JP7240092B2 - 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, the polarizing plate as described above has insufficient adhesion to other optical members, and furthermore, has problems of insufficient display characteristics when used in an image display device.

The present invention has been made to solve the above-mentioned conventional problems, and the main object thereof is to provide a polarizing plate that has high adhesion to other optical members and that can improve the display characteristics of an image display device. An object of the present invention is to provide a method for manufacturing such a polarizing plate and an image display device having such a polarizing plate.

The method for producing a polarizing plate of the present invention is a method for producing a polarizing plate having a polyester-based resin substrate and a polarizer having a thickness of 10 μm or less laminated on one side of the polyester-based resin substrate, wherein the polyester-based A laminate in which a polyvinyl alcohol-based resin layer is formed on one side of a resin substrate is dyed and stretched to make the polyvinyl alcohol-based resin layer a polarizer, and the polyester-based resin substrate and the polarizer. The above stretching includes an underwater stretching treatment with a draw ratio of 2.55 times or more, and the maximum heating temperature in the above heat treatment is 100° C. or higher.
In one embodiment, the maximum heating temperature in the heat treatment is 115° C. or lower.
According to another aspect of the invention, a polarizing plate is provided. This polarizing plate has a polyester-based resin base material and a polarizer laminated on one side of the polyester-based resin base material, and the polarizer has a thickness of 10 μm or less and a haze value of less than 1.6%. When the surface on the polarizer side is adhered to glass via an adhesive and stored at 60° C./90% Rh for 500 hours, no separation from the glass occurs.
According to another aspect of the present invention, an image display device is provided. This image display device has the above polarizing plate.

ADVANTAGE OF THE INVENTION According to this invention, the polarizing plate which has high adhesiveness with other optical members and can improve the display characteristic of an image display apparatus, the manufacturing method of such a polarizing plate, and such a polarizing plate are provided. It is possible to provide an image display device with

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the laminated body of the polyester-type resin base material and PVA-type resin layer used with the manufacturing method of the polarizing plate by one Embodiment of this invention. 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. Method for Manufacturing Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate obtained by a method for manufacturing a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 has a polyester-based resin base material 20 and a polarizer 10 laminated on one side of the polyester-based resin base material 20 . The thickness of the polarizer 10 is 10 μm or less.

The polarizing plate 100 is produced by dyeing and stretching a laminate 200 ( FIG. 2 ) in which a polyvinyl alcohol-based resin layer (PVA-based resin layer) 11 is formed on one side of a polyester-based resin base material 20 to form a PVA-based layer. It includes using the resin layer 11 as the polarizer 10 and heat-treating the laminate of the polyester-based resin base material 20 and the polarizer 10 . The stretching includes an underwater stretching treatment with a stretching ratio of 2.55 times or more, and the maximum heating temperature in the heating treatment is 100° C. or higher. The maximum heating temperature in the heat treatment is preferably 115° C. or lower. According to the above manufacturing method, it is possible to obtain a polarizing plate that achieves both adhesion with other optical members and display characteristics of an image display device. A polarizing plate obtained by a conventional manufacturing method, that is, by stretching and dyeing a laminate of a polyester-based resin base material and a PVA-based resin layer, has sufficient adhesion to other optical members and is suitable for image display devices. In some cases, it was not possible to achieve both good display characteristics. Specifically, when the polarizing plate obtained by the conventional manufacturing method as described above is placed in a high-temperature and high-humidity environment with the polarizer-side surface attached to another optical member, Peeling from the optical member may occur at both ends, or glare may occur on the display screen when used in an image display device. According to the new findings of the present invention, the crystallinity and crystal size of the polyester-based resin base material of the polarizing plate can be controlled within appropriate ranges by the above-described manufacturing method, thereby making it possible to produce the polarizing plate with other optical members. and the display characteristics (anti-glare properties) of the image display device can be achieved at the same time.

FIG. 3 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 200 of the polyester-based resin base material 20 and the PVA-based resin layer 11 is delivered from the delivery section 101, and the boric acid aqueous solution is applied by the rolls 111 and 112. (insolubilization treatment), and then immersed by rolls 121 and 122 in a 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, the laminate 200 is immersed in a drawing bath 140 of an aqueous boric acid solution, and stretched by applying tension in the longitudinal direction (longitudinal direction, transport direction, MD direction) with rolls 141 and 142 having different speed ratios ( stretching treatment in water). Next, the submerged stretched laminate 200 is 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 100 of the present embodiment is obtained by placing the laminate 200 in an oven 160 (heating treatment). After that, the obtained polarizing plate 100 is wound by the winding section 170 . Although illustration is omitted, the laminate 200 may be stretched in the air before being subjected to the insolubilization treatment. It should be noted that the manufacturing process shown in FIG. 3 is an example, and the number of times and order of the above processes are not particularly limited.

A-1. Laminate of polyester-based resin substrate and PVA-based resin layer A laminate of the polyester-based resin substrate and PVA-based resin layer can be produced by any appropriate method. Preferably, a laminate having a PVA-based resin layer formed on one side of the polyester-based resin substrate can be obtained by applying a coating liquid containing the PVA-based resin onto the polyester-based resin substrate 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. .

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-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.

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.

A coating liquid containing a PVA-based resin 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.

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.

A-2. Aerial Stretching Processing The aerial stretching processing includes a hot roll stretching step in which the laminate is stretched by a difference in peripheral speed between hot rolls while being transported in its 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.

A-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.

A-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.

A-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.

A-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, the laminate is stretched in water in a direction parallel to the direction in which the laminate is stretched in the air. 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 draw ratio in the underwater drawing treatment is, as described above, 2.55 times or more, more preferably 2.65 times or more, and still more preferably 2.75 times or more. On the other hand, the upper limit of the draw ratio is preferably 5.0 times, more preferably 5.5 times. If the draw ratio in water is too high, there is a problem that the polarizer is broken. By setting the draw ratio within the above range and setting the maximum heating temperature in the heat treatment described later within a predetermined range, peeling from the glass in a high temperature and high humidity environment is suppressed, and the haze value is reduced. A sufficiently low polarizer can be obtained. Therefore, it is possible to obtain a polarizing plate that satisfies both adhesion to other optical members and display characteristics (anti-glare properties) of an image display device.

The stretching temperature in the underwater stretching treatment is preferably 40°C to 85°C, more preferably 50°C to 70°C. 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 stretching temperature, 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, and still more preferably 6.0 times or more (including the in-air draw ratio) with respect to the original length of the laminate. 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.

A-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.

A-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 of the laminate in the width direction 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 laminate 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 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 layered product can be heated while being kept in a flat state, 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 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.

The maximum heating temperature is 100° C. or higher, more preferably 105° C. or higher, 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 upper limit of the maximum heating temperature is preferably 115°C. By setting the maximum heating temperature in the heat treatment within the above range and setting the draw ratio in the above-described underwater drawing treatment within a predetermined range, peeling from the glass in a high-temperature and high-humidity environment is suppressed, and , a polarizing plate with a sufficiently low haze value can be obtained. Therefore, it is possible to obtain a polarizing plate that satisfies both adhesion to other optical members and display characteristics (anti-glare properties) of an image display device. 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.

B. Configuration of Polarizing Plate As described above, the polarizing plate has a polyester-based resin base material and a polarizer having a thickness of 10 μm or less laminated on one side of the polyester-based resin base material. The haze value of the polarizing plate of the invention is less than 1.6%. The polarizing plate does not peel off from the glass when the polarizer side surface is adhered to the glass via an acrylic pressure-sensitive adhesive and stored at 60° C./90% Rh for 500 hours. The thickness of the polyester resin substrate is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm. The polarizer is preferably laminated on one surface of the polyester-based resin substrate (in other words, without an adhesive layer interposed therebetween). The polarizing plate preferably has an easy-adhesion layer between the polyester-based resin substrate and the polarizer. The polarizing plate may have a protective film on the opposite side of the polarizer to the polyester-based resin substrate. A polyester-based resin substrate typically functions as a protective layer of a polarizer. The polarizing plate of the present embodiment has high adhesion to another optical member when the polarizer-side surface is attached to the other optical member, and can suppress peeling in a high-temperature, high-humidity environment. It is possible to suppress glare on the display screen of the device. That is, the polarizing plate of the present invention can achieve both adhesion with other optical members and display properties (anti-glare properties) of image display devices.

A polarizer is substantially a 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.

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.

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).

C. Image Display Device The polarizing plate described in the above item B obtained by the manufacturing method described in the above item A 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 described in item B 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) Evaluation of antiglare property The haze value of the polarizing plate of each example and comparative example was measured using a haze meter (manufactured by Murakami Color Science Laboratory Co., Ltd., trade name "HN-150") according to the method specified in JIS 7136. It was measured. The antiglare property of the polarizing plate was evaluated as good (○) when the haze value was less than 1.6%, and as poor (x) when the haze value was 1.6% or more.
(3) Evaluation of Adhesion The elongated polarizing plates obtained in Examples and Comparative Examples were cut into a size of 100 mm (MD direction)×100 mm (TD direction) to obtain an evaluation sample. The polarizer side of the evaluation sample was laminated to the glass via an acrylic adhesive (thickness 20 μm, manufactured by Nitto Denko Corporation, product name “general-purpose adhesive for polarizing plate”), and at 60 ° C./90% Rh. After storage for 500 hours, the presence or absence of peeling from the glass at the edge of the evaluation sample was checked. Moreover, when the sample for evaluation was peeled off from the glass, the length of the peeled portion (peeled length) was measured. The adhesion of the polarizing plate was evaluated as good (○) when there was no peeling from the glass at the edge of the evaluation sample, and poor (×) when there was peeling from the glass at the edge of the evaluation sample. and

<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 liquid 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 laminate is placed in an oven maintained at 80°C with a plurality of heated rolls maintained at 80 to 100°C for a total contact time of 1 second with the heated rolls maintained at 100°C. It was heat-treated while being transported using a heating roll.
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 polarizing plate 1 was evaluated for haze value and adhesion. Table 1 shows the results.

<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 polarizing plate 2 was evaluated for haze value and adhesion. 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 110° C. and the total contact time was 1 second. The polarizing plate 3 was evaluated for haze value and adhesion. Table 1 shows the results.

<Example 4>
A polarizing plate 4 was obtained in the same manner as in Example 2, except that the laminate was stretched 2.55 times in the longitudinal direction (total stretch ratio: 5.1 times) while being immersed in a stretching bath (stretching treatment in water). rice field. The polarizing plate 4 was evaluated for haze value and adhesion. 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 80° C. and the total contact time was 1 second. The polarizing plate 5 was evaluated for haze value and adhesion. 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 polarizing plate 6 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 3>
The laminate was stretched 2.4 times in the longitudinal direction in an oven (in-air auxiliary stretching), and stretched 2.30 times in the longitudinal direction (total draw ratio: 5.5 times) while being immersed in a stretching bath ( A polarizing plate 7 was obtained in the same manner as in Example 1 except that the stretching treatment in water), the maximum heating temperature was 65° C., and the total contact time was 1 second. The polarizing plate 7 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 4>
A polarizing plate 8 was obtained in the same manner as in Comparative Example 3 except that the maximum heating temperature was 75° C. and the total contact time was 1 second. The polarizing plate 8 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 5>
A polarizing plate 9 was obtained in the same manner as in Comparative Example 3 except that the maximum heating temperature was 100° C. and the total contact time was 1 second. The polarizing plate 9 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 6>
A polarizing plate 10 was obtained in the same manner as in Comparative Example 3 except that the maximum heating temperature was 105° C. and the total contact time was 1 second. The polarizing plate 10 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 7>
A polarizing plate 11 was obtained in the same manner as in Comparative Example 3 except that the maximum heating temperature was 110° C. and the total contact time was 1 second. The polarizing plate 11 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 8>
The laminate was stretched 2.6 times in the longitudinal direction in an oven (in-air auxiliary stretching), and stretched 2.10 times in the longitudinal direction (total draw ratio: 5.5 times) while being immersed in a stretching bath ( A polarizing plate 12 was obtained in the same manner as in Example 1 except for the stretching treatment in water). The polarizing plate 12 was evaluated for haze value and adhesion. Table 1 shows the results.

<Comparative Example 9>
The laminate was stretched 2.4 times in the longitudinal direction in an oven (in-air auxiliary stretching), and stretched 2.50 times in the longitudinal direction (total draw ratio: 6.0 times) while being immersed in a stretching bath ( A polarizing plate 13 was obtained in the same manner as in Example 1 except for the stretching treatment in water). The polarizing plate 13 was evaluated for haze value and adhesion. Table 1 shows the results.

As is clear from Table 1, the polarizing plate obtained by setting the stretching ratio in water to 2.55 times or more and setting the maximum heating temperature in the heat treatment to 100° C. or more has good antiglare properties and adhesion. there were.

The polarizing plate manufactured by the manufacturing method 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 polarizer 11 PVA-based resin layer 20 polyester-based resin substrate 100 polarizing plate 200 laminate

Claims (2)

A method for producing a polarizing plate having a polyester-based resin substrate and a polarizer having a thickness of 10 μm or less laminated on one side of the polyester-based resin substrate,
By dyeing and stretching a laminate in which a polyvinyl alcohol-based resin layer is formed on one side of the polyester-based resin base material, the polyvinyl alcohol-based resin layer is used as a polarizer, and the polyester-based resin base material and the including heat-treating the laminate with the polarizer,
The stretching includes an underwater stretching treatment with a stretching ratio of 2.55 times or more and 2.75 times or less , and an air stretching treatment performed before the underwater stretching treatment, and the total stretching ratio of the stretching is 5. .0 times or more,
The maximum heating temperature in the heat treatment is 100 ° C. or higher,
The heat treatment is performed after the underwater stretching treatment,
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.
A method for manufacturing a polarizing plate. 2. The method for producing a polarizing plate according to claim 1, wherein the maximum heating temperature in said heat treatment is 115[deg.] C. or less.

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