TW202039599A - Polarizing film, polarizing plate, and polarizing film production method - Google Patents

Abstract

Provided is a thin polarizing film that exhibits superior durability in a high-temperature, high-humidity environment. A polarizing film according to the present invention is formed from a polyvinyl-alcohol-based resin film containing iodine, has a thickness of 8 [mu]m or less, and contains 5-350 ppm of an alcohol having a boiling point of less than 100 DEG C. In one embodiment, the alcohol having a boiling point of less than 100 DEG C is at least one alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, and isopropyl alcohol. A polarizing plate according to the present invention has said polarizing film and a protective layer that is disposed at least on one side of the polarizing film.

Description

Polarizing film, polarizing plate and manufacturing method of the polarizing film

The present invention relates to a polarizing film, a polarizing plate and a manufacturing method of the polarizing film.

Background of the invention 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 image display devices in recent years and has attracted attention. However, thin polarizing films are required to have more durability in high temperature and high humidity environments.

Prior art literature Patent literature Patent Document 1: Japanese Patent Application Publication No. 2001-343521

Problems to be solved by the invention The present invention was made in order to solve the above-mentioned conventional problems, and its main purpose is to provide a thin polarizing film, a polarizing plate and a manufacturing method of the polarizing film that are thin and have excellent durability in a high temperature and high humidity environment.

Means to solve the problem The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, with a thickness of 8 μm or less, and containing 5 ppm to 350 ppm of alcohol with a boiling point below 100°C. In one embodiment, the above-mentioned alcohol with a boiling point of less than 100° C. is at least one selected from the group consisting of methanol, ethanol, n-propanol and isopropanol. According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate has the above-mentioned polarizing film and a protective layer arranged on at least one side of the polarizing film. According to yet another aspect of the present invention, a manufacturing method of the above-mentioned polarizing film is provided. The method includes the following steps: forming a polyvinyl alcohol-based resin layer on one side of a long-shaped thermoplastic resin substrate to form a laminated body; extending and dyeing the laminated body to make the polyvinyl alcohol-based resin layer into a polarized light Film; and, the introduction of alcohol with a boiling point of less than 100 ℃ into the polarizing film. In one embodiment, the manufacturing method includes immersing the polarizing film in a treatment liquid containing alcohol having a boiling point of less than 100°C. In one embodiment, the manufacturing method further includes the step of heating the laminate after introducing the alcohol having a boiling point of less than 100° C. into the polarizing film. In one embodiment, the aforementioned extension includes underwater extension.

Invention effect According to the present invention, by introducing alcohol with a boiling point of less than 100° C. into the polarizing film, a thin polarizing film with excellent durability in a high temperature and high humidity environment can be obtained.

The form used to implement the invention 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, the thickness of which is less than 8μm, and contains 5ppm to 350ppm of alcohol with a boiling point lower than 100℃ (hereinafter sometimes referred to as low boiling alcohol ). When the polarizing film contains a predetermined amount of the low-boiling alcohol, a thin polarizing film with excellent durability in a high temperature and high humidity environment can be obtained. The low-boiling point alcohol is described later in item C of the related manufacturing method, which means that a polarizing film can be introduced between the water extension treatment and the drying shrinkage treatment. By introducing the low boiling point alcohol, we speculate that the durability under high temperature and high humidity environment can be improved due to the following mechanisms: (i) The drying efficiency is improved due to the low boiling point alcohol during the drying shrinkage treatment, thereby the orientation of PVA Improve; and, (ii) the obtained polarizing film is stabilized by the PVA-iodine complex compound due to the low boiling point alcohol, so that the decrease in optical properties during humidification can be suppressed. Furthermore, in the production of a thin polarizing film, the crystallization of PVA may be insufficient, but the introduction of a low-boiling alcohol can achieve good crystallization of PVA. As a result, with the same monomer transmittance, compared to the conventional (thick) polarizer, even a thin polarizing film with a particularly large iodine concentration and insufficient iodine stability can still be used in high temperature and high humidity environments. Excellent durability. The content of low-boiling alcohol in the polarizing film is, for example, 8 ppm to 320 ppm, preferably 20 ppm to 200 ppm, and preferably 40 ppm to 150 ppm, and more preferably 50 ppm to 120 ppm. If the content is too small, the effect of low boiling point alcohol may not be obtained. If the content is too high, the amount of introduction at the time of manufacture will increase, and the amount of volatility to the working environment will increase, which may increase the safety risk.

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. These low boiling points can improve the drying efficiency in the drying step described later, and help to improve the characteristics of the polarizing film to be obtained.

The thickness of the polarizing film is 8 μm or less as described above, preferably 7 μm or less, 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 polarizing film should exhibit dichroism at any wavelength from 380nm to 780nm. The monomer transmittance of the polarizing film is preferably 42.0% or more, preferably 42.5% or more, and more preferably 43.0% or more. On the other hand, the monomer transmittance is preferably 47.0% or less, and more preferably 46.0% or less. The degree of polarization of the polarizing film is preferably above 99.90%, more preferably above 99.95%. On the other hand, the degree of polarization is preferably 99.998% or less. According to the embodiment of the present invention, it is possible to achieve both high monomer transmittance and high polarization degree, and as described above, it is possible to achieve excellent durability in a high temperature and high humidity environment. The above-mentioned 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 polarization change ΔP of the polarizing film after a durability test at a temperature of 60°C and a relative humidity of 95% for 120 hours is preferably above -0.70%, preferably above -0.55%, and even more preferably above 0.20%. The upper limit of ΔP may be, for example, 0.0% or more, and ΔP may be, for example, 0.10% or less. ΔP is expressed by the following formula. ΔP=P ₁₂₀ -P _{0 In the} above formula, P ₁₂₀ is the degree of polarization after the endurance test, and P ₀ is the degree of polarization before the endurance test (the degree of polarization described above). That is, the polarizing film of the embodiment of the present invention has the following characteristics: the decrease in the degree of polarization is small in a high temperature and high humidity environment, and the degree of polarization may increase.

The polarizing film can be made of a single resin film, or a laminate of two or more layers. Specific examples of the polarizing film obtained using the laminate include a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating. The polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced by, for example, applying a PVA-based resin solution to the resin substrate, and It is dried to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and the laminate is stretched and dyed to form the PVA-based resin layer into a polarizing film. In the embodiment of the present invention, a low boiling point alcohol is introduced into the polarizing film. Thereby, the above-mentioned excellent durability under high temperature and high humidity environment can be realized. It is suitable to form a polyvinyl alcohol resin layer containing halide and polyvinyl alcohol resin on one side of the resin substrate. Stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching. In addition, the stretching may further include the following step according to the needs: before stretching in the boric acid aqueous solution, the laminate is stretched in the air at a high temperature (for example, 95°C or higher). In addition, in this embodiment, it is preferable that the laminated system is subjected to a drying shrinkage treatment in which it is heated while being transported in the longitudinal direction to shrink it by 2% or more in the width direction. Representatively, the manufacturing method of this embodiment includes sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the laminate. By introducing auxiliary extension, the crystallinity of PVA can be improved even when PVA is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, at the same time, the orientation of PVA can be improved in advance to prevent problems such as degradation or dissolution of the orientation of PVA when immersed in water in the subsequent dyeing step or stretching step, and high optical properties can be achieved. In addition, when the PVA-based resin layer is immersed in a liquid, compared to the case where the PVA-based resin layer does not contain a halide, it is possible to suppress the orientation disorder of the polyvinyl alcohol molecules and the decrease in orientation. Therefore, it is possible to improve the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment. In addition, by drying and shrinking the laminate in the width direction, the optical properties can be improved. The obtained resin substrate/polarizing film laminate can be used directly (that is, the resin substrate can also be used as the protective layer of the polarizing film), or the resin substrate can be peeled from the resin substrate/polarizing film laminate and then peeled off. Lay any appropriate protective layer according to the purpose for later use. The detailed content of the manufacturing method of the polarizing film will be explained in item C.

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. In addition, as described above, one of the first protective layer and the second protective layer may be a resin substrate used for the production of 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 cellulose triacetate (TAC), polyester, polyvinyl alcohol, polycarbonate, polyamide, and polyamide. Transparent resins such as imine-based, polyether-based, poly-based, polystyrene, polynorbornene, polyolefin, (meth)acrylic and acetate-based, etc. In addition, thermosetting resins such as (meth)acrylic type, urethane type, (meth)acrylate urethane type, epoxy type, and polysilicon type resin, or ultraviolet curing type resin, etc. may also be mentioned. Other examples include glassy polymers such as silicone polymers. In addition, the polymer film described in JP 2001-343529 A (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 amide 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 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and more It is preferably 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 5 μm to 200 μm, more preferably 10 μm to 100 μm, and more preferably 10 μm to 60 μm. 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 is obtained by the transmission 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 of 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 to form the PVA-based resin layer into a polarizing film; and, introducing a low boiling point alcohol into the polarizing film. By introducing a low boiling point alcohol, a polarizing film with excellent durability under high temperature and high humidity environments 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 laminated body, and the drying and shrinking treatment system heats the laminated body while conveying the laminated body in the longitudinal direction. , Thereby making it shrink by more than 2% in the width direction. At this time, the introduction of the low-boiling alcohol should be carried out between the water extension treatment and the drying shrinkage treatment. The content of the halide 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℃~120℃. The shrinkage in the width direction of the laminate after drying and shrinking is preferably 2% or more. According to the manufacturing method, the polarizing film described in the above item A can be obtained. In particular, a polarizing film with excellent optical properties (representatively, monomer transmittance and unit polarization) can be obtained by the following method: After making a laminate containing a halogenated PVA-based resin layer, the laminate The stretching performs multi-stage stretching including aerial auxiliary stretching and underwater stretching, and then the stretched laminate is heated by heating rollers.

C-1. Making multilayer 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 halide and PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As mentioned above, the halide content in the PVA resin layer is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA 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 (comma 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-adhesion layer may be formed on the thermoplastic resin substrate. By performing the above 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, JP 2012-73580 A. In this manual, the entire record of the bulletin is used as a reference.

C-1-2. Coating liquid The coating liquid system contains a halide and a PVA-based resin as described above. The above-mentioned coating liquid represents a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. As the solvent, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane and other polyols, ethylene oxide Amines such as diamine 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 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 liquid is preferably 5 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 surface active agent include nonionic surface active agents. These can be used 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%, more preferably 99.0 mol%~99.93 mol%. The degree of saponification is determined 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 according to 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 the PVA resin, and more preferably 10 parts by weight to 15 parts by weight relative to 100 parts by weight of the PVA resin. If the amount of halide is more 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 resin layer will increase the orientation of the polyvinyl alcohol molecules in the PVA resin layer. However, if the extended PVA resin layer is immersed in a water-containing liquid, there will be polyethylene A situation where the orientation of alcohol molecules is disordered and the orientation is reduced. Especially when the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, in order to stabilize the extension of the thermoplastic resin, when the laminate is stretched in boric acid water at a relatively high temperature, the degree of orientation tends to decrease It's remarkable. 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. The temperature before and after is performed at a higher temperature. At this time, the orientation of the PVA at the beginning of the extension will decrease before it rises due to the extension in the water. In this regard, by making a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate, and stretching the laminate in the air before stretching in boric acid water (assisted extension), 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 to the case where the PVA-based resin layer does not contain a halide, it is possible to suppress the orientation disorder of the polyvinyl alcohol molecules and the decrease in orientation. Thereby, it is possible to improve the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid through 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 decrease in extension due to the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water extension. , So that 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 Lower, as a result, the crystallization of the PVA-based resin is relatively low, and sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary extension, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, at the same time, the orientation of the PVA-based resin is increased 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 stretcher 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 treatment includes a heating roller stretching step in which the laminate is conveyed in the longitudinal direction and 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 and stretched by expanding the distance between the tenters in the traveling direction (the increase in the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (vertical to the direction of travel) is set to be arbitrarily close. Preferably, the extension ratio relative to the direction of travel 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. The "maximum extension ratio" in this specification means the extension ratio before the laminate is about to break, and it is a value that is 0.2 lower than its value after confirming the extension ratio at which the laminate is fractured.

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, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate +10°C or higher, and especially suitable for Tg+15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at the temperature, the rapid progress of crystallization of the PVA-based resin can be suppressed, thereby suppressing defects caused by the crystallization (for example, the orientation of the PVA-based resin layer is hindered by the stretching).

C-3. Insoluble treatment, dyeing treatment and cross-linking treatment If necessary, after the aerial auxiliary extension treatment and before the underwater extension treatment or dyeing treatment, an insolubilization treatment is performed. 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 representative). If necessary, a cross-linking treatment is 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 a boric acid aqueous solution. The details of the insolubilization treatment, dyeing treatment, and crosslinking treatment are described in, for example, JP 2012-73580 A (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 above-mentioned 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-rate 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). It is preferable to choose free end extension. The extension of the laminated body can be carried out in one stage or in multiple stages. When it is performed in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios 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, the PVA-based resin layer can be given rigidity to withstand the tension during stretching and water-insoluble water resistance. 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 the iodide are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight relative to 100 parts by weight of water.

The 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 stretch 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 to plasticize the thermoplastic resin base material with water, it may not be possible to stretch 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 of the laminate 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 stretching ratio can be achieved by using an underwater stretching method (boric acid underwater stretching).

C-5. Import low boiling point alcohol In the embodiment of the present invention, the low-boiling alcohol is introduced after the underwater stretching treatment (and before the drying shrinkage treatment described later). The introduction of the low boiling point alcohol can be carried out in any appropriate manner. For example, the layered body may be immersed in a treatment liquid containing a low boiling point alcohol, or the surface of the polarizing film of the layered body may be coated with a treatment liquid containing a low boiling point alcohol. Representatively, the introduction of low-boiling alcohol can be carried out by impregnation. The impregnation can be performed in any appropriate pattern. For example, a low-boiling alcohol can be added to the washing bath of the washing treatment to form a bath of the treatment liquid, a bath of the treatment liquid can be used instead of the cleaning bath, or a bath of the treatment liquid can be provided separately from the cleaning bath. Representatively, low-boiling alcohol can be added to the washing bath (washing liquid) of the washing treatment. The low-boiling alcohol concentration of the treatment liquid (cleaning liquid) is preferably 5 wt% to 35 wt%.

C-6. Drying shrinkage treatment The above-mentioned drying shrinkage treatment is preferably carried out after introducing the low-boiling alcohol. By introducing a low-boiling alcohol and then performing a drying shrinkage treatment, the drying efficiency can be improved, and as a result, the orientation of the PVA can be improved.

The drying shrinkage treatment can be performed by heating the area by heating the entire area, or by heating the conveying roller (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 along the heating roller, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, even at a relatively low drying temperature. It can still 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, and curling is suppressed. In addition, by using a heating roller, the laminate can be dried while maintaining a flat state. Therefore, not only the generation of curls but also the generation of wrinkles can be suppressed. In this case, the laminated body 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 obtained by drying and shrinking should be 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 shrinkage process, 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. However, 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 appearance of the obtained polarizing film can be maintained well. Moreover, by synergistic effect with the effect of low boiling point alcohol, the appearance can be maintained while improving the orientation of PVA. In addition, the degree of 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 example of the figure, there are 6 conveying rollers, but there is no particular limitation as long as there are a plurality of conveying rollers. 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 with air supply mechanism. By combining drying with heating rollers and hot-air drying, rapid temperature changes between 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℃. As long as the temperature is above, the appearance of the obtained polarizing film can be maintained well. Moreover, by synergistic effect with the effect of low boiling point alcohol, the appearance can be maintained while improving the orientation of PVA. Moreover, 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 thermoplastic resin substrate/polarizing film laminate obtained in the above manner can be directly used as a polarizer (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 laminate Thermoplastic resin substrate, used as a polarizing plate with a protective layer/polarizing film; also can be used as a protective layer/polarizing film/protective layer by attaching another protective layer to the peeling surface of the thermoplastic resin substrate Polarizing plate. Example

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 The polarizing plates obtained in the examples and comparative examples were cut into 10 cm ² and used as measurement samples. After sealing the measurement sample into a 20mL headspace vial, heat the sample containing ethanol at 175°C for 30 minutes with a headspace sampler (HSS), and heat the sample containing isopropanol at 215°C for 30 minutes , And inject 1 mL of the heated gas phase portion into a gas chromatograph (manufactured by Agilent Technologies, product name "6890N"), and calculate the alcohol content from the peak area corresponding to each alcohol type using the following calibration curve. Ethanol calibration curve y=4.743E ⁺⁰⁰ x + 3.105E ^-02 Isopropanol calibration curve y=4.565E ⁺⁰⁰ x + 8.922E ^-03 (3) Monomer transmittance and degree of polarization refer to Examples and Comparative Examples The polarizing plate (protective film/polarizing film) was measured with an ultraviolet-visible spectrophotometer (LPF-200 manufactured by Otsuka Electronics), and the measured monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were respectively As Ts, Tp and Tc of polarizing film. These Ts, Tp, and Tc are Y values obtained by measuring the 2-degree field of view (C light source) of JIS Z8701 and calibrating the optical performance and visual sensitivity. In addition, the refractive index of the protective film is 1.50, and the refractive index of the surface of the polarizing film on the opposite side of the protective film 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 Next, the polarizing plate is subjected to a durability test at a temperature of 85°C and a relative humidity of 85% for 120 hours. Obtain the orthogonal transmittance polarization degree P ₁₂₀ after the endurance test in the same way as above. In addition, the durability test was performed by bonding the polarizing film side of the polarizing plate to the glass plate through the adhesive layer, and putting the obtained test sample into a humidifying oven. (4) Humidification durability From the polarization degrees P ₀ and P ₁₂₀ before and after the endurance test in (3) above, ΔP is obtained by the following formula. ΔP=P ₁₂₀ -P ₀ ΔP is a parameter that changes with the transmittance of the monomer. Therefore, when comparing, it must be compared with a polarizing plate whose monomer transmittance before the test is substantially the same. Therefore, the following is based on Comparative Example 1 to evaluate the durability in a high temperature and high humidity environment. ◎: Compared to Comparative Example 1, ΔP is significantly larger (the absolute value in the negative direction is significantly smaller) ○: Compared to Comparative Example 1, ΔP is larger (the absolute value in the negative direction is smaller) △: Compared to Comparative Example 1, ΔP equal ×: Compared to Comparative Example 1, ΔP is smaller (the absolute value in the negative direction is larger)

[Example 1] The thermoplastic resin substrate is a long strip of amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100 μm) 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 the 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 obtained laminate was subjected to uniaxial extension of the free end 2.4 times in the longitudinal direction (long side direction) between rollers of different peripheral speeds in an oven at 130°C (air-assisted extension treatment). Next, the laminate was cut into 15cm×10cm in the auxiliary extension axis direction, and the short sides of the cut laminate were fixed with a special extension jig and immersed in an insoluble bath at a liquid temperature of 30°C (relative to water 100 parts by weight of boric acid aqueous solution obtained by blending 3 parts by weight of boric acid) for 30 seconds (insolubilization treatment). Next, adjust the concentration of the dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water), so that the final polarizing film monomer The transmittance (Ts) becomes 43.0%±0.2%, and it is immersed in it for 60 seconds (dyeing treatment). Next, it was immersed 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 30°C for 30 seconds (crosslinking treatment ). Then, while immersing the layered body in a boric acid aqueous solution (4.0% by weight of boric acid concentration and 5.0% by weight of potassium iodide) at a liquid temperature of 70°C, uniaxial stretching was performed in the longitudinal direction (long side direction) so that the total stretching ratio was 5.5 times ( Extension treatment in water). Then, the laminate was immersed in a treatment bath (aqueous solution of potassium iodide 3 wt% and ethanol 5 wt%) at a liquid temperature of 20°C for 3 seconds to wash the laminate while introducing ethanol into the PVA resin layer (polarizing film) (Washing treatment and introduction of ethanol). After that, it was dried in an oven maintained at 60°C for 4 minutes (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 (protective film), and then peeled off the resin substrate. Polarizing plate with protective layer/polarizing film. The concentration of ethanol in the polarizing film of the obtained polarizing plate was 45 ppm.

For the obtained polarizing plate (essentially a polarizing film), the monomer transmittance and ΔP are listed in Table 1. The evaluation results of (4) above are also listed in Table 1.

[Example 2] A polarizing plate was produced in the same manner as in Example 1, except that the ethanol concentration of the treatment bath was set to 20% by weight. 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 the ethanol concentration of the treatment bath was 25% by weight. 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 4] A polarizing plate was produced in the same manner as in Example 1, except that the ethanol concentration of the treatment bath was 2% by weight. 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 5] In the same manner as in Example 4, a polarizing plate was produced. The obtained polarizing plate was subjected to a durability test at a temperature of 60°C and a relative humidity of 95% for 120 hours to obtain ΔP. The procedure of the endurance test is as described in (3) above. With respect to the obtained ΔP, the durability was evaluated based on Comparative Example 3 (described later) in the following manner. The results are listed in Table 1. ◎: Compared to Comparative Example 3, ΔP is significantly larger (the absolute value in the negative direction is significantly smaller) ○: Compared with Comparative Example 3, ΔP is larger (the absolute value in the negative direction is smaller) △: Compared with Comparative Example 3, ΔP is the same ×: Compared with Comparative Example 3, ΔP is smaller (the absolute value of the negative direction is larger)

[Example 6] In the same manner as in Example 1, a polarizing plate was produced. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are listed in Table 1.

[Example 7] A polarizing plate was produced in the same manner as in Example 2. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are listed in Table 1.

[Example 8] In the same manner as in Example 3, a polarizing plate was produced. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are listed in Table 1.

[Example 9] A polarizing plate was produced in the same manner as in Example 3 except that the immersion time of the treatment bath was set to 10 seconds. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are listed in Table 1.

[Example 10] Adjust the concentration of the dye bath so that the monomer transmittance of the polarizing film becomes 42.0%±0.2%, and the alcohol type of the washing treatment bath is isopropanol and the concentration is set to 5% by weight. Other than that In the same manner as in Example 5, a polarizing plate was produced. The obtained polarizing plate was subjected to the same endurance test as in Example 5, and evaluated according to the following criteria. The results are listed in Table 1. ◎: Compared with Comparative Example 4, ΔP is significantly larger (the absolute value in the negative direction is significantly smaller) ○: Compared with Comparative Example 4, ΔP is larger (the absolute value in the negative direction is smaller) △: Compared with Comparative Example 4, ΔP is the same ×: Compared with Comparative Example 4, ΔP is smaller (the absolute value of the negative direction is larger)

[Example 11] A polarizing plate was produced in the same manner as in Example 10 except that the isopropanol concentration of the treatment bath was set to 20% by weight. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are listed in Table 1.

[Example 12] A polarizing plate was produced in the same manner as in Example 10 except that the isopropanol concentration of the treatment bath was 25% by weight. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are listed in Table 1.

[Comparative Example 1] A polarizing plate was produced in the same manner as in Example 1, except that low-boiling alcohol was not 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 2] Without adding low-boiling alcohol to the washing bath (washing liquid), and in order to improve the drying efficiency, the temperature of the drying oven after the partial washing bath was set to 130°C, except that it was made in the same manner as in Example 1. Out of the polarizing plate. However, since the film shrinks by heating and causes wrinkles and/or dents, it is impossible to obtain a measurement sample that can be evaluated.

[Comparative Example 3] In the same manner as in Comparative Example 1, a polarizing plate was produced. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are listed in Table 1.

[Comparative Example 4] Except for adjusting the concentration of the dye bath so that the monomer transmittance of the polarizing film becomes 42.0%±0.2%, a polarizing plate was produced in the same manner as in Comparative Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are listed in Table 1.

[Table 1]

[Reference example 1] A long roll of PVA-based resin film (made by Kuraray, product name "PS4500") with a thickness of 45 μm was uniaxially stretched in the longitudinal direction using a roll stretcher to achieve a total stretch ratio of 6.0 times. At the same time, swelling, dyeing, cross-linking and washing treatments are applied, and finally a drying treatment is applied to produce a 17μm thick polarizing film. That is, a thick polarizing film into which low-boiling alcohol was not introduced was produced. A UV curable adhesive (thickness 1.0μm) is applied to both sides of the polarizing film to form a protective layer (protective film) of cycloolefin film (made by ZEON, product name "ZT12") and acrylic resin film. An adhesive layer is provided on the surface of the olefin-based film to obtain a polarizing plate with a protective layer/polarizing film/protective layer/adhesive layer. Next, except that the conditions of the durability test were set to a temperature of 65°C, a relative humidity of 90%, and a test time of 500 hours, it was used for the same evaluation as in Example 1, and ΔP was obtained by the following formula. The results are shown in Table 2. The durability of Reference Example 2 described later was evaluated based on the ΔP of this reference example. ΔP=P ₅₀₀ -P ₀

[Reference example 2] The long roll material of the laminate of PVA-based resin/resin base material used in Example 1 was stretched uniaxially in the longitudinal direction using a roll stretcher to achieve a total stretch ratio of 2.4 times, and simultaneously applied swelling and dyeing , Cross-linking and washing treatment, and finally drying treatment to produce a polarizing film with a thickness of 5μm. That is, a thin polarizing film into which low-boiling point alcohol was not introduced was produced. An adhesive layer was placed on the protective layer on the surface of the polarizing film in the same manner as in Reference Example 1, to obtain a polarizing plate with a protective layer/polarizing film/protective layer/adhesive layer. Except for the use of this polarizer, it was used for the same evaluation as in Reference Example 1, and evaluated based on the following criteria. The results are shown in Table 2. ◎: Compared to Reference Example 1, ΔP is significantly larger (the absolute value of the negative direction is significantly smaller) ○: Compared with Reference Example 1, ΔP is larger (the absolute value in the negative direction is smaller) △: Compared to Reference Example 1, ΔP is the same ×: Compared to Reference Example 1, ΔP is smaller (the absolute value of the negative direction is larger)

[Table 2]

It is obvious from Table 1 that the polarizing plate (polarizing film) of the embodiment of the present invention contains a predetermined amount of low-boiling alcohol, and thus has excellent durability in a high temperature and high humidity environment. And, as Table 2 clearly shows, durability under high temperature and high humidity environment is a unique issue for thin polarizing films.

Industrial availability The polarizing film and polarizing plate of the present invention can be suitably used for liquid crystal 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: conveyor 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, composed of a polyvinyl alcohol resin film containing iodine, with a thickness of 8μm or less, and containing 5 ppm to 350 ppm of alcohol with a boiling point below 100°C. The polarizing film of claim 1, wherein the aforementioned alcohol with a boiling point of less than 100° C. is at least one selected from the group consisting of methanol, ethanol, n-propanol, and isopropanol. A polarizing plate, comprising: the polarizing film of claim 1 or 2 and a protective layer arranged on at least one side of the polarizing film. A method for manufacturing a polarizing film is a method for manufacturing the polarizing film of claim 1 or 2, The manufacturing method includes the following steps: Form a polyvinyl alcohol-based resin layer on one side of the elongated thermoplastic resin substrate to form a laminate; Extending and dyeing the laminated body to make the polyvinyl alcohol resin layer into a polarizing film; and An alcohol with a boiling point lower than 100°C is introduced into the polarizing film. The manufacturing method of claim 4, which comprises: immersing the polarizing film in a treatment solution containing the alcohol having a boiling point of less than 100°C. According to the manufacturing method of claim 4 or 5, it further includes the step of heating the laminate after introducing the alcohol with a boiling point of less than 100° C. into the polarizing film. The manufacturing method according to any one of claims 4 to 6, wherein the aforementioned extension includes underwater extension.

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