JP7376494B2 - Polarizing plate, method for manufacturing the same, and image display device including the polarizing plate - Google Patents

Description

The present invention relates to a polarizing plate, a method for manufacturing the same, and an image display device including the polarizing plate.

Due to its image forming method, a liquid crystal display device, which is a typical image display device, has a polarizing film (typically a polarizing film laminate containing a polarizing film and an optical functional layer) on both sides of a liquid crystal cell. For example, a polarizing plate)) is arranged. Furthermore, with the spread of thin displays, displays equipped with organic EL panels (OLEDs) and displays using display panels using inorganic light-emitting materials such as quantum dots (QLEDs) have been proposed. 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) resin layer and then subjecting it to a dyeing treatment to obtain a polarizing film on the resin base material is available. It has been proposed (for example, Patent Document 1). According to such a method, since a thin polarizing film can be obtained, it is attracting attention as it can contribute to the slimming down of recent image display devices. However, the conventional thin polarizing films as described above have insufficient optical properties, and there is a demand for further improvement in the optical properties of thin polarizing films. Furthermore, in recent years, the uses of image display devices have expanded significantly, and, for example, the use of in-vehicle image display devices (eg, car navigation devices, rear monitors) has expanded. Along with this, the polarizing film laminate is required to have excellent durability under harsh heating environments (e.g., high temperature environments), and polarizing films and polarizing film laminates that can achieve such durability are required. The body is in demand.

Special Publication No. 2012-516468

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizing plate that has excellent durability even under harsh heating environments.

The polarizing plate of the present invention includes a polarizing film having a thickness of 8 μm or less and protective films disposed on both sides of the polarizing film, and is heated at 100°C with a glass plate attached to both sides via an adhesive layer. After being left for 60 hours, the amount of change ΔP in the degree of polarization expressed by the following formula is -1.0% to 0.0%:
ΔP (%) = P ₆₀ - P ₀
Here, P ₀ is the degree of polarization before heating, and P ₆₀ is the degree of polarization after heating for 60 hours.
In one embodiment, the polarizing plate has a single transmittance change amount ΔTs expressed by the following formula after being left at 100° C. for 60 hours with glass plates bonded to both sides with adhesive layers interposed therebetween. is 0.0% to 1.5%:
ΔTs (%) = Ts ₆₀ - Ts ₀
Here, Ts ₀ is the single transmittance before heating, and Ts ₆₀ is the single transmittance after heating for 60 hours.
In one embodiment, the single transmittance Ts ₀ is 41.8% to 43.0%.
In one embodiment, the moisture permeability of the protective film is 200 g/m ² ·24 h or less.
According to another aspect of the present invention, an image display device is provided. This image display device includes a display cell and the above-mentioned polarizing plate disposed on the viewing side of the display cell.
In one embodiment, the image display device is configured to be mounted on a vehicle.
According to yet another aspect of the present invention, a method for manufacturing a polarizing plate is provided. This manufacturing method includes forming a polyvinyl alcohol resin layer containing iodide or sodium chloride and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to form a laminate; , the polyvinyl alcohol-based resin is subjected to an auxiliary stretching process in the air, a dyeing process, a stretching process in water, and a drying shrinkage process in which it shrinks by 2% or more in the width direction by heating while conveying in the longitudinal direction. The method includes making the layer a polarizing film; and laminating protective films on both sides of the polarizing film.

According to the present invention, addition of a halide (typically potassium iodide) to polyvinyl alcohol (PVA)-based resin, two-stage stretching including aerial assisted stretching and underwater stretching, and drying and shrinkage using heated rolls. By employing these in combination, it is possible to obtain a polarizing film that is thin and has excellent durability even under harsh heating environments (for example, changes in polarization degree and single transmittance before and after heating are small). By using such a polarizing film, it is possible to realize a polarizing plate that has excellent durability even under harsh heating environments.

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of dry shrinkage treatment using a heating roll.

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

A. Overall Configuration of Polarizing Plate 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 11 and protective films 12 and 13 disposed on both sides of the polarizing film 11. Either one of the protective films 12 and 13 may be omitted depending on the purpose and desired configuration. In an embodiment of the present invention, the polarizing film is typically a polyvinyl alcohol (PVA) resin film containing a dichroic substance (for example, iodine), and has a thickness of 8 μm or less.

In the embodiment of the present invention, the polarizing plate has a change amount ΔP in the degree of polarization expressed by the following formula after being left at 100°C for 60 hours with glass plates bonded to both sides via adhesive layers. is -1.0% to 0.0%:
ΔP (%) = P ₆₀ - P ₀
Here, P ₀ is the degree of polarization before heating, and P ₆₀ is the degree of polarization after heating for 60 hours. That is, the polarizing plate according to the embodiment of the present invention is characterized in that the degree of polarization decreases little even when placed in a harsh heating environment of 100°C. ΔP is preferably -0.5% to 0.0%, more preferably -0.2% to 0.0%. Preferably, the polarizing plate has a single transmittance change ΔTs of 0.0% after being left at 100°C for 60 hours with glass plates bonded to both sides via adhesive layers. ~1.5%:
ΔTs (%) = Ts ₆₀ - Ts ₀
Here, Ts ₀ is the single transmittance before heating, and Ts ₆₀ is the single transmittance after heating for 60 hours. That is, the polarizing plate according to the embodiment of the present invention is preferably characterized in that the increase in single transmittance is small even when placed in a harsh heating environment of 100°C. ΔTs is preferably 0.0% to 1.0%, more preferably 0.0% to 0.7%. Here, the degree of polarization and the single transmittance are essentially the characteristics of the polarizing film, but since the constituent elements other than the polarizing film in the polarizing plate do not substantially affect the degree of polarization and the single transmittance, the polarization of the polarizing film The degree of polarization and single transmittance of the polarizing plate are substantially the same as the single transmittance of the polarizing plate. It is estimated that such characteristics of the polarizing plate can be realized by the following mechanism of the polarizing film: Iodine in the polarizing film is a PVA/I ^3- complex (having absorption near 480 nm), PVA/I ^5- Although it exists in multiple states such as complex (having absorption in the vicinity of 600 nm) and iodine ion that does not form a complex (having absorption in the ultraviolet region around 210 nm), it is mainly PVA/I ^3- complex and PVA/I ⁵ . ^- Due to the complex, the polarizing film exhibits absorption dichroism in visible light. Generally, under high temperature conditions, the PVA/I ^5- complex becomes unstable and the amount of PVA/I ^5- complex decreases. This causes a phenomenon in which the polarizing film and the polarizing film laminate (for example, a polarizing plate) turn red in a crossed nicol state (heat reddening). Furthermore, when an image display device is constructed by bonding a polarizing plate to a display cell using an adhesive, a high temperature and high humidity condition occurs due to moisture contained in the polarizing plate and the adhesive, resulting in PVA/I ^3- complex and PVA/I ^{5 -} The deterioration of the complex becomes noticeable, and in addition to the above-mentioned heat reddening, a decrease in the degree of polarization and an increase in single transmittance become noticeable. According to an embodiment of the present invention, as described below, the addition of a halide (typically, potassium iodide) to a polyvinyl alcohol (PVA)-based resin, two-stage stretching including aerial auxiliary stretching and underwater stretching; In addition, by employing a combination of drying and shrinkage using a heating roll, a polarizing film with excellent stability of the PVA/I ^3- complex and PVA/I ^5- complex can be obtained even under a harsh heating environment. As a result, it is possible to realize a polarizing plate that has excellent durability even under harsh heating environments (typically, red discoloration is suppressed and changes in polarization degree and single transmittance are small).

B. Polarizing Film As described above, the polarizing film is composed of a PVA-based resin film containing a dichroic substance (for example, iodine). The polarizing film is essentially a PVA resin film in which iodine is adsorbed and oriented. Any suitable resin may be employed as the PVA resin forming the PVA resin film. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The degree of saponification of the PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA resin having such a degree of saponification, a polarizing film with excellent durability can be obtained. If the degree of saponification is too high, there is a risk of gelation.

The iodine concentration in the polarizing film is 5.0% by weight or more, preferably 5.0% to 12.0% by weight, more preferably 5.5% to 10.0% by weight. Note that in this specification, "iodine concentration" means the total amount of iodine contained in the polarizing film. More specifically, in the polarizing film, iodine exists in the form of I ⁻ , I ₂ , I ₃ ⁻ , PVA/I ^3- complex, PVA/I ^5- complex, etc., and the iodine concentration in this specification is , means the concentration of iodine including all these forms. The iodine concentration can be calculated, for example, from the fluorescent X-ray intensity determined by fluorescent X-ray analysis and the film (polarizing film) thickness. According to the embodiments of the present invention, it is possible to achieve excellent durability in a harsh heating environment in a polarizing film having such a high iodine concentration.

As described above, the thickness of the polarizing film is 8 μm or less, preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and still more preferably 2 μm to 5 μm. According to the embodiments of the present invention, excellent durability under harsh heating environments can be achieved in such a very thin polarizing film.

The polarizing film preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. The single transmittance (single transmittance before heating) Ts ₀ of the polarizing film is preferably 41.8% to 43.0%, more preferably 41.9% to 42.8%. The degree of polarization (degree of polarization before heating) P ₀ of the polarizing film is preferably 99.900% or more, more preferably 99.950% or more. The above-mentioned single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically determined by the following formula based on parallel transmittance Tp and cross transmittance Tc measured using an ultraviolet-visible spectrophotometer and corrected for visibility.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50). It is measured using an ultraviolet-visible spectrophotometer using the body as the measurement object. Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film in contact with the air interface, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. . Therefore, for example, when using a protective film with a refractive index other than 1.50, the measured value of transmittance may be corrected according to the refractive index of the surface of the protective film that is in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective 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 transmission axis reflectance when using a protective film with a refractive index of 1.50, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. It is. For example, when a base material (cycloolefin film, film with a hard coat layer, etc.) having a surface refractive index of 1.53 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 measurement, it is possible to convert it to the transmittance when using a protective film with a surface refractive index of 1.50. According to the calculation based on the above formula, when the transmittance _T1 of the polarizing film is changed by 2%, the amount of change in the correction value C is 0.03% or less, and the transmittance of the polarizing film is less than the correction value C. The effect on the value of is limited. Furthermore, when the protective film has absorption other than surface reflection, appropriate correction can be made depending on the amount of absorption.

Any suitable polarizing film may be employed as the polarizing film. A polarizing film can typically be produced using a laminate of two or more layers.

A specific example of a polarizing film obtained using a laminate includes a polarizing film obtained using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material. A polarizing film obtained using a laminate of a resin base material and a PVA resin layer coated on the resin base material can be obtained by, for example, applying a PVA resin solution to the resin base material and drying it. Forming a PVA-based resin layer thereon to obtain a laminate of a resin base material and a PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer a polarizing film; obtain. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, the stretching may further include stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in the boric acid aqueous solution, if necessary. The obtained resin base material/polarizing film laminate may be used as is (that is, the resin base material may be used as a protective layer for the polarizing film), or the resin base material may be peeled from the resin base material/polarizing film laminate. However, any appropriate protective layer may be laminated on the peeled surface depending on the purpose. Details of the method for manufacturing such a polarizing film are described in, for example, Japanese Patent Application Publication No. 2012-73580. The entire description of this publication is incorporated herein by reference.

A polarizing film is typically formed by forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to form a laminate, and the above-mentioned. A method comprising subjecting the laminate to, in this order, an auxiliary stretching process in the air, a dyeing process, a stretching process in water, and a drying shrinkage process in which the laminate is shrunk by 2% or more in the width direction by heating while conveying in the longitudinal direction. It can be made by As a result, a polarizing film that is thin and has excellent durability even under harsh heating environments can be obtained. The method for manufacturing a polarizing film will be described in detail in Section E below as a step included in the method for manufacturing a polarizing plate.

C. Protective Film The protective films 12 and 13 are formed of any suitable film that can be used as a protective film for a polarizing film. Specific examples of materials that are the main components of the film include cellulose resins such as triacetylcellulose (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, and polysulfones. Examples include transparent resins such as polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate. Further, thermosetting resins or ultraviolet curable resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone resins may also be mentioned. Other examples include glassy polymers such as siloxane polymers. Furthermore, the polymer film described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in its side chain. For example, a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer can be used. The polymer film may be, for example, an extrusion molded product of the resin composition. The protective film is preferably made of a cycloolefin resin such as a polynorbornene resin. This is because appropriate moisture permeability can be achieved.

The moisture permeability of the protective film is preferably 200 g/m ² ·24 h or less, more preferably 100 g/m ² ·24 h or less, even more preferably 50 g/m ² ·24 h or less, and particularly preferably 20 g/m 2 ·24 h or less. ^m2・24h or less. The lower the moisture permeability is, the more preferable it is, and the lower limit of the moisture permeability may be, for example, 2 g/m ² ·24 h. If the moisture permeability is within this range, red discoloration can be further suppressed and changes in the degree of polarization and single transmittance can be further reduced in a high temperature environment. The moisture permeability is measured according to the moisture permeability test (cup method) of JIS Z0208.

When the polarizing plate 100 is applied to an image display device, the protective film (outer protective film) 12 disposed on the opposite side from the display cell may be subjected to hard coat treatment, antireflection treatment, antisticking treatment, A surface treatment such as anti-glare treatment may be applied. Additionally/or, the outer protective film 12 may optionally be provided with a treatment to improve visibility when viewed through polarized sunglasses (typically, an (elliptical) circularly polarizing function, an ultra-high (providing a phase difference) may be applied. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Such a polarizing plate has excellent visibility for a vehicle driver wearing sunglasses, and therefore can be suitably applied to a vehicle-mounted image display device.

The thickness of the outer protective film 12 is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and even more preferably 10 μm to 60 μm. In addition, when surface treatment is performed, the thickness of the outer protective film is the thickness including the thickness of the surface treatment layer.

The thickness of the protective film (inner protective film) 13 disposed on the display cell side when the polarizing plate 100 is applied to an image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and even more preferably 10 μm to 60 μm. It is. In one embodiment, the inner protective film is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. say. In another embodiment, the inner protective film is a retardation layer having 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 retardation measured with light having a wavelength of 550 nm at 23° C., and is determined by the formula: Re=(nx−ny)×d. "Rth (550)" is the retardation in the thickness direction measured using light with a wavelength of 550 nm at 23° C., and is determined by the formula: Rth=(nx−nz)×d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., fast phase direction). "nz" is the refractive index in the thickness direction (axial direction), "d" is the thickness (nm) of the layer (film).

D. Polarizing Plate with Cover Glass As described above, the polarizing plate according to the embodiment of the present invention has excellent durability even under a harsh heating environment when sandwiched between glass plates, so it can be suitably configured as a polarizing plate with cover glass. obtain. A polarizing plate with a cover glass typically includes the polarizing plate described in items A to C above, and a cover glass laminated on the viewing side (outer protective film 12 side) of the polarizing plate with an interlayer filler interposed therebetween. and has. The interlayer filler is comprised of any suitable adhesive. Examples of interlayer fillers include those described in Japanese Patent No. 6071459. The description of the publication is incorporated herein by reference. The thickness of the interlayer filler is preferably 50 μm to 300 μm, more preferably 100 μm to 250 μm. Since the cover glass has a structure well known and commonly used in the industry, a detailed description thereof will be omitted.

E. Method for manufacturing a polarizing plate According to an embodiment of the present invention, a method for manufacturing a polarizing plate includes forming a polyvinyl alcohol resin containing iodide or sodium chloride and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material. Forming layers to form a laminate; The laminate is subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying to shrink by 2% or more in the width direction by heating while conveying in the longitudinal direction. and shrinkage treatment in this order to turn the polyvinyl alcohol resin layer into a polarizing film; and laminating protective films on both sides of the polarizing film. The content of the halide in the PVA resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin. The drying shrinkage treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. According to this manufacturing method, it is possible to obtain a polarizing film that is thin and has excellent durability even under harsh heating environments. Obtainable. In particular, by producing a laminate including a PVA resin layer containing a halide, stretching the laminate in multiple stages including auxiliary stretching in the air and stretching in water, and heating the laminate after stretching with a heating roll. , it is possible to obtain a polarizing film that has excellent durability even under harsh heating environments and has suppressed variations in optical properties. Specifically, by using a heating roll in the drying shrinkage process, the entire laminate can be uniformly shrunk while being transported. Thereby, the polarizing film as described above can be stably produced.

E-1. Preparation of Laminate Any suitable method may be adopted as a method for producing a laminate of a thermoplastic resin base material and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA resin layer on the thermoplastic resin base material. As mentioned above, the content of the halide in the PVA resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin.

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

The thickness of the PVA 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 subjected to surface treatment (for example, corona treatment, etc.), or an easily 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 resin layer can be improved.

E-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, it may take a long time for the thermoplastic resin base material to absorb water in the underwater stretching treatment described below, 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 base material absorbs water and can be plasticized by the water acting as a plasticizer. As a result, stretching stress can be significantly reduced and stretching 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 a significant decrease in the dimensional stability of the thermoplastic resin base material during production, resulting in deterioration of the appearance of the resulting polarizing film. Furthermore, it is possible to prevent the base material from breaking during underwater stretching or from peeling off the PVA resin layer from the thermoplastic resin base material. Note that 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 determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120°C or lower. By using such a thermoplastic resin base material, it is possible to sufficiently ensure the stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. Furthermore, in consideration of plasticizing the thermoplastic resin base material with water and performing underwater stretching satisfactorily, the temperature is preferably 100° C. or lower, and 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 may be deformed (e.g., unevenness, sagging, wrinkles, etc.) when applying and drying a coating solution containing the above-mentioned PVA-based resin. It is possible to prevent this problem and produce a good laminate. Further, the PVA resin layer can be stretched well at a suitable temperature (for example, about 60° C.). Note that the glass transition temperature of the thermoplastic resin base material can be adjusted by, for example, heating using a crystallizing material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

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

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

In a preferred embodiment, the thermoplastic resin base material is comprised of a polyethylene terephthalate-based resin having isophthalic acid units. This is because such a thermoplastic resin base material has extremely excellent stretchability and can suppress crystallization during stretching. This is thought to be due to the fact that the introduction of the isophthalic acid unit imparts a large bend to the main chain. Polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin base material with extremely excellent stretchability can be obtained. On the other hand, the content 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 the content to such a content ratio, the degree of crystallinity can be favorably increased in the drying shrinkage treatment described below.

The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin base material is stretched in the lateral direction. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In addition, in this specification, "orthogonal" also includes a case where they are substantially orthogonal. Here, "substantially orthogonal" includes a case where the angle is 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 relative to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin base material is preferably 1.5 times to 3.0 times.

Any suitable method may be employed as a method for stretching the thermoplastic resin base material. Specifically, fixed end stretching or free end stretching may be used. The stretching method may be a dry method or a wet method. The thermoplastic resin base material may be stretched in one step or in multiple steps. In the case of multi-stage stretching, the above-mentioned stretching ratio is the product of the stretching ratios of each stage.

E-1-2. Coating Liquid The coating liquid contains a halide and a PVA resin as described above. The coating liquid is typically a solution in which the halide and the PVA resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin base material can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin. Because the coating liquid (as a result, the PVA resin layer) contains a halide, when the PVA resin layer is immersed in the liquid, the polyvinyl alcohol molecules are lower than when the PVA resin layer does not contain a halide. Disturbance of the orientation and deterioration of the orientation can be suppressed. This can improve the optical properties of a polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

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

The PVA-based resin is as described in Section B above.

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

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

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

Generally, by stretching the PVA resin layer, the orientation of the polyvinyl alcohol molecules in the PVA resin increases. However, when the stretched PVA resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules increases. The orientation may be disturbed and the orientation may be deteriorated. In particular, when stretching a laminate of a thermoplastic resin and a PVA resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin, The tendency of the degree of orientation to decrease is remarkable. For example, while it is common for a PVA film alone to be stretched in boric acid water at 60°C, a laminate of A-PET (thermoplastic resin base material) and a PVA resin layer is stretched. It is carried out at a high temperature of around 70°C, and in this case, the orientation of PVA at the initial stage of stretching may decrease before it increases due to underwater stretching. In contrast, by producing a laminate of a PVA resin layer containing a halide and a thermoplastic resin base material, and stretching the laminate at high temperature in air (auxiliary stretching) before stretching it in boric acid water. , crystallization of the PVA resin in the PVA resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disturbance in the orientation of polyvinyl alcohol molecules and deterioration of orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

E-2. Auxiliary Stretching Treatment in Air In particular, in order to obtain high optical properties, a two-stage stretching method is selected that combines dry stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching as in two-stage stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin base material, and prevent excessive crystallization of the thermoplastic resin base material during subsequent stretching in boric acid water. This solves the problem that the stretchability is lowered due to this, and the laminate can be stretched to a higher magnification. Conventionally, when applying PVA-based resin onto a thermoplastic resin base material, in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material, the application temperature was lower than when applying PVA-based resin onto a metal drum. As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of PVA-based resin even when applying PVA-based resin onto thermoplastic resin, making it possible to achieve high optical properties. Become. Furthermore, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in orientation and dissolution of the PVA-based resin when it is immersed in water during the subsequent dyeing and stretching processes. It becomes possible to achieve high optical properties.

The stretching method for aerial auxiliary stretching may be fixed end stretching (for example, stretching using a tenter stretching machine) or free end stretching (for example, uniaxial stretching by passing the laminate between rolls with different circumferential speeds). However, in order to obtain high optical properties, free end stretching may be actively employed. In one embodiment, the aerial stretching process includes a heating roll stretching step of stretching the laminate using a difference in peripheral speed between heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching process typically includes a zone stretching process and a heated roll stretching process. Note that 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 heated roll stretching step are performed in this order. In another embodiment, the film is stretched in a tenter stretching machine by gripping the end portion of the film and widening the distance between the tenters in the machine direction (the widening of the distance between the tenters becomes the stretching ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is set to be arbitrarily close. Preferably, the stretching ratio in the machine direction can be set to be closer to free end stretching. In the case of free end stretching, the shrinkage rate in the width direction is calculated as (1/stretching ratio) ^1/2 .

Aerial assisted stretching may be performed in one step or in multiple steps. In the case of multi-stage stretching, the stretching ratio is the product of the stretching ratios of each stage. The stretching direction in the aerial auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The stretching ratio in the aerial auxiliary stretching is preferably 2.0 times to 3.5 times. The maximum stretching ratio when the aerial auxiliary stretching and underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times the original length of the laminate. That's all. In this specification, the "maximum stretching ratio" refers to the stretching ratio immediately before the laminate breaks, and the stretching ratio at which the laminate breaks is separately confirmed, and it refers to a value 0.2 lower than that value.

The stretching temperature of the in-air auxiliary stretching can be set to any appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, etc. The stretching temperature is preferably at least the glass transition temperature (Tg) of the thermoplastic resin base material, more preferably at least the glass transition temperature (Tg) of the thermoplastic resin base material +10°C, particularly preferably at least Tg +15°C. 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 to suppress defects caused by the crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching). can.

E-3. Insolubilization treatment If necessary, insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or dyeing treatment. The above-mentioned insolubilization treatment is typically performed by immersing the PVA 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 a decrease in orientation of PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight per 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C.

E-4. Dyeing Process The above dyeing process is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, this is carried out by adsorbing iodine to the PVA resin layer. The adsorption method includes, for example, immersing the PVA resin layer (laminate) in a dye containing iodine, applying the dye to the PVA resin layer, and applying the dye to the PVA resin layer. Examples include a method of spraying. Preferably, the method involves immersing the laminate in a dyeing solution (dyeing bath). This is because iodine can be adsorbed well.

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

The dyeing conditions (concentration, liquid temperature, immersion time) should be set so that the single transmittance of the final polarizing film is 43.5% or more and the degree of polarization is 99.940% or more. I can do it. As for such staining conditions, preferably, an iodine aqueous solution is used as the staining liquid, and the ratio of the contents of iodine and potassium iodide in the iodine aqueous solution is 1:5 to 1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. Thereby, a polarizing film having the optical properties as described above can be obtained.

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

E-5. Crosslinking treatment If necessary, crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The above crosslinking treatment is typically performed by immersing the PVA resin layer in a boric acid aqueous solution. By performing the crosslinking treatment, water resistance is imparted to the PVA-based resin layer, and in the subsequent underwater stretching, it is possible to prevent a decrease in the orientation of PVA when immersed in high-temperature water. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight per 100 parts by weight of water. Moreover, when crosslinking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further include an iodide. By blending iodide, it is possible to suppress elution of iodine adsorbed to the PVA-based resin layer. The amount of iodide to be blended is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

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

Any suitable method can be used to stretch the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method in which the laminate is passed between rolls having different circumferential speeds and uniaxially stretched) may be used. Preferably, free end stretching is chosen. The laminate may be stretched in one step or in multiple steps. When performing multi-stage stretching, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios of each stage.

Stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, it is possible to impart rigidity to the PVA-based resin layer to withstand tension applied during stretching, and water resistance that does not dissolve in water. Specifically, boric acid can generate a tetrahydroxyborate anion in an aqueous solution and crosslink with the PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, which can be stretched well, and a polarizing film having excellent optical properties can be manufactured.

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

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

The stretching temperature (the liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, it is possible to stretch to a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin 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., there is a possibility that the stretching cannot be performed satisfactorily even if the plasticization of the thermoplastic resin base material by water is taken into account. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a possibility that excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by underwater stretching is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high stretching ratio, a polarizing film with extremely excellent optical properties can be manufactured. Such a high stretching ratio can be achieved by employing an underwater stretching method (boric acid underwater stretching).

E-7. Drying Shrinkage Treatment The drying shrinkage treatment described above may be performed by zone heating performed by heating the entire zone, or may be performed by heating a conveyance roll (using a so-called heating roll) (heated roll drying method). Preferably, both are used. By drying using a heating roll, heating curl of the laminate can be efficiently suppressed, and a polarizing film with excellent appearance can be manufactured. Specifically, by drying the laminate along a heating roll, it is possible to efficiently promote crystallization of the thermoplastic resin base material and increase the degree of crystallinity, which is relatively low. Even at drying temperatures, the degree of crystallinity of the thermoplastic resin base material can be increased favorably. As a result, the thermoplastic resin base material has increased rigidity and is in a state where it can withstand shrinkage of the PVA resin layer due to drying, thereby suppressing curling. Furthermore, by using a heating roll, the laminate can be dried while maintaining it in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the optical properties of the laminate can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, particularly preferably 4% to 6%. By using a heating roll, the laminate can be continuously contracted in the width direction while being conveyed, and high productivity can be achieved. Furthermore, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment.

FIG. 2 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, 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. The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin base material surface).

The drying conditions can be controlled by adjusting the heating temperature of the conveying roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, particularly preferably 70°C to 80°C. It is possible to satisfactorily increase the degree of crystallinity of the thermoplastic resin, to satisfactorily suppress curling, and to produce an optical laminate having extremely excellent durability. Note that the temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six conveyance rolls are provided, but there is no particular restriction on the number of conveyance rolls as long as there is a plurality of conveyance rolls. Usually 2 to 40 conveyance rolls, preferably 4 to 30 conveyance rolls are provided. 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 even more preferably 1 to 10 seconds.

The heating roll may be provided within a heating furnace (for example, an oven) or may be provided on a normal production line (at room temperature). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, a sharp 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. Further, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. Note that the wind speed is the wind speed within the heating furnace, and can be measured with a mini-vane digital anemometer.

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

E-9. Production of Polarizing Plate In the manner described above, the PVA-based resin layer becomes a polarizing film, and a laminate of polarizing film/thermoplastic resin base material can be produced. In one embodiment, a polarizing film/thermoplastic resin base material laminate is used as a polarizing plate. In this case, the thermoplastic resin substrate can function as a protective film. In another embodiment, a protective film is bonded to the surface of the polarizing film of a laminate of polarizing film/thermoplastic resin base material, and a polarizing plate having the configuration of protective film/polarizing film/thermoplastic resin base material is obtained. obtain. Also in this case, the thermoplastic resin base material can function as a protective film (one protective film). In yet another embodiment, a protective film is bonded to the polarizing film surface of a laminate of a polarizing film/thermoplastic resin base material, and then the thermoplastic resin base material is peeled off to change the structure of the protective film/polarizing film. A polarizing plate having the following properties can be obtained. In yet another embodiment, a protective film is bonded to the polarizing film surface of a laminate of polarizing film/thermoplastic resin base material, the thermoplastic resin base material is then peeled off, and another protective film is further attached to the peeled surface. A polarizing plate having a structure of protective film/polarizing film/another protective film can be obtained by bonding them together. Note that, for example, any suitable adhesive may be used to bond the polarizing film and the protective film. Specific examples of the adhesive include active energy ray-curable adhesives (typically, ultraviolet ray-curable adhesives) and water-based adhesives.

F. Image Display Device A polarizing plate according to an embodiment of the present invention can be applied to an image display device. Therefore, the present invention also encompasses an image display device. The image display device of the present invention includes a display cell and a polarizing plate disposed on the viewing side of the display cell. Representative examples of image display devices include liquid crystal display devices, organic electroluminescence (EL) display devices, and quantum dot display devices. Since the polarizing plate according to the embodiment of the present invention has a remarkable effect in a harsh heating environment, the image display device is preferably an image display device that can be used in a harsh heating environment. A typical example of such an image display device is an in-vehicle image display device. Since the image display device employs a configuration well known in the industry, detailed explanation will be omitted.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. The method for measuring each characteristic is as follows. Note that 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) Changes in single transmittance and polarization degree under high temperature environment Samples for image display devices obtained in Examples and Comparative Examples (Glass plate/adhesive/protective film/polarizing film/protective film/adhesive/glass plate ), the single transmittance Ts ₀ , parallel transmittance Tp ₀ and orthogonal transmittance Tc ₀ were measured using a UV-visible spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., LPF-200). These Ts ₀ , Tp ₀ and Tc ₀ are Y values measured using a 2-degree visual field (C light source) of JIS Z8701 and subjected to visibility correction. Note that the measurement wavelength was 380 nm to 780 nm.
From the obtained Tp ₀ and Tc ₀ , the degree of polarization P ₀ was determined by the following formula.
Polarization degree P ₀ (%) = {(Tp ₀ −Tc ₀ )/(Tp ₀ +Tc ₀ )} ^1/2 ×100
Next, the image display device compatible sample was heated by leaving it in a hot air oven at a temperature of 100°C for 60 hours, and the single transmittance Ts ₆₀ and P ₆₀ after heating were measured in the same manner as above, and the single transmittance before and after heating was measured. The rate change ΔTs and the polarization degree change ΔP were determined from the following equations.
ΔTs (%) = Ts ₆₀ - Ts ₀
ΔP (%) = P ₆₀ - P ₀

[Example 1-1 to Example 1-6]
1. Preparation of Polarizing Film As a thermoplastic resin base material, a long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. was used. One side of the resin base material was subjected to corona treatment.
100 weight PVA resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name "Gosefaimer Z410") at a ratio of 9:1. 13 parts by weight of potassium iodide was added to 13 parts by weight of potassium iodide 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 with a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched free end to 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed for 30 seconds in an insolubilization bath (boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. (insolubilization treatment).
Next, the final polarizing film was added to a dyeing bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 to 100 parts by weight of water) at a liquid temperature of 30°C. The sample was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 41.9% to 42.8% (staining treatment).
Next, it was immersed for 30 seconds in a crosslinking bath (an aqueous boric acid 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) at a liquid temperature of 40°C. (Crosslinking treatment).
Thereafter, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70°C, the total stretching ratio was 5.5 in the longitudinal direction between rolls having different circumferential speeds. Uniaxial stretching was performed to double the size (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heating roll whose surface temperature was maintained at 75°C for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.
In this way, a polarizing film with a thickness of 5 μm was formed on the resin base material. Furthermore, the same procedure was repeated except that the concentration of the dye bath was changed as described above, and a total of six polarizing films having different single transmittances were produced.

2. Preparation of Polarizing Plate A 13 μm thick cycloolefin film (manufactured by Nippon Zeon Co., Ltd., ZF-14, transparent Humidity: 10 g/(m ² 24 h)) were bonded together using an ultraviolet curable adhesive. Specifically, the curable adhesive was applied to have a total thickness of 1.0 μm, and then bonded together using a roll machine. Thereafter, the adhesive was cured by irradiating UV light from the protective film side. Next, the resin base material was peeled off, and a cycloolefin film with a thickness of 23 μm (manufactured by Nippon Zeon Co., Ltd., ZF-12, moisture permeability 10 g/(m ² · 24 h)) was applied as a protective film B to the peeled surface. A polarizing plate having a configuration of protective film A/polarizing film/protective film B was produced by bonding and curing via a curable adhesive.

3. Preparation of sample compatible with image display device The polarizing plate obtained above was cut into a size of 45 cm x 40 cm so that the absorption axis of the polarizer became the long side, and an adhesive (200 μm thick acrylic A glass plate was bonded via an acid monomer-free adhesive (manufactured by Nitto Denko Co., Ltd., trade name "LUCIACS CS9868"), and an acrylic adhesive layer with a thickness of 20 μm was bonded to the transparent film A side. Glass plates were bonded together to create a sample compatible with an image display device. The obtained image display device compatible sample was subjected to the evaluation described in (2) above. The results are shown in Table 1.

[Example 2-1 to Example 2-2]
Two polarizing films with different single transmittances were prepared by adjusting the concentration of the dye bath, and using the polarizing film, a 20 μm thick triacetyl cellulose film (manufactured by Konica Minolta, Inc.) was used as protective film B. A sample compatible with an image display device was prepared in the same manner as in Example 1, except that "KC2CT" with a moisture permeability of 1200 g/(m ² 24 h) was used. The obtained image display device compatible sample was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1-1 to Comparative Example 1-7]
A total of seven polarizing films with different single transmittances were prepared in the same manner as in Example 1, except that potassium iodide was not used in the coating solution and the single transmittance was changed by adjusting the concentration of the dye bath. Created. A sample compatible with an image display device was produced in the same manner as in Example 1 except that these polarizing films were used. The obtained image display device compatible sample was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2-1 to Comparative Example 2-2]
Two polarizing films having different single transmittances were produced in the same manner as in Example 1, except that the single transmittance was changed by adjusting the concentration of the dye bath. A sample compatible with an image display device was produced in the same manner as in Example 1 except that these polarizing films were used. The obtained image display device compatible sample was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference example 1]
1. Preparation of Polarizer A polyvinyl alcohol film having an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a 20°C swelling bath (water bath) for 30 seconds between rolls with different circumferential speed ratios and stretched 2.4 times in the transport direction while swelling (swelling step). The original polyvinyl alcohol film (completely stretched in the transport direction) was immersed for 45 seconds in a 30°C dyeing bath (an aqueous solution with an iodine concentration of 0.03% by weight and a potassium iodide concentration of 0.3% by weight). The film was stretched 3.7 times in the transport direction (dying process) based on the polyvinyl alcohol film (without polyvinyl alcohol film). Next, the dyed polyvinyl alcohol film was immersed for 20 seconds in a 40°C cross-linking bath (an aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight) to restore the original polyvinyl alcohol. The film was stretched up to 4.2 times in the transport direction (crosslinking step). Furthermore, the obtained polyvinyl alcohol film was immersed for 50 seconds in a stretching bath at 64.5°C (an aqueous solution with a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight). After stretching the polyvinyl alcohol film up to 6.0 times in the transport direction (stretching step), it was immersed in a 20°C cleaning bath (an aqueous solution with a potassium iodide concentration of 3.0% by weight) for 5 seconds. (Washing process). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to produce a polarizer.

2. Preparation of polarizing plate As an adhesive, polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetoacetylation 5 mol%) and methylolmelamine were used. An aqueous solution containing them at a weight ratio of 3:1 was used. Using this adhesive, a 23 μm thick cycloolefin film (manufactured by Nippon Zeon Co., Ltd., ZT-12, moisture permeability 10 g/( m ² 24h)) was used as the protective film D on the other side of the polarizer, and a 40 μm thick triacetyl cellulose film with a hard coat layer (moisture permeability 340 g/(m ² 24h), manufactured by Konica Minolta, product) was used. KC4UYW) is laminated using a roll laminating machine, and then heated and dried in an oven (temperature: 60°C, time: 10 minutes) to create a polarized light having the following structure: protective film C/polarizer/protective film D. A board was made.

3. Preparation of sample compatible with image display device The polarizing plate obtained above was cut into a size of 45 cm x 40 cm so that the absorption axis of the polarizer became the long side, and an adhesive (200 μm thick acrylic A glass plate was bonded via an acid monomer-free adhesive (manufactured by Nitto Denko Co., Ltd., trade name ``LUCIACS CS9868''), and an acrylic adhesive layer with a thickness of 20 μm was bonded to the transparent film C side. Glass plates were bonded together to create a sample compatible with an image display device. The obtained image display device compatible sample was subjected to the evaluation described in (2) above. The results are shown in Table 1.

As is clear from Table 1, both ΔP and ΔTs of the image display device compatible sample (substantially the polarizing plate) of the example of the present invention are significantly smaller than those of the comparative example, and it can be used in a harsh heating environment. It has excellent durability with little change in optical properties even when exposed to light. That is, in a polarizing plate including a thin polarizing film, durability under a harsh heating environment can be significantly improved by using a specific polarizing film obtained by the method described in this specification. Furthermore, as is clear from a comparison of Examples 1-5 and 1-6, in which the individual transmittance of the polarizing film is about the same, and Examples 2-1 and 2-2, COP with low moisture permeability was used as a protective film. By using it, durability is further improved. In addition, as is clear from Reference Example 1, the problem of durability under such a harsh heating environment is a problem unique to polarizing plates including thin polarizing films.

The polarizing plate of the present invention is suitably used in image display devices such as liquid crystal display devices, organic EL display devices, and quantum dot display devices, and is particularly suitable for image display devices that can be used in harsh heating environments (for example, in-vehicle display devices). image display devices).

11 Polarizing film 12 Protective film 13 Protective film 100 Polarizing plate

Claims (4)

a polarizing film made of a polyvinyl alcohol resin film containing a dichroic substance and having a thickness of 8 μm or less; and protective films disposed on both sides of the polarizing film;
The polarizing film further contains iodide or sodium chloride,
The content of iodide or sodium chloride in the polarizing film is 5 parts by weight to 20 parts by weight based on 100 parts by weight of polyvinyl alcohol resin,
The polarizing film has a single transmittance Ts ₀ of 41.8% to 43.0%,
Each of the protective films is made of a cycloolefin resin, and has a moisture permeability of 20 g/m ^2.24 h or less ,
After the glass plates are bonded together on both sides via adhesive layers and left at 100°C for 60 hours, the amount of change ΔP in the degree of polarization expressed by the following formula is -1.0% to 0.0%. Yes , polarizing plate :
ΔP (%) = P ₆₀ - P ₀
Here, P ₀ is the degree of polarization before heating, P ₆₀ is the degree of polarization after heating for 60 hours, and P ₀ is expressed by the following formula:
P ₀ (%) = {(Tp ₀ - Tc ₀ )/(Tp ₀ +Tc ₀ )} ^1/2 ×100
In the above formula, Tp ₀ is the parallel transmittance, Tc ₀ is the orthogonal transmittance, and Tp ₀ and Tc ₀ are the Y values measured using a 2-degree visual field (C light source) of JIS Z8701 and subjected to visibility correction. It is . An image display device comprising a display cell and the polarizing plate according to claim 1 disposed on a viewing side of the display cell. The image display device according to claim 2, configured to be mounted on a vehicle. A method for manufacturing a polarizing plate according to claim 1, comprising:
A coating solution containing 100 parts by weight of polyvinyl alcohol resin and 5 to 20 parts by weight of iodide or sodium chloride is applied to one side of a long thermoplastic resin base material and dried. Forming a polyvinyl alcohol resin layer containing sodium and polyvinyl alcohol resin to form a laminate;
The laminate is subjected in this order to an auxiliary stretching treatment in the air, a dyeing treatment, a stretching treatment in water, and a drying shrinkage treatment in which it shrinks by 2% or more in the width direction by heating while conveying in the longitudinal direction. The polyvinyl alcohol resin layer is a polarizing film, and a protective film is laminated on both sides of the polarizing film.
manufacturing methods, including

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