KR20230129451A - Method of manufacturing polarizing film - Google Patents

Abstract

The present invention includes subjecting a polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment, and contacting the surface of the polyvinyl alcohol-based resin film with an aqueous solvent in this order, and the aqueous solvent and the aqueous solvent at a wavelength λ nm. The ratio of the transmittance after contact to the transmittance of the polyvinyl alcohol-based resin film before contact (ΔTs(λ)) satisfies the relationship of ΔTs (415) > ΔTs (470) > ΔTs (550). provides.

Description

Method of manufacturing polarizing film

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

In recent years, image display devices represented by liquid crystal displays and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices) are rapidly becoming popular. In an organic EL display device, it is known to prevent problems such as external light reflection and background reflection by disposing a circularly polarizing plate including a λ/4 plate on the viewing side of the organic EL cell (e.g., Patent Documents 1 and 2). .

On the other hand, organic EL display devices require large power consumption for light emission, so energy saving is required.

Japanese Patent Publication No. 2002-311239 Japanese Patent Publication No. 2002-372622

The present invention was made to solve the above-described conventional problems, and its main purpose is to provide a polarizing film capable of reducing 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 contacting the surface of the polyvinyl alcohol-based resin film with an aqueous solvent in this order, at a wavelength λ nm. The ratio of the transmittance after contact (ΔTs (λ)) to the transmittance of the polyvinyl alcohol-based resin film before contact with the aqueous solvent satisfies the relationship of ΔTs (415) > ΔTs (470) > ΔTs (550). A method of making a membrane is provided.

In one embodiment, the temperature of the aqueous solvent is between 20°C and 70°C.

In one embodiment, the moisture content of the polyvinyl alcohol-based resin film in contact with the aqueous solvent is 15% by weight or less.

In one embodiment, the thickness of the polyvinyl alcohol-based resin film in contact with the aqueous solvent is 12 μm or less.

In one embodiment, subjecting the polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment forms a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate. This includes forming a laminate into a laminate, and subjecting the laminate to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrink treatment to shrink the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction, in this order. do.

In one embodiment, the manufacturing method is a manufacturing method of a polarizing film having a haze of 1% or less.

According to the method for manufacturing a polarizing film according to an embodiment of the present invention, a polyvinyl alcohol (PVA)-based resin film that has undergone dyeing and stretching treatment is subjected to contact treatment with an aqueous solvent. As a result, the transmittance of the PVA-based resin film in the wavelength range of at least 415 nm to 550 nm increases, 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) = after contact) Ts(λ)/Ts(λ) before contact (hereinafter, ΔTs(λ) may be referred to as ‘rate of increase in transmittance’) satisfies the relationship of ΔTs(415)>ΔTs(470)>ΔTs(550). do. A polarizing film obtained by such a manufacturing method can transmit light on the short wavelength side more actively than light on the long wavelength side. Therefore, by using such a polarizing film, even when the amount of blue light emission, which consumes large power, is reduced, a decrease in luminance in the short wavelength region can be suppressed, resulting in energy saving and high performance of the organic EL display device. Compatibility of luminance becomes possible.

1 is a schematic diagram showing an example of dry shrinkage treatment using a heating roll.

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

A. Method of manufacturing polarizing film

The method for producing a polarizing film according to an embodiment of the present invention includes subjecting a polyvinyl alcohol (PVA)-based resin film to dyeing treatment and stretching treatment (step I), and contacting the surface of the PVA-based resin film with an aqueous solvent. (Step II) in this order, and the ratio (ΔTs (λ)) of the transmittance after contact to the transmittance of the polyvinyl alcohol-based resin film before contact with the aqueous solvent at a wavelength λ nm is ΔTs (415)> It satisfies the relationship of ΔTs(470)>ΔTs(550). In the PVA-based resin film after dyeing, iodine is in the form of I ^- , I ₂ , I ₃ ^- , PVA-I ₃ ^- complex, PVA-I ₅ ^- complex, etc. As it exists, I ^- , I ₂ and I ₃ ^- have absorption in the ultraviolet region (e.g., around a wavelength of 290 nm to 360 nm), and the PVA-I ₃ ^- complex and PVA-I ₅ ^- complex each have a wavelength around 470 nm. and wavelength 600nm There is absorption in the vicinity. Therefore, the relationship of ΔTs (415) > ΔTs (470) > ΔTs (550) before and after contact with an aqueous solvent is established for the total iodine present in the PVA-based resin film: I ^- , I ₂ , I ₃ ^- And it is thought to indicate that the proportion occupied by the PVA-I ₃ ^- complex decreased (in other words, the proportion occupied by the PVA-I ₅ ^- complex increased).

A-1. Process I

In process I, the PVA-based resin film is subjected to dyeing treatment and stretching treatment, thereby producing a PVA-based resin film (hereinafter referred to as 'non-discolored raw film') that exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. (sometimes called) is obtained. The non-discolored original film is typically in a state in which it can function as a polarizing film.

In one embodiment, the transmittance (single transmittance: Ts) of the undiscolored raw film is preferably 41.0% or more, more preferably 42.0% or more, and even more preferably 42.5% or more. On the other hand, the transmittance of the unbleached original film is preferably 46.0% or less, more preferably 45.0% or less. The polarization degree of the undiscolored raw film is preferably 98.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. Meanwhile, the polarization degree of the undiscolored raw 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. Typically, the degree of polarization can be obtained by the following equation based on the parallel transmittance (Tp) and orthogonal transmittance (Tc) measured using an ultraviolet/visible spectrophotometer and subjected to visibility correction.

Polarization degree (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film (uncolored raw film) of 12 μm or less is typically a laminate of a polarizing film (surface refractive index: 1.53) and a protective layer (refractive index: 1.50). It is measured using an ultraviolet/visible spectrophotometer, using the body as the measurement object. Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the surface in contact with the air interface of the protective layer, the reflectance at the interface of each layer changes, and as a result, the measured transmittance may change. Therefore, for example, when using a protective layer with a refractive index other than 1.50, the measured transmittance may be corrected according to the refractive index of the surface in contact with the air interface of the protective layer. Specifically, the correction value C of the transmittance is expressed by the following equation 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 It is the transmission axis reflectance when a protective layer with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer used, and T ₁ is the transmittance of the polarizing film. For example, when a base material (cycloolefin-based film, film with a hard coat layer, etc.) with a surface refractive index of 1.53 is used as a protective layer, the correction amount C is approximately 0.2%. In this case, by adding 0.2% to the transmittance obtained by measurement, it is possible to convert the polarizing film with a surface refractive index of 1.53 to the transmittance when using a protective layer with a refractive index of 1.50. In addition, according to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T ₁ of the polarizing film is changed by 2% is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. Additionally, when the protective layer has absorption other than surface reflection, appropriate correction can be made depending on the amount of absorption.

The transmittance (Ts ₄₁₅ ) of the undiscolored raw film at a wavelength of 415 nm may be, for example, less than 40%.

The water 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, still more preferably 1% to 5% by weight. If the moisture content of the undiscolored raw film is within the corresponding range, dissolution, wrinkling, etc. can be prevented upon contact with the aqueous solvent in step II.

The thickness of the undiscolored raw film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, further preferably 1 μm to 7 μm, and even more preferably 2 μm or less. It is ㎛~5㎛.

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, thereby producing an undiscolored original film. An unbleached original film produced using a laminate of two or more layers can appropriately maintain excellent optical properties (typically, single transmittance and polarization degree) while avoiding wrinkles and the like even after contact with an aqueous solvent. there is.

A-1-1. Production of non-discolored raw film using a two-layer or more laminate

The production of a non-discolored raw film using a two-layer or more laminate is, for example, performed by subjecting a PVA-based resin film containing a halide and a PVA-based resin to dyeing and stretching treatments in the form of a laminate with a long thermoplastic resin substrate. You can. Specifically, the uncolored raw film is formed 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 to form a laminate, and forming the laminate with an air gap. It can be produced by a method that includes performing an auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrink treatment in which the material is shrunk by 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The dry shrink treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction due to drying shrinkage treatment is preferably 2% or more. According to this manufacturing method, a non-discolored raw film with a high degree of orientation of the PVA-based resin and excellent optical properties can be obtained.

A-1-1-1. Fabrication of laminates

Arbitrary suitable methods can be adopted as a method of producing the laminated body of a thermoplastic resin base material and a PVA system resin layer. Preferably, a PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying it. As described above, the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

As a method of applying the coating liquid, any suitable method can be adopted. For example, roll coat method, spin coat method, wire bar coat method, dip coat method, die coat method, curtain coat method, spray coat method, knife coat method (comma coat method, etc.), etc. The application/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 subjected to surface treatment (e.g., corona treatment, etc.), and an easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA system resin layer can be improved.

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

The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, and more preferably 0.3% or more. A thermoplastic resin substrate can be plasticized by absorbing water and the water acting as a plasticizer. As a result, stretching stress can be significantly reduced and stretching can be performed at a high magnification. Meanwhile, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as significantly deteriorating the dimensional stability of the thermoplastic resin base material during production and deterioration in the appearance of the obtained unbleached original film. In addition, it is possible to prevent breakage of the substrate during stretching in water or peeling of the PVA-based resin layer from the thermoplastic resin substrate. Additionally, the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifier into the constituent material. The water absorption rate is a value obtained in accordance with JIS K 7209.

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 crystallization of the PVA-based resin layer. In addition, considering plasticization of the thermoplastic resin base material with water and satisfactory stretching in water, the temperature is more preferably 100°C or lower, and more preferably 90°C or lower. Meanwhile, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin base material, problems such as deformation of the thermoplastic resin base material (e.g., occurrence of unevenness, sagging, wrinkles, etc.) when applying and drying the coating liquid containing the PVA-based resin are prevented, A laminate can be produced satisfactorily. Additionally, stretching of the PVA-based resin layer can be favorably performed at an appropriate temperature (for example, about 60°C). Additionally, the glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a denaturing group into the constituent material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

As a constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be employed. As the thermoplastic resin, for example, ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof etc. can be mentioned. Among these, norbornene-type resin and amorphous polyethylene terephthalate-type resin are preferable.

In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate-based resin is preferably used. Among them, amorphous (hard to crystallize) polyethylene terephthalate-based resins are particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acid, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycol. there is.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate-based resin having isophthalic acid units. This is because such thermoplastic resin substrates have extremely excellent stretchability and crystallization during stretching can be suppressed. This is thought to be due to imparting a large bend to the main chain by introducing an isophthalic acid unit. Polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The content of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more with respect to the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent stretchability is obtained. On the other hand, the content of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less with respect to the total of all repeating units. By setting 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 a long thermoplastic resin base material. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate, which will be described later. Additionally, in this specification, 'orthogonal' also includes cases of substantially orthogonal. Here, 'substantially orthogonal' includes the case of 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 relative to the glass transition temperature (Tg). The stretch ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

As a method for stretching the thermoplastic resin substrate, any suitable method may be employed. Specifically, fixed-end stretching may be used or free-end stretching may be used. The stretching method may be dry or wet. Stretching of the thermoplastic resin substrate may be performed in one step or may be performed in multiple steps. When carried out in multiple steps, the above-mentioned draw ratio is the product of the draw ratios of each step.

As described above, the coating liquid contains a halide and a PVA-based resin. The coating liquid is typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. I can hear it. These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhering to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight based on 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 the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

As the PVA-based resin, any suitable resin may be employed. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be calculated according to JIS K 6726-1994. By using a PVA-based resin with such a degree of saponification, a non-discolored raw film with excellent durability can be obtained. If the degree of saponification is too high, there is a risk of gelation.

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 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

As the halide, any suitable halide can be employed. Examples include iodide and sodium chloride. As iodide, potassium iodide, sodium iodide, and lithium iodide are mentioned, for example. Among these, potassium iodide is preferable.

The amount of halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA-based resin, and more preferably 10 parts by weight to 15 parts by weight based on 100 parts by weight of the PVA-based resin. am. If the amount of the halide with respect to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out and the final 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, but when the stretched PVA-based resin layer is immersed in a water-containing liquid, the orientation of the polyvinyl alcohol molecules increases. It may be disturbed and the orientation may deteriorate. In particular, when the laminate of the thermoplastic resin substrate and the PVA-based resin layer is stretched in boric acid, the orientation degree tends to decrease when the laminate is stretched in boric acid at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate. This is remarkable. For example, while stretching of a PVA film alone in boric acid is generally performed at 60°C, stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of around 70°C. In this case, the orientation of PVA at the beginning of stretching may decrease in the stage before it increases by underwater stretching. In contrast, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base is produced, and the laminate is stretched at high temperature in air (auxiliary stretching) before stretching in boric acid water, so that the PVA-based laminate after auxiliary stretching is obtained. Crystallization of the PVA-based resin in the resin layer can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disruption of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. As a result, the optical properties of the undiscolored raw film obtained through treatment processes such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid can be improved.

A-1-1-2. Aerial assisted stretching treatment

In particular, in order to obtain high optical properties, a two-step stretching method is selected, combining dry stretching (auxiliary stretching) and boric acid underwater stretching. By introducing auxiliary stretching, such as two-stage stretching, stretching can be achieved while suppressing crystallization of the thermoplastic resin base, and the problem of excessive crystallization of the thermoplastic resin base during subsequent stretching in boric acid water is solved to reduce stretchability, thereby solving the problem of lamination. The sieve can be stretched at a higher magnification. Furthermore, when applying PVA-based resin on a thermoplastic resin substrate, the application temperature needs to be lowered compared to when applying PVA-based resin on a typical metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate. As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause the problem of not being able to obtain sufficient optical properties. In contrast, by introducing auxiliary stretching, even when applying PVA-based resin on a thermoplastic resin substrate, it becomes possible to increase the crystallinity of the PVA-based resin and achieve high optical properties. Moreover, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in the orientation or dissolution of the PVA-based resin when immersed in water during the subsequent dyeing or stretching treatment, thereby maintaining high optical properties. It becomes possible to achieve

The stretching method for aerial auxiliary stretching may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxial stretching by passing the laminate between rolls with different circumferential speeds). This may be possible, but in order to obtain high optical properties, free end stretching can be actively employed. In one embodiment, the air stretching process includes a heating roll stretching process in which the laminate is stretched by a difference in peripheral speed between heating rolls while conveying the laminate in its longitudinal direction. The air stretching process typically includes a zone stretching process and a heated roll stretching process. Additionally, the order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be performed first, or the heating roll stretching process may be performed first. The zone stretching process may be omitted. In one embodiment, the zone stretching process and the heated roll stretching process are performed in this order. Furthermore, in another embodiment, the end portion of the laminate is held in a tenter stretching machine and stretched by expanding the distance between the tenters in the flow direction (the expansion of the distance between the tenters becomes the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to be arbitrarily close. Preferably, the stretch ratio in the flow direction can be set to be closer to free end stretching. In the case of free end stretching, the shrinkage rate in the width direction is calculated as = (1/stretch ratio) ^1/2 .

Air assisted stretching may be performed in one step or may be performed in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in aerial assisted stretching is preferably approximately the same as the stretching direction in underwater stretching.

The draw ratio in aerial assisted stretching is preferably 2.0 times to 3.5 times. The maximum draw ratio when combining aerial auxiliary stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more relative to the original length of the laminate. In this specification, 'maximum draw ratio' refers to the draw ratio just before the laminated body breaks. Separately, the draw ratio at which the laminated body breaks is confirmed and is 0.2 lower than that value.

The stretching temperature for air-assisted stretching can be set to any appropriate value depending on the forming material of the thermoplastic resin base material, stretching method, etc. The stretching temperature is preferably higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably higher than the glass transition temperature (Tg) of the thermoplastic resin substrate +10°C or higher, and particularly preferably higher than Tg+15°C. On the other hand, the upper limit of stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, and problems caused by the crystallization (for example, interference with the orientation of the PVA-based resin layer due to stretching) can be suppressed. The crystallization index of the PVA-based resin after aerial auxiliary stretching is preferably 1.3 to 1.8, and more preferably 1.4 to 1.7. The crystallization index of PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement is performed using polarized light as the measurement light, and the crystallization index is calculated according to the following formula using the intensities of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.

Crystallization index=(I _C /I _R )

step,

I _C : Intensity of 1141cm ^-1 when measured by incident measurement light

_IR : Intensity of 1440cm ^-1 when measured by incident measurement light

am.

A-1-1-3. Insolubilization treatment

If necessary, insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing insolubilization treatment, water resistance can be imparted to the PVA-based resin layer and the orientation of PVA can be prevented from decreasing when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight based on 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, this is carried out by adsorbing iodine on the PVA-based resin layer. As the adsorption method, for example, a method of immersing the PVA-based resin layer (laminated body) in a dyeing solution containing iodine, a method of coating the dyeing solution on the PVA-based resin layer, and spraying the dyeing solution on the PVA-based resin layer. How to do it, etc. Preferably, it is the method of immersing a layered product in a dyeing solution (dyeing bath). This is because iodine can adsorb satisfactorily.

The dyeing solution is preferably an aqueous iodine solution. The amount of iodine mixed 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 iodide to the iodine aqueous solution. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.3 part by weight to 5 parts by weight, based on 100 parts by weight of water. The liquid temperature during dyeing of the dyeing solution is preferably 20°C to 50°C in order to suppress dissolution of the PVA-based resin. When immersing the PVA-based resin layer in the dye 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.

Dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained unbleached raw film becomes a desired value. As such dyeing conditions, preferably, an iodine aqueous solution is used as the dyeing solution, and the iodine aqueous solution and the potassium iodide content ratio are set to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. As a result, a non-discolored raw film having optical properties as described later can be obtained.

When dyeing treatment is performed continuously after a treatment of immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath mixes into the dyeing bath, causing the boric acid concentration of the dyeing bath to increase. It may change over time, and as a result, dyeing properties may become unstable. In order to suppress the destabilization of dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is adjusted to be preferably 4 parts by weight, more preferably 2 parts by weight, based on 100 parts by weight of water. On the other hand, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and still more preferably 0.5 part by weight, based on 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath in which boric acid is previously mixed. As a result, the rate of change in boric acid concentration when boric acid from the treatment bath is mixed into the dyeing bath can be reduced. The amount of boric acid mixed in advance in the dyeing bath (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 parts by weight, based on 100 parts by weight of water. It is 1.5 parts by weight.

A-1-1-5. Cross-linking treatment

If necessary, crosslinking treatment is performed after dyeing treatment and before underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and in subsequent underwater stretching, it is possible to prevent a decrease in the orientation of PVA when immersed in high-temperature water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight based on 100 parts by weight of water. In addition, when crosslinking treatment is performed after the dyeing treatment, it is preferable to additionally add iodide. By mixing iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide to be added is preferably 1 part by weight to 5 parts by weight based on 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

A-1-1-6. Underwater stretching treatment

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically, about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched at a high magnification rate while suppressing its crystallization. It can be stretched. As a result, a non-discolored raw film with excellent optical properties can be manufactured.

Arbitrary appropriate methods can be adopted as the method of stretching the laminate. Specifically, fixed-end stretching may be used, or free-end stretching may be used (for example, a method of uniaxial stretching by passing the laminate between rolls with different circumferential speeds). Preferably, free end stretching is selected. Stretching of the laminate may be performed in one step or may be performed in multiple steps. When carried out in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of each step.

Stretching in water is preferably performed by immersing the layered product in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water can be imparted to the PVA-based resin layer. Specifically, boric acid can generate tetrahydroxyboric acid anion in an aqueous solution and cross-link it with PVA-based resin through hydrogen bonding. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer, allow it to be stretched satisfactorily, and produce a non-bleaching original film having excellent optical properties.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water, which is 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, based on 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a non-discolored raw film with higher characteristics can be produced. Additionally, in addition to boric acid or borate salts, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

Preferably, iodide is added to the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight, based on 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, it can be extended 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, there is a risk that satisfactory stretching may not be possible even considering plasticization of the thermoplastic resin base material by water. On the other hand, as the temperature of the stretching bath becomes higher, the solubility of the PVA-based resin layer increases, and there is a risk that excellent optical properties may not be obtained. The immersion time for the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater stretching is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretch 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 such a high draw ratio, it is possible to produce a non-discolored raw film with excellent optical properties. Such a high draw ratio can be achieved by employing an underwater stretching method (boric acid underwater stretching).

A-1-1-7. Dry shrink treatment

In the dry shrinkage treatment, for example, a laminate of a long thermoplastic resin substrate and a PVA-based resin film is heated while conveyed 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 is 15% by weight or less. From the viewpoint of obtaining a stable appearance, the moisture content is more preferably 12% by weight or less, and even more preferably 10% by weight. % or less, more preferably 1% to 5% by weight.

The drying shrink treatment may be performed by zone heating by heating the entire zone, or it may be performed by heating the conveyance roll (using a so-called heating roll) (heat roll drying method). Preferably, both sides are used. By drying using a heating roll, heating curl of the laminate can be efficiently suppressed, and a non-discolored raw film with excellent appearance can be produced. Specifically, by drying the laminate while pouring it over a heating roll, crystallization of the thermoplastic resin substrate can be efficiently promoted and the degree of crystallinity can be increased, and even at a relatively low drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. You can do it. As a result, the rigidity of the thermoplastic resin substrate increases, and it becomes able to withstand shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Additionally, by using a heating roll, the laminate can be dried while maintaining it in a flat state, thereby suppressing not only curl but also wrinkles. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction through dry shrinkage treatment. This is because the orientation of PVA and PVA/iodine complex can be effectively increased. The shrinkage rate 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 a heating roll, the laminated body can be continuously shrunk in the width direction while being transported, and high productivity can be realized.

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

Drying conditions can be controlled by adjusting the heating temperature of the conveyance rolls (temperature of the heating rolls), the number of heating rolls, and the contact time with the heating rolls. 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. While the crystallinity of the thermoplastic resin can be increased satisfactorily and curling can be suppressed satisfactorily, an optical laminate having extremely excellent durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. In the illustrated example, although six conveyance rolls are provided, there is no particular restriction as long as there are a plurality of conveyance rolls. The conveyance rolls are usually provided in 2 to 40 pieces, preferably 4 to 30 pieces. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second 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, an oven) or may be provided in a normal manufacturing line (under a room temperature environment). Preferably, it is provided in a heating furnace provided with blowing means. By using heating roll drying and hot air drying together, rapid temperature changes between heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 20°C to 100°C. Additionally, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of hot air is preferably about 10 m/s to 30 m/s. In addition, the wind speed is the wind speed within the heating furnace, and can be measured using a minivane type digital anemometer.

A-1-1-8. Other processing

Preferably, the washing treatment is performed after the underwater stretching treatment and before the dry shrink treatment. The washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

The contact between the undiscolored raw film and the aqueous solvent in step II may be performed by contacting only one side of the undecolorized raw film with the aqueous solvent, or by contacting both sides with the aqueous solvent. Accordingly, in one embodiment, the undiscolored raw film produced using the above-mentioned laminate can be provided to process II as the laminate of [undiscolored raw film/thermoplastic resin base]. In another embodiment, a protective layer is bonded to the surface of the undiscolored raw film of the laminate of [non-discolored raw film/thermoplastic resin base] to produce a laminate of [protective layer/undiscolored raw film/thermoplastic resin base], and the laminate is From this, the thermoplastic resin substrate is peeled off to produce a laminate (polarizing plate) of [protective layer/unbleached original film], and the obtained laminate can be used in step II. In another embodiment, any suitable functional layer (phase difference layer, pressure sensitive adhesive layer, etc. ) can also be provided to process II.

A-1-2. Fabrication of unbleached original film using a single-layer PVA-based resin film

The production of a non-discolored raw film using a single-layer PVA-based resin film involves dyeing and stretching a long PVA-based resin film that is self-supporting (i.e., does not require support by a substrate) (typically in an aqueous solution of boric acid). uniaxial stretching using a roll stretching machine), and then the moisture content is preferably 15% by weight or less, more preferably 12% by weight or less, even more preferably 10% by weight or less, and even more preferably 1% by weight to 5% by weight. This can be done by drying to % by weight. The dyeing is performed, for example, by immersing the PVA-based resin film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment or may be performed while dyeing. Additionally, it may be dyed after stretching. If necessary, swelling treatment, cross-linking treatment, washing treatment, etc. are performed on the PVA-based resin film. For example, by immersing the PVA-based resin film in water and washing it before dyeing, not only can contamination and anti-blocking agents on the surface of the PVA-based resin film be removed, but also the PVA-based resin film can be swelled to prevent staining, etc.

As described above, the contact between the undiscolored raw film and the aqueous solvent in step II may be carried out by contacting only one side of the undiscolored raw film with the aqueous solvent, or by contacting both sides with the aqueous solvent. Therefore, in one embodiment, the non-discolored raw film produced using the single-layer PVA-based resin film can be directly submitted to Process II. In another embodiment, a protective layer is bonded to one side of an undiscolored raw film to produce a laminate of [protective layer/undiscolored raw film], and the laminate can be submitted to process II. In another embodiment, the laminate of [protective layer/non-discolored raw film] provided with any appropriate functional layer (phase contrast layer, adhesive layer, etc.) on the protective layer side may be subjected to process II.

A-2. Process II

In Step II, an aqueous solvent is brought into contact with the surface of the PVA-based resin film (non-discolored raw film) that has undergone Step I. By contact with an aqueous solvent, I ^- , I ₂ , I ₃ ^- and PVA-I ₃ ^- The polyiodine ion forming the complex is PVA-I ₅ ^- forming the complex. As a result of the polyiodine ions being eluted from the uncolored raw film preferentially, the transmittance on the short wavelength side increases more significantly, the rate of increase in transmittance (ΔTs(λ)) at the wavelength λnm is ΔTs(415)>ΔTs(470)>ΔTs. The relationship of (550) can be satisfied.

As the aqueous solvent, any suitable solvent can be used as long as it can elute the dichroic substance (typically iodine) from the unbleached original film. The aqueous solvent may be, for example, water or a mixture of water and a water-soluble organic solvent. 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 contact method with the aqueous solvent is not particularly limited, and any appropriate method such as immersion, spraying, and application may be used. Immersion is preferable from the viewpoint of uniformly contacting the entire surface of the unbleached raw film surface with the aqueous solvent.

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

You may perform a drying process after contact with an aqueous solvent as needed. The drying temperature may be, for example, 20 °C to 100 °C, preferably 30 °C to 80 °C. The moisture content of the polarizing film after drying is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, still more preferably 1% to 5% by weight.

B. Polarizer

The polarizing film obtained by the method for manufacturing the polarizing film described in paragraph A is composed of a PVA-based resin film containing a dichroic material (typically iodine), and has a higher transmittance than the undiscolored original film at least in the wavelength range of 415 nm to 550 nm. have Specifically, the rate of increase in transmittance (ΔTs(λ)) at the wavelength λnm satisfies the relationship of ΔTs(415)>ΔTs(470)>ΔTs(550). The increase rate of transmittance (ΔTs(415)) at a wavelength of 415 nm may exceed, for example, 1.05, preferably 1.1 or more, and more preferably 1.10 to 2.2. If ΔTs (415) is within the range, the amount of blue light emission, which consumes large power, can be reduced, contributing to energy saving of the organic EL display device.

Ts ₄₁₅ and Ts ₅₅₀ of the polarizing film may be any appropriate values depending on the purpose. Ts ₄₁₅ may be, for example, 40% or more, preferably 41% or more, more preferably 42% or more, and may also be, for example, 80% or less, preferably 60% or less, and more preferably 50% or less. In addition, Ts ₅₅₀ may be, for example, 40% or more, preferably 42% or more, more preferably 43% or more, and may also be, for example, 70% or less, preferably 60% or less, more preferably 50% or less. there is.

The polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance (single transmittance: Ts) of the polarizing film is preferably 41% or more, more preferably 42% or more, and even 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, and more preferably 48% or less. In addition, 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, even more preferably 96.0% or more, even more preferably 99.0% or more, and even more preferably 99.0% or more. Preferably it is 99.5% or more, and preferably is 99.998% or less. The transmittance and polarization degree are obtained in the same manner as the transmittance and polarization degree of an undiscolored raw 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% by weight to 10% by weight, and even more preferably 4% by weight to 8% by weight. In addition, in this specification, 'iodine concentration' means the amount of all iodine contained in the polarizing film. More specifically, in the polarizing film, iodine exists in the form of I ^- , I ₂ , I ₃ ^- , PVA-I ₃ ^- complex, PVA-I ₅ ^- complex, etc., and the iodine concentration in this specification is in these forms. It means the concentration of iodine including all. Iodine concentration can be calculated, for example, from fluorescence X-ray intensity and film (polarizing film) thickness by fluorescence 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, still more preferably 1 µm to 7 µm, still more preferably 2 µm to 12 µm. It is 5㎛.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. The measurement method for each characteristic is as follows. Additionally, unless otherwise specified, 'part' and '%' in Examples and Comparative Examples are based on weight.

(1) Thickness

Measurements were made using the product name 'Linear Gauge MODEL D-10HS' (manufactured by Ozaki Seisakusho).

(2) Group transmittance and polarization degree

For the laminate of the PVA-based resin film (polarizing film or non-discoloration original film) and the protective layer obtained in Examples and Comparative Examples, from the side of the PVA-based resin film, an ultraviolet/visible ray spectrophotometer (LPF-200 manufactured by Otsuka Electronics Co., Ltd.) The single transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) measured using ') were respectively used as Ts, Tp, and Tc of the PVA-based resin film. 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. Additionally, 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 polarization degree P was determined by the following formula.

Polarization degree P(%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

Additionally, the measured Ts at wavelengths of 415 nm, 470 nm, and 550 nm were set to Ts ₄₁₅ , Ts ₄₇₀ , and Ts ₅₅₀ , respectively.

In addition, as for the spectrophotometer, "V-7100" manufactured by Nippon Bunko Co., Ltd. can perform equivalent measurements, and it has been confirmed that equivalent measurement results can be obtained even when any spectrophotometer is used.

(3) moisture content

The non-discolored raw film immediately after the drying treatment (when stretched into a laminate, the stretched base material is peeled off) is cut into a size of 100 mm × 100 mm or more, and the weight before treatment is measured with an electronic balance. After that, it was placed in a heating oven maintained at 120°C for 2 hours, the weight after taking out (weight after treatment) was measured, and the moisture content was determined using the following formula.

Moisture rate [%] = (weight before treatment - weight after treatment) / weight before treatment × 100

(4) Haze

Measurements were made according to JISK7136 using a haze meter (NDH-5000) manufactured by Nippon Denshoku Kogyo Co., Ltd.

[Example 1-1]

1. Production of polarizing film and polarizing plate

A long roll of 30㎛ thick PVA-based resin film (manufactured by Kuraray, product name 'PE3000') was stretched 2.2 times in the conveyance direction while immersed in a water bath at 30°C, and then coated with 30% iodine concentration of 0.04% by weight and potassium concentration of 0.3% by weight. While dyeing by immersing in an aqueous solution at ℃, it was stretched three times based on the film (original length) that was not stretched at all. Next, this stretched film was further stretched to 3.3 times its original length while immersed in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide at 30°C, and then further stretched to 3.3 times the original length, and then immersed in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide. While immersed in a 5% by weight aqueous solution at 60°C, it was further stretched up to 6 times its original length, and finally dried in an oven maintained at 60°C for 5 minutes to form a polarizing film (non-discolored) with a thickness of 12㎛. The original membrane a1) was produced. The moisture content of the obtained undiscolored raw film a1 was 10.0% by weight, and the single transmittance was 42.5%.

A PVA-based resin aqueous solution (manufactured by Japan Synthetic Chemical Industry Co., Ltd., brand name 'Gosephimer (registered trademark) Z-200', resin concentration: 3% by weight) was applied to one side of the obtained undiscolored raw film (a1), and a cycloolefin-based film was formed. (Zeonor, manufactured by Japan Zeon Corporation, thickness: 25 μm) was bonded together to obtain an optical laminate having the structure of [non-discolored raw film a1/protective layer]. In addition, 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-based film with a hard coat layer (manufactured by ZEON, product name 'G-Film', total thickness 27 ㎛) (Film thickness 25㎛ + Hard coat layer thickness 2㎛)) etc. can be exemplified.

The optical layered body was cut into a size of 45 mm × 50 mm, and immersed in water at 23 ° C. for 31 hours in a state where it was bonded to a glass plate so that the surface on the non-discolored original film side was exposed through an acrylic pressure-sensitive adhesive layer (thickness of 15 μm). Next, a polarizing plate having the structure of [polarizing film A1/protective layer] was obtained by drying at 50°C for 5 minutes.

[Example 1-2]

A polarizing plate having the 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.

[Example 1-3]

A polarizing plate having the 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.

[Example 1-4]

Instead of being immersed in 23 ° C. water for 31 hours, a polarizing plate having a configuration of [Polarizing film A4 / protective layer] was obtained in the same manner as in Example 1-1 except that it was immersed in 65 ° C. water for 3 minutes.

[Comparative Example 1]

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

[Example 2-1]

As a thermoplastic resin substrate, an amorphous isophthalic copolymerization polyethylene terephthalate film (thickness: 100 μm), which is long and has a Tg of about 75°C, was used, and corona treatment was performed on one side of the resin substrate.

Polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name 'Gosephamer') were mixed in a ratio of 9:1 to 100 parts by weight of a PVA-based resin 13 parts by weight of potassium iodide The added product was dissolved in water to prepare a PVA aqueous solution (coating solution).

The 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, thereby producing a laminate.

The obtained laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (air auxiliary stretching treatment).

Next, the laminate was immersed in an insolubilization bath (boric acid aqueous 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 (insolubilization treatment).

Next, in a dyeing bath (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) at a liquid temperature of 30°C, the single transmittance (Ts) of the finally obtained undiscolored raw film was 42.3. It was immersed for 60 seconds while adjusting the concentration to % (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 40°C for 30 seconds (crosslinking treatment).

Thereafter, the laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 70°C (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight), while the total draw ratio was 5.5 in the machine direction (longitudinal direction) between rolls having different circumferential speeds. Uniaxial stretching was performed to double the weight (underwater stretching treatment).

Thereafter, the laminate was immersed in a washing bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (washing treatment).

Afterwards, it was dried in an oven maintained at about 90°C and brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75°C (dry shrink treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 2%.

In this way, a non-discolored raw film with a moisture content of 4.5% and a thickness of 5㎛ was formed on the resin substrate, and a UV-curable cycloolefin-based film (Zeonor, manufactured by Zeon Corporation, thickness: 25㎛) was applied to the surface of the non-discolored raw film. They were bonded together with an adhesive (thickness: 1.0 μm), and then the resin substrate was peeled off to obtain an optical laminate having the structure of [non-discolored raw film b1/protective layer].

The optical laminate was cut to a size of 45 mm x 50 mm, bonded to a glass plate with an acrylic adhesive layer (thickness of 15 μm) so that the surface of the non-discolored raw film was exposed, and immersed in water at 50°C for 9 minutes. Next, a polarizing plate having the structure of [polarizing film B1/protective layer] was obtained by drying at 50°C for 5 minutes.

[Example 2-2]

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

[Example 2-3]

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

[Example 2-4]

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

[Comparative Example 2]

An optical laminate having the structure of [non-discolored raw film b1/protective layer] produced in the same manner as in Example 2-1 was used as a polarizing plate.

Various properties were evaluated for the non-discolored raw film and polarizing film obtained in the above Examples and Comparative Examples. The results are shown in Table 1.

[Table 1]

As can be seen from Table 1, according to the manufacturing method of the example, the increase rate (ΔTs(λ)) of the transmittance at the wavelength λ nm of the PVA-based resin film before and after contact with water is ΔTs (415) > ΔTs (470) It can be seen that the relationship of >ΔTs (550) is satisfied, 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 polarization degree) and has increased transmittance of short-wavelength light.

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

Claims (6)

providing a polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment, and
and contacting the surface of the polyvinyl alcohol-based resin film with an aqueous solvent in this order,
The ratio of the transmittance (ΔTs(λ)) after contact to the transmittance of the polyvinyl alcohol-based resin film before contact with the aqueous solvent at a wavelength λnm is the relationship of ΔTs(415)>ΔTs(470)>ΔTs(550). A method of manufacturing a polarizing film that satisfies the above. According to paragraph 1,
A production method wherein the temperature of the aqueous solvent is 20°C to 70°C. According to claim 1 or 2,
A production method wherein the moisture content of the polyvinyl alcohol-based resin film contacted with the aqueous solvent is 15% by weight or less. According to any one of claims 1 to 3,
A production method wherein the polyvinyl alcohol-based resin film that contacts the aqueous solvent has a thickness of 12 μm or less. According to any one of claims 1 to 4,
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
A manufacturing method comprising performing an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrink treatment in which the laminate is shrunk by 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. . According to any one of claims 1 to 5,
A method for producing a polarizing film having a haze of 1% or less.