TWI775958B - Polarizing plate, image display device, and manufacturing method of polarizing plate - Google Patents

Abstract

The present invention provides a method for manufacturing a polarizing plate, which has high adhesion to other optical components and can improve the display characteristics of an image display device. The method for producing a polarizing plate of the present invention is a method for producing a polarizing plate, the polarizing plate: having a polyester-based resin substrate; and a polarizer, which is laminated on one side of the polyester-based resin substrate and has a thickness of 10 μm or less; And the manufacturing method includes: dyeing and extending the laminate in which the polyvinyl alcohol-based resin layer is formed on one side of the polyester-based resin substrate to make the polyvinyl-alcohol-based resin layer into a polarizer; The laminated body of the resin substrate and the polarizer is subjected to heat treatment; wherein, 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 more.

Description

Polarizing plate, image display device, and manufacturing method of polarizing plate

The present invention relates to a polarizing plate, an image display device and a manufacturing method of the polarizing plate.

Background of the Invention A document proposes a method of producing a thin polarizer by forming a polyvinyl alcohol-based resin layer on a polyester-based resin substrate, extending and dyeing the laminate (for example, Patent Document 1). The manufacturing method of the polarizer is attracting attention because it can contribute to the thinning of, for example, an image display device.

The above-mentioned polarizer can be used in a state of being laminated on the above-mentioned 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 laminated body of the polyester-based resin substrate and the polarizer can be directly used as a polarizer without using a protective film for the polarizer, which can contribute to cost reduction of, for example, an image display device.

prior art literature Patent Literature Patent Document 1: Japanese Patent Laid-Open No. 2000-338329 Patent Document 2: Japanese Patent No. 4979833

Summary of Invention The problem to be solved by the invention However, the above-mentioned polarizing plate has insufficient adhesion with other optical members, and when it is used in an image display device, there is a problem of insufficient display characteristics.

The present invention is made in order to solve the above-mentioned conventional problems, and its main object is to provide a polarizing plate which has high adhesion to other optical members and can improve the display characteristics of an image display device; a manufacturing method of the polarizing plate, and An image display device provided with the polarizing plate.

means of solving problems The method for producing a polarizing plate of the present invention is a method for producing a polarizing plate comprising: a polyester-based resin substrate; and a polarizer, which is laminated on one side of the polyester-based resin substrate and has a thickness of 10 μm or less ; and the manufacturing method comprises: dyeing and extending a laminate having a polyvinyl alcohol-based resin layer formed on one side of the polyester-based resin substrate to make the polyvinyl-alcohol-based resin layer into a polarizer; and , heat-treating the laminate of the polyester-based resin substrate and the polarizer; wherein 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 more. In one embodiment, the maximum heating temperature in the above-mentioned heat treatment is 115°C or lower. According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate has: a polyester-based resin substrate, and a polarizer laminated on one side of the polyester-based resin substrate; wherein the polarizer has a thickness of 10 μm or less, and a haze value of less than 1.6%; and, The above-mentioned polarizer-side surface was bonded to glass through an adhesive and stored at 60° C./90%Rh for 500 hours, without peeling off from the above-mentioned glass. According to another aspect of the present invention, an image display device is provided. The image display device includes the above-mentioned polarizing plate.

Invention effect According to the present invention, a polarizing plate can be provided, which has high adhesion to other optical components and can improve the display characteristics of an image display device; a manufacturing method of the polarizing plate; and an image display device including the polarizing plate.

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

A. Manufacturing method of polarizing plate 1 is a schematic cross-sectional view of a polarizing plate produced by a method for producing a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes a polyester-based resin substrate 20 and a polarizer 10 laminated on one side of the polyester-based resin substrate 20 . The thickness of the polarizer 10 is 10 μm or less.

The manufacturing method of the polarizing plate 100 includes: dyeing and extending the laminate 200 ( FIG. 2 ) in which the polyvinyl alcohol-based resin layer (PVA-based resin layer) 11 is formed on one side of the polyester-based resin substrate 20 to The PVA-based resin layer 11 is used to form the polarizer 10 ; and the laminate of the polyester-based resin base 20 and the polarizer 10 is heat-treated. The above-mentioned stretching includes an underwater stretching treatment with a stretching ratio of 2.55 times or more, and the maximum heating temperature in the above-mentioned heat treatment is 100° C. or more. The maximum heating temperature of the above-mentioned heat treatment is preferably 115°C or lower. According to the above-mentioned manufacturing method, a polarizing plate can be obtained, which has both the adhesion with other optical members and the display characteristics of the image display device. The polarizing plate obtained by the conventional manufacturing method, that is, by extending and dyeing the laminate of the polyester-based resin base material and the PVA-based resin layer, cannot achieve both sufficient adhesion with other optical members and good image display device performance. Displays the condition of the characteristic. Specifically, when the polarizer-side surface of the polarizer produced by the above-mentioned conventional manufacturing method is attached to another optical member and placed in a high-temperature and high-humidity environment, both ends of the polarizer in the extending direction Parts may peel off from the optical member, or glare may be generated on the display screen when it is used in an image display device. According to the new findings of the present invention, it is known that by the above-mentioned production method, the degree of crystallinity and crystal size of the polyester resin base material of the polarizing plate can be controlled within an appropriate range, whereby the adhesion with other optical members can be achieved performance and display characteristics (anti-glare) of image display devices.

FIG. 3 is a schematic diagram showing a manufacturing process of a polarizing plate according to an embodiment. The manufacturing process of the polarizing plate of the present embodiment is represented by releasing the laminated body 200 of the polyester-based resin substrate 20 and the PVA-based resin layer 11 from the release part 101 , and immersing it in the rollers 111 and 112 . After the bath 110 of the boric acid aqueous solution (insolubility treatment), it is immersed in the bath 120 of a dichroic substance (iodine) and an aqueous solution of potassium iodide by the rollers 121 and 122 (dyeing treatment). Next, it is immersed in the bath 130 of the aqueous solution of boric acid and potassium iodide by the rollers 131 and 132 (crosslinking treatment). Next, while placing the layered body 200 in the stretching bath 140 of the boric acid aqueous solution, the rollers 141 and 142 having different speed ratios are stretched by applying tension in the longitudinal direction (longitudinal direction, conveying direction, and MD direction) (underwater stretching treatment). ). Next, the layered body 200 stretched in water is immersed in a bath 150 of an aqueous potassium iodide solution by means of rollers 151 and 152 (washing treatment), and then subjected to drying treatment (not shown in the drawing). Next, the laminated body 200 is put into the oven 160 (heat treatment), thereby producing the polarizing plate 100 of the present embodiment. After that, the obtained polarizing plate 100 is wound by the winding unit 170 . Although not shown in the drawings, the air stretching process may be performed before the insolubilization process is performed on the layered body 200 . In addition, the manufacturing process shown in FIG. 3 is only an example, and the frequency|count, order, etc. of the said process are not specifically limited.

A-1. Laminated product of polyester-based resin base material and PVA-based resin layer The laminate of the polyester-based resin base material and the PVA-based resin layer can be produced by an arbitrary and appropriate method. Preferably, a coating liquid containing a PVA-based resin is coated on a polyester-based resin substrate and dried, whereby a laminate in which a PVA-based resin layer is formed on one side of the polyester-based resin substrate can be obtained . In one embodiment, the composition for forming an easily bonding layer is coated on a polyester-based resin substrate and dried to form an easily bonding layer, and a PVA-based resin layer is formed on the easily bonding layer.

As the material for forming the polyester resin base material, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) can be used. , isophthalic acid, copolymerized PET (PET-G) containing cyclohexane ring-containing alicyclic dicarboxylic acids or alicyclic diols, etc., other polyesters, and their copolymers or blends things etc. Among them, amorphous (uncrystallized) PET or copolymerized PET is preferably used. Since these resins are amorphous in an unstretched state and have excellent stretchability suitable for high-rate stretching, heat resistance and dimensional stability can be imparted by crystallization by stretching and heating. In addition, it is possible to secure the heat resistance of a practical level to coat and dry the PVA-based resin in an unstretched state.

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, the crystallization of the PVA-based resin layer can be suppressed, and extensibility can be sufficiently ensured. Considering the viewpoints of plasticizing the polyester-based resin base material with water and smooth underwater stretching, the temperature is more preferably 120° C. or lower. In one embodiment, the glass transition temperature of the polyester-based resin substrate is preferably 60°C or higher. By using the polyester-based resin substrate, the polyester-based resin substrate can be prevented from being deformed (for example, uneven, slumped, wrinkled, etc.) during coating and drying of the coating liquid containing the PVA-based resin described later. and other adverse situations. In addition, the laminated body 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. In addition, glass transition temperature (Tg) is the value calculated|required based on JISK7121.

In one embodiment, the water absorption rate of the polyester-based resin substrate is preferably 0.2% or more, more preferably 0.3% or more. Such polyester-based resin substrates absorb water, and water acts as a plasticizer to plasticize. As a result, the elongation stress can be greatly reduced in water elongation, and the elongation is 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 deterioration of the appearance of the resulting laminate due to a marked decrease in the dimensional stability of the polyester-based resin base material during production. It is possible to prevent the PVA-based resin layer from being broken or peeled off from the polyester-based resin substrate when extended in water. In addition, the water absorption rate is the value calculated|required based on JISK7209.

The thickness of the polyester-based resin base material (thickness before extension described later) is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, when extending in water, the polyester-based resin substrate may take a long time to absorb water, thereby causing an excessive load on the extending.

Any appropriate resin can be used as the PVA-based resin forming the PVA-based resin layer. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of the PVA 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 is obtained according to JIS K 6726-1994. By using the PVA-based resin having the above degree of saponification, a polarizer excellent in durability can be obtained. When the degree of saponification is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be calculated|required based on JISK6726-1994.

The coating liquid containing the PVA-based resin means that a solution obtained by dissolving the above-mentioned PVA-based resin in a solvent is used. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylene glycol Amines such as diamine and ethylene triamine. These may 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 relative to 100 parts by weight of the solvent. As long as it is the said resin density|concentration, a uniform coating film which adheres to a polyester-type resin base material can be formed. In one embodiment, the coating liquid contains a halide. Any appropriate halide can be used as the above-mentioned halide. For example, iodide and sodium chloride are mentioned. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among them, potassium iodide is preferred. The amount of halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin, more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA resin. If the amount of the halide is more than 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may overflow and the polarizer finally produced may become cloudy. The laminate of the halide-containing PVA-based resin layer and the polyester-based resin substrate is stretched at high temperature (assisted stretching) in air before stretching in boric acid water, thereby promoting the PVA-based resin layer after the assisted stretching. Crystallization of PVA-based resins. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of orientation of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed more than when the PVA-based resin layer does not contain a halide. Thereby, the optical properties of the finally obtained polarizer can be improved.

Additives can also be mixed in the coating liquid. Examples of additives include plasticizers, surfactants, and the like. As a plasticizer, polyhydric alcohols, such as ethylene glycol and glycerol, are mentioned, for example. As a surfactant, a nonionic surfactant is mentioned, for example. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer. Moreover, as an additive, an easily attachable component is mentioned. The adhesiveness between the polyester-based resin substrate and the PVA-based resin layer can be improved by using the easy-adhesion component. As a result, inconveniences such as peeling of the PVA-based resin layer from the polyester-based base material can be suppressed, and dyeing and underwater stretching, which will be described later, can be performed favorably. As the easy-to-attach component, modified PVA such as acetylacetate modified PVA can be used.

As the coating method of the coating liquid, an arbitrary and appropriate method can be adopted. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a blade coating method (comma coating method, etc.) etc. are mentioned. The coating and 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 (eg, corona treatment, etc.), or the composition for forming an easily bonding layer (coating treatment) may be applied to the polyester-based resin substrate. ). The adhesiveness between the polyester-based resin base material and the PVA-based resin layer can be improved by performing the above-mentioned treatment. As a result, inconveniences such as peeling of the PVA-based resin layer from the polyester-based resin base material can be suppressed, and dyeing and stretching, which will be described later, can be performed favorably.

The composition for forming an easily bonding layer preferably contains a polyvinyl alcohol-based component. Arbitrary and appropriate PVA-type resin can be used for a polyvinyl alcohol-type component. Specifically, polyvinyl alcohol and modified polyvinyl alcohol may be mentioned. The modified polyvinyl alcohol includes, for example, polyvinyl alcohol modified with an acetylacetyl group, a carboxylic acid group, an acryl group and/or a urethane group. Among these, PVA modified with an acetyl acetyl group is suitable. A polymer having at least a repeating unit represented by the following general formula (I) is preferably used for the acetylacetate group-modified PVA.

[Chemical formula 1]

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 acetylacetate group-modified PVA is preferably 1000-10000, more preferably 1200-5000. The degree of saponification of the acetylacetate-modified PVA should preferably be above 97 mol%. The pH of the 4 wt % aqueous solution of the acetylacetate group-modified PVA is preferably 3.5 to 5.5.

The composition for forming an easily bonding layer may further contain a polyolefin-based component, a polyester-based component, a polyacrylic-based component, and the like according to the purpose and the like. The composition for forming an easily bonding layer preferably further contains a polyolefin-based component.

Arbitrary and appropriate polyolefin-type resin can be used for the said polyolefin-type component. The main component of the polyolefin-based resin, that is, the olefin component, includes, for example, olefin-based hydrocarbons having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, and 1-hexene. These may 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 preferably used, and ethylene is more preferably used.

Among the monomer components constituting the above-mentioned polyolefin-based resin, the proportion of the olefin component is preferably 50% by weight to 95% by weight.

The above-mentioned polyolefin-based resin preferably contains a carboxyl group and/or an acid anhydride group thereof. The above-mentioned polyolefin-based resin can be dispersed in water, so that the easy-adhesion layer can be formed smoothly. Examples of the monomer components having the functional group include unsaturated carboxylic acids and their anhydrides, half esters of unsaturated dicarboxylic acids, and half amides. Specific examples of these include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, and crotonic acid. The molecular weight of the polyolefin resin is, for example, 5,000 to 80,000.

In the composition for forming an easily bonding layer, the blending ratio of the polyvinyl alcohol-based component and the polyolefin-based component (the former: the latter (solid content)) is preferably 5:95 to 60:40, and more preferably 20:80 to 20:40. 50:50. When there are too many polyvinyl alcohol-type components, sufficient adhesiveness may not be acquired. Specifically, when the polarizer is peeled off from the polyester-based resin base material, the peeling force required for peeling off the polarizer may decrease and sufficient adhesion may not be obtained. On the other hand, when there are too few polyvinyl alcohol-type components, the external appearance of the polarizing plate obtained may be damaged. Specifically, when forming the easy-adhesive layer, there is a fear that problems such as cloudiness of the coating film may occur, and it may be difficult to obtain a polarizing plate excellent in appearance.

The composition for forming an easily bonding layer is preferably an aqueous system. The composition for forming an easily bonding layer may contain an organic solvent. Ethanol, isopropanol, etc. are mentioned as an organic solvent. The solid content concentration of the composition for forming an easily bonding layer is preferably 1.0% by weight to 10% by weight.

Arbitrary and appropriate methods can be employ|adopted for the coating method of the composition for easy bonding layer formation. After coating the composition for forming an easily bonding layer, the coating film may be dried. The drying temperature is, for example, 50°C or higher.

A-2. Air extension processing The air-stretching treatment includes a heat-roller stretching step in which the above-mentioned laminated body is conveyed in the longitudinal direction thereof while being stretched by the difference in peripheral speed between the heat-rollers. The in-air stretching process typically includes a zone stretching step and a thermal roll stretching step. In addition, the sequence of the area extending step and the heating roller extending step is not limited. The area extending step may be performed first, or the heating roller extending step may be performed first. The region extension step can also be omitted. In one embodiment, the area extending step and the heating roller extending step are performed in sequence.

The stretching temperature of the laminate can be set to an arbitrary and appropriate value according to the forming material of the polyester-based resin base material, the stretching method, and the like. The stretching temperature of the air stretching treatment is preferably above the glass transition temperature (Tg) of the polyester resin substrate, and the glass transition temperature (Tg)+10°C or higher of the polyester resin substrate is more suitable, especially Tg+15°C or higher. suitable. On the other hand, the upper limit of the stretching temperature of the laminate is preferably 170°C. Stretching at such a temperature can suppress rapid progress of crystallization of the PVA-based resin, thereby suppressing inconveniences caused by the crystallization (eg, hindering the orientation of the PVA-based resin layer due to elongation).

A-3. Insolubility Treatment The above-mentioned insolubilization treatment is performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. 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 relative to 100 parts by weight of water. The temperature of the insoluble bath (boric acid aqueous solution) is preferably 20°C to 50°C. The insolubilization treatment is preferably carried out before the above-mentioned stretching in water or the above-mentioned dyeing treatment.

A-4. Dyeing treatment The dyeing of the PVA-based resin layer is typically performed by adsorbing iodine to the PVA-based resin layer. The adsorption method includes, for example, a method of immersing a PVA-based resin layer (layered body) in an iodine-containing dyeing solution, a method of applying the dyeing solution to the PVA-based resin layer, and spraying the dyeing solution to PVA method on the resin layer, etc. A method of immersing the PVA-based resin layer (layered body) in the dyeing solution is preferably employed. This is because it can adsorb iodine well.

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

The dyeing treatment can be performed at an arbitrary and appropriate timing. It is more suitable to carry out before extending in water.

A-5. Cross-linking treatment The above-mentioned crosslinking treatment is typically performed by immersing the PVA-based resin layer (layered body) in an aqueous solution of boric acid. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the above dyeing treatment, it is preferable to further blend iodide. By blending the iodide, the elution of the iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of the iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 60°C. The cross-linking treatment is preferably carried out before the extension treatment in water. A more ideal embodiment is to carry out in-air extension treatment, dyeing treatment and cross-linking treatment in sequence.

A-6. Underwater extension treatment The manufacturing steps of the polarizing plate are as described above, and include: subjecting the laminate to an underwater stretching treatment in a stretching bath. Specifically, underwater extension is performed in a direction parallel to the air extension direction of the above-mentioned laminate. By stretching in water, it can be stretched at a lower temperature than the glass transition temperature of the polyester resin substrate or the PVA resin layer (representatively about 80°C), and the crystallization of the PVA resin layer can be suppressed. Simultaneous high-magnification extension. As a result, a polarizer having excellent optical properties (eg, degree of polarization) can be produced. In addition, in this specification, "parallel direction" includes the case of 0°±5.0°, preferably 0°±3.0°, more preferably 0°±1.0°.

The stretching ratio of the underwater stretching treatment is 2.55 times or more as described above, preferably 2.65 times or more, and more preferably 2.75 times or more. On the other hand, the upper limit of the stretching ratio is preferably 5.0 times, more preferably 5.5 times. If the elongation ratio in water is too high, the polarizer will be broken. By setting the elongation ratio within the above-mentioned range and setting the maximum heating temperature in the heat treatment described later within the predetermined range, it is possible to obtain a glass with a suppressed peeling-off from the glass and a sufficient haze value under a high-temperature and high-humidity environment. Low polarizer. Therefore, it is possible to obtain a polarizing plate which has both the adhesion with other optical members and the display characteristics (anti-glare) of the image display device.

The extension temperature of the water extension treatment is preferably 40°C to 85°C, more preferably 50°C to 70°C. As long as the temperature is as described above, the PVA-based resin layer can be inhibited from being dissolved, and at the same time, it can be stretched at a high rate. Specifically, as described above, in consideration of the relationship with the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the polyester-based resin substrate is preferably 60° C. or higher. At this time, if the stretching temperature is lower than 40° C., even if it is considered to plasticize the polyester-based resin base material with water, it may not be possible to stretch well. On the other hand, the higher the stretching temperature, the higher the solubility of the PVA-based resin layer, and there is a fear that excellent optical properties cannot be obtained. The immersion time for the layered body to be immersed in the stretching bath is preferably 15 seconds to 5 minutes.

As the stretching method of the underwater stretching treatment, an arbitrary and appropriate method can be adopted. Specifically, it can be a fixed end extension or a free end extension. The extending direction of the laminated body is substantially the extending direction (longitudinal direction) of the above-mentioned air extending. The extension of the laminate may be performed in one stage or in multiple stages.

The stretching in water is preferably performed by immersing the layered body in an aqueous solution of boric acid (stretching in water with boric acid). By using the boric acid aqueous solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity capable of withstanding the tension applied during stretching and water resistance insoluble in water. Specifically, boric acid generates tetrahydroxyboronic acid anion in an aqueous solution and can be cross-linked with PVA-based resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer and good extension can be obtained, and a polarizer having excellent optical properties (eg, degree of polarization) can be produced.

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

If a dichroic substance (represented by iodine) has been adsorbed on the PVA-based resin layer by dyeing treatment in advance, it is suitable to mix the iodide in the stretching bath (boric acid aqueous solution). By blending the iodide, the elution of the iodine adsorbed on the PVA-based resin layer can be suppressed. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among them, potassium iodide is preferred. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight, relative to 100 parts by weight of water.

By combining the above-mentioned polyester resin base material with water stretching (boric acid water stretching), high-magnification stretching is possible, and a polarizer having excellent optical properties (eg, degree of polarization) can be produced. Specifically, the maximum stretching ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more with respect to the original length of the laminate (including the aerial stretching ratio). In this specification, the "maximum stretching ratio" means the stretching ratio before the layered body breaks, and is a value lower than the value by 0.2 after confirming the stretching ratio at which the layered body breaks. In addition, the maximum stretching ratio of the laminate using the above-mentioned polyester resin base material is higher when it is stretched in water than when it is stretched only by air stretching.

A-7. Cleaning treatment Typically, the cleaning treatment can be performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. The drying temperature in the drying treatment is preferably 30°C to 100°C.

A-8. Heat treatment The heat treatment is performed after extending in water. The polyester-based resin base material can be crystallized by the heat treatment. The heat treatment is typically performed by heating the conveyance rollers arranged in the heating mechanism 160 (using a so-called hot roller roller (heat roller)) (heat roller heating method). In one embodiment, the heating mechanism 160 is an oven, but a heating method (oven heating method) by sending hot air into the oven may be used in combination. By using the hot roller heating method and the oven heating method together, rapid temperature changes between the hot rollers can be suppressed, and the shrinkage in the width direction of the laminate can be easily controlled. The temperature in the oven should be 30℃~100℃. Moreover, the heating time of the oven is preferably 1 second to 300 seconds. The wind speed of the hot air should be about 10m/s~30m/s. In addition, the wind speed is the wind speed in the oven, which can be measured by a miniature fan-blade digital anemometer.

Heating with a hot roller can suppress curling and produce a polarizer with an excellent appearance. Specifically, heating the layered body in a state where the layered body follows the hot roller can effectively promote the crystallization of the polyester-based resin base material and increase the degree of crystallinity, even at a relatively low heating temperature. , the crystallinity of the polyester resin substrate can still be well increased. As a result, the rigidity of the polyester-based resin base material increases, and the PVA-based resin layer is in a state where it can withstand the shrinkage of the PVA-based resin layer due to heating, thereby suppressing curling. Moreover, since the laminated body can be heated while maintaining a flat state by using a hot roller, not only curling but also wrinkle generation can be suppressed.

In the heating mechanism 160, a plurality of heat roller rollers can be arranged, and each heat roller roller can be set to different temperatures. In the heating mechanism 160, usually 2 to 20 heat rollers can be arranged, and 4 to 10 are more preferably arranged. The contact time (total contact time) between the laminate and the hot roller is preferably 1 second to 300 seconds. The heating conditions can be controlled by adjusting the temperature of the hot rollers, the number of the hot rollers, and the contact time with the hot rollers.

Among the plurality of heat rollers, when the temperature of the heat roller set to the highest temperature is the "maximum heating temperature", the maximum heating temperature is 100°C or higher, more preferably 105°C or higher. 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-mentioned range, and setting the stretching ratio in the above-mentioned underwater stretching treatment within the predetermined range, it is possible to obtain a situation where peeling from glass is suppressed in a high temperature and high humidity environment. And the haze value is low enough polarizing plate. Therefore, it is possible to obtain a polarizing plate which has both the adhesion with other optical members and the display characteristics (anti-glare) of the image display device. In addition, the temperature of the hot roller can be measured by a contact thermometer. The contact time of the laminated body to the hot rollers kept at the highest heating temperature (when there are multiple hot rollers with the highest heating temperature, the total contact time) is preferably 0.2 seconds to 2 seconds, more preferably 0.5 seconds ~2 seconds. In addition, "contact time" means the time until it leaves|separates after the arbitrary point on a laminated body contacts the outer peripheral surface of the heat roll roll member which was maintained at the highest heating temperature.

B. The composition of the polarizing plate The polarizing plate has, as described above, a polyester-based resin substrate, and a polarizer laminated on one side of the polyester-based resin substrate and having a thickness of 10 μm or less. The haze value of the polarizing plate of the present invention is less than 1.6%. The polarizing plate does not peel off from the glass after the polarizer side surface is bonded to the glass through an acrylic adhesive and stored at 60°C/90%Rh for 500 hours. The thickness of the polyester resin base material is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm. The polarizer is preferably laminated on one side of the polyester resin base material (in other words, without interposing an adhesive layer). The polarizing plate preferably has an easy-bonding layer between the polyester-based resin substrate and the polarizer. The polarizing plate may also have a protective film on the opposite side of the polarizer to the polyester-based resin substrate. The polyester-based resin base material functions as a protective layer of the polarizer. The polarizing plate of the present embodiment has high adhesion to other optical members when the polarizer-side surface is bonded to the optical member, can prevent peeling in a high temperature and high humidity environment, and can prevent the display screen of the image display device from being damaged. glare. Therefore, the polarizing plate of the present invention can achieve both the adhesion with other optical members and the display characteristics (anti-glare) of the image display device.

The polarizer is essentially a PVA-based resin layer in which iodine is oriented by adsorption. The thickness of the polarizer is 10 μm or less as described above, 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 optical properties of the resulting polarizer may be degraded. The polarizer should exhibit absorption dichroism at any wavelength from 380nm to 780nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more, and more preferably 42.0% or more. The degree of polarization of the polarizer should preferably be above 99.8%, preferably above 99.9%, and more preferably above 99.95%.

Examples of materials for forming the protective film include (meth)acrylic resins, cellulose-based resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin-based resins, olefin-based resins such as polypropylene, and polyterephthalene. Ester-based resins such as ethylene formate-based resins, polyamide-based resins, polycarbonate-based resins, copolymer resins of these, and the like. The thickness of the protective film is preferably 10 μm to 100 μm.

The easily bonding layer may be a layer formed substantially only from the composition for forming an easily bonding layer, or may be a layer or region in which the composition for forming an easily bonding layer and a polarizer forming material are mixed (including compatible). By forming the easily adhesive layer, excellent adhesion can be obtained. The thickness of the easy-bonding layer should preferably be set to about 0.05 μm to 1 μm. The easily bonding layer can be confirmed by, for example, observing a cross section of a polarizing plate with a scanning electron microscope (SEM).

C. Video display device The polarizing plate described in the above item B produced by the manufacturing method described in the above item A can be applied to image display devices such as liquid crystal display devices. Therefore, the present invention includes an image display device using the above-mentioned polarizing plate. An image display device according to an embodiment of the present invention includes the polarizing plate described in the above-mentioned item B. Example

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. In addition, the measurement method and evaluation method of each characteristic are as follows. (1) Thickness Measured using a digital micrometer (manufactured by Anritsu, product name "KC-351C"). (2) Anti-glare evaluation The haze value of the polarizing plate of each Example and the comparative example was measured by the method prescribed|regulated by JIS 7136 using a haze meter (made by Murakami Color Research Institute, trade name "HN-150"). In the evaluation of the anti-glare property of the polarizing plate, if the haze value was less than 1.6%, it was regarded as good (○), and when the haze value was 1.6% or more, it was regarded as poor (x). (3) Adhesion evaluation 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 prepare samples for evaluation. The polarizer side of the above-mentioned evaluation sample was pasted with an acrylic adhesive (thickness: 20 μm, manufactured by Nitto Denko Co., Ltd., product name "General-purpose adhesive for polarizers"), and stored at 60°C/90°C. After 500 hours at %Rh, it was confirmed whether or not the edge of the sample for evaluation was peeled off from the glass. Then, when the evaluation sample peeled off from the glass, the length of the peeled portion (peeling length) was measured. In the evaluation of the adhesion of the polarizing plate, when the edge of the sample for evaluation was not peeled off from the glass, it was regarded as good (◯), and when the edge of the sample for evaluation was peeled from the glass, it was regarded as poor (x).

<Example 1> The polyester-based resin base material was a long-length amorphous copolyethylene terephthalate (IPA copolyethylene terephthalate) film (thickness: 100 μm, IPA modification degree: 5 mol%) ). (modification degree=[ethylene isophthalate unit]/[ethylene terephthalate unit+ethylene isophthalate unit]) Corona treatment is performed on one side of the polyester resin base material (Treatment condition: 50W·min/m ² ), the modified polyolefin resin of acetyl acetyl group modified polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") was dispersed in water A mixed solution (solid content concentration: 4.0%) obtained by mixing pure water (Unitika Corporation, trade name "ARROW BASE SE1030N") was applied to the corona-treated surface so that the thickness after drying was 2000 nm. The undercoat layer was formed by drying at 65°C for 2 minutes. Here, the mixing ratio of the solid content of the acetylacetate-modified PVA and the modified polyolefin in the mixed solution is 30:70. Next, at 25°C, 90 parts by weight of PVA (polymerization degree 4200, saponification degree 99.2 mol %) and acetylacetate modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") 10 parts by weight of PVA-based resin, and an aqueous solution of 13 parts by weight of potassium iodide with respect to 100 parts by weight of PVA-based resin, and dried at 60°C for 3 minutes to form a thickness 13μm PVA-based resin layer. A layered body was produced as described above. In an oven at 140° C., the obtained layered body was uniaxially stretched at the free end twice in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds (assisted in-air stretching). Next, the layered body was immersed in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubility treatment). Next, it was immersed in a dyeing bath (aqueous iodine solution obtained by mixing 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 in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (crosslinking treatment) at a liquid temperature of 40°C. ). Then, the layered body was immersed in a stretching bath (stretching bath temperature: 67° C.) of a boric acid aqueous solution (an aqueous solution prepared by blending 3 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water). , while performing uniaxial stretching to 2.75 times (total stretching ratio: 5.5 times) in the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds (underwater stretching treatment). Then, the layered body was immersed in a cleaning bath (aqueous solution obtained by mixing 3.5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30°C (cleaning treatment). Next, in an oven having a plurality of heating rollers kept at 80 to 100°C and kept at 80°C, the contact time of the laminate with the heating rollers kept at 100°C was 1 second in total, The heat treatment is performed while conveying the laminated body using a heating roller. The elongated polarizing plate 1 in which the polarizer of thickness 5 micrometers was laminated|stacked on the polyester resin base material in the above-mentioned way was produced. The polarizing plate 1 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Example 2> Polarizing plate 2 was produced in the same manner as in Example 1, except that the maximum heating temperature was set to 105° C. and the total contact time was set to 1 second. The polarizing plate 2 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Example 3> Polarizing plate 3 was produced in the same manner as in Example 1, except that the maximum heating temperature was set to 110° C. and the total contact time was set to 1 second. The polarizing plate 3 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Example 4> 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 stretching ratio: 5.1 times) while being immersed in a stretching bath (underwater stretching treatment). The polarizing plate 4 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 1> Polarizing plate 5 was produced in the same manner as in Example 1, except that the maximum heating temperature was set to 80° C. and the total contact time was set to 1 second. The polarizing plate 5 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 2> Polarizing plate 6 was produced in the same manner as in Example 1, except that the maximum heating temperature was set to 95° C. and the total contact time was set to 1 second. The polarizing plate 6 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

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

<Comparative Example 4> Polarizing plate 8 was produced 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 used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 5> Polarizing plate 9 was produced in the same manner as in Comparative Example 3, except that the maximum heating temperature was set to 100° C. and the total contact time was set to 1 second. The polarizing plate 9 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 6> A polarizing plate 10 was produced in the same manner as in Comparative Example 3, except that the maximum heating temperature was set to 105° C. and the total contact time was set to 1 second. The polarizing plate 10 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 7> A polarizing plate 11 was produced in the same manner as in Comparative Example 3, except that the maximum heating temperature was set to 110° C. and the total contact time was set to 1 second. The polarizing plate 11 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 8> The layered body was stretched 2.6 times in the longitudinal direction in an oven (assisted stretching in the air), and further stretched 2.10 times in the longitudinal direction while being immersed in a stretching bath (total stretching ratio: 5.5 times) (underwater stretching treatment), other than that The polarizing plate 12 was produced in the same manner as in Example 1. The polarizing plate 12 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

<Comparative Example 9> The layered body was stretched 2.4 times in the longitudinal direction in an oven (assisted stretching in the air), and further stretched 2.50 times in the longitudinal direction while being immersed in a stretching bath (total stretching ratio: 6.0 times) (underwater stretching treatment), other than that In the same manner as in Example 1, a polarizing plate 13 was produced. The polarizing plate 13 was used for evaluation of haze value and adhesion. The results are listed in Table 1.

[Table 1]

As apparent from Table 1, the anti-glare property and the adhesiveness of the polarizing plate obtained by setting the underwater stretching ratio to 2.55 times or more and the maximum heating temperature in the heat treatment to 100° C. or more were favorable.

industrial availability The polarizing plate produced by the manufacturing method of the present invention can be suitably used in image display devices such as liquid crystal display devices and organic EL display devices.

10‧‧‧Polarizer 11‧‧‧PVA resin layer 20‧‧‧Polyester resin substrate 100‧‧‧Polarizer 101‧‧‧Release Department 110‧‧‧Bath of aqueous solution of boric acid 111, 112, 121, 122, 131, 132, 141, 142, 151, 152‧‧‧Rollers 120‧‧‧Aqueous bath of dichroic substance (iodine) and potassium iodide 130‧‧‧Bath of aqueous solution of boric acid and potassium iodide 140‧‧‧Extension bath of boric acid aqueous solution 150‧‧‧Bath of potassium iodide aqueous solution 160‧‧‧Oven (heating mechanism) 170‧‧‧Coiler 200‧‧‧Laminate

FIG. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. 2 is a schematic cross-sectional view of a laminate of a polyester-based resin substrate and a PVA-based resin layer used in a method for producing a polarizing plate according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing a manufacturing process of a polarizing plate according to an embodiment.

10‧‧‧Polarizer

20‧‧‧Polyester resin substrate

100‧‧‧Polarizer

Claims (2)

A manufacturing method of a polarizing plate, the polarizing plate has: a polyester resin base material; and a polarizer, which is laminated on one side of the polyester resin base material and has a thickness of 10 μm or less; and the manufacturing method comprises: adding the aforementioned dyeing and extending a laminate having a polyvinyl alcohol-based resin layer formed on one side of a polyester-based resin substrate to make the polyvinyl-alcohol-based resin layer into a polarizer; and combining the polyester-based resin substrate with the aforementioned The laminated body of the polarizer is subjected to heat treatment; wherein, the stretching includes an underwater stretching treatment with a stretching ratio of 2.55 times or more, the maximum heating temperature in the heating treatment is 100°C or more, and the heating treatment is maintained at the time at the maximum heating temperature 0.2 seconds to 2 seconds. The manufacturing method of a polarizing plate according to claim 1, wherein the maximum heating temperature in the aforementioned heating treatment is 115°C or lower.

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