CN111045134A - Polarizing plate with retardation layer and image display device using the same - Google Patents

Polarizing plate with retardation layer and image display device using the same Download PDF

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CN111045134A
CN111045134A CN201910966857.1A CN201910966857A CN111045134A CN 111045134 A CN111045134 A CN 111045134A CN 201910966857 A CN201910966857 A CN 201910966857A CN 111045134 A CN111045134 A CN 111045134A
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layer
polarizing plate
retardation layer
retardation
stretching
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CN111045134B (en
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后藤周作
柳沼宽教
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Nitto Denko Corp
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Nitto Denko Corp
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3083—Birefringent or phase retarding elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3016—Polarising elements involving passive liquid crystal elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
    • G02B5/3041—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid comprising multiple thin layers, e.g. multilayer stacks
    • G02B5/305—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid comprising multiple thin layers, e.g. multilayer stacks including organic materials, e.g. polymeric layers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/33—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being semiconductor devices, e.g. diodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00

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 a phase difference layer of the present invention comprises a polarizing plate and a phase difference layer, and the polarizing plate comprises a polarizing film and a protective layer provided on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic material, and has a thickness of 8 [ mu ] m or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more. The retardation layer is an alignment fixing layer of a liquid crystal compound.

Description

Polarizing plate with retardation layer and image display device using the 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. In an image display device, a polarizing plate and a retardation plate are typically used. In actual use, a polarizing plate with a retardation layer in which a polarizing plate and a retardation plate are integrated is widely used (for example, patent document 1), and recently, with the increasing demand for the reduction in thickness of an image display device, the demand for the reduction in thickness of a polarizing plate with a retardation layer is also increasing. In recent years, demands for a curved image display device and/or a curved or foldable image display device have been increasing, and further thinning and further softening of a polarizing plate and a polarizing plate with a retardation layer have been also demanded. For the purpose of reducing the thickness of a polarizing plate with a retardation layer, a protective layer of a polarizing film and a retardation film, which greatly contribute to the thickness, have been reduced in thickness. However, if the protective layer and the retardation film are thinned, the effect of shrinkage of the polarizing film is relatively large, and there are problems that the image display device is warped and the operability of the polarizing plate with the retardation layer is degraded.
In order to solve the above-described problems, it is necessary to make the polarizing film thin together. However, if the thickness of the polarizing film is simply reduced, the optical characteristics are degraded. More specifically, there is a trade-off in the selection relationship that one or both of the degree of polarization and the monomer transmittance are reduced to a degree that is not allowed in practical use. 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 conventional problems, and a main object of the present invention is to provide a polarizing plate with a retardation layer, which is thin, has excellent handleability, and has excellent optical characteristics.
Means for solving the problems
The polarizing plate with a phase difference layer of the present invention comprises a polarizing plate and a phase difference layer, and the polarizing plate comprises a polarizing film and a protective layer provided on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic material, and has a thickness of 8 [ mu ] m or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more. The retardation layer is an alignment-fixing layer of a liquid crystal compound.
In one embodiment, the polarizing plate with a retardation layer has a basis weight of 6.5mg/cm2The following.
In one embodiment, the total thickness of the polarizing plate with a retardation layer is 60 μm or less.
In one embodiment, the retardation layer is a single layer of an alignment-fixing layer of a liquid crystal compound, Re (550) of the retardation layer is 100nm to 190nm, and an angle formed between a slow axis of the retardation layer and an absorption axis of the polarizing film is 40 ° to 50 °.
In one embodiment, the retardation layer has a laminated structure of a 1 st liquid crystal compound alignment fixing layer and a 2 nd liquid crystal compound alignment fixing layer; the Re (550) of the alignment fixing layer of the 1 st liquid crystal compound is 200nm to 300nm, and the angle formed by the slow axis and the absorption axis of the polarizing film is 10 degrees to 20 degrees; re (550) of the alignment fixing layer of the 2 nd liquid crystal compound is 100 to 190nm, and an angle formed by a slow axis and an absorption axis of the polarizing film is 70 to 80 degrees.
In one embodiment, the polarizing film is 50cm2The difference between the maximum value and the minimum value of the single transmittance in the region (1) is 0.2% or less.
In one embodiment, the polarizing plate with a retardation layer has a width of 1000mm or more, and the difference between the maximum value and the minimum value of the monomer transmittance at a position of the polarizing film in the width direction is 0.5% or less.
In one embodiment, the polarizing film has a monomer transmittance of 46% or less and a degree of polarization of 99% or less.
In one embodiment, the polarizing plate with a retardation layer further includes another retardation layer on the outer side of the retardation layer, and the refractive index characteristic of the other retardation layer exhibits 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 on the outside of the retardation layer.
According to another aspect of the present invention, there is provided an image display device including the above polarizing plate with a retardation layer.
In one embodiment, the image display device is an organic electroluminescence display device or an inorganic electroluminescence display device.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a polarizing film having a thin shape and very excellent optical characteristics can be obtained by combining 2-stage stretching including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution with addition of a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) resin, and drying and shrinking by a heating roller. By using such a polarizing film, a polarizing plate with a retardation layer which is thin, excellent in handling properties, 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 cross-sectional view of a polarizing plate with a retardation layer according to still another embodiment of the present invention.
Fig. 4 is a schematic view showing an example of drying shrinkage treatment using a heating roller in the method for producing a polarizing film used for a polarizing plate with a retardation layer of the present invention.
Description of the symbols
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 retardation layer
102 polarizing plate with phase difference layer
Detailed Description
Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.
(definitions of wording 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 the in-plane refractive index is maximized (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 (film) is d (nm), the following formula can be used: re (λ) was obtained as (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), the following formula can be used: rth (λ) is obtained as (nx-nz) × d.
(4) Coefficient of Nz
The Nz coefficient is obtained by Nz ═ Rth/Re.
(5) Angle of rotation
In the present specification, when referring to an angle, the angle includes both clockwise and counterclockwise with respect to the reference direction. Thus, for example, "45" means ± 45 °.
A. Integral constitution 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 with retardation layer 100 of the present embodiment includes a polarizing plate 10 and a retardation layer 20. The polarizing plate 10 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. Depending on the purpose, one of the 1 st protective layer 12 and the 2 nd protective layer 13 may be omitted. For example, when the retardation layer 20 can also function as a protective layer of the polarizing film 11, the 2 nd protective layer 13 may be omitted. In the embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The polarizing film has a thickness of 8 μm or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more.
As shown in fig. 2, in the polarizing plate with retardation layer 101 of the other embodiment, another retardation layer 50 and/or a conductive layer or an isotropic substrate with conductive layer 60 may be provided. The other retardation layer 50 and the conductive layer or the isotropic substrate with a conductive layer 60 are typically provided outside the retardation layer 20 (on the side opposite to the polarizing plate 10). The refractive index characteristics of the other retardation layers typically show a relationship of nz > nx ═ ny. Typically, another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are provided in this order from the retardation layer 20 side. The other retardation layer 50 and the conductive layer or the isotropic substrate with conductive layer 60 are typically any layers provided as needed, and either one 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 of providing a conductive layer or an isotropic substrate with a conductive layer, a polarizing plate with a retardation layer can be applied to a so-called in-cell touch panel type input display device in which a touch sensor is introduced between an image display unit (for example, an organic EL unit) and a polarizing plate.
In the embodiment of the present invention, the 1 st retardation layer 20 is an alignment fixing layer of a liquid crystal compound. The 1 st retardation layer 20 may be a single layer of the alignment-fixing layers shown in fig. 1 and 2, or may have a laminated structure of the 1 st alignment-fixing layer 21 and the 2 nd alignment-fixing layer 22 shown in fig. 3.
The above embodiments may be combined as appropriate, and the constituent elements in the above embodiments may be changed as is obvious to those skilled in the art. For example, the 2 nd retardation layer 50 and/or the conductive layer or the isotropic substrate 60 with a conductive layer may be provided in the polarizing plate with retardation layer 102 of fig. 3. 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 contain another retardation layer. The optical properties (for example, refractive index property, 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 a sheet or a long polarizing plate. In the present specification, the "elongated shape" refers to an elongated shape having a length sufficiently long with respect to a width, and includes, for example, an elongated shape having a length 10 times or more, preferably 20 times or more with respect to a width. The polarizing plate with a retardation layer in a long form may be wound in a roll form.
In actual use, an adhesive layer (not shown) may be provided on the side of the retardation layer opposite to the polarizing plate, and the polarizing plate with the retardation layer may be attached to the image display unit. Further, it is preferable that a release film is temporarily stuck to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. By temporarily attaching the release film, the adhesive layer can be protected and formed into a roll.
The total thickness of the polarizing plate with a retardation layer is preferably 60 μm or less, more preferably 55 μm or less, still more preferably 50 μm or less, and particularly preferably 40 μm or less. The lower limit of the total thickness may be, for example, 28 μm. According to the embodiment of the present invention, a very thin polarizing plate with a retardation layer can be thus realized. Such a polarizing plate with a retardation layer can have very excellent flexibility and folding durability. Such a polarizing plate with a phase difference layer can be particularly suitably used for a curved image display device and/or a curved or bendable image display device. The total thickness of the polarizing plate with a retardation layer is the total thickness of all layers constituting the polarizing plate with a retardation layer except for the adhesive layer for adhering the polarizing plate 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 the thickness of the adhesive layer for adhering the polarizing plate with a retardation layer to an adjacent member such as an image display unit and the like and the thickness of the release film which can be temporarily adhered to the surface thereof).
The polarizing plate with a retardation layer according to the embodiment of the present invention has a basis weight of, for example, 6.5mg/cm2Hereinafter, 2.0mg/cm is preferable2～6.0mg/cm2More preferably 3.0mg/cm2～5.5mg/cm2More preferably 3.5mg/cm2～5.0mg/cm2. When the display panel is thin, the panel may be slightly deformed by the weight of the polarizing plate with a retardation layer, and display defects may occur, and the thickness of the display panel may be 6.5mg/cm2The polarizing plate with retardation layer of the following unit weight can prevent such panel deformation. In addition, the polarizing plate having the retardation layer per unit weight is excellent in handling property even when the polarizing plate is made thin, and exhibits very excellent flexibility and folding durability.
Hereinafter, the constituent elements of the polarizing plate with retardation layer will be described in more detail.
B. Polarizing plate
B-1 polarizing film
As described above, the polarizing film 11 has a thickness of 8 μm or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more. Generally, the monomer transmittance and the absorbance have a trade-off relationship with each other, and if the monomer transmittance is increased, the absorbance decreases, and if the absorbance is increased, the monomer transmittance decreases. Therefore, it has been difficult to practically use a thin polarizing film satisfying optical characteristics of a single transmittance of 45% or more and a degree of polarization of 97% or more. One of the features of the present invention is to use a thin polarizing film having excellent optical characteristics such as a single transmittance of 45% or more and a degree of polarization of 97% or more, and in which variation in optical characteristics is suppressed.
The thickness of the polarizing film is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and still more preferably 2 μm to 5 μm.
The polarizing film preferably exhibits absorption dichroism at any wavelength of 380nm to 780 nm. The single transmittance of the polarizing film is preferably 46% or less. The polarization degree of the polarizing film is preferably 97.5% or more, more preferably 98% or more. On the other hand, the degree of polarization is preferably 99% or less. The monomer transmittance is typically a Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting the visibility. The degree of polarization is typically determined from the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring with an ultraviolet-visible spectrophotometer and correcting the visibility, and is obtained by the following equation.
Degree of polarization (%) { (Tp-Tc)/(Tp + Tc) }1/2×100
In one embodiment, the transmittance of a thin polarizing film having a thickness of 8 μm or less is typically measured using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (surface refractive index: 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 in contact with the air interface of the protective film, and as a result, the measured value of the transmittance may change. Therefore, for example, in the case of using a protective film having a refractive index of not 1.50, the measured value of the transmittance can be corrected based on the refractive index of the surface in contact with the air interface of the protective film. Specifically, the correction value C of the transmittance is the reflectance R of polarized light parallel to the transmission axis at the interface between the protective film and the air layer1(transmission axis reflectance) is represented 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)
Wherein R is0Is to makeTransmission axis reflectance, n, in the case of using a protective film having a refractive index of 1.501Is the refractive index, T, of the protective film used1Is the transmittance of the polarizing film. For example, when a base material (a cycloolefin film, a film with a hard coat layer, or the like) having a surface refractive index of 1.53 is used as the protective film, the correction amount C is about 0.2%. In this case, 0.2% is added to the transmittance obtained by the measurement, and the transmittance can be converted to the transmittance when a protective film having a surface 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 the correction value C at 2% change is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. In the case where the protective film has absorption other than surface reflection, appropriate correction can be made in accordance with the absorption amount.
In one embodiment, the width of the polarizing plate with a retardation layer is 1000mm or more, and therefore the width of the polarizing film is 1000mm or more. In this case, the difference (D1) between the maximum value and the minimum value of the monomer transmittance at a position in the width direction of the polarizing film is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.3% or less. The lower the D1, the more preferable, the lower limit of D1 may be, for example, 0.01%. When D1 is within the above range, a polarizing plate with a retardation layer having excellent optical properties can be industrially produced. In another embodiment, the polarizing film is at 50cm2The difference (D2) between the maximum value and the minimum value of the single transmittance in the region (a) is preferably 0.2% or less, more preferably 0.15% or less, and still more preferably 0.1% or less. The lower the D2, the more preferable, the lower limit of D2 may be, for example, 0.01%. When D2 is within the above range, it is possible to suppress brightness unevenness on the display screen when the polarizing plate with a retardation layer is used in an image display device.
As the polarizing film, any suitable polarizing film may be used. The 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 on the resin substrate by coating. A polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced by the following method: for example, a laminate of a resin base and a PVA type resin layer is obtained by applying a PVA type resin solution to a resin base and drying the solution to form a PVA type resin layer on the resin base; the laminate was stretched and dyed to obtain a polarizing film from the PVA type resin layer. In the present embodiment, the stretching typically includes immersing the laminate in an aqueous boric acid solution to perform stretching. Further, the stretching may further include stretching the laminate in a gas atmosphere at a high temperature (for example, 95 ℃ or higher) before the stretching in the aqueous boric acid solution, as necessary. The obtained resin substrate/polarizing film laminate can be used as it is (that is, the resin substrate can be used as a protective layer for a polarizing film), and the resin substrate can be peeled off from the resin substrate/polarizing film laminate and any suitable protective layer according to the purpose can 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 disclosure of this publication is incorporated herein by reference.
The method of manufacturing 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 form a laminate; and subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment of shrinking the laminate by 2% or more in the width direction by heating while conveying the laminate in the longitudinal direction. Thus, a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more, excellent optical characteristics, and suppressed variation in optical characteristics can be provided. That is, by introducing the auxiliary stretching, even when the PVA is coated on the thermoplastic resin, the crystallinity of the PVA can be improved, 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 degradation of the orientation and dissolution of the PVA when immersed in water in the subsequent dyeing step and stretching step, and to realize high optical characteristics. In addition, when the PVA-based resin layer is immersed in a liquid, disturbance of orientation of polyvinyl alcohol molecules and reduction of orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained in a treatment step of immersing the laminate in a liquid, such as a dyeing treatment or a stretching treatment in an aqueous solution. 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 may be 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), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth) acrylic acids, and transparent resins such as acetates. Further, there may be mentioned a heat-curable resin such as (meth) acrylic resins, carbamates, (meth) acrylic carbamates, epoxy resins, silicone resins, and ultraviolet-curable resins. In addition to these, for example, a glassy polymer such as a siloxane polymer can be cited. 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 examples thereof include: a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrusion molded product of the above resin composition.
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, as will be described later. Therefore, the 1 st protective layer 12 may be subjected to surface treatment such as hard coating treatment, antireflection treatment, anti-sticking treatment, antiglare treatment, or the like, as necessary. In addition, or alternatively, in the case of performing visual recognition by polarized sunglasses, the 1 st protective layer 12 may be subjected to a process for improving the visual recognition (typically, imparting a (elliptical) polarization function, imparting an ultra-high retardation) as necessary. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through a polarizing lens such as a polarizing sunglass. Therefore, the polarizing plate with a retardation layer is also suitable 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 30 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 0 to 10nm and the retardation Rth (550) in the thickness direction is-10 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, it is preferable that the 2 nd protective layer be omitted.
B-3. method for producing polarizing film
The polarizing film may be manufactured by a method including the steps of: for example, a polyvinyl alcohol resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol resin (PVA-based resin) is formed on one side of a long thermoplastic resin base material to form a laminate; and subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment of shrinking the laminate in the width direction by 2% or more by heating while conveying the laminate 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 roll, and the temperature of the heated roll is preferably 60 to 120 ℃. The shrinkage rate of the laminate subjected to the drying shrinkage treatment in the width direction 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 polarization degree) and suppressed variations in optical characteristics can be obtained by producing a laminate including a halide-containing PVA-based resin layer, subjecting the laminate to stretching in multiple stages including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and heating the stretched laminate with a heating roller. Specifically, by using a heating roller in the drying and shrinking process, the entire laminate can be uniformly shrunk while being conveyed. Thus, not only the optical characteristics of the obtained polarizing film can be improved, but also a polarizing film excellent in optical characteristics can be stably produced, and variations in optical characteristics (particularly, cell transmittance) of the polarizing film can be suppressed.
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. Preferably, the PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying the coating liquid. 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-wound bar coating, dip coating, die coating, flow coating, spray coating, blade coating (doctor blade coating, etc.), and the like. The coating/drying temperature of the coating liquid is preferably 50 ℃ or higher.
The thickness of the PVA based resin layer is preferably 3 to 40 μm, and more preferably 3 to 20 μm.
Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment) to form an easy-adhesion layer 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, the PVA-based resin layer may be difficult to form. When the thickness exceeds 300 μm, for example, in a stretching treatment in an aqueous solution described later, it takes 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 substrate absorbs water, and the water acts as a plasticizer to plasticize the thermoplastic resin substrate. As a result, the tensile stress can be greatly reduced, and the stretching can be performed at 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 substrate is prevented from being broken and the PVA based resin layer is prevented from being peeled off from the thermoplastic resin substrate when stretched in an aqueous solution. 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 type resin layer can be suppressed, and the stretchability of the laminate can be sufficiently ensured. In addition, when plasticizing of the thermoplastic resin substrate with water and stretching in an aqueous solution are considered to be favorable, the temperature 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 the coating liquid containing the PVA-based resin is applied and dried, troubles such as deformation (for example, generation of unevenness, looseness, 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, using a crystallized material in which a modifying group is introduced into a constituent material and heating the crystallized 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-based resins and amorphous polyethylene terephthalate-based resins are preferable.
In one embodiment, an amorphous (noncrystalline) polyethylene terephthalate-based resin is preferably used. Among them, amorphous (less likely to crystallize) polyethylene terephthalate resins are particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing 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 such a thermoplastic resin substrate is excellent in stretchability and can be inhibited from crystallizing during stretching. This is considered to be because the introduction of the isophthalic acid unit can impart a large curve 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 substrate having 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, relative to the total of all the repeating units. By setting such a content ratio, the crystallinity can be improved 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 elongated thermoplastic resin base material may be stretched in the transverse direction. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate described later. In the present specification, "orthogonal" means that the two are substantially orthogonal to each other. Here, "substantially orthogonal" includes a case where the angle is 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.
The stretching temperature of the thermoplastic resin 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, and 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 in multiple stages. In the case of performing in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratios in the respective stages.
B-3-1-2 coating liquid
The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid may be 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 two or more kinds may be used in combination. Of these, water is preferred. 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. When the resin concentration is such as this, a uniform coating film can be formed in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.
Additives may be added to the coating liquid. Examples of additives include: plasticizers, surfactants, and the like. Examples of the plasticizer include: polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include: a nonionic surfactant. These additives are 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. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are cited. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is 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 K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.
The average polymerization degree of the PVA-based resin may 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. Examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.
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 polarizing film finally obtained may be clouded.
Generally, the orientation of polyvinyl alcohol molecules in a PVA type resin is improved by stretching the PVA type resin layer, but if the stretched PVA type resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules may be disturbed, and the orientation may be degraded. 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 significantly reduced 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 stretching of a PVA film monomer in an aqueous boric acid solution is generally performed at 60 ℃, stretching of a laminate of a-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature such as a temperature of about 70 ℃, and in this case, the orientation of PVA at the initial stage of stretching is reduced in a stage before it is raised by stretching in an aqueous solution. On the other hand, by preparing a laminate of a halide-containing PVA type resin layer 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 type resin in the PVA type 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, disturbance of the orientation of the polyvinyl alcohol molecules and reduction in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment or a stretching treatment in an aqueous solution.
B-3-2 auxiliary stretching treatment in gas atmosphere
In particular, in order to obtain high optical characteristics, a 2-stage stretching method combining dry stretching (auxiliary stretching) and stretching in an aqueous boric acid solution is selected. By introducing the auxiliary stretching as in the 2-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 at a higher magnification. Further, when the PVA type resin is coated on the 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 the PVA type resin is coated on a general metal drum, and as a result, there is a problem that crystallization of the PVA type resin is relatively lowered and sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when the PVA type resin is coated on the thermoplastic resin, the crystallinity of the PVA type resin can be improved, and high optical characteristics can be realized. Further, by simultaneously improving the orientation of the PVA-based resin in advance, when the PVA-based resin is immersed in water in the subsequent dyeing step or stretching step, problems such as a decrease in the orientation and dissolution of the PVA-based resin can be prevented, and high optical characteristics can be realized.
The stretching method for assisting stretching in a gas atmosphere 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 by passing the laminate between rolls having different peripheral speeds), and the free-end stretching is actively employed for obtaining high optical characteristics. In one embodiment, the stretching treatment in a gas atmosphere includes a heated roller stretching step of stretching the laminate by a difference in peripheral speed between heated rollers while conveying the laminate in the longitudinal direction thereof. The stretching treatment in a gas atmosphere typically includes a zone stretching step and a heated roller stretching step. The order of the area stretching step and the heating roller stretching step is not limited, and the area stretching step may be performed first or the heating roller stretching step may be performed first. The zone stretching process may be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed in this order. In another embodiment, the tenter stretching machine grips the film end portions, and stretches the film by expanding the distance between the tenters in the transport direction (the expansion of the distance between the tenters is the stretching magnification). At this time, the distance of the tenter in the width direction (the direction perpendicular to the conveying direction) is arbitrarily set close. Preferably, the stretching ratio in the transport direction may be set so as to stretch closer to the free end. At the free endIn the case of stretching, the shrinkage in the width direction (1/stretching ratio) is determined1/2To calculate.
The auxiliary stretching in a gas atmosphere may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching magnification is the product of the stretching magnifications in each stage. The stretching direction in the auxiliary stretching in the gas atmosphere is preferably substantially the same as the stretching direction in the aqueous solution.
The stretching ratio in the auxiliary stretching in a gas atmosphere is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of auxiliary stretching in a combined gas atmosphere and stretching in an aqueous solution is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more, with respect to the original length of the laminate. In the present specification, "maximum stretching ratio" means a stretching ratio immediately before the laminate is broken, and further, a stretching ratio at which the laminate is confirmed to be broken, and "maximum stretching ratio" means a value smaller than this value by 0.2.
The stretching temperature for assisting stretching in a gas atmosphere may be set to any appropriate value depending on the material for forming the thermoplastic resin substrate, 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, rapid progress of crystallization of the PVA type resin can be suppressed, and defects caused by the crystallization (for example, inhibition of orientation of the PVA type resin layer by stretching) can be suppressed. The crystallization index of the PVA resin after auxiliary stretching in a gas atmosphere 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 an ATR method using a fourier transform infrared spectrophotometer. Specifically, the measurement was carried out using polarized light as the measurement light, and the spectrum obtained was used at 1141cm-1And 1440cm-1The crystallization index was calculated from the following equation.
Crystallization index ═ IC/IR)
Wherein the content of the first and second substances,
IC: the incident measurement light was measured at 1141cm-1Strength of
IR: the incident measurement light was measured at 1440cm-1The strength of (2).
B-3-3. insolubilization
If necessary, after the stretching treatment is assisted in a gas atmosphere, an insolubilization treatment is performed before the stretching treatment in an aqueous solution and the dyeing treatment. The insolubilization treatment is typically 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 of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine; a method of applying the dyeing liquid to a PVA-based resin layer; a method of spraying the dyeing solution on the PVA-based resin layer, and the like. A method of immersing the laminate in a dyeing solution (dyeing bath) is preferable. This is because iodine can be adsorbed well.
The staining solution is preferably an aqueous iodine solution. The amount of iodine 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 add an iodide to 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, titanium iodide, and the like. Of these, potassium iodide is preferred. 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 the dissolution of the PVA based resin, the liquid temperature at the time of dyeing with the dyeing liquid is preferably 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 of the polarizing film to be finally obtained is 45% or more and the degree of polarization is 97% or more. As such dyeing conditions, it is preferable to use an aqueous iodine solution as the dyeing liquid, and the ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is 1:5 to 1: 20. The ratio of the iodine content to the potassium iodide content in the iodine aqueous solution is preferably 1:5 to 1: 10. Thus, a polarizing film having the above-described optical characteristics can be obtained.
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, whereby the boric acid concentration in the dyeing bath changes with time, and as a result, the dyeing property may become 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 that it is preferably 4 parts by weight, more preferably 2 parts by weight, per 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 containing boric acid in advance. This can reduce the rate of change in the boric acid concentration when boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid to be blended in the dyeing bath in advance (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of water.
B-3-5. Cross-linking treatment
If necessary, the crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in an aqueous solution. The crosslinking treatment is typically 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 orientation of the PVA can be prevented from being lowered when the PVA is immersed in high-temperature water during subsequent stretching in an aqueous solution. 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 incorporate an iodide. The iodine compound can suppress elution of iodine adsorbed on the PVA-based resin layer. 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 aqueous solution
The stretching treatment in an aqueous solution is performed by immersing the laminate in a stretching bath. The stretching treatment in an aqueous solution allows stretching at a temperature lower than the glass transition temperature (typically, about 80 ℃) of the thermoplastic resin substrate or the PVA type resin layer, and allows stretching at a high magnification while suppressing crystallization of the PVA type resin layer. As a result, a polarizing film having excellent optical characteristics can be produced.
Any suitable method can 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 passing the laminate between rollers having different peripheral speeds to perform uniaxial stretching). Free end stretching is preferably chosen. The laminate may be stretched in one stage or in multiple stages. In the case of performing the stretching in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios in the respective stages.
The stretching in an aqueous solution is preferably performed by immersing the laminate in an aqueous solution of boric acid (stretching in an aqueous solution of boric acid). By using an aqueous boric acid solution as a stretching bath, rigidity capable of withstanding tension applied during stretching and water resistance insoluble in water can be imparted to the PVA-based resin layer. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution and can be crosslinked with the PVA-based resin by hydrogen bonds. 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 properties 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. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. An aqueous solution obtained by dissolving a boron compound such as borax other than boric acid or a borate, glyoxal, glutaraldehyde, or the like in a solvent may also be used.
Preferably, an iodide is added to the stretching bath (aqueous boric acid solution). The iodine compound can suppress elution of iodine adsorbed on the PVA-based resin layer. 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 stretching temperature (liquid temperature of the stretching bath) is preferably 40 to 85 ℃, more preferably 60 to 75 ℃. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while dissolution thereof is suppressed. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher in view of the relationship with the formation of the PVA-based resin layer. In this case, when the stretching temperature is lower than 40 ℃, there is a possibility that the thermoplastic resin substrate cannot be stretched well even when plasticization of the thermoplastic resin substrate by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the less excellent optical characteristics may be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.
The stretching ratio by stretching in an aqueous solution is preferably 1.5 times or more, and 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 stretch ratio, a polarizing film having very excellent optical characteristics can be produced. Such a high draw ratio can be achieved by employing a drawing method in an aqueous solution (drawing in an aqueous boric acid solution).
B-3-7. drying shrinkage treatment
The drying shrinkage treatment may be performed by heating the entire area to perform area heating, or may be performed by heating a transport roller (using a so-called hot roller) (hot roller drying method). Preferably both are utilized. By drying using a heating roller, the heating curl of the laminate can be efficiently suppressed, and a polarizing film having excellent appearance can be produced. Specifically, by drying the laminate in a state of being along the heating roller, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and the crystallinity of the thermoplastic resin substrate can be favorably increased even at a relatively low drying temperature. As a result, the thermoplastic resin substrate has increased rigidity and is able to withstand shrinkage of the PVA type resin layer due to drying, and curling can be suppressed. Further, since the laminate can be dried while being kept flat 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, whereby the optical characteristics can be improved. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate subjected to the drying shrinkage treatment in the width direction is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heated roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.
Fig. 4 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 which are 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 transport roller (temperature of the heating roller), the number of heating rollers, the contact time 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, the curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roller may be measured by a contact thermometer. In the illustrated example, 6 transport rollers are provided, but there is no particular limitation as long as there are a plurality of transport rollers. The number of the transport 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 manufacturing line (room temperature environment). Preferably, the air blowing mechanism is provided in a heating furnace having an air blowing mechanism. By using drying with a heating roller and hot air drying in combination, a rapid temperature change between the heating rollers can be suppressed, and 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 the aqueous solution 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 retardation layer 20 is an alignment fixing layer of a liquid crystal compound as described above. By using the liquid crystal compound, the difference between nx and ny of the resulting retardation layer can be greatly increased as compared with a non-liquid crystal material, and therefore, the thickness of the retardation layer for obtaining a desired in-plane retardation can be greatly reduced. As a result, the polarizing plate with a retardation layer can be further thinned and lightened. In the present specification, the "alignment-fixing layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. As described later, the "alignment fixing layer" is a concept including an alignment fixing layer obtained by curing a liquid crystal monomer. In the present embodiment, the rod-like liquid crystal compound is typically aligned in the slow axis direction of the retardation layer (homogeneous alignment).
Examples of the liquid crystal compound include: the liquid crystal phase is a nematic liquid crystal compound (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The mechanism of developing the liquid crystallinity of the liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.
When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer or a crosslinkable monomer. This is because the alignment state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After the liquid crystal monomers are aligned, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the above-described alignment state can be fixed thereby. Here, the polymer is formed by polymerization and the 3-dimensional network structure is formed by crosslinking, but they are non-liquid crystalline. Therefore, the 1 st retardation layer formed does not undergo transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change specific to the liquid crystalline compound, for example. As a result, the 1 st retardation layer is a retardation layer which is not affected by temperature change and has very excellent stability.
The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the kind thereof. Specifically, the temperature range is preferably 40 to 120 ℃, more preferably 50 to 100 ℃, and most preferably 60 to 90 ℃.
As the liquid crystal monomer, any suitable liquid crystal monomer can be used. For example, the polymerizable mesogenic compounds described in Japanese patent application laid-open No. 2002-533742(WO00/37585), EP358208(US5211877), EP66137(US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, GB2280445 and the like can be used. Specific examples of such polymerizable mesogenic compounds include, for example, trade name LC242 from BASF, trade name E7 from Merck, and trade name LC-Sillicon-CC3767 from Wacker-Chem. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.
The alignment fixing layer of the liquid crystal compound may be formed by: a surface of a given substrate is subjected to an alignment treatment, and a coating liquid containing a liquid crystal compound is applied to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, thereby fixing the alignment state. In one embodiment, the substrate is any suitable resin film, and the orientation fixing layer formed on the substrate may be transferred to the surface of the polarizing plate 10. In another embodiment, the substrate may be the 2 nd protective layer 13. In this case, since the transfer step is omitted and the alignment fixing layer (1 st retardation layer) can be formed and then laminated continuously by roll-to-roll, the productivity can be further improved.
As the alignment treatment, any suitable alignment treatment may be employed. Specifically, there may be mentioned: mechanical orientation treatment, physical orientation treatment, chemical orientation treatment. Specific examples of the mechanical orientation treatment include rubbing treatment and stretching treatment. Specific examples of the physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of the chemical alignment treatment include oblique vapor deposition and photo-alignment treatment. The treatment conditions for the various alignment treatments may be any suitable conditions according to the purpose.
The alignment of the liquid crystal compound can be performed as follows: the treatment is performed at a temperature at which a liquid crystal phase is exhibited according to the kind of the liquid crystal compound. By performing such temperature treatment, the liquid crystal compound is brought into a liquid crystal state, and the liquid crystal compound is aligned in accordance with the alignment treatment direction of the substrate surface.
In one embodiment, the fixing of the alignment state is performed by cooling the aligned liquid crystal compound as described above. In the case where the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state can be fixed by subjecting the aligned liquid crystal compound to polymerization treatment or crosslinking treatment as described above.
Specific examples of liquid crystal compounds and methods for forming alignment fixing layers are described in Japanese patent laid-open No. 2006-163343. The description of this publication is incorporated herein by reference.
As another example of the alignment-fixing layer, a mode in which a discotic liquid crystal compound is aligned in any state of vertical alignment, hybrid alignment, and tilt alignment can be cited. Typically, the discotic liquid crystal compound has a discotic surface aligned substantially perpendicular to the film surface of the 1 st retardation layer. The discotic liquid crystalline compound being substantially perpendicular means that the average value of the angle formed between the film surface and the disc surface of the discotic liquid crystalline compound is preferably 70 ° to 90 °, more preferably 80 ° to 90 °, and still more preferably 85 ° to 90 °. The discotic liquid crystal compound generally refers to a liquid crystal compound having a discotic molecular structure in which a cyclic nucleus such as benzene, 1,3, 5-triazine, calixarene, or the like is disposed at the center of a molecule and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group, or the like is radially substituted as a side chain thereof. Typical examples of the discotic liquid crystal include studies reported by c.destrande et al, studies reported by mol.cryst.liq.cryst.71, page 111 (1981), study reports by triphenylene derivatives, truxene derivatives, phthalocyanine derivatives, b.kohne et al, studies reported by angelw.chem.96, page 70 (1984), and study reports by j.m.lehn et al, studies reported by j.chem.soc.chem.commun, page 1794 (1985), studies reported by j.zhang et al, studies reported by j.am.chem.soc.116, and macrocycles such as azacrown ethers and phenylacetylenes described by 2655 (1994). Other specific examples of the discotic liquid-crystalline compound include: compounds described in Japanese patent laid-open Nos. 2006-133652, 2007-108732, and 2010-244038. The disclosures of the above documents and publications are incorporated herein by reference.
In one embodiment, the 1 st retardation layer 20 is a single layer of an alignment fixing layer of a liquid crystal compound, as shown in fig. 1 and 2. When the 1 st retardation layer 20 is composed of a single layer of an alignment-fixing layer of a liquid crystal compound, the thickness thereof is preferably 0.5 to 7 μm, more preferably 1 to 5 μm. By using the liquid crystal compound, an in-plane retardation equivalent to that of the resin film can be realized with a thickness significantly thinner than that of the resin film.
Representatively, the refractive index characteristic of the 1 st retardation layer shows a relationship of nx > ny ═ nz. The 1 st retardation layer is typically provided for imparting antireflection properties to the polarizing plate, and when the 1 st retardation layer is a single layer of the alignment-fixing layer, it can 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. Note that "ny ═ nz" herein 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 or ny < nz may be used in some cases within a range not impairing the effects of the present invention.
The Nz coefficient of the 1 st retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3. When the obtained polarizing plate with a retardation layer is used in an image display device, the obtained polarizing plate with a retardation layer satisfies such a relationship, and thus a very excellent reflection hue can be achieved.
The 1 st retardation layer may exhibit reverse dispersion wavelength characteristics in which the phase difference value increases according to the wavelength of the measurement light, may exhibit positive wavelength dispersion characteristics in which the phase difference value decreases according to the wavelength of the measurement light, and may exhibit flat wavelength dispersion characteristics in which the phase difference value hardly changes according to the wavelength of the measurement light. In one embodiment, the 1 st retardation layer exhibits reverse 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 angle θ formed by the slow axis of the 1 st retardation layer 20 and the absorption axis of the polarizing film 11 is preferably 40 ° to 50 °, more preferably 42 ° to 48 °, and still more preferably about 45 °. When the angle θ is in such a range, the 1 st retardation layer is made to be a λ/4 plate as described above, whereby a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained.
In another embodiment, the 1 st retardation layer 20 may have a laminated structure of a 1 st alignment-fixing layer 21 and a 2 nd alignment-fixing layer 22, as shown in fig. 3. In this case, either one of the 1 st alignment fixing layer 21 and the 2 nd alignment fixing layer 22 may function as a λ/4 plate, and the other may function as a λ/2 plate. Therefore, the thicknesses of the 1 st alignment fixing layer 21 and the 2 nd alignment fixing layer 22 can be adjusted so as to obtain a desired in-plane retardation of the λ/4 plate or the λ/2 plate. For example, when the 1 st alignment fixing layer 21 functions as a λ/2 wave plate and the 2 nd alignment fixing layer 22 functions as a λ/4 wave plate, the thickness of the 1 st alignment fixing layer 21 is, for example, 2.0 μm to 3.0 μm, and the thickness of the 2 nd alignment fixing layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane retardation Re (550) of the 1 st alignment fixing layer is preferably 200nm to 300nm, more preferably 230nm to 290nm, and still more preferably 250nm to 280 nm. As for the alignment fixed layer of a single layer, the in-plane retardation Re (550) of the 2 nd alignment fixed layer is as described above. The angle formed by the slow axis of the orientation fixing layer 1 and the absorption axis of the polarizing film is preferably 10 ° to 20 °, more preferably 12 ° to 18 °, and still more preferably about 15 °. The angle formed by the slow axis of the 2 nd alignment-fixing layer and the absorption axis of the polarizing film is preferably 70 ° to 80 °, more preferably 72 ° to 78 °, and still more preferably about 75 °. With such a configuration, characteristics close to ideal reverse wavelength dispersion characteristics can be obtained, and as a result, very excellent antireflection characteristics can be realized. The liquid crystal compounds constituting the 1 st and 2 nd alignment fixing layers, the methods for forming the 1 st and 2 nd alignment fixing layers, the optical characteristics, and the like are as described above with respect to the single-layer alignment fixing layer.
D. Phase difference layer 2
The 2 nd retardation layer may be a so-called negative type C plate whose refractive index characteristics exhibit a relationship of nz > nx ═ ny, as described above. By using a negative C plate as the 2 nd retardation layer, reflection in an oblique direction can be prevented well, and a wide viewing angle of the antireflection function can be realized. 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 homeotropic alignment-alignable liquid crystal material (liquid crystal compound) 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 [0020] to [0028] of Japanese patent laid-open publication 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, spray coating, 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, 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 alone may be used as a constituent layer of the polarizing plate with a retardation layer, or may be formed as a laminate with the substrate (substrate with a conductive layer) and laminated on the 1 st retardation layer (or the 2 nd retardation layer in the case where the 2 nd retardation layer is present). The substrate is preferably 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 material include: materials having a main skeleton of a resin not having a conjugated system such as norbornene-based resins and olefin-based resins; and materials having a cyclic structure such as a lactone ring or a glutarimide ring in the main chain of the acrylic resin. When such a material is used, the retardation exhibited by the molecular chains in accordance with their orientation can be suppressed to a small level when the isotropic base material is formed. 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 of the conductive layer and/or the conductive layer-carrying isotropic substrate may be patterned as desired. By patterning, the conductive portion and the insulating portion can be formed. As a result, an electrode can be formed. The electrodes can function as touch sensor electrodes that sense contact with the touch panel. As the pattern forming method, any appropriate method can be adopted. Specific examples of the pattern forming 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 visible side. The polarizing plate with a phase difference layer is laminated such that the phase difference layer is on the image display cell (for example, liquid crystal cell, organic EL cell, or inorganic EL cell) (such that the polarizing film is on the visible side). In one embodiment, the image display device may have a curved shape (substantially a curved display screen), and/or may be curved or bendable. In such an image display device, the effect of the polarizing plate with a retardation layer according to the present invention is remarkable.
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. Unless otherwise specified, "parts" and "%" in examples and comparative examples are based on weight.
(1) Thickness of
The thickness of 10 μm or less was measured by using an interference film thickness meter (available from Otsuka electronics Co., Ltd., product name "MCPD-3000"). The thickness of more than 10 μm is measured using a digital micrometer (product name "KC-351C" manufactured by Anritsu Co., Ltd.).
(2) Transmittance and degree of polarization of monomer
For the polarizing film/protective layer laminate (polarizing plate) used in examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer (V-7100, manufactured by japan spectrographic corporation) were used as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values obtained by measuring and correcting visibility with a 2-degree field of view (C light source) according to JIS Z8701. The refractive index of the protective layer was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
From the Tp and Tc thus obtained, the degree of polarization P was determined by the following equation.
Polarization degree P (%) { (Tp-Tc)/(Tp + Tc) }1/2×100
The spectrophotometer can be measured similarly with LPF-200 manufactured by Otsuka electronics Co., Ltd. For example, the monomer transmittance Ts and the polarization degree P were obtained by measurement using V-7100 and LPF-200 for samples 1 to 3 of the polarizing plates having the same configurations as in the following examples, and the measured values thereof are shown in table 1. As shown in Table 1, it was found that the difference between the measured value of the monomer transmittance of V-7100 and the measured value of the monomer transmittance of LPF-200 was 0.1% or less, and that the same measurement results were obtained in all cases where any of the spectrophotometers was used.
[ Table 1]
Figure BDA0002230756990000261
For example, when a polarizing plate having an anti-glare (AG) surface-treated adhesive and having a diffusing property is used as a measurement target, different measurement results can be obtained depending on the spectrophotometer, and in this case, the difference between the measurement values depending on the spectrophotometer can be compensated by performing numerical conversion based on the measurement values obtained when the same polarizing plate is measured by each spectrophotometer.
(3) Variation in optical characteristics of long polarizing film
From the polarizing plates used in examples and comparative examples, measurement samples were cut out at 5 positions at equal intervals in the width direction, and the single transmittance at the central portion of each of the 5 measurement samples was measured in the same manner as in the above (2). Next, the difference between the maximum value and the minimum value among the single transmittance measured at each measurement position was calculated, and this value was used as the variation in the optical properties of the long polarizing film.
(4) Deviation of optical characteristics of single-sheet polarizing film
From the polarizing plates used in examples and comparative examples, 100mm × 100mm measurement samples were cut out, and a single-sheet polarizing plate (50 cm)2) The deviation of the optical characteristics of (1). Specifically, the cell transmittances were measured at positions approximately 1.5cm to 2.0cm inward from the midpoint of each of the 4 sides of the measurement sample and at 5 positions in total in the central portion in the same manner as in the above (2). Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and the calculated value was used as the variation in the optical properties of the single-sheet polarizing film.
(5) 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. When the test specimen was set on a flat surface with the glass plate facing downward, the height of the highest portion from the flat surface was defined as the amount of warpage.
(6) Unit weight
The polarizing plates with retardation layers obtained in examples and comparative examples were cut to a given size and divided by the weight (mg) by the area (cm)2) The weight per unit area (unit weight) of the polarizing plate with a retardation layer was calculated from the above.
(7) Resistance to bending
The polarizing plates with retardation layers obtained in examples and comparative examples were cut into a size of 50mm × 100 mm. 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 using a folding resistance tester (CL 09 type-D01 manufactured by YUASA) at 20 ℃ and 50% RH. Specifically, the polarizing plate with a retardation layer was repeatedly bent in a direction parallel to the absorption axis direction so that the retardation layer side was outward, the number of times of bending until occurrence of cracks, peeling, film breakage, and the like, which caused display defects, was measured, and evaluated according to the following criteria (bending diameter: 2mm φ).
< evaluation Standard >
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
[ example 1]
1. Production of polarizing film
As the thermoplastic resin substrate, a long-sized amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75 ℃ was used. One side of the resin substrate was subjected to corona treatment.
To 100 parts by weight of a PVA resin obtained by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410" available from Nippon synthetic chemical Co., Ltd.) at a ratio of 9:1, 13 parts by weight of potassium iodide was added, and the obtained mixture was dissolved in water 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 free end of the obtained laminate was stretched in one direction in the longitudinal direction (longitudinal direction) by a factor of 2.4 in an oven at 130 ℃ between rolls having different peripheral speeds (auxiliary stretching treatment in a gas atmosphere).
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 was immersed in a dyeing bath (aqueous iodine solution prepared by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the polarizing film finally obtained became 45% or more (dyeing treatment).
Subsequently, the substrate was immersed in a crosslinking bath (an aqueous boric acid solution containing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid per 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (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 (stretching treatment in an aqueous solution) was performed between rolls having different peripheral speeds so that the total stretching ratio in the longitudinal direction (longitudinal direction) was 5.5 times.
Then, 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 ℃.
Then, while drying in an oven maintained at 90 ℃, the sheet was contacted with a SUS heating roll maintained at a surface temperature of 75 ℃ for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction by the drying shrinkage treatment was 2%.
Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate.
2. Preparation of polarizing plate
An acrylic film (surface refractive index 1.50, 40 μm) was bonded as a protective layer to the surface (surface opposite to the resin substrate) of the polarizing film obtained above with an ultraviolet-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness thereof became 1.0 μm, and was bonded using a roll machine. Then, UV light is irradiated from the protective layer side to cure the adhesive. Then, both ends were cut, and the resin base material was peeled off, thereby obtaining a long polarizing plate (width: 1300mm) having a structure of a protective layer/polarizing film. The polarizing plate (substantially polarizing film) had a single transmittance of 45.37% and a degree of polarization of 98.083%. The variation in optical characteristics of the long polarizing film was 0.25%, and the variation in optical characteristics of the single-sheet polarizing film was 0.07%.
3. Production of 1 st alignment fixing layer and 2 nd alignment fixing layer constituting retardation layer
A liquid crystal composition (coating liquid) was prepared by dissolving 10g of a polymerizable liquid crystal (product name: Paliocolor LC242, manufactured by BASF) exhibiting a nematic liquid crystal phase and 3g of a photopolymerization initiator (product name: IRGACURE907, manufactured by BASF) for the polymerizable liquid crystal compound in 40g of toluene.
[ chemical formula 1]
Figure BDA0002230756990000281
The surface of a polyethylene terephthalate (PET) film (38 μm in thickness) was rubbed with a rubbing cloth (rubbing cloth) to perform an alignment treatment. When the polarizing plate was laminated, the orientation treatment was carried out in a direction of 15 ° from the viewing side with respect to the direction of the absorption axis of the polarizing film. The liquid crystal coating liquid was applied to the alignment-treated surface by a bar coater, and heated and dried at 90 ℃ for 2 minutes, thereby aligning the liquid crystal compound. The thus-formed liquid crystal layer was irradiated with 1mJ/cm using a metal halide lamp2Of the liquid crystal to cause the liquid crystal to be in a liquid crystal stateThe layer was cured, thereby forming a liquid crystal alignment fixing layer a on the PET film. The thickness of the liquid crystal alignment fixing layer A was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Further, the liquid crystal alignment fixing layer a has a refractive index distribution of nx > ny ═ nz.
A liquid crystal alignment fixing 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 direction of the absorption axis of the polarizing film as viewed from the visible side. The thickness of the liquid crystal alignment fixing layer B was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. In addition, the liquid crystal alignment fixing layer B has a refractive index distribution of nx > ny ═ nz.
4. Production of polarizing plate with retardation layer
The liquid crystal alignment fixing layer a and the liquid crystal alignment fixing layer B obtained in the above 3 were sequentially transferred onto the surface of the polarizing film of the polarizing plate obtained in the above 2. At this time, transfer (bonding) was performed so that the angle formed by the absorption axis of the polarizing film and the slow axis of the alignment-fixing layer a became 15 ° and the angle formed by the absorption axis of the polarizing film and the slow axis of the alignment-fixing layer B became 75 °. The respective transfer (bonding) was performed with the ultraviolet-curable adhesive (thickness 1.0 μm) used in the above 2. In this way, a polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer (1 st alignment-fixing layer/adhesive layer/2 nd alignment-fixing layer) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (5) to (7) above. The warping amount is 1.8 mm.
[ example 2]
A polarizing plate with a retardation layer was produced in the same manner as in example 1, except that an acrylic film having a thickness of 20 μm was used as the protective layer. 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 warping amount was 1.5 mm.
[ example 3]
A polarizing plate with a retardation layer was produced in the same manner as in example 1, except that a 25 μm thick cellulose Triacetate (TAC) film was used as a protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 37 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The warping amount was 1.3 mm.
Comparative example 1
1. Manufacture of polarizer
A polyvinyl alcohol resin film having an average polymerization degree of 2400, a saponification degree of 99.9 mol% and a thickness of 30 μm was prepared. The polyvinyl alcohol film was stretched in the transport direction between rolls having different peripheral speed ratios by 2.4 times while being swollen by immersing it in a swelling bath (water bath) at 20 ℃ for 30 seconds (swelling step), and then, was 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, and was stretched in the transport direction by 3.7 times based on the original polyvinyl alcohol film (polyvinyl alcohol film which was not stretched at all in the transport direction) (dyeing step). The immersion 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. Preparation of polarizing plate
As the adhesive, an aqueous solution containing a polyvinyl alcohol resin having an acetoacetyl group (average polymerization degree of 1200, saponification degree of 98.5 mol%, acetoacetylation ratio of 5 mol%) and methylolmelamine at a weight ratio of 3:1 was used. Using this adhesive, a hard-coated cellulose Triacetate (TAC) film having a thickness of 25 μm was bonded to one surface of the polarizer obtained above by a roll laminator, and after a TAC film having a thickness of 25 μm was bonded to the other surface of the polarizer, the resultant was dried by heating in an oven (temperature 60 ℃ c. for 5 minutes), thereby producing a polarizing plate having a structure of protective layer 1 (thickness 25 μm)/adhesive layer/polarizer/adhesive layer/protective layer 2 (thickness 25 μm).
3. Production of polarizing plate with retardation layer
On the surface of the protective layer 2 of the polarizing plate obtained in the above 2, the liquid crystal alignment fixing layer a and the liquid crystal alignment fixing layer B were sequentially transferred 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 (1 st alignment fixing layer/adhesive layer/2 nd alignment fixing layer) was produced. The total thickness of the obtained polarizing plate with a retardation layer was 68 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in example 1. The warping amount was 4.2 mm.
Comparative example 2
Polarizing film production was attempted in the same manner as in example 1, except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio in the auxiliary stretching treatment in a gas atmosphere was 1.8 times, and a heating roll was not used in the drying and shrinking treatment, but the PVA-based resin layer was dissolved in the dyeing treatment and the stretching treatment in an aqueous solution, and thus a polarizing film could not be produced. Therefore, a polarizing plate with a retardation layer cannot be produced.
Comparative example 3
1. Preparation of polarizing plate
A long polarizing plate (width: 1300mm) having a protective layer/polarizing film structure was obtained in the same manner as in example 1, except that a TAC film having a thickness of 25 μm was used as the protective layer.
2. Production of retardation film constituting retardation layer
2-1 polymerization of polyester carbonate resins
Polymerization was carried out using a batch polymerization apparatus comprising 2 vertical reactors each equipped with a stirring blade and a reflux cooler controlled to 100 ℃. Charging bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl]29.60 methane substanceAmounts of 0.046mol, 29.21 parts by mass (0.200mol) of Isosorbide (ISB), 42.28 parts by mass (0.139mol) of Spiroglycol (SPG), 63.77 parts by mass (0.298mol) of diphenyl carbonate (DPC) and 1.19X 10 parts by mass of calcium acetate 1 hydrate 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 when the internal temperature reached 100 ℃. 40 minutes after the start of the temperature increase, the internal temperature was set to 220 ℃ and the pressure reduction was started while maintaining the temperature, and the pressure reached 13.3kPa after 90 minutes from the temperature reached 220 ℃. Phenol vapor produced as a by-product during the polymerization reaction was introduced into a reflux condenser at 100 ℃ to return some of the monomer components contained in the phenol vapor to the reactor, and phenol vapor that had not condensed was introduced into a condenser at 45 ℃ to be recovered. After nitrogen gas was introduced into the 1 st reactor and the atmospheric pressure was temporarily returned, the reaction solution oligomerized 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 for 50 minutes. Then, polymerization was carried out until a given stirring power was reached. When the predetermined power was reached, nitrogen gas was introduced into the reactor to recover the pressure, the polyester carbonate resin produced was extruded into water, and the strands were cut to obtain pellets.
2-2. production of retardation film
After the obtained polyester carbonate resin (pellets) was dried under vacuum at 80 ℃ for 5 hours, a long resin film having a thickness of 135 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 ℃), chilled rolls (set temperature: 120 to 130 ℃) and a winder. The obtained resin film in a long form was stretched at a stretching temperature of 133 ℃ and a stretching ratio of 2.8 times in the width direction, to obtain a retardation film having a thickness of 53 μm. The obtained retardation film had an Re (550) of 141nm, an Re (450)/Re (550) of 0.82 and an Nz coefficient of 1.12.
3. Production of polarizing plate with retardation layer
The retardation film obtained in the above 2 was bonded to the surface of the polarizing film of the polarizing plate obtained in the above 1 with an acrylic adhesive (thickness: 5 μm). At this time, 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 were at an angle of 45 °. In this way, a polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/pressure-sensitive adhesive layer/retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (6) and (7).
The structures of the polarizing plates with retardation layers obtained in examples 1 to 3 and comparative examples 1 and 3 and the respective evaluation results are shown in table 2.
[ Table 2]
Figure BDA0002230756990000321
[ evaluation ]
As is clear from table 2 and a comparison between example 1 and comparative example 2, the polarizing plate with a retardation layer of the example of the present invention is thin, can suppress warpage after a heat test, and is excellent in optical characteristics. In addition, the weight per unit area of the polarizing plate with a retardation layer is set to a predetermined value or less, whereby the folding endurance is improved.
Industrial applicability
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.

Claims (12)

1. A polarizing plate with a phase difference layer, comprising a polarizing film and a protective layer provided on at least one side of the polarizing film,
the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic material, has a thickness of 8 μm or less, a monomer transmittance of 45% or more, and a degree of polarization of 97% or more,
the retardation layer is an alignment-fixing layer of a liquid crystal compound.
2. The method of claim 1The polarizing plate with a retardation layer had a basis weight of 6.5mg/cm2The following.
3. The polarizing plate with a retardation layer according to claim 1 or 2, which has a total thickness of 60 μm or less.
4. The polarizing plate with a retardation layer according to any one of claims 1 to 3,
the phase difference layer is a single layer of an alignment fixing layer of a liquid crystal compound,
the Re (550) of the retardation layer is 100nm to 190 nm.
The slow axis of the phase difference layer and the absorption axis of the polarization film form an angle of 40-50 degrees.
5. The polarizing plate with a retardation layer according to any one of claims 1 to 3,
the phase difference layer has a laminated structure of a 1 st liquid crystal compound alignment fixing layer and a 2 nd liquid crystal compound alignment fixing layer,
the Re (550) of the alignment fixing layer of the 1 st liquid crystal compound is 200nm to 300nm, the angle formed by the slow axis and the absorption axis of the polarizing film is 10 to 20 degrees,
re (550) of the alignment fixing layer of the 2 nd liquid crystal compound is 100 to 190nm, and an angle formed by a slow axis and an absorption axis of the polarizing film is 70 to 80 degrees.
6. The polarizing plate with a phase difference layer according to any one of claims 1 to 5, wherein the polarizing film is at 50cm2The difference between the maximum value and the minimum value of the single transmittance in the region (1) is 0.2% or less.
7. The polarizing plate with a phase difference layer according to any one of claims 1 to 5, having a width of 1000mm or more, wherein a difference between a maximum value and a minimum value of a monomer transmittance at a position of the polarizing film in a width direction is 0.5% 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 a monomer transmittance of 46% or less and a degree of polarization of 99% or less.
9. The polarizing plate with a retardation layer according to any one of claims 1 to 8, further comprising another retardation layer having a refractive index characteristic showing a relationship of nz > nx ═ ny on the outer side of the retardation layer.
10. The polarizing plate with a retardation layer according to any one of claims 1 to 9, further comprising a conductive layer or an isotropic substrate with a conductive layer on the outer side of the retardation layer.
11. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 1 to 10.
12. The image display device according to claim 11, which is an organic electroluminescent display device or an inorganic electroluminescent display device.
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