CN112840252A - Polarizing plate with phase difference layer and image display device using same - Google Patents

Abstract

The invention provides a polarizing plate with a retardation layer, which is thin, excellent in handling property and excellent in optical characteristics. The polarizing plate with the phase difference layer comprises a polarizing film and a protective layer positioned on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, and has a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and an orthogonal absorbance per 1 μm of the thickness at a wavelength of 550nm of 0.85 or more. The retardation layer has Re (550) of 100 to 190nm and Re (450)/Re (550) of 0.8 to less than 1. The angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40-50 degrees.

Description

Polarizing plate with phase difference layer and image display device using same

Technical Field

The present invention relates to a polarizing plate with a retardation layer and an image display device using the same.

Background

In recent years, image display devices typified by liquid crystal display devices and Electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have rapidly spread. Typically, a polarizing plate and a retardation plate are used in an image display device. In practical applications, a polarizing plate with a retardation layer, which is formed by integrating a polarizing plate and a retardation plate, is widely used (for example, patent document 1), and recently, with the increasing demand for the thinning of an image display device, the demand for the thinning of a polarizing plate with a retardation layer is also increasing. In addition, in recent years, demands for a curved image display device and/or a flexible or bendable image display device have been increasing, and in such a case, a polarizing plate and a polarizing plate with a retardation layer are also required to be further thinned and further softened. For the purpose of reducing the thickness of a polarizing plate with a retardation layer, a protective layer for a polarizing film and a retardation film which greatly contribute to the thickness have been reduced in thickness. However, when the protective layer and the retardation film are thinned, the effect of shrinkage of the polarizing film is relatively increased, and there are problems that the image display device is warped and the workability of the polarizing plate with the retardation layer is degraded.

In order to solve the above problem, it is also necessary to make the polarizing film thin in a lump. However, if the thickness of the polarizing film is merely reduced, the optical characteristics are degraded. More specifically, one or both of the degree of polarization and the monomer transmittance in a trade-off relationship are reduced to a level that is not practically tolerable. As a result, the optical characteristics of the polarizing plate with a retardation layer are also insufficient.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3325560

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described conventional problems, and a main object thereof is to provide a polarizing plate with a retardation layer which is thin, excellent in handleability, and excellent in optical characteristics.

Means for solving the problems

The polarizing plate with the phase difference layer comprises a polarizing film and a protective layer positioned on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, and has a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and an orthogonal absorbance per 1 μm of the thickness at a wavelength of 550nm of 0.85 or more. The Re (550) of the retardation layer is 100 to 190nm, the Re (450)/Re (550) is 0.8 or more and less than 1, and the angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40 to 50 degrees.

In one embodiment, the protective layer is made of a base material having an elastic modulus of 3000MPa or more.

In one embodiment, the polarizing plate with a retardation layer has a total thickness of 90 μm or less, a front reflection hue of 3.5 or less, and the protective layer is formed of a resin film having an elastic modulus of 3000MPa or more.

In one embodiment, the protective layer is formed of a cellulose triacetate resin film.

In one embodiment, the polarizing plate includes the polarizing film and the protective layer disposed only on one side of the polarizing film, and the retardation layer is attached to the polarizing film via an adhesive layer.

In one embodiment, the retardation layer is made of a polycarbonate resin film.

In one embodiment, the retardation layer is formed of a polycarbonate resin film having a thickness of 40 μm or less.

In one embodiment, the polarizing film has an orthogonal absorbance A at a wavelength of 470nm₄₇₀With orthogonal absorbance A at a wavelength of 600nm₆₀₀Ratio of (A)₄₇₀/A₆₀₀) Is 0.7 to 2.00.

In one embodiment, the polarizing film has an orthogonal b value of more than-10 and +10 or less.

In one embodiment, the polarizing film has an orthogonal absorbance A at a wavelength of 550nm₅₅₀Is 2.0 or more.

In one embodiment, the polarizing plate with a retardation layer further includes another retardation layer outside the retardation layer, and refractive index characteristics of the other retardation layer show a relationship of nz > nx ═ ny.

In one embodiment, the polarizing plate with a retardation layer further includes a conductive layer or an isotropic substrate with a conductive layer outside the retardation layer.

In one embodiment, the polarizing plate with the retardation layer is a long polarizing plate, the polarizing film has an absorption axis in the longitudinal direction, and 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. In one embodiment, the polarizing plate with a retardation layer is wound in a roll.

According to another aspect of the present invention, there is provided an image display device. The image display device comprises the polarizing plate with the phase difference layer.

In one embodiment, the image display device is an organic electroluminescence display device or an inorganic electroluminescence display device.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a polarizing film having extremely excellent optical characteristics can be obtained while being thin by combining 2-stage stretching including in-air auxiliary stretching and underwater stretching, and drying and shrinking by a heating roller, which are performed by adding a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) resin. By using such a polarizing film, a polarizing plate with a retardation layer which is thin, excellent in handleability and excellent in optical characteristics can be realized.

Drawings

Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention.

Fig. 3 is a schematic view showing an example of drying and shrinking treatment using a heating roller in the method for producing a polarizing film used for a polarizing plate with a retardation layer according to the present invention.

Detailed Description

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

(definitions of terms and symbols)

The terms and symbols in the present specification are defined as follows.

(1) Refractive index (nx, ny, nz)

"nx" is a refractive index in a direction in which an in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is a refractive index in the thickness direction.

(2) In-plane retardation (Re)

"Re (. lamda)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of. lamda.nm. For example, "Re (550)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of 550 nm. When the thickness of the layer (thin film) is d (nm), Re (λ) is represented by the formula: re (λ) ═ (nx-ny) × d.

(3) Retardation in thickness direction (Rth)

"Rth (λ)" is a phase difference in the thickness direction measured at 23 ℃ with light having a wavelength of λ nm. For example, "Rth (550)" is a phase difference in the thickness direction measured at 23 ℃ with light having a wavelength of 550 nm. When the thickness of the layer (film) is d (nm), Rth (λ) is expressed by the following formula: rth (λ) ═ n x-nz × d.

(4) Coefficient of Nz

The Nz coefficient can be obtained by Nz ═ Rth/Re.

(5) Angle of rotation

When an angle is referred to in this specification, the angle includes angles in both clockwise and counterclockwise directions with respect to a reference direction. Thus, for example, "45" means ± 45 °.

A. Integral structure of polarizing plate with phase difference layer

Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. The polarizing plate 100 with a retardation layer according to the present embodiment includes a polarizing plate 10 and a retardation layer 20. The polarizing plate 10 includes: the protective film includes a polarizing film 11, a 1 st protective layer 12 disposed on one side of the polarizing film 11, and a 2 nd protective layer 13 disposed on the other side of the polarizing film 11. One of the 1 st protective layer 12 and the 2 nd protective layer 13 may be omitted depending on the purpose. For example, when the retardation layer 20 can also function as a protective layer for the polarizing film 11, the 2 nd protective layer 13 can be omitted. In the embodiment of the present invention, the polarizing film is formed of a polyvinyl alcohol resin film containing a dichroic material. The polarizing film has a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and an orthogonal absorbance per 1 μm of thickness (hereinafter referred to as unit absorbance) at a wavelength of 550nm of 0.85 or more.

As shown in fig. 2, in the polarizing plate with retardation layer 101 according to another embodiment, another retardation layer 50 and/or a conductive layer or an isotropic substrate with conductive layer 60 may be provided. The retardation layer 50 and the conductive layer or the isotropic substrate with a conductive layer 60 are typically disposed outside the retardation layer 20 (on the side opposite to the polarizing plate 10). The other retardation layer is typically one having refractive index characteristics showing a relationship of nz > nx ═ ny. The retardation layer 50 and the conductive layer or the isotropic substrate with conductive layer 60 are typically provided in this order from the side of the retardation layer 20. The retardation layer 50 and the conductive layer or the isotropic substrate with conductive layer 60 are typically optional layers provided as needed, and either or both of them may be omitted. For convenience, the retardation layer 20 may be referred to as a 1 st retardation layer, and the other retardation layer 50 may be referred to as a 2 nd retardation layer. In the case where a conductive layer or an isotropic substrate with a conductive layer is provided, a polarizing plate with a retardation layer can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between an image display unit (for example, an organic EL unit) and a polarizing plate.

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

The above embodiments may be combined as appropriate, and a change which is obvious in the art may be applied to the constituent elements of the above embodiments. For example, the configuration in which the isotropic base material 60 with a conductive layer is provided outside the 2 nd retardation layer 50 may be replaced with an optically equivalent configuration (for example, a laminate of the 2 nd retardation layer and the conductive layer).

The polarizing plate with a retardation layer according to the embodiment of the present invention may further include another retardation layer. The optical properties (e.g., refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, and the like of the other retardation layer can be appropriately set according to the purpose.

The polarizing plate with a retardation layer of the present invention may be in the form of a sheet or a long sheet. In the present specification, the "elongated shape" refers to an elongated shape having a length sufficiently long with respect to the width, and includes, for example, an elongated shape having a length 10 times or more, preferably 20 times or more with respect to the width. The long polarizing plate with a retardation layer may be rolled up in a roll. When the polarizing plate with a retardation layer is long, the polarizing plate and the retardation layer are also long. In this case, the polarizing film preferably has an absorption axis in the longitudinal direction. The 1 st 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. When the polarizing film and the 1 st retardation layer have such a structure, a polarizing plate with a retardation layer can be produced by roll-to-roll.

In actual use, an adhesive layer (not shown) is provided on the side of the retardation layer opposite to the polarizing plate, and the polarizing plate with the retardation layer can be attached to the image display unit. Further, it is preferable to temporarily adhere a release film to the surface of the pressure-sensitive adhesive layer until the polarizing plate with a retardation layer is used. By temporarily adhering the release film, a roll can be formed while protecting the adhesive layer.

Front reflection color phase of polarizing plate with phase difference layer

Preferably 3.5 or less, more preferably 3.0 or less. When the front reflection hue is within the above range, undesirable coloring and the like can be suppressed, and as a result, a polarizing plate with a retardation layer having excellent reflection characteristics can be obtained.

The total thickness of the polarizing plate with a retardation layer is preferably 140 μm or less, more preferably 120 μm or less, still more preferably 100 μm or less, yet more preferably 90 μm or less, and yet more preferably 85 μm or less. The lower limit of the total thickness may be, for example, 30 μm. According to the embodiments of the present invention, such an extremely thin polarizing plate with a retardation layer can be realized. Such a polarizing plate with a retardation layer can have extremely excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be suitably used particularly for a curved image display device and/or a flexible or bendable image display device. The total thickness of the polarizing plate with a retardation layer is the sum of the thicknesses of all layers constituting the polarizing plate with a retardation layer, excluding a pressure-sensitive adhesive layer for adhering the polarizing plate with a retardation layer to an external adherend such as a panel or glass (that is, the total thickness of the polarizing plate with a retardation layer does not include a pressure-sensitive adhesive layer for adhering the polarizing plate with a retardation layer to an adjacent member such as an image display unit and a thickness of a release film capable of being temporarily adhered to the surface thereof).

Hereinafter, the constituent elements of the polarizing plate with a retardation layer will be described in more detail.

B. Polarizing plate

B-1. polarizing film

The polarizing film 11 has a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and a unit absorbance at a wavelength of 550nm of 0.85 or more as described above. In general, the monomer transmittance and the unit absorbance have a trade-off relationship with each other, and when the monomer transmittance is increased, the unit absorbance decreases, and when the unit absorbance is increased, the monomer transmittance decreases. Therefore, it has been difficult to put a thin polarizing film satisfying optical characteristics such as a monomer transmittance of 43.0% or more and a unit absorbance at a wavelength of 550nm of 0.85 or more into practical use. The present invention is characterized by using a thin polarizing film having excellent optical characteristics such that the monomer transmittance is 43.0% or more and the unit absorbance at a wavelength of 550nm is 0.85 or more.

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

The polarizing film preferably exhibits absorption dichroism at an arbitrary wavelength of 380nm to 780 nm. The polarizing film preferably has a monomer transmittance of 44.0% or less, more preferably 43.5% or less. The polarization degree of the polarizing film is preferably 99.990% or more, and preferably 99.998% or less. The monomer transmittance is typically a Y value measured by an ultraviolet-visible spectrophotometer and corrected for visibility. The polarization degree is typically determined by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring and correcting the visibility using an ultraviolet-visible spectrophotometer.

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

In one embodiment, the transmittance of a thin polarizing film having a thickness of 8 μm or less is typically measured by using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (refractive index of surface: 1.53) and a protective film (refractive index: 1.50) as a measurement target. The reflectance at the interface of each layer changes 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, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film having a refractive index other than 1.50 is used, the measured value of the transmittance can be corrected based on the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance is the reflectance R of the polarized light parallel to the transmission axis at the interface between the protective film and the air layer₁The (transmission axis reflectance) is expressed by the following equation.

C＝R₁-R₀

R₀＝((1.50-1)²/(1.50+1)²)×(T₁/100)

R₁＝((n₁-1)²/(n₁+1)²)×(T₁/100)

Here, R₀The transmission axis reflectance, n, when a protective film having a refractive index of 1.50 was used₁The refractive index of the protective film used, T₁The transmittance of the polarizing film. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, or the like) is used as the protective film, the correction amount C is about 0.2%. In this case, the transmittance obtained by the measurement is added to 0.2%, and the polarizing film having a refractive index of 1.53 on the surface can be converted into a transmittance when a protective film having a refractive index of 1.50 is used. The transmittance T of the polarizing film was calculated based on the above formula₁The amount of change in correction value C when the change is 2% is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of correction value C is limited. This is achieved byIn addition, when the protective film has absorption other than surface reflection, appropriate correction can be made in accordance with the amount of absorption.

The polarizing film has a unit absorbance at a wavelength of 550nm of 0.85 or more, preferably 0.9 or more, more preferably 1.0 or more, and still more preferably 1.3 or more, as described above. The upper limit of the unit absorbance may be, for example, 1.9. Orthogonal absorbance A at wavelength λ nm_λThe orthogonal transmittance Tc is obtained by the following equation.

Orthogonal absorbance log10(100/Tc)

Absorbance per unit at wavelength 550nm was determined by using the above-obtained orthogonal absorbance A₅₅₀Divided by the thickness. The unit absorbance of the polarizing plate with a retardation layer substantially corresponds to the unit absorbance of the polarizing film.

When the polarizing plate with the retardation layer is used in an organic Electroluminescence (EL) display device and an inorganic EL display device (for example, a quantum dot display device), the orthogonal absorbance A is₅₅₀For example, it may be 2.0 or more (for example, the unit absorbance is 0.85 or more, and the thickness is 2.5 μm or more). When the polarizing plate with phase difference layer is used in liquid crystal display device, the cross absorbance A₅₅₀For example, it may be 3.0 or more.

Preferably, the polarizing film has an orthogonal absorbance A at a wavelength of 470nm₄₇₀With orthogonal absorbance A at a wavelength of 600nm₆₀₀Ratio of (A)₄₇₀/A₆₀₀) Is 0.7 or more, more preferably 0.75 or more, still more preferably 0.80 or more, and particularly preferably 0.85 or more. Ratio (A)₄₇₀/A₆₀₀) Preferably 2.00 or less, more preferably 1.33 or less. Ratio (A)₄₇₀/A₆₀₀) Within such a range, good polarization performance can be achieved over the entire visible light region. When the iodine amount in a thin polarizing film is limited, it is difficult for the conventional technique to make the above-mentioned unit absorbance and ratio (a)₄₇₀/A₆₀₀) Both are in desired ranges, however, the polarizing film used in the present invention can make both of them in desired ranges.

Further, the orthogonal b value of the polarizing film is, for example, more than-10, preferably-7 or more, and more preferably-5 or more. The orthogonal b value is preferably +10 or less, more preferably +5 or less. The orthogonal b value indicates a hue when the polarizing films (eventually, polarizing plates with a retardation layer) are arranged in an orthogonal state, and a larger absolute value of the value indicates that the orthogonal hue (black display of the image display device) appears to be more colored. For example, when the orthogonal b value is lower than-10, the black display appears bluish and the display performance is degraded. That is, according to the embodiments of the present invention, a polarizing plate with a retardation layer that can realize an excellent hue in black display can be obtained. The orthogonal b value can be measured by a spectrophotometer represented by V-7100.

As the polarizing film, any suitable polarizing film may be used. A polarizing film can be typically produced using a laminate of two or more layers.

Specific examples of the polarizing film obtained using the laminate include a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating the resin substrate. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer formed by coating the resin substrate can be produced, for example, by: coating a PVA-based resin solution on a resin base material, and drying the coating to form a PVA-based resin layer on the resin base material, thereby obtaining a laminate of the resin base material and the PVA-based resin layer; the laminate is stretched and dyed to form a polarizing film from the PVA-based resin layer. In the present embodiment, the stretching typically includes: the laminate was immersed in an aqueous boric acid solution to be stretched. Further, the stretching may further include, if necessary: the laminate is subjected to in-air stretching at a high temperature (e.g., 95 ℃ or higher) before stretching in an aqueous boric acid solution. The obtained resin substrate/polarizing film laminate (that is, the resin substrate may be used as a protective layer for the polarizing film) may be used as it is, or the resin substrate may be peeled from the resin substrate/polarizing film laminate and an arbitrary appropriate protective layer suitable for the purpose may be laminated on the peeled surface. Details of such a method for producing a polarizing film are described in, for example, japanese patent laid-open No. 2012-73580. The entire contents of this publication are incorporated herein by reference.

A method for producing a polarizing film typically includes: 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 prepare a laminate; and subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order, wherein the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Thus, a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and a unit absorbance at a wavelength of 550nm of 0.85 or more, and having excellent optical characteristics can be provided. That is, by introducing the auxiliary stretching, the crystallinity of the PVA can be improved even when the PVA is coated on the thermoplastic resin, and high optical characteristics can be realized. Further, by simultaneously improving the orientation of the PVA in advance, it is possible to prevent problems such as a decrease in the orientation of the PVA and dissolution of the PVA when immersed in water in a subsequent dyeing step or stretching step, and to realize high optical characteristics. Further, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and reduction of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical properties of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment. Further, the optical characteristics can be improved by shrinking the laminate in the width direction by the drying shrinkage treatment.

B-2 protective layer

The 1 st protective layer 12 and the 2 nd protective layer 13 are each formed of any appropriate film that can be used as a protective layer for a polarizing film. Specific examples of the material to be the main component of the film include cellulose resins such as Triacetylcellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyether sulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth) acrylic acid-based, acetate-based transparent resins, and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone resins, ultraviolet-curable resins, and the like can be mentioned. Other examples of the polymer include glassy polymers such as siloxane polymers. Further, the polymer film described in Japanese patent application laid-open No. 2001-343529 (WO01/37007) may be used. As a material of the film, 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 a nitrile group in a side chain can be used, and for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be mentioned. The polymer film may be, for example, an extrusion molded product of the resin composition. In one embodiment, the protective layer (particularly, the protective layer on the visual recognition side) contains a TAC-based resin. By using a TAC-based resin film as the protective layer, the bending durability can be improved.

As described later, the polarizing plate with a retardation layer of the present invention is typically disposed on the viewing side of an image display device, and the 1 st protective layer 12 is typically disposed on the viewing side thereof. Therefore, the 1 st protective layer 12 may be subjected to surface treatment such as hard coating treatment, antireflection treatment, adhesion prevention treatment, and antiglare treatment as needed. Further, the 1 st protective layer 12 may be subjected to a process for improving visibility when performing visibility through polarized sunglasses (typically, imparting a (elliptical) polarization function and imparting an ultra-high retardation) as necessary. By performing such processing, excellent visibility can be achieved even when the display screen is visually recognized through a polarizing lens such as a polarizing sunglass. Therefore, the polarizing plate with a retardation layer can be suitably used for an image display device that can be used outdoors.

The thickness of the first protective layer 1 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and still more preferably 10 μm to 35 μm. When the surface treatment is performed, the thickness of the outer protective layer is a thickness including the thickness of the surface treatment layer.

In one embodiment, the 2 nd protective layer 13 is preferably optically isotropic. In the present specification, "optically isotropic" means that the in-plane retardation Re (550) is from 0nm to 10nm, and the retardation Rth (550) in the thickness direction is from-10 nm to +10 nm. In one embodiment, the 2 nd protective layer 13 may be a phase difference layer having any suitable phase difference value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110nm to 150 nm. The thickness of the 2 nd protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and still more preferably 10 μm to 30 μm. From the viewpoint of reduction in thickness and weight, the 2 nd protective layer may preferably be omitted.

B-3. method for producing polarizing film

The polarizing film can be produced, for example, by a method including the steps of: forming a polyvinyl alcohol resin layer (PVA resin layer) containing a halide and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin base material to produce a laminate; and subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order, wherein the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The shrinkage rate in the width direction of the laminate by the drying shrinkage treatment is preferably 2% or more. According to such a production method, the polarizing film described in the above item B-1 can be obtained. In particular, a polarizing film having excellent optical characteristics (typically, monomer transmittance and absorbance per unit at a wavelength of 550 nm) can be obtained by producing a laminate including a halide-containing PVA-based resin layer, stretching the laminate in multiple stages including air-assisted stretching and underwater stretching, and heating the stretched laminate with a heating roller.

B-3-1 preparation of laminate

As a method for producing a laminate of the thermoplastic resin substrate and the PVA-based resin layer, any appropriate method can be adopted. It is preferable that: the PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating solution containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying the coating solution. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.

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

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

Before the PVA-based resin layer is formed, the thermoplastic resin substrate may be subjected to a surface treatment (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-3-1-1. thermoplastic resin base Material

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

The water absorption of the thermoplastic resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. The thermoplastic resin base material absorbs water, and the water functions as a plasticizer to plasticize the resin. As a result, the tensile stress can be greatly reduced, and the film can be stretched to a high magnification. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as a significant decrease in dimensional stability of the thermoplastic resin substrate during production and deterioration in appearance of the obtained polarizing film. Further, the base material can be prevented from being broken when stretched in water or the PVA-based resin layer can be prevented from being peeled from the thermoplastic resin base material. The water absorption of the thermoplastic resin base material can be adjusted by, for example, introducing a modifying group into the constituent material. The water absorption is a value determined in accordance with JIS K7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ℃ or lower. By using such a thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed, and the stretchability of the laminate can be sufficiently ensured. Further, when the plasticization of the thermoplastic resin substrate by water is considered and the underwater stretching is favorably performed, it is more preferably 100 ℃ or lower, and still more preferably 90 ℃ or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ℃ or higher. By using such a thermoplastic resin substrate, when a coating liquid containing the PVA-based resin is applied and dried, defects such as deformation (for example, generation of irregularities, slackening, wrinkles, and the like) of the thermoplastic resin substrate can be prevented, and a laminate can be produced satisfactorily. Further, the PVA-based resin layer can be favorably stretched at an appropriate temperature (for example, about 60 ℃). The glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, heating using a crystallized material in which a modifying group is introduced into a constituent material. The glass transition temperature (Tg) is a value determined in accordance with JIS K7121.

As the constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be used. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Of these, norbornene resin and amorphous polyethylene terephthalate resin are preferable.

In one embodiment, an amorphous (noncrystalline) polyethylene terephthalate-based resin is preferably used. Among them, amorphous (hardly crystallized) 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 dicarboxylic acids; and a copolymer comprising cyclohexanedimethanol and diethylene glycol as diols.

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

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, the stretching is performed in the transverse direction of the long thermoplastic resin base material. The transverse direction is preferably a direction orthogonal to the stretching direction of the laminate described later. In the present specification, "orthogonal" also includes the case of substantially orthogonal. Here, "substantially orthogonal" includes a case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.

The stretching temperature of the thermoplastic resin substrate is preferably from Tg-10 ℃ to Tg +50 ℃ relative to the glass transition temperature (Tg). The stretch ratio of the thermoplastic resin base material is preferably 1.5 to 3.0 times.

As the method for stretching the thermoplastic resin substrate, any suitable method can be adopted. Specifically, the fixed end stretching may be performed, or the free end stretching may be performed. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage, or may be performed in a plurality of stages. When the stretching is performed in a plurality of stages, the stretching ratio is the product of the stretching ratios of the respective stages.

B-3-1-2 coating liquid

As described above, the coating liquid contains a halide and a PVA-based resin. The coating liquid is typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Among these, water is preferable. The concentration of the PVA-based 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 can be formed which adheres closely to the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.

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

As the PVA-based resin, any suitable resin can be used. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K6726-. By using the PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the saponification degree is too high, gelation may occur.

The average polymerization degree of the PVA-based resin can be appropriately selected according to the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined in accordance with JIS K6726-.

As the halide, any suitable halide can be used. For example, iodide and sodium chloride may be cited. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferable.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA-based resin. When the amount of the halide exceeds 20 parts by weight based on 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, since the PVA-based resin layer is stretched, the orientation of polyvinyl alcohol molecules in the PVA-based resin is high, and when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules 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 an aqueous boric acid solution, the orientation degree tends to be remarkably decreased when the laminate is stretched in an aqueous boric acid solution at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. For example, while the PVA film itself is usually stretched in an aqueous boric acid solution at 60 ℃, the laminate of a-PET (thermoplastic resin substrate) and a PVA-based resin layer is stretched at a high temperature of about 70 ℃, and in this case, the orientation of the PVA at the initial stage of stretching may be reduced in a stage before it is improved by underwater stretching. On the other hand, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching the laminate in an aqueous boric acid solution, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the alignment disorder and the decrease in alignment of the polyvinyl alcohol molecules 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 a treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

B-3-2 auxiliary stretching treatment in air

In particular, in order to obtain high optical characteristics, a two-stage stretching method in which dry stretching (auxiliary stretching) and stretching in an aqueous boric acid solution are combined is selected. By introducing the auxiliary stretching as in the two-stage stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization, the problem of the reduction in stretchability due to excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in an aqueous boric acid solution can be solved, and the laminate can be stretched to a higher magnification. Further, when a PVA-based resin is coated on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature needs to be lowered as compared with the case where a PVA-based resin is coated on a normal metal drum, and as a result, there is a possibility that crystallization of the PVA-based resin becomes relatively low and sufficient optical characteristics cannot be obtained. In contrast, by introducing the auxiliary stretching, even when the PVA-based resin is applied to the thermoplastic resin, the crystallinity of the PVA-based resin can be improved, and high optical characteristics can be realized. Further, by simultaneously improving the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in orientation or dissolution of the PVA-based resin when immersed in water in a subsequent dyeing step or stretching step, and to realize high optical characteristics.

The stretching method of the air-assisted stretching may be fixed-end stretching (for example, a method of stretching using a tenter) or free-end stretching (for example, a method of uniaxially stretching a laminate between rolls having different peripheral speeds), and the free-end stretching is actively employed for obtaining high optical characteristics. In one embodiment, the in-air stretching process includes a heated roller stretching step of stretching the laminate by a circumferential speed difference between heated rollers while conveying the laminate in a longitudinal direction thereof. Typically, the aerial drawing process comprises a zone stretcherAnd a heating roller stretching process. The order of the zone stretching step and the heated roller stretching step is not limited, and the zone stretching step may be performed first, or the heated roller stretching step may be performed first. The segment stretching process may be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed in this order. In addition, in another embodiment, in the tenter stretching machine, stretching is performed by holding the film end portions and expanding the distance between the tenters along the moving direction (expansion of the distance between the tenters becomes the stretching magnification). At this time, the distance of the tenter in the width direction (direction perpendicular to the moving direction) is set to be arbitrarily close. The stretch ratio in the moving direction is preferably set so as to be closer to the free end stretch. In the case of free end stretching, the shrinkage in the width direction (1/stretching ratio)^1/2To calculate.

The aerial auxiliary stretching may be performed in one stage or may be performed in a plurality of stages. When the stretching is performed in a plurality of stages, the stretching ratio is the product of the stretching ratios of the respective stages. The stretching direction in the in-air auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The stretching ratio in the air-assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of combining the in-air auxiliary stretching and the underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more, with respect to the original length of the laminate. In the present specification, the "maximum draw ratio" means a draw ratio immediately before the laminate breaks, and means a value lower than the value by 0.2 when the draw ratio at which the laminate breaks is separately confirmed.

The stretching temperature of the in-air auxiliary stretching may 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 not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, and particularly preferably not less than Tg +15 ℃. On the other hand, the upper limit of the stretching temperature is preferably 170 ℃. By stretching at such a temperature, the stretching can be suppressedThe crystallization of the PVA-based resin proceeds rapidly, and defects caused by the crystallization (for example, the orientation of the PVA-based resin layer by stretching) are suppressed. The crystallization index of the PVA resin after the in-air auxiliary stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by ATR method using a fourier transform infrared spectrometer. Specifically, measurement was carried out using polarized light as measurement light, and 1141cm of the obtained spectrum was used^-1And 1440cm^-1The crystallization index of (d) was calculated according to the following equation.

Crystallization index ═ I_C/I_R)

Wherein the content of the first and second substances,

I_C: 1141cm when measurement light is incident thereon^-1The strength of (a) is high,

I_R: 1440cm of the sample measured by incidence of measuring light^-1The strength of (2).

B-3-3. insolubilization

If necessary, after the in-air auxiliary stretching treatment, the insolubilization treatment is performed before the stretching treatment in water and the dyeing treatment. Typically, the insolubilization treatment is performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the PVA can be prevented from being degraded in orientation when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20 to 50 ℃.

B-3-4. dyeing treatment

The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically, iodine). Specifically, iodine is adsorbed to the PVA-based resin layer. Examples of the adsorption method include a method in which the PVA-based resin layer (laminate) is immersed in a dyeing solution containing iodine, a method in which the PVA-based resin layer is coated with the dyeing solution, and a method in which the PVA-based resin layer is sprayed with the dyeing solution. A method of immersing the laminate in a dyeing solution (dyeing bath) is preferred. 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 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend an iodide into the aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferable. The amount of the iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, based on 100 parts by weight of water. In order to suppress dissolution of the PVA-based resin, the dyeing liquid is preferably dyed at a liquid temperature of 20 to 50 ℃. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably 5 seconds to 5 minutes, and more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, and immersion time) can be set so that the monomer transmittance and the absorbance per unit at a wavelength of 550nm of the finally obtained polarizing film become desired values. As such dyeing conditions, preferred are: an iodine aqueous solution is used as a staining solution, and the content ratio of iodine to potassium iodide in the iodine aqueous solution is set to be 1: 5-1: 20. The content ratio of iodine to potassium iodide in the iodine aqueous solution is preferably 1: 5-1: 10. This makes it possible to obtain a polarizing film having the above-described optical characteristics.

When the dyeing treatment is continuously performed after the treatment (typically, insolubilization treatment) of immersing the laminate in a treatment bath containing boric acid, the boric acid contained in the treatment bath is mixed into the dyeing bath, and the concentration of the boric acid in the dyeing bath changes with time, and as a result, the dyeing property may be unstable. In order to suppress the instability of dyeing properties as described above, the upper limit of the boric acid concentration in the dyeing bath is adjusted so as to be preferably 4 parts by weight, more preferably 2 parts by weight, based on 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and further preferably 0.5 part by weight, based on 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath previously compounded with boric acid. This can reduce the rate of change in the boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The compounding amount of boric acid previously compounded into the dyeing bath (i.e., the content of boric acid not originating from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of water.

B-3-5. Cross-linking treatment

If necessary, a crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in water. Typically, the crosslinking treatment is performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and the PVA can be prevented from being degraded in orientation when immersed in high-temperature water during subsequent underwater stretching. The concentration of the aqueous boric acid solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further contain an iodide. By adding an iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The amount of the iodide is preferably 1 to 5 parts by weight based on 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20 ℃ to 50 ℃.

B-3-6 stretching treatment in water

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. By the underwater stretching treatment, the thermoplastic resin substrate and the PVA resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80 ℃), and the PVA resin layer can be stretched to a high magnification while suppressing crystallization thereof. As a result, a polarizing film having excellent optical characteristics can be produced.

Any suitable method may be used for stretching the laminate. Specifically, the stretching may be performed at a fixed end or at a free end (for example, a method of uniaxially stretching the laminate by passing the laminate between rollers having different peripheral speeds). Free end stretching is preferably chosen. The stretching of the laminate may be performed in one stage, or may be performed in a plurality of stages. When the stretching is performed in a plurality of stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios in the respective stages.

The underwater stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in an aqueous boric acid solution). By using an aqueous boric acid solution as a stretching bath, rigidity capable of withstanding the tension applied during stretching and water resistance not dissolving in water can be imparted to the PVA-based resin layer. Specifically, boric acid can be crosslinked with the PVA-based resin by generating a tetrahydroxyborate anion in an aqueous solution and by means of a hydrogen bond. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and the PVA-based resin layer can be stretched well, whereby a polarizing film having excellent optical characteristics can be produced.

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

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

The drawing temperature (liquid temperature of the drawing bath) is preferably 40 to 85 ℃ and more preferably 60 to 75 ℃. At such a temperature, the PVA-based resin layer can be stretched to a high magnification while suppressing dissolution thereof. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ℃, there is a possibility that the thermoplastic resin substrate cannot be satisfactorily stretched even when plasticization of the thermoplastic resin substrate by water is considered. On the other hand, as the temperature of the stretching bath is higher, the solubility of the PVA-based resin layer is higher, and thus excellent optical characteristics 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 stretch ratio of the laminate is preferably 5.0 times or more, and more preferably 5.5 times or more, the original length of the laminate. By realizing such a high stretching ratio, a polarizing film having extremely excellent optical characteristics can be produced. Such a high stretch ratio can be achieved by using an underwater stretching method (stretching in an aqueous boric acid solution).

B-3-7. drying shrinkage treatment

The drying shrinkage treatment may be performed by heating the entire zone to heat the zone, or may be performed by heating the transport roller (using a so-called hot roller) (hot roller drying method). Both are preferably used. By drying the laminate with a heating roller, the laminate can be effectively prevented from curling by heating, and a polarizing film having excellent appearance can be produced. Specifically, by drying the laminate in a state where the laminate is along the heating roller, the crystallization of the thermoplastic resin substrate can be effectively promoted to increase the crystallinity, and the crystallinity of the thermoplastic resin substrate can be favorably increased even at a low drying temperature. As a result, the thermoplastic resin substrate has increased rigidity and is resistant to shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, since the laminate can be dried while maintaining a flat state by using the heating roller, not only curling but also wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, and the optical properties can be improved. This is because: the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

Fig. 3 is a schematic diagram showing an example of the drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying rollers R1 to R6 are disposed so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but the conveying rollers R1 to R6 may be disposed so as to continuously heat only one surface (for example, the surface of the thermoplastic resin substrate) of the laminate 200.

The drying conditions can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers, the time of contact with the heating roller, and the like. The temperature of the heating roller is preferably 60 to 120 ℃, more preferably 65 to 100 ℃, and particularly preferably 70 to 80 ℃. The 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 roller can be measured by a contact thermometer. In the example shown in the figure, 6 conveying rollers are provided, but there is no particular limitation as long as there are a plurality of conveying rollers. The number of the conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roller may be installed in a heating furnace (for example, an oven) or may be installed in a general production line (room temperature environment). Preferably, the heating furnace is provided with an air blowing means. By using drying by the heating roller and hot air drying in combination, a rapid temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot wind is preferably about 10m/s to 30 m/s. The wind speed is the wind speed in the heating furnace, and can be measured by a digital wind speed meter of a miniature blade type.

B-3-8 other treatment

It is preferable to perform the washing treatment after the stretching treatment in water and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

C. 1 st phase difference layer

The 1 st phase difference layer 20 may have any suitable optical and/or mechanical properties according to the purpose. The 1 st phase difference layer 20 typically has a slow axis. In one embodiment, the angle θ formed by the slow axis of the 1 st retardation layer 20 and the absorption axis of the polarizing film 11 is 40 ° to 50 °, preferably 42 ° to 48 °, and more preferably about 45 °, as described above. When the angle θ is within such a range, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained by forming the 1 st retardation layer into a λ/4 plate as described later.

The 1 st retardation layer preferably has a refractive index characteristic showing a relationship of nx > ny ≧ nz. The 1 st retardation layer is typically provided to impart antireflection characteristics to the polarizing plate, and in one embodiment, may function as a λ/4 plate. In this case, the in-plane retardation Re (550) of the 1 st retardation layer is preferably 100nm to 190nm, more preferably 110nm to 170nm, and still more preferably 130nm to 160 nm. Here, "ny ═ nz" includes not only the case where ny and nz are completely equal but also the case where ny and nz are substantially equal. Therefore, ny < nz may be used as long as the effect of the present invention is not impaired.

The Nz coefficient of the 1 st retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. 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 realized.

The 1 st phase difference layer may exhibit anomalous dispersion wavelength characteristics in which a phase difference value becomes larger with the wavelength of the measurement light, may exhibit normal wavelength dispersion characteristics in which a phase difference value becomes smaller with the wavelength of the measurement light, and may exhibit flat wavelength dispersion characteristics in which a phase difference value hardly changes with the wavelength of the measurement light. In one embodiment, the 1 st phase difference layer shows anomalous dispersion wavelength characteristics. In this case, Re (450)/Re (550) of the retardation layer is preferably 0.8 or more and less than 1, and more preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection characteristics can be achieved.

The absolute value of photoelastic coefficient contained in the 1 st phase difference layer is preferably 2X 10^-11m²A value of not more than N, more preferably 2.0X 10^-13m²/N～1.5×10^-11m²More preferably 1.0X 10^-12m²/N～1.2×10^-11m²A resin of/N. If the absolute value of the photoelastic coefficient is within such a range, the phase difference is less likely to change when a shrinkage stress is generated during heating. As a result, thermal unevenness of the resulting image display device can be prevented favorably.

The 1 st retardation layer is typically formed of a stretched film of a resin film. In one embodiment, the thickness of the 1 st retardation layer is preferably 70 μm or less, and more preferably 45 to 60 μm. If the thickness of the 1 st retardation layer is within such a range, the curl during heating can be favorably suppressed, and the curl during bonding can be favorably adjusted. In an embodiment in which the 1 st retardation layer is composed of a polycarbonate resin film as described later, the thickness of the 1 st retardation layer is preferably 40 μm or less, more preferably 10 to 40 μm, and still more preferably 20 to 30 μm. The 1 st retardation layer is made of a polycarbonate resin film having such a thickness, and can suppress the occurrence of curling and contribute to the improvement of folding durability and reflection hue.

The 1 st retardation layer 20 may be formed of any appropriate resin film that satisfies the above-described characteristics. Typical examples of such resins include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cycloolefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins may be used alone or in combination (e.g., blending, copolymerization). When the 1 st retardation layer is formed of a resin film exhibiting anomalous dispersion wavelength 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 appropriate polycarbonate-based resin can be used as long as the effects of the present invention can be obtained. For example, 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, and a structural unit derived from at least 1 dihydroxy compound selected from the group consisting of alicyclic diol, alicyclic dimethanol, diethylene glycol, triethylene glycol, or polyethylene glycol, and alkylene glycol or spiro glycol. Preferably, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound and a structural unit derived from an isosorbide-based dihydroxy compound, and contains a structural unit derived from alicyclic dimethanol and/or a structural unit derived from diethylene glycol, triethylene glycol or polyethylene glycol; more preferably, the resin composition contains 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 diethylene glycol, triethylene glycol, or polyethylene glycol. The polycarbonate-based resin may contain a structural unit derived from another dihydroxy compound, if necessary. The details of the polycarbonate-based resin which can be suitably used in the present invention are described in, for example, Japanese patent application laid-open Nos. 2014-10291, 2014-26266, 2015-212816, 2015-212817, and 2015-212818, and the descriptions are incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110 ℃ to 150 ℃, more preferably 120 ℃ to 140 ℃. If the glass transition temperature is too low, the heat resistance tends to be poor, and there is a possibility that dimensional change occurs after film formation, or the image quality of the obtained organic EL panel may be degraded. If the glass transition temperature is too high, the molding stability during film molding may be deteriorated or the transparency of the film may be impaired. The glass transition temperature can be determined in accordance with JIS K7121 (1987).

The molecular weight of the polycarbonate-based resin can be expressed by reduced viscosity. Reduced viscosity the polycarbonate concentration was precisely adjusted to 0.6g/dL using methylene chloride as a solvent, and then measured at 20.0 ℃ C. + -0.1 ℃ C. using a Ubbelohde viscometer tube. The lower limit of the reduced viscosity is usually preferably 0.30dL/g, more preferably 0.35 dL/g. The upper limit of the reduced viscosity is usually preferably 1.20dL/g, more preferably 1.00dL/g, and still more preferably 0.80 dL/g. If the reduced viscosity is less than the lower limit, the mechanical strength of the molded article may be reduced. On the other hand, if the reduced viscosity is higher than the above upper limit, the flowability during molding may be lowered, which may cause a problem of lowering productivity and moldability.

As the polycarbonate resin film, a commercially available film may be used. Specific examples of the commercially available products include trade names "PURE-ACE WR-S", "PURE-ACE WR-W", "PURE-ACE WR-M" manufactured by Dichen corporation and trade name "NRF" manufactured by Nindon electric corporation.

The 1 st retardation layer 20 can be obtained by, for example, stretching a film made of the above-mentioned polycarbonate resin. As a method for forming a film from a polycarbonate resin, any appropriate molding method can be used. Specific examples thereof include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., casting), calendering, hot pressing, and the like. Extrusion or cast coating is preferred. This is because the smoothness of the obtained film can be improved and good optical uniformity can be obtained. The molding conditions may be appropriately set depending on the composition and type of the resin used, the desired properties of the retardation film, and the like. As described above, since many film products are commercially available as polycarbonate-based resins, the commercially available films can be directly subjected to stretching treatment.

The thickness of the resin film (unstretched film) may be set to any appropriate value depending on the desired thickness of the 1 st retardation layer, desired optical properties, stretching conditions to be described later, and the like. Preferably 50 to 300. mu.m.

The stretching may be performed by any suitable stretching method and stretching conditions (e.g., stretching temperature, stretching ratio, and stretching direction). Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinking, and fixed end shrinking may be used alone, or may be used simultaneously or sequentially. The stretching direction may be performed in various directions or dimensions such as a longitudinal direction, a width direction, a thickness direction, and an oblique direction. The stretching temperature is preferably from Tg-30 ℃ to Tg +60 ℃ and more preferably from Tg-10 ℃ to Tg +50 ℃ relative to the glass transition temperature (Tg) of the resin film.

By appropriately selecting the stretching method and the stretching conditions, a retardation film having the desired optical properties (e.g., refractive index properties, in-plane retardation, Nz coefficient) can be obtained.

In one embodiment, the retardation film can be produced by uniaxially stretching the resin film or fixed-end uniaxially stretching. As a specific example of the fixed-end uniaxial stretching, a method of stretching a resin film in a width direction (transverse direction) while moving the resin film in a longitudinal direction is exemplified. The stretch ratio is preferably 1.1 to 3.5 times.

In another embodiment, the retardation film can be produced by continuously stretching a long resin film in a diagonal direction at the angle θ with respect to the longitudinal direction. By using the oblique stretching, a long stretched film having an orientation angle of an angle θ (having a slow axis in the direction of the angle θ) with respect to the longitudinal direction of the film can be obtained, and for example, a roll-to-roll can be used when the film is laminated with a polarizing film, whereby the production process can be simplified. The angle θ may be an angle formed by an absorption axis of a polarizing film in the polarizing plate with a retardation layer and a slow axis of the retardation layer. As described above, the angle θ is preferably 40 ° to 50 °, more preferably 42 ° to 48 °, and still more preferably about 45 °.

As the stretching machine used for the oblique stretching, for example, a tenter type stretching machine which applies a conveying force, a stretching force or a drawing force at different speeds in the lateral direction and/or the longitudinal direction. The tenter type stretching machine includes a transverse uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, and any suitable stretching machine can be used as long as it can continuously stretch a long resin film obliquely.

By appropriately controlling the respective left and right speeds in the stretching machine, a retardation layer (substantially long retardation film) having the desired in-plane retardation and a slow axis in the desired direction can be obtained.

The stretching temperature of the film varies depending on the in-plane retardation value and thickness desired for the retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature is preferably from Tg-30 ℃ to Tg +30 ℃, more preferably from Tg-15 ℃ to Tg +15 ℃, and most preferably from Tg-10 ℃ to Tg +10 ℃. By performing stretching at such a temperature, the 1 st retardation layer having suitable characteristics can be obtained in the present invention. The Tg is the glass transition temperature of the constituent material of the thin film.

D. Phase difference layer 2

As described above, the 2 nd retardation layer may be a so-called Positive C-plate (Positive C-plate) having refractive index characteristics showing a relationship of nz > nx ═ ny. By using the positive C plate as the 2 nd retardation layer, the oblique reflection can be prevented well, and the antireflection function can be made wide in viewing angle. In this case, the retardation Rth (550) in the thickness direction of the 2 nd retardation layer is preferably from-50 nm to-300 nm, more preferably from-70 nm to-250 nm, still more preferably from-90 nm to-200 nm, and particularly preferably from-100 nm to-180 nm. Here, "nx ═ ny" includes not only a case where nx and ny are strictly equal but also a case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of the 2 nd retardation layer may be less than 10 nm.

The 2 nd retardation layer having a refractive index characteristic of nz > nx ═ ny may be formed of any suitable material. The 2 nd retardation layer is preferably formed of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) which 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 compounds and the methods for forming the retardation layer described in paragraphs [0020] to [0028] of Japanese patent laid-open No. 2002-333642. In this case, the thickness of the 2 nd retardation layer is preferably 0.5 to 10 μm, more preferably 0.5 to 8 μm, and still more preferably 0.5 to 5 μm.

E. Conductive layer or isotropic substrate with conductive layer

The conductive layer can be formed by forming a metal oxide film on any suitable substrate by any suitable film forming method (for example, vacuum deposition, sputtering, CVD, ion plating, spraying, or the like). Examples of the metal oxide 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 preferable.

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

The conductive layer may be transferred from the substrate to the 1 st retardation layer (or the 2 nd retardation layer in the case where the 2 nd retardation layer is present) and the conductive layer itself may be a constituent layer of the polarizing plate with a retardation layer, or may be laminated on the 1 st retardation layer (or the 2 nd retardation layer in the case where the 2 nd retardation layer is present) in the form of a laminate with the substrate (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 for a polarizing plate with a retardation layer.

As the optically isotropic substrate (isotropic substrate), any appropriate isotropic substrate can be used. Examples of the material constituting the isotropic base include a material having a resin not having a conjugated system such as a norbornene-based resin or an olefin-based resin as a main skeleton, and a material having a cyclic structure such as a lactone ring or a glutarimide ring in a main chain of an acrylic resin. When such a material is used, the retardation accompanying the molecular chain orientation can be suppressed to a small level when forming an isotropic base material. The thickness of the isotropic base material 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 necessary. By patterning, the conductive portion and the insulating portion can be formed. As a result, an electrode can be formed. The electrodes may function as touch sensor electrodes for sensing contact to the touch panel. As the patterning method, any appropriate method may be adopted. Specific examples of the patterning method include a wet etching method and a screen printing method.

F. Image display device

The polarizing plate with a retardation layer described in the above items a to E can be applied to an image display device. Accordingly, the present invention includes an image display device using such a polarizing plate with a retardation layer. Typical examples of the image display device include a liquid crystal display device and an Electroluminescence (EL) display device (for example, an organic EL display device and an inorganic EL display device). An image display device according to an embodiment of the present invention includes the polarizing plate with a retardation layer described in the above items a to E on the viewing side. The polarizing plate with a retardation layer is laminated such that the retardation layer is on the image display unit (for example, liquid crystal unit, organic EL unit, or inorganic EL unit) (such that the polarizing film is on the visual recognition side). In one embodiment, the image display device has a curved shape (substantially a curved display screen), and/or may be flexed or bent. In such an image display device, the polarizing plate with a retardation layer according to the present invention is remarkably effective.

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 property is as follows. In the examples and comparative examples, "part(s)" and "%" are based on weight unless otherwise specified.

(1) Thickness of

The thickness of 10 μm or less was measured using an interferometric film thickness gauge (manufactured by tsukamur electronics co., ltd., product name "MCPD-3000"). The thickness of more than 10 μm was measured using a digital micrometer (product name "KC-351C" manufactured by Anritsu Co., Ltd.).

(2) Monomer transmittance, unit absorbance and orthogonal absorbance

The polarizing plates used in examples and comparative examples were measured using an ultraviolet-visible spectrophotometer (product name V-7100, manufactured by japan spectro corporation), and the measured monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were used as the polarizing film Ts, Tp, and Tc, respectively. These Ts, Tp and Tc are Y values obtained by measuring and correcting the visual sensitivity using a 2-degree visual field (C light source) according to JIS Z8701. The refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film was 1.53.

Orthogonal transmittance Tc measured at a measurement wavelength of 550nm₅₅₀The orthogonal absorbance A was obtained by the following formula₅₅₀Divided by the thickness as the unit absorbance. Further, the orthogonal transmittance Tc at a wavelength of 470nm was measured₄₇₀Determination of orthogonal Absorbance A₄₇₀From the measurement of the orthogonal transmittance Tc at a wavelength of 600nm₆₀₀Determination of orthogonal Absorbance A₆₀₀。

Orthogonal absorbance log10(100/Tc)

The spectrophotometer may be equally measured using LPF-200 manufactured by tsukamur electronic corporation, or the like.

(3) Quadrature b value

The polarizing plates used in examples and comparative examples were measured using an ultraviolet-visible spectrophotometer (product name "V7100" by japan spectrophotometers) to determine the color in the cross-prism state. Shows that: the more the orthogonal b value is low (negative value and absolute value is large), the more the color becomes blue rather than neutral.

(4) Warp of

The polarizing plates with retardation layers obtained in examples and comparative examples were cut into a size of 110mm × 60 mm. At this time, the polarizing film is cut so that the absorption axis direction thereof is the longitudinal direction. The cut polarizing plate with a retardation layer was bonded to a glass plate having a size of 120mm × 70mm and a thickness of 0.2mm with an adhesive to prepare a test sample. The test sample was put into a heating oven maintained at 85 ℃ for 24 hours, and the amount of warpage after removal was measured. The height of the portion of the test specimen which is the highest from the flat surface when the test specimen is left on the flat surface with the glass plate facing downward is defined as the warpage amount.

(5) Durability to bending

The polarizing plates with retardation layers obtained in examples and comparative examples were cut into 50mm × 100mm sizes. At this time, the polarizing film is cut so that the absorption axis direction thereof is the short side direction. The cut polarizing plate with a retardation layer was subjected to a bending test at 20 ℃ and 50% RH using a folding resistance tester (manufactured by YUASA, CL09 type-D01). Specifically, the polarizing plate with a retardation layer was repeatedly bent in a direction parallel to the absorption axis direction with the retardation layer side as the outer side, the number of times of bending until occurrence of cracks, peeling, film breakage, or the like, which may cause display defects, was measured, and evaluation was performed according to the following criteria (bending diameter:

)。

< evaluation criteria >

Less than 1 ten thousand times: failure of the product

More than 1 ten thousand times and less than 3 ten thousand times: good wine

More than 3 ten thousand times: superior food

(6) Front reflection color phase

The polarizing plates with retardation layers obtained in examples and comparative examples were bonded to a reflection plate (trade name "DMS-X42" manufactured by TORAY FLIM Co., Ltd.; reflectance 86%, reflection hue a in the absence of a polarizing plate) using an acrylic adhesive having no ultraviolet absorbing function^＊＝-0.22、b^＊0.32), a measurement sample was prepared. In this case, the retardation layer side of the polarizing plate with the retardation layer laminated thereon is opposed to the reflection plate. The measurement sample was measured with a spectrocolorimeter (CM-2600 d, manufactured by Konica Minolta) in an SCE format, and a was measured^＊And b^＊Substituting the value of √ a^＊2+b^＊2) And the front reflection hue is obtained.

(7) Modulus of elasticity

The film to be measured was measured in accordance with JIS K6734: 2000 was molded into a tensile test dumbbell shape having a parallel portion width of 10mm and a length of 40mm, and the molded product was measured according to JIS K7161: 1994, tensile test was conducted to determine the tensile modulus. Here, the longitudinal direction generally coincides with the stretching direction of the polarizing film.

[ example 1]

1. Production of polarizing film

As the thermoplastic resin substrate, an amorphous copolymerized polyethylene terephthalate isophthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75 ℃ in a long form was used. One surface of the resin substrate is subjected to corona treatment.

In the following, with 9: 1A PVA-based resin in which polyvinyl alcohol (having a polymerization degree of 4200 and a saponification degree of 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410", manufactured by Nippon synthetic chemical industries, Ltd.) were mixed was dissolved in water by adding 13 parts by weight of potassium iodide to prepare an aqueous PVA solution (coating solution).

The aqueous PVA solution was applied to the corona-treated surface of the resin substrate and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

The resultant laminate was uniaxially stretched to 2.4 times at the free end in the longitudinal direction (longitudinal direction) between rolls of different peripheral speeds in an oven at 130 ℃ (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the polarizing film obtained finally was immersed in a dyeing bath (aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds while adjusting the concentration thereof so that the monomer transmittance (Ts) and the absorbance per unit at a wavelength of 550nm of the polarizing film obtained finally became desired values (dyeing treatment).

Next, the substrate was immersed for 30 seconds in a crosslinking bath (aqueous boric acid solution prepared by adding 3 parts by weight of potassium iodide and 5 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 40 ℃ (crosslinking treatment).

Then, while immersing the laminate in an aqueous boric acid solution (boric acid concentration 4.0 wt%) having a liquid temperature of 70 ℃, uniaxial stretching was performed between rolls having different peripheral speeds in the longitudinal direction (longitudinal direction) so that the total stretching ratio became 5.5 times (underwater stretching treatment).

Thereafter, the laminate was immersed in a cleaning bath (aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) at a liquid temperature of 20 ℃.

Thereafter, the sheet was dried in an oven maintained at 90 ℃ and contacted with an SUS heated roll maintained at 75 ℃ for about 2 seconds (drying shrinkage treatment). The shrinkage in the width direction of the laminate by the drying shrinkage treatment was 5.2%.

In the above operation, a polarizing film having a thickness of 4.6 μm was formed on the resin substrate.

2. Manufacture of polarizing plate

A cycloolefin film (thickness: 28 μm, elastic modulus: 2100MPa) with a hard coat layer (refractive index: 1.53) was bonded to the surface (the surface not opposed to the resin substrate) of the polarizing film obtained above as a protective layer via an ultraviolet-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness was 1.0 μm, and was bonded using a roll mill. Then, the adhesive is cured by irradiating UV light from the protective layer side. Then, after cutting both ends, the resin substrate was peeled off to obtain a long polarizing plate (width: 1300mm) having a structure of a protective layer/adhesive layer/polarizing film. The polarizing plate (substantially a polarizing film) had a monomer transmittance of 43.15% and a polarization degree of 99.995%. Further, the absorbance per unit at a wavelength of 550nm was 0.97, A₄₇₀/A₆₀₀Is 0.87 and the orthogonal b value is-3.0.

3. Production of retardation film constituting retardation layer

3-1 polymerization of polyester carbonate-based resin

Polymerization was carried out using a batch polymerization apparatus composed of 2 vertical reactors each equipped with a stirring blade and a reflux condenser controlled to 100 ℃. Adding bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl]29.60 parts by mass (0.046mol) of methane, 29.21 parts by mass (0.200mol) of Isosorbide (ISB), and 42.28 parts by mass of Spiroglycol (SPG)(0.139mol), diphenyl carbonate (DPC)63.77 parts by mass (0.298mol), and calcium acetate monohydrate 1.19X 10 as a catalyst^-2Mass portion (6.78X 10)^-5mol). After the inside of the reactor was replaced with nitrogen gas under reduced pressure, the reactor was heated with a heat medium, and stirring was started at a point when the internal temperature reached 100 ℃. After 40 minutes from the start of the temperature increase, the internal temperature was set to 220 ℃ and the pressure reduction was started while controlling the temperature so as to be maintained, so that the pressure became 13.3kPa after 90 minutes from the time when the temperature reached 220 ℃. Phenol vapor by-produced in association with the polymerization reaction was introduced into a reflux condenser at 100 ℃ to return a small amount of monomer components contained in the phenol vapor to the reactor, and the phenol vapor that was not condensed was introduced into a condenser at 45 ℃ to be recovered. After nitrogen gas was introduced into the 1 st reactor and the pressure was once returned to atmospheric pressure, the reaction liquid after oligomerization in the 1 st reactor was transferred to the 2 nd reactor. Subsequently, the temperature increase and pressure reduction in the 2 nd reactor were started, and the internal temperature was 240 ℃ and the pressure was 0.2kPa after 50 minutes. Thereafter, the polymerization was carried out until a predetermined stirring power was reached. At the time point when the predetermined power was reached, nitrogen gas was introduced into the reactor to recover the pressure, and the polyester carbonate-based resin thus produced was extruded into water, and strands were cut to obtain pellets.

3-2 preparation of retardation film

The obtained polyester carbonate resin (pellets) was dried under vacuum at 80 ℃ for 5 hours, and then a long resin film having a thickness of 130 μm was produced using a film forming apparatus equipped with a single screw extruder (manufactured by Toshiba machine Co., Ltd., cylinder set temperature: 250 ℃), a T-die (width 200mm, set temperature: 250 ℃), a cooling roll (set temperature: 120 to 130 ℃) and a winder. The obtained long resin film was stretched while adjusting the retardation so as to obtain a predetermined retardation, thereby obtaining a retardation film having a thickness of 48 μm. The stretching conditions were a stretching temperature of 143 ℃ in the width direction and a stretching ratio of 2.8 times. The obtained retardation film had Re (550) of 141nm, Re (450)/Re (550) of 0.86 and an Nz coefficient of 1.12.

4. Manufacture of polarizing plate with phase difference layer

The retardation film obtained in the above 3 was bonded to the polarizing film surface of the polarizing plate obtained in the above 2 via an acrylic adhesive (thickness 5 μm). At this time, the polarizing film was bonded so that the absorption axis and the slow axis of the retardation film form an angle of 45 °. In the above manner, a polarizing plate with a retardation layer having a composition 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 87 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (4) to (6) above. The results are shown in Table 1.

[ example 2-1]

1. Production of polarizing film

In the same manner as in example 1, a polarizing film having a thickness of 4.6 μm was formed on a resin substrate.

2. Manufacture of polarizing plate

A polarizing plate having a structure of a protective layer/an adhesive layer/a polarizing film was produced in the same manner as in example 1, except that a Triacetylcellulose (TAC) film with a hard coat layer (hard coat layer thickness 7 μm, TAC thickness 25 μm, elastic modulus: 3600MPa) was used as the protective layer. The polarizing plate (substantially, a polarizing film) had a single transmittance of 43.0% and a polarization degree of 99.995%. Further, the absorbance per unit at a wavelength of 550nm was 0.97, A₄₇₀/A₆₀₀Is 0.87 and the orthogonal b value is-2.0.

3. Production of retardation film constituting retardation layer

A polyester carbonate resin (pellet) obtained in the same manner as in example 1 except that the melt kneading was carried out at 0.7 parts by mass of PMMA was dried under vacuum at 80 ℃ for 5 hours, and then a long resin film having a thickness of 105 μm was produced using a film forming apparatus equipped with a single screw extruder (manufactured by Toshiba mechanical Co., Ltd., cylinder set temperature: 250 ℃), a T-die (width 200mm, set temperature: 250 ℃), a chill roll (set temperature: 120 to 130 ℃) and a winder. The obtained long resin film was stretched 2.8 times in the width direction at 138 ℃ while adjusting the film so that a predetermined retardation could be obtained, to obtain a retardation film having a thickness of 38 μm. The resulting retardation film had Re (550) of 144nm and Re (450)/Re (550) of 0.86.

4. Manufacture of polarizing plate with phase difference layer

The retardation film obtained in the above 3 was bonded to the polarizing film surface of the polarizing plate obtained in the above 2 via an acrylic adhesive (thickness 5 μm). In this case, the polarizing film and the retardation film were bonded so that the absorption axis of the polarizing film and the slow axis of the retardation film form an angle of 45 °. In the above manner, a polarizing plate with a retardation layer having a composition 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 81 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The results are shown in Table 1.

[ examples 2-2]

A long 105 μm-thick polyester carbonate resin film obtained in the same manner as in example 2-1 was stretched in the width direction while adjusting the thickness so as to obtain a predetermined retardation, to obtain a 38 μm-thick retardation film. The Re (550) of the resulting retardation film was 140 nm.

A polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained in the same manner as in example 2-1, except that the retardation film was used as the retardation layer. The total thickness of the obtained polarizing plate with a retardation layer was 81 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The results are shown in Table 1.

[ examples 2 to 3]

A long 105 μm-thick polyester carbonate resin film obtained in the same manner as in example 2-1 was stretched in the width direction while adjusting the thickness so as to obtain a predetermined retardation, to obtain a 38 μm-thick retardation film. The Re (550) of the resulting retardation film was 149 nm.

A polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained in the same manner as in example 2-1, except that the retardation film was used as the retardation layer. The total thickness of the obtained polarizing plate with a retardation layer was 81 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The results are shown in Table 1.

Comparative example 1

1. Fabrication of polarizing elements

A polyvinyl alcohol resin film having an average polymerization degree of 2,400, a saponification degree of 99.9 mol% and a thickness of 30 μm was prepared. The polyvinyl alcohol film was stretched 2.4 times in the transport direction while being swollen by immersing it in a swelling bath (water bath) at 20 ℃ for 30 seconds at a peripheral speed ratio between different rolls (swelling step), and then stretched 3.7 times in the transport direction based on the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the transport direction) while being immersed and dyed in a dyeing bath (aqueous solution having an iodine concentration of 0.03 wt% and a potassium iodide concentration of 0.3 wt%) at 30 ℃ so that the monomer transmittance after final stretching became a desired value (dyeing step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film was stretched 4.2 times in the transport direction based on the original polyvinyl alcohol film while being immersed in a crosslinking bath (aqueous solution having a boric acid concentration of 3.0 wt% and a potassium iodide concentration of 3.0 wt%) at 40 ℃. The obtained polyvinyl alcohol film was immersed in a stretching bath (an aqueous solution having a boric acid concentration of 4.0 wt% and a potassium iodide concentration of 5.0 wt%) at 64 ℃ for 50 seconds, stretched 6.0 times in the transport direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a cleaning bath (an aqueous solution having a potassium iodide concentration of 3.0 wt%) at 20 ℃ for 5 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 30 ℃ for 2 minutes to prepare a polarizer (thickness: 12 μm).

2. Manufacture of polarizing plate

As the binder, the following aqueous solutions were used: an aqueous solution containing an acetoacetyl group-containing polyvinyl alcohol resin (average degree of polymerization of 1,200, degree of saponification of 98.5 mol%, degree of acetoacetylation of 5 mol%) and methylolmelamine. A polarizing plate having a structure of protective layer 1 (thickness 32 μm)/adhesive layer/polarizing material/adhesive layer/protective layer 2 was produced by using the adhesive so that the thickness of the adhesive layer became 0.1 μm, adhering a cellulose Triacetate (TAC) film with a hard coat (hard coat thickness 7 μm, TAC thickness 25 μm, elastic modulus: 3600MPa) to one surface of the obtained polarizing material with a roll laminator, adhering a TAC film with a thickness of 25 μm to the other surface of the polarizing material, and then drying the resultant mixture by heating in an oven (temperature 60 ℃ C., time 5 minutes).

3. Manufacture of polarizing plate with phase difference layer

A retardation film was attached to the surface of the protective layer 2 of the polarizing plate obtained in the above 2. in the same manner as in example 1, and a polarizing plate with a retardation layer having a structure of protective layer 1/adhesive layer/polarizer/adhesive layer/protective layer 2/adhesive layer/retardation layer was produced. The total thickness of the obtained polarizing plate with a retardation layer was 122 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1.

Comparative example 2

1. Fabrication of polarizing elements

A polarizing plate (thickness: 12 μm) was produced in the same manner as in comparative example 1.

2. Manufacture of polarizing plate

In the same manner as in comparative example 1, a polarizing plate having a structure of protective layer 1 (thickness: 32 μm)/adhesive layer/polarizer/adhesive layer/protective layer 2 (thickness: 25 μm) was produced.

3. Production of 1 st oriented cured layer and 2 nd oriented cured layer constituting phase difference layer

A liquid crystal composition (coating liquid) was prepared by dissolving 10g of a polymerizable liquid crystal (product name "Paliocolor LC 242" manufactured by BASF) exhibiting a nematic liquid crystal phase and 3g of a photopolymerization initiator (product name "IRGACURE 907" manufactured by BASF) for the polymerizable liquid crystal compound in 40g of toluene.

The surface of a polyethylene terephthalate (PET) film (38 μm in thickness) was rubbed with a rubbing cloth to conduct orientation treatment. The orientation treatment was performed in a direction of 15 ° with respect to the absorption axis direction of the polarizer when viewed from the visual recognition side in the lamination to the polarizer. Applying the liquid crystal coating liquid to the alignment layer by using a bar coaterThe surface was treated and heat-dried at 90 ℃ for 2 minutes, thereby aligning the liquid crystal compound. Using a metal halide lamp at 1mJ/cm²The liquid crystal layer thus formed was irradiated with light and cured, thereby forming a liquid crystal alignment cured layer a on the PET film. The thickness of the liquid crystal alignment cured layer A was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Further, the liquid crystal alignment cured layer a has a refractive index distribution of nx > ny ═ nz.

A liquid crystal alignment cured layer B was formed on the PET film in the same manner as described above, except that the coating thickness was changed and the alignment treatment direction was set to be 75 ° with respect to the absorption axis direction of the polarizer when viewed from the visual recognition side. The thickness of the liquid crystal alignment cured layer B was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. Further, the liquid crystal alignment cured layer B has a refractive index distribution of nx > ny ═ nz. Further, Re (450)/Re (550) of the liquid crystal alignment cured layers A and B was 1.11.

4. Manufacture of polarizing plate with phase difference layer

The liquid crystal alignment cured layer a and the liquid crystal alignment cured layer B obtained in the above 3 were sequentially transferred to the surface of the polarizing plate obtained in the above 2 on the protective layer 2 side. At this time, transfer (bonding) was performed so that the angle formed by the absorption axis of the polarizer and the slow axis of the orientation cured layer a became 15 ° and the angle formed by the absorption axis of the polarizer and the slow axis of the orientation cured layer B became 75 °. Each transfer (bonding) was performed with an ultraviolet-curable adhesive (thickness 1 μm). In the above manner, a polarizing plate with a retardation layer having a constitution of protective layer 1/adhesive layer/polarizer/adhesive layer/protective layer 2/adhesive layer/retardation layer (1 st alignment cured layer/adhesive layer/2 nd alignment cured layer) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 75 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The results are shown in Table 1.

Comparative example 3

1. Production of polarizing film

A polarizing film having a thickness of 4.6 μm was formed on a resin substrate in the same manner as in example 2-1.

2. Manufacture of polarizing plate

An acrylic film (surface refractive index 1.50, 20 μm) was bonded as a protective layer to the surface (the surface opposite to the resin substrate) of the polarizing film obtained above via an ultraviolet-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness was 1.0 μm, and was bonded using a roll mill. Then, the adhesive is cured by irradiating UV light from the protective layer side. Then, after cutting both ends, the resin substrate was peeled off to obtain a long polarizing plate (width: 1300mm) having a structure of a protective layer/adhesive layer/polarizing film. The polarizing plate (substantially, a polarizing film) had a single transmittance of 43.0% and a polarization degree of 99.995%. Further, the absorbance per unit at a wavelength of 550nm was 0.97, A₄₇₀/A₆₀₀Is 0.87 and the orthogonal b value is-2.0.

3. Manufacture of polarizing plate with phase difference layer

In the same manner as in comparative example 2, the liquid crystal alignment cured layer a and the liquid crystal alignment cured layer B obtained in the same manner as in comparative example 2 were sequentially transferred onto the surface of the polarizing film of the polarizing plate obtained in the above 2. In the above manner, a polarizing plate with a retardation layer having a constitution of a protective layer/an adhesive layer/a polarizing film/an adhesive layer/a phase difference layer (1 st orientation cured layer/adhesive layer/2 nd orientation cured layer) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 32 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The results are shown in Table 1.

Comparative example 4

A polarizing film and a polarizing plate were produced in the same manner as in example 1, except that potassium iodide was not added to the PVA aqueous solution (coating solution), the shrinkage ratio in the width direction was set to 0.1% or less without using a heating roll in the drying shrinkage treatment, and the monomer transmittance of the polarizing film was adjusted by adjusting the concentration of the dyeing bath. The polarizing plate (substantially a polarizing film) had a monomer transmittance of 43.13% and a polarization degree of 99.881%. Further, the absorbance per unit at a wavelength of 550nm was 0.67. A polarizing plate with a retardation layer was produced in the same manner as in example 1, except that this polarizing plate was used.

[ Table 1]

[ evaluation ]

As is clear from comparison of example 1 with comparative examples 1,2 and 4, the polarizing film produced by the predetermined method is thin but exhibits excellent optical characteristics. It is found that by using such a polarizing film, a polarizing plate with a retardation layer which is thin and has excellent optical characteristics and in which warpage after a heat test is significantly suppressed (as a result, excellent handling properties) can be obtained. Further, it is found that when the retardation layer is used in combination with a polycarbonate resin (including a polyester carbonate resin) film, an excellent reflection hue can be obtained. Further, the bending characteristics can be further improved by reducing the thickness of the polycarbonate resin to 40 μm or less, making the total thickness of the polarizing plate with a retardation layer 85 μm or less, and using a substrate having an elastic modulus of 3000MPa or more, preferably a TAC film, as a protective layer. On the other hand, the polarizing plate with a retardation layer of comparative example 3 was thin and had excellent optical characteristics, and the warpage after the heat test was significantly suppressed, but the reflection hue was large, and was not satisfactory in terms of display characteristics.

Industrial applicability of the invention

The polarizing plate with a retardation layer of the present invention can be suitably used as a circular polarizing plate for liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

Description of the reference numerals

10 polarizing plate

11 polarizing film

12 st protective layer

13 nd 2 protective layer

20 phase difference layer

100 polarizing plate with phase difference layer

101 polarizing plate with phase difference layer

Claims (16)

1. A polarizing plate with a phase difference layer comprises a polarizing film and a protective layer on at least one side of the polarizing film,

the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, and has a thickness of 8 μm or less, a monomer transmittance of 43.0% or more, and an orthogonal absorbance per 1 μm of thickness at a wavelength of 550nm of 0.85 or more,

the phase difference layer has Re (550) of 100 to 190nm, Re (450)/Re (550) of 0.8 or more and less than 1,

the angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40-50 degrees.

2. The polarizing plate with a retardation layer according to claim 1, wherein the protective layer is composed of a base material having an elastic modulus of 3000MPa or more.

3. The polarizing plate with a retardation layer according to claim 1 or 2, which has a total thickness of 90 μm or less,

a front reflection color of 3.5 or less,

the protective layer is formed of a resin film having an elastic modulus of 3000MPa or more.

4. The polarizing plate with a retardation layer according to any one of claims 1 to 3, wherein the protective layer is composed of a cellulose triacetate resin film.

5. The polarizing plate with a phase difference layer according to any one of claims 1 to 4, wherein the polarizing plate comprises the polarizing film and the protective layer disposed only on one side of the polarizing film,

the phase difference layer is bonded to the polarizing film via an adhesive layer.

6. The polarizing plate with a retardation layer according to any one of claims 1 to 5, wherein the retardation layer is composed of a polycarbonate-based resin film.

7. The polarizing plate with a retardation layer according to any one of claims 1 to 6, wherein the retardation layer is composed of a polycarbonate-based resin film having a thickness of 40 μm or less.

8. The polarizing plate with a phase difference layer according to any one of claims 1 to 7, wherein the polarizing film has an orthogonal absorbance A at a wavelength of 470nm₄₇₀With orthogonal absorbance A at a wavelength of 600nm₆₀₀Ratio of (A)₄₇₀/A₆₀₀Is 0.7 to 2.00.

9. The polarizing plate with a phase difference layer according to any one of claims 1 to 8, wherein the orthogonal b value of the polarizing film is greater than-10 and +10 or less.

10. The polarizing plate with a phase difference layer according to any one of claims 1 to 9, wherein the polarizing film has an orthogonal absorbance a at a wavelength of 550nm₅₅₀Is 2.0 or more.

11. The polarizing plate with a retardation layer according to any one of claims 1 to 10, wherein an additional retardation layer having a refractive index characteristic showing a relationship of nz > nx ═ ny is further provided outside the retardation layer.

12. The polarizing plate with a retardation layer according to any one of claims 1 to 11, further comprising a conductive layer or an isotropic substrate with a conductive layer on the outer side of the retardation layer.

13. The polarizing plate with a retardation layer according to any one of claims 1 to 12, which is in a long form,

the polarizing film has an absorption axis in a longitudinal direction,

the retardation layer is an obliquely stretched film having a slow axis in a direction forming an angle of 40 DEG to 50 DEG with respect to the longitudinal direction.

14. The polarizing plate with a retardation layer according to claim 13, which is wound in a roll.

15. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 1 to 12.

16. The image display device according to claim 15, which is an organic electroluminescent display device or an inorganic electroluminescent display device.

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