JP7240363B2 - Dyed triacetylcellulose film, polarizing plate using the film, method for producing polarizing plate, polarizing plate with retardation layer, image display device, and image adjustment method for image display device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dyed triacetylcellulose film, a polarizing plate using the film, a method for producing a polarizing plate, a polarizing plate with a retardation layer, an image display device, and an image adjustment method for an image display device.

2. Description of the Related Art In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. Polarizing plates and retardation plates are typically used in image display devices. Practically, a polarizing plate with a retardation layer in which a polarizing plate and a retardation plate are integrated is widely used (for example, Patent Document 1). Accordingly, there is an increasing demand for thinner polarizing plates and polarizing plates with retardation layers. One of means for reducing the thickness of the polarizing plate and the polarizing plate with the retardation layer is to reduce the thickness of the polarizing film. However, when a polarizing plate including a thin polarizing film or a polarizing plate with a retardation layer is used in an image display device, there is a problem that the reflected hue becomes bluish.

Japanese Patent No. 3325560

The present invention has been made to solve the above-described conventional problems, and its main purpose is to provide a polarizing plate and a polarizing plate with a retardation layer that can achieve a neutral reflection hue when applied to an image display device, and , to provide a dyed triacetyl cellulose film capable of realizing such a polarizing plate and a polarizing plate with a retardation layer.

The dyed triacetylcellulose film according to the embodiment of the present invention is dyed with iodine, has a transmittance of 65% or less at a wavelength of 400 nm, and a transmittance Y of 80% or more after visual sensitivity correction.
According to another aspect of the invention, a polarizing plate is provided. The polarizing plate includes a polarizing film and a protective layer disposed on at least one side of the polarizing film. The polarizing film has a thickness of 8 μm or less, and the protective layer is composed of the dyed triacetyl cellulose film described above.
According to still another aspect of the present invention, there is provided a method for producing the above polarizing plate. In this manufacturing method, a polyvinyl alcohol-based resin layer is formed on one side of a long thermoplastic resin substrate to form a laminate; as a polarizing film; dyeing a triacetyl cellulose film with iodine so that the transmittance at a wavelength of 400 nm is 65% or less and the transmittance Y corrected for visibility is 80% or more; and the dyeing laminating a triacetyl cellulose film to the polarizing film.
In one embodiment, the dyeing includes immersing the triacetylcellulose film in an iodine aqueous solution having an iodine concentration of 0.1% by weight or more.
According to still another aspect of the present invention, a polarizing plate with a retardation layer is provided. This retardation layer-attached polarizing plate includes the above polarizing plate and a retardation layer disposed on the side opposite to the viewing side of the polarizing plate. Re (550) of the retardation layer is 100 nm to 190 nm, Re (450) / Re (550) is 0.8 or more and less than 1, the slow axis of the retardation layer and the polarizing film of the polarizing plate and the absorption axis are 40° to 50°.
In one embodiment, the retardation layer is composed of a polycarbonate-based resin film.
In one embodiment, the retardation layer-attached polarizing plate further has another retardation layer outside the retardation layer, and the refractive index characteristic of the another retardation layer is nz>nx=ny. Show relationship.
In one embodiment, the retardation layer-attached polarizing plate is elongated, the polarizing film has an absorption axis in the longitudinal direction, and the retardation layer is 40° to the longitudinal direction. It is an obliquely stretched film having a slow axis in a direction forming an angle of 50°. In one embodiment, the retardation layer-attached polarizing plate can be wound into a roll.
A polarizing plate with a retardation layer according to another embodiment of the present invention includes the polarizing plate described above and a retardation layer disposed on the side opposite to the viewing side of the polarizing plate. The retardation layer has a laminated structure of a first liquid crystal compound alignment layer and a second liquid crystal compound alignment solid layer. Re (550) of the alignment fixed layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle formed by the slow axis and the absorption axis of the polarizing film is 10° to 20°; Re(550) of the alignment fixed layer of the liquid crystal compound is 100 nm to 190 nm, and the angle between the slow axis and the absorption axis of the polarizing film is 70° to 80°.
In one embodiment, the retardation layer-attached polarizing plate further has a conductive layer or a conductive layer-attached isotropic substrate outside the retardation layer.
According to still another aspect of the present invention, an image display device is provided. This image display device includes the polarizing plate or the polarizing plate with a retardation layer.
In one embodiment, the image display device is an organic electroluminescence display device or an inorganic electroluminescence display device.
According to still another aspect of the present invention, an image adjustment method for an image display device is provided. This method includes adhering the above polarizing plate or the above polarizing plate with a retardation layer to the viewing side of the image display cell to bring the reflection hue close to neutral.

According to the present invention, an iodine-dyed triacetyl cellulose film having a predetermined transmittance at a predetermined wavelength and a predetermined visibility-corrected transmittance Y is used as a protective layer for a polarizing film, thereby improving the image display device. A polarizing plate and a polarizing plate with a retardation layer that can realize a neutral reflection hue when applied can be realized.

1 is a schematic view showing an example of drying shrinkage treatment using a heating roll in a method for producing a polarizing film used in a polarizing plate or a polarizing plate with a retardation layer according to an embodiment of the invention; FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention; FIG. FIG. 4 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the invention;

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

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) refractive index (nx, ny, nz)
"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 in-plane direction orthogonal to the slow axis (i.e., fast axis direction) and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
“Re(λ)” is an in-plane retardation measured at 23° C. with light having a wavelength of λ nm. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. For example, “Rth(550)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) is determined by the formula: Rth(λ)=(nx−nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is obtained by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise directions with respect to a reference direction. Thus, for example, "45°" means ±45°.

A. Polarizing Plate According to an embodiment of the present invention, an iodine dyed triacetyl cellulose (TAC) film is provided. This dyed TAC film has a transmittance of 65% or less at a wavelength of 400 nm, and a transmittance Y corrected for visual sensitivity (hereinafter also referred to as Y-value transmittance) of 80% or more. A dyed TAC film can be suitably used as a protective layer of a polarizing plate. A polarizing plate according to an embodiment of the present invention includes a polarizing film and a protective layer disposed on at least one side of the polarizing film. That is, the protective layer may be provided on both sides of the polarizing film, may be provided only on the viewing side of the polarizing film, or may be provided only on the side opposite to the viewing side of the polarizing film. In embodiments of the invention, at least one of the protective layers is composed of a dyed TAC film. According to one embodiment, in the polarizing plate having the viewer-side protective layer/polarizing film structure, the viewer-side protective layer is composed of a dyed TAC film.

A-1. Polarizing Film The polarizing film is typically composed of a polyvinyl alcohol (PVA) resin film containing iodine. The thickness of the polarizing film is typically 8 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and still more preferably 3 μm or less. The lower limit of the thickness of the polarizing film may be 1 μm in one embodiment and 2 μm in another embodiment.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, and still more preferably 43.0% or more. On the other hand, the single transmittance is preferably 47.0% or less, more preferably 46.0% or less. The polarization degree of the polarizing film is preferably 99.95% or more, more preferably 99.99% or more. On the other hand, the degree of polarization is preferably 99.998% or less. The polarizing film used in the embodiments of the present invention can thus achieve both a high single transmittance and a high degree of polarization. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The single transmittance is a value when the refractive index of one surface of the polarizing plate is converted to 1.50 and the refractive index of the other surface is converted to 1.53. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film 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 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 of the protective film in contact with the air interface, the reflectance at each layer interface may change, resulting in a change in the measured transmittance. . Thus, for example, if a protective film with a refractive index not equal to 1.50 is used, the transmittance measurements 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 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 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 substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as the protective film, the correction amount C is approximately 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance of the polarizing film having a surface refractive index of 1.53 and the protective film having a refractive index of 1.50 is used. It is possible to convert to a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance _T1 of the polarizing film is changed by 2% is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

The polarizing film may be produced using a single resin film, or may be produced using a laminate of two or more layers.

A specific example of a polarizing film obtained using a laminate is a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. A polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material can be obtained, for example, by applying a PVA-based resin solution to the resin base material and drying the resin base material. forming a PVA-based resin layer thereon to obtain a laminate of a resin substrate 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, stretching may further include stretching the laminate in air at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution, if necessary.

More specifically, the method for producing a polarizing film includes forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate. Then, the laminate is subjected in this order to an in-air auxiliary stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process that shrinks the laminate by 2% or more in the width direction by heating while being transported in the longitudinal direction. including. Thereby, a polarizing film having a thickness of 8 μm or less and excellent optical properties can be provided. That is, by introducing auxiliary stretching, it is possible to improve the crystallinity of PVA even when PVA is coated on a thermoplastic resin, and to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of orientation and dissolution of PVA when immersed in water in the subsequent dyeing process or stretching process, resulting in high optical properties. can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and deterioration of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. Details of the manufacturing method of the polarizing film will be described later in Section B.

A-2. Protective layer As described above, in the embodiment of the present invention, a protective layer arranged on the viewing side (hereinafter referred to as a viewing side protective layer) and a protective layer arranged on the side opposite to the viewing side (hereinafter referred to as an inner protective layer) At least one is composed of a dyed TAC film. From the viewpoint of thinning and weight reduction of the polarizing plate, the inner protective layer can preferably be omitted. Therefore, according to one embodiment, in the polarizing plate having the configuration of visible-side protective layer/polarizing film, the visible-side protective layer is Consists of dyed TAC film. By using a dyed TAC film for the visible-side protective layer and/or the inner protective layer, the reflective hue of the image display device becomes bluish even when a thin (e.g., thickness of 8 μm or less) polarizing film is used. As a result, a very good (neutral) reflection hue can be realized.

If a viewing side protective layer and an inner protective layer are provided, and only one of them is composed of a dyed TAC film, the other protective layer is formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based resins. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films 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 a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

The transmittance of the dyed TAC film at a wavelength of 400 nm is 65% or less, preferably 60% or less, more preferably 55% or less, still more preferably 40% or less, and particularly preferably 35% or less. . The lower limit of the transmittance can be, for example, 0.1%. If the transmittance is within such a range, the reflection hue can be further improved. Furthermore, the dyed TAC film has a Y-value transmittance of 80% or more, preferably 85% or more, more preferably 90% or more. A higher Y-value transmittance is more preferable. The upper limit of the Y-value transmittance can be, for example, 98%. One of the characteristics of dyed TAC films is that the transmittance at a wavelength of 400 nm decreases significantly while the Y-value transmittance can maintain a high value.

The above effects of the dyed TAC film are presumed to be due to the following mechanism: The thin polarizing film has a small iodine content (absolute amount). The polarizing film used in the embodiment of the present invention is produced by the method described in Section B below, so that the iodine content (absolute amount) is small but PVA- Since the total amount ^of I ₅ ^-ions and I ₃ -ions that are the source of the I ₅ ^-complex and PVA-I ₃ ^-complex can be maintained within a desired range, the single transmittance and the degree of polarization can be high while being thin. level can be maintained. However, due to the small iodine content (absolute amount), the thin polarizing film tends to absorb less light of short wavelengths (for example, 400 nm or less). According to embodiments of the present invention, the use of a dyed TAC film as the protective layer allows the protective layer to absorb short wavelength light. As a result, the polarizing plate as a whole can sufficiently absorb short-wavelength light, and the short-wavelength absorptivity of the thin polarizing film can be compensated for. As a result, while maintaining the excellent characteristics of the thin polarizing film used in the embodiment of the present invention, it is possible to prevent the reflection hue of the image display device from becoming bluish. neutral) reflection hues can be achieved. Furthermore, if excessive iodine is contained in the thin polarizing film, a PVA-iodine complex is formed, and the Y-value transmittance also decreases at the same time. On the other hand, since iodine is not complexed in the TAC film, the absorption of iodine is limited to short wavelengths, and it is possible to suppress short wavelength transmittance while maintaining the Y value transmittance.

The visible side protective layer may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc., if necessary. Further/or, the visible-side protective layer may optionally be treated to improve visibility when viewed through polarized sunglasses (typically, imparting an (elliptically) polarizing function, ultra-high-level imparting 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. Therefore, the polarizing plate or the polarizing plate with a retardation layer can be suitably applied to an image display device that can be used outdoors.

The thickness of the visible-side protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 35 μm. In addition, when the surface treatment is performed, the thickness of the viewer side protective layer is the thickness including the thickness of the surface treatment layer.

The inner protective layer is preferably optically isotropic in one embodiment. As used herein, “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. The inner protective layer, in one embodiment, can be 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. The thickness of the inner protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm. As described above, from the viewpoint of thinning and weight saving, the inner protective layer may be preferably omitted.

B. Manufacturing method of polarizing plate B-1. Method for manufacturing polarizing film The polarizing film is formed by, for example, forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate. is formed to form a laminate, and the laminate is subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and heating while conveying in the longitudinal direction to shrink by 2% or more in the width direction Drying and shrinkage treatment in this order. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage ratio in the width direction of the laminate due to drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above section A-1 can be obtained. In particular, a laminate containing a PVA-based resin layer containing a halide is produced, the laminate is stretched in multiple stages including auxiliary stretching in the air and stretching in water, and the laminate after stretching is heated with a heating roll. , a polarizing film having excellent optical properties (typically, single transmittance and degree of polarization) can be obtained.

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

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

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

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

B-1-1-1. Thermoplastic Resin Substrate Any appropriate thermoplastic resin film can be employed as the thermoplastic resin substrate. Details of the thermoplastic resin substrate are described, for example, in Japanese Patent Application Laid-Open No. 2012-73580 or Japanese Patent No. 6470455. These publications are incorporated herein by reference in their entirety.

B-1-1-2. 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 solvents include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

Any appropriate resin can be adopted as the PVA-based resin. Details of the PVA-based resin are described, for example, in JP-A-2012-73580 or Japanese Patent No. 6470455 (above).

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

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

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

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

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

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

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

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

B-1-3. Insolubilization Treatment, Dyeing Treatment, and Crosslinking Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a cross-linking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. Details of the insolubilization treatment, dyeing treatment and cross-linking treatment are described in, for example, JP-A-2012-73580 or Japanese Patent No. 6470455 (above).

B-1-4. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, a polarizing film having excellent optical properties can be produced.

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

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

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

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

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

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

B-1-5. Drying Shrinkage Treatment The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heated roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress heat curling of the laminate and produce a polarizing film having an excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, which is relatively low. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.

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

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

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

B-1-6. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

As described above, a laminate of thermoplastic resin substrate/polarizing film can be produced.

B-2. Dyeing of TAC film On the other hand, the TAC film is dyed with iodine. Staining can be done in any suitable manner. Dyeing is carried out, for example, by immersing a long TAC film in a dyeing solution (typically an iodine aqueous solution) while conveying it by rolls. Dyeing is carried out so that the resulting dyed TAC film has a transmittance of 65% or less at a wavelength of 400 nm and a Y-value transmittance of 80% or more. The transmittance and Y-value transmittance can be controlled by appropriately adjusting the iodine concentration of the iodine aqueous solution, the temperature of the iodine aqueous solution, and the dyeing time (immersion time). The iodine concentration of the iodine aqueous solution may vary depending on the dyeing time (immersion time). The iodine concentration of the iodine aqueous solution is preferably 0.1 wt% or more, more preferably 0.5 wt% to 5.0 wt%, and still more preferably 1.0 wt% to 3.0 wt%. be. If the iodine concentration is too low, the desired transmittance may not be obtained even after a long dyeing treatment. The temperature of the aqueous iodine solution is preferably 20°C to 30°C. Dyeing time may vary depending on the iodine concentration of the aqueous iodine solution. Dyeing time is preferably 30 seconds or longer, more preferably 50 to 400 seconds. If the dyeing time is too short, the desired transmittance may not be obtained. On the other hand, unnecessarily lengthening the dyeing time is not effective in terms of production efficiency.

B-3. Preparation of polarizing plate On the polarizing film surface of the thermoplastic resin substrate / polarizing film laminate obtained in the above section B-1, the dyeing obtained in the above section B-2 is applied via any appropriate adhesive. Laminate the TAC film. Examples of adhesives include water-based adhesives and active energy ray-curable adhesives. In this way, a laminate of thermoplastic resin substrate/polarizing film/dyed TAC film can be produced. This laminate may be used as it is as a polarizing plate. In this case, the thermoplastic resin substrate can function as the inner protective layer. Alternatively, the thermoplastic resin substrate may be peeled off from the thermoplastic resin substrate/polarizing film/dyed TAC film laminate, and the dyed TAC film/polarizing film laminate may be used as the polarizing plate. Alternatively, the thermoplastic resin substrate is peeled off from the thermoplastic resin substrate/polarizing film/dyed TAC film laminate, and the resin film is laminated as an inner protective layer on the peeled surface, and the dyed TAC film/polarizing film/inner protective layer is laminated. A stack of layers may be used as a polarizer.

C. Polarizing plate with retardation layer C-1. Overall Configuration of Retardation Layer-Equipped Polarizing Plate FIG. 2 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. A polarizing plate 100 with a retardation layer of this embodiment has a polarizing plate 10 and a retardation layer 20 . The polarizing plate is the polarizing plate described in the above items A and B. The illustrated polarizing plate 10 includes a polarizing film 11 , a viewer-side protective layer 12 and an inner protective layer 13 . As mentioned above, preferably the inner protective layer 13 may be omitted. In the retardation layer-attached polarizing plate, the retardation layer is typically arranged on the opposite side of the polarizing plate to the viewing side.

As shown in FIG. 3, in a retardation layer-attached polarizing plate 101 according to another embodiment, another retardation layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided. Another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are typically provided on the side of the retardation layer 20 opposite to the polarizing plate 10 (the side opposite to the viewing side). Another retardation layer typically exhibits a refractive index characteristic of nz>nx=ny. Another retardation layer 50 and a conductive layer or an isotropic substrate 60 with a conductive layer are typically provided in this order from the retardation layer 20 side. The separate retardation layer 50 and the conductive layer or the isotropic substrate with a conductive layer 60 are typically optional layers provided as needed, and either or both of them may be omitted. For the sake of convenience, the retardation layer 20 may be referred to as a first retardation layer, and the other retardation layer 50 may be referred to as a second retardation layer. In addition, when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner It can be applied to a touch panel type input display device.

In the embodiment of the present invention, Re(550) of the first retardation layer 20 is 100 nm to 190 nm, and Re(450)/Re(550) is 0.8 or more and less than 1. Furthermore, the angle between the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is 40° to 50°.

The above-described embodiments may be combined as appropriate, and the constituent elements in the above-described embodiments may be modified as is obvious in the art. For example, the configuration in which the isotropic substrate 60 with a conductive layer is provided outside the second retardation layer 50 is replaced with an optically equivalent configuration (for example, a laminate of the second retardation layer and the conductive layer). good too.

The retardation layer-attached polarizing plate may further include other retardation layers. Other optical properties of the retardation layer (for example, refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. can be appropriately set according to the purpose.

The retardation layer-attached polarizing plate may be sheet-shaped or elongated. As used herein, the term "long shape" means an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. include. The elongated retardation layer-attached polarizing plate can be wound into a roll. When the retardation layer-attached polarizing plate is elongated, the polarizing plate and the retardation layer are also elongated. In this case, the polarizing film preferably has an absorption axis in the longitudinal direction. The first retardation layer is preferably an obliquely stretched film having a slow axis in a direction forming an angle of 40° to 50° with respect to the longitudinal direction. If the polarizing film and the first retardation layer have such structures, the retardation layer-attached polarizing plate can be produced by roll-to-roll.

Practically, an adhesive layer (not shown) is provided on the side of the retardation layer opposite to the polarizing plate, so that the polarizing plate with the retardation layer can be attached to the image display cell. Furthermore, it is preferable that a release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. Temporarily attaching the release film protects the pressure-sensitive adhesive layer and enables roll formation.

The total thickness of the retardation layer-attached polarizing plate is preferably 140 μm or less, more preferably 120 μm or less, even more preferably 100 μm or less, even more preferably 90 μm or less, and even more preferably 85 μm or less. be. A lower limit for the total thickness can be, for example, 80 μm. According to the embodiment of the present invention, a polarizing plate with such an extremely thin retardation layer can be realized. Such a retardation layer-attached polarizing plate can have extremely excellent flexibility and bending durability. Such a retardation layer-attached polarizing plate can be particularly suitably applied to a curved image display device and/or a bendable or foldable image display device. The total thickness of the retardation layer-attached polarizing plate refers to the total thickness of the retardation layer-attached polarizing plate, excluding the pressure-sensitive adhesive layer for adhering the retardation layer-attached polarizing plate to an external adherend such as a panel or glass. The total thickness of all layers (that is, the total thickness of the retardation layer-attached polarizing plate is the adhesive layer for attaching the retardation layer-attached polarizing plate to an adjacent member such as an image display cell and the temporary not including the thickness of the release film that may be applied).

The first retardation layer, the second retardation layer, and the conductive layer or the isotropic substrate with the conductive layer are specifically described below. The first retardation layer may be an alignment fixed layer of a liquid crystal compound (hereinafter referred to as a liquid crystal alignment fixed layer). The liquid crystal alignment fixed layer will be described in section C-4 as a modified example of the first retardation layer.

C-2. First Retardation Layer The first retardation layer 20 can have any appropriate optical and/or mechanical properties depending on the purpose. The first retardation layer 20 typically has a slow axis. In one embodiment, the angle θ between the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is 40° to 50° as described above, preferably 42° to 48°. and more preferably about 45°. If the angle θ is in such a range, by using a λ / 4 plate as the first retardation layer as described later, very good circular polarization properties (as a result, very good antireflection properties) can be obtained.

The first retardation layer preferably exhibits a refractive index characteristic of nx>ny≧nz. The first retardation layer is typically provided to impart antireflection properties to the polarizing plate, and in one embodiment can function as a λ/4 plate. In this case, the in-plane retardation Re(550) of the first retardation layer is 100 nm to 190 nm, preferably 110 nm to 170 nm, more preferably 130 nm to 160 nm, as described above. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, it is possible that ny<nz to the extent that the effects of the present invention are not impaired.

The Nz coefficient of the first retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, particularly preferably 0.9 to 1.5. 3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.

The first retardation layer may exhibit a reverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, or has a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light. It may also show a flat wavelength dispersion characteristic in which the phase difference value hardly changes even with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse dispersion wavelength characteristics. In this case, Re(450)/Re(550) of the retardation layer is 0.8 or more and less than 1 as described above, preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection properties can be achieved.

The absolute value of the photoelastic coefficient of the first retardation layer is preferably 2×10 ⁻¹¹ m ² /N or less, more preferably 2.0×10 ⁻¹³ m ^{2 /} N to 1.5×10 ⁻¹¹ m ² /N, more preferably 1.0×10 ⁻¹² m ² /N to 1.2× ^{10 −11} m ² /N of resin. If the absolute value of the photoelastic coefficient is within such a range, the phase difference is less likely to change when shrinkage stress occurs during heating. As a result, heat unevenness in the obtained image display device can be satisfactorily prevented.

The first retardation layer is typically composed of a stretched resin film. The thickness of the first retardation layer is preferably 70 μm or less, more preferably 45 μm to 60 μm. If the thickness of the first retardation layer is within such a range, it is possible to satisfactorily control curling during bonding while satisfactorily suppressing curling during heating.

The first retardation layer 20 can be composed of any suitable resin film that can satisfy the above characteristics. Representative examples of such resins include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, and polyamide resins. , polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins may be used alone or in combination (eg, blended, copolymerized). When the first retardation layer is composed of a resin film exhibiting reverse wavelength dispersion characteristics, a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter sometimes simply referred to as a polycarbonate-based resin) can be suitably used.

As the polycarbonate-based resin, any suitable polycarbonate-based resin can be used as long as the effects of the present invention can be obtained. For example, a polycarbonate-based resin includes a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, an alicyclic diol, an alicyclic dimethanol, di-, tri- or polyethylene glycol, and an alkylene and a structural unit derived from at least one dihydroxy compound selected from the group consisting of glycols or spiroglycols. Preferably, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, a structural unit derived from an alicyclic dimethanol, and/or di-, tri- or polyethylene glycol. More preferably, a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from di-, tri- or polyethylene glycol. . The polycarbonate-based resin may contain structural units derived from other dihydroxy compounds as necessary. The details of the method for forming the polycarbonate-based resin and the first retardation layer that can be suitably used for the first retardation layer are, for example, JP-A-2014-10291, JP-A-2014-26266, JP-A-2014-26266, JP-A-2015-212816, JP-A-2015-212817, and JP-A-2015-212818, and the descriptions of these publications are incorporated herein by reference.

C-3. Second Retardation Layer As described above, the second retardation layer can be a so-called positive C plate whose refractive index characteristics exhibit a relationship of nz>nx=ny. By using a positive C plate as the second retardation layer, it is possible to satisfactorily prevent reflection in oblique directions and widen the viewing angle of the antireflection function. In this case, the thickness direction retardation Rth (550) of the second retardation layer is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, still more preferably −90 nm to −200 nm, particularly preferably -100 nm to -180 nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the second retardation layer can be less than 10 nm.

The second retardation layer having refractive index characteristics of nz>nx=ny can be made of any suitable material. The second retardation layer preferably consists of a film containing a liquid crystal material fixed in homeotropic alignment. A liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in [0020] to [0028] of JP-A-2002-333642. In this case, the thickness of the second retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, still more preferably 0.5 μm to 5 μm.

C-4. Modified Example of First Retardation Layer The first retardation layer 20 may have a laminated structure of a first liquid crystal alignment fixed layer and a second liquid crystal alignment fixed layer. In this case, one of the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer can function as a λ/4 plate, and the other can function as a λ/2 plate. Therefore, the thicknesses of the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer can be adjusted so as to obtain the desired in-plane retardation of the λ/4 plate or the λ/2 plate. For example, when the first liquid crystal alignment fixed layer functions as a λ/2 plate and the second liquid crystal alignment fixed layer functions as a λ/4 plate, the thickness of the first liquid crystal alignment fixed layer is, for example, 2.0 μm to 3.0 μm, and the thickness of the second liquid crystal alignment fixed layer is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane retardation Re(550) of the first liquid crystal alignment fixed layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, still more preferably 250 nm to 280 nm. The in-plane retardation Re(550) of the second liquid crystal alignment fixed layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, still more preferably 130 nm to 160 nm. The angle formed by the slow axis of the first liquid crystal alignment fixed layer and the absorption axis of the polarizing film is preferably 10° to 20°, more preferably 12° to 18°, and still more preferably about 15°. is. The angle formed by the slow axis of the second liquid crystal alignment fixed layer and the absorption axis of the polarizing film is preferably 70° to 80°, more preferably 72° to 78°, and still more preferably about 75°. is. With such a configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, very excellent antireflection characteristics can be realized. Both the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer typically exhibit a relationship of nx>ny=nz in refractive index characteristics. Both the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer preferably have an Nz coefficient of 0.9 to 1.5, more preferably 0.9 to 1.3. For the liquid crystal compounds constituting the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer, and the method for forming the first liquid crystal alignment fixed layer and the second liquid crystal alignment fixed layer, see, for example, JP-A-2006-163343 It is described in the publication. The description of the publication is incorporated herein by reference. In addition, when the first retardation layer has such a laminated structure, the second retardation layer can typically be omitted.

C-5. Conductive layer or isotropic substrate with conductive layer It may be formed by depositing a metal oxide film thereon. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The conductive layer may be transferred from the base material to the first retardation layer (or the second retardation layer if present), and the conductive layer alone may be used as a constituent layer of the polarizing plate with the retardation layer. It may be laminated on the first retardation layer (or, if present, on the second retardation layer) as a laminate with a substrate (a substrate with a conductive layer). Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used as an isotropic substrate with a conductive layer in a polarizing plate with a retardation layer.

Any appropriate isotropic substrate can be employed as the optically isotropic substrate (isotropic substrate). Materials constituting the isotropic base material include, for example, norbornene-based resins, olefin-based resins, and other resins that do not have a conjugated system as the main skeleton, and acrylic resins that have cyclic structures such as lactone rings and glutarimide rings. Examples include materials that are present in the main chain. By using such a material, it is possible to suppress the development of retardation due to the orientation of molecular chains when forming an isotropic base material. The thickness of the isotropic substrate is preferably 50 μm or less, more preferably 35 μm or less. The lower limit of the thickness of the isotropic base material is, for example, 20 μm.

The conductive layer and/or the conductive layer of the isotropic substrate with a conductive layer may be patterned as required. The patterning may form conductive portions and insulating portions. As a result, electrodes can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. Any appropriate method can be adopted as a patterning method. Specific examples of the patterning method include wet etching and screen printing.

D. Image Display Device The polarizing plate described in the above items A and B or the polarizing plate with a retardation layer described in the above item C can be applied to an image display device. Accordingly, embodiments of the present invention include image display devices using such polarizing plates or polarizing plates with retardation layers. Typical examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices). An image display device according to an embodiment of the present invention includes a polarizing plate or a polarizing plate with a retardation layer on its viewing side. The retardation layer-attached polarizing plate is laminated so that the retardation layer is on the image display cell (for example, liquid crystal cell, organic EL cell, inorganic EL cell) side (so that the polarizing film is on the viewing side). In one embodiment, the image display device has a curved shape (substantially a curved display screen) and/or is bendable or bendable. By using the polarizing plate or the polarizing plate with a retardation layer as described above, the reflection hue of the image display device can be brought closer to neutral. Therefore, according to embodiments of the present invention, an image adjustment method for such an image display device can also be provided.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.
(1) Thickness A thickness of 10 μm or less was measured using an interferometric film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). A thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).
(2) Single Transmittance and Degree of Polarization For the polarizing plates used in Examples and Comparative Examples, single transmittance Ts, parallel transmittance Tp, measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation V-7100), The orthogonal transmittance Tc was defined as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction. The protective layer of the polarizing plates used in Examples and Comparative Examples has a hard coat (HC) layer on the surface, and the protective layer has a refractive index of 1.50 and the HC layer has a refractive index of 1.50. was 53. The refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
As for the spectrophotometer, LPF-200 manufactured by Otsuka Electronics Co., Ltd. can be used for equivalent measurement.
The transmittance is the value when the surface refractive index is 1.50/1.53 for both the transmittance of the protective layer and the transmittance of the polarizing plate, and the combination of the surface refractive indices of the measurement configuration is the value. If different, a theoretical correction was made based on the amount of change in the air interface reflection (surface reflection) due to the change in the surface refractive index. For example, when measuring the configuration of TAC with HC layer/polarizing film (with a transmittance of 40%), the combination of surface refractive indices is 1.53/1.53, so the measured value is +0.2%. This can be converted to the transmittance of the polarizing plate at 1.50/1.53. The transmittance of the HC layer-attached TAC film alone was not corrected because the combination of refractive indices was 1.50/1.53.
(3) Front reflection hue The polarizing plates with retardation layers obtained in Examples and Comparative Examples were coated with an acrylic pressure-sensitive adhesive having no ultraviolet absorption function to form a reflector (manufactured by Toray Film Co., Ltd., trade name “DMS-X42”). ; reflectance 86%, reflection hue a ^* =−0.22, b ^* =0.32 without polarizing plate) to prepare a measurement sample. At this time, the retardation layer side of the retardation layer-attached polarizing plate was attached so as to face the reflector. The measurement sample is measured by the SCE method using a spectrophotometer (CM-2600d manufactured by Konica Minolta), and the values of a ^* and b ^* are substituted into √(a ^*2 +b ^*2 ). , the front reflection hue was obtained.

[Example 1-1]
1. Preparation of Polarizing Film As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75° C. was used. Corona treatment was applied to one side of the resin substrate.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER Z410") mixed at 9:1: 100 weight of PVA-based resin 13 parts by weight of potassium iodide was added to 10 parts and dissolved in water to prepare an aqueous PVA solution (coating solution).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched 2.4 times at the free end in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the finally obtained polarizing film is placed in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was a desired value (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, while immersing the laminate in an aqueous solution (boric acid concentration: 4.0% by weight, potassium iodide: 5.0% by weight) at a liquid temperature of 70°C, the laminate is vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the total stretching ratio was 5.5 times (underwater stretching treatment).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
After that, 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 (drying shrinkage treatment). The shrinkage ratio in the width direction of the laminate due to the drying shrinkage treatment was 5.2%.
Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate.

2. Dyeing of TAC film An HC-TAC film in which an HC layer having a thickness of 7 μm and a refractive index of 1.53 was formed on a long TAC film (manufactured by Konica Minolta, trade name “KC-2UA”, thickness 25 μm) was transported by roll. It was immersed in a dyeing bath (iodine aqueous solution with an iodine concentration of 1.0% by weight) at a liquid temperature of 25°C. The immersion time was 60 seconds. The obtained dyed TAC film had a transmittance of 59.8% at a wavelength of 400 nm and a transmittance Y value of 90.1%.

3. Preparation of polarizing plate The above 1. The surface of the polarizing film obtained in 2 (the surface opposite to the resin base material) is coated with the above 2. The HC layer-attached dyed TAC film obtained in 1. was pasted together via an ultraviolet curable adhesive. Specifically, the curable adhesive was applied so as to have a total thickness of 1.0 μm, and was bonded using a roll machine. The adhesive was then cured by irradiation with UV light from the TAC film side. Next, after slitting both ends, the resin substrate was peeled off to obtain a long polarizing plate (width: 1300 mm) having a structure of protective layer (dyed TAC film)/adhesive layer/polarizing film. The single transmittance of the polarizing plate (substantially, the polarizing film) was 43.0%, and the degree of polarization was 99.995%.

4. Preparation of Retardation Film Constituting Retardation Layer 4-1. Polymerization of polyester carbonate-based resin Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with a stirring blade and a reflux condenser controlled at 100°C. Bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane 29.60 parts by mass (0.046 mol), isosorbide (ISB) 29.21 parts by mass (0.200 mol), spiroglycol (SPG) 42 .28 parts by mass (0.139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC) and 1.19 × 10 ^-2 parts by weight of calcium acetate monohydrate as a catalyst (6.78 × 10 ^{- 5} mol) was charged. After the interior of the reactor was replaced with nitrogen under reduced pressure, heating was performed with a heating medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating, the internal temperature was allowed to reach 220°C, and the pressure was reduced at the same time as controlling to maintain this temperature. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. After nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was brought to 240° C. and the pressure to 0.2 kPa in 50 minutes. After that, polymerization was allowed to proceed until a predetermined stirring power was obtained. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the polyester carbonate-based resin produced was extruded into water, and strands were cut to obtain pellets.

4-2. Preparation of retardation film After vacuum drying the obtained polyester carbonate resin (pellet) at 80 ° C. for 5 hours, a single screw extruder (Toshiba Machine Co., Ltd., cylinder setting temperature: 250 ° C.), T die (width 200 mm , set temperature: 250° C.), a chill roll (set temperature: 120 to 130° C.), and a winder were used to prepare a long resin film having a thickness of 135 μm. The resulting long resin film was stretched in the width direction at a stretching temperature of 133° C. and a stretching ratio of 2.8 to obtain a retardation film with a thickness of 48 μm. Re(550) of the obtained retardation film was 144 nm, Re(450)/Re(550) was 0.82, and Nz coefficient was 1.12.

5. Production of polarizing plate with retardation layer 3 above. The polarizing film surface of the polarizing plate obtained in 4. above. The retardation film obtained in 1. was pasted together via an acrylic pressure-sensitive adhesive (thickness: 5 μm). At this time, the absorption axis of the polarizing film and the slow axis of the retardation film were attached so as to form an angle of 45°. Thus, a polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 84 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluation of (3) above. Table 1 shows the results.

[Example 1-2]
A TAC film was dyed in the same manner as in Example 1-1, except that the dyeing time was 120 seconds. The resulting dyed TAC film had a transmittance of 52.8% at a wavelength of 400 nm and a transmittance Y value of 89.2%. A polarizing plate with a retardation layer was produced in the same manner as in Example 1-1, except that this dyed TAC film was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Example 1-3]
A TAC film was dyed in the same manner as in Example 1-1, except that the dyeing time was 300 seconds. The resulting dyed TAC film had a transmittance of 31.9% at a wavelength of 400 nm and a transmittance Y value of 88.4%. A polarizing plate with a retardation layer was produced in the same manner as in Example 1-1, except that this dyed TAC film was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Comparative Example 1]
A polarizing plate with a retardation layer was produced in the same manner as in Example 1-1, except that an undyed TAC film was used. The undyed TAC film had a transmittance of 68.5% at a wavelength of 400 nm and a transmittance Y value of 92.1%. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Example 2-1]
A polarizing film having a single transmittance of 44.0% was produced by adjusting the dyeing conditions. A polarizing plate with a retardation layer was produced in the same manner as in Example 1-1 except that this polarizing film was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Example 2-2]
A polarizing plate with a retardation layer was produced in the same manner as in Example 1-2 except that the polarizing film produced in Example 2-1 was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Example 2-3]
A polarizing plate with a retardation layer was produced in the same manner as in Example 1-3 except that the polarizing film produced in Example 2-1 was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[Comparative Example 2]
A polarizing plate with a retardation layer was produced in the same manner as in Comparative Example 1 except that the polarizing film produced in Example 2-1 was used. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. Table 1 shows the results.

[evaluation]
As is clear from Table 1, according to the examples of the present invention, by using the dyed TAC film as the protective layer, the reflection hue can be brought closer to a neutral state than in the comparative examples.

The retardation layer-attached polarizing plate of the present invention is suitably used as a circularly polarizing plate for liquid crystal display devices, organic EL display devices and inorganic EL display devices.

REFERENCE SIGNS LIST 10 polarizing plate 11 polarizing film 12 viewing side protective layer 13 inner protective layer 20 retardation layer 100 polarizing plate with retardation layer 101 polarizing plate with retardation layer

Claims (15)

A dyed triacetyl cellulose film dyed with iodine, having a transmittance of 65% or less at a wavelength of 400 nm and a transmittance Y of 80% or more after visual sensitivity correction. comprising a polarizing film and a protective layer disposed on at least one side of the polarizing film;
The polarizing film has a thickness of 8 μm or less,
wherein the protective layer is composed of the dyed triacetylcellulose film of claim 1;
Polarizer. forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate to form a laminate;
subjecting the laminate to a dyeing treatment and a stretching treatment to form a polyvinyl alcohol-based resin layer as a polarizing film;
dyeing a triacetyl cellulose film with iodine so that the transmittance at a wavelength of 400 nm is 65% or less and the luminosity-corrected transmittance Y is 80% or more;
laminating the dyed triacetylcellulose film to the polarizing film;
The method for producing a polarizing plate according to claim 2, comprising: 4. The method of manufacturing a polarizing plate according to claim 3, wherein said dyeing includes immersing said triacetylcellulose film in an iodine aqueous solution having an iodine concentration of 0.1% by weight or more. A polarizing plate according to claim 2, and a retardation layer disposed on the opposite side of the polarizing plate from the viewing side,
Re (550) of the retardation layer is 100 nm to 190 nm, Re (450) / Re (550) is 0.8 or more and less than 1,
The angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film of the polarizing plate is 40° to 50°.
A polarizing plate with a retardation layer. 6. The polarizing plate with a retardation layer according to claim 5, wherein the retardation layer is composed of a polycarbonate-based resin film. 7. The retardation layer according to claim 5 or 6, further comprising another retardation layer outside the retardation layer, wherein the refractive index characteristic of the another retardation layer exhibits a relationship of nz>nx=ny Polarizer. elongated,
The polarizing film has an absorption axis in the longitudinal direction,
The retardation layer is an obliquely stretched film having a slow axis in a direction forming an angle of 40° to 50° with respect to the longitudinal direction,
The polarizing plate with a retardation layer according to any one of claims 5 to 7. 9. The retardation layer-attached polarizing plate according to claim 8, which can be wound into a roll. A polarizing plate according to claim 2, and a retardation layer disposed on the opposite side of the polarizing plate from the viewing side,
The retardation layer has a laminated structure of a first liquid crystal compound alignment fixed layer and a second liquid crystal compound alignment fixed layer,
Re (550) of the alignment fixed layer of the first liquid crystal compound is 200 nm to 300 nm, the angle formed by the slow axis and the absorption axis of the polarizing film is 10 ° to 20 °,
Re (550) of the alignment fixed layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle formed by the slow axis and the absorption axis of the polarizing film is 70° to 80°.
A polarizing plate with a retardation layer. 11. The polarizing plate with a retardation layer according to claim 5, further comprising a conductive layer or an isotropic substrate with a conductive layer outside the retardation layer. An image display device comprising the polarizing plate according to claim 2 . An image display device comprising the retardation layer-attached polarizing plate according to any one of claims 5 to 11. 14. The image display device according to claim 12 or 13, which is an organic electroluminescence display device or an inorganic electroluminescence display device. An image display comprising: bonding the polarizing plate according to claim 2 or the polarizing plate with a retardation layer according to any one of claims 5 to 11 to the viewing side of the image display cell to bring the reflected hue close to neutral. Image adjustment method of the device.

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