TW202316149A - Method for manufacturing polarizing film with both high optical properties and excellent appearance - Google Patents

Abstract

An object of the present invention is to provide a polarizing film having both high optical properties and excellent appearance. The solution of the present invention is to provide a method for manufacturing a polarizing film according to an embodiment of the present invention. The method comprises a step of obtaining a resin film having a first film thickness (T1) through a treatment using water; an adjusting step of reducing the film thickness of the resin film from the first film thickness (T1) to a second film thickness (T2); and a drying step of drying the resin film having the second film thickness (T2), wherein the ratio (T2/T1) of the second film thickness (T2) to the first film thickness (T1) is less than 1. The film thickness of the resin film is reduced from the second film thickness (T2) to the third film thickness (T3) by the drying step, and the ratio (T3/T2) of the third film thickness (T3) to the second film thickness (T2) is 0.90 or less. In the manufacturing method, the adjustment is performed by placing the resin film in an environment with a humidity above 35%RH.

Description

Manufacturing method of polarizing film

The invention relates to a manufacturing method of a polarizing film.

In a liquid crystal display device which is a typical image display device, polarizing films are arranged on both sides of a liquid crystal cell because of an image forming method. Also, with the popularization of thin displays, a display (OLED) equipped with an organic electroluminescent (EL) panel and a display (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, which is prone to problems such as external light reflection or background reflection. Therefore, it is known to prevent these problems by disposing a circular polarizing plate having a polarizing film and a λ/4 plate on the viewing side. As a method for producing a polarizing film, for example, a method of stretching a laminate having a resin base material and a polyvinyl alcohol (PVA) resin layer, followed by dyeing to obtain a polarizing film on the resin base material has been proposed (for example, Patent Document 1). A thin polarizing film can be obtained by using the method, and thus it contributes to the thinning of image display devices in recent years and has drawn attention.

However, a thin polarizing film has the problem that it is difficult to achieve both high optical properties and good appearance. Specifically, there is a tendency that the higher the optical characteristics are, the more easily the appearance problem will occur. The poor appearance of the polarizing film may affect the display characteristics of the image display device. For example, if the polarizing film has stripe marks, it may be seen as poor appearance (texture) in the composition of the laminated film (such as a circular polarizing plate). Current Technical Literature patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2001-343521

The problem to be solved by the invention The present invention is made to solve the above-mentioned problems, and its main purpose is to provide a polarizing film having both high optical characteristics and excellent appearance.

means to solve problems According to an embodiment of the present invention, a method for manufacturing a polarizing film is provided. The manufacturing method includes: a step of obtaining a resin film having a first film thickness (T1) through treatment with water; an adjusting step of reducing the film thickness of the aforementioned resin film from the aforementioned first film thickness (T1) to the second Two film thickness (T2); And, drying step, it is to have the resin film of aforementioned second film thickness (T2) to dry; The ratio of aforementioned second film thickness (T2) with respect to aforementioned first film thickness (T1) (T2/T1) is less than 1; The film thickness of resin film is reduced to the 3rd film thickness (T3) from aforementioned 2nd film thickness (T2) by aforementioned drying; aforementioned 3rd film thickness (T3) is relative to aforementioned 2nd The film thickness (T2) ratio (T3/T2) is 0.90 or less; the aforementioned manufacturing method is to place the aforementioned resin film in an environment with a humidity above 35% RH for the aforementioned conditioning. In one embodiment, the above adjustment is performed by placing the above resin film in an environment with a temperature lower 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 at which the conditioning is performed and the humidity at which the drying is performed is 30% RH or more. In one embodiment, the above-mentioned drying is carried out by placing the above-mentioned resin film in an environment with a temperature of 60° C. or higher and a humidity of 10% RH or lower. In one embodiment, the first film thickness ( T1 ), the second film thickness ( T2 ) and the third film thickness ( T3 ) satisfy the relationship (T2/T1)/(T3/T2)≧1. In one embodiment, the first film thickness ( T1 ) is 5 μm or more. In one embodiment, a polarizing film having a thickness of 7 μm or less is obtained by the above-mentioned manufacturing method.

Invention effect According to the embodiments of the present invention, a polarizing film having both high optical properties and excellent appearance can be obtained.

Embodiments of the present invention will be described below, but the present invention is not limited by these embodiments.

(Definition of terms and symbols) Definitions of terms and symbols in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the in-plane refractive index reaches the maximum (that is, the direction of the slow axis), "ny" is the refractive index in the direction that is perpendicular to the slow axis in the plane (that is, the direction of the fast axis), and "nz" is The index of refraction in the thickness direction. (2) In-plane retardation (Re) "Re(λ)" is the in-plane phase difference measured at 23°C with light having a wavelength of λnm. For example, "Re(550)" is an in-plane retardation measured at 23° C. with light having a wavelength of 550 nm. When the thickness of the layer (thin film) is set as d (nm), Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d. (3) Phase difference in thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured at 23°C with light having a wavelength of λnm. For example, "Rth(550)" is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. When the thickness of the layer (thin film) is set to d (nm), Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d. (4) Nz coefficient The Nz coefficient can be obtained by Nz=Rth/Re.

A method of manufacturing a polarizing film according to an embodiment of the present invention includes: a step of obtaining a resin film having a first film thickness (T1) through treatment with water; an adjustment step of making the film thickness of the resin film from the first film thickness (T1) reducing to a second film thickness (T2); and, a drying step of drying the resin film having the second film thickness (T2).

A. Resin film The above-mentioned resin film can be, for example, formed a laminate by forming a resin layer (typically a polyvinyl alcohol-based resin layer) on a resin substrate, stretching the laminate and dyeing it with a dichroic substance such as iodine (for example, by adsorption obtained by staining with iodine).

A-1. Laminated body Fig. 1 is a schematic cross-sectional view showing a schematic configuration of a laminate according to an embodiment of the present invention. The laminated body 1 has a thermoplastic resin substrate (for example, a long strip) 2 and a polyvinyl alcohol (PVA)-based resin layer 3 . Preferably, the laminate 1 is produced by forming a PVA-based resin layer 3 including PVA-based resin and halides on a thermoplastic resin substrate 2 . Specifically, the PVA-based resin layer 3 is formed by applying and drying a coating liquid containing a PVA-based resin and a halide on the thermoplastic resin substrate 2 .

The thickness of the thermoplastic resin base material is preferably 20 μm-300 μm, more preferably 50 μm-200 μm. When it is less than 20 μm, it may be difficult to form a PVA-based resin layer. When the thickness is larger than 300 μm, for example, it may take time for the thermoplastic resin substrate to absorb water during underwater stretching described later, and an excessive load may be required during stretching.

The water absorption rate of the thermoplastic resin substrate is preferably above 0.2%, more preferably above 0.3%. The thermoplastic resin substrate can absorb water, and the water can act as a plasticizer to be plasticized. As a result, elongation stress can be greatly reduced and elongation to a high magnification can be achieved. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. According to such a water absorption rate, the dimensional stability of a thermoplastic resin base material falls remarkably at the time of manufacture, and defects, such as deterioration of the quality of the polarizing film obtained, can be prevented. In addition, when stretching in water, the thermoplastic resin base material can be prevented from being broken or the PVA-based resin layer can be prevented from peeling off. The water absorption of the thermoplastic resin substrate can be adjusted by, for example, introducing a modifying group into the constituent material. In addition, the water absorption rate is the value calculated|required based on JISK7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably below 120°C. By using such a thermoplastic resin base material, crystallization of the PVA-based resin layer can be suppressed, and the extensibility of the laminate can be sufficiently ensured. Furthermore, considering the use of water to plasticize the thermoplastic resin base material and to carry out the water stretching well, the Tg is preferably below 100°C, more preferably below 90°C. On the other hand, the Tg of the thermoplastic resin substrate is preferably 60°C or higher. According to the Tg, defects such as deformation (such as unevenness, looseness, wrinkling, etc.) of the thermoplastic resin substrate can be prevented when the coating liquid is applied and dried, and a laminate can be produced favorably. In addition, the stretching of the above-mentioned resin layer can be performed well at an appropriate temperature (for example, about 60° C.). The Tg of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material and heating it using a crystallized material. In addition, the glass transition temperature (Tg) is the value obtained based on JISK7121.

As a constituent material of the thermoplastic resin base material, any appropriate thermoplastic resin can be employed. Examples of thermoplastic resins include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as northylene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, and polycarbonate-based resins. resins, such copolymer resins. Among these, a northylene-based resin and an amorphous polyethylene terephthalate-based resin are preferable.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (difficult to crystallize) polyethylene terephthalate resins are particularly preferably used. Specific examples of amorphous polyethylene terephthalate-based resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, or copolymers further containing cyclohexane Copolymers of dimethanol or diethylene glycol as diols.

In another embodiment, a polyethylene terephthalate resin having an isophthalic acid unit can be suitably used. This is because it has excellent elongation and can suppress crystallization during elongation. We think that this is because the introduction of the isophthalic acid unit imparts a large deflection to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably at least 0.1 mol %, more preferably at least 1.0 mol %, based on the total of all repeating units. This is because a thermoplastic resin substrate with excellent extensibility can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. This is because the degree of crystallization can be favorably increased in drying described later.

The thermoplastic resin substrate may have been stretched in advance (for example, before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin substrate is extended in the transverse direction. The transverse direction is preferably a direction perpendicular to the extending direction of the laminate described later. In addition, in this specification, "orthogonal" also includes substantially orthogonal cases. Here, "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, 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 elongation ratio of the thermoplastic resin substrate should be 1.5 times to 3.0 times. Any appropriate method can be adopted as the stretching method of the thermoplastic resin base material. Specifically, it can be extended from a fixed end, or can be extended from a free end. The extension method can be dry or wet. Extension can be carried out in one stage or in multiple stages. When it is performed in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratios in each stage.

A representative example of the above coating liquid is a solution obtained by dissolving a PVA-based resin and a halide in a solvent. Examples of the solvent include polyalcohols such as water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and trimethylolpropane, Amines such as ethylenediamine and diethylenetriamine. These may be used alone, or two or more kinds may be used in combination. The medium is preferably water. The content of the PVA-based resin in the coating solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. According to the said range, the uniform coating film adhered to a thermoplastic resin base material can be formed. The content of the halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Examples of the PVA-based resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. 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 the PVA-based resin is usually 85 mol %-100 mol %, preferably 95.0 mol %-99.95 mol %, more preferably 99.0 mol %-99.93 mol %. A polarizing film excellent in durability can be obtained by using a PVA-based resin having such a degree of saponification. When the saponification is too high, gelation may occur. In addition, the degree of saponification can be obtained in accordance with JIS K 6726-1994.

The average degree of polymerization of PVA-based resin is usually 1000-10000, preferably 1200-4500, more preferably 1500-4300. In addition, the average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

Any appropriate halide can be used as the above-mentioned halide. Examples thereof include iodides such as potassium iodide, sodium iodide, and lithium iodide, and chlorides such as sodium chloride. Potassium iodide is preferred among these. By using a halide, a polarizing film having high optical characteristics can be obtained. Specifically, the crystallization of the PVA-based resin after in-air assisted stretching described later is promoted, and the orientation disorder and orientation reduction of polyvinyl alcohol molecules in the subsequent wet treatment (such as dyeing and underwater stretching described later) are suppressed, and A polarizing film with high optical properties can be obtained.

When preparing the coating liquid, it is preferable to mix 5 to 20 parts by weight of the halide with respect to 100 parts by weight of the PVA-based resin, more preferably 10 to 15 parts by weight. Specifically, the content of the halide in the obtained PVA-based resin layer is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA-based resin. When the amount of the halide is large relative to the PVA-based resin, for example, the halide overflows and the obtained polarizing film may become cloudy.

Additives may also be blended in the coating solution. As an additive, a plasticizer and a surfactant are mentioned, for example. As a plasticizer, polyalcohols, such as ethylene glycol and glycerin, are mentioned, for example. As a surfactant, a nonionic surfactant is mentioned, for example. These are used in order to improve the uniformity, dyeability, and extensibility of the obtained PVA-type resin layer, for example.

Examples of coating methods for the above-mentioned coating solution include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (cutaway wheel coating). coating method, etc.). The coating and drying temperature of the coating solution should be above 50°C.

The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin substrate can be subjected to surface treatment (such as corona treatment, etc.), and an easy-adhesive layer can also be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

A-2. Extension The stretching is preferably carried out by dry stretching (assisted stretching in the air) of the above-mentioned laminate and then stretching in water. By assisted stretching, stretching can be carried out while suppressing the crystallization of the thermoplastic resin base material mentioned above, which can solve the problem of excessive crystallization of the thermoplastic resin base material in water stretching (such as boric acid water stretching), which reduces the extensibility, and can be Laminates extend to higher magnifications. Moreover, when using a thermoplastic resin base material, since the said coating temperature is set low, the crystallization of PVA-type resin becomes relatively low, and the problem that sufficient optical characteristics cannot be obtained arises. On the other hand, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be improved even when a thermoplastic resin is used. In addition, by improving the orientation of the PVA-based resin in advance, it is possible to prevent problems such as lowering of the orientation of the PVA-based resin or dissolution during subsequent wet processing. In this way, a polarizing film with high optical properties can be obtained.

The method of auxiliary stretching in the air can be fixed end stretching (such as stretching method using a tenter stretching machine), or free end stretching (such as uniaxial stretching method of passing the laminate through rollers with different peripheral speeds). Free end extensions should be used. For example, heating roll stretching is used, in which the above-mentioned laminate is stretched using a difference in peripheral speed between the heating rolls while being conveyed in the longitudinal direction. In one embodiment, the air-assisted stretching includes a zone stretching step in a hot space (zone) and a heated roller stretching step. The sequence of the zone stretching step and the heating roll stretching step is not limited, for example, the zone stretching step and the heating roll stretching step are performed sequentially. In another embodiment, in the tenter stretching machine, stretching is performed by holding the end of the film and increasing the distance between the tenters in the direction of travel (the increase in the distance between the tenters becomes the stretching ratio ). At this time, the distance in the width direction of the tenter frame (direction perpendicular to the traveling direction) is preferably set so as to extend closer to the free end relative to the stretching ratio in the traveling direction. In the case of free end extension, the shrinkage rate in the width direction is calculated by the formula: shrinkage rate in the width direction=(1/extension ratio) ^1/2 .

The extension magnification of the auxiliary extension in the air should be 2.0 times to 3.5 times. Aerial assisted extension can be carried out in one stage or in multiple stages. When it is performed in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The extension direction in the auxiliary extension in the air should be roughly the same as the extension direction in the water extension described later.

The stretching temperature of the in-air assisted stretching can be set to any appropriate value according to the thermoplastic resin substrate used, the stretching method, and the like, for example. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above Tg+10°C, more preferably above Tg+15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By performing stretching at the above-mentioned temperature, rapid crystallization of the PVA-based resin can be suppressed, and defects caused by the crystallization (for example, prevention of orientation of the PVA-based resin layer by stretching) can be suppressed.

The above-mentioned underwater stretching means that the laminate is dipped in a stretching bath. According to underwater stretching, stretching can be carried out at a temperature lower than the glass transition temperature (typically about 80°C) of the above-mentioned thermoplastic resin substrate or PVA-based resin layer, and can be stretched to high magnification while suppressing the crystallization of the PVA-based resin layer . As a result, a polarizing film having high optical characteristics can be obtained.

The method of underwater stretching can be fixed end stretching or free end stretching (for example, the method of uniaxial stretching by passing the laminated body between rollers with different peripheral speeds). Free end extensions should be used. The extension of the laminate may be performed in one stage or in multiple stages. When it is performed in multiple stages, the elongation ratio of the laminate described later is the product of the elongation ratios of each stage.

The underwater stretching is preferably carried out by immersing the laminate in an aqueous solution of boric acid (boric acid underwater stretching). By using a boric acid aqueous solution as a stretching bath, the PVA-based resin layer can be given rigidity that can withstand the tension applied at the time of stretching and water resistance that is insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anion in aqueous solution and cross-link with PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer to be stretched favorably, and a polarizing film having high optical properties can be obtained.

The above boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight relative to 100 parts by weight of water, more preferably 2.5 to 6 parts by weight, more preferably 3 to 5 parts by weight. By setting the concentration of boric acid to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be produced. In addition, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent in addition to boric acid or borate can also be used.

It is convenient to mix iodide in the above-mentioned extension bath (boric acid aqueous solution). By mixing iodide, the dissolution of iodine adsorbed by the PVA-based resin layer can be suppressed. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, more preferably 60°C or higher, and may be 65°C or higher. If it is the above-mentioned temperature, it can be extended to a high magnification, and a polarizing film with high optical characteristics 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-based resin layer. At this time, if the stretching temperature is lower than 40° C., good stretching may not be possible even considering plasticizing the thermoplastic resin base material with water. Moreover, even if it stretches at the said temperature, the polarizing film which has an excellent appearance can be obtained by performing film thickness adjustment mentioned later. On the other hand, the stretching temperature is preferably below 75°C, more preferably below 70°C, and may also be below 65°C. The higher the stretching temperature is, the higher the solubility of the PVA-based resin layer may be, and high optical properties may not be obtained. According to the stretching temperature, a polarizing film having a more excellent appearance can be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio obtained by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total elongation ratio of the laminated body (the elongation ratio of combined aerial auxiliary extension and underwater extension) should be more than 5.0 times, more preferably 5.5 times or more, more preferably 6.0 times or more relative to the original length of the laminated body. By achieving such a high elongation ratio, a polarizing film with extremely excellent optical characteristics can be manufactured. The high elongation ratio can be achieved by adopting an underwater elongation method (boric acid elongation).

A-3. Dyeing The above-mentioned dyeing is typically carried out by allowing the PVA-based resin layer to absorb iodine. As an iodine adsorption method, for example, a method of immersing a PVA-based resin layer (laminated body) in a dyeing solution containing iodine, a method of applying the dyed solution to a PVA-based resin layer, spraying the dyed solution on a PVA-based resin layer, etc. liquid method. A method of immersing the laminate in a dye solution (dye bath) is preferable. This is because iodine can be adsorbed well.

The above-mentioned dyeing solution is preferably iodine aqueous solution. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is advisable to mix iodide in the iodine aqueous solution. Specific examples of iodide are as described above. Potassium iodide is preferably used. The blending amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, relative to 100 parts by weight of water. In order to inhibit the dissolution of PVA resin, the liquid temperature of the dyeing solution should be 20°C~50°C during dyeing. When immersing the PVA-based resin layer 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, more preferably 30 seconds to 90 seconds.

Dyeing conditions (concentration, liquid temperature, immersion time) can be set so that, for example, the monomer transmittance of the finally obtained polarizing film becomes 42.0% or more and the degree of polarization becomes 99.98% or more. As the dyeing conditions, for example, in an iodine aqueous solution as a dyeing solution, the content ratio of iodine to potassium iodide is preferably 1:5 to 1:20, more preferably 1:5 to 1:10.

When dyeing is carried out after immersing the laminate in a treatment bath containing boric acid (for example, the insolubilization treatment described later), boric acid may be mixed into the dyeing bath to change the concentration of boric acid in the dyeing bath, and the dyeability may become unstable. . In order to suppress the destabilization of the dyeability, the concentration of boric acid in the dyeing bath is adjusted to be preferably 4 parts by weight or less, more preferably 2 parts by weight or less, with respect to 100 parts by weight of water. On the other hand, the concentration of boric acid in the dyeing bath is preferably at least 0.1 parts by weight, more preferably at least 0.2 parts by weight, and more preferably at least 0.5 parts by weight with respect to 100 parts by weight of water. In one embodiment, dyeing is performed using a dyeing bath previously containing boric acid. According to such a form, the rate of change of boric acid concentration when boric acid is mixed into a dyeing bath can be reduced. The amount of boric acid pre-blended in the dyeing bath (not derived from the boric acid content of the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight relative to 100 parts by weight of water.

A-4. Other processing If necessary, an insolubilization treatment is performed after the above-mentioned aerial assisted stretching and before underwater stretching and dyeing. The insolubilization treatment is typically carried out by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of PVA can be prevented from being lowered when immersed in water. The concentration of the boric acid aqueous solution in the insolubility treatment is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The temperature of the insolubilization treatment (liquid temperature of the boric acid aqueous solution) is preferably 20°C to 50°C.

If necessary, a cross-linking treatment is performed after dyeing and before water extension. Typically, the crosslinking treatment is performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of PVA can be prevented from being lowered during subsequent underwater stretching. The concentration of the boric acid aqueous solution in the crosslinking treatment is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. It is suitable to mix iodide in aqueous solution of boric acid. By mixing iodide, the elution of iodine adsorbed by the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The blending amount of iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. The temperature of the crosslinking treatment (the liquid temperature of the boric acid aqueous solution) is preferably 20°C to 50°C.

It is advisable to wash after stretching in water. Typically, washing is performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

B. Film thickness of resin film The resin film after the above-mentioned treatment with water has a first film thickness ( T1 ), and the film thickness of the resin film is adjusted. As shown in FIG. 2 , the film thickness of the resin film may have a correlation with the moisture content of the resin film. Specifically, we believe that the dimensional change in the in-plane direction of the resin film due to water absorption is restrained by the resin base material with low water absorption, and the resin film expands in the thickness direction according to the amount of water absorption. Therefore, it is considered that there is a correlation between the film thickness of the resin film after the treatment with water (for example, after the above-mentioned washing) and the water content of the resin film. In addition, the graph in Fig. 2 shows the film thickness and water content of the resin film after water treatment when the laminate is stretched in water under various stretching conditions (specifically, the concentration of boric acid in the stretching bath) shown in Table 1 below. Charts plotted from rate data. The approximate curve in the graph is an approximate curve obtained from the drawing data by the least square method in such a manner that it becomes an exponential function. The water content in Fig. 2 is calculated by the following formula based on the dry weight method. Moisture content of resin film = (weight of resin film treated with water - weight of resin film after drying) / weight of resin film after drying

[Table 1]

The first film thickness ( T1 ) is, for example, 4.0 μm or more, preferably 4.5 μm or more, more preferably 5 μm or more, may be 6 μm or more, or may be 7 μm or more. On the other hand, the first film thickness ( T1 ) is, for example, 20 μm or less, preferably 12 μm or less.

Fig. 3 is a schematic diagram showing an example of a manufacturing process of a polarizing film. The laminated body 1 of the resin substrate and the PVA-based resin layer is dipped in a boric acid aqueous solution bath 101 using a conveying roll (insolubilization treatment), and then immersed in an aqueous solution bath 102 of a dichroic substance (iodine) and potassium iodide (dyeing treatment) . Next, it is immersed in the aqueous solution bath 103 of boric acid and potassium iodide (crosslinking process). Next, the laminate 1 is stretched while being immersed in the boric acid aqueous stretching bath 104 while applying tension in the conveying direction with rollers having different speed ratios (underwater stretching treatment). Next, the laminate 1 stretched in water is immersed in a potassium iodide aqueous solution bath 105 to be washed (washing treatment). In addition, although not shown, for example, before the insolubilization treatment, the above-mentioned aerial auxiliary stretching may be performed on the laminate 1 .

The laminate 1 after the treatment with water (after passing through the water bath) is sent to the conditioning area 110 and then to the drying area 120 .

By passing through the adjustment area 110, the film thickness of the resin film (PVA-based resin layer) of the laminate 1 can be adjusted from the first film thickness (T1) to the second film thickness (T2) (adjustment step). Specifically, the resin film has a first film thickness ( T1 ) at the entrance of the conditioning area 110 , and the resin film has a second film thickness ( T2 ) at the exit of the conditioning area 110 (entry of the drying area 120 ).

The second film thickness ( T2 ) is preferably not less than 3.5 μm and not more than 8.6 μm, more preferably not less than 5.5 μm and not more than 8.3 μm. The ratio (T2/T1) of the second film thickness (T2) to the first film thickness (T1) is preferably not less than 0.85, more preferably not less than 0.86. On the other hand, T2/T1 is less than 1, preferably not more than 0.95, more preferably not more than 0.93, more preferably not more than 0.90.

The temperature in the adjustment area 110 is preferably lower than 40°C, preferably lower than 35°C, and can also be lower than 30°C. On the other hand, the temperature in the adjustment area 110 is preferably above 20°C, and may also be above 22°C. The aforementioned second film thickness (T2) can be well achieved by taking a predetermined time by placing the resin film in the temperature environment. The humidity in the conditioning area 110 is preferably above 35%RH, more preferably above 40%RH. On the other hand, the humidity in the conditioning area 110 is, for example, 65% RH or less. The aforementioned second film thickness (T2) can be well achieved by taking a predetermined time by placing the resin film in the humidity environment.

The passing time of the adjustment area 110 is, for example, 5 seconds to 4 minutes. The passing time of the conditioning area 110 corresponds to, for example, the time for the resin film to be left in a predetermined environment. In addition, in the conditioning area 110, the temperature and humidity may not always be kept constant, for example, it should be kept within the range of the above-mentioned temperature and humidity.

The reduction rate (R1) of the film thickness in the adjustment step is preferably 3.6 μm/min or less, more preferably 3.2 μm/min or less, more preferably 3.0 μm/min or less. On the other hand, R1 is, for example, 2.0 μm/min or more.

By passing through the drying zone 120, the film thickness of the resin film is reduced from the second film thickness (T2) to the third film thickness (T3) (drying step). Specifically, the resin film has a second film thickness ( T2 ) at the entrance of the drying area 120 , and the resin film has a third film thickness ( T3 ) at the exit of the drying area 120 .

The third film thickness ( T3 ) is preferably not less than 3.0 μm and not more than 7.0 μm, more preferably not less than 4.0 μm and not more than 6.5 μm. The ratio (T3/T2) of the third film thickness (T3) to the second film thickness (T2) is 0.90 or less, preferably 0.85 or less, more preferably 0.80 or less, more preferably 0.75 or less. On the other hand, T3/T2 is, for example, 0.70 or more, preferably 0.72 or more. The ratio (T2/T1)/(T3/T2) of (T2/T1) to (T3/T2) is preferably 1 or more. Also, the ratio (T3/T1) of the third film thickness (T3) to the first film thickness (T1) is preferably 0.80 or less, more preferably 0.75 or less. On the other hand, T3/T1 is, for example, 0.50 or more.

The film thickness reduction rate (R2) in the drying step is preferably at least 0.8 μm/min, more preferably at least 1.2 μm/min, more preferably at least 1.6 μm/min. On the other hand, R2 is preferably 3.0 µm/min or less.

Drying can be performed in any suitable manner. For example, it may be performed by heating the entire drying area 120 (area heating method), or may be performed by heating a conveying roller in the drying area 120 (heating roller method). The heating roll method is preferable, and both are more preferable. By using a heating roller, heating curl of a laminate can be suppressed efficiently, and the polarizing film of excellent quality can be manufactured. Specifically, by drying the laminated body along the state of an additional hot roller, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted, the degree of crystallization can be increased, and the thermoplasticity can be made even at a relatively low drying temperature. The crystallinity of the resin substrate increases favorably. As a result, the rigidity of the thermoplastic resin substrate is increased to be in a state where the shrinkage of the resin film due to drying can be tolerated, thereby suppressing curling. Moreover, since the layered body can be dried while maintaining a flat state by using a heating roll, not only curl but also generation|occurrence|production of a wrinkle can be suppressed.

By drying, the laminated body can be shrunk in the width direction, and optical characteristics can be improved. This is because, for example, the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction due to drying is preferably 1%~10%, more preferably 2%~8%, more preferably 4%~7%. By using the heating roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be realized.

Fig. 4 is a schematic view showing an example of drying using heating rollers in the drying zone. In the example shown in the figure, drying is carried out while conveying the laminated body 1 by conveying rollers R1 to R6 heated to a predetermined temperature and guide rollers G1 to G4. In the illustrated example, the conveying rollers are arranged so that the resin film surface of the laminate 1 and the thermoplastic resin substrate surface can be alternately and continuously heated, but for example, only one side of the laminate (for example, the thermoplastic resin substrate surface) may be continuously heated. way to configure the conveyor roller.

In one embodiment, the drying conditions can be controlled by adjusting the heating temperature of the conveying rollers (temperature of the heating rollers), the number of the heating rollers, and the contact time with the heating rollers. The temperature of the heating roller is preferably 60°C~120°C, more preferably 65°C~100°C, more preferably 70°C~90°C. Depending on the temperature, it is possible to impart extremely excellent durability to the laminate while increasing the crystallinity of the thermoplastic resin and suppressing curling. Moreover, the film thickness of the said resin film can be achieved favorably. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the illustrated example, six conveying rollers are provided, but there are no particular limitations as long as there are plural conveying rollers. Conveyor rollers are usually set at 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, more preferably 1 second to 20 seconds, more preferably 1 second to 10 seconds.

The drying area 120, which may also be provided with heating rollers, is preferably heated. For example, the drying area 120 is a space within a furnace such as an oven. According to such an aspect, rapid temperature change between heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature in the drying area 120 is preferably above 60°C, more preferably above 70°C, more preferably above 80°C, especially above 85°C. On the other hand, from the viewpoint of suppressing the occurrence of wrinkles, the temperature in the drying area 120 is, for example, preferably 105°C or lower, more preferably 95°C or lower. The humidity in the drying area 120 is preferably below 10%RH, more preferably below 5%RH. On the other hand, the humidity in the drying area 120 is, for example, 1% RH or more. It is advisable to set the air supply state in the heating furnace. At this time, the wind speed of the hot air is, for example, about 10 m/sec to 30 m/sec. In addition, the wind speed in the heating furnace can be measured with a mini vane type digital anemometer.

The temperature in the drying zone 120 is preferably higher than the temperature in the conditioning zone 110 . The difference between the temperature in the drying zone 120 and the temperature in the conditioning zone 110 (the difference between the drying temperature and the conditioning temperature) is preferably 25°C or higher and 70°C or lower, preferably 40°C or higher, more preferably 50°C above, especially above 55°C. The humidity in the conditioning area 110 is preferably higher than the humidity in the drying area 120 . The difference between the humidity in the conditioning area 110 and the drying area 120 (the difference between the humidity for conditioning and the humidity for drying) is preferably 30%RH to 70%RH, more preferably 35%RH or more.

The passing time of the drying area 120 is, for example, 5 seconds to 4 minutes. The passing time of the drying area 120 corresponds to, for example, the time for the resin film to be placed in a predetermined environment. In addition, in the drying area 120 , the temperature and humidity may not always be kept constant, for example, it is preferable to keep them within the range of the above-mentioned temperature and humidity.

By drying the resin film after the conditioning step, a polarizing film with high optical characteristics and excellent appearance can be obtained. The inventors of the present invention have found that, for example, by managing the film thickness of the resin film before drying, it is possible to balance the optical properties and appearance, which are generally considered to be in a trade-off relationship.

C. Polarizing film The polarizing film obtained by 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, more preferably 6 μm or less. According to the embodiment of the present invention, the polarizing film with the above thickness can take into account both high optical properties and excellent appearance. On the other hand, the thickness of the polarizing film is preferably at least 1 μm, more preferably at least 2 μm.

The polarizing film should exhibit absorption dichroism at any wavelength between 380nm and 780nm. The single transmittance (Ts) of the polarizing film is preferably above 41.0%, more preferably above 42.0%, more preferably above 42.5%. On the other hand, the single transmittance of the polarizing film is, for example, 44.2% or less. The degree of polarization (P) of the polarizing film is preferably above 99.95%, more preferably above 99.98%, more preferably above 99.99%. On the other hand, the degree of polarization of the polarizing film is, for example, 99.996% or less.

The above monomer transmittance represents the Y value measured with a UV-visible spectrophotometer and subjected to sensitivity correction. The above degree of polarization can be representatively obtained by the following formula based on the parallel transmittance Tp and the cross transmittance Tc measured with an ultraviolet-visible spectrophotometer and corrected for visual sensitivity. Degree of polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

The boric acid content of the polarizing film is preferably less than 25%, more preferably less than 20%. By having such boric acid content, higher optical properties can be achieved. Also, even at the above-mentioned content of boric acid, an excellent appearance can still be achieved through the adjustment of the above-mentioned film thickness. The boric acid content of the polarizing film is preferably more than 10%, more preferably more than 13%, more preferably more than 16%. Depending on the boric acid content, the appearance will be more excellent. In addition, the boric acid content of the polarizing film is adjusted, for example, by adjusting the concentration of boric acid in the above-mentioned stretching in water.

D. Polarizer A polarizing plate according to an embodiment of the present invention has the above-mentioned polarizing film and a protective layer or retardation layer disposed on at least one side of the polarizing film.

Fig. 5 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 has: a polarizing film 10, which has a first main surface 10a and a second main surface 10b facing each other; a protective layer 20, which is arranged on the first main surface 10a side of the polarizing film 10; a retardation layer 30 , which is arranged on the second main surface 10 b side of the polarizing film 10 ; and the adhesive layer 40 . In this embodiment, the retardation layer 30 functions as a protective layer of the polarizing film 10 .

The protective layer 20 can be formed of any suitable thin film that can be used as a protective layer of a polarizing film. Specific examples of the material constituting the main component of the film include cellulose-based resins such as cellulose triacetate (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyamide-based resins, etc. Cycloolefin-based, polyolefin-based, (meth)acrylic-based, acetate-based transparent resins such as imide-based, polyether-based, polysulfuric-based, polystyrene-based, polynorthylene-based, etc. In addition, the above-mentioned resin substrate can also be used as a protective layer of a polarizing film.

The polarizing plate 100 represents that the upper side is disposed on the viewing side of the image display device. Therefore, the protective layer 20 may also be subjected to surface treatments such as hard coat (HC) treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment as required. The thickness of the protective layer 20 is preferably 5 μm-80 μm, more preferably 10 μm-40 μm, more preferably 10 μm-30 μm. In addition, when surface treatment is performed, the thickness of the protective layer 20 is the thickness including the thickness of the surface treatment layer.

Any appropriate configuration can be employed as the retardation layer 30 . In one embodiment, the retardation layer 30 is an alignment solidified layer (liquid crystal alignment solidification layer) using a liquid crystal compound. By using liquid crystal compounds, the difference between nx and ny of the resulting retardation layer can be much larger than that of non-liquid crystal materials, so the thickness of the retardation layer used to obtain the desired in-plane retardation can be significantly reduced. In the present specification, the "alignment solidified layer" refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within the layer and its orientation state is fixed. In addition, the "alignment hardening layer" is a concept including the alignment hardening layer obtained by hardening a liquid crystal monomer.

The retardation layer 30 represents a layer including a layer whose refractive index characteristic shows the relationship of nx>ny=nz. In addition, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, ny>nz or ny<nz may exist within the range that does not impair the effects of the present invention. The Nz coefficient of the retardation layer is preferably 0.9-1.5, more preferably 0.9-1.3.

Any appropriate configuration can be adopted as the adhesive layer 40 . Specific examples include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, quantity, 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 with desired properties that meet 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˜20 μm.

Each member constituting the polarizing plate can be laminated through any appropriate adhesive layer (not shown). Specific examples of the adhesive layer include an adhesive layer and an adhesive layer. Specifically, the retardation layer 30 can be bonded to the polarizing film 10 through an adhesive layer (active energy ray curing adhesive is preferred), or can be bonded to the polarizing film 10 through an adhesive layer.

Although not shown, in actual use, a release liner is attached to the surface of the adhesive layer 40 . The release liner can be temporarily adhered until the polarizer is ready for use. By using a release liner, for example, the adhesive layer can be protected and a polarizing plate roll can be formed.

The polarizing plate can be in the shape of a strip or a single sheet. In this specification, "elongated" means a long and thin shape whose length is sufficiently long relative to the width, for example, refers to a long and thin shape whose length is 10 times or more, preferably 20 times or more, relative to the width. The long polarizing plate can be wound into a roll.

Example Hereinafter, the present invention will be specifically described by means of examples, but the present invention is not limited by these examples. In addition, unless otherwise stated, the thickness is the value measured by the following measuring method. (thickness) The thickness of 10 μm or less was measured using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7100F"). A thickness of more than 10 μm was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").

[Example 1] (Resin film production) As the thermoplastic resin substrate, a long amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of about 75°C was used. Corona treatment is performed on one side of the resin substrate. Polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mole%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") were mixed at a weight ratio of 9:1. 13 parts by weight of potassium iodide was added to 100 parts by weight of the PVA-based resin to prepare an aqueous PVA solution (coating solution). The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm to produce a laminate. The obtained laminate was uniaxially stretched at the free end to 3.0 times in the longitudinal direction (long side direction) between rollers with different peripheral speeds in an oven at 130°C (assisted stretching in the air). Next, the laminated body was immersed for 30 seconds in an insoluble bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40° C. (insolubility treatment). Next, dip for 60 seconds while adjusting the concentration in a dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30°C so that the finally obtained The single transmittance (Ts) of the polarizing film is 42.5% or more (dyed). Next, it was immersed for 30 seconds in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40° C. (crosslinking treatment). Then, the laminated body was immersed in a boric acid aqueous solution (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C. between rollers with different circumferential speeds in the longitudinal direction (longitudinal direction) so that the total Uniaxial stretching (underwater stretching) was carried out so that the stretching ratio became 5.5 times. Then, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20° C. (washing). According to the above method, a resin film is obtained on the resin substrate.

(Adjustment of film thickness) Next, the laminate was left in an environment of 23.4° C. and 47% RH (conditioning area) for 20 seconds to reduce the film thickness of the resin film.

(dry) After that, the laminate was placed in an oven (dry area) kept at 90° C. and 2% RH for 1 minute. During this time, it was brought into contact with a heating roller made of SUS arranged in an oven to maintain a surface temperature of 75° C. for about 2 seconds. Thereby, a polarizing film with a thickness of 5 μm was obtained on the resin substrate. In addition, the shrinkage rate of the laminate in the width direction due to drying was 6.1%.

In addition, the temperature and humidity in the oven (drying area) and the temperature and humidity during film thickness adjustment (adjustment area) before entering the oven were measured using a temperature and humidity data recorder (manufactured by Testo, product name "175 H1 ”) to proceed.

(Production of Polarizing Plate) On the polarizing film side of the laminate of the above-mentioned resin substrate and polarizing film, an HC-TAC film (thickness 32 μm) was pasted through an ultraviolet curable 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 in thickness) is formed on a TAC film (25 μm in thickness), and is bonded with the TAC film on the polarizing film side.

[Example 2] A polarizing film and a polarizing plate were obtained by the same procedures as in Example 1. In addition, the temperature of the conditioning area was 24.1° C., and the humidity was 45% RH.

[Example 3] The thickness of the PVA-based resin layer contained in the laminate was set to 15 μm, and the laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 64° C. and extended in water. The polarized light was obtained in the same manner as in Example 1. films and polarizers. In addition, the temperature of the conditioning area was 22.8° C., and the humidity was 47% RH.

[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 having a liquid temperature of 64° C., and stretched in water. In addition, the temperature of the conditioning area was 23.1° C., and the humidity was 44% RH.

[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 left to stand in an environment of 37.7° C. and 23% RH for 20 seconds to adjust the film thickness.

[Comparative example 2] A polarizing film and a polarizing plate were obtained by the same procedures as in Comparative Example 1. In addition, the temperature of the conditioning area was 37.5° C., and the humidity was 25% RH.

The following evaluations were performed on Examples and Comparative Examples. The evaluation results are summarized in Table 2. <Evaluation> 1. Film thickness of resin film The film thickness of the resin film was measured using a spectroscopic interference film thickness meter (manufactured by Ocean Insight, spectrometer "USB2000+", light source "HL-2000", fiber "OCF-103995") (on-line measurement). Measurements were performed at the entrance of the conditioning area, the exit of the conditioning area (the entrance of the drying area) and the exit of the drying area to obtain film thicknesses T1, T2, and T3. In addition, when measuring the film thickness of the resin film formed on the resin base material, a film thickness meter is arrange|positioned at the resin base material side. 2. Boronic acid content The spectrum of the polarizing film was measured using a Fourier transform infrared spectrometer (manufactured by Perkinelmer, model "Frontier FT-IR"), and the content of boric acid in the polarizing film was calculated from the obtained spectral results. Specifically, it is calculated from the peak intensities of 2940 cm ^-1 derived from (-CH ₂ -) bonds and 665 cm ^-1 derived from borate esters. In addition, the sample for measurement was collected at the outlet of the drying area. 3. Monomer transmittance and polarization degree Use a UV-visible spectrophotometer (manufactured by JASCO Corporation, V-7100) to measure the polarizing plates of Examples and Comparative Examples, and measure the monomer transmittance Ts, parallel transmittance The ratio Tp and the orthogonal transmittance Tc are respectively used as Ts, Tp and Tc of the polarizing film. These Ts, Tp, and Tc are measured according to the 2-degree field of view (C light source) of JIS Z8701, and the Y values are corrected for the sensitivity. The degree of polarization P was obtained from the obtained Tp and Tc by the following formula. Polarization degree P(%)={(Tp-Tc)/(Tp+Tc)} ^{1 /2} ×100 4. Appearance Observe the appearance of the polarizing plates of the examples and comparative examples with the naked eye (whether there are streaks or not). (Evaluation Criteria) Good: Streaks are not recognized by the naked eye Defective: Streaks are recognized by the naked eye

[Table 2]

In the polarizing plate of Comparative Example 1, streak marks (along the extending direction of the polarizing film) shown in FIG. 6 were confirmed.

Industrial availability The polarizing film according to the embodiment of the present invention is suitable for use in image display devices such as liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

1: laminated body 2: Thermoplastic resin substrate 3: Resin layer (resin film) 10: Polarizing film 10a: the first main surface of the polarizing film 10b: The second main surface of the polarizing film 20: protective layer 30: Retardation layer 40: Adhesive layer 100: polarizer 101: boric acid aqueous solution bath 102: Aqueous bath of dichroic substance (iodine) and potassium iodide 103: Aqueous bath of boric acid and potassium iodide 104: boric acid aqueous solution extension bath 105: Potassium iodide aqueous solution bath 110: Adjustment area 120: dry area G1~G4: guide roller R1~R6: conveyor roller

Fig. 1 is a schematic cross-sectional view showing a schematic configuration of a laminate according to an embodiment of the present invention. Fig. 2 is a graph showing the relationship between the film thickness and moisture content of a resin film after treatment with water. Fig. 3 is a schematic diagram showing an example of a manufacturing process of a polarizing film. Fig. 4 is a schematic view showing an example of drying using heating rollers in the drying zone. Fig. 5 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment of the present invention. FIG. 6 is an observation photo of a polarizing plate of Comparative Example 1. FIG.

1: laminated body

101: boric acid aqueous solution bath

102: Aqueous bath of dichroic substance (iodine) and potassium iodide

103: Aqueous bath of boric acid and potassium iodide

104: boric acid aqueous solution extension bath

105: Potassium iodide aqueous solution bath

110: Adjustment area

120: dry area

Claims (8)

A method of manufacturing a polarizing film, comprising: a step of obtaining a resin film having a first film thickness (T1) through treatment with water; an adjustment step of reducing the film thickness of the aforementioned resin film from the aforementioned first film thickness (T1) to a second film thickness (T2); and a drying step, which is to dry the resin film having the aforementioned second film thickness (T2); The ratio (T2/T1) of the second film thickness (T2) to the first film thickness (T1) is less than 1, The film thickness of the resin film is reduced from the second film thickness (T2) to the third film thickness (T3) by the aforementioned drying, and the ratio of the aforementioned third film thickness (T3) to the aforementioned second film thickness (T2) ( T3/T2) is below 0.90; In the aforementioned manufacturing method, the aforementioned conditioning is performed by placing the aforementioned resin film in an environment with a humidity of 35% RH or higher. The manufacturing method according to claim 1, which is to place the above-mentioned resin film in an environment with a temperature lower than 40° C. for the above-mentioned adjustment. The production method according to claim 1 or 2, wherein 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. The manufacturing method according to claim 1 or 2, wherein the difference between the humidity at which the conditioning is performed and the humidity at which the drying is performed is 30% RH or more. The manufacturing method according to claim 1 or 2, which is to place the aforementioned resin film in an environment with a temperature above 60° C. and a humidity below 10% RH to perform the aforementioned drying. The manufacturing method according to claim 1 or 2, wherein the aforementioned first film thickness (T1), the aforementioned second film thickness (T2) and the aforementioned third film thickness (T3) satisfy (T2/T1)/(T3/T2)≥ 1 relationship. The manufacturing method according to claim 1 or 2, wherein the first film thickness (T1) is 5 μm or more. According to the manufacturing method of claim 1 or 2, a polarizing film with a thickness of 7 μm or less is obtained.

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