TW202125002A - Polarizing film, polarizing plate, and image display device - Google Patents

Abstract

The present invention provides a polarizing film which has a low profile, which maintains optical characteristics, and for which dimensional changes are suppressed. This polarizing film is constituted by a polyvinyl alcohol resin film containing iodine. The unit transmissivity of the polarizing film is at least 43.0%. An alignment characteristic index (P-98)/F of the polarizing film is at least 7, as calculated from a degree of polarization P and an alignment index F.

Description

Polarizing film, polarizing plate and image display device

The invention relates to a polarizing film, a polarizing plate and an image display device.

In the liquid crystal display device, which is a representative image display device, polarizing films are arranged on both sides of the liquid crystal cell according to the image forming method. As a manufacturing method of 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). By this method, a thinner polarizing film can be obtained, so it can contribute to the thinning of display panels such as liquid crystal panels and organic EL panels (and, as a result, the thinning of image display devices), it is attracting attention. However, the display panel using the thin polarizing film may be warped due to the change in the size of the polarizing film (representative of shrinkage).

Regarding the above-mentioned warpage problem, although the shrinkage can be alleviated by reducing the stretching magnification during the production of the polarizing film, once the stretching magnification is lowered, the optical properties will decrease. Therefore, it is difficult to obtain a polarizing film that has both dimensional stability and optical properties. Prior art literature Patent literature

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

The problem to be solved by the invention The present invention was made in order to solve the above-mentioned conventional problems, and its main object is to provide a thin polarizing film that can maintain optical characteristics and suppress dimensional changes.

Means to solve the problem According to one aspect of the present invention, a polarizing film is provided, which is composed of a polyvinyl alcohol resin film containing iodine, with a monomer transmittance of 43.0% or more, and an orientation characteristic index calculated from the degree of polarization: P and the orientation function: F : (P-98)/F is 7 or more. In one embodiment, the single transmittance of the polarizing film is 44.5% or less. In one embodiment, the thickness of the above-mentioned polarizing film is 8 µm or less. In one embodiment, the above-mentioned polarizing film contains alcohol. In one embodiment, the above-mentioned alcohol includes at least one selected from ethanol and glycerol. According to another aspect of the present invention, a polarizing plate including the above-mentioned polarizing film is provided. According to another aspect of the present invention, an image display device equipped with the above-mentioned polarizing plate is provided.

Invention effect According to the present invention, it is possible to obtain a thin polarizing film that maintains optical characteristics and suppresses dimensional changes.

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

A. Polarizing film The polarizing film of the embodiment of the present invention is composed of iodine-containing polyvinyl alcohol (PVA) resin film, with a monomer transmittance of 43.0% or more, and the orientation characteristic index calculated from the degree of polarization: P and the orientation function: F: (P-98)/F is 7 or more. For a polarizing film composed of a PVA-based resin film, generally, the higher the orientation of the PVA-based resin, the higher the degree of polarization, and this orientation mainly follows the stretching ratio of the PVA-based resin film. Therefore, in the conventional polarizing film, if the orientation is relaxed in order to suppress the dimensional change, the degree of polarization will be reduced. In this regard, the polarizing film of the embodiment of the present invention has an orientation characteristic index: (P-98)/F of 7 or more, so that dimensional stability and optical properties can be balanced.

The orientation characteristic index of the polarizing film: (P-98)/F (here, P is the degree of polarization (%) of the polarizing film, F is the orientation function of the polarizing film) is 7 or more, preferably 8 or more, more preferably 9 Above, more preferably 10 or more. The upper limit of the orientation characteristic index may be 20, for example. The orientation characteristic index is a value that becomes smaller when the degree of polarization is low and/or when the degree of orientation is high. Therefore, an orientation characteristic index of 7 or more means that both high polarization degree and orientation relaxation are achieved.

The polarizing film should exhibit absorption dichroism at any wavelength from 380nm to 780nm. The monomer transmittance of the polarizing film is 43.0% or more, preferably 43.5% or more, more preferably 43.7% or more. On the other hand, the transmittance of the monomer should be below 44.5%, more preferably below 44.5%. The degree of polarization of the polarizing film is preferably over 99.50%, more preferably over 99.60%, and more preferably over 99.70%. The above monomer transmittance represents the Y value obtained by measuring and calibrating the visual sensitivity using an ultraviolet-visible spectrophotometer. In addition, the single-body transmittance is a value obtained when the refractive index of one surface of the polarizing plate is converted to 1.50, and the refractive index of the other surface is converted to 1.53. The above-mentioned degree of polarization is representatively calculated based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring with an ultraviolet-visible light spectrophotometer and performing visual sensitivity correction, using the following equations. Polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

The orientation function (F) of the polarizing film is, for example, 0.25 or less, preferably 0.23 or less, and more preferably 0.20 or less. In addition, the orientation function (F) is, for example, 0.1 or more, and may be, for example, 0.15 or more. If the orientation function is too small, it may not be possible to obtain practically acceptable monomer transmittance and/or polarization.

The orientation function (F) of the polarizing film is obtained by, for example, a Fourier Transform Infrared Spectrophotometer (FT-IR) and polarized light as the measurement light, and obtained by attenuated total reflection spectroscopy (ATR: attenuated total reflection) measurement. Specifically, the measurement is performed in a state where the extension direction of the polarizing film is parallel and perpendicular to the polarization direction of the measurement light, and ^{the intensity of the obtained absorbance spectrum at 2941 cm -1} is used to calculate according to the following formula. Here, the intensity I is a value ^{of 2941 cm -1} /3330 cm ^{-1 taking 3330 cm -1} as the reference peak. In addition, when F=1, it is fully oriented, and when F=0, it is random. In addition, we believe that ^{the peak of 2941 cm -1} is caused by the absorption of the vibration of the PVA main chain (-CH _{2 -) in the polarizing film.} F=(3＜cos ² θ＞-1)/2 =(1-D)/[c(2D+1)] =-2×(1-D)/(2D+1) However, c=( 3cos ² β-1)/ ^{2, when the vibration is 2941cm -1} , β=90°. θ: The angle of the molecular chain relative to the extension direction β: The angle of the transition dipole moment relative to the molecular chain axis D=(I _⊥ )/(I _// ) (At this time, the more the PVA molecule is oriented, the greater D is) I _⊥ ：Measure the absorption intensity when the polarization direction of light is perpendicular to the extension direction of the polarizing film _{I // ：Measure the absorption intensity when the polarization direction of light is parallel to the extension direction of the polarizing film}

The polarizing film preferably contains alcohol. The content ratio of the alcohol in the polarizing film can be, for example, 1.0×10 ^-3 % by weight to 1.0% by weight. Since the polarizing film contains alcohol, the orientation characteristic index can be easily set within the above-mentioned desired range. As a result, a thin polarizing film that maintains optical properties and suppresses dimensional changes can be suitably obtained. The present invention is not limited by the mechanism by which the effect can be obtained, but can be presumed as follows. That is, the PVA-based resin film constituting the polarizing film has been partially crystallized, and the orientation of the molecular chain in the crystal part that has little influence on the optical properties is strengthened by the interaction of the hydroxyl group (representatively, the hydrogen bond), but the interaction The polarizing film will be weakened by introducing alcohol into the polarizing film, thereby the orientation of the periphery of the crystal portion will be relaxed, or the flexibility will be improved. As a result, the PVA-based resin film will be low in elasticity while maintaining the optical properties, thereby suppressing polarized light. The dimensional change (shrinkage) of the film.

As the above-mentioned alcohol, an alcohol having a boiling point of less than 100°C (hereinafter sometimes referred to as a low boiling point alcohol) may be used, an alcohol having a boiling point of 100°C or higher (hereinafter sometimes referred to as a high boiling point alcohol) may be used, or a combination of these may be used. The boiling point of the high boiling point alcohol is preferably 150°C or higher, preferably 180°C or higher, and more preferably 250°C or higher. The upper limit of the boiling point may be 310°C, for example.

Representative examples of low boiling point alcohols include lower monohydric alcohols with 1 to 4 carbon atoms. Specific examples include methanol, ethanol, n-propanol, isopropanol, and tertiary butanol. The low boiling point alcohol may be used alone or in combination of two or more kinds. It is preferably methanol, ethanol, n-propanol, and isopropanol.

The content ratio of the low boiling point alcohol in the polarizing film is, for example, 10 ppm to 300 ppm, preferably 20 ppm to 200 ppm, more preferably 40 ppm to 150 ppm, and more preferably 50 ppm to 120 ppm. If the content ratio is too small, the directional relaxation effect may not be obtained. If the content ratio is too high, the amount of volatility to the working environment will increase due to the increase in the amount of introduction during manufacturing, and the safety risk may increase.

Representative examples of high boiling point alcohols include higher alcohols, alcohols having a ring structure (for example, aromatic alcohols, alicyclic alcohols), and polyhydric alcohols. Specific examples include glycerol, ethylene glycol, butanol, phenol, and pentanol. The high boiling point alcohol may be used alone or in combination of two or more kinds. It is preferably glycerol and ethylene glycol.

The content ratio of the high boiling point alcohol in the polarizing film is, for example, 0.1% by weight to 1.0% by weight, preferably 0.1% by weight to 0.9% by weight, more preferably 0.1% by weight to 0.8% by weight, and more preferably 0.2% by weight to 0.7% by weight %, particularly preferably 0.2% by weight to 0.6% by weight. If the content ratio is too small, the directional relaxation effect may not be obtained. If the content ratio is too high, the degree of polarization may decrease and increase in a high-temperature and high-humidity environment.

The thickness of the polarizing film is, for example, 8 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and more preferably 3 μm or less. The lower limit of the thickness of the polarizing film may be 1 μm in one embodiment, and may be 2 μm in another embodiment.

The shrinkage of the polarizing film in the absorption axis direction after heating at a temperature of 85°C for 120 hours should be less than 1.10%, more preferably less than 1.05%, more preferably less than 1.00%, and particularly preferably less than 0.95%. In addition, the shrinkage ratio refers to the shrinkage ratio of a sample having a size of 10 cm in the absorption axis direction×10 cm in the transmission axis direction.

B. Polarizing plate Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 has a polarizing film 10, a first protective layer 20 arranged on one side of the polarizing film 10, and a second protective layer 30 arranged on the other side of the polarizing film 10. The polarizing film 10 is based on the polarizing film of the present invention described in item A above. It is also possible to omit one of the first protective layer 20 and the second protective layer 30. One of the first protective layer and the second protective layer may also be a resin substrate used to manufacture the above-mentioned polarizing film.

The first and second protective films are formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of the material that becomes the main component of the film include cellulose resins such as triacetate cellulose (TAC), or polyesters, polyvinyl alcohols, polycarbonates, polyamides, and polyamides. Transparent resins such as imine-based, polyether-based, poly-based, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate-based transparent resins, etc. In addition, thermosetting resins such as (meth)acrylic, urethane, (meth)acrylate urethane, epoxy, and silicone resins, or ultraviolet curable resins, etc. may also be mentioned. Other examples include glassy polymers such as silicone polymers. In addition, the polymer film described in Japanese Patent Laid-Open No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted iminium group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example, Examples include resin compositions having alternating copolymers composed of isobutylene and N-methylmaleimide and acrylonitrile-styrene copolymers. The polymer film may be, for example, an extruded product of the above-mentioned resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) arranged on the side opposite to the display panel is typically 300μm or less, preferably 100μm or less, more preferably 5μm~80μm, more preferably It is 10µm~60µm. In addition, when the surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5μm~200μm, more preferably 10μm~100μm, and more preferably 10μm~60μm. In one embodiment, the inner protective layer is a retardation layer having any appropriate retardation value. At this time, the in-plane retardation Re (550) of the retardation layer is 110 nm to 150 nm, for example. "Re(550)" is the in-plane phase difference measured with light with a wavelength of 550nm at 23°C and can be obtained by the formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is the largest (that is, the slow axis direction), and "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (that is, the fast axis direction) , "Nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

C. Manufacturing method of polarizing film The manufacturing method of the polarizing film according to one embodiment of the present invention includes the following steps: apply a PVA-based resin solution to one side of a long-shaped thermoplastic resin substrate and dry it to form a PVA-based resin layer to form a laminate; The laminate is stretched and dyed, and the PVA-based resin layer is made into a polarizing film; and alcohol is introduced into the polarizing film. By introducing alcohol, a polarizing film that maintains excellent optical properties and suppresses dimensional changes can be realized. Preferably, the PVA-based resin solution further contains a halide. Preferably, the above-mentioned manufacturing method includes the following steps: sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the layered body, and the drying and shrinking treatment system heats the layered body while conveying the layered body in the longitudinal direction. , Thereby making it shrink by more than 2% in the width direction. At this time, the introduction of alcohol should preferably be carried out between the water extension treatment and the drying shrinkage treatment. The PVA-based resin layer is dyed to form a complex with iodine, and the orientation and crystallinity are improved by the stretching treatment, and then alcohol is introduced, thereby selectively relaxing the periphery of the crystalline part of the PVA-based resin layer Orientation caused by the interaction of hydroxyl groups, or increased flexibility. The halide content in the PVA-based resin solution (the PVA-based resin layer as a result) is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage should be treated with a heating roller, and the temperature of the heating roller should be 60°C~120°C. The shrinkage rate in the width direction of the laminate is preferably 2% or more after drying and shrinking. According to the manufacturing method, the polarizing film described in the above item A can be suitably obtained. In particular, a polarizing film with excellent optical properties (representatively, monomer transmittance and polarization) can be obtained by the following method: After making a laminate containing a PVA-based resin layer containing a halide, the laminate is extended Perform multi-stage stretching including aerial auxiliary stretching and underwater stretching, and then heat the stretched laminate with heating rollers.

C-1. Making a layered body Any appropriate method can be adopted as a method of producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating solution containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried, thereby forming a PVA-based resin layer on the thermoplastic resin substrate. As mentioned above, the halide content in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted for the coating method of the coating liquid. 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 knife coating method (cutting wheel coating method, etc.) etc. are mentioned. The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or higher.

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

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

C-1-1. Thermoplastic resin substrate As the thermoplastic resin substrate, any appropriate thermoplastic resin film can be used. The details of the thermoplastic resin film substrate are described in, for example, Japanese Patent Laid-Open No. 2012-73580. In this manual, the entire record of the bulletin is used as a reference.

C-1-2. Coating liquid The coating liquid may contain a halide and a PVA-based resin as described above. The above-mentioned coating liquid represents a solution obtained by dissolving the above-mentioned halide and the above-mentioned PVA-based resin in a solvent. As the solvent, for example, water, dimethyl sulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane and other polyhydric alcohols, extension Amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more kinds. Among these, water is better. The concentration of the PVA-based resin of the solution is preferably 3 parts by weight to 20 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film that adheres to the thermoplastic resin substrate can be formed. The halide content in the coating solution is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives can also be blended in the coating liquid. Examples of additives include plasticizers and surfactants. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerol. Examples of the surfactant include nonionic surfactants. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

Any appropriate resin can be adopted for the above-mentioned PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol%~100 mol%, preferably 95.0 mol%~99.95 mol%, and more preferably 99.0 mol%~99.93 mol%. The degree of saponification can be obtained according to JIS K 6726-1994. By using the PVA-based resin with the aforementioned degree of saponification, a polarizing film with excellent durability can be obtained. When the saponification degree is too high, there is a risk of 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 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

Any appropriate halide can be used as the above-mentioned halide. Examples include iodide and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of PVA-based resin, and preferably 10 parts by weight to 15 parts by weight relative to 100 parts by weight of PVA-based resin. If the amount of halide is greater than 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may overflow and the resulting polarizing film may become cloudy.

Generally speaking, the extension of the PVA-based resin layer will increase the orientation of the polyvinyl alcohol molecules in the PVA resin layer. However, if the extended PVA-based resin layer is immersed in a water-containing liquid, there will be polyethylene The orientation of alcohol molecules is disordered and the orientation is reduced. Especially when the laminate of a thermoplastic resin base material and a PVA-based resin layer is stretched in boric acid water, in order to stabilize the elongation of the thermoplastic resin base material, the laminate is stretched in boric acid water at a relatively high temperature. The tendency of the orientation degree to decrease is obvious. For example, the extension of the PVA film monomer in boric acid water is generally performed at 60°C. In contrast, the extension of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is performed at 70°C. It is carried out at a higher temperature before and after the temperature. At this time, the orientation of the PVA in the initial stage of the stretching will decrease in the stage before it rises due to the stretching in the water. In this regard, by making a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate, and performing high-temperature extension in the air (assisted extension) of the laminate before extension in boric acid water, the post-assisted extension can be promoted. The crystallization of the PVA resin in the PVA 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, it is possible to suppress the orientation disorder and the decrease in orientation of the polyvinyl alcohol molecules more. Thereby, it is possible to improve the optical properties of the polarizing film obtained through the treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

C-2. Air auxiliary extension processing Especially in order to obtain high optical properties, a two-stage extension method combining dry extension (auxiliary extension) and extension in boric acid water is selected. Like the two-stage extension method, by introducing the auxiliary extension, the extension can be performed while suppressing the crystallization of the thermoplastic resin substrate, which solves the problem of the extension of the thermoplastic resin substrate due to the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid extension. , And the laminate can be stretched at a higher magnification. In addition, when applying PVA-based resin to a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature must be higher than that when PVA-based resin is applied to a general metal roller. If it is lower, the crystallization of the PVA-based resin is relatively low and the problem that sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary extension, even when the PVA-based resin is coated on the thermoplastic resin substrate, the crystallinity of the PVA-based resin can be improved, and high optical properties can be achieved. In addition, at the same time, the orientation of the PVA-based resin is improved in advance to prevent problems such as the decrease in orientation or dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step or the stretching step, and high optical properties can be achieved.

The extension method of aerial auxiliary extension can be fixed end extension (for example, using a tenter stretching machine for extension), or free end extension (for example, a method of uniaxial extension by passing the laminated body between rollers with different peripheral speeds) , But in order to obtain high optical characteristics, free end extension can be actively used. In one embodiment, the in-flight stretching process includes a heating roller stretching step in which the laminate is conveyed along its longitudinal direction while being stretched using the difference in peripheral speed between the heating rollers. The air extension process means that the above system includes a zone extension step and a heating roller extension step. In addition, the sequence of the area extension step and the heating roller extension step is not limited, and the area extension step may be performed first, or the heating roller extension step may be performed first. The region extension step can also be omitted. In one embodiment, the area extension step and the heating roller extension step are sequentially performed. In another embodiment, the end of the film is gripped in a tenter stretcher, and the distance between the tenters is expanded in the flow direction to extend (the increase in the distance between the tenters is the stretch magnification). At this time, the distance of the tenter in the width direction (vertical to the flow direction) is set to be arbitrarily close. Preferably, the extension ratio relative to the flow direction can be set to use the free end extension for approaching. When the free end is extended, it is calculated as the shrinkage rate in the width direction=(1/stretching ratio) ^1/2.

Air assist extension can be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The extension direction of the aerial auxiliary extension should be approximately the same as the extension direction of the underwater extension.

The extension ratio of aerial auxiliary extension should be 2.0 to 3.5 times. The maximum extension ratio when combining aerial auxiliary extension and underwater extension is preferably 5.0 times or more relative to the original length of the laminate, preferably 5.5 times or more, and more preferably 6.0 times or more. In this specification, the "maximum extension ratio" means the extension ratio before the laminate body breaks, and it is a value that is 0.2 lower than the value after confirming the extension ratio at which the laminate body fractures.

The extension temperature of the air-assisted extension can be set to any appropriate value according to the forming material and extension method of the thermoplastic resin substrate. The elongation temperature is preferably higher than the glass transition temperature (Tg) of the thermoplastic resin substrate. The glass transition temperature (Tg) of the thermoplastic resin substrate (Tg) + 10°C or higher is more suitable, and the Tg + 15°C or higher is particularly suitable. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at the temperature can suppress the rapid progress of the crystallization of the PVA-based resin, thereby suppressing defects caused by the crystallization (for example, hindering the orientation of the PVA-based resin layer due to the stretching).

C-3. Insoluble treatment, dyeing treatment and cross-linking treatment If necessary, the insolubilization treatment can be performed after the aerial auxiliary extension treatment and before the underwater extension treatment or the dyeing treatment. The above-mentioned insolubilization treatment means that the PVA-based resin layer is immersed in an aqueous boric acid solution. The dyeing process described above is performed by dyeing the PVA-based resin layer with a dichroic substance (iodine in the representative). If necessary, a cross-linking treatment may be performed after the dyeing treatment and before the water extension treatment. The above-mentioned crosslinking treatment can typically be performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The details of the insolubilization treatment, the dyeing treatment, and the crosslinking treatment are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 (mentioned above).

C-4. Water extension treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. The stretching treatment in water can stretch at a temperature lower than the glass transition temperature of the thermoplastic resin substrate or PVA resin layer (typically around 80°C), and can suppress the crystallization of the PVA resin layer at the same time Perform high-magnification extension. As a result, a polarizing film with excellent optical properties can be produced.

Any appropriate method can be adopted for the extension method of the laminate. Specifically, it may be a fixed-end extension or a free-end extension (for example, a method of uniaxially extending the laminate through rollers with different peripheral speeds). Preferably, the free end extension is selected. The extension of the laminated body can be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the stretching magnification (maximum stretching magnification) of the laminate described later is the product of the stretching magnifications of each stage.

The stretching in water is preferably performed by immersing the layered body in an aqueous boric acid solution (borate stretching in water). By using an aqueous solution of boric acid as a stretching bath, rigidity and water-insoluble water resistance can be imparted to the PVA-based resin layer to withstand the tension applied during stretching. Specifically, boric acid generates tetrahydroxyborate anions in an aqueous solution and can be cross-linked with PVA-based resins through hydrogen bonds. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and the PVA-based resin layer can be stretched well, thereby producing a polarizing film with excellent optical properties.

The above-mentioned boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water which is a solvent. The concentration of boric acid is preferably 1 part by weight to 10 parts by weight relative to 100 parts by weight of water, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight. By setting the concentration of boric acid 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 characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, and glutaraldehyde in a solvent can also be used.

It is advisable to mix iodide in the above-mentioned extension bath (aqueous boric acid solution). By blending iodide, the elution of iodine that has been adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight relative to 100 parts by weight of water, and more preferably 0.5 parts by weight to 8 parts by weight.

The extension temperature (liquid temperature of the extension bath) is preferably 40℃~85℃, more preferably 60℃~75℃. As long as the temperature is above, the dissolution of the PVA-based resin layer can be suppressed, and at the same time, it can be stretched at a high rate. Specifically, as described above, considering the relationship with the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher. At this time, if the stretching temperature is lower than 40°C, even if it is considered that the thermoplastic resin base material is plasticized with water, it may not be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and it may not be possible to obtain excellent optical properties. The immersion time for the laminate to be immersed in the extension bath is preferably 15 seconds to 5 minutes.

The stretching magnification for stretching in water is preferably 1.5 times or more, preferably 3.0 times or more. The total extension ratio of the laminate is preferably 5.0 times or more, and more preferably 5.5 times or more relative to the original length of the laminate. By achieving the high stretching magnification, a polarizing film with extremely excellent optical properties can be manufactured. The high stretch magnification can be achieved by using an underwater stretch method (boric acid stretch in water).

C-5. Introduction of alcohol In the embodiment of the present invention, the alcohol is introduced after the underwater stretching treatment (and representatively, before the drying shrinkage treatment described later). The introduction of alcohol can be carried out in any appropriate manner. For example, the layered body may be immersed in an alcohol-containing treatment liquid, or the surface of the polarizing film of the layered body may be coated with an alcohol-containing treatment liquid. Representatively, the introduction of alcohol can be carried out by dipping. The impregnation can be carried out in any appropriate pattern. For example, alcohol may be added to the washing bath of the washing treatment to form a bath of the treatment liquid, a bath of the treatment liquid may be used instead of the washing bath, or a bath of the treatment liquid may be provided separately from the washing bath. Representatively, alcohol can be added to the washing bath (washing liquid) of the washing treatment. When it is a low-boiling alcohol, the alcohol concentration of the treatment liquid (cleaning liquid) should be 5% by weight to 35% by weight. When it is a high-boiling alcohol, the alcohol concentration of the treatment liquid (cleaning liquid) should be 0.03% by weight to 1.0% by weight. %. The immersion time for the layered body to be immersed in the treatment liquid (washing liquid) is preferably 1 second to 20 seconds, more preferably 3 seconds to 10 seconds.

C-6. Drying shrinkage treatment The drying shrinkage treatment can be performed by heating the area by heating the entire area, or by heating the conveying roller (using a so-called heating roller) (heat roller drying method). It is preferable to use both. By using a heating roller to dry it, heating and curling of the laminate can be effectively suppressed, and a polarizing film with excellent appearance can be produced. Specifically, by drying the laminate in a state where the laminate is moved along the heating roller, the crystallization of the above-mentioned thermoplastic resin substrate can be efficiently promoted and the crystallinity can be increased, even at a relatively low drying temperature. It can well increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin base material is increased and the PVA-based resin layer can withstand the shrinkage of the PVA-based resin layer due to drying, so that curling is suppressed. In addition, by using a heating roller, the laminate can be dried while maintaining a flat state. Therefore, not only can the generation of curls be suppressed, but also the generation of wrinkles can be suppressed. At this time, the laminate can be shrunk in the width direction through a drying shrinkage treatment to improve optical properties. It is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate in the width direction of the laminated body undergoing drying shrinkage treatment is preferably 1%~10%, more preferably 2%~8%, especially 4%~6%.

Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment. In the drying and shrinking 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 predetermined temperature. In the example of the figure, the conveying rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, the conveying rollers R1 to R6 may be arranged to only continuously heat the laminate 200 One side (such as the thermoplastic resin substrate side).

By adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers and the contact time with the heating roller, etc., the drying conditions can be controlled. The temperature of the heating roller is preferably 60℃~120℃, more preferably 65℃~100℃, especially 70℃~80℃. As long as the temperature is above, the crystallinity of the thermoplastic resin can be increased well, curling can be well suppressed, and an optical laminate having extremely excellent durability can be produced. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the illustrated example, there are 6 conveying rollers, but there is no particular limitation as long as the conveying rollers are plural. The number of conveying rollers is usually 2-40, preferably 4-30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, preferably 1 to 20 seconds, and more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven), or can be installed in a general manufacturing line (at room temperature). It is suitable to be installed in a heating furnace equipped with an air supply mechanism. By combining drying with heating rollers and hot air drying, sudden temperature changes between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air should be about 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured by a mini fan blade type digital anemometer.

C-7. Other The laminated body of the thermoplastic resin substrate/polarizing film obtained by the above method can be directly used as a polarizing plate (the thermoplastic resin substrate can be used as a protective layer); it can also be peeled off after the protective layer is attached to the surface of the polarizing film of the laminated body The thermoplastic resin substrate is used as a polarizing plate with a protective layer/polarizing film composition; another protective layer can also be attached to the peeling surface of the thermoplastic resin substrate to make a protective layer/polarizing film/protective layer Constitute the polarizing plate to use.

D. Image display device The polarizing film described in the above item A and/or the polarizing plate described in the item B can be applied to an image display device. Therefore, the present invention includes an image display device using the polarizing film and/or polarizing plate. Representative examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices).

Examples Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measuring methods of each characteristic are as follows. In addition, as long as there is no special note, the "parts" and "%" in the examples and comparative examples are the basis of weight. (1) The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Alcohol concentration of polarizing film <ethanol concentration> The polarizing film is cut into 10 cm ² and used as a measurement sample. After sealing the measurement sample in a 20 mL headspace vial, it was heated in a headspace sampler (HSS) at 175°C for 30 minutes, and 1 mL of the heated gas phase portion was injected into a gas chromatograph (manufactured by Agilent Technologies, Inc., Product name "6890N"), calculate the ethanol content from the peak area corresponding to ethanol using the following calibration curve. y=4.743E ⁺⁰⁰ x+3.105E ^-02 <Glycerol Concentration> Freeze and crush the polarizing film and take about 0.02g into a screw-top bottle, add 0.5ml of methanol and permeate and extract for more than one night, and then use 0.45μm The extract was filtered through a membrane filter, and 1 μL of the filtrate was injected into a gas chromatograph (manufactured by Agilent Technologies, product name "6890N"), and the glycerol content was calculated from the peak area corresponding to glycerol using the following calibration curve. y=5.666E ^{― 01} x+1.833E ^-00 (3) Monomer transmittance and degree of polarization For the polarizing plate (protective layer/polarizing film) of the Examples and Comparative Examples, an ultraviolet-visible light spectrophotometer (manufactured by Otsuka Electronics Co., Ltd.) LPF-200) was measured, and the measured monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were used as the Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values obtained by measuring the 2-degree field of view (C light source) of JIS Z8701 and performing visual sensitivity calibration. In addition, the refractive index of the protective layer is 1.50, and the refractive index of the surface of the polarizing film on the side opposite to the protective layer is 1.53. From the obtained Tp and Tc, the degree of polarization is obtained by the following formula. Polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100 IR) (manufactured by Perkin Elmer, trade name: "Frontier"), using polarized infrared light as the measuring light to measure attenuated total reflection (ATR: attenuated total reflection) on the surface of the polarizing film (the peeling surface of the PET substrate) . The microcrystalline system to make the polarizing film adhere to uses germanium, and the incident angle of the measuring light is set to be incident at 45°. The calculation of the directional function is carried out according to the following procedure. The polarized infrared light (measuring light) to be incident is set to be polarized light (s-polarized light) that vibrates parallel to the surface on which the germanium crystal sample is adhered. Measure each absorbance spectrum in the vertical (⊥) and parallel (//) configuration. From the obtained absorbance spectrum, calculate (2941 ^{cm -1} intensity) I ^{with (3330 cm -1} intensity) as a reference. I _⊥ ^{is the (2941cm -1} intensity)/(3330 cm ^-1 intensity) obtained from the absorbance spectrum obtained when the extension direction of the polarizing film is arranged perpendicular to the polarization direction of the measured light (⊥). In addition, I _// is obtained from the absorbance spectrum obtained when the extension direction of the polarizing film is arranged parallel to the polarization direction of the measurement light (//) (2941 cm ^-1 intensity)/(3330 cm ^-1 intensity). When thereto, (2941cm ^-1 intensity) -based bottom of the absorbance spectrum 2770cm ^-1 and 2990cm ^-1 2941cm ^-1 when the absorbance of the baseline, (3330cm ^-1 intensity) based 3650cm ^-1 to 2990cm ^-1 and a baseline The absorbance of 3330cm ^-1. Use the obtained I _⊥ and I _{// to} calculate the orientation function F according to formula 1. In addition, when F=1, it is fully oriented, and when F=0, it is random. It is believed that ^{the peak of 2941 cm -1} is due to the absorption of the vibration of the PVA main chain (-CH _{2 -) in the polarizing film.} It is believed that ^{the peak of 3330 cm -1} is due to the absorption of the vibration of the hydroxyl group of PVA. (Equation 1) F=(3＜cos ² θ＞-1)/2 =(1-D)/[c(2D+1)] However, c=(3cos ² β-1)/2, as above When using 2941cm ^-1 , β=90°⇒F=-2×(1-D)/(2D+1). θ: the angle of the molecular chain relative to the extension direction β: the angle of the transition dipole moment relative to the molecular chain axis D=(I _⊥ )/(I _// ) I _⊥ : the polarization direction of the measured light is in line with the extension direction of the polarizing film _{Vertical absorption intensity I //} ：Measure the absorption intensity when the polarization direction of the light is parallel to the extension direction of the polarizing film The size of 10 cm × 10 cm in the transmission axis direction was used to prepare a test piece. The obtained test piece was put into an oven at 85°C, and the shrinkage rate in the absorption axis direction after heating for 120 hours was measured.

[Example 1] The thermoplastic resin substrate uses a long strip of amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100µm) with a Tg of about 75°C. And applied corona treatment to one side of the resin substrate. In a 9:1 mixture of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetyl acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410"). To 100 parts by weight of resin, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating liquid). The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 µm to produce a laminate. The resulting laminate was uniaxially stretched to 2.4 times in the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds in an oven at 130°C (air-assisted stretching treatment). Next, the layered body was immersed in an insoluble bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment). Next, adjust the concentration in a dyeing bath (100 parts by weight of water and an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7) at a liquid temperature of 30°C, while immersing in it for 60 seconds. Make the monomer transmittance (Ts) of the polarizing film finally obtained to be about 44% to 45% (dyeing treatment). Next, it was immersed in a cross-linking 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 with a liquid temperature of 40°C) for 30 seconds (cross-linking treatment) ). Then, while immersing the layered body in a boric acid aqueous solution (boric acid concentration 4.0% by weight, potassium iodide 5.0% by weight) at a liquid temperature of 70°C, uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to Make the total extension ratio up to 5.5 times (underwater extension treatment). Then, the laminate was immersed in a treatment bath (4 wt% potassium iodide, 6 wt% ethanol aqueous solution) at a liquid temperature of 20°C for 5 seconds to clean the laminate while introducing it into the PVA-based resin layer (polarizing film) Ethanol (washing treatment and introduction of ethanol). After that, while drying in an oven maintained at 90°C, the contact surface temperature was maintained at 75°C with a SUS heating roller for about 2 seconds (drying treatment). Through the above procedures, a polarizing film with a thickness of 5.0 μm was formed on the resin substrate. A cycloolefin-based film (manufactured by ZEON, product name "G-Film") is bonded to the surface of the polarizing film through a UV curable adhesive (thickness 1.0μm) as a protective layer, and then the resin substrate is peeled off to obtain a protective layer/ Polarizing plate made of polarizing film. The concentration of ethanol in the polarizing film of the obtained polarizing plate was 15 ppm.

The characteristics of the obtained polarizing plate (substantially a polarizing film) were evaluated. The results are listed in Table 1.

[Example 2] In the same manner as in Example 1, a polarizing plate was produced. The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Example 3] A polarizing plate was produced in the same manner as in Example 1, except that no ethanol was added to the treatment bath and 0.2% by weight of glycerol was added. The concentration of glycerol in the polarizing film of the obtained polarizing plate was 0.3% by weight. And the obtained polarizing plate (or polarizing film) was used for the same evaluation as in Example 1. The results are listed in Table 1.

＜Comparative Examples 1~3＞ A polarizing plate was produced in the same manner as in Example 1, except that no alcohol was added to the washing bath (washing liquid). The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Comparative Example 4] A polarizing plate was produced in the same manner as in Example 1, except that alcohol was not added to the washing bath (washing liquid) and the stretching treatment was performed so that the total stretching magnification was 3.5 times. The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Table 1]

It can be seen from Table 1 that the polarizing plate (polarizing film) of the example having an orientation characteristic index of 7 or more maintains excellent optical properties, and the dimensional change is suppressed.

Industrial availability The polarizing film and polarizing plate of the present invention can be suitably used for image display devices such as liquid crystal display devices and organic EL display devices.

10: Polarizing film 20: The first protective layer 30: The second protective layer 100: Polarizing plate 200: layered body G1~G4: guide roller R1~R6: Conveying roller

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment using a heating roller.

10: Polarizing film

20: The first protective layer

30: The second protective layer

100: Polarizing plate

Claims (7)

A polarizing film made of polyvinyl alcohol resin film containing iodine, Its monomer transmittance is above 43.0%, and The orientation characteristic index calculated from the degree of polarization: P and the orientation function: F: (P-98)/F is 7 or more. For example, the polarizing film of claim 1 has a single transmittance of 44.5% or less. For example, the polarizing film of claim 1 or 2 has a thickness of 8 μm or less. The polarizing film of any one of claims 1 to 3, which contains alcohol. The polarizing film of claim 4, wherein the aforementioned alcohol includes at least one selected from ethanol and glycerol. A polarizing plate comprising the polarizing film according to any one of claims 1 to 5. An image display device provided with the polarizing plate as claimed in claim 6.

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