Method for manufacturing a polarizing film

Abstract

Provided is a method for producing a polarizing film, which successively includes: 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, the proportion of the transmittance of the polyvinyl alcohol-based resin film after contact with the aqueous solvent relative to the transmittance before contact at a wavelength λ nm (ΔTs(λ)) satisfying the relationship ΔTs(415) > ΔTs(470) > ΔTs(550).

Description

Technical Field

[0001] This invention relates to a method for manufacturing polarizing films. Background Technology

[0002] In recent years, image display devices, represented by liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have become increasingly popular. In organic EL display devices, it is known to prevent problems such as reflection of external light or background reflection by placing a circular polarizer containing a λ / 4 plate on the visible side of the organic EL cell (e.g., Patent Documents 1 and 2).

[0003] On the other hand, since organic EL display devices consume a lot of power for light emission, energy saving is required.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-311239

[0007] Patent Document 2: Japanese Patent Application Publication No. 2002-372622 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The present invention was made to solve the above-mentioned prior art problems, and its main objective is to provide a polarizing film that can reduce the power consumption of organic EL display devices.

[0010] Methods for solving problems

[0011] According to one aspect of the present invention, a method for manufacturing a polarizing film is provided, comprising: subjecting a polyvinyl alcohol-based resin film to a dyeing process and a stretching process; and bringing an aqueous solvent into contact with the surface of the polyvinyl alcohol-based resin film, wherein the ratio of the transmittance of the polyvinyl alcohol-based resin film after contact with the aqueous solvent at a wavelength λnm to the transmittance before contact (ΔTs(λ)) satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550).

[0012] In one embodiment, the temperature of the aqueous solvent is 20°C to 70°C.

[0013] In one embodiment, the moisture content of the polyvinyl alcohol-based resin film in contact with the aqueous solvent is less than 15% by weight.

[0014] In one embodiment, the thickness of the polyvinyl alcohol-based resin film in contact with the aqueous solvent is 12 μm or less.

[0015] In one embodiment, subjecting the above-mentioned polyvinyl alcohol-based resin film to dyeing and stretching treatment includes: forming a laminate by forming a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin on one side of a strip-shaped thermoplastic resin substrate; and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, wherein the drying shrinkage treatment involves heating while conveying along the length direction to shrink by more than 2% along the width direction.

[0016] In one embodiment, the above manufacturing method is a method for manufacturing a polarizing film with a haze of 1% or less.

[0017] Invention Effects

[0018] According to an embodiment of the present invention, a method for manufacturing a polarizing film involves subjecting a polyvinyl alcohol (PVA) resin film, which has undergone dyeing and stretching treatment, to a contact treatment with an aqueous solvent. As a result, the transmittance of the PVA resin film in at least the wavelength region of 415 nm to 550 nm increases, and the ratio of the transmittance of the PVA resin film after contact with the aqueous solvent at wavelength λ nm to the transmittance before contact (ΔTs(λ) = Ts(λ) after contact / Ts(λ) before contact; hereinafter, ΔTs(λ) is sometimes referred to as the "rate of increase in transmittance") satisfies the relationship ΔTs(415) > ΔTs(470) > ΔTs(550). The polarizing film obtained by this manufacturing method allows for more active transmission of light on the shorter wavelength side than light on the longer wavelength side. Therefore, by using such a polarizing film, even when reducing the amount of power-consuming blue light emission, the reduction in brightness in the shorter wavelength region can be suppressed, resulting in a balance between energy saving and high brightness in organic EL display devices. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating an example of a drying shrinkage process using heated rollers. Detailed Implementation

[0020] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0021] A. Manufacturing method of polarizing film

[0022] The method for manufacturing a polarizing film according to an embodiment of the present invention includes, in sequence: subjecting a polyvinyl alcohol (PVA) resin film to a dyeing and stretching process (step I); and contacting the surface of the PVA resin film with an aqueous solvent (step II), wherein the ratio of the transmittance of the PVA resin film after contact with the aqueous solvent at a wavelength λnm to the transmittance before contact (ΔTs(λ)) satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550). Iodine is used in the dyed PVA resin film... - I2, I3 - PVA-I3 - Complex, PVA-I5 - It exists in the form of complexes, etc. - I2 and I3 - PVA-I3 exhibits absorption in the ultraviolet region (e.g., near 290 nm to 360 nm). - Complexes and PVA-I5 - The complexes exhibit absorption near wavelengths of 470 nm and 600 nm, respectively. Therefore, it is assumed that the relationship ΔTs(415) > ΔTs(470) > ΔTs(550) before and after contact with the aqueous solvent represents the total iodine content relative to the total iodine present in the PVA-based resin film. - I2, I3 - and PVA-I3 - The proportion of complexes decreases (in other words, PVA-I5) - The proportion of complexes increases.

[0023] A-1. Process I

[0024] In step I, the PVA-based resin film is subjected to dyeing and stretching treatments, thereby obtaining a PVA-based resin film exhibiting dichroic absorption at any wavelength from 380 nm to 780 nm (hereinafter, sometimes referred to as "unbleached original film"). The unbleached original film is, in a representative sense, in a state where it can function as a polarizing film.

[0025] In one embodiment, the transmittance (monomer transmittance: Ts) of the unbleached original 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 unbleached original film is preferably 98.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. On the other hand, the polarization degree of the unbleached original film is preferably 99.998% or less. The aforementioned transmittance is representative of the Y value measured using a UV-Vis spectrophotometer and corrected for visual sensitivity. The aforementioned polarization degree is representative of the parallel transmittance Tp and orthogonal transmittance Tc measured using a UV-Vis spectrophotometer and corrected for visual sensitivity, and is calculated using the following formula.

[0026] Degree of polarization (%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0027] In one embodiment, the transmittance of a thin polarizing film (unbleached original film) less than 12 μm is typically measured using a laminate of the polarizing film (surface refractive index: 1.53) and a protective layer (protective film) (refractive index: 1.50), and is measured using a UV-Vis spectrophotometer. Depending on the refractive index of the polarizing film surface and / or the refractive index of the protective layer surface in contact with the air interface, the reflectance at the interfaces of the layers may vary, resulting in changes to the measured transmittance. Therefore, for example, when using a protective layer with a refractive index other than 1.50, the measured transmittance can be corrected based on the refractive index of the protective layer surface in contact with the air interface. Specifically, the transmittance correction value C is expressed using the reflectance R1 (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer, and is given by the following formula.

[0028] C = R1 - R0

[0029] R0=((1.50-1) 2 / (1.50+1) 2 )×(T1 / 100)

[0030] R1=((n1-1) 2 / (n1+1) 2 )×(T1 / 100)

[0031] Here, R0 is the transmissivity of the protective layer with a refractive index of 1.50, n1 is the refractive index of the protective layer, and T1 is the transmittance of the polarizing film. For example, when using a substrate with a surface refractive index of 1.53 (such as a cycloolefin film or a film with a hard coating) as the protective layer, the correction amount C becomes approximately 0.2%. In this case, by adding 0.2% to the measured transmittance, the transmittance of the polarizing film with a surface refractive index of 1.53 can be converted to the transmittance of the protective layer with a refractive index of 1.50. It should be noted that, according to the calculation based on the above formula, the change in the correction value C when the transmittance T1 of the polarizing film changes by 2% is less than 0.03%, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. Furthermore, when the protective layer has absorption other than surface reflection, appropriate corrections can be made according to the amount of absorption.

[0032] Transmittance (Ts) of the unbleached original film at a wavelength of 415 nm 415 For example, it can be less than 40%.

[0033] 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 even more preferably 1% to 5% by weight. If the moisture content of the unbleached original film is within this range, dissolution, wrinkling, etc., can be prevented when it comes into contact with an aqueous solvent in step II.

[0034] 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, and even more preferably 2 μm to 5 μm.

[0035] In step I, a single-layer PVA-based resin film is subjected to dyeing and stretching processes, thereby producing an unbleached base film. Alternatively, a laminate containing two or more layers (PVA-based resin layer, PVA-based resin film) is subjected to dyeing and stretching processes, thereby also producing an unbleached base film. Unbleached base films produced using laminates with two or more layers can avoid wrinkling even after contact with aqueous solvents, and appropriately maintain excellent optical properties (typically monomer transmittance and polarization).

[0036] A-1-1. Production of unbleached original film using two or more layers of laminate

[0037] The production of an unbleached base film using two or more layers can be achieved, for example, by subjecting a PVA-based resin film containing halides and PVA-based resin to a dyeing and stretching process in a laminated state with a strip-shaped thermoplastic resin substrate. Specifically, the unbleached base film can be produced by a method comprising the following steps: forming a PVA-based resin layer (PVA-based resin film) containing halides and PVA-based resin on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an air-assisted stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process, wherein the drying shrinkage process involves heating while conveying along the length direction to shrink by 2% or more in the width direction. The halides in the PVA-based resin layer are preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage process is preferably performed using a heated roller, and the temperature of the heated roller is preferably 60°C to 120°C. The shrinkage rate in the width direction of the laminate treated with the drying shrinkage process is preferably 2% or more. Using this manufacturing method, it is possible to obtain an unbleached original film with high orientation of PVA resin and excellent optical properties.

[0038] A-1-1-1. Construction of Layered Bodies

[0039] Any suitable method can be used as a method for manufacturing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a PVA-based resin layer is formed on the thermoplastic resin substrate by coating the surface of the substrate with a coating liquid containing a halide and a PVA-based resin and then drying it. As described above, the halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0040] Any suitable method can be used for coating the coating liquid. Examples include roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, and doctor blade coating (such as comma blade coating). The preferred coating and drying temperature for the above coating liquid is 50°C or higher.

[0041] The thickness of the PVA-based resin layer is preferably 3μm to 40μm, and more preferably 3μm to 20μm.

[0042] Before forming the PVA-based resin layer, the thermoplastic resin substrate can be surface-treated (e.g., corona treatment), or an easy-to-adhere layer can be formed on the thermoplastic resin substrate. Such treatments can improve the adhesion between the thermoplastic resin substrate and the PVA-based resin layer.

[0043] The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may become difficult to form the PVA-based resin layer. If it exceeds 300 μm, for example, in the water stretching treatment described later, the thermoplastic resin substrate may require a long time to absorb water, and the stretching may require an excessive load.

[0044] The thermoplastic resin substrate preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. When the thermoplastic resin substrate absorbs water, the water acts as a plasticizer, thus plasticizing the substrate. As a result, tensile stress can be significantly reduced, allowing for high-ratio stretching. 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 significant reduction in the dimensional stability of the thermoplastic resin substrate during manufacturing, which could lead to deterioration of the appearance of the resulting unbleached original film. Furthermore, it is possible to prevent substrate breakage during stretching in water, or peeling of the PVA-based resin layer from the thermoplastic resin substrate. It should be noted that the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing modifying groups into the constituent materials. The water absorption rate is a value determined according to JIS K7209.

[0045] The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. Using such a thermoplastic resin substrate helps suppress the crystallization of the PVA-based resin layer and ensures sufficient stretchability of the laminate. Furthermore, considering the good plasticization and underwater stretching of the water-based thermoplastic resin substrate, it is more preferable to be 100°C or lower, and further, 90°C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. Using such a thermoplastic resin substrate, when coating and drying the coating liquid containing the aforementioned PVA-based resin, it is possible to prevent deformation of the thermoplastic resin substrate (e.g., unevenness, loosening, wrinkles, etc.), thus producing a good laminate. Furthermore, the stretching of the PVA-based resin layer can be performed well at a suitable temperature (e.g., around 60°C). It should be noted that the glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material or by heating with a crystallizing material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

[0046] As a constituent material of the thermoplastic resin base material, any suitable thermoplastic resin can be used. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cyclic olefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymers thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferred.

[0047] In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate (PET) resin is preferably used. Particularly preferred are amorphous (non-crystallizable) PET resins. Specific examples of amorphous PET resins include copolymers further comprising isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further comprising cyclohexanediethanol or diethylene glycol as diols.

[0048] In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having isophthalic acid units. This is because such a thermoplastic resin substrate exhibits excellent tensile strength and suppresses crystallization during stretching. This is believed to be due to the significant bending of the main chain achieved by introducing isophthalic acid units. The polyethylene terephthalate resin has terephthalic acid units and ethylene glycol units. The content of isophthalic acid units relative to the total number of repeating units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more. This is because a thermoplastic resin substrate with excellent tensile strength can be obtained. On the other hand, the content of isophthalic acid units relative to the total number of repeating units is preferably 20 mol% or less, more preferably 10 mol% or less. By setting such a content ratio, the degree of crystallinity can be effectively increased during the drying shrinkage treatment described later.

[0049] The thermoplastic resin substrate can also be stretched beforehand (before forming the PVA-based resin layer). In one embodiment, the thermoplastic resin substrate is stretched transversely along its length. The transverse direction is preferably orthogonal to the stretching direction of the laminate described later. It should be noted that in this specification, "orthogonal" also includes substantially orthogonal. Here, "substantially orthogonal" includes a value of 90° ± 5.0°, preferably 90° ± 3.0°, and more preferably 90° ± 1.0°.

[0050] The stretching temperature of the thermoplastic resin substrate relative to its glass transition temperature (Tg) is preferably Tg-10℃ to Tg+50℃. The stretching ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

[0051] Any suitable method can be used for stretching thermoplastic resin substrates. Specifically, it can be stretching from a fixed end or from a free end. The stretching method can be dry or wet. The stretching of the thermoplastic resin substrate can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio mentioned above is the product of the stretching ratios of each stage.

[0052] The coating solution, as described above, comprises a halide and a PVA-based resin. The coating solution is typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylenediamine, and amines such as diethylenetriamine. These can be used alone or in combination. Water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. Such a resin concentration allows for the formation of a uniform coating film that adheres closely to the thermoplastic resin substrate. The content of the halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0053] Additives can also be incorporated into the coating solution. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. They can be used to further improve the uniformity, dyeability, or tensile strength of the resulting PVA-based resin layer.

[0054] Any suitable resin can be used as the PVA-based resin mentioned above. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of PVA-based resins is typically 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 PVA-based resins with such a degree of saponification, a durable, unbleached film can be obtained. If the saponification is too high, gelation may occur.

[0055] The average degree of polymerization of PVA-based resins can be appropriately selected according to the purpose. The average degree of polymerization is typically 1000–10000, preferably 1200–4500, and more preferably 1500–4300. It should be noted that the average degree of polymerization can be determined according to JIS K 6726-1994.

[0056] Any suitable halide can be used as the aforementioned halide. Examples include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Potassium iodide is preferred among them.

[0057] The amount of halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of PVA-based resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of PVA-based resin. If the amount of halide relative to 100 parts by weight of PVA-based resin exceeds 20 parts by weight, halide may bleed out, resulting in a cloudy, unbleached original film.

[0058] Generally, stretching a PVA-based resin layer increases the orientation of polyvinyl alcohol molecules within it. However, immersing the stretched PVA-based resin layer in a water-containing liquid can sometimes disrupt the orientation of polyvinyl alcohol molecules, leading to a decrease in orientation. This is particularly true when stretching a laminate of a thermoplastic resin substrate and a PVA-based resin layer in boric acid water. In order to stabilize the stretching of the thermoplastic resin substrate, the laminate is stretched at a relatively high temperature in boric acid water, resulting in a significant tendency to decrease orientation. For example, PVA film monomers are typically stretched in boric acid water at 60°C. In contrast, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at temperatures as high as around 70°C. In this case, the orientation of the PVA in the initial stretching stage may decrease before the initial increase from stretching in water. In contrast, by fabricating a laminate of a PVA-based resin layer containing halogens and a thermoplastic resin substrate, and then subjecting the laminate to high-temperature stretching in air (assisted stretching) before stretching in boric acid solution, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after assisted stretching can be promoted. As a result, when the PVA-based resin layer is immersed in liquid, the disorder of polyvinyl alcohol molecular orientation and the reduction of orientation can be suppressed compared to the case where the PVA-based resin layer does not contain halogens. Therefore, the optical properties of the unbleached original film obtained through processing steps such as dyeing and underwater stretching by immersing the laminate in liquid can be improved.

[0059] A-1-1-2. Aerial Assisted Stretching Treatment

[0060] In particular, to obtain high optical properties, a two-stage stretching method combining dry stretching (assisted stretching) and stretching in boric acid solution was chosen. By introducing assisted stretching as in two-stage stretching, stretching can be performed while suppressing the crystallization of the thermoplastic resin substrate. This solves the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate during subsequent stretching in boric acid solution, allowing the laminate to be stretched at a higher magnification. Furthermore, when coating a PVA-based resin onto a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature needs to be lowered compared to coating PVA-based resin on a conventional metal roller. As a result, the crystallization of the PVA-based resin may be relatively lower, leading to insufficient optical properties. In contrast, by introducing assisted stretching, even when coating a PVA-based resin onto a thermoplastic resin substrate, the crystallinity of the PVA-based resin can be improved, achieving high optical properties. Furthermore, by improving the orientation of the PVA resin beforehand, problems such as the reduction of the orientation and dissolution of the PVA resin can be prevented when it is immersed in water during subsequent dyeing or stretching processes, thus achieving high optical properties.

[0061] The aerial stretching method can be fixed-end stretching (e.g., stretching using a tenter frame) or free-end stretching (e.g., uniaxial stretching by passing the laminate between rollers with different circumferential speeds), but free-end stretching is preferred to obtain high optical properties. In one embodiment, the aerial stretching process includes a heated roller stretching step that stretches the laminate by utilizing the difference in circumferential speed between heated rollers while conveying it along its length. The aerial stretching process typically includes a zone stretching step and a heated roller stretching step. It should be noted that the order of the zone stretching step and the heated roller stretching step is not limited; the zone stretching step can be performed first, or the heated roller stretching step can be performed first. The zone stretching step can also be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed sequentially. Furthermore, in another embodiment, the laminate is stretched by holding the ends in a tenter frame and increasing the distance between the tenter frames along the flow direction (the increase in the distance between the tenter frames is called the stretching ratio). In this case, the distance between the tenter frames in the width direction (the direction perpendicular to the flow direction) is set in an arbitrarily close manner. Preferably, the stretch ratio relative to the flow direction is set in a manner that approximates the stretch ratio at the free end. In the case of stretching at the free end, the shrinkage rate in the width direction is calculated as (1 / stretch ratio). 1 / 2 To calculate.

[0062] Aerial assisted stretching can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio is the product of the stretching ratios of each stage. Preferably, the stretching direction in aerial assisted stretching is approximately the same as that in underwater stretching.

[0063] The stretching ratio in aerial-assisted stretching is preferably 2.0 to 3.5 times. When combining aerial-assisted stretching with underwater stretching, the maximum stretching ratio relative to the original length of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more. In this specification, "maximum stretching ratio" refers to the stretching ratio just before the laminate breaks; the stretching ratio at which the laminate breaks is defined as a value 0.2 lower than this value.

[0064] The stretching temperature for air-assisted stretching can be set to any suitable value depending on the forming material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above the glass transition temperature (Tg) + 10°C, and particularly preferably above Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the rapid progression of crystallization of the PVA-based resin can be suppressed, and adverse conditions caused by this crystallization (e.g., hindering the orientation of the stretched PVA-based resin layer) can be suppressed. The crystallization index of the PVA-based resin after air-assisted stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured using a Fourier transform infrared spectrophotometer by the ATR method. Specifically, the measurement is performed using polarized light as the measurement light, and the 1141 cm⁻¹ of the obtained spectrum is used. -1 and 1440cm -1 The strength is calculated using the following formula to determine the crystallinity index.

[0065] Crystallization index = (I C / I R )

[0066] in,

[0067] I C 1141 cm when the incident light is measured -1 intensity

[0068] I R : 1440cm when the incident light is measured -1 The intensity.

[0069] A-1-1-3. Insoluble treatment

[0070] As needed, an insoluble treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment and dyeing treatment. This insoluble treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing this insoluble treatment, the PVA-based resin layer can be given water resistance, preventing a decrease in the orientation of the PVA when immersed in water. The concentration of this aqueous boric acid solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The temperature of the insoluble bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0071] A-1-1-4. Staining Treatment

[0072] The aforementioned staining process is typically performed by staining the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, this is achieved by adsorbing iodine onto the PVA-based resin layer. Examples of adsorption methods include immersing the PVA-based resin layer (laminated structure) in an iodine-containing staining solution, coating the PVA-based resin layer with the staining solution, and spraying the PVA-based resin layer with the staining solution. Immersing the laminate in a staining solution (staining bath) is preferred because iodine is readily adsorbed.

[0073] The dyeing solution is preferably an aqueous iodine solution. The amount of iodine added relative to 100 parts by weight of water is preferably 0.05 to 0.5 parts by weight. To improve the solubility of iodine relative to water, it is preferable to add an iodide to the aqueous iodine 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. Among these, potassium iodide is preferred. The amount of iodide added relative to 100 parts by weight of water is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight. To suppress the dissolution of PVA-based resin, the dyeing temperature is preferably 20°C to 50°C. When immersing the PVA-based resin layer in the dyeing solution, to ensure the transmittance of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds.

[0074] The dyeing conditions (concentration, liquid temperature, immersion time) can be set in such a way that the monomer transmittance of the final unbleached original film is at a desired value. As such dyeing conditions, an aqueous iodine solution is preferably used as the dyeing solution, and the ratio of iodine to potassium iodide in the aqueous iodine solution is set to 1:5 to 1:20. The ratio of iodine to potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. Thus, an unbleached original film with the optical properties described later can be obtained.

[0075] When dyeing is performed continuously after immersing the laminate in a treatment bath containing boric acid (typically an insoluble treatment), the boric acid concentration in the dyeing bath sometimes changes over time due to the boric acid in the treatment bath mixing into the dyeing bath, resulting in unstable dyeability. To suppress such instability, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. 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 even more preferably 0.5 parts by weight, relative to 100 parts by weight of water. In one embodiment, a dyeing bath pre-contained with boric acid is used for dyeing. This reduces the proportion of boric acid concentration changes that occur when boric acid from the treatment bath mixes into the dyeing bath. The amount of boric acid pre-mixed in the dyeing bath (i.e., the amount of boric acid not derived from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of water.

[0076] A-1-1-5. Crosslinking treatment

[0077] As needed, a crosslinking treatment is performed after dyeing and before underwater stretching. Typically, this crosslinking treatment involves immersing the PVA-based resin layer in an aqueous boric acid solution. This crosslinking treatment imparts water resistance to the PVA-based resin layer, preventing a decrease in PVA orientation during subsequent underwater stretching when immersed in high-temperature water. The concentration of this aqueous boric acid solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Furthermore, when performing the crosslinking treatment after the dyeing process, it is preferable to further incorporate an iodide. Incorporating an iodide suppresses the dissolution of iodine adsorbed by the PVA-based resin layer. The amount of iodide incorporated is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodides are described above. The temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0078] A-1-1-6. Underwater stretching treatment

[0079] The underwater stretching process involves immersing the laminate in a stretching bath. By using underwater stretching, stretching can be performed at a temperature lower than the glass transition temperature (typically around 80°C) of the aforementioned thermoplastic resin substrate and PVA-based resin layer, allowing the PVA-based resin layer to be stretched at a high ratio while suppressing crystallization. As a result, an unbleached original film with excellent optical properties can be manufactured.

[0080] The stretching method for the laminate can be any suitable method. Specifically, it can be fixed-end stretching or free-end stretching (e.g., uniaxial stretching by passing the laminate between rollers with different circumferential speeds). Free-end stretching is preferred. The stretching of the laminate can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio (maximum stretching ratio) of the laminate, as described later, is the product of the stretching ratios of each stage.

[0081] Water stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity that withstands the tension applied during stretching and water resistance that is insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anions in aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be well stretched while imparting rigidity and water resistance, and an unbleached original film with excellent optical properties can be produced.

[0082] The aforementioned boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration relative to 100 parts by weight of water is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight. 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, enabling the production of an unbleached original film with higher properties. It should be noted that, in addition to boric acid or borate, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc., in a solvent can also be used.

[0083] It is preferable to incorporate an iodide in the aforementioned stretching bath (boric acid aqueous solution). Incorporating an iodide helps suppress the leaching of iodine adsorbed by the PVA-based resin layer. Specific examples of iodides are described above. The concentration of the iodide relative to 100 parts by weight of water is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight.

[0084] 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 temperatures, stretching at a high ratio can be achieved while suppressing the dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher, based on its relationship with the formation of the PVA-based resin layer. In this case, if the stretching temperature is below 40°C, even considering the plasticization of the thermoplastic resin substrate caused by water, good stretching may not be possible. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer becomes, potentially resulting in suboptimal optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0085] The stretching ratio achieved by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate relative to its original length is preferably 5.0 times or more, more preferably 5.5 times or more. By achieving such a high stretching ratio, it is possible to manufacture an unbleached original film with extremely excellent optical properties. Such a high stretching ratio can be achieved by using a stretching method in water (boric acid water stretching).

[0086] A-1-1-7. Drying and Shrinkage Treatment

[0087] The aforementioned drying shrinkage treatment involves, for example, heating a laminate of a strip-shaped thermoplastic resin substrate and a PVA-based resin film while conveying it along its length, causing it to shrink by 2% or more along its width. In the drying shrinkage treatment, it is preferable to dry until the moisture content of the PVA-based resin film is 15% by weight or less. From the viewpoint of obtaining a stable appearance, it is preferable to dry until the moisture content is more preferably 12% by weight or less, even more preferably 10% by weight or less, and even more preferably 1% to 5% by weight.

[0088] The drying shrinkage treatment can be performed by area heating, which involves heating the entire area, or by heating the conveyor rollers (using so-called heated rollers) (heated roller drying method). Both methods are preferred. Using heated rollers for drying effectively suppresses heat curling of the laminate, producing an unbleached original film with excellent appearance. Specifically, by drying the laminate along the heated rollers, the crystallization of the thermoplastic resin substrate is effectively promoted, increasing the degree of crystallinity. Even at relatively low drying temperatures, the degree of crystallinity of the thermoplastic resin substrate is significantly increased. As a result, the thermoplastic resin substrate gains increased rigidity, becoming resistant to shrinkage of the PVA-based resin layer caused by drying, thus suppressing curling. Furthermore, by using heated rollers, the laminate can be dried while maintaining a flat state, thus suppressing not only curling but also wrinkle formation. At this time, the laminate shrinks in the width direction through the drying shrinkage treatment, thereby improving optical properties. This is because the orientation of PVA and PVA / iodine complexes can be effectively improved. The shrinkage rate in the width direction of the laminate treated by drying shrinkage is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rollers, the laminate can be continuously shrunk in the width direction while being transported, thus achieving high productivity.

[0089] Figure 1This is a schematic diagram illustrating an example of a drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being transported by conveyor rollers R1 to R6 and guide rollers G1 to G4, which are heated to a predetermined temperature. In the example shown, the conveyor rollers R1 to R6 are arranged in such a way that the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate are continuously heated alternately. However, for example, the conveyor rollers R1 to R6 may also be arranged in such a way that only one surface of the laminate 200 (e.g., the thermoplastic resin substrate surface) is continuously heated.

[0090] The drying conditions can be controlled by adjusting the heating temperature of the conveyor rollers (temperature of the heating rollers), the number of heating rollers, and the contact time with the heating rollers. The temperature of the heating rollers is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. This effectively increases the crystallinity of the thermoplastic resin, thus effectively suppressing curling, and enables the manufacture of optical laminates with extremely excellent durability. It should be noted that the temperature of the heating rollers can be measured using a contact thermometer. In the example shown, six conveyor rollers are provided, but there is no particular limitation on the number of conveyor rollers. Typically, two to 40 conveyor rollers are provided, preferably four to 30. The contact time (total contact time) between the laminate and the heating rollers is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0091] The heating rollers can be installed inside a heating furnace (e.g., an oven) or in a typical manufacturing line (at room temperature). Preferably, they are installed in a heating furnace equipped with an air supply mechanism. By combining drying using the heating rollers with hot air drying, abrupt temperature changes between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The hot air drying temperature is preferably 20°C to 100°C. Furthermore, the hot air drying time is preferably 1 second to 300 seconds. The hot air velocity is preferably around 10 m / s to 30 m / s. It should be noted that this velocity is the velocity inside the heating furnace and can be measured using a small impeller-type digital anemometer.

[0092] A-1-1-8. Other treatments

[0093] The washing process is preferably performed after the stretching treatment in water and before the drying and shrinkage treatment. Typically, this washing process involves immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0094] In step II, the contact between the unbleached base film and the aqueous solvent can be achieved by contacting only one side of the unbleached base film with the aqueous solvent, or by contacting both sides with the aqueous solvent. Therefore, in one embodiment, the unbleached base film produced using the above-described laminate can be supplied to step II in the form of a laminate of [unbleached base film / thermoplastic resin substrate]. In another embodiment, a laminate of [protective layer / unbleached base film / thermoplastic resin substrate] can be produced by bonding a protective layer to the surface of the unbleached base film of the laminate of [unbleached base film / thermoplastic resin substrate], and the thermoplastic resin substrate can be peeled off from the laminate to produce a laminate of [protective layer / unbleached base film] (polarizer), and the resulting laminate can be supplied to step II. In another embodiment, any suitable functional layer (phase difference layer, adhesive layer, etc.) may be provided on the substrate side of the laminate of [unbleached original film / thermoplastic resin substrate] or on the protective layer side of the laminate of [protective layer / unbleached original film] before being supplied to step II.

[0095] A-1-2. Preparation of unbleached original film using a single-layer PVA-based resin film

[0096] The production of an unbleached base film using a single-layer PVA-based resin film can be performed by dyeing and stretching a self-supporting (i.e., without the need for a substrate) strip of PVA-based resin film (typically, uniaxial stretching using a roller stretching machine in a boric acid aqueous solution), followed by drying until 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% to 5% by weight. The dyeing is performed, for example, by immersing the PVA-based resin film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching can be performed after dyeing or simultaneously with dyeing. Alternatively, dyeing can be performed after stretching. As needed, the PVA-based resin film can be subjected to swelling treatment, crosslinking treatment, washing treatment, etc. For example, by immersing the PVA-based resin film in water for washing before dyeing, not only can stains and anti-blocking agents on the surface of the PVA-based resin film be washed away, but the PVA-based resin film can also swell to prevent uneven dyeing.

[0097] As described above, the contact between the unbleached base film and the aqueous solvent in step II can be achieved by contacting only one side of the unbleached base film with the aqueous solvent, or by contacting both sides with the aqueous solvent. Therefore, in one embodiment, the unbleached base film made using the above-described single-layer PVA-based resin film can be directly supplied to step II. In another embodiment, a protective layer can be laminated onto one side of the unbleached base film to form a [protective layer / unbleached base film] stack, and this stack can be supplied to step II. In yet another embodiment, any suitable functional layer (phase difference layer, adhesive layer, etc.) can be provided on the protective layer side of the [protective layer / unbleached base film] stack and supplied to step II.

[0098] A-2. Process II

[0099] In step II, an aqueous solvent is brought into contact with the surface of the PVA-based resin film (unbleached original film) from step I. Through contact with the aqueous solvent, layer I is formed. - I2, I3 - and PVA-I3 - The polyiodide ratio of the complex forms PVA-I5. - The polyiodide ions of the complex preferentially dissolve from the undecolorized original film, and the transmittance on the short wavelength side increases more. As a result, the rate of increase in transmittance at wavelength λnm (ΔTs(λ)) can satisfy the relationship ΔTs(415)>ΔTs(470)>ΔTs(550).

[0100] As an aqueous solvent, any suitable solvent can be used as long as it allows the dichroic substance (representatively iodine) to dissolve from the unbleached original film. Examples of aqueous solvents include water or a mixture of water and a water-soluble organic solvent. Preferred examples of water-soluble organic solvents include lower monohydric alcohols with 1 to 4 carbon atoms, such as methanol, ethanol, n-propanol, and isopropanol, as well as polyhydric alcohols such as glycerol and ethylene glycol.

[0101] There are no particular limitations on the method of contact with the aqueous solvent; any suitable method such as dipping, spraying, or coating can be used. From the viewpoint of ensuring uniform contact between the entire surface of the unbleached original film and the aqueous solvent, dipping is preferred.

[0102] The contact time with the aqueous solvent and the temperature of the aqueous solvent during contact can be determined based on the desired Ts. 415 、Ts 470 and Ts 550 And so on, and should be set appropriately. By extending the contact time or increasing the temperature of the aqueous solvent, there is an effect on transmittance (especially Ts). 415The tendency for the concentration of ions to increase. The contact time can be, for example, less than 10 minutes, preferably 60 seconds to 9 minutes, more preferably 60 seconds to 4 minutes. The temperature of the aqueous solvent can preferably be 20°C to 70°C, more preferably 30°C to 65°C, and even more preferably 40°C to 60°C.

[0103] If necessary, drying can also be performed after contact with an 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 even more preferably 1% by weight to 5% by weight.

[0104] B. Polarizing film

[0105] The polarizing film obtained by the polarizing film manufacturing method described in section A is composed of a PVA-based resin film containing a dichroic substance (typically iodine), and has a higher transmittance than the unbleached original film, at least in the wavelength region of 415 nm to 550 nm. Specifically, the rate of increase in transmittance at wavelength λ nm (ΔTs(λ)) satisfies the relationship ΔTs(415) > ΔTs(470) > ΔTs(550). The rate of increase in transmittance at wavelength 415 nm (ΔTs(415)) can, for example, be greater than 1.05, preferably greater than 1.1, and more preferably 1.10 to 2.2. If ΔTs(415) is within this range, the amount of power-consuming blue light emission can be reduced, which contributes to the energy saving of organic EL display devices.

[0106] Ts of polarizing film 415 and Ts 550 It can be any suitable value depending on the purpose. 415 For example, it can be 40% or more, preferably 41% or more, more preferably 42% or more; furthermore, it can be 80% or less, preferably 60% or less, more preferably 50% or less. Additionally, Ts 550 For example, it can be 40% or more, preferably 42% or more, more preferably 43% or more, and furthermore, for example, it can be 70% or less, preferably 60% or less, more preferably 50% or less.

[0107] The polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance (monomer 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 even more preferably 48% or less. Furthermore, the degree of polarization 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, even more preferably 99.5% or more, and preferably 99.998% or less. The above-mentioned transmittance and degree of polarization are obtained in the same manner as the transmittance and degree of polarization of the unbleached original film.

[0108] The haze of the polarizing film is preferably 1% or less, more preferably 0.8% or less, and even 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.

[0109] The iodine concentration in the polarizing film is preferably 3% by weight or more, more preferably 4% to 10% by weight, and even more preferably 4% to 8% by weight. It should be noted that in this specification, "iodine concentration" refers to the total amount of iodine contained in the polarizing film. More specifically, the iodine concentration in the polarizing film is... - I2, I3 - PVA-I3 - Complex, PVA-I5 - Iodine exists in complex and other forms, and the iodine concentration mentioned in this specification refers to the concentration containing all of these forms of iodine. The iodine concentration can be calculated, for example, from the fluorescence X-ray intensity and the film (polarizing film) thickness analyzed using fluorescence X-rays.

[0110] 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, and even more preferably 2 μm to 5 μm.

[0111] Example

[0112] The present invention will now be specifically described through examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are described below. It should be noted that, unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight.

[0113] (1) Thickness

[0114] The measurement was conducted using the product name "Linear Gauge MODEL D-10HS" (manufactured by Ozaki Seisakusho).

[0115] (2) Monomer transmittance and polarization degree

[0116] For the laminates of PVA-based resin films (polarizing films or unbleached original films) and protective layers obtained in the examples and comparative examples, the monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc, measured from the PVA-based resin film side using a UV-Vis spectrophotometer (Otsuka Electronics Co., Ltd. "LPF-200"), are taken as the Ts, Tp, and Tc of the PVA-based resin film, respectively. These Ts, Tp, and Tc are Y values ​​measured using a 2-degree field of view (C light source) of JIS Z8701 and corrected for visual sensitivity. It should be noted that the refractive index of the protective layer is 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer is 1.53.

[0117] The degree of polarization P can be calculated from the obtained Tp and Tc using the following formula.

[0118] Degree of polarization P(%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0119] Furthermore, Ts measured at wavelengths of 415 nm, 470 nm, and 550 nm will be used as Ts, respectively. 415 、Ts 470 and Ts 550 .

[0120] It should be noted that the same measurements can be performed using a spectrophotometer such as the "V-7100" manufactured by Japan Spectrophotometer Co., Ltd., confirming that the same measurement results can be obtained when using any spectrophotometer.

[0121] (3) Moisture content

[0122] The freshly dried, unbleached original film (with the substrate peeled off during the stretching process in a laminated manner) was cut into pieces larger than 100mm × 100mm, and its weight before treatment was measured using an electronic balance. It was then placed in a heating oven maintained at 120℃ for 2 hours, and its weight after removal (post-treatment weight) was measured. The moisture content was calculated using the following formula.

[0123] Moisture content [%] = (Weight before treatment - Weight after treatment) / Weight before treatment × 100

[0124] (4) Haze

[0125] The measurement was performed using a product named "NDH-5000" manufactured by Nippon Denshoku Kogyo Co., Ltd., in accordance with JIS K7136.

[0126] [Example 1-1]

[0127] 1. Fabrication of polarizing films and polarizers

[0128] A long roll of 30 μm thick PVA-based resin film (manufactured by KURARAY, product name "PE3000") was immersed in a 30°C water bath and stretched to 2.2 times its original length along the conveying direction. Then, it was immersed in a 30°C aqueous solution of 0.04 wt% iodine and 0.3 wt% potassium for dyeing, while simultaneously stretching it to 3 times its original length from the unstretched film (original length). Next, while immersing the stretched film in a 30°C aqueous solution of 3 wt% boric acid and 3 wt% potassium iodide, it was further stretched to 3.3 times its original length. Then, while immersing it in a 60°C aqueous solution of 4 wt% boric acid and 5 wt% potassium iodide, it was further stretched to 6 times its original length. Finally, it was dried in an oven maintained at 60°C for 5 minutes, thus producing a 12 μm thick polarizing film (unbleached original film a1). The resulting unbleached original film a1 had a moisture content of 10.0% by weight and a monomer transmittance of 42.5%.

[0129] A PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight) is coated on one side of the obtained unbleached original film a1, and a cyclic olefin film (manufactured by Zeon Corporation, Zeonor, thickness: 25 μm) is laminated thereon to obtain an optical laminate with the structure of [unbleached original film a1 / protective layer]. It should be noted that, as a protective layer, a protective layer with a hard coating can also be used. For example, a cyclic olefin film with a hard coating (manufactured by ZEON Corporation, product name "G-Film", total thickness 27 μm (film thickness 25 μm + hard coating thickness 2 μm)) can be used as an example of such a protective layer.

[0130] The aforementioned optical laminate was cut into 45mm × 50mm pieces and bonded to a glass plate with the unbleached original film side surface exposed via an acrylic adhesive layer (15μm thick). The laminate was then immersed in water at 23°C for 31 hours. Next, it was dried at 50°C for 5 minutes, thereby obtaining a polarizer with a [polarizing film A1 / protective layer] structure.

[0131] [Examples 1-2]

[0132] Instead of immersing in water at 23°C for 31 hours, the polarizer was immersed in water at 55°C for 9 minutes. Otherwise, the procedure was the same as in Example 1-1 to obtain a polarizer with a structure of [polarizing film A2 / protective layer].

[0133] [Examples 1-3]

[0134] Instead of immersing in water at 23°C for 31 hours, the polarizer was immersed in water at 60°C for 4 minutes. Otherwise, the procedure was the same as in Example 1-1 to obtain a polarizer with the structure of [polarizing film A3 / protective layer].

[0135] [Examples 1-4]

[0136] Instead of immersing in water at 23°C for 31 hours, the polarizer was immersed in water at 65°C for 3 minutes. Otherwise, the procedure was the same as in Example 1-1 to obtain a polarizer with the structure of [polarizing film A4 / protective layer].

[0137] [Comparative Example 1]

[0138] An optical laminate with a structure of [unbleached original film a1 / protective layer], which was prepared in the same manner as in Example 1-1, was used as a polarizer.

[0139] [Example 2-1]

[0140] As a thermoplastic resin substrate, a strip-shaped amorphous polyethylene terephthalate copolymer film (thickness: 100 μm) with a Tg of approximately 75 °C is used to corona treat one side of the resin substrate.

[0141] Add 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (manufactured by Japan Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") in a ratio of 9:1, and dissolve the resulting substance in water to prepare a PVA aqueous solution (coating solution).

[0142] A 13 μm thick PVA-based resin layer is formed by coating the corona-treated surface of a resin substrate with the above-mentioned PVA aqueous solution and drying it at 60°C, thereby creating a laminate.

[0143] The resulting laminate was stretched uniaxially to 2.4 times its original length in an oven at 130°C (air-assisted stretching treatment).

[0144] Next, the laminate was immersed in an insoluble bath (an aqueous solution of boric acid prepared 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 (insoluble treatment).

[0145] Next, the mixture was immersed for 60 seconds in a staining bath at 30°C (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) while adjusting the concentration so that the monomer transmittance (Ts) of the final unbleached original film was 42.3% (staining treatment).

[0146] Next, immerse the sample in a crosslinking bath (an aqueous solution of boric acid prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

[0147] Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4 wt% and potassium iodide concentration 5 wt%) at a liquid temperature of 70°C, while being uniaxially stretched (underwater stretching treatment) along the longitudinal direction (length direction) between rollers with different circumferential speeds, with a total stretching ratio of 5.5 times.

[0148] The laminate was then immersed in a washing bath at 20°C (an aqueous solution of 4 parts by weight of potassium iodide relative to 100 parts by weight of water) for washing treatment.

[0149] Subsequently, while drying in an oven maintained at approximately 90°C, the laminate is brought into contact with SUS heated rollers maintained at a surface temperature of approximately 75°C (drying shrinkage treatment). The width-direction shrinkage rate of the laminate produced by the drying shrinkage treatment is 2%.

[0150] In this manner, an unbleached base film with a moisture content of 4.5% and a thickness of 5 μm is formed on a resin substrate. A cycloolefin film (manufactured by Zeon Corporation, Zeonor, thickness: 25 μm) is then bonded to the surface of the unbleached base film using a UV-curable adhesive (1.0 μm thick). Afterward, the resin substrate is peeled off to obtain an optical laminate with the structure of [unbleached base film b1 / protective layer].

[0151] The aforementioned optical laminate was cut into 45mm × 50mm pieces and bonded to a glass plate with the unbleached original film side surface exposed via an acrylic adhesive layer (15μm thick). The laminate was then immersed in water at 50°C for 9 minutes. Next, it was dried at 50°C for 5 minutes, thereby obtaining a polarizer with a [polarizing film B1 / protective layer] structure.

[0152] [Example 2-2]

[0153] Instead of immersing in water at 50°C for 9 minutes, the polarizer was immersed in water at 55°C for 3 minutes. Otherwise, the procedure was the same as in Example 2-1 to obtain a polarizer with a [polarizing film B2 / protective layer] structure.

[0154] [Examples 2-3]

[0155] Instead of immersing in water at 50°C for 9 minutes, the polarizer was immersed in water at 60°C for 2 minutes. Otherwise, the procedure was the same as in Example 2-1 to obtain a polarizer with the structure of [polarizing film B3 / protective layer].

[0156] [Examples 2-4]

[0157] Instead of immersing in water at 50°C for 9 minutes, the polarizer was immersed in water at 60°C for 3 minutes. Otherwise, the procedure was the same as in Example 2-1 to obtain a polarizer with the structure of [polarizing film B4 / protective layer].

[0158] [Comparative Example 2]

[0159] An optical laminate with a structure of [unbleached original film b1 / protective layer], which was prepared in the same manner as in Example 2-1, was used as a polarizer.

[0160] Various properties of the unbleached original film and polarizing film obtained in the above embodiments and comparative examples were evaluated.

[0161] The results are shown in Table 1.

[0162]

[0163] As shown in Table 1, it is known that if the manufacturing method of the embodiment is used, the rate of increase in transmittance (ΔTs(λ)) of the PVA-based resin film at wavelength λnm before and after contact with water satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550), with a larger rate of increase in transmittance at wavelength 415nm. The polarizing film obtained by such manufacturing method has practically acceptable optical properties (representatively, monomer transmittance and degree of polarization), and the transmittance of short-wavelength light is increased.

[0164] Industrial availability

[0165] The polarizing film of the present invention is suitable for use in image display devices such as liquid crystal display devices and EL display devices, especially organic EL display devices.

Claims

1. A method for manufacturing a polarizing film, comprising the following steps: Polyvinyl alcohol-based resin films are used for dyeing and stretching processes; and The polyvinyl alcohol-based resin film was immersed in an aqueous solvent at 20°C to 70°C for 60 seconds to 10 minutes. The ratio of the transmittance after immersion at wavelength λnm to the transmittance of the polyvinyl alcohol resin film before immersion in the aqueous solvent (ΔTs(λ)) satisfies the relationship ΔTs(415)>ΔTs(470)>ΔTs(550).

2. The manufacturing method according to claim 1, wherein, The temperature of the aqueous solvent is 30℃~65℃.

3. The production method according to claim 1 or 2, wherein The moisture content of the polyvinyl alcohol-based resin film impregnated in the aqueous solvent is less than 15% by weight.

4. The production method according to claim 1 or 2, wherein The thickness of the polyvinyl alcohol-based resin film impregnated in the aqueous solvent is less than 12 μm.

5. The production method according to claim 1 or 2, wherein The polyvinyl alcohol-based resin film is subjected to dyeing and stretching treatments, including: A laminate is formed by forming a polyvinyl alcohol-based resin film containing halides and polyvinyl alcohol-based resin on one side of a long strip of thermoplastic resin substrate; and The laminate was subjected to aerial assisted stretching, dyeing, underwater stretching, and drying shrinkage treatment in sequence. The drying shrinkage treatment involved heating while conveying the laminate along its length, resulting in a shrinkage of more than 2% along its width.

6. The manufacturing method according to claim 1 or 2 is a method for manufacturing a polarizing film with a haze of less than 1%.

Images