Method for manufacturing polarizing films

Abstract

To provide a polarizing film that combines high optical properties with excellent appearance. [Solution] A method for manufacturing a polarizing film according to an embodiment of the present invention includes the steps of: obtaining a resin film having a first moisture content (W1) through treatment with water; adjusting the moisture content of the resin film from the first moisture content (W1) to a second moisture content (W2); and drying the resin film having the second moisture content (W2), wherein the ratio of the second moisture content (W2) to the first moisture content (W1) (W2 / W1) is less than 1; the drying reduces the moisture content of the resin film from the second moisture content (W2) to a third moisture content (W3); the ratio of the third moisture content (W3) to the second moisture content (W2) (W3 / W2) is 0.25 or less; and the adjustment is performed by placing the resin film in an environment with a humidity of 35% RH or higher.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a polarizing film.

Background Art

[0002] In a liquid crystal display device, which is a typical image display device, polarizing films are disposed on both sides of a liquid crystal cell due to its image forming method. Further, with the spread of thin displays, displays (OLED) equipped with an organic electroluminescence (EL) panel and displays (QLED) using a display panel using an inorganic light emitting material such as quantum dots have been proposed. These panels have a highly reflective metal layer and are likely to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circular polarizing plate having a polarizing film and a λ / 4 plate on the viewing side. As a method for manufacturing a polarizing film, for example, a method has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA) - based resin layer is stretched and then dyed to obtain a polarizing film on the resin substrate (for example, Patent Document 1). According to such a method, since a thin polarizing film can be obtained, it has attracted attention as being able to contribute to the thinning of recent image display devices.

[0003] However, there is a problem that it is not easy for a thin polarizing film to achieve both high optical properties and good appearance. Specifically, the higher the optical properties, the more likely appearance problems are to occur. Poor appearance of the polarizing film may affect the display characteristics of the image display device. For example, if streak - like marks occur on the polarizing film, it may be visually recognized as a poor appearance (texture) in the configuration of the laminated film (for example, a circular polarizing plate).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] This invention was made to solve the above problems, and its main objective is to provide a polarizing film that combines high optical properties with excellent appearance. [Means for solving the problem]

[0006] According to embodiments of the present invention, a method for manufacturing a polarizing film is provided. This manufacturing method includes the steps of: obtaining a resin film having a first moisture content (W1) through treatment with water; adjusting the moisture content of the resin film from the first moisture content (W1) to a second moisture content (W2); and drying the resin film having the second moisture content (W2), wherein the ratio of the second moisture content (W2) to the first moisture content (W1) (W2 / W1) is less than 1; the drying reduces the moisture content of the resin film from the second moisture content (W2) to a third moisture content (W3); the ratio of the third moisture content (W3) to the second moisture content (W2) (W3 / W2) is 0.25 or less; and the adjustment is performed by placing the resin film in an environment with a humidity of 35% RH or higher. In one embodiment, the above adjustment is performed by placing the resin film in an environment with a temperature of less than 40°C. In one embodiment, the difference between the temperature at which the drying is performed and the temperature at which the adjustment is performed is 25°C or more. In one embodiment, the difference between the humidity used for adjustment and the humidity used for drying is 30%RH or more. In one embodiment, the resin film is dried in an environment with a temperature of 60°C or higher and a humidity of 10%RH or lower. In one embodiment, the ratio (W2 / W1) of the second moisture content (W2) to the first moisture content (W1) is 0.4 or greater. In one embodiment, the above-mentioned first moisture content (W1) is 30% or more. In one embodiment, a polarizing film with a thickness of 7 μm or less is obtained by the above manufacturing method. [Effects of the Invention]

[0007] According to embodiments of the present invention, a polarizing film can be obtained that combines high optical properties with excellent appearance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing the general structure of a laminate according to one embodiment of the present invention. [Figure 2] This graph shows the relationship between the film thickness and moisture content of a resin film after treatment with water. [Figure 3] This is a schematic diagram showing an example of the manufacturing process for polarizing films. [Figure 4] This is a schematic diagram showing an example of drying using heated rollers in the drying zone. [Figure 5] This is a schematic cross-sectional view showing the general configuration of a polarizing plate according to one embodiment of the present invention. [Figure 6] This is an observation photograph of the polarizing plate in Comparative Example 1. [Modes for carrying out the invention]

[0009] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0010] (Definitions of terms and symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Thickness Directional Phase Difference (Rth) "Rth(λ)" is the thickness directional phase difference measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the thickness directional phase difference measured with light of wavelength 550 nm at 23°C. When the thickness of the layer (film) is d (nm), Rth(λ) is obtained by the formula: Rth(λ) = (nx - nz) × d. (4) Nz Coefficient The Nz coefficient is obtained by Nz = Rth / Re.

[0011] The method for manufacturing a polarizing film according to one embodiment of the present invention includes a step of obtaining a resin film having a first moisture content (W1) through a treatment using water, an adjustment step of adjusting the moisture content of the resin film from the first moisture content (W1) to a second moisture content (W2), and a drying step of drying the resin film having the second moisture content (W2).

[0012] A. Resin Film The above resin film can be obtained, for example, by forming a resin layer (typically a polyvinyl alcohol-based resin layer) on a resin substrate to produce a laminate, and stretching and dyeing this laminate with a dichroic substance such as iodine (for example, dyeing by adsorption of iodine).

[0013] A-1. Laminate FIG. 1 is a schematic cross-sectional view showing the schematic configuration of a laminate according to one embodiment of the present invention. The laminate 1 has a thermoplastic resin substrate (for example, in a long shape) 2 and a polyvinyl alcohol (PVA)-based resin layer 3. Preferably, the laminate 1 is produced by forming a PVA-based resin layer 3 containing a PVA-based resin and a halide on the thermoplastic resin substrate 2. Specifically, a coating solution containing a PVA-based resin and a halide is applied onto the thermoplastic resin substrate 2 and dried to form the PVA-based resin layer 3.

[0014] The thickness of the thermoplastic resin substrate 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 the PVA-based resin layer. If it exceeds 300 μm, for example, in the underwater stretching described later, it may take time for the thermoplastic resin substrate to absorb water, and it may require an excessive load to stretch.

[0015] The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or higher, and more preferably 0.3% or higher. Such a thermoplastic resin substrate can absorb water, and the water acts as a plasticizer, causing plasticization. As a result, the tensile stress is significantly reduced, and it can be stretched to a high magnification. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or lower, and more preferably 1.0% or lower. With such a water absorption rate, it is possible to prevent problems such as a significant decrease in the dimensional stability of the thermoplastic resin substrate during manufacturing, which would lead to deterioration of the quality of the resulting polarizing film. It is also possible to prevent the thermoplastic resin substrate from breaking or the PVA-based resin layer from peeling off during underwater stretching. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined in accordance with JIS K 7209.

[0016] The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin substrate, it is possible to sufficiently ensure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate by water and the ability to perform underwater stretching well, the Tg is more preferably 100°C or lower, and even more preferably 90°C or lower. On the other hand, the Tg of the thermoplastic resin substrate is preferably 60°C or higher. With such a Tg, when applying and drying the coating liquid, it is possible to prevent defects such as deformation of the thermoplastic resin substrate (e.g., the occurrence of unevenness, sagging, wrinkles, etc.) and to produce a well-made laminate. In addition, the stretching of the resin layer can be performed well at a suitable temperature (e.g., around 60°C). The Tg of the thermoplastic resin substrate can be adjusted, for example, by introducing modifying groups into the constituent materials or by heating with a crystallizing material. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

[0017] Any suitable thermoplastic resin can be used as the constituent material of the thermoplastic resin substrate. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferred.

[0018] In one embodiment, amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among these, amorphous (less crystallized) polyethylene terephthalate resin is particularly preferred. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and / or cyclohexanedicarboxylic acid as the dicarboxylic acid, and copolymers further containing cyclohexanedimethanol or diethylene glycol as the glycol.

[0019] In another embodiment, a polyethylene terephthalate resin having isophthalic acid units is preferably used. This is because it has excellent stretchability and crystallization during stretching can be suppressed. This is thought to be due to the introduction of isophthalic acid units, which gives the main chain a large degree of bending. The polyethylene terephthalate resin has terephthalic acid units and ethylene glycol units. The content of isophthalic acid units is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more, relative to the total of all repeating units. This is because a thermoplastic resin substrate with excellent stretchability can be obtained. On the other hand, the content of isophthalic acid units is preferably 20 mol% or less, and more preferably 10 mol% or less, relative to the total of all repeating units. This is because the degree of crystallinity can be increased well during drying, which will be described later.

[0020] The thermoplastic resin substrate may be stretched beforehand (for example, before forming the PVA resin layer). In one embodiment, the thermoplastic resin substrate is stretched transversely in a long shape. The transverse direction is preferably perpendicular to the stretching direction of the laminate described later. In this specification, "perpendicular" also includes substantially perpendicular directions. Here, "substantially perpendicular" includes the case where the direction is 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°. The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C relative to the glass transition temperature (Tg) of the thermoplastic resin substrate. The stretching ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times. Any suitable method can be used to stretch the thermoplastic resin substrate. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be dry or wet. The stretching may be carried out in one stage or in multiple stages. If it is carried out in multiple stages, the stretching ratio is the product of the stretching ratios of each stage.

[0021] The above coating solution is typically a solution obtained by dissolving a PVA-based resin and a halide in a solvent. Examples of solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The content of the PVA-based resin in the coating solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. Within this range, a uniform coating film that adheres closely to the thermoplastic resin substrate can be formed. The content of the halide in the coating solution is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.

[0022] Examples of the above-mentioned PVA-based resins include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers are obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of PVA-based resins 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%. By using PVA-based resins with such a degree of saponification, a polarizing film with excellent durability can be obtained. If the degree of saponification is too high, there is a risk of gelation. The degree of saponification can be determined in accordance with JIS K 6726-1994.

[0023] The average degree of polymerization of PVA resins is typically 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

[0024] Any suitable halide can be used as the above-mentioned halide. For example, iodides such as potassium iodide, sodium iodide, and lithium iodide, and chlorides such as sodium chloride can be used. Among these, potassium iodide is preferred. By using a halide, a polarizing film with high optical properties can be obtained. Specifically, the crystallization of the PVA resin after the air-assisted stretching described later is promoted, and in subsequent wet processing (e.g., dyeing and water stretching described later), disorder in the orientation and decrease in orientation of polyvinyl alcohol molecules are suppressed, and a polarizing film with high optical properties can be obtained.

[0025] In preparing the coating solution, it is preferable to blend 5 to 20 parts by weight of halogen with 100 parts by weight of PVA resin, and more preferably 10 to 15 parts by weight. Specifically, the halogen content in the resulting PVA resin layer is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, per 100 parts by weight of PVA resin. If the amount of halogen relative to the PVA resin is too high, for example, the halogen may bleed out, and the resulting polarizing film may become cloudy.

[0026] Additives may be added to the coating solution. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These are used, for example, to improve the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

[0027] Examples of application methods for the above coating solution include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The application and drying temperature of the coating solution is preferably 50°C or higher.

[0028] The thickness of the above PVA-based resin layer is preferably 3 μm to 40 μm, and more preferably 3 μm to 20 μm.

[0029] Before forming the PVA resin layer, the thermoplastic resin substrate may be subjected to surface treatment (e.g., corona treatment), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatments, the adhesion between the thermoplastic resin substrate and the PVA resin layer can be improved.

[0030] A-2. Stretching The stretching described above is preferably carried out by dry stretching (air-assisted stretching) of the laminate followed by underwater stretching. Auxiliary stretching allows stretching while suppressing crystallization of the thermoplastic resin substrate, solving the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate in boric acid underwater stretching, and enabling stretching of the laminate to a higher magnification. Furthermore, when using a thermoplastic resin substrate, the coating temperature may be set low, which can lead to a problem where the crystallization of the PVA resin is relatively low and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA resin can be increased even when using a thermoplastic resin. In addition, by increasing the orientation of the PVA resin in advance, problems such as a decrease in the orientation of the PVA resin or dissolution can be prevented during subsequent wet processing. In this way, a polarizing film with high optical properties can be obtained.

[0031] The method of aerial assisted stretching may be fixed-end stretching (for example, stretching using a tenter stretcher) or free-end stretching (for example, uniaxial stretching by passing the laminate between rolls with different peripheral speeds). Preferably, free-end stretching is employed. For example, heated roll stretching is employed, in which the laminate is stretched by the difference in peripheral speed between heated rolls while being conveyed in its longitudinal direction. In one embodiment, aerial assisted stretching includes a zone stretching step in a hot space (zone) and a heated roll stretching step. The order of the zone stretching step and the heated roll stretching step is not limited, but for example, the zone stretching step and the heated roll stretching step are performed in this order. In another embodiment, in a tenter stretcher, the film end is gripped and stretched by widening the distance between tenters in the flow direction (the widening of the distance between tenters becomes the stretching ratio). At this time, the distance of tenters in the width direction (perpendicular to the flow direction) is preferably set to be closer to the stretching ratio in the flow direction than that of free-end stretching. In the case of free-end stretching, the shrinkage rate in the width direction is given by the formula: Shrinkage rate in the width direction = (1 / stretching ratio) 1 / 2 It is calculated as follows.

[0032] The extension ratio for aerial assisted extension is preferably 2.0 to 3.5 times. Aerial assisted extension may be performed in one stage or in multiple stages. When performed in multiple stages, the extension ratio is the product of the extension ratios of each stage. The extension direction in aerial assisted extension is preferably substantially the same as the extension direction of underwater extension described later.

[0033] The stretching temperature in air-assisted stretching is set to an arbitrary appropriate value depending on the thermoplastic resin substrate used, the stretching method, etc. Preferably, the stretching temperature is above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above Tg+10°C, and even more preferably above Tg+15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress the rapid crystallization of the PVA-based resin and suppress problems caused by such crystallization (for example, hindering the orientation of the PVA-based resin layer by stretching).

[0034] The above underwater stretching is typically performed by immersing the laminate in a stretching bath. Underwater stretching allows stretching at a temperature lower than the glass transition temperature (typically around 80°C) of the thermoplastic resin substrate or PVA-based resin layer, enabling high-magnification stretching of the PVA-based resin layer while suppressing its crystallization. As a result, a polarizing film with high optical properties can be obtained.

[0035] The method of underwater stretching may be fixed-end stretching or free-end stretching (for example, uniaxial stretching by passing the laminate between rolls with different peripheral speeds). Preferably, free-end stretching is used. The stretching of the laminate may be carried out in one stage or in multiple stages. In the case of multiple stages, the stretching ratio of the laminate, as described later, is the product of the stretching ratios of each stage.

[0036] Stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, the PVA resin layer can be given rigidity to withstand the tension applied during stretching and water resistance that prevents it from dissolving in water. Specifically, boric acid can generate tetrahydroxyborate anions in the aqueous solution and crosslink with the PVA resin by hydrogen bonding. As a result, the PVA resin layer can be given rigidity and water resistance, allowing for good stretching and the acquisition of a polarizing film with high optical properties.

[0037] The above-mentioned aqueous boric acid solution is preferably obtained by dissolving boric acid and / or a borate in water, which is the solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and even more preferably 3 to 5 parts by weight, per 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 polarizing film with higher properties can be produced. In addition to boric acid or a borate, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc., in a solvent can also be used.

[0038] Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By adding an iodide, the elution of iodine adsorbed on the PVA resin layer can be suppressed. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of the iodide is preferably 0.05 to 15 parts by weight, and more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

[0039] The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, more preferably 60°C or higher, and may also be 65°C or higher. At such temperatures, high magnification stretching is possible, and a polarizing film with high optical properties can be obtained. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA resin layer. In this case, if the stretching temperature is below 40°C, even considering the plasticization of the thermoplastic resin substrate by water, it may not be possible to stretch it well. Furthermore, even if stretched at such temperatures, a polarizing film with an excellent appearance can be obtained by adjusting the moisture content as described later. On the other hand, the stretching temperature is preferably 75°C or lower, more preferably 70°C or lower, and may also be 65°C or lower. The higher the stretching temperature, the higher the solubility of the PVA resin layer, and it may not be possible to obtain high optical properties. With such stretching temperatures, a polarizing film with an even better appearance can be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0040] The stretching ratio by underwater stretching is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretching ratio of the laminate (stretching ratio combining air-assisted stretching and underwater stretching) is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more, relative to the original length of the laminate. By achieving such high stretching ratios, it is possible to manufacture polarizing films with extremely excellent optical properties. Such high stretching ratios can be achieved by employing an underwater stretching method (boric acid underwater stretching).

[0041] A-3. Dyeing The above dyeing is typically performed by adsorbing iodine onto a PVA-based resin layer. Methods for iodine adsorption include, for example, immersing the PVA-based resin layer (laminated structure) in a dyeing solution containing iodine, coating the PVA-based resin layer with the dyeing solution, or spraying the dyeing solution onto the PVA-based resin layer. Preferably, the laminate is immersed in the dyeing solution (dyeing bath) because this allows for good adsorption of iodine.

[0042] The above-mentioned dyeing solution is preferably an iodine aqueous solution. The amount of iodine added is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. To increase the solubility of iodine in water, it is preferable to add iodide to the iodine aqueous solution. Specific examples of iodide are as described above. Potassium iodide is preferably used. The amount of iodide added is preferably 0.1 to 10 parts by weight, and more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The temperature of the dyeing solution during dyeing is preferably 20°C to 50°C to suppress the dissolution of the PVA resin. When immersing the PVA resin layer in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes, and more preferably 30 seconds to 90 seconds, to ensure the permeability of the PVA resin layer.

[0043] The staining conditions (concentration, liquid temperature, immersion time) can be set, for example, so that the transmittance of the final polarizing film is 42.0% or higher and the degree of polarization is 99.98% or higher. As such staining conditions, for example, it is preferable that the ratio of iodine to potassium iodide content in the iodine aqueous solution used as the staining solution is 1:5 to 1:20, and more preferably 1:5 to 1:10.

[0044] When dyeing is performed immediately after a treatment in which a laminate is immersed in a treatment bath containing boric acid (for example, the immobilization treatment described later), boric acid may mix into the dyeing bath, changing the boric acid concentration in the dyeing bath and potentially leading to unstable dyeing properties. To suppress such instability in dyeing properties, the boric acid concentration in the dyeing bath is adjusted to preferably 4 parts by weight or less, more preferably 2 parts by weight or less, per 100 parts by weight of water. On the other hand, the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of water. In one embodiment, dyeing is performed using a dyeing bath that contains boric acid beforehand. This configuration can reduce the rate of change in boric acid concentration when boric acid is mixed into the dyeing bath. The amount of boric acid to be added to the dyeing bath in advance (the amount of boric acid not derived from the above treatment bath) is preferably 0.1 to 2 parts by weight, and more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of water.

[0045] A-4. Other processing If necessary, an insolubilization treatment is performed after the above-mentioned aerial assisted stretching, but before underwater stretching and dyeing. The insolubilization treatment is typically performed by immersing the 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, and a decrease in the orientation of PVA when immersed in water can be prevented. The concentration of the aqueous boric acid solution in the insolubilization treatment is preferably 1 to 4 parts by weight per 100 parts by weight of water. The temperature of the insolubilization treatment (temperature of the aqueous boric acid solution) is preferably 20°C to 50°C.

[0046] If necessary, a crosslinking treatment is performed after dyeing and before underwater stretching. Typically, the crosslinking treatment is carried out by immersing the PVA resin layer in an aqueous boric acid solution. By applying the crosslinking treatment, water resistance can be imparted to the PVA resin layer, and a decrease in the orientation of PVA can be prevented during subsequent underwater stretching. The concentration of the aqueous boric acid solution in the crosslinking treatment is preferably 1 to 5 parts by weight per 100 parts by weight of water. It is preferable to add iodide to the aqueous boric acid solution. By adding iodide, the elution of iodine adsorbed on the PVA resin layer can be suppressed. Specific examples of iodide are as described above. The amount of iodide to add is preferably 1 to 5 parts by weight per 100 parts by weight of water. The temperature of the crosslinking treatment (temperature of the aqueous boric acid solution) is preferably 20°C to 50°C.

[0047] Preferably, washing is performed after stretching in water. Typically, washing is carried out by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0048] B. Moisture content of the resin film The resin film that has undergone the above-described treatment with water has a first moisture content (W1), and the moisture content of such a resin film is adjusted. In one embodiment, as shown in Figure 2, the moisture content of the resin film is determined from the thickness of the resin film. The resin film's in-plane dimensional change due to water absorption is constrained by the resin substrate with low water absorption, and it is thought that the resin film expands in the thickness direction according to the amount of water absorbed. Therefore, it is thought that there is a correlation between the thickness of the resin film after treatment with water (for example, after the above-described washing) and the moisture content of the resin film. The graph in Figure 2 plots the data of the thickness of the resin film and the moisture content after treatment with water when the laminate was stretched in water under various stretching conditions (specifically, the boric acid concentration of the stretching bath) shown in Table 1 below. The approximation curve in the graph is an approximation curve obtained by the least squares method so that it is an exponential function from the plotted data. The moisture content in Figure 2 was calculated based on the dry weight method using the following formula. Moisture content of the resin film = (Weight of the resin film after treatment with water - Weight of the resin film after drying) / Weight of the resin film after drying

[0049] [Table 1]

[0050] The first moisture content (W1) is, for example, 20% or more, preferably 30% or more, may be 40% or more, may be 50% or more, or may be 60% or more. On the other hand, the first moisture content (W1) is, for example, 90% or less, preferably 80% or less, and more preferably 70% or less.

[0051] Figure 3 is a schematic diagram showing an example of the manufacturing process for a polarizing film. A laminate 1 of a resin substrate and a PVA-based resin layer is immersed in a bath 101 of boric acid aqueous solution by a conveyor roll (insolubilization treatment), and then immersed in a bath 102 of an aqueous solution of a dichroic substance (iodine) and potassium iodide (dyeing treatment). Next, it is immersed in a bath 103 of an aqueous solution of boric acid and potassium iodide (crosslinking treatment). Next, the laminate 1 is stretched by applying tension in the conveying direction with rolls of different speed ratios while immersed in a stretching bath 104 of boric acid aqueous solution (underwater stretching treatment). Next, the underwater stretched laminate 1 is immersed in a bath 105 of an aqueous solution of potassium iodide and washed (washing treatment). Although not shown in the figure, for example, the laminate 1 may undergo the above-mentioned air-assisted stretching before the insolubilization treatment.

[0052] After treatment with water (having passed through the water bath), the laminate 1 is transported to the conditioning zone 110, and then to the drying zone 120.

[0053] By passing through the adjustment zone 110, the resin film (PVA-based resin layer) of the laminate 1 can have its moisture content adjusted from the first moisture content (W1) to the second moisture content (W2) (adjustment step). Specifically, at the entrance to the adjustment zone 110, the resin film has the first moisture content (W1), and at the exit of the adjustment zone 110 (entrance to the drying zone 120), the resin film has the second moisture content (W2).

[0054] The second moisture content (W2) is, for example, 5% to 70%, preferably 15% to 60%, more preferably 20% to 50%, and even more preferably 20% to 45%. The ratio of the second moisture content (W2) to the first moisture content (W1) (W2 / W1) is preferably 0.4 or more, more preferably 0.5 or more. On the other hand, W2 / W1 is less than 1, preferably 0.8 or less, and more preferably 0.7 or less.

[0055] The temperature in the control zone 110 is preferably less than 40°C, more preferably 35°C or lower, and may also be 30°C or lower. On the other hand, the temperature in the control zone 110 is preferably 20°C or higher, and may also be 22°C or higher. By placing the resin film in an environment with such temperatures, the above-mentioned second moisture content (W2) can be successfully achieved over a predetermined period of time. The humidity in the control zone 110 is preferably 35%RH or higher, and more preferably 40%RH or higher. On the other hand, the humidity in the control zone 110 is, for example, 65%RH or lower. By placing the resin film in an environment with such humidity, the above-mentioned second moisture content (W2) can be successfully achieved over a predetermined period of time.

[0056] The passage time through the control zone 110 is, for example, 5 seconds to 4 minutes. The passage time through the control zone 110 corresponds, for example, to the time the resin film is left in an environment under predetermined conditions. In the control zone 110, the temperature and humidity do not necessarily have to be constant, but it is preferable that they are kept within the above temperature and humidity ranges.

[0057] The rate of decrease in moisture content (R1) during the adjustment process is, for example, 1.5% / second or less, preferably 1.3% / minute or less. On the other hand, R1 is, for example, 0.7% / minute or more.

[0058] By passing through the drying zone 120, the resin film reduces its moisture content from the second moisture content (W2) to the third moisture content (W3) (drying process). Specifically, at the entrance to the drying zone 120, the resin film has the second moisture content (W2), and at the exit of the drying zone 120, the resin film has the third moisture content (W3).

[0059] The third moisture content (W3) is, for example, 1% to 20%, preferably 1% to 10%, and more preferably 2% to 7%. The ratio of the third moisture content (W3) to the second moisture content (W2) (W3 / W2) is 0.25 or less, preferably 0.2 or less, more preferably 0.15 or less, even more preferably 0.14 or less, and particularly preferably 0.13 or less. On the other hand, W3 / W2 is, for example, 0.05 or more, and preferably 0.08 or more. The ratio of the third moisture content (W3) to the first moisture content (W1) (W3 / W1) is preferably 0.1 or less, more preferably 0.09 or less, and even more preferably 0.08 or less. On the other hand, W3 / W1 is, for example, 0.01 or more.

[0060] The rate of decrease in moisture content (R2) during the drying process is, for example, 0.2% / second or more and 0.8% / second or less, preferably 0.2% / second or more and 0.7% / second or less.

[0061] Drying can be carried out by any suitable method. For example, it may be carried out by heating the entire drying zone 120 (zone heating method), or by heating the conveying rolls in the drying zone 120 (heated roll method). Preferably, the heated roll method is used, and more preferably, both methods are used. By using heated rolls, heat curling of the laminate can be efficiently suppressed, and a high-quality polarizing film can be manufactured. Specifically, by drying the laminate while it is aligned with the heated rolls, the crystallization of the thermoplastic resin substrate can be efficiently promoted and the degree of crystallinity can be increased, and even at relatively low drying temperatures, the degree of crystallinity of the thermoplastic resin substrate can be increased well. As a result, the rigidity of the thermoplastic resin substrate increases, making it able to withstand the shrinkage of the resin film due to drying, and curling is suppressed. Furthermore, by using heated rolls, the laminate can be dried while being kept in a flat state, so not only curling but also wrinkles can be suppressed.

[0062] Drying can shrink the laminate in the width direction, improving its optical properties. For example, it can effectively enhance the orientation of PVA and PVA / iodine complexes. The shrinkage rate in the width direction of the laminate due to drying is preferably 1% to 10%, more preferably 2% to 8%, and even more preferably 4% to 7%. By using heated rolls, the laminate can be continuously shrunk in the width direction while being transported, achieving high productivity.

[0063] Figure 4 is a schematic diagram showing an example of drying using heated rolls in a drying zone. In the illustrated example, the laminate 1 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls are arranged to continuously heat the resin film surface and the thermoplastic resin substrate surface of the laminate 1 alternately, but for example, the transport rolls may be arranged to continuously heat only one side of the laminate (for example, the thermoplastic resin substrate surface).

[0064] In one embodiment, drying conditions can be controlled by adjusting the heating temperature of the conveying rolls (temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably 60°C to 120°C, more preferably 65°C to 100°C, and even more preferably 70°C to 90°C. Such temperatures can increase the degree of crystallinity of the thermoplastic resin, suppress curling, and provide the laminate with extremely excellent durability. Furthermore, a good moisture content can be achieved in the resin film. The temperature of the heating rolls can be measured using a contact thermometer. In the illustrated example, six conveying rolls are provided, but there is no particular limit to the number of conveying rolls as long as there are multiples. Typically, 2 to 40 conveying rolls are provided, preferably 4 to 30. The contact time between the laminate and the heating rolls (total contact time) is preferably 1 second to 300 seconds, more preferably 1 second to 20 seconds, and even more preferably 1 second to 10 seconds.

[0065] The drying zone 120, which may be provided with heating rolls, is preferably heated. For example, the drying zone 120 is the space inside a heating furnace (e.g., an oven). With this configuration, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature in the drying zone 120 is preferably 60°C or higher, more preferably 70°C or higher, even more preferably 80°C or higher, and particularly preferably 85°C or higher. On the other hand, the temperature in the drying zone 120 is preferably 105°C or lower, and more preferably 95°C or lower, from the viewpoint of suppressing the occurrence of wrinkles. The humidity in the drying zone 120 is preferably 10%RH or lower, and more preferably 5%RH or lower. On the other hand, the humidity in the drying zone 120 is, for example, 1%RH or higher. It is preferable that the heating furnace is in a blown air state. In this case, the wind speed of the hot air is, for example, about 10 m / s to 30 m / s. The wind speed inside the heating furnace can be measured with a mini vane type digital anemometer.

[0066] The temperature in the drying zone 120 is preferably higher than the temperature in the control zone 110. The difference between the temperature in the drying zone 120 and the temperature in the control zone 110 (the difference between the drying temperature and the control temperature) is preferably 25°C or higher and 70°C or lower, more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 55°C or higher. The humidity in the control zone 110 is preferably higher than the humidity in the drying zone 120. The difference between the humidity in the control zone 110 and the humidity in the drying zone 120 (the difference between the control humidity and the drying humidity) is preferably 30%RH or higher and 70%RH or lower, more preferably 35%RH or higher.

[0067] The passage time through the drying zone 120 is, for example, 5 seconds to 4 minutes. The passage time through the drying zone 120 corresponds, for example, to the time the resin film is left in an environment under predetermined conditions. In the drying zone 120, the temperature and humidity do not necessarily have to be constant, but it is preferable that they be kept within the above temperature and humidity ranges.

[0068] By drying the resin film after it has undergone the adjustment process, a polarizing film can be obtained that possesses both high optical properties and excellent appearance. The inventors have found that, for example, by controlling the moisture content of the resin film before drying, it is possible to achieve a balance between optical properties and appearance, which are generally considered to be in a trade-off relationship.

[0069] C. Polarizing film The polarizing film obtained according to the embodiment of the present invention is composed of a PVA-based resin film containing a dichroic substance such as iodine. The thickness of the polarizing film is, for example, 10 μm or less, preferably 8 μm or less, more preferably 7 μm or less, and even more preferably 6 μm or less. According to the embodiment of the present invention, a polarizing film of such thickness can achieve both high optical properties and excellent appearance. On the other hand, the thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more.

[0070] The polarizing film preferably exhibits absorption dichroism at a wavelength of any of 380 nm to 780 nm. The transmittance (Ts) of the polarizing film is preferably 41.0% or higher, more preferably 42.0% or higher, and even more preferably 42.5% or higher. On the other hand, the transmittance of the polarizing film is, for example, 44.2% or lower. The degree of polarization (P) of the polarizing film is preferably 99.95% or higher, more preferably 99.98% or higher, and even more preferably 99.99% or higher. On the other hand, the degree of polarization of the polarizing film is, for example, 99.996% or lower.

[0071] The above single-element transmittance is typically the Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting for luminous sensitivity. The above polarization degree is typically determined by the following formula based on the parallel transmittance Tp and orthogonal transmittance Tc, which are measured with an ultraviolet-visible spectrophotometer and corrected for luminous sensitivity. Degree of polarization (%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0072] The boric acid content of the polarizing film is preferably 25% or less, more preferably 20% or less. Having such a boric acid content allows for the achievement of higher optical properties. Furthermore, even with such a boric acid content, excellent appearance can be achieved by adjusting the moisture content. The boric acid content of the polarizing film is preferably 10% or more, more preferably 13% or more, and even more preferably 16% or more. Such a boric acid content allows for even better appearance. The boric acid content of the polarizing film can be adjusted, for example, by adjusting the boric acid concentration during the water stretching process.

[0073] D. Polarizing plate A polarizing plate according to one embodiment of the present invention comprises the polarizing film and a protective layer or phase difference layer disposed on at least one side of the polarizing film.

[0074] Figure 5 is a schematic cross-sectional view showing the general configuration of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 includes a polarizing film 10 having a first main surface 10a and a second main surface 10b facing each other, a protective layer 20 disposed on the first main surface 10a side of the polarizing film 10, and a phase difference layer 30 and an adhesive layer 40 disposed on the second main surface 10b side of the polarizing film 10. In this embodiment, the phase difference layer 30 can function as a protective layer for the polarizing film 10.

[0075] The protective layer 20 can be formed from any suitable film that can be used as a protective layer for the polarizing film. Specific examples of materials that make up the main component of such a film include cellulosic resins such as triacetylcellulose (TAC), and transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, cycloolefin, polyolefin, (meth)acrylic, and acetate. The above-mentioned resin substrates may also be used as the protective layer for the polarizing film.

[0076] The polarizing plate 100 is typically placed on the viewing side of the image display device. Therefore, the protective layer 20 may be subjected to surface treatments such as hard coat (HC) treatment, anti-reflective treatment, anti-sticking treatment, and anti-glare treatment as needed. The thickness of the protective layer 20 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 30 μm. If surface treatment is applied, the thickness of the protective layer 20 includes the thickness of the surface treatment layer.

[0077] As the retardation layer 30, any appropriate configuration can be adopted. In one embodiment, an alignment and curing layer of a liquid crystal compound (liquid crystal alignment and curing layer) is used for the retardation layer 30. By using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be made significantly larger than that of a non-liquid crystal material, so that the thickness of the retardation layer for obtaining a desired in-plane retardation can be made significantly smaller. In this specification, the "alignment and curing layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment and curing layer" is a concept that includes an alignment and curing layer obtained by curing a liquid crystal monomer.

[0078] Typically, the retardation layer 30 includes a layer having a refractive index characteristic showing a relationship of nx > ny = nz. Note that "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within a range that does not impair the effects of the present invention, ny > nz or ny < nz may occur. The Nz coefficient of the retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3.

[0079] As the adhesive layer 40, any appropriate configuration can be adopted. Specific examples include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, number, combination, and blending ratio of the monomers forming the base resin of the adhesive, as well as the blending amount of the crosslinking agent, reaction temperature, reaction time, etc., an adhesive having desired characteristics according to the purpose can be prepared. The base resin of the adhesive may be used alone or in combination of two or more. The base resin is preferably an acrylic resin (specifically, the adhesive layer is preferably composed of an acrylic adhesive). The thickness of the adhesive layer is, for example, 10 μm to 20 μm.

[0080] Each component constituting the polarizing plate can be laminated via any suitable adhesive layer (not shown). Specific examples of adhesive layers include adhesive layers and tack layers. Specifically, the phase difference layer 30 may be bonded to the polarizing film 10 via an adhesive layer (preferably using an active energy ray curable adhesive), or it may be bonded to the polarizing film 10 via a tack layer.

[0081] Although not shown in the diagram, a release liner is practically bonded to the surface of the adhesive layer 40. The release liner can be temporarily attached until the polarizing plate is ready for use. By using the release liner, for example, the adhesive layer is protected and the polarizing plate can be rolled.

[0082] The polarizing plate may be elongated or in sheet form. In this specification, "elongated" means an elongated shape in which the length is sufficiently longer than the width, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, than the width. The elongated polarizing plate can be wound into a roll. [Examples]

[0083] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the thickness is the value measured by the measurement method described below. (Thickness) Thicknesses of 10 μm or less were measured using a scanning electron microscope (JEOL Ltd., product name "JSM-7100F"). Thicknesses exceeding 10 μm were measured using a digital micrometer (Anritsu Corporation, product name "KC-351C").

[0084] [Example 1] (Fabrication of resin film) As the thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) in a long length, with a water absorption rate of 0.75% and a Tg of approximately 75°C was used. One side of the resin substrate was subjected to corona treatment. A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosephymer Z410") in a weight ratio of 9:1. A PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60°C to form a 13 μm thick PVA-based resin layer, thereby creating a laminate. The resulting laminate was uniaxially stretched 3.0 times in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130°C (air-assisted stretching). Next, the laminate was immersed for 30 seconds in an insolubilization bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) (insolubilization treatment). Next, the polarizing film was immersed for 60 seconds in a staining bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) while adjusting the concentration so that the final polarizing film's single-element transmittance (Ts) would be 42.5% or higher (staining). Next, the material was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous 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) (crosslinking treatment). Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide concentration 5 wt%) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to achieve a total stretch ratio of 5.5 times (underwater stretching). Subsequently, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (washing). In this way, a resin film was obtained on the resin substrate.

[0085] (Adjusting moisture content) Next, the laminate was placed in an environment of 23.4°C and 47%RH (a controlled zone) for 20 seconds to reduce the moisture content of the resin film.

[0086] (Drying) The laminate was then placed in an oven (drying zone) maintained at 90°C and 2% RH for 1 minute. During this time, it was in contact with a SUS heating roll placed inside the oven and maintained at a surface temperature of 75°C for approximately 2 seconds. Thus, a polarizing film with a thickness of 5 μm was obtained on the resin substrate. The shrinkage rate in the width direction of the laminate due to drying was 6.1%.

[0087] The temperature and humidity inside the oven (drying zone), as well as the temperature and humidity during the moisture content adjustment before entering the oven (adjustment zone), were measured using a temperature and humidity data logger (testo, product name "175 H1").

[0088] (Fabrication of polarizing plates) A HC-TAC film (32 μm thick) was bonded to the polarizing film side of the laminate of the resin substrate and polarizing film via an ultraviolet-curing adhesive, and then the resin substrate was peeled off from the polarizing film to obtain a polarizing plate. The HC-TAC film is a film in which a hard coat (HC) layer (7 μm thick) is formed on a TAC film (25 μm thick), and it was bonded so that the TAC film was on the polarizing film side.

[0089] [Example 2] A polarizing film and a polarizing plate were obtained using the same procedure as in Example 1. The temperature in the controlled zone was 24.1°C and the humidity was 45%RH.

[0090] [Example 3] A polarizing film and a polarizing plate were obtained in the same manner as in Example 1, except that the thickness of the PVA-based resin layer contained in the laminate was set to 15 μm, and the laminate was immersed in a boric acid aqueous solution at a liquid temperature of 64°C and stretched in water. The temperature of the control zone was 22.8°C and the humidity was 47% RH.

[0091] [Example 4] A polarizing film and a polarizing plate were obtained in the same manner as in Example 1, except that the laminate was immersed in a boric acid aqueous solution at a liquid temperature of 64°C and stretched in water. The temperature of the controlled zone was 23.1°C and the humidity was 44%RH.

[0092] [Comparative Example 1] A polarizing film and a polarizing plate were obtained in the same manner as in Example 1, except that the laminate was placed in an environment of 37.7°C and 23%RH for 20 seconds to adjust the moisture content.

[0093] [Comparative Example 2] A polarizing film and a polarizing plate were obtained using the same procedure as in Comparative Example 1. The temperature of the control zone was 37.5°C and the humidity was 25%RH.

[0094] The following evaluations were conducted on the examples and comparative examples. The evaluation results are summarized in Table 2. <Rating> 1. Moisture content of the resin film The film thickness of the resin film was measured (in-line measurement) using a spectroscopic interferometry film thickness gauge (Ocean Insight Co., Ltd., spectrometer "USB2000+", light source "HL-2000", fiber "OCF-103995"). The obtained values ​​were converted to moisture content based on the graph shown in Figure 2. Measurements were taken at the inlet of the control zone, the outlet of the control zone (inlet of the drying zone), and the outlet of the drying zone to determine the moisture content W1, W2, and W3. When measuring the film thickness of the resin film formed on the resin substrate, the film thickness gauge was placed on the resin substrate side. 2. Boric acid content The spectrum of the polarizing film was measured using a Fourier transform infrared spectrometer (PerkinElmer, model "Frontier FT-IR"), and the boric acid content in the polarizing film was calculated from the obtained spectral results. Specifically, the 2940 cm⁻¹ (2940 cm⁻¹) originating from the (-CH₂-) bond was calculated. -1 and 665 cm derived from boric acid esters -1 The peak intensity was calculated from the values. The measurement samples were collected at the exit of the drying zone. 3. Transmittance and polarization of a single element For the polarizing plates of the examples and comparative examples, the single-plate transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc, measured using a UV-Vis spectrophotometer (JASCO Corporation, V-7100), were defined as the Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc values ​​are Y values ​​obtained by measuring under a 2-degree field of view (C light source) according to JIS Z8701 and correcting for luminous sensitivity. From the obtained Tp and Tc, the degree of polarization P was determined using the following formula. Polarization degree P(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 4. Exterior The appearance of the polarizing plates in the examples and comparative examples (presence or absence of streaks) was observed visually. (Evaluation Criteria) Good: No streaks or marks were visible to the naked eye. Defect: Streaky marks are visible to the naked eye.

[0095] [Table 2]

[0096] The polarizing plate in the comparative example showed streaky marks (along the stretching direction of the polarizing film) as shown in Figure 6. [Industrial applicability]

[0097] The polarizing film according to the embodiment of the present invention is suitably used in image display devices such as liquid crystal displays, organic EL displays, and inorganic EL displays. [Explanation of Symbols]

[0098] 1. Laminate 2 Thermoplastic resin base material 3. Resin layer (resin film) 10 Polarizing film 20 protective layer 100 polarizing plates

Claims

[Claim 1] A step to obtain a resin film having a primary moisture content (W1) through treatment with water, An adjustment step to reduce the moisture content of the resin film from the first moisture content (W1) to the second moisture content (W2), The process includes a drying step of drying the resin film having the second moisture content (W2), The ratio (W2 / W1) of the second moisture content (W2) to the first moisture content (W1) is less than 1. The drying process reduces the moisture content of the resin film from the second moisture content (W2) to the third moisture content (W3), and the ratio of the third moisture content (W3) to the second moisture content (W2) (W3 / W2) is 0.25 or less. The resin film is placed in an environment with a humidity of 35% RH or higher to perform the adjustment. A method for manufacturing polarizing films.

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