solid content concentration of the easily adhesive layer-forming composition is preferably 1.0% by weight to 10% by weight.

Any appropriate method can be adopted as a method for applying the easily adhesive layer-forming composition. After applying the easily adhesive layer-forming composition, the coating film may be dried. The drying temperature is, for example, 50° C. or higher.

F. Method for producing polarizing plate The method for producing the polarizing plate of the present invention includes forming a PVA-based resin layer on one side of a polyester-based resin base material to form a laminate, and dyeing and stretching the laminate to produce a PVA-based resin. This includes forming the layer into a polarizer, and heat-treating the laminate of the polyester-based resin base material and the polarizer after stretching. The temperature of the drawing bath is 67°C or less and the maximum heating temperature in the heat treatment is 102°C or more, or the temperature of the drawing bath is 69°C or less and the maximum heating temperature in the heat treatment is 105°C. °C or higher.

FIG. 2 is a schematic diagram showing a manufacturing process of a polarizing plate according to one embodiment. Typically, in the manufacturing process of the polarizing plate according to the present embodiment, the laminate 10′ of the polyester-based resin base material and the PVA-based resin layer is fed out from the feeding section 101, and the boric acid aqueous solution is applied by the rolls 111 and 112. After immersion in bath 110 (insolubilization treatment), rolls 121 and 122 immerse in bath 120 of an aqueous solution of a dichroic substance (iodine) and potassium iodide (dyeing treatment). It is then immersed by rolls 131 and 132 in a bath 130 of an aqueous solution of boric acid and potassium iodide (crosslinking treatment). Next, while being immersed in a drawing bath 140 of boric acid aqueous solution, the laminate 10′ is stretched by applying tension in the longitudinal direction (longitudinal direction, transport direction, MD direction) with rolls 141 and 142 having different speed ratios. The PVA-based resin layer is made into a polarizer by (underwater stretching treatment). The submerged stretched laminate 10' is then immersed (washing treatment) in a bath 150 of an aqueous potassium iodide solution by rolls 151 and 152, and subjected to a drying treatment (not shown). Next, the polarizing plate 10 of the present embodiment is obtained by putting the laminate 10 ′ into the heating means 160 and heating (heating treatment). After that, the obtained polarizing plate 10 is wound by the winding section 170 . Although not shown, the laminate 10' may be stretched in the air before being subjected to the insolubilization treatment. Note that the manufacturing process shown in FIG. 2 is an example, and the number of times and order of the above processes are not particularly limited.

F-1. Production of Laminate Any appropriate method can be adopted as a method for forming a PVA-based resin layer on a polyester-based resin substrate. Preferably, the PVA-based resin layer is formed by applying a coating liquid containing the PVA-based resin onto the polyester-based resin base material and drying it. In one embodiment, an easy-adhesion layer-forming composition is applied onto a polyester-based resin substrate and dried to form an easy-adhesion layer, and a PVA-based resin layer is formed on the easy-adhesion layer. do.

The material for forming the polyester-based resin base material is as described in section C above. The thickness of the polyester-based resin substrate (thickness before stretching, which will be described later) is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If the thickness is less than 20 μm, it may be difficult to form the PVA-based resin layer. If it exceeds 300 μm, for example, in stretching in water, it may take a long time for the polyester-based resin base material to absorb water, and an excessive load may be required for stretching.

The coating liquid is typically a solution obtained by dissolving the PVA-based resin in a solvent. Examples of solvents include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the polyester-based resin substrate. In one embodiment, the coating liquid contains a halide. Any appropriate halide can be employed as the halide. Examples include iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred. The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA resin. Department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained polarizer may become cloudy. By subjecting a laminate of a PVA-based resin layer containing a halide and a polyester-based resin base material to high-temperature stretching (auxiliary stretching) in the air before stretching in boric acid water, the PVA-based resin layer after auxiliary stretching Crystallization of the PVA-based resin can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the finally obtained polarizer.

Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Surfactants include, for example, nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer. Moreover, as an additive, an easy-adhesion component is mentioned, for example. Adhesion between the polyester-based resin substrate and the PVA-based resin layer can be improved by using the easily-adhesive component. As a result, for example, problems such as peeling of the PVA-based resin layer from the polyester-based resin substrate can be suppressed, and dyeing and stretching in water, which will be described later, can be performed satisfactorily. Modified PVA such as acetoacetyl-modified PVA is used as the easy-adhesion component, for example.

Any appropriate method can be adopted as a method for applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

The thickness of the PVA-based resin layer (thickness before stretching, which will be described later) is preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the polyester-based resin substrate may be subjected to surface treatment (for example, corona treatment, etc.), or a composition for forming an easy-adhesion layer is applied (coated) on the polyester-based resin substrate. process). By performing such a treatment, the adhesion between the polyester-based resin substrate and the PVA-based resin layer can be improved. As a result, for example, problems such as peeling of the PVA-based resin layer from the polyester-based resin substrate can be suppressed, and dyeing and stretching, which will be described later, can be performed satisfactorily.

F-2. In-air stretching process The stretching method for auxiliary in-air stretching may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., uniaxially stretching through a laminate between rolls with different peripheral speeds. method). In one embodiment, the in-air stretching process includes a hot roll stretching step in which the laminate is stretched by a peripheral speed difference between hot rolls while being transported in the longitudinal direction. The air drawing process typically includes a zone drawing process and a hot roll drawing process. The order of the zone stretching process and the hot roll stretching process is not limited, and the zone stretching process may be carried out first, or the hot roll stretching process may be carried out first. The zone drawing step may be omitted. In one embodiment, the zone drawing step and the hot roll drawing step are performed in this order.

The stretching temperature of the laminate can be set to any appropriate value depending on the forming material of the polyester-based resin substrate, the stretching method, and the like. The stretching temperature in the air stretching treatment is preferably the glass transition temperature (Tg) of the polyester resin substrate or higher, more preferably the glass transition temperature (Tg) of the polyester resin substrate +10°C or higher, and particularly preferably Tg +15°C. That's it. On the other hand, the upper limit of the stretching temperature of the laminate is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can.

F-3. Insolubilization Treatment The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Water resistance can be imparted to the PVA-based resin layer by performing the insolubilization treatment. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the insolubilization treatment is performed before the above-mentioned stretching in water and the above-mentioned dyeing treatment.

F-4. Dyeing Treatment The dyeing of the PVA-based resin layer is typically carried out by allowing the PVA-based resin layer to adsorb iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. A spraying method and the like can be mentioned. A preferred method is to immerse the PVA-based resin layer (laminate) in a dyeing solution. This is because iodine can be well adsorbed.

The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.1 to 0.5 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 an iodide to the iodine aqueous solution. Specific examples of iodides are as described above. The amount of iodide compounded is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes in order to ensure the transmittance of the PVA-based resin layer. In addition, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the degree of polarization or single transmittance of the finally obtained polarizer falls within a predetermined range. In one embodiment, the immersion time is set so that the obtained polarizer has a degree of polarization of 99.98% or more. In another embodiment, the immersion time is set so that the single transmittance of the obtained polarizer is 40% to 44%.

Dyeing treatment can be performed at any appropriate timing. Preferably, it is carried out before stretching in water.

F-5. Crosslinking Treatment The crosslinking treatment is typically performed by immersing the PVA-based resin layer (laminate) in an aqueous boric acid solution. The cross-linking treatment can impart water resistance to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when cross-linking treatment is carried out after the dyeing treatment, it is preferable to further add an iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 60°C. Preferably, the cross-linking treatment is performed before the underwater stretching treatment. In a preferred embodiment, stretching in the air, dyeing and cross-linking are performed in this order.

F-6. In-Water Stretching Treatment As described above, the manufacturing process of the polarizing plate includes the underwater stretching treatment of the laminate in a stretching bath. Specifically, it is stretched in water in a direction parallel to the stretching direction of the laminate. According to underwater stretching, stretching can be performed at a temperature lower than the glass transition temperature (typically, about 80° C.) of the polyester-based resin base material or the PVA-based resin layer, and the PVA-based resin layer is prevented from crystallizing. It can be stretched to a high magnification while suppressing the stretching. As a result, a polarizer having excellent optical properties (eg degree of polarization) can be produced. In the present specification, the "parallel direction" includes the case of 0 ° ± 5.0 °, preferably 0 ° ± 3.0 °, more preferably 0 ° ± 1.0 ° .

The stretching temperature for the underwater stretching (liquid temperature of the stretching bath) is 69° C. or lower, more preferably 67° C. or lower. The lower limit of the liquid temperature of the drawing bath is preferably 40°C, more preferably 50°C. By setting the liquid temperature of the stretching bath within the above range, together with the maximum heating temperature in the heat treatment described below, the elastic modulus of the polyester-based resin substrate can be adjusted to a value within the preferred range. Furthermore, if it is the above temperature, it can extend|stretch by high magnification, suppressing melt|dissolution of a PVA-type resin layer. Specifically, as described above, the glass transition temperature (Tg) of the polyester-based resin substrate is preferably 60° C. or higher in relation to the formation of the PVA-based 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 polyester-based resin base material 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 layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

Any appropriate method can be adopted for the stretching method in the underwater stretching treatment. Specifically, the drawing may be fixed end drawing or free end drawing. The stretching direction of the laminate is substantially the stretching direction (longitudinal direction) of the in-air stretching. The laminate may be stretched in one step or in multiple steps.

The stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be satisfactorily stretched, and a polarizer having excellent optical properties (for example, degree of polarization) can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight with respect to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizer with higher properties can be produced. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

When a dichroic substance (typically iodine) is previously adsorbed to the PVA-based resin layer by dyeing, iodide is preferably added to the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Examples of iodides 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. Among these, potassium iodide is preferred. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

By combining the polyester-based resin base material and the stretching in water (stretching in boric acid water), it is possible to stretch at a high magnification, and a polarizer having excellent optical properties (for example, degree of polarization) can be produced. . Specifically, the maximum draw ratio is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 5.5 times or more relative to the original length of the laminate (including the draw ratio of the laminate). 6.0 times or more. As used herein, the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks. In addition, the maximum draw ratio of the laminate using the above-mentioned polyester-based resin base material can be higher when it is subjected to underwater stretching than when it is stretched only by in-air stretching.

F-7. Cleaning Treatment The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide. The drying temperature in the drying treatment is preferably 30°C to 100°C.

F-8. Heat Treatment Heat treatment is performed after the underwater stretching. The heat treatment may promote crystallization of the polyester-based resin base material. The heat treatment is typically performed by heating a conveying roll arranged in the heating means 160 (using a so-called hot drum roll (heating roll)) (hot drum roll heating method). In one embodiment, the heating means 160 is an oven, and a heating method by blowing hot air into the oven (oven heating method) may also be used. By using both the hot drum roll heating method and the oven heating method, sharp temperature changes between the hot drum rolls can be suppressed, and shrinkage in the width direction of the laminate 10' can be easily controlled. . The temperature in the oven furnace is preferably between 30°C and 100°C. Also, the heating time in the oven is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in the oven and can be measured with a mini-vane digital anemometer.

By heating using a hot drum roll, curling can be suppressed and a polarizer with excellent appearance can be produced. Specifically, by heating the laminated body 10 ′ while being placed along a hot drum roll, the crystallization of the polyester resin base material can be efficiently promoted to increase the degree of crystallinity. Even at a relatively low heating temperature, the degree of crystallinity of the polyester-based resin substrate can be favorably increased. As a result, the rigidity of the polyester-based resin base material increases, and the polyester-based resin base material becomes in a state capable of withstanding the shrinkage of the PVA-based resin layer due to heating, thereby suppressing curling. Moreover, by using a hot drum roll, the laminated body 10' can be heated while being kept flat, so that not only curling but also wrinkling can be suppressed.

A plurality of heated drum rolls may be arranged within the heating means 160 and each heated drum roll may be set to a different temperature. Within the heating means 160, typically 2 to 20, preferably 4 to 10 heated drum rolls may be arranged. The contact time (total contact time) between the laminate 10' and the hot drum roll is preferably 1 second to 300 seconds. The heating conditions can be controlled by adjusting the temperature of the hot drum rolls, the number of hot drum rolls, the contact time with the hot drum rolls, and the like.

When the temperature of the hot drum roll set to the highest temperature among the plurality of hot drum rolls is defined as the "maximum heating temperature", the maximum heating temperature is 102°C or higher, more preferably 105°C or higher, and further It is preferably 110° C. or higher. The upper limit of the maximum heating temperature is preferably 150°C, more preferably 120°C. By setting the maximum heating temperature in the heat treatment within the above range, together with the temperature of the drawing bath in the underwater drawing treatment, the durability index of the polyester-based resin base material can be adjusted to a value within the preferred range. The temperature of the hot drum roll can be measured with a contact thermometer. The contact time of the laminate with the hot drum roll kept at the highest heating temperature (the total contact time when there are multiple hot drum rolls with the highest heating temperature) is preferably 0.2 seconds to 2 seconds. , more preferably 0.5 seconds to 2 seconds. The term "contact time" refers to the time from when an arbitrary point on the laminate comes into contact with the outer peripheral surface of the hot drum roll kept at the maximum heating temperature until it leaves.

G. Image Display Device The polarizing plate described in items A to E above obtained by the manufacturing method described in item F above can be applied to an image display device such as a liquid crystal display device. Therefore, the present invention includes an image display device using the polarizing plate. An image display device according to an embodiment of the present invention includes the polarizing plate according to any one of items A to E above.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method and evaluation method for each characteristic are as follows.
(1) Thickness Measured using a digital micrometer (manufactured by Anritsu, product name “KC-351C”).
(2) Elastic Modulus The polyester-based resin substrates of the polarizing plates obtained in Examples and Comparative Examples were measured using a nanoindenter ("Triboindenter" manufactured by Hysitron Inc.) under the following measurement conditions. The elastic modulus was measured by the static method. Specifically, the probe (indenter) of the nanoindenter is pushed into the surface of the polarizing plate on the polyester resin substrate side, and the contact stiffness S obtained from the displacement-load hysteresis curve and the relationship between the indenter and the polyester resin substrate are measured. It was calculated by the following formula from the contact projected area A between
Elastic modulus (E)=S×π ^1/2 /2A ^1/2
(Measurement condition)
・Measurement method: single indentation method ・Measurement temperature: 25°C
・Indentation speed: about 2 nm/sec
・Indentation depth: about 2000 nm
・Probe: Diamond, Berkovich type (triangular pyramid type)
(3) Evaluation of Adhesion The elongated polarizing plates obtained in Examples and Comparative Examples were cut into a size of 150 mm (MD direction)×200 mm (TD direction) to obtain evaluation samples. The polarizer side of the evaluation sample is attached to the glass via an acrylic adhesive and stored at 60 ° C./90% Rh for 500 hours, and then the edge of the evaluation sample is checked for peeling from the glass. bottom. In addition, when the sample for evaluation was peeled off from the glass, the length of the peeled portion was measured.

<Example 1>
A long amorphous isophthalic acid-copolymerized polyethylene terephthalate (IPA-copolymerized PET) film (thickness: 100 μm, degree of IPA modification: 5 mol %) was used as the polyester-based resin substrate. (Degree of modification = [ethylene isophthalate unit]/[ethylene terephthalate unit + ethylene isophthalate unit])
Corona treatment (treatment conditions: 50 W min/m ² ) was applied to one side of the polyester-based resin base material, and acetoacetyl-modified polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name " GOSEFIMER Z200") modified polyolefin resin aqueous dispersion (manufactured by Unitika Ltd., trade name "Arrowbase SE1030N") and pure water (solid content concentration 4.0%), the thickness after drying is It was coated so as to have a thickness of 2000 nm and dried at 65° C. for 2 minutes to form an undercoat layer. Here, the solid content blending ratio of the acetoacetyl-modified PVA and the modified polyolefin in the mixed solution was 30:70. Next, on the surface of the undercoat layer, 90 parts by weight of PVA (degree of polymerization: 4200, degree of saponification: 99.2 mol%) and 10 parts by weight of acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER Z410") were applied. The mixed PVA-based resin and an aqueous solution containing 13 parts by weight of potassium iodide per 100 parts by weight of the PVA-based resin were applied at 25° C. and dried at 60° C. for 3 minutes to form a PVA with a thickness of 13 μm. A system resin layer was formed. Thus, a laminate was produced.
The resulting laminate was uniaxially stretched twice in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 140° C. (in-air auxiliary stretching).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Then, immerse in a dyeing bath (iodine aqueous solution obtained by blending 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. for 60 seconds. (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, the laminate was subjected to a stretching bath (stretching bath temperature: 67° C.), the film was uniaxially stretched by 2.75 times (total draw ratio: 5.5 times) in the machine direction (longitudinal direction) between rolls with different circumferential speeds (underwater stretching treatment).
After that, the laminate was immersed in a cleaning bath having a liquid temperature of 30° C. (an aqueous solution obtained by mixing 100 parts by weight of water with 3.5 parts by weight of potassium iodide) (cleaning treatment).
Next, the laminated body is placed in an oven having a plurality of heating rolls maintained at 80 to 110° C., and the contact time with the heating rolls maintained at 110° C., which is the maximum heating temperature, in an oven maintained at 80° C. The heat treatment was carried out while being transported using a heating roll so that the total of the time was 1 second.
Thus, a long polarizing plate 1 in which a polarizer having a thickness of 5 μm was laminated on a polyester-based resin substrate was obtained. The elastic modulus of the polyester-based resin base material of the polarizing plate 1 was 3.15 GPa. When the polarizing plate 1 was subjected to the adhesion evaluation described above, no peeling from the glass occurred.

<Example 2>
A polarizing plate 2 was obtained in the same manner as in Example 1 except that the maximum heating temperature was 105° C. and the total contact time was 1 second. The elastic modulus of the polyester resin base material of the polarizing plate 2 was 2.85 GPa. The polarizing plate 2 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Example 3>
A polarizing plate 3 was obtained in the same manner as in Example 1 except that the maximum heating temperature was 102° C. and the total contact time was 1 second. The elastic modulus of the polyester resin base material of the polarizing plate 3 was 2.70 GPa. The polarizing plate 3 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Example 4>
In the same manner as in Example 1, except that the laminate was stretched in water using a stretching bath having a stretching bath temperature of 69°C, the maximum heating temperature was 105°C, and the total contact time was 1 second. A polarizing plate 4 was obtained. The elastic modulus of the polyester-based resin base material of the polarizing plate 4 was 2.72 GPa. The polarizing plate 4 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Comparative Example 1>
A polarizing plate 5 was obtained in the same manner as in Example 1 except that the maximum heating temperature was 100° C. and the total contact time was 1 second. The elastic modulus of the polyester resin base material of the polarizing plate 5 was 2.65 GPa. The polarizing plate 5 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Comparative Example 2>
A polarizing plate 6 was obtained in the same manner as in Example 1 except that the maximum heating temperature was 95° C. and the total contact time was 1 second. The elastic modulus of the polyester-based resin base material of the polarizing plate 6 was 2.37 GPa. The polarizing plate 6 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Comparative Example 3>
A polarizing plate 7 was obtained in the same manner as in Example 1 except that the temperature in the furnace was set to 60° C., the maximum heating temperature was set to 60° C., and the total contact time was set to 1 second. The elastic modulus of the polyester-based resin base material of the polarizing plate 7 was 2.10 GPa. The polarizing plate 7 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

<Comparative Example 4>
A polarizing plate 8 was obtained in the same manner as in Example 4 except that the maximum heating temperature was 102° C. and the total contact time was 1 second. The elastic modulus of the polyester resin base material of the polarizing plate 8 was 2.57 GPa. The polarizing plate 8 was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Comparative Example 5>
A polarizing plate 9 was obtained in the same manner as in Example 4 except that the maximum heating temperature was 100° C. and the total contact time was 1 second. The elastic modulus of the polyester resin base material of the polarizing plate 9 was 2.50 GPa. The polarizing plate 9 was subjected to the same evaluation as in Example 1. Table 1 shows the results.

As is clear from Table 1, the polarizing plate having an elastic modulus of 2.70 GPa or more did not peel off from the glass even when placed in a high-temperature and high-humidity environment.

The polarizing plate of the present invention is suitably used for image display devices such as liquid crystal display devices and organic EL display devices.

REFERENCE SIGNS LIST 10 polarizing plate 11 polyester resin substrate 12 polarizer

Claims (5)

Having a polyester resin base material and a polarizer laminated on one side of the polyester resin base material,
The thickness of the polarizer is 10 μm or less,
A method for producing a polarizing plate, wherein the elastic modulus of the polyester-based resin base material is 2.70 GPa or more,
forming a polyvinyl alcohol-based resin layer on one side of the polyester-based resin base material to form a laminate;
forming the polyvinyl alcohol-based resin layer into a polarizer by dyeing and stretching the laminate, and heat-treating the laminate of the polyester-based resin base material and the polarizer after the stretching. ,
The temperature of the drawing bath in the drawing is 67° C. or lower, and the maximum heating temperature in the heat treatment is 102° C. or higher, or
The temperature of the drawing bath in the drawing is 69° C. or lower, and the maximum heating temperature in the heat treatment is 105° C. or higher,
Manufacture of a polarizing plate, wherein in the heat treatment, the laminate is heated to the maximum heating temperature while being placed along a hot drum roll, and the time for which the maximum heating temperature is maintained is 0.2 seconds to 2 seconds. Method. 2. The method for producing a polarizing plate according to claim 1, wherein the polarizer is laminated on one side of the polyester-based resin base without an adhesive layer interposed therebetween. 3. The method for producing a polarizing plate according to claim 1, wherein an easy-adhesion layer is provided between the polyester-based resin base material and the polarizer. 4. The method for producing a polarizing plate according to claim 1, wherein the polyester-based resin substrate functions as a protective layer of the polarizer. A method for manufacturing an image display device, comprising the method for manufacturing a polarizing plate according to any one of claims 1 to 4.

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