JP2022112801A - Method of manufacturing polarizing film - Google Patents

Abstract

To provide a polarizing film which may reduce power consumption of an organic EL display device.SOLUTION: The present invention provides a method of manufacturing a polarizing film, the method comprising subjecting a polyvinyl alcohol-based resin film to dying treatment and stretching treatment, and bringing an aqueous solvent into contact with a surface of the polyvinyl alcohol-based resin film, performed in the described order. A ratio ΔTs(λ) of transmittance of the polyvinyl alcohol-based resin film after being in contact with the aqueous solvent to transmittance thereof before being in contact with the aqueous solvent at a wavelength of λ nm satisfies a relationship expressed as: ΔTs(415)>ΔTs(470)>ΔTs(550).SELECTED DRAWING: None

Description

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

2. Description of the Related Art In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. It is known that in an organic EL display device, problems such as external light reflection and background reflection can be prevented by placing a circularly polarizing plate including a λ/4 plate on the viewing side of the organic EL cell (for example, Patent Documents 1 and 2).

On the other hand, since the organic EL display device consumes a large amount of power for light emission, there is a demand for energy saving.

JP-A-2002-311239 Japanese Patent Application Laid-Open No. 2002-372622

SUMMARY OF THE INVENTION The present invention has been made to solve the above conventional problems, and a main object thereof is to provide a polarizing film capable of reducing the power consumption of an organic EL display device.

According to one aspect of the present invention, subjecting a polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment, and bringing an aqueous solvent into contact with the surface of the polyvinyl alcohol-based resin film, in this order, and having a wavelength of λ nm The ratio of the transmittance after contact to the transmittance of the polyvinyl alcohol resin film before contact with the aqueous solvent (ΔTs (λ)) has a relationship of ΔTs (415)>ΔTs (470)>ΔTs (550) is provided.
In one embodiment, the temperature of the aqueous solvent is 20°C to 70°C.
In one embodiment, the water content of the polyvinyl alcohol-based resin film with which the aqueous solvent is brought into contact is 15% by weight or less.
In one embodiment, the polyvinyl alcohol-based resin film with which the aqueous solvent is brought into contact has a thickness of 12 μm or less.
In one embodiment, subjecting the polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment is a polyvinyl alcohol-based resin containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate. Forming a membrane to form a laminate, and subjecting the laminate to auxiliary stretching in the air, dyeing, stretching in water, and heating while transporting in the longitudinal direction, thereby shrinking in the width direction by 2% or more. and drying shrinkage treatment to make it dry, and applying in this order.
In one embodiment, the manufacturing method is a method for manufacturing a polarizing film having a haze of 1% or less.

According to the manufacturing method of the polarizing film according to the embodiment of the present invention, the polyvinyl alcohol (PVA) resin film that has undergone the dyeing treatment and the stretching treatment is subjected to the contact treatment with the aqueous solvent. As a result, the transmittance of the PVA-based resin film increases at least in the wavelength region of 415 nm to 550 nm, and the ratio of the transmittance after contact to the transmittance of the PVA-based resin film before contact with the aqueous solvent at the wavelength λ nm (ΔTs ( λ)=Ts(λ) after contact/Ts(λ) before contact; > satisfies the relationship of ΔTs (550). A polarizing film obtained by such a manufacturing method can more positively transmit light on the short wavelength side than light on the long wavelength side. Therefore, by using such a polarizing film, even when the amount of blue light emission, which consumes a large amount of power, is reduced, it is possible to suppress the decrease in luminance in the short wavelength region, and as a result, the organic EL display device can be It is possible to achieve both energy saving and high luminance.

FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll.

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

A. Method for producing polarizing film The method for producing a polarizing film according to an embodiment of the present invention comprises subjecting a polyvinyl alcohol (PVA) resin film to dyeing treatment and stretching treatment (step I), and contacting with an aqueous solvent (step II), in this order, the ratio of the transmittance after contact to the transmittance of the polyvinyl alcohol resin film before contact with the aqueous solvent at a wavelength of λ nm (ΔTs (λ)) satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550). In the PVA-based resin film after dyeing, iodine exists in the form of I ⁻ , I ₂ , I ₃ ⁻ , PVA-I ₃ ^-complex , PVA-I ₅ ^-complex , etc., but I ⁻ , I ₂ and I ₃ ^- has absorption in the ultraviolet region (for example, wavelengths around 290 nm to 360 nm), and PVA-I ₃ ^-complex and PVA-I ₅ ^-complex have absorptions around wavelengths of 470 nm and 600 nm, respectively. Therefore, the fact that the relationship ΔTs (415)>ΔTs (470)>ΔTs (550) holds before and after contact with the aqueous solvent means that I ⁻ , I ₂ , This is thought to indicate that the ratio of I ₃ ⁻ and PVA-I ₃ ^-complex decreased (in other words, the ratio of PVA-I ₅ ^-complex increased).

A-1. Process I
In step I, the PVA-based resin film is subjected to dyeing treatment and stretching treatment, whereby a PVA-based resin film exhibiting absorption dichroism at any wavelength of 380 nm to 780 nm (hereinafter referred to as "unbleached original film" (sometimes referred to as ). The unbleached original film is typically in a state capable of functioning as a polarizing film.

In one embodiment, the transmittance of the unbleached original film (single transmittance: Ts) is preferably 41.0% or more, more preferably 42.0% or more, and still more preferably 42.5%. That's it. On the other hand, the transmittance of the unbleached original film is preferably 46.0% or less, more preferably 45.0% or less. The degree of polarization of the unbleached original film is preferably 98.0% or more, more preferably 99.0% or more, still more preferably 99.9% or more. On the other hand, the degree of polarization of the unbleached original film is preferably 99.998% or less. The transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film (unbleached original film) of 12 μm or less is typically the polarizing film (surface refractive index: 1.53) and the protective layer (protective film) ( A laminate with a refractive index of 1.50) is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the protective layer contacting the air interface, the reflectance at each layer interface may change, resulting in a change in the measured transmittance. . Thus, for example, if a protective layer with a refractive index other than 1.50 is used, the transmittance measurements may be corrected according to the refractive index of the surface of the protective layer that is in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer.
C=R ₁ -R ₀
R ₀ = ((1.50−1) ² /(1.50+1) ² )×(T ₁ /100)
R ₁ = ((n ₁ −1) ² /(n ₁ +1) ² )×(T ₁ /100)
Here, R ₀ is the transmission axis reflectance when a protective layer having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer used, and T ₁ is the transmittance of the polarizing film. is. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is approximately 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance when using a polarizing film with a surface refractive index of 1.53 and a protective layer with a refractive index of 1.50 It is possible to convert to a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T1 of the polarizing film is changed by ₂ % is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

The transmittance (Ts ₄₁₅ ) of the unbleached original film at a wavelength of 415 nm can be, for example, less than 40%.

The moisture content of the unbleached original film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% to 5% by weight. If the moisture content of the unbleached original film is within this range, it is possible to prevent dissolution, wrinkles, and the like from occurring during contact with the aqueous solvent in step II.

The thickness of the unbleached original film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, even more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm.

In step I, a single-layer PVA-based resin film is subjected to dyeing treatment and stretching treatment, whereby an unbleached original film can be produced. Alternatively, a laminate of two or more layers including a PVA-based resin layer (PVA-based resin film) may be subjected to dyeing treatment and stretching treatment to prepare an unbleached original film. The unbleached base film prepared using a laminate of two or more layers avoids the occurrence of wrinkles and the like even after contact with an aqueous solvent, and has excellent optical properties (typically, single transmittance and degree of polarization) can be preferably maintained.

A-1-1. Production of an unbleached original film using a laminate of two or more layers In the production of an unbleached original film using a laminate of two or more layers, for example, a PVA-based resin film containing a halide and a PVA-based resin is elongated. It can be carried out by dyeing and stretching in the state of a laminate with a thermoplastic resin substrate having a shape. Specifically, the unbleached original film is a laminate obtained by forming a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of a long thermoplastic resin substrate. Then, the laminate is subjected to an auxiliary aerial stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment that shrinks by 2% or more in the width direction by heating while being conveyed in the longitudinal direction, in this order. It can be made by a method comprising applying. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage ratio in the width direction of the laminate due to drying shrinkage treatment is preferably 2% or more. According to such a production method, it is possible to obtain an unbleached raw film having a high degree of orientation of the PVA-based resin and excellent optical properties.

A-1-1-1. Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a 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 described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted as a method for applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

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

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

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

The thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. Thermoplastic resin substrates can absorb water and be plasticized with the water acting like a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high draw ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as deterioration of the appearance of the obtained unbleached base film due to a marked decrease in the dimensional stability of the thermoplastic resin substrate during production. . Moreover, it is possible to prevent breakage of the base material and separation of the PVA-based resin layer from the thermoplastic resin base material during stretching in water. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption is a value determined according to JIS K7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin substrate, it is possible to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the satisfactory stretching in water, the temperature is preferably 100° C. or lower, more preferably 90° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, deformation of the thermoplastic resin substrate (for example, generation of unevenness, sagging, wrinkles, etc.) occurs when the coating liquid containing the PVA-based resin is applied and dried. It is possible to prevent the problem of and produce a good laminate. Moreover, the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60°C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K7121.

Any appropriate thermoplastic resin may be employed as a constituent material of the thermoplastic resin base material. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. is mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

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

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

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

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

Any appropriate method can be adopted as a method for stretching the thermoplastic resin substrate. Specifically, the drawing may be fixed end drawing or free end drawing. The stretching method may be a dry method or a wet method. The stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performing in multiple stages, the above-mentioned draw ratio is the product of the draw ratios in each step.

The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of solvents include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

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

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

Any appropriate halide can be employed as the halide. Examples include iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

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

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer increases. orientation may be disturbed and the orientation may be lowered. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. When the film is stretched, the tendency of the degree of orientation to decrease is remarkable. For example, the stretching of a single PVA film in boric acid water is generally carried out at 60° C., whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is It is carried out at a high temperature of about 70° C., and in this case, the orientation of PVA at the initial stage of stretching may be lowered before it is increased by stretching in water. On the other hand, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate at a high temperature (auxiliary stretching) in air before stretching in boric acid water, , the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical properties of the unbleached base film obtained through a treatment step in which the laminate is immersed in a liquid, such as dyeing treatment and stretching treatment in water.

A-1-1-2. Aerial Auxiliary Stretching In order to obtain particularly high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected. By introducing auxiliary stretching, such as two-step stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water. It is possible to solve the problem that stretchability is reduced by stretching, and stretch the laminate at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying the PVA-based resin on a normal metal drum As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when the PVA-based resin is applied onto a thermoplastic resin substrate, thereby achieving high optical properties. It becomes possible. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing treatment or stretching treatment. , making it possible to achieve high optical properties.

The stretching method of the in-air auxiliary stretching may be fixed edge stretching (e.g., a method of stretching using a tenter stretching machine) or free edge stretching (e.g., a method of uniaxially stretching the laminate through rolls having different peripheral speeds). Although good, free-end drawing may be positively employed in order to obtain high optical properties. In one embodiment, the in-air stretching process includes a heating roll stretching step in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction. The air drawing process typically includes a zone drawing process and a hot roll drawing process. The order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be carried out first, or the heating roll stretching process may be carried out first. The zone drawing step may be omitted. In one embodiment, the zone drawing step and the heated roll drawing step are performed in this order. In another embodiment, the laminate is stretched by gripping the ends of the laminate and widening the distance between the tenters in the machine direction in a tenter stretching machine (the widening of the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close. Preferably, the draw ratio in the machine direction can be set to be closer to the free end draw. In the case of free end stretching, the shrinkage ratio in the width direction is calculated by (1/stretching ratio) ^1/2 .

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

The draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The maximum draw ratio when the auxiliary drawing in the air and the drawing in water are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times the original length of the laminate. That's it. As used herein, the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks.

The stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can. The crystallization index of the PVA-based resin after auxiliary stretching in air is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement is performed using polarized light as measurement light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm ⁻¹ and 1440 cm ⁻¹ of the obtained spectrum.
_{Crystallization} index = (IC/ _IR )
however,
I _C : Intensity at 1141 cm ⁻¹ when measurement light is incident and measured I _R : Intensity at 1440 cm ⁻¹ when measurement light is incident and measured.

A-1-1-3. Insolubilization Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C.

A-1-1-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is carried out by allowing the PVA-based resin layer to adsorb iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. A spraying method and the like can be mentioned. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.

The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the iodine aqueous solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc. Among these, potassium iodide is preferred. The amount of iodide compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the finally obtained unbleached raw film has a desired single transmittance. As for such dyeing conditions, it is preferable to use an iodine aqueous solution as a dyeing solution and to set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. As a result, an unbleached original film having optical properties as described below can be obtained.

When dyeing treatment is performed continuously after the treatment of immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration in the dyeing bath may change over time, resulting in unstable dyeability. In order to suppress the destabilization of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. adjusted. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. is. In one embodiment, the dyeing process is performed using a dyeing bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. , more preferably 0.5 to 1.5 parts by weight.

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

A-1-1-6. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, an unbleached original film having excellent optical properties can be produced.

Any appropriate method can be adopted as a method for stretching the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds) may be used. Free-end drawing is preferably chosen. The laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the product of the draw ratios in each step.

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

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

Preferably, an iodide is added to the drawing bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodides 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, per 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the film can be stretched at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater drawing is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high draw ratio, it is possible to produce an unbleached base film with extremely excellent optical properties. Such a high draw ratio can be achieved by adopting an underwater drawing method (boric acid solution drawing).

A-1-1-7. Drying Shrinkage Treatment In the drying shrinkage treatment, for example, a laminate of a long thermoplastic resin base material and a PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. In the drying shrinkage treatment, it is preferable to dry the PVA-based resin film until the moisture content becomes 15% by weight or less, and from the viewpoint of obtaining a stable appearance, the moisture content is preferably 12% by weight or less, and further preferably. It is preferred to dry to 10% by weight or less, even more preferably 1% to 5% by weight.

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress heat curling of the laminate and produce an unbleached original film with excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, which is relatively low. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.

FIG. 1 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate. The transport rolls R1 to R6 may be arranged so as to continuously heat only the plastic resin substrate surface).

The drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and the like. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The degree of crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as the number of transport rolls is plural. Conveying rolls are usually 2 to 40, preferably 4 to 30 in number. The contact time (total contact time) between the laminate and the heating roll is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, oven), or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature for hot air drying is preferably 20°C to 100°C. Moreover, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in the heating furnace and can be measured with a mini-vane digital anemometer.

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

The contact between the unbleached original film and the aqueous solvent in step II may be performed by contacting only one side of the unbleached original film with the aqueous solvent, or by contacting both sides with the aqueous solvent. . Therefore, in one embodiment, the unbleached original film produced using the laminate can be subjected to step II as it is as the laminate of [unbleached original film/thermoplastic resin substrate]. In another embodiment, a protective layer is attached to the surface of the unbleached original film of the laminate of [unbleached original film/thermoplastic resin substrate] to form [protective layer/unbleached original film/thermoplastic resin substrate]. Producing a laminate, peeling the thermoplastic resin substrate from the laminate to produce a laminate (polarizing plate) of [protective layer/unbleached original film], and subjecting the obtained laminate to step II. can be done. In yet another embodiment, any suitable function is provided on the substrate side of the laminate of [unbleached base film/thermoplastic resin substrate] or on the protective layer side of the laminate of [protective layer/unbleached base film]. A layer provided with a layer (retardation layer, pressure-sensitive adhesive layer, etc.) can also be subjected to step II.

A-1-2. Preparation of unbleached original film using single-layer PVA-based resin film ) A long PVA-based resin film is dyed and stretched (typically, uniaxially stretched using a roll stretcher in an aqueous boric acid solution), and then the moisture content is preferably 15% by weight or less, more preferably is 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight. The dyeing is performed by, for example, immersing the PVA-based resin film in an iodine aqueous solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the PVA-based resin film is subjected to swelling treatment, cross-linking treatment, washing treatment, and the like. For example, by immersing the PVA-based resin film in water and washing it with water before dyeing, it is possible not only to wash away stains and anti-blocking agents on the surface of the PVA-based resin film, but also to swell the PVA-based resin film for dyeing. Unevenness and the like can be prevented.

As described above, the contact between the unbleached original film and the aqueous solvent in step II may be performed by contacting only one surface of the unbleached original film with the aqueous solvent, or by contacting both surfaces with the aqueous solvent. may be broken. Therefore, in one embodiment, the unbleached original film produced using the single-layer PVA-based resin film can be subjected to step II as it is. In another embodiment, a protective layer is attached to one side of the unbleached original film to prepare a laminate of [protective layer/unbleached original film], and the laminate can be subjected to step II. In yet another embodiment, the laminate of [protective layer/unbleached original film] provided with any suitable functional layer (retardation layer, adhesive layer, etc.) on the protective layer side is subjected to step II. can also

A-2. Process II
In step II, the surface of the PVA-based resin film (unbleached original film) that has undergone step I is brought into contact with an aqueous solvent. Upon contact with an aqueous solvent, polyiodine ions forming I ⁻ , I ₂ , I ₃ ^- and PVA-I ₃ ^-complexes preferentially over polyiodine ions forming PVA-I ₅ ^-complexes to the unbleached original. As a result of elution from the film and a greater increase in the transmittance on the short wavelength side, the transmittance increase rate (ΔTs(λ)) at the wavelength λnm satisfies the relationship ΔTs (415) > ΔTs (470) > ΔTs (550) can satisfy

Any appropriate solvent can be used as the aqueous solvent as long as it can elute the dichroic substance (typically iodine) from the unbleached original film. The aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent. Preferred examples of the water-soluble organic solvent include lower monoalcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol, and polyhydric alcohols such as glycerin and ethylene glycol.

The method of contact with the aqueous solvent is not particularly limited, and any appropriate method such as immersion, spraying, or coating can be used. Immersion is preferred from the viewpoint of bringing the entire surface of the unbleached original film into contact with the aqueous solvent uniformly.

The contact time with the aqueous solvent and the temperature of the aqueous solvent during contact can be appropriately set according to desired Ts ₄₁₅ , Ts ₄₇₀ and Ts ₅₅₀ and the like. Increasing the contact time or increasing the temperature of the aqueous solvent tends to increase the transmittance (particularly Ts ₄₁₅ ). The contact time can be, for example, 10 minutes or less, preferably 60 seconds to 9 minutes, more preferably 60 seconds to 4 minutes. The temperature of the aqueous solvent can be preferably 20°C to 70°C, more preferably 30°C to 65°C, even more preferably 40°C to 60°C.

If necessary, drying treatment may be performed after contact with the aqueous solvent. The drying temperature can be, for example, 20°C to 100°C, preferably 30°C to 80°C. The moisture content of the dried polarizing film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% to 5% by weight. is.

B. Polarizing film The polarizing film obtained by the method for producing a polarizing film described in Section A is composed of a PVA-based resin film containing a dichroic substance (typically iodine), and has a wavelength range of at least 415 nm to 550 nm. It has a higher transmittance than the original bleaching film. Specifically, the transmittance increase rate (ΔTs(λ)) at the wavelength λnm satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550). The transmittance increase rate (ΔTs(415)) at a wavelength of 415 nm exceeds, for example, 1.05, preferably 1.1 or more, and more preferably 1.10 to 2.2. If ΔTs(415) is within this range, it is possible to reduce the amount of blue light emission that consumes a large amount of power, thereby contributing to energy saving of the organic EL display device.

The Ts ₄₁₅ and Ts ₅₅₀ of the polarizing film can be any suitable value depending on the purpose. Ts ₄₁₅ can be, for example, 40% or more, preferably 41% or more, more preferably 42% or more, and can be, for example, 80% or less, preferably 60% or less, more preferably 50% or less. Also, Ts ₅₅₀ may be, for example, 40% or more, preferably 42% or more, more preferably 43% or more, and may be, for example, 70% or less, preferably 60% or less, more preferably 50% or less.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The transmittance of the polarizing film (single transmittance: Ts) is preferably 41% or more, more preferably 42% or more, and still more preferably 42.5% or more. On the other hand, the transmittance of the polarizing film is, for example, 65% or less, preferably 50% or less, more preferably 48% or less. Further, the polarization degree of the polarizing film is, for example, 40.0% or more, preferably 90.0% or more, more preferably 94.0% or more, still more preferably 96.0% or more, and still more It is preferably 99.0% or more, still more preferably 99.5% or more, and preferably 99.998% or less. The above transmittance and degree of polarization are obtained in the same manner as the transmittance and degree of polarization of the unbleached original film.

The haze of the polarizing film is preferably 1% or less, more preferably 0.8% or less, still more preferably 0.6% or less. If the haze is within this range, an organic EL display device with a high contrast ratio can be obtained.

The iodine concentration in the polarizing film is preferably 3% by weight or more, more preferably 4% to 10% by weight, and more preferably 4% to 8% by weight. In this specification, "iodine concentration" means the total amount of iodine contained in the polarizing film. More specifically, iodine exists in the form of I ⁻ , I ₂ , I ₃ ⁻ , PVA-I ₃ ^-complex , PVA-I ₅ ^-complex , etc. in the polarizing film. , means the concentration of iodine including all these forms. The iodine concentration can be calculated, for example, from the fluorescent X-ray intensity and film (polarizing film) thickness obtained by fluorescent X-ray analysis.

The thickness of the polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, even more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.
(1) Thickness Measured using the product name “Linear Gauge MODEL D-10HS” (manufactured by Ozaki Seisakusho).
(2) Individual Transmittance and Degree of Polarization For laminates of PVA-based resin films (polarizing films or unbleached original films) and protective layers obtained in Examples and Comparative Examples, ultraviolet-visible spectroscopy was performed from the PVA-based resin film side. Single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using a photometer (“LPF-200” manufactured by Otsuka Electronics Co., Ltd.) were defined as Ts, Tp, and Tc of the PVA-based resin film, respectively. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction. The refractive index of the protective layer was 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
Also, the measured Ts at wavelengths of 415 nm, 470 nm and 550 nm were defined as Ts ₄₁₅ , Ts ₄₇₀ and Ts ₅₅₀ , respectively.
Equivalent measurement can be performed with a spectrophotometer such as "V-7100" manufactured by JASCO Corporation, and equivalent measurement results can be obtained using any spectrophotometer. has been confirmed.
(3) Moisture content The unbleached raw film immediately after drying (when the laminate is stretched, the stretched substrate is peeled off) is cut into a size of 100 mm × 100 mm or more, and the weight before processing is measured with an electronic balance. . After that, it was placed in a heating oven maintained at 120° C. for 2 hours, the weight after removal (weight after treatment) was measured, and the moisture content was determined by the following formula.
Moisture content [%] = (weight before treatment - weight after treatment) / weight before treatment x 100
(4) Haze Measured according to JISK7136 using a product name "Haze meter (NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[Example 1-1]
1. Preparation of polarizing film and polarizing plate A long roll of PVA-based resin film (manufactured by Kuraray, product name "PE3000") having a thickness of 30 µm was stretched 2.2 times in the transport direction while being immersed in a water bath at 30°C. While immersed in an aqueous solution of 0.04% by weight of iodine and 0.3% by weight of potassium at 30° C. for dyeing, the film was stretched 3 times with respect to the unstretched film (original length). Next, while immersing this stretched film in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide at 30° C., the stretched film is further stretched to 3.3 times its original length. While immersed in a 60°C aqueous solution with a concentration of 4% by weight and a concentration of potassium iodide of 5% by weight, it is further stretched to 6 times its original length, and finally dried in an oven maintained at 60°C for 5 minutes. Thus, a polarizing film (unbleached original film a1) having a thickness of 12 μm was produced. The obtained unbleached original film a1 had a moisture content of 10.0% by weight and a single transmittance of 42.5%.

A PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOSEFIMER (registered trademark) Z-200”, resin concentration: 3% by weight) was applied to one side of the obtained unbleached raw film a1. An olefin film (Zeonor, manufactured by Nippon Zeon Co., Ltd., thickness: 25 μm) was laminated to obtain an optical laminate having a structure of [unbleached original film a1/protective layer]. As the protective layer, a protective layer provided with a hard coat layer may be used. As such a protective layer, for example, a cycloolefin film with a hard coat layer (manufactured by ZEON, product name "G-Film , total thickness of 27 μm (film thickness of 25 μm+hard coat layer thickness of 2 μm), and the like.

The above optical layered body was cut into a size of 45 mm × 50 mm and attached to a glass plate via an acrylic pressure-sensitive adhesive layer (thickness 15 µm) so that the unbleached base film side surface was exposed. was immersed in for 31 hours. Then, by drying at 50° C. for 5 minutes, a polarizing plate having a structure of [polarizing film A1/protective layer] was obtained.

[Example 1-2]
A polarizing plate having a structure of [polarizing film A2/protective layer] was obtained in the same manner as in Example 1-1, except that instead of immersing in water at 23° C. for 31 hours, it was immersed in water at 55° C. for 9 minutes. rice field.

[Example 1-3]
A polarizing plate having a structure of [polarizing film A3/protective layer] was obtained in the same manner as in Example 1-1, except that instead of immersing in water at 23° C. for 31 hours, it was immersed in water at 60° C. for 4 minutes. rice field.

[Example 1-4]
A polarizing plate having a structure of [polarizing film A4/protective layer] was obtained in the same manner as in Example 1-1, except that instead of immersing in water at 23° C. for 31 hours, it was immersed in water at 65° C. for 3 minutes. rice field.

[Comparative Example 1]
An optical laminate having a structure of [unbleached original film a1/protective layer] prepared in the same manner as in Example 1-1 was used as a polarizing plate.

[Example 2-1]
A long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to corona treatment.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER") were mixed at a ratio of 9:1, and 100 parts by weight of PVA-based resin. was added with 13 parts by weight of potassium iodide and dissolved in water to prepare an aqueous PVA solution (coating solution).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the finally obtained polarizing plate was placed in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 42.3% (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., the laminate was moved vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
Thereafter, while drying in an oven maintained at about 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75° C. (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 2%.
In this way, an unbleached original film having a moisture content of 4.5% and a thickness of 5 μm was formed on the resin substrate, and a cycloolefin film (Zeonor, manufactured by Nippon Zeon Co., Ltd.) was formed on the surface of the unbleached original film. thickness: 25 μm) were bonded together with a UV curable adhesive (thickness: 1.0 μm), and then the resin substrate was peeled off to obtain an optical laminate having a structure of [unbleached base film b1/protective layer].

The above optical layered body was cut into a size of 45 mm × 50 mm, and attached to a glass plate so that the unbleached original film side surface became an exposed surface via an acrylic pressure-sensitive adhesive layer (thickness 15 μm). for 9 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate having a structure of [polarizing film B1/protective layer] was obtained.

[Example 2-2]
A polarizing plate having a structure of [polarizing film B2/protective layer] was obtained in the same manner as in Example 2-1, except that instead of immersing in water at 50°C for 9 minutes, it was immersed in water at 55°C for 3 minutes. rice field.

[Example 2-3]
A polarizing plate having a structure of [polarizing film B3/protective layer] was obtained in the same manner as in Example 2-1, except that instead of immersing in water at 50°C for 9 minutes, it was immersed in water at 60°C for 2 minutes. rice field.

[Example 2-4]
A polarizing plate having a structure of [polarizing film B4/protective layer] was obtained in the same manner as in Example 2-1, except that instead of immersing in water at 50°C for 9 minutes, it was immersed in water at 60°C for 3 minutes. rice field.

[Comparative Example 2]
An optical laminate having a structure of [unbleached original film b1/protective layer] prepared in the same manner as in Example 2-1 was used as a polarizing plate.

Various properties of the unbleached original films and the polarizing films obtained in the above Examples and Comparative Examples were evaluated. Table 1 shows the results.

As can be seen from Table 1, according to the production method of the example, before and after contact with water, the transmittance increase rate (ΔTs (λ)) of the PVA-based resin film at the wavelength λnm is ΔTs (415) > ΔTs (470 )>ΔTs(550), and the rate of increase in transmittance at a wavelength of 415 nm is large. The polarizing film obtained by such a manufacturing method has practically acceptable optical properties (typically, single transmittance and degree of polarization) and has an increased transmittance for short-wavelength light. there is

The polarizing film of the present invention can be suitably used in image display devices such as liquid crystal display devices and EL display devices, particularly organic EL display devices.

Claims (6)

subjecting the polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment, and bringing the surface of the polyvinyl alcohol-based resin film into contact with an aqueous solvent in this order,
The ratio of the transmittance after contact to the transmittance of the polyvinyl alcohol resin film before contact with the aqueous solvent at a wavelength of λ nm (ΔTs (λ)) is ΔTs (415) > ΔTs (470) > ΔTs (550) A method for manufacturing a polarizing film that satisfies the relationship of The production method according to claim 1, wherein the temperature of the aqueous solvent is 20°C to 70°C. 3. The production method according to claim 1, wherein the polyvinyl alcohol resin film with which the aqueous solvent is brought into contact has a moisture content of 15% by weight or less. 4. The manufacturing method according to any one of claims 2 and 3, wherein the polyvinyl alcohol-based resin film with which the aqueous solvent is brought into contact has a thickness of 12 [mu]m or less. subjecting the polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment,
Forming a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and
The laminate is subjected to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while being conveyed in the longitudinal direction, in this order. , The manufacturing method according to any one of claims 1 to 4. 6. The manufacturing method according to any one of claims 1 to 5, which is a method for manufacturing a polarizing film having a haze of 1% or less.

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