TW202229943A - Polarizing plate manufacturing method, image display device manufacturing method, and method for adjusting transmittance of polarizing film - Google Patents

Abstract

The present invention provides a method for adjusting the transmittance of a polarizing film after producing the same. A polarizing plate manufacturing method according to the present invention comprises, in the order given, a step for obtaining a primary polarizing film by subjecting a polyvinyl alcohol-based resin film to a dyeing treatment and to a stretching treatment in a boric acid aqueous solution and thereafter drying the film until the moisture content reaches 15 wt% or less, and a step for obtaining a secondary polarizing film by bringing the surface of the primary polarizing film into contact with an aqueous solvent and thereby altering the transmittance of the film.

Description

Method for manufacturing polarizing plate, method for manufacturing image display device, and method for adjusting transmittance of polarizing film

The present invention relates to a method for manufacturing a polarizing plate, a method for manufacturing an image display device, and a method for adjusting the transmittance of a polarizing film.

In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) are rapidly spreading. In the liquid crystal display device, polarizers are arranged on both sides of the liquid crystal cell based on its image forming method. In addition, it is known that in organic EL display devices, by arranging a circular polarizer including a λ/4 plate on the viewing side of the organic EL unit, problems such as reflection of external light and reflection of background are prevented (for example, Patent Documents 1 and 2). .

The polarizing plate usually has a structure in which a protective layer is arranged on at least one side of a polarizing film produced by dyeing and extending a polyvinyl alcohol-based resin film, and is attached to images such as liquid crystal cells and organic EL cells through an adhesive layer. Display unit. prior art literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2002-311239 Patent Document 2: Japanese Patent Laid-Open No. 2002-372622

[Problems to be Solved by Invention]

Previously, a method of adjusting the transmittance of the polarizing film after the production of the polarizing film has not been known, so the transmittance of the polarizing film cannot be adjusted after the polarizing plate is attached to the image display unit. On the other hand, since the brightness of the image display device may be uneven due to individual differences in the quality of the image display unit or the backlight unit, etc., it is desirable to develop an image display unit after the protective layer is laminated or attached to the image display unit. The method of adjusting the transmittance of the polarizing film afterward.

The present invention was established in order to solve the above-mentioned problems, and its main purpose is to provide a method for adjusting the transmittance of a polarizing film after its production. [Technical means to solve problems]

According to an aspect of the present invention, there is provided a method for manufacturing a polarizing plate, which sequentially includes: after the polyvinyl alcohol-based resin film is subjected to dyeing treatment and extension treatment in a boric acid aqueous solution, drying the film until the moisture content becomes 15 The step of obtaining a primary polarizing film by weight % or less; and the step of obtaining a secondary polarizing film by changing the transmittance by contacting the surface of the primary polarizing film with an aqueous solvent. In one embodiment, the exposed surface of the primary polarizing film in a state in which one surface is exposed and the other surface is protected is brought into contact with the aqueous solvent. In one embodiment, the above-mentioned step of obtaining a primary polarizing film includes: sequentially placing the polyvinyl alcohol-based resin film comprising a halide and a polyvinyl alcohol-based resin in a state of a laminate with an elongated thermoplastic resin substrate. For air-assisted stretching treatment, dyeing treatment, stretching treatment in boric acid aqueous solution, and drying shrinkage treatment; the drying shrinkage treatment includes: conveying the laminate in the longitudinal direction and heating it, thereby making it in the width direction. The upper shrinkage is 2% or more, and it is dried until the water content of the polyvinyl alcohol-based resin film becomes 15% by weight or less. In one embodiment, the halide is iodide or sodium chloride. In one embodiment, the thickness of the primary polarizing film is 12 μm or less. According to another aspect of the present invention, there is provided a method for manufacturing an image display device, which sequentially includes: sequentially including a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less The polarizing film, the protective layer, and the polarizing plate of the adhesive layer are laminated on the image display unit through the adhesive, and the surface of the polarizing film opposite to the side where the protective layer is arranged is used as the exposed surface; and The step of changing the transmittance by contacting the exposed surface of the polarizing film with an aqueous solvent. In one embodiment, the image display device is a liquid crystal display device or an organic EL display device. According to yet another aspect of the present invention, there is provided a method for adjusting the transmittance of a polarizing film, comprising the steps of: making a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less The surface of the polarizing film is in contact with the aqueous solvent. [Effect of invention]

According to the present invention, the transmittance of the polarizing film can be changed afterwards by contacting the surface of the polarizing film produced by dyeing and extending a polyvinyl alcohol-based resin film with an aqueous solvent. In addition, after stretching in a boric acid aqueous solution, it is dried until the moisture content becomes below a specific value to stabilize the appearance, and the surface of the polarizing film in this state is brought into contact with the aqueous solvent to increase the transmittance. changes, so the penetration rate can be fine-tuned. As a result, for example, uneven brightness among image display devices can be reduced, which is effective in situations where it is necessary to make the appearance of a plurality of display screens consistent, especially when a plurality of display screens are combined to display images (large-scale public displays, digital signage) Wait).

Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited to these embodiments. Furthermore, the polarizing plate obtained by the manufacturing method of the polarizing plate according to the embodiment of the present invention includes at least a polarizing film, preferably a polarizing film and a protective layer disposed on one side or both sides of the polarizing film.

A. Manufacturing method of polarizing plate The manufacturing method of the polarizing plate according to the embodiment of the present invention sequentially includes: after subjecting the polyvinyl alcohol (PVA)-based resin film to dyeing treatment and extension treatment in boric acid aqueous solution (boric acid aqueous extension treatment), drying the film until it contains water A step of obtaining a primary polarizing film with a ratio of 15% by weight or less; and a step of obtaining a secondary polarizing film by changing the transmittance by contacting the surface of the primary polarizing film with an aqueous solvent. According to the manufacturing method of the polarizing plate, the surface of the temporarily produced polarizing film (primary polarizing film) is contacted with an aqueous solvent to decolorize, whereby the transmittance can be changed and adjusted to a desired value afterwards. In addition, by subjecting the polarizing film (primary polarizing film) in a state of high alignment and stable appearance through boric acid aqueous extension treatment and drying treatment to the aqueous solvent, it is possible to avoid excessive reduction in the degree of polarization and the occurrence of wrinkles. The penetration rate is appropriately adjusted while pleating, dissolving, etc.

In the manufacturing method of the polarizing plate according to the embodiment of the present invention, only one side of the primary polarizing film can be brought into contact with the aqueous solvent to change the transmittance, or both sides can be brought into contact with the aqueous solvent to make the transmittance happen. Variety.

In the manufacturing method of the polarizing plate of one embodiment of the present invention, the exposed surface of the primary polarizing film in the state where one surface is exposed and the other surface is protected is brought into contact with an aqueous solvent to change the transmittance. For example, the manufacturing method of the polarizing plate of this embodiment may include the step of producing a polarizing plate between the step of obtaining the primary polarizing film and the step of obtaining the secondary polarizing film, and the polarizing plate has one surface of the primary polarizing film exposed. And the other side is protected by a protective layer.

A-1. Steps to obtain a polarizing film In the step of obtaining a primary polarizing film, after the PVA-based resin film is subjected to dyeing treatment and boric acid water stretching treatment, it is dried until the moisture content becomes 15% by weight or less, thereby obtaining a primary polarizing film. The primary polarizing film may be produced using a single-layer PVA-based resin film, or may be produced using a laminate of two or more layers including a PVA-based resin layer (PVA-based resin film). The primary polarizing film obtained by using a laminate of two or more layers can properly maintain excellent optical properties (representative monomer transmittance and degree of polarization) while avoiding the occurrence of wrinkles, even after contact with an aqueous solvent.

A-1-1. Production of primary polarizing film using two or more layers of laminate The production of a primary polarizing film using a laminate of two or more layers can be carried out, for example, by the following method. In the state of the laminated body, it is sequentially subjected to air-assisted stretching treatment, dyeing treatment, stretching treatment in boric acid aqueous solution, and drying shrinkage treatment. A laminate of a thermoplastic resin substrate and a PVA-based resin film can be formed as a laminate by, for example, forming a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of an elongated thermoplastic resin substrate. get. The drying shrinkage treatment includes, for example, heating the laminate of the elongated thermoplastic resin base material and the PVA-based resin film while conveying it in the longitudinal direction to shrink it by 2% or more in the width direction, And drying is performed until the moisture content of this PVA-type resin film becomes 15 weight% or less. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. According to such a production method, a primary polarizing film having a high degree of orientation of the PVA-based resin and excellent optical properties can be obtained.

A-1-1-1. Fabrication of laminated body Any appropriate method can be adopted as a method of producing the laminate of the thermoplastic resin base material and the PVA-based resin layer. Preferably, the PVA-based resin layer is formed on the thermoplastic resin substrate by applying and drying a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

As a coating method of the coating liquid, any appropriate method can be adopted. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a blade coating method Wheel coating method, etc.) and so on. The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or higher.

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

Before forming the PVA-based resin layer, a surface treatment (eg, corona treatment, etc.) may be performed on the thermoplastic resin substrate, and an easy-bonding layer may also be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA-type resin layer can be improved.

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

The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water functions as a plasticizer for plasticization. As a result, the stretching stress can be greatly reduced, and the stretching can be performed at a high magnification. On the other hand, the water absorption of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, the dimensional stability of the thermoplastic resin base material can be prevented from being significantly lowered during production, and abnormalities such as deterioration of the appearance of the resulting polarizing film can be prevented. Moreover, when extending|stretching in water, a base material can be prevented from breaking or peeling of the PVA-based resin layer from the thermoplastic resin base material. In addition, the water absorption rate of a thermoplastic resin base material can be adjusted by, for example, introducing a modification group into a constituent material. The water absorption rate is the value calculated|required based on JISK7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120° C. or lower. By using such a thermoplastic resin base material, the crystallization of the PVA-based resin layer can be suppressed, and the extensibility of the laminate can be sufficiently ensured. Furthermore, considering that plasticization by water and water stretching of the thermoplastic resin base material are performed well, it is more preferably 100°C or lower, and still more preferably 90°C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, it is possible to prevent abnormalities such as deformation (for example, unevenness, slack, or wrinkles) of the thermoplastic resin substrate during coating and drying of the coating liquid containing the PVA-based resin, thereby preventing abnormality such as deformation of the thermoplastic resin substrate. A laminated body is produced well. Moreover, the PVA-type resin layer can be extended well at an appropriate temperature (for example, about 60 degreeC). In addition, the glass transition temperature of a thermoplastic resin base material can be adjusted by, for example, introducing a modification group into a constituent material and heating using a crystallizing material. The glass transition temperature (Tg) is a value determined based on JIS K 7121.

As the constituent material of the thermoplastic resin substrate, any appropriate thermoplastic resin can be used. Examples of thermoplastic resins include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as noralkene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, and polycarbonates. Ester-based resins, copolymer resins of these, and the like. Among these, noralkene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, it is preferable to use an amorphous (uncrystallized) polyethylene terephthalate-based resin. Among them, it is particularly preferable to use an amorphous (hardly crystallized) polyethylene terephthalate-based resin. Specific examples of the amorphous polyethylene terephthalate-based resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and further containing cyclohexane Dimethanol or diethylene glycol are used as copolymers of diols.

In a preferred embodiment, the thermoplastic resin substrate comprises a polyethylene terephthalate-based resin having isophthalic acid units. The reason for this is that such a thermoplastic resin base material is extremely excellent in elongation and can suppress crystallization during elongation. The reason for this is considered to be that the main chain is largely bent by introducing the isophthalic acid unit. The polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol % or more, and more preferably 1.0 mol % or more with respect to the total of all repeating units. The reason for this is that a thermoplastic resin substrate having extremely excellent extensibility can be obtained at this content ratio. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol % or less, more preferably 10 mol % or less, with respect to the total of all repeating units. By setting it to such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment to be described later.

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, it extends along the transverse direction of the elongated thermoplastic resin substrate. The lateral direction is preferably a direction orthogonal to the extending direction of the laminate described later. In addition, in this specification, "orthogonal" also includes the case of being substantially orthogonal. Here, "substantially orthogonal" includes the case of 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°.

The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C with respect to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin substrate is preferably 1.5 times to 3.0 times.

As a method of extending the thermoplastic resin substrate, any appropriate method can be adopted. Specifically, it can be a fixed end extension or a free end extension. The extension method can be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or in multiple stages. When carried out in multiple stages, the above stretching ratio is the product of the stretching ratios of the respective stages.

The coating liquid contains the halide and the PVA-based resin as described above. Typically, the above-mentioned coating liquid is a solution obtained by dissolving the above-mentioned halide and the above-mentioned PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and polyols such as trimethylolpropane. amines such as ethylenediamine, diethylenetriamine, etc. These may be used alone, or two or more of them may be used in combination. Among these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Additives can be formulated in the coating liquid. As an additive, a plasticizer, a surfactant, etc. are mentioned, for example. As a plasticizer, polyalcohols, such as ethylene glycol and glycerol, are mentioned, for example. As a surfactant, a nonionic surfactant is mentioned, for example. These can be used to further improve the uniformity, dyeability, and extensibility of the resulting PVA-based resin layer.

Any appropriate resin can be used as the above-mentioned PVA-based resin. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be calculated|required based on JISK6726-1994. By using the PVA-based resin having such a degree of saponification, a polarizing film excellent in durability can be obtained. When the saponification is too high, there is a possibility of causing gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. In addition, the average degree of polymerization can be calculated|required based on JISK6726-1994.

As the above-mentioned halide, any appropriate halide can be used. For example, iodide and sodium chloride are mentioned. As an iodide, potassium iodide, sodium iodide, and lithium iodide are mentioned, for example. Among these, potassium iodide is preferable.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin, more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA resin. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out, and the resulting polarizing film may become cloudy.

Usually, the alignment of polyvinyl alcohol molecules in the PVA-based resin layer is increased by extending the PVA-based resin layer, but when the stretched PVA-based resin layer is immersed in a liquid containing water, polyvinyl alcohol is present. A situation in which the molecular alignment is disordered and the alignment is reduced. In particular, when the laminate of the thermoplastic resin substrate and the PVA-based resin layer is extended in boric acid water, the laminate is extended in boric acid water at a relatively high temperature in order to stabilize the elongation of the thermoplastic resin substrate. , at this time, the above-mentioned tendency of the degree of alignment to decrease is obvious. For example, the stretching of the PVA film alone in boric acid water is usually carried out at 60°C. In contrast, the stretching of the laminate of A-PET (thermoplastic resin substrate) and the PVA-based resin layer is performed at a temperature of about 70°C. It is carried out at a high temperature, and in this case, the orientation of the PVA in the initial stage of stretching can be reduced in the stage before it is raised by underwater stretching. In this regard, by producing a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate, and subjecting the laminate to high temperature stretching (assisted stretching) in the air before stretching in boric acid water, it is possible to promote the subsequent stretching after assisted stretching. Crystallization of the PVA-based resin in the PVA-based resin layer of the laminate. As a result, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the alignment disorder of the polyvinyl alcohol molecules and the decrease in alignment can be suppressed. Thereby, the optical characteristics of the polarizing film obtained by the process process of immersing a laminated body in liquid, such as dyeing process and underwater extension process, can be improved.

A-1-1-2. Air Auxiliary Extension Processing In particular, in order to obtain higher optical properties, a 2-stage stretching method combining dry stretching (assisted stretching) and boric acid aqueous stretching was selected. By introducing auxiliary stretching in two-stage stretching, the crystallization of the thermoplastic resin substrate can be suppressed and the stretching can be carried out, which solves the problem that the elongation is reduced due to excessive crystallization of the thermoplastic resin substrate during the subsequent stretching in boric acid water. The problem is that the laminate can be stretched at a higher magnification. Furthermore, in the case of coating the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the coating temperature than when the PVA-based resin is usually coated on the metal drum. As a result, there may be a problem that the crystallization of the PVA-based resin becomes relatively low and sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin substrate, the crystallinity of the PVA-based resin can be improved, so that higher optical properties can be realized. 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 and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing treatment and stretching treatment, so that higher optical properties can be achieved. .

The stretching method of air-assisted stretching can be either fixed-end stretching (such as a method of stretching using a tenter stretching machine) or free-end stretching (such as a method of uniaxial stretching by passing the laminated body between rolls with different peripheral speeds) , in order to obtain higher optical properties, the free end extension can be actively used. In one embodiment, the in-air stretching treatment includes a heating roll stretching step of stretching using the difference in peripheral speed between heating rolls while conveying the above-mentioned layered body in the longitudinal direction. The air stretching process typically includes a zone stretching step and a heating roll stretching step. Furthermore, the sequence of the zone stretching step and the heating roller stretching step is not limited, and the zone stretching step may be performed first, or the heating roller stretching step may be performed first. The region extension step can also be omitted. In one embodiment, the zone stretching step and the heating roller stretching step are performed in sequence. Moreover, in another embodiment, by holding the end of the layered body in the tenter stretching machine, and extending the distance between the tenters in the traveling direction (the extension of the distance between the tenters is stretching magnification). At this time, the distance of the tenter in the width direction (vertical direction with respect to the traveling direction) is set to be arbitrarily close. Preferably, the extension ratio relative to the traveling direction can be set closer to the extension of the free end. When the free end is stretched, it is calculated by the shrinkage ratio in the width direction=(1/extension ratio) ^1/2 .

Aerial assist extension can be carried out in one stage or in multiple stages. When carried out in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The extension direction of the auxiliary extension in the air is preferably substantially the same as the extension direction of the underwater extension.

The stretching ratio of the aerial auxiliary stretching is preferably 2.0 times to 3.5 times. The maximum stretching ratio in the case of combining aerial auxiliary stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more with respect to the original length of the layered body. In this specification, the "maximum elongation ratio" refers to the elongation ratio immediately before fracture of the laminate, and this value also refers to the elongation ratio for confirming the fracture of the laminate and is 0.2 lower than the elongation ratio at the time of fracture.

The stretching temperature of the air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate+10°C, and particularly preferably Tg+15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By extending at such a temperature, rapid progress of crystallization of the PVA-based resin can be suppressed, and abnormality caused by the crystallization (eg, hindering the alignment of the PVA-based resin layer by stretching) can be suppressed. The crystallographic index of the PVA-based resin after air-assisted stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallographic index of the PVA-based resin can be measured by the ATR (Attenuated Total Reflection) method using a Fourier transform infrared spectrometer. Specifically, the measurement was performed using polarized light as measurement light, and the crystallographic index was calculated according to the following formula using the intensities of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum. Crystal Index=( _IC /IR) Wherein, _IC is the intensity of ₁₁₄₁ cm _- ¹ when measuring with incident measuring light, and IR is the intensity at 1440 cm ^-1 when measuring with incident measuring light.

A-1-1-3. Insolubilization treatment If necessary, insolubilization treatment may be performed after air-assisted stretching treatment, underwater stretching treatment and dyeing treatment. The above-mentioned insolubilization treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the insolubilization treatment, the PVA-based resin layer can be provided with water resistance, and the PVA orientation can be prevented from being lowered when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C.

A-1-1-4. Dyeing treatment The above-mentioned dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (representative iodine). Specifically, it is performed by adsorbing iodine in the PVA-based resin layer. As the adsorption method, for example, a method of immersing a PVA-based resin layer (layered body) in a dyeing solution containing iodine, a method of coating the dyeing solution on the PVA-based resin layer, and spraying the dyeing solution can be mentioned. Methods to PVA-based resin layers, etc. The method of immersing the laminated body in a dyeing liquid (dyeing bath) is preferable. The reason for this is that iodine can be adsorbed well.

The above-mentioned dyeing solution is preferably an aqueous iodine 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 improve the solubility of iodine in water, it is preferable to prepare iodide in an aqueous iodine solution. 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. Wait. Among these, potassium iodide is preferable. The compounding amount of the 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 suppress the dissolution of the PVA-based resin, the temperature of the dyeing solution during dyeing is preferably 20°C to 50°C. When the PVA-based resin layer is immersed in the dyeing solution, in order to ensure the penetration rate of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the monomer transmittance of the polarizing film finally obtained becomes a desired value. As such dyeing conditions, it is preferable to use an iodine aqueous solution as a dyeing solution, and to set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. Thereby, a primary polarizing film having optical properties as described later can be obtained.

In the case of continuous dyeing treatment after immersion of the laminate in a treatment bath containing boric acid (representatively, insolubilization treatment), the boric acid concentration in the dyeing bath is adjusted by mixing boric acid contained in the treatment bath into the dyeing bath. It may change over time, and as a result, the dyeability may become unstable. The upper limit of the boric acid concentration in the dyeing bath is adjusted so that it is preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water, in order to suppress the above-mentioned instability of the dyeability. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and still more preferably 0.5 part by weight relative to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath prepared by pre-mixing boric acid. Thereby, the ratio of the change of the boric acid concentration in the case where the boric acid of the above-mentioned treatment bath is mixed into the dyeing bath can be reduced. The amount of boric acid prepared in the dyeing bath in advance (ie, the content of boric acid not derived from the 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. parts by weight.

A-1-1-5. Crosslinking Treatment Crosslinking treatment may be carried out after the dyeing treatment and before the water stretching treatment if necessary. The above-mentioned crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By carrying out the crosslinking treatment, the PVA-based resin layer can be given water resistance, and can prevent the PVA from being immersed in high-temperature water from being degraded in orientation during subsequent water extension. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Moreover, in the case where the crosslinking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further prepare an iodide. By preparing the iodide, the elution of the iodine adsorbed in the PVA-based resin layer can be suppressed. The compounding amount of the iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

A-1-1-6. Water extension treatment The underwater stretching treatment is performed by immersing the layered body in a stretching bath. According to the underwater stretching treatment, the stretching can be performed at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin substrate or the PVA-based resin layer, which can suppress the crystallization of the PVA-based resin layer. Extend at high magnification. As a result, a polarizing film having excellent optical properties can be produced.

Any appropriate method can be adopted as the method of extending the layered body. Specifically, it may be a fixed-end extension or a free-end extension (for example, a method of uniaxially extending the laminate by passing between rolls with different peripheral speeds). Preferably, the free end extension is selected. The extension of the laminate may be performed in one stage or in multiple stages. When carried out in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios of the respective stages.

The underwater stretching is typically performed by immersing the layered body in a boric acid aqueous solution (boric acid water stretching). By using the boric acid aqueous solution as the stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding tension during stretching and water resistance insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anion in an aqueous solution, and crosslink with PVA-based resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, so that it can be extended well, and a primary polarizing film having excellent optical properties can be produced.

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

Preferably, the iodide is prepared in the above-mentioned extension bath (boric acid aqueous solution). By preparing the iodide, the elution of the iodine adsorbed in the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of the 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 to 85°C, more preferably 60°C to 75°C. At such a temperature, it is possible to extend at a high rate while suppressing the dissolution of the PVA-based resin layer. 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., there is a possibility that the stretching may not be performed favorably even in consideration of plasticization of the thermoplastic resin base material by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical properties cannot be obtained. The immersion time of the layered body in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio of the stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the layered body is preferably 5.0 times or more, and more preferably 5.5 times or more, with respect to the original length of the layered body. By achieving such a high draw ratio, a primary polarizing film with extremely excellent optical properties can be produced. Such a higher extension ratio can be achieved by using an underwater extension method (boric acid water extension).

A-1-1-7. Drying shrinkage treatment The above-mentioned drying shrinkage treatment includes, for example, heating the laminate of the elongated thermoplastic resin substrate and the PVA-based resin film while conveying it in the longitudinal direction to shrink it by 2% or more in the width direction. , and dried until the moisture content of the PVA-based resin film becomes 15% by weight or less. From the viewpoint of obtaining a stable appearance, drying is preferably performed until the moisture content becomes 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% by weight to 5% by weight.

The drying shrinkage treatment may be performed by zone heating performed by heating the entire area, or may be performed by heating a conveyance roll (so-called using a heating roll) (heating roll drying method). It is preferable to use both. By drying it using a heating roll, the heating curl of the laminated body can be effectively suppressed, and a primary polarizing film having an excellent appearance can be produced. Specifically, the crystallization of the thermoplastic resin base material can be effectively promoted by drying the layered body in a state where the laminate runs along the heating roller, so that the degree of crystallinity can be increased, and even at a relatively low drying temperature, The crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the shrinkage of the PVA-based resin layer due to drying is brought into a state, and curling is suppressed. Moreover, since the laminated body can be dried while maintaining a flat state by using a heating roll, not only the generation of curls but also the generation of wrinkles can be suppressed. In this case, the optical properties of the laminate can be improved by shrinking it in the width direction by drying shrinkage treatment. The reason is that the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate in the width direction of the laminate during the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roller, the laminated body can be continuously shrunk in the width direction while being conveyed, and high productivity can be realized.

FIG. 1 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage treatment, the layered body 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a specific temperature. In the illustrated example, the conveyance rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate, but for example, only one surface of the layered body 200 (for example, the thermoplastic resin substrate) may be provided. Resin base material surface) is heated continuously, and conveyance rollers R1-R6 are arrange|positioned.

Drying conditions can be controlled by adjusting the heating temperature of the conveying roller (heating roller temperature), the number of heating rollers, and the contact time with the heating roller. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The degree of crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. In addition, the temperature of a heating roll can be measured with a contact thermometer. In the illustrated example, although six conveyance rollers are provided, it is not particularly limited as long as there are plural conveyance rollers. Usually, 2 to 40 conveyance rollers are provided, and 4 to 30 are preferably provided. The contact time (total contact time) of the laminate and the heating roll is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (eg, an oven), or can be installed in a normal production line (at room temperature). Preferably, it is installed in a heating furnace equipped with an air supply mechanism. By combining the drying with the heating roller and the hot air drying, the rapid temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30°C to 100°C. Moreover, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. In addition, this wind speed is the wind speed in a heating furnace, and can be measured with a small vane type digital anemometer.

A-1-1-8. Other processing Preferably, the washing process is performed after the underwater stretching process and before the drying shrinkage process. The above-mentioned cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

A-1-2. Production of primary polarizing film using single-layer PVA-based resin film The production of a primary polarizing film using a single-layer PVA-based resin film can be carried out by the following methods: dyeing and extending in boric acid water (representative (uniaxially stretched by a roll stretcher), and then dried until the moisture content becomes 15 wt % or less, preferably 12 wt % or less, more preferably 10 wt % or less, and more preferably 1 wt % % to 5% by weight. The above-mentioned dyeing is performed, for example, by immersing a PVA-based resin film in an aqueous iodine solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The stretching can be carried out after the dyeing treatment, or can be carried out while dyeing. Moreover, you may dye after extending|stretching. The PVA-based resin film is subjected to swelling treatment, crosslinking treatment, washing treatment and the like as necessary. For example, by immersing the PVA-based resin film in water and washing it before dyeing, not only the dirt and anti-blocking agent on the surface of the PVA-based resin film can be removed, but also the PVA-based resin film can be swelled to prevent uneven dyeing.

A-1-3. Primary Polarizing Film The primary polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance (single transmittance: Ts) of the primary polarizing film is preferably 41.5% or more, more preferably 42.0% or more, and still more preferably 42.5% or more. On the other hand, the transmittance of the primary polarizing film is preferably 46.0% or less, more preferably 45.0% or less. The degree of polarization of the primary polarizing film is preferably 98.0% or more, more preferably 99.0% or more, and still more preferably 99.9% or more. On the other hand, the degree of polarization of the primary polarizing film is preferably 99.998% or less. The above-mentioned transmittance is representatively measured using an ultraviolet-visible spectrophotometer, and the Y value is obtained by correcting the visual sensitivity. The above-mentioned degree of polarization is typically measured using an ultraviolet-visible spectrophotometer, and the parallel transmittance Tp and the orthogonal transmittance Tc are obtained by correcting the visual sensitivity. Based on the parallel transmittance Tp and the orthogonal transmittance Tc was obtained from the following formula. Polarization degree (%)={(Tp－Tc)/(Tp＋Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film with a thickness of 12 μm or less is typically a laminate of a polarizing film (surface refractive index: 1.53) and a protective layer (protective film) (refractive index: 1.50) as a measurement object, Measured using a UV-Vis spectrophotometer. Depending on the surface refractive index of the polarizing film and/or the surface of the protective layer in contact with the air interface, the reflectance of each layer at the interface changes, and as a result, the measured value of transmittance may change. Therefore, for example, when a protective layer with a refractive index other than 1.50 is used, the measured value of the transmittance can be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance is represented by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer. C=R ₁ -R ₀ R ₀ =((1.50-1) ² /(1.50+1) ² )×(T ₁ /100) R ₁ =((n ₁ -1) ² /(n ₁ +1) ² ) ×(T ₁ /100) Here, R ₀ is the transmission axis reflectance when a protective layer with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer used, and T ₁ is the transmittance of the polarizing film. For example, when a base material having a surface refractive index of 1.53 (a cycloolefin-based film, a film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is about 0.2%. In this case, by adding 0.2% to the measured transmittance, the transmittance of the polarizing film with a surface refractive index of 1.53 can be converted into the transmittance when a protective layer with a refractive index of 1.50 is used. Furthermore, according to the calculation based on the above formula, the change amount of the correction value C when the transmittance T1 _of the polarizing film is changed by 2% is less than 0.03%, and the transmittance of the polarizing film has a limited influence on the correction value C value. . In addition, when the protective layer has absorption other than surface reflection, it can be appropriately corrected according to the amount of absorption.

The thickness of the primary polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 8 μm, still more preferably 1 μm to 7 μm, and still more preferably 2 μm to 5 μm. When the thickness is small, it has the advantage that the polarizing film is less likely to be wrinkled when it is in contact with an aqueous solvent.

The moisture content of the primary polarizing film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% by weight to 5% by weight. If the moisture content is in the above-mentioned range, the penetration rate can be changed without significantly impairing the appearance at the time of contact with an aqueous solvent.

A-2. The steps of making polarizers In the step of producing the polarizing plate, a polarizing plate having the following structure is produced: a protective layer and an arbitrary functional layer are laminated on one side of the primary polarizing film, and the other side is an exposed surface. As the functional layer, any appropriate functional layer can be selected depending on the purpose, and specific examples thereof include a retardation layer, an adhesive layer, and the like. Furthermore, the step of producing the polarizing plate is an arbitrary step. Therefore, depending on the purpose, the laminate having the composition of [thermoplastic resin substrate/primary polarizing film] produced by the method described in item A-1-1, or the single-layer PVA described in item A-1-2 will be used The primary polarizing film made of the resin film is directly supplied to the step of obtaining the secondary polarizing film.

2A to 2C are respectively schematic cross-sectional views illustrating an example of the polarizing plate produced in the step of producing the polarizing plate. The polarizing plate 100A shown in FIG. 2A includes a polarizing film (primary polarizing film) 10 and a protective layer 20 disposed on one side of the polarizing film (primary polarizing film) 10 . to expose. The polarizing plate 100A can be, for example, by laminating the protective layer to the laminate having the [thermoplastic resin substrate/primary polarizing film] obtained by the method described in the item A-1-1 through an adhesive layer or an adhesive layer. The primary polarizing film side surface of the body was then obtained by peeling off the thermoplastic resin substrate. Alternatively, the polarizing plate 100A can be obtained by attaching a protective layer to one surface of the primary polarizing film obtained by the method described in the item A-1-2 through an adhesive layer or an adhesive layer.

The polarizing plate 100B shown in FIG. 2B sequentially includes: a polarizing film (primary polarizing film) 10, a protective layer 20, a retardation layer 30, and an adhesive layer 40, and the polarizing film (primary polarizing film) 10 and the polarizing film 10 are provided with a protective layer The side opposite to the side of the layer 20 is set as an exposed surface. The polarizing plate 100B can be formed by, for example, adhering the retardation layer 30 to the side surface of the protective layer 20 of the polarizing plate 100A through an adhesive layer or an adhesive layer, and then disposing the adhesive layer 40 on the surface of the retardation layer 30 . get. Alternatively, the polarizing plate 100B can attach the retardation layer 30 to the side surface of the thermoplastic resin substrate of the laminate having the above-mentioned [thermoplastic resin substrate/primary polarizing film] through an adhesive layer or an adhesive layer, and then , obtained by disposing the adhesive layer 40 on the surface of the retardation layer 30 . In this case, the thermoplastic resin base material functions as the protective layer 20 . In addition, the retardation layer 30 of the illustrated example may have a single-layer structure, or may be a laminated structure in which two or more retardation layers are laminated.

The polarizing plate 100C shown in FIG. 2C includes in sequence: a polarizing film (primary polarizing film) 10, a protective layer 20, and an adhesive layer 40, and the polarizing film (primary polarizing film) 10 is disposed on the opposite side of the protective layer 20 The side is set as the exposed surface. The polarizing plate 100C can be obtained, for example, by disposing the adhesive layer 40 on the side surface of the protective layer 20 of the polarizing plate 100A. Alternatively, the polarizing plate 100C can be obtained by providing the adhesive layer 40 on the side surface of the thermoplastic resin substrate of the laminate having the above-mentioned [thermoplastic resin substrate/primary polarizing film]. In this case, the thermoplastic resin base material functions as the protective layer 20 .

Although not shown, it is preferable that a release film is temporarily adhered to the surface of the adhesive layer 40 before the polarizing plate is put into use.

The protective layer 20 is formed of any suitable film that can be used as a protective layer of a polarizing film. The retardation layer 30 may be, for example, a thermoplastic resin film or a liquid crystal alignment cured layer. In addition, as the adhesive for forming the adhesive layer 40, any appropriate adhesive can be used, and among them, an acrylic adhesive using an acrylic polymer as a base polymer is preferably used. Such protective layers, retardation layers, and adhesive layers are well known to those skilled in the art, and therefore detailed descriptions thereof are omitted.

A-3. Steps to obtain secondary polarizing film In the step of obtaining the secondary polarizing film, the transmittance of the primary polarizing film is changed by contacting the surface of the primary polarizing film with an aqueous solvent. Specifically, the primary polarizing film is contacted with an aqueous solvent to decolorize the primary polarizing film, thereby obtaining a secondary polarizing film having a desired transmittance.

As the aqueous solvent, any appropriate aqueous solvent can be used as long as the dichroic substance can be eluted from the primary polarizing film. The aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent. As the water-soluble organic solvent, lower monoalcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, and isopropanol, and polyhydric alcohols such as glycerol and ethylene glycol can be preferably exemplified.

The content ratio of the water-soluble organic solvent in the aqueous solvent is, for example, 20% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.

The method of contacting with the aqueous solvent is not particularly limited, and any appropriate method such as dipping, spraying, and coating can be used. For locally adjusting the penetration rate, spraying or coating is preferable, and for comprehensively adjusting the penetration rate, dipping is preferable.

The contact time with the aqueous solvent and the temperature of the aqueous solvent at the time of contact can be appropriately set according to the desired change in penetration rate. By increasing the contact time or increasing the temperature of the aqueous solvent, the amount of change in the penetration rate tends to increase. The contact time may be, for example, 10 minutes or less, preferably 1 second to 5 minutes, and more preferably 2 seconds to 3 minutes. The temperature of the aqueous solvent is preferably 20°C to 70°C, more preferably 30°C to 65°C, and still more preferably 40°C to 60°C.

If necessary, the polarizing film may be dried after being contacted with an aqueous solvent. The drying temperature may be, for example, 30°C to 100°C, preferably 30°C to 80°C. The moisture content of the polarizing film (secondary polarizing film) after drying is typically 15 wt % or less, preferably 12 wt % or less, more preferably 10 wt % or less, and still more preferably 1 to 5 wt %.

The secondary polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance (single transmittance: Ts) of the secondary polarizing film can be appropriately adjusted depending on the purpose. The transmittance of the secondary polarizing film is preferably 41.5% or more, more preferably 42% or more, and still more preferably 42.5% or more. On the other hand, the transmittance of the secondary polarizing film is, for example, 70% or less, preferably 50% or less, and more preferably 46% or less. In one embodiment, the secondary polarizing film may have a transmittance higher than that of the primary polarizing film by, for example, 0.1%-1.5%. In addition, the degree of polarization of the secondary polarizing film is, for example, 90% or more, preferably 92.0% or more, more preferably 94.0% or more, still more preferably 96.0% or more, still more preferably 99.0% or more, still more preferably 99.5 % or more, and preferably 99.998% or less. The above transmittance and polarization degree are values obtained in the same manner as the transmittance and polarization degree of the primary polarizing film.

The thickness of the secondary polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 8 μm, still more preferably 1 μm to 7 μm, and still more preferably 2 μm to 5 μm. The thickness of the secondary polarizing film may be substantially the same as that of the primary polarizing film.

A-4. Other steps The above-mentioned manufacturing method of the polarizing plate may further include any appropriate steps as needed. For example, after the step of obtaining the secondary polarizing film, the step of changing the transmittance by contacting the surface of the secondary polarizing film with an aqueous solvent may be further included. The step of changing the penetration rate can be repeated two or more times. Also, for example, a step of protecting the exposed surface by layering any appropriate layer (protective layer, retardation layer, adhesive layer, etc.) on the exposed area of the finally obtained polarizing film (eg, secondary polarizing film) may be included.

3A and 3B are schematic cross-sectional views of an example of a polarizing plate obtained after the step of protecting the exposed surface of the polarizing film, respectively. The polarizing plate 100D includes a first protective layer 20 a , a polarizing film (secondary polarizing film) 10 , a second protective layer 20 b , a retardation layer 30 , and an adhesive layer 40 in this order. For example, the polarizing plate 100D can be provided with the second protective layer 20b, the retardation layer 30 and the adhesive layer 40 in sequence on the exposed surface of the polarizing film 10 of the polarizing plate 100A (FIG. 2A) obtained through the step of obtaining the secondary polarizing film. and obtained. Alternatively, it can be obtained by bonding the first protective layer 20a to the exposed surface of the polarizing film 10 of the polarizing plate 100B (FIG. 2B) obtained through the step of obtaining the secondary polarizing film.

The polarizing plate 100E includes a first protective layer 20 a , a polarizing film (secondary polarizing film) 10 , a second protective layer 20 b , and an adhesive layer 40 in this order. In the polarizing plate 100E, the second protective layer 20b may have a desired retardation and function as a retardation layer (eg, a λ/4 plate) as described below. The polarizing plate 100E can be obtained, for example, by sequentially disposing the second protective layer 20b and the adhesive layer 40 on the exposed surface of the polarizing film 10 of the polarizing plate 100A ( FIG. 2A ) obtained by changing the transmittance. Alternatively, it can be obtained by attaching the first protective layer 20a to the exposed surface of the polarizing film 10 of the polarizing plate 100C (FIG. 2C) obtained through the step of changing the transmittance.

In one embodiment, the adhesive layer 40 can be used to attach the polarizers 100D and 100E to an image display unit (eg, a liquid crystal unit, an organic EL unit). In this embodiment, when a polarizing plate is applied to an image display device, the first protective layer 20a is a protective layer (outer protective layer) disposed on the opposite side of the image display unit, and the second protective layer 20b is disposed on the opposite side of the image display unit. The protective layer on the image display unit side (inner protective layer).

The thickness of the outer protective layer is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and still more preferably 10 μm to 60 μm. Furthermore, when the surface treatment is carried out, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

The thickness of the inner protective layer is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm.

In one embodiment, the inner protective layer is optically isotropic. In this specification, "being optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm, and the thickness direction retardation Rth(550) is -10 nm to +10 nm. Here, "Re(550)" is the in-plane retardation measured by light with a wavelength of 550 nm at 23° C., and can be obtained from the formula: Re=(nx−ny)×d. In addition, "Rth(550)" is the retardation in the thickness direction measured by light with a wavelength of 550 nm at 23°C, and can be obtained according to the formula: Rth(λ)=(nx−nz)×d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index becomes the largest (that is, the direction of the slow axis), and "ny" is the direction orthogonal to the slow axis in the plane (that is, the direction of the advancing axis). ), "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

In another embodiment, the inner protective layer is a retardation layer with any suitable retardation value. In this embodiment, the in-plane retardation Re(550) of the inner protective layer may be, for example, 110 nm˜150 nm. The inner protective layer can function as a circular polarizer by arranging such an inner protective layer in such a manner that the angle formed by the retardation axis of the inner protective layer and the retardation axis of the absorption axis of the polarizing film is clockwise or counterclockwise. The above is, for example, 35° to 55°, preferably 38° to 52°, more preferably 40° to 50°, further preferably 42° to 48°, and particularly preferably 44° to 46°.

The retardation layer 30 may be a retardation layer having desired in-plane retardation and/or retardation in the thickness direction depending on the purpose. For example, when the inner protective layer is optically isotropic, the in-plane retardation Re(550) of the retardation layer can be 110 nm˜150 nm. The retardation layer can function as a circular polarizer by arranging such a retardation layer in such a manner that the angle formed by the retardation axis of the retardation layer and the retardation axis of the absorption axis of the polarizing film is clockwise or counterclockwise. The above is, for example, 35° to 55°, preferably 38° to 52°, more preferably 40° to 50°, further preferably 42° to 48°, and particularly preferably 44° to 46°.

B. Manufacturing Method of Image Display Device The manufacturing method of the image display device according to the embodiment of the present invention sequentially includes: step (I), sequentially including polarized light composed of a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15 wt % or less The polarizing plate of the film, the protective layer, and the adhesive layer is laminated on the image display unit through the adhesive, and the surface of the polarizing film on the opposite side to the side where the protective layer is arranged is used as the exposed surface; and step (II) , so that the exposed surface of the polarizing film is brought into contact with an aqueous solvent to change the transmittance. According to the manufacturing method of such an image display device, the transmittance of the polarizing film can be adjusted after being attached to the image display unit, so that regardless of the individual differences in the quality of the image display unit or the backlight unit, it is possible to obtain An image display device with the required brightness.

B-1. Step (I) The polarizing plate laminated on the image display unit sequentially includes a polarizing film composed of a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer, as long as the The surface of the polarizing film on the side where the protective layer is not arranged is exposed, and can have any structure. For example, the polarizing film can also be exposed by attaching the polarizing plate to the image display unit with the exposed surface of the polarizing film protected by the surface protective film, and peeling off the surface protective film before contacting with the aqueous solvent.

In one embodiment, the polarizing plate laminated on the image display unit may further include a retardation layer. As the polarizing plate laminated on the image display unit, the polarizing plate having the structure illustrated in FIGS. 2B and 2C can be exemplified. In addition, for the polarizing film, protective layer, retardation layer, and adhesive layer included in the polarizing plate, the descriptions of the primary polarizing film, protective layer, retardation layer, and adhesive layer described in item A can be applied, respectively.

As the image display device manufactured by the above-mentioned manufacturing method, a liquid crystal display device or an organic EL display device can be preferably exemplified. Therefore, as the above-mentioned image display unit, a liquid crystal cell or an organic EL cell can be preferably used. A plurality of image display devices can be combined to display a single image as a whole, and can be used as a digital signage.

B-2. Step (II) In the step of changing the transmittance, the exposed surface of the polarizing film is brought into contact with an aqueous solvent to change the transmittance. Specifically, by contacting with an aqueous solvent to decolorize the dichroic material, the transmittance of the polarizing film can be changed and adjusted to a desired value. Regarding the procedure for changing the penetration rate, the same explanation as in item A-3 can be applied. From the viewpoint of preventing the image display unit from coming into contact with the aqueous solvent, coating or spraying can be preferably used as a contact method with the aqueous solvent. The description of the secondary polarizing film described in the item A-3 can be applied to the polarizing film after changing the transmittance.

The above-mentioned manufacturing method of the image display device may further include the step of protecting the exposed surface of the polarizing film after the step of changing the transmittance as required. The protection of the exposed surface of a polarizing film can be performed by laminating|stacking a protective layer, a support base material, etc. on the exposed surface through adhesive layers, such as an adhesive layer and an adhesive layer.

C. Adjustment method of transmittance of polarizing film According to another aspect of the present invention, there is provided a method for adjusting the transmittance of a polarizing film, which includes making the surface of the polarizing film composed of a PVA-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less and Aqueous solvent contacting step. According to the adjustment method of the transmittance of the polarizing film, by contacting the polarizing film with an aqueous solvent to decolorize the polarizing film, the transmittance of the polarizing film can be adjusted to a desired value (the representative value increases).

As the polarizing film to be brought into contact with the aqueous solvent, the primary polarizing film described in the item A-1 is preferably used. In addition, regarding the contact between the polarizing film and the aqueous solvent, the same description as in the item A-3 can be applied. [Example]

Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows. In addition, unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight. (1) Thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Monomer transmittance and degree of polarization For the laminates (polarizing plates) of polarizing films and protective layers obtained in the examples and comparative examples, an ultraviolet-visible spectrophotometer (“LPF-200” manufactured by Otsuka Electronics Co., Ltd.) was used. ) The monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured from the polarizing film side are set as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values obtained by measuring according to the 2-degree field of view (C light source) of JIS Z8701 and corrected for visual sensitivity. Furthermore, the refractive index of the protective layer was 1.53, and the refractive index of the surface of the polarizing film on the opposite side to the protective layer was 1.53. From the obtained Tp and Tc, the polarization degree P was calculated|required based on the following formula. Polarization degree P(%)={(Tp－Tc)/(Tp＋Tc)} ^1/2 × 100 In addition, the spectrophotometer can also be measured with "V-7100" manufactured by Nippon Shoko Co., Ltd. It has been confirmed Even in the case of using any kind of spectrophotometer, the same measurement results can be obtained. (3) Moisture content The primary polarizing film immediately after the drying treatment (the stretched substrate is peeled off when the laminate is stretched) is cut into a size of 100 mm×100 mm or more, and the weight before treatment is measured with an electronic balance. After that, it was put into a heating oven maintained at 120° C. and maintained for 2 hours, the weight after taking out (post-treatment weight) was measured, and the moisture content was determined according to the following formula. Moisture content [%] = (weight before treatment - weight after treatment) / weight before treatment × 100

[Example 1-1] A long roll of PVA-based resin film (manufactured by Kuraray, product name "PE3000") with a thickness of 30 μm was immersed in a water bath at 30° C. and stretched 2.2 times in the conveying direction, and then immersed in an iodine concentration The dyeing was carried out in a 30°C aqueous solution with a potassium concentration of 0.04 wt % and a potassium concentration of 0.3 wt %, and it was stretched to 3 times the standard of a completely unstretched film (original length). Next, while immersing the stretched film in a 30° C. aqueous solution with a boric acid concentration of 3 wt % and a potassium iodide concentration of 3 wt %, the stretched film was further stretched to 3.3 times the original length, and then immersed in a boric acid concentration of 4 wt %, In an aqueous solution at 60°C with a potassium iodide concentration of 5% by weight, one side was extended to 6 times the original length standard, and finally dried in an oven kept at 60°C for 5 minutes, thereby producing a polarizing film with a thickness of 12 μm (primary polarizing film). ). The moisture content of the obtained primary polarizing film was 10% by weight. The monomer transmittance of the polarizing film is 42.5%. Next, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight) was coated on one side of the polarizing film, and a cycloolefin-based film was attached. (Zeonor Co., Ltd., Japan, thickness: 25 μm), a polarizing plate (before treatment) having a composition of [primary polarizing film/protective layer] was obtained.

The above-mentioned polarizing plate (before treatment) was cut into a size of 100 mm×100 mm, and the side surface of the primary polarizing film was attached to the glass plate through an acrylic adhesive layer (thickness 15 μm) so that the side surface of the primary polarizing film became an exposed surface, and in this state Immerse in water at 55°C for 6 minutes. Then, it dried for 5 minutes at 50 degreeC, and obtained the polarizing plate (after processing) which has a [secondary polarizing film/protective layer] structure.

[Example 1-2] Except that the immersion in water at 55°C for 6 minutes was replaced by immersion in water at 55°C for 9 minutes, the same procedure as in Example 1-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) back).

[Example 1-3] Except that the immersion in water at 55°C for 6 minutes was replaced by immersion in water at 60°C for 4 minutes, it was carried out in the same manner as in Example 1-1 to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) back).

[Example 1-4] Except that the immersion in water at 55°C for 6 minutes was replaced by immersion in water at 65°C for 3 minutes, the same procedure as in Example 1-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) back).

[Example 2-1] A strip of amorphous poly(ethylene terephthalate) film (thickness: 100 μm) with a Tg of about 75°C was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to corona treatment . PVA-based resin was obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetylacetate modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") at a ratio of 9:1 , 13 parts by weight of potassium iodide was added to 100 parts by weight of the PVA-based resin, and the resultant was dissolved in water to prepare an aqueous PVA solution (coating liquid). The above-mentioned PVA aqueous solution was apply|coated to the corona-treated surface of a resin base material, and it dried at 60 degreeC, and formed the PVA-type resin layer of thickness 13 micrometers, and produced the laminated body. In an oven at 130° C., the obtained laminate was uniaxially stretched to 2.4 times in the longitudinal direction (longitudinal direction) (a mid-air stretching treatment). Next, the layered body was immersed for 30 seconds in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C (insolubilization treatment). Then, in a dyeing bath with a liquid temperature of 30° C. (with respect to 100 parts by weight of water, an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7), the monomer transmittance of the polarizing plate finally obtained ( Ts) was 42.3%, and the density|concentration was adjusted, and it was immersed for 60 seconds (dyeing process) on one side. 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 laminate was immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70° C., and the total stretching ratio in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds became 5.5 times of uniaxial extension (in-water extension treatment). Then, the layered body was immersed in a cleaning bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment). After that, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75°C while drying in an oven maintained at about 90°C (drying shrinkage treatment). The shrinkage rate in the width direction of the layered body subjected to drying shrinkage treatment was 2%. In this way, a polarizing film (primary polarizing film) with a moisture content of 4.5% by weight and a thickness of 5 μm was formed on the resin substrate, and a cycloolefin-based film (manufactured by Zeon Co., Ltd., Japan) was bonded with a UV curable adhesive (thickness 1.0 μm). , Zeonor, thickness: 25 μm) was attached to the surface of the primary polarizing film, and then the resin substrate was peeled off to obtain a polarizing plate (before treatment) with the composition of [primary polarizing film/protective layer].

The above-mentioned polarizing plate (before treatment) was cut into a size of 100 mm×100 mm, and the side surface of the primary polarizing film was attached to the glass plate through an acrylic adhesive layer (thickness 15 μm) so that the side surface of the primary polarizing film became an exposed surface, and in this state Immerse in water at 50°C for 9 minutes. Then, it dried for 5 minutes at 50 degreeC, and obtained the polarizing plate (after processing) which has a [secondary polarizing film/protective layer] structure.

[Example 2-2] Except that the immersion in water at 50°C for 9 minutes was replaced by immersion in water at 55°C for 3 minutes, the same procedure as in Example 2-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) back).

[Example 2-3] Except that the immersion in water at 50°C for 9 minutes was replaced by immersion in water at 60°C for 1 minute, the same procedure as in Example 2-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) structure. back).

[Example 2-4] Except that the immersion in water at 50°C for 9 minutes was replaced by immersion in water at 60°C for 2 minutes, the same procedure as in Example 2-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]). back).

[Example 2-5] Except that the immersion in water at 50°C for 9 minutes was replaced by immersion in water at 60°C for 3 minutes, the same procedure as in Example 2-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) structure. back).

[Example 3-1] The iodine concentration of the dyeing bath was changed, and the transmittance of the obtained polarizing film was adjusted to be 44.3%, except that it was carried out in the same manner as in Example 2-1 to obtain a polarized light having a composition of [primary polarizing film/protective layer] plate (before treatment). The moisture content of the obtained primary polarizing film was 4.5% by weight.

The above-mentioned polarizing plate (before treatment) was cut into a size of 100 mm×100 mm, and the side surface of the primary polarizing film was attached to the glass plate through an acrylic adhesive layer (thickness 15 μm) so that the side surface of the primary polarizing film became an exposed surface, and in this state Immerse in water at 50°C for 6 minutes. Then, it dried for 5 minutes at 50 degreeC, and obtained the polarizing plate (after processing) which has a [secondary polarizing film/protective layer] structure.

[Example 3-2] Except that the immersion in water at 50°C for 6 minutes was replaced by immersion in water at 55°C for 3 minutes, the same procedure as in Example 3-1 was performed to obtain a polarizing plate (treated with a [secondary polarizing film/protective layer]) back).

The transmittance and polarization degree of the polarizing plate (before treatment) and the polarizing plate (after treatment) obtained in the above examples were measured. The results are shown in Table 1. [Table 1] Polarizing film thickness Ts(%) before treatment P before treatment (%) contact conditions Ts(%) after treatment P(%) after treatment Variation in Ts (ΔTs) Example 1-1 12 μm 42.5 99.996 55℃, 6 min 42.7 99.98 0.2 Example 1-2 55℃, 9 min 42.8 99.56 0.3 Examples 1-3 60℃, 4 min 43.1 99.85 0.6 Examples 1-4 65℃, 3 min 43.0 99.11 0.5 Example 2-1 5 μm 42.3 99.990 50℃, 9 min 45.5 94.62 3.2 Example 2-2 55℃, 3 min 43.2 99.86 0.9 Example 2-3 60℃,1min 42.5 99.99 0.2 Example 2-4 60℃, 2 min 43.4 99.87 1.1 Example 2-5 60℃, 3 min 43.2 94.35 0.9 Example 3-1 5 μm 44.3 99.112 50℃, 6 min 45.6 95.29 0.8 Example 3-2 55℃, 3 min 44.9 97.52 0.6

As is clear from Table 1, according to the manufacturing method of the Example, the transmittance of the polarizing film can be changed after the polarizing plate is produced by laminating the protective layer. [Industrial Availability]

The manufacturing method of the polarizing plate of this invention can be suitably used for manufacturing an image display apparatus.

10: Polarizing film 20: Protective layer 20a: 1st protective layer 20b: 2nd layer of protection 30: retardation layer 40: Adhesive layer 100: polarizer 100A: polarizer 100B: polarizer 100C: polarizer 100D: polarizer 100E: polarizer 200: Laminate R1, R2, R3, R4, R5, R6: conveying rollers G1, G2, G3, G4: Guide rollers

FIG. 1 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll. 2A is a schematic cross-sectional view illustrating an example of a polarizing plate produced in a step of producing a polarizing plate. 2B is a schematic cross-sectional view illustrating an example of the polarizing plate produced in the step of producing the polarizing plate. 2C is a schematic cross-sectional view illustrating an example of the polarizing plate produced in the step of producing the polarizing plate. 3A is a schematic cross-sectional view of an example of a polarizing plate obtained by a step of protecting the exposed surface of the secondary polarizing film. 3B is a schematic cross-sectional view of an example of a polarizing plate obtained by a step of protecting the exposed surface of the secondary polarizing film.

10: Polarizing film

20: Protective layer

100A: polarizer

Claims (8)

A method for manufacturing a polarizing plate, which sequentially comprises: after subjecting a polyvinyl alcohol-based resin film to dyeing treatment and extension treatment in a boric acid aqueous solution, drying it until the moisture content becomes less than 15% by weight to obtain a primary polarizing film steps; and The step of obtaining a secondary polarizing film by changing the transmittance by contacting the surface of the primary polarizing film with an aqueous solvent. The method for producing a polarizing plate of claim 1, wherein the exposed surface of the primary polarizing film in a state in which one surface is exposed and the other surface is protected is brought into contact with the aqueous solvent. The method for producing a polarizing plate according to claim 1 or 2, wherein the above-mentioned step of obtaining a primary polarizing film comprises: placing a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin on the elongated thermoplastic resin substrate. In the state of the layered body, it is subjected to air-assisted stretching treatment, dyeing treatment, stretching treatment in boric acid aqueous solution and drying shrinkage treatment in sequence; The drying shrinkage treatment includes heating the laminated body while conveying it in the longitudinal direction to shrink it by 2% or more in the width direction, and drying it until the polyvinyl alcohol-based resin film contains water. The ratio is 15% by weight or less. The method for producing a polarizing plate according to claim 3, wherein the halide is iodide or sodium chloride. The manufacturing method of a polarizing plate according to any one of claims 1 to 4, wherein the thickness of the primary polarizing film is 12 μm or less. A method of manufacturing an image display device, which includes sequentially including a polarizing film, a protective layer, and an adhesive that are composed of a polyvinyl alcohol-based resin film containing a dichroic substance and have a moisture content of 15 wt% or less The polarizing plate of the layer is laminated on the image display unit through the adhesive, and the surface of the polarizing film on the side opposite to the side where the protective layer is arranged is used as the exposed surface; and The step of changing the transmittance by contacting the exposed surface of the polarizing film with an aqueous solvent. The method for manufacturing an image display device according to claim 6, wherein the image display device is a liquid crystal display device or an organic EL display device. A method for adjusting the transmittance of a polarizing film, comprising the steps of: contacting the surface of the polarizing film, which is composed of a polyvinyl alcohol-based resin film containing a dichroic substance and has a moisture content of 15% by weight or less, with an aqueous solvent.

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