TWI835751B - Polarizing plate, image display device and manufacturing method of polarizing plate - Google Patents

Abstract

The present invention provides a polarizing plate with small thermal shrinkage behavior and suppressed peeling. The polarizing plate has a polyester resin base material and a polarizing element laminated on one side of the polyester resin base material; the thickness of the polarizing element is 10 μm or less; and the polyester resin base material is non-polarizing. When the absorption intensity at 1340cm ^-1 measured by FT-IR of the ATR method is P(1340) and the absorption intensity at 1410cm ^-1 is P(1410), the value of P(1340)/P(1410) is 0.60 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 method for manufacturing the polarizing plate.

Background of the invention There is a document proposing a method of forming a polyvinyl alcohol-based resin layer on a polyester-based resin base material, and then stretching and dyeing the laminate to produce a thin polarizer (for example, Patent Document 1). The manufacturing method of the polarizer is attracting attention because it can contribute to thinning of image display devices, for example.

The above-mentioned polarizing element can be used in a state of being laminated on the above-mentioned polyester-based resin base material, and in this case, the polyester-based resin base material is used as a protective layer of the polarizing element (Patent Document 2). Thereby, the laminate of the polyester resin base material and the polarizer can be directly used as a polarizing plate without using a protective film for laminating the polarizer, which can contribute to cost reduction of image display devices, for example.

Prior art documents Patent documents Patent document 1: Japanese Patent Publication No. 2000-338329 Patent document 2: Japanese Patent Publication No. 4979833

Summary of the invention The problem to be solved by the invention However, when the polarizing element side surface of the above-mentioned polarizing plate is bonded to other optical components such as a display unit or a phase difference plate through an adhesive, when the heat shrinkage behavior of the polyester resin base material is large, it will be exposed to high temperature and high humidity environments. The lower polarizing plate may peel off.

The present invention is made to solve the above-mentioned previous problems, and its main purpose is to provide a polarizing plate with small thermal shrinkage and suppressed peeling, an image display device having the above-mentioned polarizing plate, and a method for manufacturing the polarizing plate.

Means for Solving the Problem The polarizing plate of the present invention comprises: a polyester resin substrate and a polarizer laminated on one side of the polyester resin substrate; wherein the thickness of the polarizer is less than 10 μm; and when the absorption intensity of 1340 cm ^-1 measured by FT-IR of the non-polarized ATR method is P(1340) and the absorption intensity of 1410 cm ^-1 is P(1410), the value of P(1340)/P(1410) of the polyester resin substrate is greater than 0.60. In one embodiment, the polarizer is laminated on one side of the polyester resin substrate without a bonding layer. In one embodiment, there is an easy bonding layer between the polyester resin substrate and the polarizer. In one embodiment, the polyester resin substrate functions as a protective layer of the polarizer. According to another aspect of the present invention, an image display device is provided. The image display device has the polarizer. According to another aspect of the present invention, a method for manufacturing the polarizer can be provided. The manufacturing method includes: forming a polyvinyl alcohol resin layer on one side of the above-mentioned polyester resin substrate to form a laminate; dyeing and stretching the above-mentioned laminate to make the above-mentioned polyvinyl alcohol resin layer into a polarizer; and, after the above-mentioned stretching, heating the laminate of the above-mentioned polyester resin substrate and the above-mentioned polarizer; wherein the temperature of the stretching bath during the above-mentioned stretching is below 67°C and the highest heating temperature during the above-mentioned heating treatment is above 102°C, or the temperature of the stretching bath during the above-mentioned stretching is below 69°C and the highest heating temperature during the above-mentioned heating treatment is above 105°C.

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

The following describes the embodiments of the present invention, but the present invention is not limited to these embodiments.

A. Overall structure of polarizing plate FIG1 is a cross-sectional view of a polarizing plate of one embodiment of the present invention. As shown in FIG1 , the polarizing plate 10 comprises a polyester resin substrate 11 and a polarizing element 12 laminated on one side of the polyester resin substrate 11. The thickness of the polarizing element 12 is less than 10 μm. When the absorption intensity of 1340 cm ^-1 of the polyester resin substrate 11 measured by FT-IR (Fourier transform infrared spectroscopy) of the ATR method (attenuated total reflection spectroscopy) using non-polarized light as the measuring light is P(1340) and the absorption intensity of 1410 cm ^-1 is P(1410), the value of P(1340)/P(1410) is greater than 0.60. The polarizer 12 is preferably laminated in close contact with one side of the polyester resin substrate 11 (in other words, without a bonding layer in between). The polarizing plate 10 preferably has an easy bonding layer (not shown in the figure) between the polyester resin substrate 11 and the polarizer 12. The polarizing plate 10 may also have a protective film (not shown in the figure) on the side of the polarizer 12 opposite to the polyester resin substrate 11. The polyester resin substrate 11 typically functions as a protective layer for the polarizer 12. In the past, when the polarizer side of the polarizer was bonded to other optical components and placed in a high temperature and high humidity environment, the polarizing plate may peel off from the optical component at both ends in the extension direction of the polarizing plate. In contrast, when the polarizing plate 10 of the present embodiment is bonded to other optical components on the side of the polarizer 12, the thermal shrinkage of the polyester resin substrate 11 is smaller, and peeling in a high temperature and high humidity environment can be suppressed.

B. Polarizer The polarizer is essentially a polyvinyl alcohol resin layer (PVA resin layer) in which iodine is adsorbed and oriented. The thickness of the polarizer is less than 10μm as mentioned above, and preferably less than 7.5μm, and more preferably less than 5μm. On the other hand, the thickness of the polarizer is preferably greater than 0.5μm, and more preferably greater than 1.5μm. If the thickness is too thin, the optical properties of the resulting polarizer may be reduced. The polarizer preferably exhibits absorption dichroism at any wavelength of 380nm~780nm. The single body transmittance of the polarizer is preferably greater than 40.0%, preferably greater than 41.0%, and more preferably greater than 42.0%. The polarization degree of the polarizer is preferably greater than 99.8%, preferably greater than 99.9%, and more preferably greater than 99.95%.

The PVA resin forming the above-mentioned PVA resin layer can be any and appropriate resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol%~100 mol%, preferably 95.0 mol%~99.95 mol%, and more preferably 99.0 mol%~99.93 mol%. The saponification degree is obtained according to JIS K 6726-1994. By using a PVA resin with the above-mentioned saponification degree, a polarizer with excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelling.

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 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

C. Polyester Resin Base Material The polyester resin base material is as described above. Let the absorption intensity at 1340 cm ^-1 measured by FT-IR of the ATR method using non-polarized light as the measurement light be P (1340), 1410 cm When the absorption strength of ^-1 is P(1410), the value of P(1340)/P(1410) (hereinafter sometimes also referred to as the durability index) is 0.60 or more. The durability index should be 0.60~1.20, more preferably 0.65~1.00. This can suppress the shrinkage of the polyester-based resin base material in a high-temperature and high-humidity environment. As a result, when the polarizing plate is bonded to the optical component, the polyester-based resin base material can be suppressed from peeling off from the optical component. The above durability index can be obtained by appropriately setting the temperature of the stretching bath when the laminate of the polyester resin base material and the polyvinyl alcohol resin layer is stretched in water, and the temperature after stretching in water in the manufacturing method of the polarizing plate described below. The maximum heating temperature during heat treatment is controlled within the desired value range.

The materials for forming the polyester resin substrate include, for example: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), isophthalic acid, copolymerized PET (PET-G) containing alicyclic dicarboxylic acids or alicyclic diols containing cyclohexane rings, other polyesters, and copolymers or blends thereof. Among them, it is preferred to use amorphous (uncrystallized) PET or copolymerized PET. Since these resins are amorphous in the unstretched state and have excellent elongation suitable for high-rate stretching, they can be crystallized by stretching and heating to impart heat resistance and dimensional stability. In addition, heat resistance can be ensured to a feasible level for coating and drying the PVA resin in the unstretched state.

The glass transition temperature (Tg) of the polyester resin base material is preferably 170°C or lower. By using this type of polyester-based resin base material, crystallization of the PVA-based resin layer can be suppressed while sufficient elongation can be ensured. Considering the viewpoints of plasticizing the polyester resin base material with water and smooth extension in water, the temperature is more preferably 120°C or lower. In one embodiment, the glass transition temperature of the polyester resin base material is preferably 60°C or higher. By using the polyester-based resin base material, it is possible to prevent the polyester-based resin base material from deforming (for example, unevenness, sagging, wrinkles, etc.) when coating and drying a coating liquid containing PVA-based resin described below. Wait for bad situations. In addition, the laminated body can be stretched at a suitable temperature (for example, about 60°C to 70°C). In another embodiment, when the coating liquid containing PVA-based resin is applied and dried, the glass transition temperature may be lower than 60° C. as long as the polyester-based resin base material is not deformed. In addition, the glass transition temperature (Tg) is a value calculated based on JIS K 7121.

In one embodiment, the water absorption rate of the polyester resin substrate is preferably 0.2% or more, more preferably 0.3% or more. This type of polyester resin substrate absorbs water, and the water acts as a plasticizer to plasticize. As a result, the extension stress can be greatly reduced during extension in water, and excellent elongation is achieved. On the other hand, the water absorption rate of the polyester resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using this type of polyester resin substrate, it is possible to prevent the dimensional stability of the polyester resin substrate from being significantly reduced during manufacturing, resulting in deterioration in the appearance of the resulting laminate, and other undesirable situations. It is also possible to prevent the PVA resin layer from breaking during extension in water or peeling off from the polyester resin substrate. In addition, the water absorption rate is a value obtained according to JIS K 7209.

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

D. Protective film As described above, the polarizing plate 10 may have a protective film on the side of the polarizer 12 opposite to the polyester resin base material 11 . Examples of materials for forming the protective film include (meth)acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins, olefin resins such as polypropylene, and polyterephthalene. Ester resins such as ethylene formate resin, polyamide resins, polycarbonate resins, copolymer resins thereof, etc. The thickness of the protective film should be 10μm~100μm.

E. Easy-adhesion layer As described above, the polarizing plate 10 may have an easy-adhesion layer between the polyester resin substrate 11 and the polarizing element 12. The easy-adhesion layer may be a layer substantially formed only by the composition for forming the easy-adhesion layer, or may be a layer or region formed by mixing (including compatibility) the composition for forming the easy-adhesion layer with the forming material of the polarizing element. By forming the easy-adhesion layer, excellent adhesion can be obtained. The thickness of the easy-adhesion layer is preferably set to about 0.05μm~1μm. 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 the easily adhesive layer preferably contains a polyvinyl alcohol-based component. As the polyvinyl alcohol-based component, any appropriate PVA-based resin can be used. Specifically, polyvinyl alcohol and modified polyvinyl alcohol can be cited. Examples of modified polyvinyl alcohol include polyvinyl alcohol modified with acetyl acetyl group, carboxylic acid group, acryl group and/or urethane group. Among these, it is more suitable to use acetyl-acetyl-modified PVA. Acetyl acetyl-modified PVA is preferably a polymer having at least a repeating unit represented by the following general formula (I).

[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 acetyl acetyl-based modified PVA is preferably 1,000~10,000, and 1,200~5,000 is more suitable. The degree of saponification of acetyl-acetyl-modified PVA should be above 97 mol%. The pH of the 4% by weight aqueous solution of acetyl acetyl-modified PVA is preferably 3.5~5.5.

The easy-adhesion layer forming composition may further contain a polyolefin component, a polyester component, a polyacrylic acid component, etc. according to the purpose, etc. The easy-adhesion layer forming composition preferably further contains a polyolefin component.

Any appropriate polyolefin resin can be used as the polyolefin component. Examples of the olefin component, which is the main component of the polyolefin-based resin, include 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 them, olefin 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 olefin components is preferably 50% to 95% by weight.

The polyolefin-based resin preferably contains carboxyl groups and/or acid anhydride groups thereof. The above-mentioned polyolefin-based resin can be dispersed in water and can smoothly form an easily adhesive layer. Examples of the monomer component having the functional group include unsaturated carboxylic acid and its anhydride, half-ester of unsaturated dicarboxylic acid, and half-amide. 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 polyolefin resin is, for example, 5,000 to 80,000.

In the composition for forming the easy-adhesion layer, the mixing ratio of the polyvinyl alcohol-based component and the polyolefin-based component (the former: the latter (solid component)) is preferably 5:95~60:40, and more preferably 20:80~50:50. If the polyvinyl alcohol-based component is too much, sufficient adhesion may not be obtained. Specifically, the peeling force required to peel the polarizer from the polyester resin substrate may be reduced and sufficient adhesion may not be obtained. On the other hand, if the polyvinyl alcohol-based component is too little, the appearance of the resulting polarizing plate may be damaged. Specifically, when forming the easy-adhesion layer, undesirable conditions such as white muddiness of the coating film may occur, making it difficult to obtain a polarizing plate with excellent appearance.

The composition for forming an easy bonding layer is preferably aqueous. The composition for forming an easy bonding layer 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 bonding layer is preferably 1.0 wt% to 10 wt%.

Any appropriate method can be used as the coating method of the composition for forming an easily adhesive layer. After applying the composition for forming an easily adhesive 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 the polarizing plate of the present invention comprises: forming a PVA resin layer on one side of a polyester resin substrate to form a laminate; dyeing and stretching the laminate to make the PVA resin layer into a polarizer; and, after stretching, heat-treating the laminate of the polyester resin substrate and the polarizer. The temperature of the stretching bath is below 67°C and the highest heating temperature during the heating treatment is above 102°C, or the temperature of the stretching bath is below 69°C and the highest heating temperature during the heating treatment is above 105°C.

FIG2 is a schematic diagram showing the manufacturing steps of a polarizing plate of an embodiment. The manufacturing steps of the polarizing plate of this embodiment are representatively to release the laminate 10' of the polyester resin substrate and the PVA resin layer from the release part 101, and immerse it in a bath 110 of an aqueous solution of boric acid by rollers 111 and 112 (insolubilization treatment), and then immerse it in a bath 120 of an aqueous solution of a dichroic substance (iodine) and potassium iodide by rollers 121 and 122 (dyeing treatment). Then, immerse it in a bath 130 of an aqueous solution of boric acid and potassium iodide by rollers 131 and 132 (crosslinking treatment). Next, while the laminate 10' is immersed in a stretching bath 140 of an aqueous boric acid solution, the rollers 141 and 142 with different speed ratios are used to apply tension in the longitudinal direction (long side direction, conveying direction, MD direction) to stretch it (in-water stretching treatment), thereby making the PVA resin layer into a polarizer. Next, the laminate 10' stretched in water is immersed in a bath 150 of an aqueous potassium iodide solution by rollers 151 and 152 (washing treatment), and then subjected to a drying treatment (not shown in the figure). Next, the laminate 10' is sent to a heating mechanism 160 for heating (heating treatment), thereby producing the polarizing plate 10 of this embodiment. Afterwards, the produced polarizing plate 10 is rolled up by the rolling unit 170. Although omitted in the figure, the laminate 10' may be subjected to an air stretching treatment before being subjected to an insolubilization treatment. In addition, the manufacturing steps shown in FIG2 are only an example, and the number and sequence of the above-mentioned treatments are not particularly limited.

F-1. Preparation of laminate The method of forming a PVA-based resin layer on a polyester-based resin substrate may be any appropriate method. Preferably, a coating liquid containing a PVA-based resin is applied to a polyester-based resin substrate and dried to form the PVA-based resin layer. In one embodiment, a composition for forming an easy-adhesion layer is applied to a polyester-based resin substrate and dried to form an easy-adhesion layer, and a PVA-based resin layer is formed on the easy-adhesion layer.

The forming material of the above-mentioned polyester resin base material is as described in the above-mentioned item C. The thickness of the polyester resin base material (thickness before stretching described below) 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 stretching in water, the polyester resin base material may take a long time to absorb water and cause excessive load on the stretching.

The above-mentioned coating liquid represents a solution in which the above-mentioned PVA resin is dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylidene Amines such as diamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is the best. The PVA resin concentration of the solution should be 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film that adheres closely to the polyester resin base material can be formed. In one embodiment, the coating liquid contains a halide. Any appropriate halide may be used as the above-mentioned halide. Examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferred. The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA resin. If the amount of the halide is greater than 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may overflow and the finally produced polarizer may become white and turbid. The laminate of the halide-containing PVA-based resin layer and the polyester-based resin base material is stretched at high temperature in the air (auxiliary stretching) before stretching in boric acid water, thereby promoting the PVA-based resin layer after the auxiliary stretching. Crystallization of PVA-based resin. As a result, when the PVA-based resin layer is immersed in a liquid, the orientation disorder and the decrease in orientation of the polyvinyl alcohol molecules are more suppressed than when the PVA-based resin layer does not contain a halide. In this way, the optical properties of the final polarizer can be improved.

Additives may also be blended into the coating liquid. Examples of additives include plasticizers, surfactants, etc. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer. Examples of additives include easy-adhesion components. By using easy-adhesion components, the adhesion between the polyester resin base material and the PVA resin layer can be improved. As a result, problems such as peeling off of the PVA-based resin layer from the polyester-based base material can be suppressed, and dyeing and water stretching described below can be performed favorably. Modified PVA such as acetyl-acetyl modified PVA can be used as the easy-adhering component.

The coating liquid can be applied by any appropriate method. For example, roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, doctor blade coating (comma coating, etc.), etc. The coating and drying temperature of the coating liquid is preferably 50°C or above.

The thickness of the PVA-based resin layer (thickness before stretching described below) is preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the polyester-based resin base material may be subjected to surface treatment (such as corona treatment, etc.), or the polyester-based resin base material may be coated with a composition for forming an easy-adhesive layer (coating treatment). ). By performing the above treatment, the adhesion between the polyester resin base material and the PVA resin layer can be improved. As a result, problems such as peeling off of the PVA-based resin layer from the polyester-based resin base material can be suppressed, and dyeing and stretching described below can be performed satisfactorily.

F-2. In-air stretching treatment The stretching method for in-air auxiliary stretching can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching by passing the laminate through rollers of different circumferential speeds). In one embodiment, the in-air stretching treatment includes a hot roller stretching step, which is to transport the laminate along its long side while stretching it with the circumferential speed difference between the hot rollers. The in-air stretching treatment typically includes a zone stretching step and a hot roller stretching step. In addition, the order of the zone stretching step and the hot roller stretching step is not limited, and the zone stretching step can be performed first, or the hot roller stretching step can be performed first. The zone stretching step can also be omitted. In one embodiment, the area extension step and the hot roller extension step are performed sequentially.

The stretching temperature of the laminate can be set to an arbitrary and appropriate value according to the forming material of the polyester resin substrate, the stretching method, etc. The stretching temperature of the air stretching treatment is preferably above the glass transition temperature (Tg) of the polyester resin substrate, and more preferably above the glass transition temperature (Tg) of the polyester resin substrate + 10°C, and particularly preferably above Tg + 15°C. On the other hand, the upper limit of the stretching temperature of the laminate is preferably 170°C. Stretching at the above temperature can inhibit the rapid progress of crystallization of the PVA resin, thereby inhibiting the adverse conditions caused by the crystallization (for example, hindering the orientation of the PVA resin layer due to stretching).

F-3. Insolubility treatment The above-mentioned insolubility treatment is typically performed by immersing the PVA resin layer in a boric acid aqueous solution. By performing the insolubility treatment, water resistance can be imparted to the PVA 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 insolubility bath (boric acid aqueous solution) is preferably 20°C to 50°C. The insolubility treatment is preferably performed before the above-mentioned in-water stretching or the above-mentioned dyeing treatment.

F-4. Dyeing treatment The dyeing of the PVA-based resin layer is typically performed by adsorbing iodine to the PVA-based resin layer. Examples of the adsorption method include: a method of immersing the PVA-based resin layer (laminated body) in a dyeing liquid containing iodine, a method of applying the dyeing liquid on the PVA-based resin layer, and a method of spraying the dyeing liquid onto the PVA Methods on the resin layer, etc. It is preferable to use a method of immersing the PVA-based resin layer (laminated body) in a dyeing solution. This is because it can adsorb iodine 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 advisable to mix iodide into the iodine aqueous 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, more preferably 0.1 to 10 parts by weight. In order to inhibit the dissolution of PVA-based resin, the liquid temperature of the dyeing solution during dyeing should be 20℃~50℃. 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, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or single transmittance of the finally obtained polarizer falls within a predetermined range. 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 such that the single transmittance of the obtained polarizer becomes 40% to 44%.

Dyeing can be performed at any appropriate time. It is better to do it before extending in the water.

F-5. Crosslinking treatment The crosslinking treatment is typically performed by immersing the PVA resin layer (laminated body) in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA resin layer. The concentration of the aqueous boric acid 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 dyeing treatment, an iodide is preferably further blended. By blending an iodide, the elution of iodine adsorbed to the PVA 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 iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20°C to 60°C. The crosslinking treatment is preferably performed before the in-water stretching treatment. The ideal implementation form is to carry out air stretching treatment, dyeing treatment and cross-linking treatment in sequence.

F-6. Underwater stretching treatment The manufacturing steps of the polarizing plate are as described above, including: subjecting the laminate to an underwater stretching treatment in a stretching bath. Specifically, the laminate is stretched in an underwater direction parallel to the stretching direction of the laminate. By stretching in an underwater manner, the laminate can be stretched at a temperature lower than the glass transition temperature (typically about 80°C) of the polyester resin substrate or the PVA resin layer, and a high-ratio stretching can be performed while suppressing the crystallization of the PVA resin layer. As a result, a polarizer with excellent optical properties (such as polarization degree) can be produced. In addition, in this specification, "parallel direction" includes 0°±5.0°, preferably 0°±3.0°, and more preferably 0°±1.0°.

The stretching temperature (liquid temperature of the stretching bath) for stretching in water is preferably below 69°C, and more preferably below 67°C. The lower limit of the liquid temperature of the stretching bath is preferably 40°C, and more preferably 50°C. By setting the liquid temperature of the stretching bath within the above range, the durability index of the polyester resin substrate can be adjusted to a value within the ideal range by adding and multiplying it with the maximum heating temperature in the heat treatment described later. Moreover, as long as the temperature is as mentioned above, the dissolution of the PVA resin layer can be suppressed, and at the same time, it can be stretched at a high ratio. Specifically, as mentioned above, considering the relationship with the formation of the PVA resin layer, the glass transition temperature (Tg) of the polyester resin substrate is preferably above 60°C. At this time, if the stretching temperature is lower than 40°C, even if the polyester resin substrate is plasticized by 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 resin layer, and it may not be possible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath should be 15 seconds to 5 minutes.

The extension method of the water extension treatment can adopt any appropriate method. Specifically, it can be a fixed end extension or a free end extension. The extension direction of the laminated body is essentially the extension direction (longitudinal direction) of the above-mentioned air extension. The extension of the laminated body can be carried out in one stage or in multiple stages.

The underwater stretching is preferably performed by immersing the laminate in an aqueous solution of boric acid (boric acid underwater stretching). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be given the rigidity to withstand the tension during stretching and the water resistance to be insoluble in water. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution and can crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance and can be stretched well, and a polarizer with excellent optical properties (such as polarization degree) can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or boric acid salt in a solvent, i.e., water. 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 resin layer can be effectively suppressed, and a polarizer with higher characteristics can be manufactured. In addition to boric acid or boric acid salt, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

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

By combining the above-mentioned polyester resin base material with water stretching (boric acid water stretching), high-magnification stretching is possible, and polarizers with excellent optical properties (such as polarization degree) can be produced. Specifically, the maximum stretch ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more relative to the original length of the laminated body (including the stretch ratio of the laminated body). The "maximum stretch ratio" in this specification means the stretch ratio just before the laminated body breaks, and is a value that is 0.2 lower than the value after confirming the stretch ratio at which the laminated body breaks. In addition, the maximum stretching magnification of a laminate using the above-mentioned polyester resin base material will be higher if it is stretched through water than if it is stretched only by stretching in the air.

F-7. Washing treatment The cleaning treatment can typically be performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution. The drying temperature during drying treatment should be 30℃~100℃.

F-8. Heat treatment The heat treatment is performed after stretching in water. The polyester resin substrate can be crystallized by heat treatment. The heat treatment is typically performed by heating the conveying roller arranged in the heating mechanism 160 (using a so-called hot roller roller (heating roller)) (hot roller roller heating method). In one embodiment, the heating mechanism 160 is an oven, and a heating method (oven heating method) by conveying hot air into the oven can also be used in combination. By using the hot roller roller heating method and the oven heating method in combination, the rapid temperature change between the hot roller rollers can be suppressed, and the shrinkage of the laminate 10' in the width direction can be easily controlled. The temperature inside the oven should be between 30℃ and 100℃. The heating time should be between 1 second and 300 seconds. The wind speed should be between 10m/s and 30m/s. The wind speed is the wind speed inside the oven, which can be measured with a mini fan-type digital anemometer.

Heating with a hot roller can suppress curling and produce polarizers with excellent appearance. Specifically, heating the laminated body 10' while it is along the hot roller can effectively promote the crystallization of the polyester resin base material and increase the degree of crystallization, even under low heating conditions. At high temperatures, it can still effectively increase the crystallization degree of polyester resin base materials. As a result, the rigidity of the polyester-based resin base material increases and becomes a state that can withstand shrinkage of the PVA-based resin layer due to heating, thereby suppressing curling. Furthermore, by using a heating roller, the laminate 10' can be heated while maintaining a flat state, so that not only curling but also wrinkles can be suppressed.

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

Among the multiple hot rollers, when the temperature of the hot roller set to the highest temperature is the "highest heating temperature", the highest heating temperature is 102°C or higher, preferably 105°C or higher, and more preferably 110°C or higher. The upper limit of the highest 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 added and multiplied with the temperature of the stretching bath in the underwater stretching treatment, and the durability index of the polyester resin substrate can be adjusted to a value within the ideal range. In addition, the temperature of the hot roller can be measured by a contact thermometer. The contact time of the laminate with the hot roller kept at the highest heating temperature (when there are multiple hot rollers at the highest heating temperature, the total contact time) is preferably 0.2 seconds to 2 seconds, more preferably 0.5 seconds to 2 seconds. In addition, "contact time" means the time from when any point on the laminate contacts the outer peripheral surface of the hot roller kept at the highest heating temperature to when it leaves.

G. Image display device The polarizing plate described in items A to E above, which is manufactured by the manufacturing method described in item F above, can be applied to image display devices such as liquid crystal display devices. Therefore, the present invention includes an image display device using the polarizing plate described above. The image display device of the embodiment of the present invention has the polarizing plate described in items A to E above. Example

Hereinafter, the present invention will be specifically described with reference to 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) The thickness is measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C"). (2) Durability index A Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name "SPECTRUM2000") was used for the polyester-based resin base material of the polarizing plate prepared in the Example and Comparative Example. , by FT-IR measurement using attenuated total reflection spectroscopy (non-polarized ATR method) using non-polarized light as the measurement light, the absorption intensity at 1340 cm ^-1 and the absorption intensity at 1410 cm ^-1 were measured, and the durability was calculated by the following formula index. Furthermore, assuming that the traveling direction of the infrared rays in the direction in which the polyester resin base material extends is 90° and the incident angle of the infrared rays incident on the polyester resin base material is 45°, the above-mentioned absorption intensity was measured. (Durability index) = (Absorption intensity at 1340 cm ^-1 )/(Absorption intensity at 1410 cm ^-1 ) (3) Adhesion evaluation Cut the long strip polarizing plate prepared in the Example and Comparative Example into 150 mm The dimensions of (MD direction) × 200mm (TD direction) are used to make evaluation samples. Paste the polarizer side of the above evaluation sample to the glass through an acrylic adhesive and store it at 60°C/90%Rh for 500 hours. Check whether the end of the evaluation sample has peeled off from the glass. Furthermore, if the evaluation sample peels off from the glass, measure the length of the peeled off portion.

<Example 1> A long strip of amorphous isophthalic acid copolymer polyethylene terephthalate (IPA copolymer PET) film (thickness: 100 μm, IPA modification degree: 5 mol %) was used as the polyester resin substrate. (Degree of modification = [ethylene isophthalate unit] / [ethylene terephthalate unit + ethylene isophthalate unit]) After corona treatment (treatment conditions: 50 W・min/ ^m2 ) on one side of the polyester resin substrate, a mixed solution (solid content concentration 4.0%) prepared by mixing an aqueous dispersion of a modified polyolefin resin (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") and pure water (manufactured by Unitika, trade name "ARROW BASE SE1030N") of acetylacetyl-modified polyvinyl alcohol (PVA) was applied to the corona treated surface to a thickness of 2000 nm after drying, and dried at 65°C for 2 minutes to form a base coat. Here, the solid content mixing ratio of acetyl acetyl modified PVA and modified polyolefin in the mixed solution is 30:70. Then, a PVA resin mixed with 90 parts by weight of PVA (polymerization degree 4200, saponification degree 99.2 mol%) and 10 parts by weight of acetyl acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") and 13 parts by weight of potassium iodide per 100 parts by weight of the PVA resin was applied to the base coating surface at 25°C and dried at 60°C for 3 minutes to form a PVA resin layer with a thickness of 13 μm. A laminate was prepared as described above. In an oven at 140°C, the obtained laminate was subjected to free-end uniaxial stretching in the longitudinal direction (long side direction) by 2 times between rollers of different circumferential speeds (air-assisted stretching). Then, the laminate was immersed in an insoluble bath (a boric acid aqueous 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 (insoluble treatment). Then, it was immersed in a dyeing bath (an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine with 1.5 parts by weight of potassium iodide with 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 (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) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). After that, the laminate was immersed in a stretching bath (stretching bath temperature: 67°C) of a boric acid aqueous solution (boric acid aqueous solution obtained 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) while being uniaxially stretched to 2.75 times (total stretching ratio: 5.5 times) in the longitudinal direction (long side direction) between rollers of different peripheral speeds (underwater stretching treatment). Afterwards, the laminate was immersed in a cleaning bath (an 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). Then, in an oven having multiple heating rollers maintained at 80-110°C and maintained at 80°C, the laminate was heat-treated while being transported by the heating rollers in such a manner that the laminate was in contact with the heating rollers maintained at a maximum heating temperature of 110°C for a total of 1 second. In the above manner, a long strip of polarizing plate 1 having a polarizer with a thickness of 5 μm laminated on a polyester resin substrate was obtained. The durability index of the polyester resin substrate of the polarizing plate 1 was 0.77. After the polarizing plate 1 was subjected to the above-mentioned adhesion evaluation, no peeling from the glass occurred.

<Example 2> 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 durability index of the polyester resin base material of the polarizing plate 2 is 0.67. The polarizing plate 2 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

<Example 3> Polarizing plate 3 was prepared 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 durability index of the polyester resin substrate of polarizing plate 3 was 0.61. Polarizing plate 3 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

<Example 4> The laminate was produced in the same manner as in Example 1 except that the laminate was stretched in water using a stretching bath with a stretching bath temperature of 69°C, the maximum heating temperature was set to 105°C, and the total contact time was set to 1 second. Get polarizing plate 4. The durability index of the polyester resin base material of the polarizing plate 4 is 0.62. The polarizing plate 4 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

<Comparative Example 1> Polarizing plate 5 was prepared in the same manner as in Example 1 except that the maximum heating temperature was set to 100°C and the total contact time was set to 1 second. The durability index of the polyester resin substrate of polarizing plate 5 was 0.58. Polarizing plate 5 was subjected to the same evaluation as in Example 1. 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 95° C. and the total contact time was 1 second. The durability index of the polyester resin base material of the polarizing plate 6 is 0.49. The polarizing plate 6 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

<Comparative Example 3> Polarizing plate 7 was prepared in the same manner as in Example 1 except that the furnace temperature 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 durability index of the polyester resin substrate of polarizing plate 7 was 0.39. Polarizing plate 7 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

＜Comparative Example 4＞ Polarizing plate 8 was produced in the same manner as in Example 4 except that the maximum heating temperature was 102° C. and the total contact time was 1 second. The durability index of the polyester resin base material of the polarizing plate 8 is 0.56. The polarizing plate 8 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

＜Comparative Example 5＞ Polarizing plate 9 was produced in the same manner as in Example 4 except that the maximum heating temperature was 100° C. and the total contact time was 1 second. The durability index of the polyester resin base material of the polarizing plate 9 is 0.54. The polarizing plate 9 was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Table 1]

It is obvious from Table 1 that polarizing plates with a durability index of 0.60 or above will not peel off from the glass even when placed in a high temperature and high humidity environment.

industrial availability 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‧‧‧Polarizing element 101‧‧‧Release section 110‧‧‧Bath of boric acid aqueous solution 111, 112, 121, 122, 131, 132, 141, 142, 151, 152‧‧‧Roller 120‧‧‧Bath of dichroic substance (iodine) and potassium iodide aqueous solution 130‧‧‧Bath of boric acid and potassium iodide aqueous solution 140‧‧‧Stretching bath of boric acid aqueous solution 150‧‧‧Bath of potassium iodide aqueous solution 160‧‧‧Heating mechanism 170‧‧‧Rolling section

FIG1 is a cross-sectional view of a polarizing plate in one embodiment of the present invention. FIG2 is a schematic diagram showing the manufacturing steps of a polarizing plate in one embodiment.

10‧‧‧Polarizing plate

11‧‧‧Polyester resin base material

12‧‧‧Polarizer

Claims (6)

A method for manufacturing a polarizing plate, wherein the polarizing plate comprises: a polyester resin substrate and a polarizer laminated on one side of the polyester resin substrate; the thickness of the polarizer is less than 10 μm; and the polyester resin substrate has an absorption intensity of P(1340) at 1340 cm ^-1 and P(1410 cm-1) at 1410 cm-1 measured by FT-IR of a non-polarized ATR method. ^-1 is P(1410), the value of P(1340)/P(1410) is greater than 0.60, and the manufacturing method includes: forming a polyvinyl alcohol resin layer on one side of the aforementioned polyester resin substrate to form a laminate; dyeing and stretching the aforementioned laminate to make the aforementioned polyvinyl alcohol resin layer into a polarizer; and heat-treating the laminate of the aforementioned polyester resin substrate and the aforementioned polarizer after the aforementioned stretching; wherein, the temperature of the stretching bath in the aforementioned stretching is below 67°C, and the maximum heating temperature in the aforementioned heating treatment is above 102°C, or, the temperature of the stretching bath in the aforementioned stretching is below 69°C, and the maximum heating temperature in the aforementioned heating treatment is above 105°C; and in the aforementioned heating treatment, the time maintained at the maximum heating temperature is 0.2 seconds to 2 seconds. The method for manufacturing a polarizing plate according to claim 1, wherein the polarizing element is laminated on the polyester resin base material without an adhesive layer. Unilateral. A method for manufacturing a polarizing plate as claimed in claim 1 or 2, wherein an easy-to-bond layer is provided between the aforementioned polyester resin substrate and the aforementioned polarizing element. A method for manufacturing a polarizing plate as claimed in claim 1 or 2, wherein the aforementioned polyester resin substrate functions as a protective layer of the aforementioned polarizing element. The method of manufacturing a polarizing plate according to claim 3, wherein the polyester resin base material functions as a protective layer of the polarizer. A method for manufacturing an image display device, comprising a method for manufacturing a polarizing plate as described in any one of claims 1 to 5.