JP7096700B2 - A method for manufacturing a polarizing film, a polarizing plate, a polarizing plate roll, and a polarizing film. - Google Patents

Description

The present invention relates to a polarizing film, a polarizing plate, a polarizing plate roll, and a method for manufacturing a polarizing film.

With the widespread use of thin displays, displays (OLEDs) equipped with organic EL panels and displays (QLEDs) using display panels using inorganic light emitting materials such as quantum dots have been proposed. These panels have a highly reflective metal layer, and are liable to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circular polarizing plate having a polarizing film and a λ / 4 plate on the visual recognition side. As a method for producing a polarizing film, for example, a method of stretching a laminate having a resin base material and a polyvinyl alcohol (PVA) -based resin layer and then performing a dyeing treatment to obtain a polarizing film on the resin base material is used. It has been proposed (for example, Patent Document 1). Since such a method can obtain a thin polarizing film, it is attracting attention as it can contribute to the thinning of image display devices in recent years. However, the conventional thin polarizing film as described above has insufficient optical characteristics, and further improvement of the optical characteristics of the thin polarizing film is required.

Japanese Unexamined Patent Publication No. 2001-343521

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a polarizing film having excellent optical properties, a polarizing plate, a polarizing plate roll, and a method for manufacturing such a polarizing film. To do.

The polarizing film of the present invention has a thickness of 8 μm or less, a simple substance transmittance of 46% or more, and a degree of polarization of 92% or more.
In one embodiment, the simple substance transmittance is 48% or less and the degree of polarization is 97% or less.
According to another aspect of the invention, a polarizing plate is provided. The polarizing plate has a polarizing film and a protective layer arranged on at least one side of the polarizing film.
In one embodiment, the polarizing plate has a width of 1000 mm or more, and the difference between the maximum value and the minimum value of the simple substance transmittance at a position along the width direction is 0.7% or less.
In one embodiment, the polarizing plate has a difference of 0.3% or less between the maximum value and the minimum value of the simple substance transmittance in the region of 50 cm ² .
According to another aspect of the invention, a polarizing plate roll is provided. The polarizing plate roll is formed by winding the polarizing plate into a roll shape.
According to another aspect of the present invention, there is provided a method for manufacturing a polarizing film. This manufacturing method is the above-mentioned manufacturing method of a polarizing film, in which a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin base material to form a laminate. The above-mentioned laminated body is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminated body is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Including applying in order.
In one embodiment, the content of the halide in the polyvinyl alcohol-based resin layer is 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin.
In one embodiment, the stretching ratio in the aerial auxiliary stretching treatment is 2.0 times or more.
In one embodiment, the drying shrinkage treatment step is a step of heating using a heating roll.
In one embodiment, the temperature of the heating roll is 60 ° C. to 120 ° C., and the shrinkage rate in the width direction of the laminate by the drying shrinkage treatment is 2% or more.

According to the present invention, it is possible to provide a polarizing film having excellent optical properties, having a thickness of 8 μm or less, a simple substance transmittance of 46% or more, and a degree of polarization of 92% or more.

It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is a schematic diagram which shows an example of the drying shrinkage treatment using a heating roll. It is a graph which shows the optical property of the polarizing plate obtained in an Example and a comparative example.

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

A. Polarizing film The polarizing film according to one embodiment of the present invention has a thickness of 8 μm or less, a simple substance transmittance of 46% or more, and a degree of polarization of 92% or more. In general, the single transmittance and the degree of polarization have a trade-off relationship with each other, and increasing the single transmittance may reduce the degree of polarization, and increasing the degree of polarization may reduce the single transmittance. For this reason, it has been difficult to put into practical use a thin polarizing film that satisfies the optical characteristics of a single transmittance of 46% or more and a degree of polarization of 92% or more. As described above, the polarizing film according to one embodiment of the present invention has excellent optical characteristics such that the simple substance transmittance is 46% or more and the degree of polarization is 92% or more. Further, by using the polarizing film of the present embodiment, it is possible to realize a polarizing plate in which variation in optical characteristics is suppressed. The realization of such a thin polarizing film (polarizing plate) is one of the achievements of the present invention. Such a polarizing film (polarizing plate) can be used in an image display device, and is particularly preferably used in a circular polarizing plate for an organic EL display device.

The thickness of the polarizing film is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and further preferably 2 μm to 5 μm.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance of the polarizing film is preferably 48% or less. The degree of polarization of the polarizing film is preferably 92.5% or more, more preferably 93% or more. On the other hand, the upper limit of the degree of polarization is preferably 97%. The simple substance transmittance is typically a Y value measured by using an ultraviolet-visible spectrophotometer and corrected for luminosity factor. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured by using an ultraviolet-visible spectrophotometer and corrected for luminosity factor.
Degree of polarization (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film having a thickness of 8 μm or less is typically a lamination of a polarizing film (refractive index on the surface: 1.53) and a protective film (refractive index: 1.50). It is measured using an ultraviolet-visible spectrophotometer with the body as the measurement target. 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 film, the reflectance at the interface of each layer may change, and as a result, the measured value of the transmittance may change. .. Therefore, for example, when a protective film having a refractive index of not 1.50 is used, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following equation using the reflectance _R1 (transmittance axis reflectance) of the polarized light parallel to the transmission axis at the interface between the protective film and the air layer.
C = R ₁ -R ₀
R ₀ = ((1.50-1) ² / (1.50 + 1) ² ) × (T _1/100 )
R ₁ = ((n 1-1) ² / (n _{1 +1} ) ² ) × (T _1/100 )
Here, R ₀ is the transmittance of the transmission axis when a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. Is. For example, when a base material having a surface refractive index of 1.53 (a cycloolefin-based film, a film with a hard coat layer, etc.) is used as a protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert it into the transmittance when a protective film having a surface refractive index of 1.50 is used. According to the calculation based on the above equation, 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 transmittance of the polarizing film is the correction value C. The effect on the value of is limited. Further, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the absorption amount.

As the polarizing film, any suitable polarizing film may be adopted. The polarizing film can be typically made by using a laminated body having two or more layers.

Specific examples of the polarizing film obtained by using the laminated body include a polarizing film obtained by using a laminated body of a resin base material and a PVA-based resin layer coated and formed on the resin base material. The polarizing film obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying it. A PVA-based resin layer is formed on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; the laminate is stretched and dyed to obtain a PVA-based resin layer as a polarizing film; obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further comprise, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. The obtained laminated body of the resin base material / polarizing film may be used as it is (that is, the resin base material may be used as the protective layer of the polarizing film), and the resin base material is peeled off from the laminated body of the resin base material / polarizing film. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of the method for producing such a polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

The method for producing a polarizing film of the present invention comprises forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to form a laminated body. The above-mentioned laminate includes an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. .. As a result, it is possible to provide a polarizing film having excellent optical characteristics and suppressed variation in optical characteristics, having a thickness of 8 μm or less, a simple substance transmittance of 46% or more, and a degree of polarization of 92% or more. .. That is, by introducing the auxiliary stretching, even when PVA is applied on the thermoplastic resin, the crystallinity of PVA can be enhanced and high optical characteristics can be achieved. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of PVA orientation and dissolution when immersed in water in a subsequent dyeing step or stretching step, and high optical characteristics. Will be possible to achieve. Further, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water. Further, the optical characteristics can be improved by shrinking the laminated body in the width direction by the drying shrinkage treatment.

B. Polarizer FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 has a polarizing film 10, a first protective layer 20 arranged on one side of the polarizing film 10, and a second protective layer 30 arranged on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in the above section A. One of the first protective layer 20 and the second protective layer 30 may be omitted. As described above, one of the first protective layer and the second protective layer may be a resin base material used for producing the above-mentioned polarizing film.

The polarizing plate may be long or single-lobed. When the polarizing plate has a long shape, it is preferably wound into a roll to form a polarizing plate roll. The polarizing plate has excellent optical characteristics and the variation in optical characteristics is small. In one embodiment, the polarizing plate has a width of 1000 mm or more, and the difference (D1) between the maximum value and the minimum value of the simple substance transmittance at a position along the width direction is 0.7% or less. The upper limit of D1 is preferably 0.6%, more preferably 0.5%. The smaller D1 is, the more preferable it is, but the lower limit is, for example, 0.01%. When D1 is within the above range, a polarizing plate having excellent optical properties can be industrially produced. In another embodiment, the polarizing plate has a difference (D2) between the maximum value and the minimum value of the simple substance transmittance in the region of 50 cm ² of 0.3% or less. The upper limit of D2 is preferably 0.2%, more preferably 0.15%. The smaller D2 is, the more preferable it is, but the lower limit is, for example, 0.01%. When D2 is within the above range, it is possible to suppress the variation in brightness on the display screen when the polarizing plate is used in the image display device.

The first and second protective layers are formed of any suitable film that can be used as a protective layer for the polarizing film. Specific examples of the material that is the main component of the film include cellulosic resins such as triacetylcellulose (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, and polysulfones. , Polyester-based, polynorbornene-based, polyolefin-based, (meth) acrylic-based, acetate-based transparent resins and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

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

The thickness of the protective layer (inner protective layer) arranged on the display panel side when the polarizing plate 100 is applied to the image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 10 μm to 60 μm. be. In one embodiment, the inner protective layer is a retardation layer with any suitable retardation value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. “Re (550)” is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C., and is obtained by the formula: Re = (nx−ny) × d. Here, "nx" is the refractive index in the direction in which the refractive index in the plane is maximized (that is, the slow phase axis direction), and "ny" is the direction orthogonal to the slow phase axis in the plane (that is, the phase advance axis direction). It is the refractive index in the axial direction), “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).

C. Method for manufacturing a polarizing film In the method for manufacturing a polarizing film according to one embodiment of the present invention, polyvinyl alcohol containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material is used. By forming a based resin layer (PVA-based resin layer) to form a laminated body, and by heating the laminated body while transporting it in the longitudinal direction, which is an aerial auxiliary stretching treatment, a dyeing treatment, and an underwater stretching treatment. A drying shrinkage treatment of shrinking by 2% or more in the width direction and a dry shrinkage treatment are performed 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 with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60 ° C to 120 ° C. The shrinkage ratio in the width direction of the laminated body by the dry shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above section A can be obtained. In particular, by preparing a laminate containing a PVA-based resin layer containing a halide, stretching the laminate to multi-step stretching including aerial auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. It is possible to obtain a polarizing film having excellent optical characteristics (typically, single transmittance and degree of polarization) and suppressing variation in optical characteristics. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminated body can be uniformly shrunk over the entire laminated body while being conveyed. As a result, not only the optical characteristics of the obtained polarizing film can be enhanced, but also a polarizing film having excellent optical characteristics can be stably produced, and variation in the optical characteristics (particularly, single transmittance) of the polarizing film can be suppressed. can do.

C-1. Preparation of Laminate As a method for preparing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method can be adopted. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material. 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.

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

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

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

C-1-1. Thermoplastic resin base material The thickness of the thermoplastic resin base material is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, in the underwater stretching treatment described later, it may take a long time for the thermoplastic resin base material to absorb water, and an excessive load may be required for stretching.

The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water can act as a plasticizer to plasticize. As a result, the drawing stress can be significantly reduced, and the drawing can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as deterioration of the dimensional stability of the thermoplastic resin base material at the time of manufacture and deterioration of the appearance of the obtained polarizing film. In addition, it is possible to prevent the base material from breaking during stretching in water and the PVA-based resin layer from peeling off from the thermoplastic resin base material. The water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value obtained according to 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 base material, it is possible to sufficiently secure the stretchability of the laminated body while suppressing the crystallization of the PVA-based resin layer. Further, considering that the thermoplastic resin base material is plasticized with water and well stretched in water, the temperature is more preferably 100 ° C. or lower, more preferably 90 ° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60 ° C. or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material is deformed (for example, unevenness, tarmi, wrinkles, etc.) when the coating liquid containing the PVA-based resin is applied and dried. It is possible to satisfactorily produce a laminated body by preventing the above-mentioned problems. Further, the PVA-based resin layer can be well stretched at a suitable temperature (for example, about 60 ° C.). The glass transition temperature of the thermoplastic resin base material can be adjusted, for example, by heating with a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

As the constituent material of the thermoplastic resin base material, any suitable thermoplastic resin can be adopted. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Can be mentioned. Among these, norbornene-based resin and amorphous polyethylene terephthalate-based resin are preferable.

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

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

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

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

Any suitable method can be adopted as the method for stretching the thermoplastic resin base material. Specifically, it may be a fixed end stretch or a free end stretch. The stretching method may be a dry method or a wet method. The stretching of the thermoplastic resin base material may be carried out in one step or in multiple steps. When performed in multiple stages, the above-mentioned draw ratio is the product of the draw ratios of each stage.

C-1-2. Coating liquid The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferable. The PVA-based resin concentration of 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, it is possible to form a uniform coating film in close contact with the thermoplastic resin base material. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

As the PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the 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 determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the intended purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

As the halide, any suitable halide can be adopted. For example, iodide and sodium chloride can be mentioned. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferable.

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

Generally, the stretching of the PVA-based resin layer increases the orientation of the polyvinyl alcohol molecules in the PVA-based resin. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. The tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in borate water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material, and stretching the laminate in air at a high temperature (auxiliary stretching) before stretching it in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water.

C-2. Aerial auxiliary stretching treatment In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and boric acid water stretching is selected. By introducing auxiliary stretching as in the case of two-stage stretching, it is possible to stretch while suppressing the crystallization of the thermoplastic resin base material, and excessive crystallization of the thermoplastic resin base material in the subsequent stretching in boric acid water. This solves the problem that the stretchability is lowered, and the laminated body can be stretched at a higher magnification. Furthermore, when the PVA-based resin is applied on the thermoplastic resin base material, it is compared with the case where the PVA-based resin is applied on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material. Therefore, it is necessary to lower the coating temperature, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to improve the crystallinity of the PVA-based resin even when the PVA-based resin is applied on the thermoplastic resin, and it is possible to achieve high optical characteristics. Become. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration and dissolution of the PVA-based resin when immersed in water in a subsequent dyeing step or stretching step. , It becomes possible to achieve high optical characteristics.

The stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Although good, free-end stretching can be positively adopted in order to obtain high optical properties. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the laminate by the difference in peripheral speed between the heating rolls while transporting the laminated body in the longitudinal direction thereof. The aerial stretching treatment typically includes a zone stretching step and a heating roll stretching step. The order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film is stretched by grasping the end portion of the film and widening the distance between the tenters in the flow direction (the widening of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free end stretching with respect to the stretching ratio in the flow direction. In the case of free-end stretching, the shrinkage rate in the width direction = (1 / stretching ratio) ^1/2 .

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

The draw ratio in the aerial auxiliary stretching is preferably 2.0 to 3.5 times. The maximum draw ratio when the aerial auxiliary stretching and the underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times with respect to the original length of the laminated body. That is all. In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks, and means a value 0.2 lower than that value.

The stretching temperature of the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) or higher of the thermoplastic resin base material, more preferably the glass transition temperature (Tg) of the thermoplastic resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher. On the other hand, the upper limit of the stretching temperature is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). can.

C-3. Insolubilization treatment If necessary, an insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing a PVA-based resin layer in a boric acid aqueous solution. By performing the insolubilization treatment, it is possible to impart water resistance to the PVA-based resin layer and prevent the orientation of PVA from deteriorating when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

C-4. Dyeing treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, it is carried out by adsorbing iodine on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of applying the dyeing solution to the PVA-based resin layer. Examples include a method of spraying. A method of immersing the laminate in a dyeing solution (staining bath) is preferable. This is because iodine can be adsorbed well.

The stain solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.05 part by weight to 0.5 part by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine 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. And so on. Among these, potassium iodide is preferable. The blending amount of the iodide is preferably 0.1 part by weight to 10 parts by weight, and more preferably 0.3 part by weight to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature at the time of dyeing the dyeing liquid is preferably 20 ° C. to 50 ° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds in order to secure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained polarizing film is 46% or more and the degree of polarization is 92% or more. As such a dyeing condition, an iodine aqueous solution is preferably used as the staining solution, and the ratio of the iodine and potassium iodide contents in the iodine aqueous solution is set to 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the iodine aqueous solution is 1: 5 to 1:20. The ratio of the iodine and potassium iodide contents in the iodine aqueous solution is preferably 1: 5 to 1:10. As a result, a polarizing film having the above optical characteristics can be obtained.

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

C-5. Cross-linking treatment If necessary, carry out a cross-linking treatment after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By performing the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of PVA can be prevented from being lowered when immersed in high-temperature water by subsequent stretching in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Further, when the cross-linking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linked bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

C-6. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin base material or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80 ° C.), and the PVA-based resin layer is crystallized. It is possible to stretch at a high magnification while suppressing the above. As a result, a polarizing film having excellent optical characteristics can be manufactured.

Any suitable method can be adopted as the stretching method of the laminated body. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free-end stretching is selected. The stretching of the laminate may be carried out in one step or in multiple steps. In the case of performing in multiple stages, the draw ratio (maximum draw ratio) of the laminated body described later is the product of the draw ratios of each stage.

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

The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 3.5 parts by weight to 7 parts by weight, and particularly preferably 4 parts by weight to 6 parts by weight with respect to 100 parts by weight of water. Is. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent can also be used.

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

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

The stretching ratio by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminated body is preferably 5.0 times or more, more preferably 5.5 times or more, with respect to the original length of the laminated body. By achieving such a high draw ratio, it is possible to manufacture a polarizing film having extremely excellent optical characteristics. Such a high draw ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

C-7. Dry shrinkage treatment The dry shrinkage treatment may be performed by heating the entire zone by heating the zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminated body and produce a polarizing film having an excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin substrate can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the PVA-based resin layer is in a state of being able to withstand shrinkage due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by the dry shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminated body can be continuously contracted in the width direction while being conveyed, and high productivity can be realized.

FIG. 2 is a schematic view showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin base material. For example, one surface of the laminate 200 (for example, thermoplasticity) is arranged. The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin substrate surface).

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

The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using both drying with a heating roll and hot air drying together, a steep temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30 ° C to 100 ° C. 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. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

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

なお、例えば、アンチグレア（ＡＧ）の表面処理や拡散性能を有する粘着剤を備える偏光板を測定対象とする場合、分光光度計に依存して異なる測定結果が得られ得るが、この場合、同一の偏光板をそれぞれの分光光度計で測定したときの測定値に基づいて数値換算を行うことにより、分光光度計に依存する測定値の差を補償することが可能である。
（３）長尺状の偏光板の光学特性のバラつき
実施例および参考例の長尺状の偏光板から、幅方向に沿って等間隔に５か所の各位置で測定サンプルを切り出し、５つの各測定サンプルの中央部分の単体透過率を上記（２）と同様にして測定した。次いで、各測定位置において測定された単体透過率のうちの最大値と最小値との差を算出し、この値を長尺状の偏光板の光学特性のバラつき（長尺状偏光板の幅方向に沿った位置における単体透過率の最大値と最小値との差）とした。
（４）枚葉状の偏光板の光学特性のバラつき
実施例および参考例の長尺状の偏光板から、１００ｍｍ×１００ｍｍの測定サンプルを切り出し、枚葉状の偏光板（５０ｃｍ^２）の光学特性のバラつきを求めた。具体的には、測定サンプルの４辺の各辺の中点から内側に約１．５ｃｍ～２．０ｃｍ付近の位置および中央部分の計５か所の単体透過率を上記（２）と同様にして測定した。次いで、各測定位置において測定された単体透過率のうちの最大値と最小値との差を算出し、この値を枚葉状の偏光板の光学特性のバラつき（５０ｃｍ^２の領域内における単体透過率の最大値と最小値との差）とした。 Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness Measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").
(2) Single transmittance and degree of polarization With respect to the polarizing plates (protective film / polarizing film) of the examples and comparative examples, the single transmittance Ts measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by Nippon Spectral Co., Ltd.), The parallel transmittance Tp and the orthogonal transmittance Tc were defined as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values measured by the JIS Z8701 two-degree visual field (C light source) and corrected for luminosity factor. The refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
The spectrophotometer can also be used for equivalent measurements with an LPF-200 manufactured by Otsuka Electronics Co., Ltd. As an example, Table 1 shows the measured values of the simple substance transmittance Ts and the degree of polarization P obtained by the measurement using V-7100 and LPF-200 for the sample 1 to the sample 3 of the polarizing plate having the same configuration as the following examples. show. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 was 0.1% or less, and any spectrophotometer was used. It can be seen that the same measurement result can be obtained even in some cases.

For example, when a polarizing plate provided with an antiglare (AG) surface treatment or a pressure-sensitive adhesive having diffusion performance is used as a measurement target, different measurement results can be obtained depending on the spectrophotometer, but in this case, they are the same. It is possible to compensate for the difference in the measured values depending on the spectrophotometer by performing numerical conversion based on the measured values when the polarizing plate is measured by each spectrophotometer.
(3) Variations in optical characteristics of long polarizing plates From the long polarizing plates of Examples and Reference Examples, measurement samples were cut out at 5 locations at equal intervals along the width direction, and 5 measurements were taken. The single transmittance of the central portion of each measurement sample was measured in the same manner as in (2) above. Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position is calculated, and this value is used as the variation in the optical characteristics of the long polarizing plate (in the width direction of the long polarizing plate). The difference between the maximum value and the minimum value of the single transmittance at the position along the above).
(4) Variations in the optical characteristics of the single-wafer-shaped polarizing plate A measurement sample of 100 mm × 100 mm was cut out from the long-shaped polarizing plates of Examples and Reference Examples, and variations in the optical characteristics of the single-wafer-shaped polarizing plate (50 cm ² ) were obtained. Asked. Specifically, the single transmittances at a total of 5 locations, about 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample and the central portion, are the same as in (2) above. Was measured. Next, the difference between the maximum value and the minimum value of the single-unit transmittance measured at each measurement position is calculated, and this value is used as the variation in the optical characteristics of the single-wafer-shaped polarizing plate (single-unit transmittance in the region of 50 cm ² ). The difference between the maximum value and the minimum value of).

[Example 1]
1. 1. Preparation of Polarizing Film As the thermoplastic resin base material, an amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption of 0.75%, and a Tg of about 75 ° C. was used. One side of the resin substrate was corona-treated.
100 weight of PVA-based resin in which polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") are mixed at a ratio of 9: 1. 13 parts by weight of potassium iodide was added to the part to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm, and a laminate was prepared.
The obtained laminate was stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water), the polarizing film finally obtained was charged. It was immersed for 60 seconds while adjusting the concentration so that the simple substance permeability (Ts) was 46% or more (staining treatment).
Then, it was immersed in a cross-linked bath having a liquid temperature of 40 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 5.0% by weight) having a liquid temperature of 70 ° C., the total draw ratio is 5.5 in the vertical direction (longitudinal direction) between rolls having different peripheral speeds. The uniaxial stretching was performed so as to be doubled (underwater stretching treatment).
Then, the laminate was immersed in a washing bath having a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminated body by the dry shrinkage treatment was 5.2%.
In this way, a polarizing film having a thickness of 5 μm was formed on the resin substrate. Further, the same procedure was repeated to prepare a total of five polarizing films.
2. 2. Fabrication of Polarizing Plate An acrylic film (surface refractive index 1.50, 40 μm) as a protective film is adhered to the surface of each polarizing film obtained above (the surface opposite to the resin substrate) by UV curable adhesion. They were pasted together via an agent. Specifically, the curable adhesive was coated so as to have a total thickness of 1.0 μm, and bonded using a roll machine. Then, a UV ray was irradiated from the protective film side to cure the adhesive. Then, after slitting both ends, the resin base material was peeled off to obtain five long polarizing plates (width: 1300 mm) having a protective film / polarizing film configuration.

[Reference Example 1]
Seven polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the dyeing treatment was performed so that the single transmittance (Ts) of the finally obtained polarizing film was 43% or more and less than 46%. did.

[Comparative Example 1]
Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating liquid), the stretching ratio in the aerial auxiliary stretching treatment was set to 1.8 times, and the heating roll was not used in the drying shrinkage treatment. An attempt was made to prepare a polarizing film in the same manner as in the above, but the PVA-based resin layer was dissolved in the dyeing treatment and the stretching treatment in water, and the polarizing film could not be prepared.

[Comparative Example 2]
17 polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the stretching ratio in the aerial auxiliary stretching treatment was set to 1.8 times and the heating roll was not used in the drying shrinkage treatment. However, it was not possible to produce a polarizing film having a single transmittance of 46% or more.

[Reference Example 2]
The polarizing film obtained in the same manner as in Comparative Example 2 was held in a constant temperature and constant humidity zone set to a temperature of 60 ° C. and a humidity of 90% RH for 30 minutes. Then, a polarizing plate was produced in the same manner as in Example 1.

For each of the polarizing plates of Examples and Comparative Examples, the single transmittance and the degree of polarization were measured. The results are shown in Table 2 and FIG. In FIG. 3, the approximate curve of the plot of Example 1 and the plot of Reference Example 1 and the approximate curve of the plot of Comparative Example 2 are illustrated. The approximate curve of Comparative Example 2 is an approximate curve based on a cubic polynomial approximation, and the broken line indicates an extrapolated portion of the approximate curve.

The polarizing film obtained by the production method of the comparative example did not satisfy the single transmittance of 46% or more and the degree of polarization of 92% or more at the same time. As shown by the approximate curve of the plot of Comparative Example 2, in the manufacturing method of Comparative Example 2, the degree of polarization is less than 92% when the dyeing treatment is performed so that the simple substance transmittance is 46% or more. Is expected. On the other hand, the polarizing film obtained by the production method of the example had excellent optical properties having a simple substance transmittance of 46% or more and a degree of polarization of 92% or more.

For each of the polarizing plates of Example 1 and Reference Example 2, the variation in the optical characteristics of the long-shaped and single-wafer-shaped polarizing plates was measured. The results are shown in Table 3.

The long-shaped polarizing plate obtained by the manufacturing method of the example has a variation in the single transmittance of 0.7% or less, and the single-wafer-shaped polarizing plate obtained by the manufacturing method of the example has a single transmittance. The variation in optical characteristics is 0.3% or less, and the variation in optical characteristics is suppressed to the extent that there is no problem. On the other hand, the polarizing plate of the reference example obtained through the step of humidifying the polarizing film had a large variation in optical characteristics in both the long shape and the single-wafer shape.

The polarizing plate having the polarizing film of the present invention is suitably used for a circular polarizing plate for an organic EL display device and an inorganic EL display device.

10 Polarizing film 20 First protective layer 30 Second protective layer 100 Polarizing plate

Claims (6)

A method for manufacturing a polarizing film having a thickness of 8 μm or less, a simple substance transmittance of 46% or more, and a degree of polarization of 92% or more.
A polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin base material to form a laminate, and the laminate is subjected to aerial auxiliary stretching. A production method comprising performing a treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment of shrinking by 2% or more in the width direction by heating while transporting in the longitudinal direction in this order. The manufacturing method according to claim 1 , which is a method for manufacturing a polarizing film having a simple substance transmittance of 48% or less and a degree of polarization of 97% or less. The production method according to claim 1 or 2 , wherein the content of the iodide or sodium chloride in the polyvinyl alcohol-based resin layer is 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin. The production method according to any one of claims 1 to 3 , wherein the stretching ratio in the aerial auxiliary stretching treatment is 2.0 times or more. The production method according to any one of claims 1 to 4 , wherein the drying shrinkage treatment step is a step of heating using a heating roll. The production method according to claim 5 , wherein the temperature of the heating roll is 60 ° C. to 120 ° C., and the shrinkage rate in the width direction of the laminate by the drying shrinkage treatment is 2% or more.

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