JP2023050226A - Method for producing polarizing film - Google Patents

Abstract

To provide a polarizing film having both high optical characteristics and excellent appearance.SOLUTION: A method for producing a polarizing film includes a step of obtaining a resin film having a first moisture percentage (W1) through treatment using water, an adjustment step of reducing the moisture percentage of the resin film to a second moisture percentage (W2) from the first moisture percentage (W1), and a drying step of drying a resin film having the second moisture percentage (W2), wherein a ratio (W2/W1) of the second moisture percentage (W2) to the first moisture percentage (W1) is less than 1, the moisture percentage of the resin film is reduced to a third moisture percentage (W3) from the second moisture percentage (W2) by the drying step, a ratio (W3/W2) of the third moisture percentage (W3) to the second moisture percentage (W2) is 0.25 or less, and the adjustment is performed so that the resin film is placed under an environment of humidity of 35%RH or more.SELECTED DRAWING: Figure 3

Description

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

A liquid crystal display device, which is a typical image display device, has polarizing films arranged 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 organic electroluminescence (EL) panels and displays (QLED) using display panels using inorganic light-emitting materials such as quantum dots have been proposed. These panels have highly reflective metal layers, and tend to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circularly 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 has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA) 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 a potential contribution to the thinning of image display devices in recent years.

However, a thin polarizing film has the problem that it is not easy to achieve both high optical properties and good appearance. Specifically, the higher the optical properties, the more likely problems of appearance tend to occur. Poor appearance of the polarizing film may affect the display characteristics of the image display device. For example, streak marks on the polarizing film may be visually recognized as poor appearance (texture) in the structure of the laminated film (for example, circularly polarizing plate).

JP-A-2001-343521

The present invention has been made to solve the above problems, and a main object thereof is to provide a polarizing film having both high optical properties and excellent appearance.

According to embodiments of the present invention, a method for manufacturing a polarizing film is provided. This manufacturing method includes a step of obtaining a resin film having a first moisture content (W1) through a treatment using water, and a step of changing 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 said second moisture content (W2), wherein the ratio of said second moisture content (W2) to said first moisture content (W1) (W2/W1) is less than 1, the moisture content of the resin film is reduced from the second moisture content (W2) to the third moisture content (W3) by the drying, and the The ratio (W3/W2) of the third moisture content (W3) 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 more.
In one embodiment, the adjustment is performed while the resin film is placed in an environment with a temperature of less than 40°C.
In one embodiment, the difference between the temperature at which the drying is carried out and the temperature at which the conditioning is carried out is 25° C. or more.
In one embodiment, the difference between the conditioning humidity and the drying humidity is 30% RH or more.
In one embodiment, the drying is performed by placing the resin film in an environment with a temperature of 60° C. or more and a humidity of 10% RH or less.
In one embodiment, the ratio (W2/W1) of the second moisture content (W2) to the first moisture content (W1) is 0.4 or more.
In one embodiment, the first moisture content (W1) is 30% or more.
In one embodiment, a polarizing film having a thickness of 7 μm or less is obtained by the above manufacturing method.

According to the embodiment of the present invention, it is possible to obtain a polarizing film having both high optical properties and excellent appearance.

1 is a schematic cross-sectional view showing a schematic configuration of a laminate according to one embodiment of the present invention; FIG. 5 is a graph showing the relationship between the film thickness of a resin film after treatment with water and the moisture content. It is the schematic which shows an example of the manufacturing process of a polarizing film. FIG. 4 is a schematic diagram showing an example of drying using heated rolls in a drying zone; 1 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate according to one embodiment of the present invention; FIG. 4 is an observation photograph of the polarizing plate of Comparative Example 1. FIG.

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

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the in-plane direction orthogonal to the slow axis (i.e., fast axis direction) and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
“Re(λ)” is an in-plane retardation measured at 23° C. with light having a wavelength of λ nm. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. For example, “Rth(550)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) is determined by the formula: Rth(λ)=(nx−nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is obtained by Nz=Rth/Re.

A method for producing a polarizing film according to one embodiment of the present invention comprises a step of obtaining a resin film having a first moisture content (W1) through a treatment using water; W1) to a second moisture content (W2), and a drying step of drying the resin film having the second moisture content (W2).

A. Resin film The resin film is formed by, for example, forming a resin layer (typically, a polyvinyl alcohol-based resin layer) on a resin substrate to produce a laminate, stretching the laminate, and applying a dichroic agent such as iodine. It can be obtained by dyeing with a substance (for example, dyeing by adsorption of iodine).

A-1. 1. Laminate FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a laminate according to one embodiment of the present invention. The laminate 1 has a thermoplastic resin substrate (for example, elongated) 2 and a polyvinyl alcohol (PVA) 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 a thermoplastic resin substrate 2 . Specifically, the PVA-based resin layer 3 is formed by applying a coating liquid containing a PVA-based resin and a halide onto the thermoplastic resin substrate 2 and drying it.

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

The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. Such thermoplastic resin substrates can absorb water and be plasticized by water acting like a plasticizer. As a result, the drawing stress can be greatly reduced and the film can be drawn at a high draw ratio. 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, it is possible to prevent problems such as deterioration in the quality of the polarizing film obtained due to a marked decrease in the dimensional stability of the thermoplastic resin substrate during production. In addition, it is possible to prevent the thermoplastic resin substrate from breaking and the PVA-based resin layer from peeling off during stretching in water. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. Incidentally, the water absorption is a value determined according to JIS K7209.

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 secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the excellent stretching in water, the Tg is more preferably 100° C. or less, and even more preferably 90° C. or less. On the other hand, Tg of the thermoplastic resin substrate is preferably 60° C. or higher. According to such a Tg, when the coating liquid is applied and dried, defects such as deformation of the thermoplastic resin substrate (for example, occurrence of unevenness, sagging, wrinkles, etc.) are prevented, and good lamination is performed. You can make a body. Moreover, the stretching of the resin layer can be satisfactorily performed at a suitable temperature (for example, about 60°C). The Tg of the thermoplastic resin substrate can be adjusted, for example, by heating with a crystallizing material that introduces modifying groups into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K7121.

Any appropriate thermoplastic resin may be employed as a constituent material of the thermoplastic resin base material. 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. mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, an amorphous (not crystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

In another embodiment, a polyethylene terephthalate-based resin having an isophthalic acid unit is preferably used. This is because the stretchability is extremely excellent and crystallization during stretching can be suppressed. This is probably because the introduction of the isophthalic acid unit gives the main chain a large bend. A polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The isophthalic acid unit content is preferably 0.1 mol % or more, more preferably 1.0 mol % or more, relative to the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained. On the other hand, the isophthalic acid unit content is preferably 20 mol % or less, more preferably 10 mol % or less, relative to the total of all repeating units. This is because the degree of crystallinity can be favorably increased in drying, which will be described later.

The thermoplastic resin substrate may be stretched in advance (for example, before forming the PVA-based resin layer). In one embodiment, it is stretched in the transverse direction of the elongated thermoplastic resin substrate. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In addition, in this specification, "perpendicular" also includes the case of being substantially perpendicular. 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 with respect to the glass transition temperature (Tg) of the thermoplastic resin substrate. The draw ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times. Any appropriate method can be adopted as a method for stretching the thermoplastic resin substrate. Specifically, the drawing may be fixed end drawing or free end drawing. The stretching method may be a dry method or a wet method. Stretching may be performed in one step or in multiple steps. When performing in multiple stages, the said draw ratio is a product of the draw ratio of each step.

The coating liquid is typically a solution in which a PVA-based resin and a halide are dissolved in a solvent. Examples of solvents include water, dimethylsulfoxide, 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 liquid is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. According to such a range, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Examples of the PVA-based resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. is. By using a PVA-based resin having such a degree of saponification, a polarizing film with excellent durability can be obtained. If the degree of saponification is too high, gelation may occur. The degree of saponification can be determined according to JIS K 6726-1994.

The average degree of polymerization of the PVA-based resin is generally 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

Any appropriate halide can be employed as the halide. Examples thereof include iodides such as potassium iodide, sodium iodide and lithium iodide, and chlorides such as sodium chloride. Among these, potassium iodide is preferred. By using a halide, a polarizing film having high optical properties can be obtained. Specifically, the crystallization of the PVA-based resin after the auxiliary stretching in the air described later is promoted, and in the subsequent wet treatment (for example, dyeing and stretching in water described later), the orientation of the polyvinyl alcohol molecules is disturbed and the orientation is reduced. is suppressed, and a polarizing film having high optical properties can be obtained.

In preparation of the coating liquid, it is preferable to blend 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, of the halide with respect to 100 parts by weight of the PVA-based resin. 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, with respect to 100 parts by weight of the PVA-based resin. is. If the amount of the halide relative to the PVA-based resin is large, for example, the halide may bleed out and the resulting polarizing film may become cloudy.

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

Examples of the coating method of the coating liquid include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (such as comma coating). be done. The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

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 may be surface-treated (for example, corona treatment), or an easy-adhesion layer may 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. Stretching The stretching is preferably carried out by dry stretching (in-air auxiliary stretching) and then underwater stretching. Auxiliary stretching enables stretching while suppressing crystallization of the thermoplastic resin substrate, and solves the problem that stretching in boric acid water reduces stretchability due to excessive crystallization of the thermoplastic resin substrate, The laminate can be stretched to a higher magnification. Further, when a thermoplastic resin substrate is used, the application temperature may be set low, which may cause a problem that the crystallization of the PVA-based resin is relatively low and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be enhanced even when a thermoplastic resin is used. In addition, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin during subsequent wet treatment. Thus, a polarizing film with high optical properties can be obtained.

The method of in-air auxiliary stretching may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxially stretching a laminate through rolls having different peripheral speeds). . Free end drawing is preferably employed. For example, heating roll stretching is employed in which the laminate is stretched by a difference in peripheral speed between heating rolls while being conveyed in the longitudinal direction. In one embodiment, auxiliary air-drawing includes a zone drawing step and a heated roll drawing step in a hot space (zone). Although the order of the zone stretching step and the hot roll stretching step is not limited, for example, the zone stretching step and the hot roll stretching step are carried out in this order. In another embodiment, in a tenter stretching machine, the film is stretched by gripping the ends of the film and widening the distance between the tenters in the machine direction (the widening of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the machine direction) is preferably set to be closer to the free end stretching than the draw ratio in the machine direction. In the case of free end stretching, the shrinkage rate in the width direction is calculated by the formula: shrinkage rate in the width direction=(1/stretch ratio) ^1/2 .

The draw ratio of the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The in-air auxiliary stretching may be performed in one step or in multiple steps. When it is carried out in multiple stages, the draw ratio is the product of the draw ratios in each step. The stretching direction in the in-air auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching described below.

The stretching temperature for the in-air auxiliary stretching is set to any appropriate value depending on, for example, the thermoplastic resin substrate used, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably Tg+10° C. or higher, and even more preferably Tg+15° C. or higher. 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 rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can.

The stretching in water is typically performed by immersing the laminate in a stretching bath. According to underwater stretching, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes crystallization. It can be stretched to a high magnification while suppressing the stretching. As a result, a polarizing film having high optical properties can be obtained.

The method of underwater stretching may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different circumferential speeds). Free end drawing is preferably employed. The laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio of the laminate described below is the product of the draw ratios in each step.

The stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be satisfactorily stretched, and a polarizing film having high optical properties can be obtained.

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

Preferably, an iodide is added to the drawing bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based 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. is mentioned. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 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. At such a temperature, the film can be stretched at a high magnification, and a polarizing film having 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-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered. Moreover, even if the film is stretched at such a temperature, a polarizing film having an excellent appearance can be obtained by adjusting the moisture content, which will be described later. On the other hand, the stretching temperature is preferably 75° C. or lower, more preferably 70° C. or lower, and may be 65° C. or lower. The higher the stretching temperature, the higher the solubility of the PVA-based resin layer, possibly making it impossible to obtain high optical properties. Such a stretching temperature makes it possible to obtain a polarizing film with a better appearance. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater drawing is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminate (the draw ratio obtained by combining the auxiliary stretch in air and the stretch in water) is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. Yes, more preferably 6.0 times or more. By achieving such a high draw ratio, a polarizing film with extremely excellent optical properties can be produced. Such a high draw ratio can be achieved by adopting an underwater drawing method (boric acid solution drawing).

A-3. Dyeing The dyeing is typically carried out by allowing the PVA-based resin layer to adsorb iodine. As a method for adsorbing iodine, for example, a method of immersing the PVA-based resin layer (laminate) in a staining solution containing iodine, a method of applying the staining solution to the PVA-based resin layer, and a method of applying the staining solution to the PVA-based resin layer A method of spraying is mentioned. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.

The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the iodine aqueous solution. Specific examples of iodides are as described above. Potassium iodide is preferably used. The amount of iodide compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) are set so that, for example, the finally obtained polarizing film has a single transmittance of 42.0% or more and a degree of polarization of 99.98% or more. can do. As such dyeing conditions, for example, the ratio of the contents of iodine and potassium iodide in the iodine aqueous solution, which is the dyeing solution, is preferably 1:5 to 1:20, more preferably 1:5 to 1. :10.

When dyeing is performed continuously after the treatment of immersing the laminate in a treatment bath containing boric acid (for example, the insolubilization treatment described later), boric acid is mixed into the dyeing bath and the boric acid concentration of the dyeing bath changes, Dyeability may become unstable. In order to suppress such destabilization of dyeability, the concentration of boric acid in the dyeing bath is adjusted to preferably 4 parts by weight or less, more preferably 2 parts by weight or less with respect to 100 parts by weight of water. be done. 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 still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. That's it. In one embodiment, dyeing is performed using a dyeing bath containing boric acid beforehand. According to such a form, it is possible to 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 blended in advance in the dyeing bath (content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 100 parts by weight of water. is 0.5 to 1.5 parts by weight.

A-4. Other Treatments If necessary, an insolubilization treatment is performed after the auxiliary stretching in the air and before the stretching in water and dyeing. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution in the insolubilization 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 boric acid aqueous solution) is preferably 20°C to 50°C.

If necessary, a cross-linking treatment is performed after dyeing and before stretching in water. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA during subsequent stretching in water. The concentration of the boric acid aqueous solution in the cross-linking treatment is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. It is preferable to mix an iodide with the boric acid aqueous solution. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodides are as described above. The amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. The temperature of the cross-linking treatment (liquid temperature of boric acid aqueous solution) is preferably 20°C to 50°C.

Preferably, washing is performed after stretching in water. Washing is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

B. Moisture Content of Resin Film The resin film that has undergone the 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 FIG. 2, the moisture content of the resin film is obtained from the film thickness of the resin film. In the resin film, the dimensional change in the in-plane direction due to water absorption is restrained by the resin base material with low water absorption, and the resin film is considered to expand 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 treatment with water (for example, after washing) and the moisture content of the resin film. The graph in FIG. 2 shows the resin film after treatment with water 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. Data of film thickness and moisture content are plotted. The approximate curve in the graph is an approximate curve obtained by the method of least squares so as to form an exponential function from the plot data. The moisture 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 after treatment with water−weight of resin film after drying)/weight of resin film after drying

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, more preferably 70% or less.

FIG. 3 is a schematic diagram showing an example of the manufacturing process of the polarizing film. After the laminate 1 of the resin base material and the PVA-based resin layer is immersed in a boric acid aqueous solution bath 101 by a transport roll (insolubilization treatment), a dichroic substance (iodine) and potassium iodide aqueous solution bath 102. Dip in (dyeing process). Then, it is immersed in a bath 103 of an aqueous solution of boric acid and potassium iodide (crosslinking treatment). Next, the laminate 1 is immersed in a drawing bath 104 of an aqueous boric acid solution and stretched by applying tension in the conveying direction with rolls having different speed ratios (underwater stretching). Next, the laminate 1 stretched in water is immersed in a potassium iodide aqueous solution bath 105 to be washed (washing treatment). Although not shown, for example, the laminate 1 may be subjected to the in-air auxiliary stretching before the insolubilization treatment.

Laminate 1 after treatment with water (passed through the water bath) is conveyed to conditioning zone 110 and then to drying zone 120 .

By passing through the adjustment zone 110, the moisture content of the resin film (PVA-based resin layer) of the laminate 1 can be adjusted from the first moisture content (W1) to the second moisture content (W2). (Adjustment step). Specifically, at the inlet of conditioning zone 110, the resin film has a first moisture content (W1), and at the exit of conditioning zone 110 (the inlet of drying zone 120), the resin film has a second moisture content (W2). have

The second moisture content (W2) is, for example, 5% or more and 70% or less, preferably 15% or more and 60% or less, more preferably 20% or more and 50% or less, and still more preferably 20% or more and 45%. It is below. The ratio (W2/W1) of the second moisture content (W2) to the first moisture content (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, more preferably 0.7 or less.

The temperature in the conditioning zone 110 is preferably below 40°C, more preferably below 35°C, and may be below 30°C. On the other hand, the temperature in the conditioning zone 110 is preferably 20°C or higher, and may be 22°C or higher. By placing the resin film in such a temperature environment, it is possible to satisfactorily achieve the second moisture content (W2) over a predetermined period of time. The humidity in the conditioning zone 110 is preferably 35% RH or higher, more preferably 40% RH or higher. On the other hand, the humidity in the conditioning zone 110 is, for example, 65% RH or less. By placing the resin film in such a humid environment, the second moisture content (W2) can be satisfactorily achieved over a predetermined period of time.

The transit time through regulation zone 110 is, for example, 5 seconds to 4 minutes. The transit time through the conditioning zone 110 corresponds, for example, to the time the resin film is placed in an environment with predetermined conditions. The temperature and humidity in the adjustment zone 110 may not always be constant, but are preferably kept within the above temperature and humidity ranges, for example.

The moisture content reduction rate (R1) in the adjustment step is, for example, 1.5%/second or less, preferably 1.3%/minute or less. On the other hand, R1 is, for example, 0.7%/min or more.

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 step). Specifically, at the inlet of drying zone 120, the resin film has a second moisture content (W2), and at the outlet of drying zone 120, the resin film has a third moisture content (W3).

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

The moisture content reduction rate (R2) in the drying step 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.

Drying can be done in any suitable manner. For example, it may be performed by heating the entire drying zone 120 (zone heating method), or may be performed by heating the transport rolls in the drying zone 120 (heating roll method). A heated roll system is preferably employed, and more preferably both are employed. By using the heating roll, it is possible to efficiently suppress heating curling of the laminate and to manufacture a polarizing film of excellent quality. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, which is relatively low. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the resin film due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed.

By drying, the laminate can be shrunk in the width direction and the optical properties can be improved. This is because, for example, the orientation of PVA and PVA/iodine complex can be effectively enhanced. The widthwise shrinkage of the laminate upon drying is preferably 1% to 10%, more preferably 2% to 8%, and still more preferably 4% to 7%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.

FIG. 4 is a schematic diagram showing an example of drying using heated rolls in the 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 so as to alternately and continuously heat the surface of the resin film of the laminate 1 and the surface of the thermoplastic resin substrate. The transport rolls may be arranged so as to continuously heat only the surface of the resin base material.

In one embodiment, the drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and the like. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, still more preferably 70°C to 90°C. At such a temperature, the degree of crystallinity of the thermoplastic resin can be increased to suppress curling, and extremely excellent durability can be imparted to the laminate. Moreover, the moisture content of the resin film can be satisfactorily achieved. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as the number of transport rolls is plural. Conveying rolls are usually 2 to 40, preferably 4 to 30 in number. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 second to 20 seconds, still more preferably 1 second to 10 seconds.

The drying zone 120, which may be provided with heated rolls, is preferably heated. For example, drying zone 120 is the space within a heated furnace (eg, oven). According to such a configuration, a sharp temperature change 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, more preferably 95° C. or lower, from the viewpoint of suppressing wrinkles, for example. The humidity in the drying zone 120 is preferably 10% RH or less, more preferably 5% RH or less. On the other hand, the humidity in the drying zone 120 is, for example, 1% RH or higher. It is preferable that the inside of the heating furnace is in a ventilating state. In this case, the wind speed of the hot air is, for example, about 10 m/s to 30 m/s. The wind velocity in the heating furnace can be measured with a mini-vane digital anemometer.

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

The transit time through the drying zone 120 is, for example, 5 seconds to 4 minutes. The passage time through the drying zone 120 corresponds to, for example, the time during which the resin film is placed in an environment with predetermined conditions. The temperature and humidity in the drying zone 120 may not always be constant, but are preferably kept within the above temperature and humidity ranges, for example.

By drying the resin film that has undergone the adjustment step, it is possible to obtain a polarizing film that has both high optical properties and an excellent appearance. The present inventors have found that, for example, by controlling the moisture content of the resin film before drying, it is possible to achieve both optical properties and appearance, which are considered to be in a trade-off relationship.

C. Polarizing Film A polarizing film obtained according to an 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, it is possible to achieve both high optical properties and excellent appearance in a polarizing film having such a thickness. On the other hand, the thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more.

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

The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

The boric acid content of the polarizing film is preferably 25% or less, more preferably 20% or less. Higher optical properties can be achieved by having such a boric acid content. Even with such a boric acid content, an 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, still more preferably 16% or more. With such a boric acid content, the appearance can be more excellent. The boric acid content of the polarizing film is adjusted, for example, by adjusting the boric acid concentration in the underwater stretching.

D. Polarizing Plate A polarizing plate according to one embodiment of the present invention has the above 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 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 arranged on the first main surface 10a side of the polarizing film 10, and a second main surface 10b of the polarizing film 10. It has a retardation layer 30 and an adhesive layer 40 arranged on the two main surfaces 10b side. In this embodiment, the retardation layer 30 can function as a protective layer for the polarizing film 10 .

Protective layer 20 may be formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of materials that are the main component of such films include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, Transparent resins such as polysulfone-based, polystyrene-based, polynorbornene-based cycloolefin-based, polyolefin-based, (meth)acrylic-based, and acetate-based resins can be used. The resin substrate may be used as a protective layer of the polarizing film.

The polarizing plate 100 is typically arranged on the viewing side of the image display device. Therefore, the protective layer 20 may be subjected to surface treatment such as hard coat (HC) treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, if necessary. The thickness of the protective layer 20 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm. In addition, when the 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 may be adopted as the retardation layer 30 . In one embodiment, the retardation layer 30 uses an alignment fixed layer of a liquid crystal compound (liquid crystal alignment fixed layer). By using a liquid crystal compound, the difference between nx and ny in the resulting retardation layer can be significantly increased compared to a non-liquid crystal material. can be significantly reduced. As used herein, the term "fixed alignment layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction and the alignment state is fixed. In addition, the "alignment fixed layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer.

The retardation layer 30 typically includes a layer whose refractive index characteristics exhibit a relationship of nx>ny=nz. Note that "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 be satisfied within a range that does not impair the effects of the present invention. The Nz coefficient of the retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3.

Any appropriate configuration can be adopted for 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, number, combination and compounding ratio of the monomers forming the base resin of the adhesive, as well as the compounding amount of the cross-linking agent, the reaction temperature, the reaction time, etc., an adhesive having desired properties 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 pressure-sensitive adhesive layer is preferably composed of an acrylic pressure-sensitive adhesive). The thickness of the adhesive layer is, for example, 10 μm to 20 μm.

Each member constituting the polarizing plate can be laminated via 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 may be attached to the polarizing film 10 via an adhesive layer (preferably using an active energy ray-curable adhesive), or via an adhesive layer. It may be attached to the polarizing film 10 .

Although not shown, a release liner is practically adhered to the surface of the pressure-sensitive adhesive layer 40 . The release liner can be temporarily attached until the polarizer is ready for use. By using a release liner, for example, it is possible to protect the pressure-sensitive adhesive layer and roll-form the polarizing plate.

The polarizing plate may be elongated or sheet-shaped. As used herein, the term "long shape" refers to an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. say. A long polarizing plate can be wound into a roll.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. In addition, unless otherwise specified, the thickness is a 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 exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).

[Example 1]
(Preparation of resin film)
As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. was used. Corona treatment was applied to one side of the resin substrate.
A PVA system obtained 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 "GOSEFIMER Z410") at a weight ratio of 9:1. 13 parts by weight of potassium iodide was added to 100 parts by weight of resin to prepare a PVA aqueous solution (coating liquid).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The resulting laminate was uniaxially stretched 3.0 times at the free end in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the finally obtained polarizing film is placed in a dyeing bath (iodine aqueous solution obtained by blending 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. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 42.5% or more (dyeing).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4.0% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C, the laminate is placed between rolls having different peripheral speeds in the vertical direction (longitudinal direction). Then, uniaxial stretching was performed so that the total stretching ratio was 5.5 times (stretching in water).
After that, the laminate was immersed in a washing bath having 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).
Thus, a resin film was obtained on the resin substrate.

(Adjustment of moisture content)
The laminate was then placed in an environment of 23.4° C. and 47% RH (control zone) for 20 seconds to reduce the moisture content of the resin film.

(dry)
The laminate was then placed in an oven (dry zone) maintained at 90° C. and 2% RH for 1 minute. During this time, it was placed in an oven and brought into contact with a heating roll made of SUS whose surface temperature was kept at 75° C. for about 2 seconds.
Thus, a polarizing film having a thickness of 5 μm was obtained on the resin substrate. The shrinkage ratio of the laminate in the width direction due to drying was 6.1%.

The temperature and humidity in the oven (drying zone) and the temperature and humidity in adjusting the moisture content before entering the oven (adjustment zone) were measured using a temperature and humidity data logger (manufactured by Testo, product name "175 H1"). ”).

(Preparation of polarizing plate)
After bonding an HC-TAC film (thickness 32 μm) to the polarizing film side of the laminate of the resin base material and the polarizing film via an ultraviolet curing adhesive, the resin base material is peeled off from the polarizing film to polarize the light. got a board 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 the films are laminated so that the TAC film faces the polarizing film side.

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

[Example 3]
A polarizing film was prepared in the same manner as in Example 1, except that the thickness of the PVA-based resin layer contained in the laminate was 15 μm, and the laminate was immersed in an aqueous boric acid solution at a liquid temperature of 64° C. and stretched in water. and a polarizing plate. The temperature in the conditioning zone 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 an aqueous boric acid solution at a liquid temperature of 64° C. and stretched in water. The temperature in the conditioning zone 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 placed in an environment of 37.7° C. and 23% RH for 20 seconds when adjusting the moisture content.

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

The examples and comparative examples were evaluated as follows. Table 2 summarizes the evaluation results.
<Evaluation>
1. Moisture content of resin film Measure the film thickness of the resin film using a spectroscopic interference film thickness meter (manufactured by Ocean Insight Co., Ltd., spectrometer “USB2000+”, light source “HL-2000”, fiber “OCF-103995”) (inline measurement), and the obtained measured values were converted to moisture content based on the graph shown in FIG. Measurements were taken at the regulating zone inlet, regulating zone outlet (drying zone inlet) and drying zone outlet to determine moisture content W1, W2 and W3. When measuring the film thickness of the resin film formed on the resin substrate, the film thickness meter was arranged on the resin substrate side.
2. Boric acid content Using a Fourier transform infrared spectrometer (manufactured by PerkinElmer, model "Frontier FT-IR"), the spectrum of the polarizing film was measured, and the amount of boron present in the polarizing film was determined from the resulting spectrum. Acid content was calculated. Specifically, it was calculated from peak intensities at 2940 cm ⁻¹ derived from (—CH ₂ −) bond and 665 cm ⁻¹ derived from boric acid ester. A sample for measurement was taken at the outlet of the drying zone.
3. Single transmittance and degree of polarization For the polarizing plates of Examples and Comparative Examples, single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, V-7100). were defined as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
4. Appearance The appearance (presence or absence of streak marks) of the polarizing plates of Examples and Comparative Examples was visually observed.
(Evaluation criteria)
Good: streaks are not visually confirmed Poor: streaks are visually confirmed

In the polarizing plate of the comparative example, streak marks (along the stretching direction of the polarizing film) as shown in FIG. 6 were confirmed.

The polarizing film according to the embodiment of the present invention is suitably used for image display devices such as liquid crystal display devices, organic EL display devices and inorganic EL display devices.

REFERENCE SIGNS LIST 1 laminate 2 thermoplastic resin substrate 3 resin layer (resin film)
10 polarizing film 20 protective layer 100 polarizing plate

Claims (8)

obtaining a resin film having a first moisture content (W1) through treatment with water;
an adjusting step of reducing the moisture content of the resin film from the first moisture content (W1) to the second moisture content (W2);
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,
By the drying, the moisture content of the resin film is reduced from the second moisture content (W2) to the third moisture content (W3), and the ratio (W3) of the third moisture content (W3) to the second moisture content (W2) /W2) is 0.25 or less,
The adjustment is performed by placing the resin film in an environment with a humidity of 35% RH or higher.
A method for producing a polarizing film. 2. The manufacturing method according to claim 1, wherein the adjustment is performed while the resin film is placed in an environment with a temperature of less than 40[deg.]C. The manufacturing method according to claim 1 or 2, wherein the difference between the temperature for drying and the temperature for adjusting is 25°C or more. 4. The manufacturing method according to any one of claims 1 to 3, wherein the difference between the humidity for adjusting and the humidity for drying is 30% RH or more. 5. The manufacturing method according to any one of claims 1 to 4, wherein said drying is carried out by placing said resin film in an environment with a temperature of 60[deg.] C. or more and a humidity of 10% RH or less. The production method according to any one of claims 1 to 5, wherein the ratio (W2/W1) of said second moisture content (W2) to said first moisture content (W1) is 0.4 or more. The manufacturing method according to any one of claims 1 to 6, wherein said first moisture content (W1) is 30% or more. The manufacturing method according to any one of claims 1 to 7, wherein a polarizing film having a thickness of 7 µm or less is obtained.

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