TW201935047A - Polarizing plate, image display device, and production method for polarizing plate - Google Patents

Abstract

Provided is a polarizing plate having little heat shrinkage behavior and having suppressed peeling. The polarizing plate has a polyester resin base material and a polarizer laminated on one side of the polyester resin base material. The polarizer thickness is no more than 10 [mu]m and the polyester resin base material has an elastic modulus of at least 2.70 GPa.

Description

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

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

BACKGROUND OF THE INVENTION Literatures have proposed a method of forming a polarizer by forming a polyvinyl alcohol resin layer on a polyester resin substrate and extending and dyeing the laminate (for example, Patent Document 1). The manufacturing method of the polarizer can attract attention, for example, for reducing the thickness of an image display device.

The said polarizer can be used in the state laminated | stacked on the said polyester resin base material, and at this time, a polyester resin base material is used as a protective layer of a polarizer (patent document 2). Therefore, the laminated body of the polyester-based resin substrate and the polarizer can be directly used as a polarizing plate without being used for attaching a protective film to the polarizer, which can contribute to cost reduction of, for example, an image display device.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 2000-338329 Patent Literature 2: Japanese Patent No. 4798833

SUMMARY OF THE INVENTION Problems to be Solved by the Invention However, when the surface of the polarizer side of the polarizing plate is bonded to another optical member such as a display unit or a retardation plate through an adhesive, the heat shrinkage behavior of the polyester resin substrate is large In some cases, the polarizer may peel off under high temperature and high humidity.

The present invention has been made in order to solve the above-mentioned conventional problems, and its main object is to provide a polarizing plate with small thermal shrinkage behavior and suppressed peeling, an image display device including the polarizing plate, and a method of manufacturing the polarizing plate.

Means for Solving the Problems The polarizing plate of the present invention includes a polyester resin substrate and a polarizer laminated on one side of the polyester resin substrate; wherein the thickness of the polarizer is 10 μm or less, and The coefficient of elasticity of the polyester-based resin substrate is 2.70 GPa or more.
In one embodiment, the polarizer is laminated on one side of the polyester-based resin substrate without an adhesive layer therebetween.
In one embodiment, an easy-adhesion layer is provided between the polyester-based resin substrate and the polarizer.
In one embodiment, the polyester-based resin substrate functions as a protective layer of the polarizer.
According to another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned polarizing plate.
According to another aspect of the present invention, a method for manufacturing the above-mentioned polarizing plate can be provided. The manufacturing method includes: forming a laminated body by forming a polyvinyl alcohol-based resin layer on one side of the polyester-based resin substrate; and dyeing and extending the laminated body to make the polyvinyl alcohol-based resin layer into a polarizer And, after the stretching, heat-treating the laminated body of the polyester-based resin substrate and the polarizer; wherein the temperature of the stretching bath in the stretching is 67 ° C. or lower and the highest heating temperature in the heating process The temperature is 102 ° C or higher, or the temperature of the stretching bath in the stretching is 69 ° C or lower, and the maximum heating temperature in the heat treatment is 105 ° C or higher.

Advantageous Effects of Invention According to the present invention, it is possible to provide a polarizing plate having a small thermal shrinkage behavior and suppressed peeling, an image display device including the polarizing plate, and a method for manufacturing the polarizing plate.

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

A. Overall Structure of Polarizing Plate FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. As shown in FIG. 1, the polarizing plate 10 includes a polyester-based resin substrate 11 and a polarizer 12 laminated on one side of the polyester-based resin substrate 11. The thickness of the polarizer 12 is 10 μm or less. The elastic modulus of the polyester-based resin substrate 11 is 2.70 GPa or more. The elastic modulus of the polyester-based resin substrate 11 is measured by a nano-indentation method using an indentation tester (a nano-indentation tester on the representative). More specifically, the coefficient of elasticity (E) of the polyester-based resin substrate 11 is a displacement-load hysteresis curve obtained by pressing a probe (indenter) against the surface of the polyester-based resin substrate as a measurement target, and The contact rigidity S obtained from the displacement-load hysteresis curve and the contact projection area A between the indenter and the polyester-based resin substrate are calculated by the following formula.
E = S × π ^1/2 / 2A ^1/2
The polarizer 12 is preferably laminated on one side of the polyester-based resin substrate 11 (in other words, without interposing the adhesive layer). The polarizing plate 10 is preferably provided with an easy-adhesion layer between the polyester-based resin substrate 11 and the polarizer 12 (not shown in the drawings). The polarizing plate 10 may have a protective film (not shown in the drawings) on the side of the polarizer 12 opposite to the polyester-based resin substrate 11. The polyester-based resin substrate 11 functions as a protective layer of the polarizer 12 in a representative manner. In the conventional polarizing plate, when the polarizer-side surface is attached to another optical member and placed in a high-temperature and high-humidity environment, both ends of the polarizing plate in the extending direction may peel off from the optical member. In contrast, when the polarizing plate 10 of this embodiment is bonded to the other side of the polarizer 12 surface, the thermal shrinkage behavior of the polyester resin base material 11 is small, and it can be suppressed in a high temperature and high humidity environment. Flaking.

B. Polarizer The polarizer is essentially a polyvinyl alcohol-based resin layer (PVA-based resin layer) whose iodine is adsorbed and oriented. The thickness of the polarizer is 10 μm or less as described above, and is 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, and more preferably 1.5 μm or more. If the thickness is too thin, the optical characteristics of the obtained polarizer may decrease. The polarizer should exhibit absorption dichroism at any wavelength of 380nm ~ 780nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more, and even more preferably 42.0% or more. The degree of polarization of the polarizer should be 99.8% or more, more preferably 99.9% or more, and more preferably 99.95% or more.

As the PVA-based resin forming the PVA-based resin layer, any appropriate resin can be used. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification is determined in accordance with JIS K 6726-1994. By using the PVA-based resin having the saponification degree, a polarizer having excellent durability can be obtained. When the saponification degree 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 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

C. Polyester-based resin substrate As described above, the polyester-based resin substrate has an elastic modulus of 2.70 GPa or more. The above-mentioned elastic coefficient should preferably be 2.70GPa ~ 4.50GPa, more preferably 2.80GPa ~ 3.90GPa. This can suppress shrinkage of the polyester-based resin substrate under a high-temperature and high-humidity environment. As a result, when the polarizing plate is bonded to the optical member, peeling of the polyester-based resin substrate from the optical member can be suppressed. The above-mentioned elastic coefficient can be determined by appropriately setting the temperature of the stretching bath when the laminated body of the polyester resin base material and the polyvinyl alcohol resin layer is subjected to water extension in a method for manufacturing a polarizing plate described later, and after the water extension The maximum heating temperature during heat treatment is controlled within a desired value range.

Polyester resin substrate forming material, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) can be used. Copolymerized PET (PET-G), isophthalic acid, cycloaliphatic dicarboxylic acid or cycloaliphatic diol containing cyclohexane ring, etc., other polyesters, and copolymers or blends thereof Things. Among them, it is preferable to use amorphous (uncrystallized) PET or copolymerized PET. Since these resins are amorphous in an unstretched state and have excellent elongation properties suitable for high-rate elongation, heat resistance and dimensional stability can be imparted by crystallization by elongation and heating. In addition, it is possible to ensure the heat resistance to a practical degree when the PVA-based resin is applied and dried in an unstretched state.

The glass transition temperature (Tg) of the polyester resin substrate is preferably 170 ° C or lower. By using such a polyester-based resin substrate, it is possible to suppress the crystallization of the PVA-based resin layer while ensuring sufficient extensibility. Considering the viewpoints of plasticizing the polyester-based resin substrate with water and smoothly performing water-extension, 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, it is possible to prevent deformation of the polyester-based resin substrate (for example, occurrence of unevenness, sag, or wrinkle) when applying and drying a coating solution containing a PVA-based resin described later. And so on. Moreover, the laminated body can be extended at an appropriate temperature (for example, about 60 ° C to 70 ° C). In another embodiment, when the coating liquid containing the PVA-based resin is applied and dried, as long as the polyester-based resin substrate is not deformed, the glass transition temperature may be lower than 60 ° C. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

In one embodiment, the water absorption of the polyester resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. This type of polyester resin substrate absorbs water, and water acts as a plasticizer to plasticize. As a result, the elongation stress can be greatly reduced during the elongation in water, and excellent extensibility is obtained. On the other hand, the water absorption of the polyester-based resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a polyester-based resin base material, it is possible to prevent the dimensional stability of the polyester-based resin base material from being significantly lowered during manufacturing, which may cause problems such as deterioration of the appearance of the resulting laminated body. It can also prevent breakage when stretching in water, or peeling of the PVA-based resin layer from the polyester-based resin substrate. The water absorption is a value obtained in accordance with JIS K 7209.

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

D. Protective Film The polarizing plate 10 is as described above, and may have a protective film on the side of the polarizer 12 opposite to the polyester-based resin substrate 11. Examples of the material for forming the protective film include (meth) acrylic resins, cellulose resins such as diacetyl cellulose, and triethyl cellulose, cycloolefin resins, olefin resins such as polypropylene, and polyterephthalene. Ester-based resins such as ethylene formate-based resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. The thickness of the protective film is preferably 10 μm to 100 μm.

E. Easy-Adhesive Layer The polarizing plate 10 is as described above, and may have an easy-adhesive layer between the polyester-based resin substrate 11 and the polarizer 12. The easy-adhesion layer may be a layer that is formed only of the composition for easy-adhesion layer formation, or a layer or region in which the composition for easy-adhesion layer formation and the polarizer forming material are mixed (including compatibility). By forming the easy-adhesion layer, excellent adhesion can be obtained. The thickness of the easy-adhesion layer should be about 0.05 μm to 1 μm. The easy-adhesion layer can be confirmed by observing the cross section of the polarizing plate with a scanning electron microscope (SEM), for example.

The composition for forming an easy-adhesive layer preferably contains a polyvinyl alcohol-based component. As the polyvinyl alcohol-based component, any appropriate PVA-based resin can be used. Specific examples include polyvinyl alcohol and modified polyvinyl alcohol. The modified polyvinyl alcohol may be, for example, polyvinyl alcohol modified by an acetamidine group, a carboxylic acid group, an acrylamide group, and / or a urethane group. Among these, it is more suitable to use acetamidine to modify PVA. As the acetamidine-modified PVA, a polymer having at least a repeating unit represented by the following general formula (I) is preferably used.

[Chemical Formula 1]

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

The average polymerization degree of acetamidine-modified PVA should be 1000 ~ 10000, more preferably 1200 ~ 5000. The saponification degree of acetamidine-modified PVA should be above 97 mole%. The pH of a 4% by weight aqueous solution of acetamidine-modified PVA should be 3.5 to 5.5.

The composition for forming an easy-adhesive layer may further contain a polyolefin-based component, a polyester-based component, a polyacrylic-based component, etc., depending on the purpose and the like. The composition for forming an easy-adhesive layer preferably further contains a polyolefin-based component.

The polyolefin-based component may be any appropriate polyolefin resin. The main component of the polyolefin-based resin is an olefin component. For example, olefin-based hydrocarbons having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, and 1-hexene can be mentioned. These may be used alone or in combination of two or more kinds. Among these, olefin-based hydrocarbons having 2 to 4 carbon atoms such as ethylene, propylene, isobutylene, and 1-butene are preferably used, and ethylene is more suitable.

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

The polyolefin-based resin preferably contains a carboxyl group and / or an acid anhydride group thereof. The polyolefin-based resin can be dispersed in water and can form an easy-adhesion layer smoothly. Examples of the monomer component having the functional group include unsaturated carboxylic acids and their anhydrides, half esters of unsaturated dicarboxylic acids, and hemiamine. Specific examples thereof 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 easy-adhesive 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 50:50. When there are too many polyvinyl alcohol-type components, sufficient adhesiveness may not be obtained. Specifically, there is a fear that the peeling force required when peeling the polarizer from the polyester-based resin substrate is reduced, and sufficient adhesion cannot be obtained. On the other hand, if the polyvinyl alcohol-based component is too small, the appearance of the obtained polarizing plate may be damaged. Specifically, it is difficult to obtain a polarizing plate having an excellent appearance due to defects such as white turbidity of the coating film when the easy-adhesion layer is formed.

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

As a method for applying the composition for forming an easy-to-adhesive layer, any appropriate method can be adopted. After coating the composition for forming an easy-to-adhere layer, the coating film can be dried. The drying temperature is, for example, 50 ° C or higher.

F. Manufacturing method of polarizing plate The manufacturing method of polarizing plate of the present invention includes: forming a laminated body by forming a PVA-based resin layer on one side of a polyester-based resin substrate; dyeing and extending the laminated body to PVA-based resin The layer is made into a polarizer; and the laminated body of the polyester-based resin substrate and the polarizer is subjected to heat treatment after stretching. The temperature of the extension bath is 67 ° C or lower, and the maximum heating temperature during the heat treatment is 102 ° C or higher, or the temperature of the extension bath is 69 ° C or lower, and the maximum heating temperature during the heat treatment is 105 ° C or higher.

FIG. 2 is a schematic diagram showing a manufacturing process of a polarizing plate according to an embodiment. The manufacturing process of the polarizing plate of this embodiment is to release the laminated body 10 'of the polyester-based resin substrate and the PVA-based resin layer from the release portion 101, and immerse the roller body 111 and 112 in boric acid. After being in the aqueous bath 110 (insolubilization treatment), the rollers 121 and 122 were immersed in a bath 120 of an aqueous solution of a dichroic substance (iodine) and potassium iodide (dyeing treatment). Next, the rollers 131 and 132 were immersed in a bath 130 of an aqueous solution of boric acid and potassium iodide (crosslinking treatment). Next, while the laminated body 10 'is immersed in the stretching bath 140 of the boric acid aqueous solution, the rollers 141 and 142 with different speed ratios are stretched in the longitudinal direction (long side direction, conveying direction, and MD direction) to perform stretching (under water). (Stretching treatment), whereby the PVA-based resin layer is made into a polarizer. Next, the laminated body 10 'extended in water was immersed in a bath 150 of potassium iodide aqueous solution (washing treatment) with rollers 151 and 152, and then subjected to a drying treatment (not shown in the drawing). Next, the laminated body 10 'is sent to a heating mechanism 160 for heating (heat treatment), whereby the polarizing plate 10 of this embodiment is obtained. After that, the obtained polarizing plate 10 is rolled up by a winding unit 170. Although omitted in the drawing, the air-stretching treatment may be performed before the insolubilization treatment is performed on the laminated body 10 '. The manufacturing steps shown in FIG. 2 are only examples, and the number and order of the above processes are not particularly limited.

F-1. A method for producing a laminated body to form a PVA-based resin layer on a polyester-based resin substrate may be any appropriate method. The PVA-based resin layer is preferably formed by applying a coating solution containing a PVA-based resin on a polyester-based resin substrate and drying the coating liquid. In one embodiment, a composition for forming an easy-adhesive layer is coated on a polyester-based resin substrate and dried to form an easy-adhesive layer, and a PVA-based resin layer is formed on the easy-adhesive layer.

The material for forming the polyester-based resin substrate is as described in the above item C. The thickness of the polyester resin substrate (thickness before stretching described later) is preferably 20 μm to 300 μm, and 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, it may take a long time for the polyester resin base material to absorb water during stretching in water, which may cause an excessive load on stretching.

The coating liquid represents a solution obtained by dissolving the PVA-based resin in a solvent. Examples of the solvent include water, dimethylmethylene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and ethylene glycol. Diamine, diethylene glycol and other amines. These may be used alone or in combination of two or more kinds. Of these, water is preferred. The concentration of the PVA 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 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. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred. The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA-based 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, there may be a case where the halide overflows and the resulting polarizer becomes cloudy. The laminate of the PVA-based resin layer containing a halide and the polyester-based resin substrate is stretched in air at high temperature (assisted stretching) before being stretched in boric acid water, thereby promoting the PVA-based resin layer after the stretching Crystallization of PVA-based resin. As a result, when the PVA-based resin layer is immersed in a liquid, compared to the case where the PVA-based resin layer does not contain a halide, the disorder of orientation of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed more. Thereby, the optical characteristics of the finally obtained polarizer can be improved.

Additives can also be blended in the coating solution. Examples of the additives include plasticizers and surfactants. Examples of the plasticizer include a polyhydric alcohol such as ethylene glycol or glycerin. The surfactant may be, for example, a nonionic surfactant. These can be used in order to further improve the uniformity, dyeability, and elongation of the obtained PVA-based resin layer. In addition, the additives may be easily accessible ingredients. By using the easy-contact component, the adhesion between the polyester-based resin substrate and the PVA-based resin layer can be improved. As a result, defects such as peeling of the PVA-based resin layer from the polyester-based substrate can be suppressed, and dyeing and water elongation described later can be performed favorably. Modified PVA such as acetoacetate-based modified PVA can be used as the easy-to-connect component.

The coating liquid may be applied by any appropriate method. Examples include a roll coating method, a spin coating method, a bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a doctor blade coating method (comma coating method, etc.), and the like. 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 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 a surface treatment (for example, corona treatment, etc.), or the polyester-based resin substrate may be coated with a composition for easy adhesion layer formation (coating treatment) ). By performing the treatment, the adhesion between the polyester-based resin substrate and the PVA-based resin layer can be improved. As a result, defects such as peeling of the PVA-based resin layer from the polyester-based resin substrate can be suppressed, and dyeing and stretching described later can be performed favorably.

F-2. Aerial extension processing The extension method of aerial auxiliary extension can be fixed-end extension (such as the method using a tenter stretcher), or free-end extension (such as passing the laminate through rollers with different peripheral speeds). To uniaxial extension). In one embodiment, the air-stretching process includes a hot-roller stretching step, which is performed by conveying the laminated body along the longitudinal direction of the laminated body while extending the peripheral speed difference between the hot-rollers. The aerial stretching process includes a zone stretching step and a heat roller stretching step on the representative. In addition, the order of the zone extension step and the hot roll member extension step is not limited, and the zone extension step may be performed first, or the hot roll member extension step may be performed first. The region extension step may also be omitted. In one embodiment, the area extending step and the hot roll member extending step are sequentially performed.

The extension temperature of the laminated body can be set to an arbitrary and appropriate value in accordance with the forming material and extension method of the polyester-based resin substrate. The elongation temperature of the air-stretching treatment should be above the glass transition temperature (Tg) of the polyester resin substrate, and the glass transition temperature (Tg) of the polyester resin substrate is more preferably 10 ° C or more, and Tg + 15 ° C or more suitable. On the other hand, the upper limit of the extension temperature of the laminate is preferably 170 ° C. Stretching at the above-mentioned temperature can suppress rapid progress of crystallization of the PVA-based resin, and can thereby suppress undesirable conditions caused by the crystallization (for example, the orientation of the PVA-based resin layer is hindered by the stretching).

F-3. Insolubilization treatment The above-mentioned insolubilization treatment is performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By applying the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer. 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 liquid temperature of the insoluble bath (aqueous boric acid solution) is preferably 20 ° C to 50 ° C. The insolubilization treatment is preferably performed before the above-mentioned water extension or the above-mentioned dyeing treatment.

F-4. Dyeing treatment
The dyeing of the PVA-based resin layer is representatively performed by adsorbing iodine on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (layered body) in a dye solution containing iodine, a method of applying the dye solution to a PVA-based resin layer, and spraying the dye solution to PVA. Method on the resin layer. A method of immersing a PVA-based resin layer (layered body) in a dyeing solution is preferably adopted. This is because iodine can be adsorbed well.

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

F-5. Cross-linking treatment The above-mentioned cross-linking treatment is representatively performed by immersing a PVA-based resin layer (layered body) in an aqueous boric acid solution. By performing a 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. When the crosslinking treatment is performed after the dyeing treatment, it is preferable to further mix iodide. By blending iodide, the elution of iodine which has been adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight 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 crosslinking bath (aqueous boric acid solution) should preferably be 20 ° C to 60 ° C. The cross-linking treatment is preferably performed before the elongation treatment in water. The preferred embodiment is to perform the aerial stretching treatment, the dyeing treatment, and the crosslinking treatment in this order.

F-6. The manufacturing steps of the polarizing plate for underwater stretching are as described above, and include: subjecting the laminated body to an underwater stretching treatment in an stretching bath. Specifically, it extends in water in a direction parallel to the extending direction of the laminated body. By extending in water, it can be extended at a temperature lower than the glass transition temperature (typically about 80 ° C) of the polyester-based resin substrate or PVA-based resin layer described above. At the same time, high magnification extension is performed. As a result, a polarizer having excellent optical characteristics (for example, polarization degree) can be manufactured. In this specification, the "parallel direction" includes the case of 0 ° ± 5.0 °, preferably 0 ° ± 3.0 °, and more preferably 0 ° ± 1.0 °.

The extension temperature (liquid temperature of the extension bath) in water extension is preferably below 69 ° C, more preferably below 67 ° C. The lower limit of the liquid temperature of the extension bath is preferably 40 ° C, and more preferably 50 ° C. By setting the liquid temperature of the extension bath within the above range, it can be multiplied and multiplied by the highest heating temperature in the heat treatment described later, and the elastic coefficient of the polyester-based resin substrate can be adjusted to a value within an ideal range. In addition, as long as the temperature is as described above, it is possible to suppress the dissolution of the PVA-based resin layer and to extend at a high rate. Specifically, as described above, when considering 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 the polyester resin base material is considered to be plasticized with water, it may not be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and it is feared that excellent optical characteristics cannot be obtained. The immersion time of the laminated body in the extension bath is preferably 15 seconds to 5 minutes.

Any appropriate method can be adopted as the elongation method in the water elongation treatment. Specifically, it may be a fixed end extension or a free end extension. The extending direction of the laminated body is substantially the extending direction (long side direction) of the above-mentioned aerial extension. The extension of the laminate can be performed in one stage or in multiple stages.

Extension in water is preferably performed by immersing the laminate in an aqueous solution of boric acid (extension in boric acid). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension applied during stretching and water resistance insoluble in water. Specifically, boric acid generates a tetrahydroxyborate anion in an aqueous solution, and can be crosslinked with a PVA-based resin through hydrogen bonding. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer and to extend well, and a polarizer having excellent optical characteristics (for example, polarization degree) can be produced.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and / or a 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, it is possible to effectively suppress the dissolution of the PVA-based resin layer, and to manufacture a polarizer with higher characteristics. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent may be used.

If a dichroic substance (represented by iodine) has been adsorbed on the PVA-based resin layer by a dyeing treatment in advance, it is preferable to mix iodide in the above-mentioned extension bath (aqueous boric acid solution). By blending iodide, the elution of iodine which has been 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. Of these, potassium iodide is preferred. The concentration of iodide is preferably 0.05 to 15 parts by weight, and more preferably 0.5 to 8 parts by weight relative to 100 parts by weight of water.

By combining the above-mentioned polyester-based resin substrate with water stretching (boric acid stretching in water), it is possible to stretch at a high magnification, and it is possible to produce a polarizer having excellent optical characteristics (for example, polarization degree). Specifically, the maximum extension magnification is preferably 5.0 times or more, more preferably 5.5 times or more, and more preferably 6.0 times or more relative to the original length of the multilayer body (including the extension ratio of the multilayer body). The "maximum extension ratio" in this specification means the extension ratio before the multilayer body is fractured, and it is a value that is 0.2 lower than the value after confirming the extension ratio of the multilayer body after fracture. In addition, in terms of the maximum stretching ratio of the laminated body using the polyester-based resin substrate described above, it is higher than the case where it is stretched through water as compared with the case where it is stretched only in the air.

F-7. Washing process The washing process can be performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. The drying temperature in the drying process should preferably be 30 ° C to 100 ° C.

F-8. Heat treatment The heat treatment is performed after stretching in water. The polyester resin base material can be crystallized by heat treatment. The heat treatment is representatively performed by heating a conveying roller member (using a so-called hot roller member (heating roller member)) disposed in the heating mechanism 160 (a heating roller member heating method). In one embodiment, the heating mechanism 160 is an oven, and a heating method (oven heating method) performed by sending hot air into the oven may be used in combination. By using the hot-roller heating method and the oven heating method in combination, rapid temperature changes between the hot-roller rollers can be suppressed, and the contraction in the width direction of the laminated body 10 'can be easily controlled. The temperature inside the oven should be 30 ℃ ~ 100 ℃. In addition, the heating time of the oven should be 1 second to 300 seconds. The wind speed of hot wind should be about 10m / s ~ 30m / s. In addition, the wind speed is the wind speed in the oven, and can be measured by a mini fan-type digital anemometer.

Heating with a hot-roller roll member can suppress curl and produce a polarizer with excellent appearance. Specifically, when the laminated body 10 'is heated along the state of the hot roller, it can effectively promote the crystallization of the polyester-based resin substrate and increase the degree of crystallization, even at low heating. At the temperature, the degree of crystallization of the polyester-based resin substrate can still be increased well. As a result, the rigidity of the polyester-based resin substrate is increased, and the PVA-based resin layer can withstand shrinkage due to heating, thereby suppressing curling. In addition, by using the heat roller member, the laminated body 10 'can be heated while being kept flat, so that not only curling can be suppressed, but also wrinkles can be suppressed.

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

Among the plurality of heat roller rolls, when the temperature of the heat roller roll set to the highest temperature is the "highest heating temperature", the maximum heating temperature is 102 ° C or higher, more preferably 105 ° C or higher, and more preferably Above 110 ℃. The upper limit of the maximum heating temperature is preferably 150 ° C, and more preferably 120 ° C. By setting the highest heating temperature in the heat treatment within the above range, it can be multiplied by the temperature of the extension bath in the water extension treatment, and the durability index of the polyester resin substrate can be adjusted to an ideal range. value. The temperature of the heat roller can be measured with a contact thermometer. The contact time of the laminated body to the hot roller rollers maintained at the highest heating temperature (when there are multiple hot roller rollers with the highest heating temperature, the total contact time) should be 0.2 seconds to 2 seconds, and more preferably 0.5 seconds. ~ 2 seconds. The "contact time" means the time from when any point on the laminated body comes into contact with the outer peripheral surface of the heat roller roller maintained at the highest heating temperature until it leaves.

G. Image display device The polarizing plates described in the above items A to E produced by the manufacturing method described in the above item F 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 items A to E.
Examples

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measurement method and evaluation method of each characteristic are as follows.
(1) The thickness was measured using a digital micrometer (manufactured by Anritsu, product name "KC-351C").
(2) Coefficient of elasticity The nano-indentation tester ("Triboindenter", manufactured by Hysitron Inc.) was used for the polyester resin base material of the polarizing plate obtained in the examples and comparative examples under the following measurement conditions. The coefficient of elasticity was measured by the nanoindentation method. Specifically, the probe (indenter) of the nanoindentation tester is pressed into the surface of the polyester resin base material side of the polarizing plate, and the contact rigidity S obtained from the displacement-load hysteresis curve and the indenter The contact projection area A with the polyester-based resin substrate is calculated by the following formula.
Coefficient of elasticity (E) = S × π ^1/2 / 2A ^1/2
(Measurement conditions)
・ Measurement method: Single press method ・ Measurement temperature: 25 ° C
・ Press-in speed: about 2nm / sec
・ Pressing depth: about 2000nm
・ Probe: Diamond, Berkovich type (triangular cone type)
(3) Evaluation of Adhesion The strip-shaped polarizing plates prepared in the examples and comparative examples were cut into a size of 150 mm (MD direction) x 200 mm (TD direction) to prepare evaluation samples. The polarizer side of the above-mentioned evaluation sample was adhered to the glass through an acrylic adhesive and stored at 60 ° C / 90% Rh for 500 hours, and it was confirmed whether the end portion of the evaluation sample was peeled from the glass. And if the evaluation sample peeled from glass, the length of the peeled part was measured.

<Example 1>
As the polyester-based resin substrate, a long amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm, IPA modification degree: 5 mol%) was used. (Modification degree = [ethylene isophthalate unit] / [ethylene terephthalate unit + ethylene isophthalate unit])
Corona treatment (treatment conditions: 50 W · min / m ² ) was performed on one side of the polyester resin substrate, and then ethyl acetate modified polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product "GOHSEFIMER Z200") modified polyolefin resin aqueous dispersion (manufactured by Unitika, trade name "ARROW BASE SE1030N") mixed with pure water (solid content concentration 4.0%) to make the thickness after drying The coating was applied to the corona-treated surface at 2000 nm, and dried at 65 ° C. for 2 minutes to form an undercoat layer. Here, the blending ratio of the solid content of the acetamidine-modified PVA and the modified polyolefin in the mixed liquid was 30:70. Then, 90 parts by weight of PVA (degree of polymerization 4200, degree of saponification 99.2 mole%) and acetamidine modified PVA (made by Nippon Synthetic Chemical Industry Co., Ltd., trade name) were applied to the surface of the undercoat layer at 25 ° C. "GOHSEFIMER Z410") 10 parts by weight of a PVA-based resin, and an aqueous solution of 13 parts by weight of potassium iodide based on 100 parts by weight of the PVA-based resin, and dried at 60 ° C for 3 minutes to form a thickness 13 μm PVA-based resin layer. A laminated body was produced as described above.
In an oven at 140 ° C, the obtained laminated body was subjected to free-end uniaxial extension in the longitudinal direction (long-side direction) between rollers having different peripheral speeds (air-assisted extension).
Next, the laminated body was immersed in an insoluble bath (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 (insolubilization 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 100 parts by weight of water with 100 parts by weight of water) at a temperature of 30 ° C (dyeing treatment).
Next, it was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ° C (crosslinking treatment) ).
Thereafter, the laminate was immersed in an extension bath (extension bath temperature: 67 ° C) of an aqueous solution of boric acid (aqueous solution prepared by mixing 3 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water). On one side, uniaxial stretching was performed in the longitudinal direction (long side direction) between rollers of different peripheral speeds to 2.75 times (total stretching ratio: 5.5 times) (water stretching treatment).
Then, the laminated body was immersed in a washing bath (aqueous solution obtained by mixing 3.5 parts by weight of potassium iodide with 100 parts by weight of water with respect to 100 parts by weight of water) (washing treatment).
Next, in an oven having a plurality of heated rollers maintained at 80 to 110 ° C and maintained at 80 ° C, the total contact time of the laminate to the heated rollers maintained at a maximum heating temperature of 110 ° C was 1 second in total. In one embodiment, a heating roller is used to carry out the heat treatment while conveying the laminate.
In the manner described above, a long polarizing plate 1 with a polarizer having a thickness of 5 μm laminated on a polyester resin substrate was obtained. The elasticity coefficient of the polyester-based resin substrate of the polarizing plate 1 was 3.15 GPa. After the polarizing plate 1 was subjected to the above-mentioned adhesion evaluation, peeling from the glass did not occur.

<Example 2>
A polarizing plate 2 was produced in the same manner as in Example 1 except that the maximum heating temperature was 105 ° C. and the total contact time was 1 second. The elastic modulus of the polyester-based resin substrate of the polarizing plate 2 is 2.85 GPa. The polarizing plate 2 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 3>
A polarizing plate 3 was produced in the same manner as in Example 1 except that the maximum heating temperature was set to 102 ° C. and the total contact time was set to 1 second. The elastic modulus of the polyester-based resin substrate of the polarizing plate 3 is 2.70 GPa. The polarizing plate 3 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 4>
An extension bath with an extension bath temperature of 69 ° C was used to extend the laminate in water. The maximum heating temperature was set to 105 ° C and the total contact time was set to 1 second. Got the polarizing plate 4. The elastic modulus of the polyester-based resin substrate of the polarizing plate 4 is 2.72 GPa. The polarizing plate 4 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

〈Comparative example 1〉
A polarizing plate 5 was produced in the same manner as in Example 1 except that the maximum heating temperature was 100 ° C. and the total contact time was 1 second. The elastic modulus of the polyester-based resin substrate of the polarizing plate 5 is 2.65 GPa. The polarizing plate 5 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

〈Comparative example 2〉
A polarizing plate 6 was obtained 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 elastic modulus of the polyester-based resin substrate of the polarizing plate 6 is 2.37 GPa. The polarizing plate 6 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

〈Comparative example 3〉
A polarizing plate 7 was obtained in the same manner as in Example 1 except that the temperature in the furnace was set to 60 ° C, the maximum heating temperature was set to 60 ° C, and the total contact time was set to 1 second. The elasticity coefficient of the polyester-based resin substrate of the polarizing plate 7 is 2.10 GPa. The polarizing plate 7 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

〈Comparative example 4〉
A polarizing plate 8 was produced in the same manner as in Example 4 except that the maximum heating temperature was set to 102 ° C. and the total contact time was set to 1 second. The elastic modulus of the polyester-based resin substrate of the polarizing plate 8 is 2.57 GPa. The polarizing plate 8 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

〈Comparative example 5〉
A polarizing plate 9 was produced in the same manner as in Example 4 except that the maximum heating temperature was set to 100 ° C. and the total contact time was set to 1 second. The elasticity coefficient of the polyester-based resin substrate of the polarizing plate 9 is 2.50 GPa. The polarizing plate 9 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Table 1]

It is clear from Table 1 that even if the polarizing plate having an elastic coefficient of 2.70 GPa or more is placed in a high-temperature and high-humidity environment, the glass does not peel off.

Industrial Applicability The polarizing plate of the present invention can be suitably used in image display devices such as liquid crystal display devices and organic EL display devices.

10‧‧‧ polarizing plate

10’‧‧‧ laminated body

11‧‧‧ polyester resin substrate

12‧‧‧Polarizer

101‧‧‧Release Department

110‧‧‧boric acid bath

111, 112, 121, 122, 131, 132, 141, 142, 151, 152‧‧‧ rollers

120‧‧‧ Bath of aqueous solution of dichroic substance (iodine) and potassium iodide

130‧‧‧Bath of boric acid and potassium iodide in water

140‧‧‧Extension bath of boric acid aqueous solution

150‧‧‧ bath of potassium iodide solution

160‧‧‧Heating mechanism

170‧‧‧ Take-up Department

FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a manufacturing process of a polarizing plate according to an embodiment.

Claims (6)

A polarizing plate comprising: a polyester resin substrate and a polarizer laminated on one side of the polyester resin substrate; The thickness of the polarizer is 10 μm or less, and The elastic modulus of the polyester-based resin substrate is 2.70 GPa or more. The polarizing plate according to claim 1, wherein the polarizer is laminated on one side of the polyester-based resin substrate without an adhesive layer therebetween. The polarizing plate according to claim 1 or 2, wherein the polyester-based resin substrate and the polarizer have an easy-adhesion layer therebetween. The polarizing plate according to any one of claims 1 to 3, wherein the aforementioned polyester-based resin substrate functions as a protective layer of the aforementioned polarizer. An image display device includes a polarizing plate according to any one of claims 1 to 4. A method for manufacturing a polarizing plate is a method for manufacturing a polarizing plate according to any one of claims 1 to 4, and the manufacturing method includes: Forming a polyvinyl alcohol-based resin layer on one side of the aforementioned polyester-based resin substrate to form a laminated body; Dyeing and stretching the laminated body to make the polyvinyl alcohol-based resin layer into a polarizer; and Heat-treating the laminated body of the polyester-based resin substrate and the polarizer after the stretching; The temperature of the stretching bath in the stretching is 67 ° C. or lower, and the maximum heating temperature in the heating process is 102 ° C. or higher, or, The temperature of the stretching bath in the stretching is 69 ° C or lower, and the maximum heating temperature in the heat treatment is 105 ° C or higher.