CN111045135B - Polarizing plate with retardation layer and image display device using same - Google Patents

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

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Publication number
CN111045135B
CN111045135B CN201910966866.0A CN201910966866A CN111045135B CN 111045135 B CN111045135 B CN 111045135B CN 201910966866 A CN201910966866 A CN 201910966866A CN 111045135 B CN111045135 B CN 111045135B
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layer
polarizing plate
retardation layer
polarizing film
stretching
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CN111045135A (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
    • G02B5/3016—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
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3083—Birefringent or phase retarding elements

Abstract

The invention provides a polarizing plate with a phase difference layer, which is thin, has excellent handling property and excellent optical properties. The polarizing plate with a phase difference layer of the present invention has a polarizing plate including a polarizing film and a protective layer provided on at least one side of the polarizing film, and a phase difference layer. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic material, has a thickness of 8 [ mu ] m or less, a monomer transmittance of 48% or more, and a polarization degree of 85% 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 same
Technical Field
The present invention relates to a polarizing plate with a retardation layer and an image display device using the polarizing plate with the retardation layer.
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) are rapidly spreading. In an image display device, a polarizing plate and a phase difference plate are typically used. In practical 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, as the desire for the reduction in thickness of an image display device increases, the desire for the reduction in thickness of a polarizing plate with a retardation layer also increases. In addition, in recent years, there has been an increasing demand for curved image display devices and/or bendable image display devices, and further thinning and softening of polarizing plates and polarizing plates with retardation layers have been demanded. To reduce the thickness of a polarizing plate with a retardation layer, a protective layer of a polarizing film that contributes to a large thickness and a retardation film are thinned. However, if the protective layer and the retardation film are thinned, the influence of shrinkage of the polarizing film becomes 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 lowered.
In order to solve the above-described problems, it is necessary to thin the polarizing film as well. However, if the thickness of the polarizing film is simply thinned, the optical characteristics are degraded. More specifically, one or both of the degree of polarization and the monomer transmittance, which have a trade-off relationship, are reduced to a degree that is not allowed in practical use. As a result, the optical characteristics of the polarizing plate with the retardation layer are also insufficient.
Prior art literature
Patent literature
Patent document 1: japanese patent No. 3325560
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above-described conventional problems, and its main object is to provide a polarizing plate with a retardation layer, which is thin, excellent in handleability, and excellent in optical characteristics.
Means for solving the problems
The polarizing plate with a phase difference layer of the present invention has a polarizing plate including a polarizing film and a protective layer provided on at least one side of the polarizing film, and a phase difference layer. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic material, has a thickness of 8 [ mu ] m or less, a monomer transmittance of 48% or more, and a polarization degree of 85% 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 unit weight of 6.5mg/cm 2 The following is given.
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 layer of a liquid crystal compound, re (550) of the retardation layer is 100nm to 190nm, and an angle between a slow axis of the retardation layer and an absorption axis of the polarizing film is 40 DEG to 50 deg.
In one embodiment, the retardation layer has a laminated structure of an alignment fixing layer of the 1 st liquid crystal compound and an alignment fixing layer of the 2 nd liquid crystal compound; re (550) of the orientation-fixing layer of the 1 st liquid crystal compound is 200nm to 300nm, and an angle formed between a slow axis of the Re (550) and an absorption axis of the polarizing film is 10 DEG to 20 DEG; re (550) of the orientation-fixing layer of the 2 nd liquid crystal compound is 100nm to 190nm, and an angle formed between a slow axis thereof and an absorption axis of the polarizing film is 70 DEG to 80 deg.
In one embodiment, the polarizing film is at 50cm 2 The difference between the maximum value and the minimum value of the transmittance of the monomer in the region of (2) is 0.5% or less.
In one embodiment, the polarizing plate with the retardation layer has a width of 1000mm or more, and a difference between a maximum value and a minimum value of the transmittance of the monomer at a position along the width direction of the polarizing film is 1% or less.
In one embodiment, the polarizing film has a single transmittance of 50% or less and a polarization degree of 92% or less.
In one embodiment, the polarizing plate with a retardation layer further includes another retardation layer outside the retardation layer, and refractive index characteristics of the other retardation layer show a relationship of nz > nx=ny.
In one embodiment, the polarizing plate with a retardation layer further includes a conductive layer or an isotropic substrate with a conductive layer outside the retardation layer.
According to another aspect of the present invention, there is provided an image display device including the polarizing plate with a retardation layer described above.
In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a thin polarizing film having very excellent optical characteristics can be obtained by using a combination of adding a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) -based resin, 2-stage stretching including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and drying and shrinkage by a heating roller. By using such a polarizing film, a polarizing plate with a retardation layer having a thin shape, excellent handleability, and excellent 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 diagram showing an example of a drying shrinkage process using a heating roller in the method for producing a polarizing film of a polarizing plate with a retardation layer according to the present invention.
Symbol description
10. Polarizing plate
11. Polarizing film
12. 1 st protective layer
13. 2 nd protective layer
20. Phase difference layer
100. Polarizing plate with phase difference layer
101. Polarizing plate with phase difference layer
102. Polarizing plate with phase difference layer
Detailed Description
Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.
(definition of terms and symbols)
The terms and symbols in the present specification are defined as follows.
(1) Refractive index (nx, ny, nz)
"nx" is a refractive index in a direction in which the refractive index in the plane reaches the maximum (i.e., the slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is a refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re (λ)" is the in-plane retardation measured at 23℃with light of wavelength λnm. For example, "Re (550)" is the 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) = (nx-ny) ×d was obtained as Re (λ).
(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 λnm. 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) = (nx-nz) ×d to obtain Rth (λ).
(4) Nz coefficient
The Nz coefficient is obtained by nz=rth/Re.
(5) Angle of
In this specification, when referring to an angle, the angle includes both clockwise and counterclockwise with respect to a reference direction. Thus, for example, "45" means ± 45 °.
A. Integral structure of polarizing plate with phase difference layer
Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. The polarizing plate 100 with a retardation layer 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. One of the 1 st protective layer 12 and the 2 nd protective layer 13 may be omitted according to the purpose. For example, when the retardation layer 20 can also function as a protective layer for the polarizing film 11, the 2 nd protective layer 13 may be omitted. In an embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance. The polarizing film has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a polarization degree of 85% or more.
As shown in fig. 2, in another embodiment of the polarizing plate with a retardation layer 101, another retardation layer 50 and/or a conductive layer or an isotropic substrate with a conductive layer 60 may be provided. The other retardation layer 50 and the conductive layer or the conductive-layer-attached isotropic substrate 60 are typically disposed outside the retardation layer 20 (on the opposite side of the polarizing plate 10). The refractive index characteristics of the other retardation layers representatively show a relationship of nz > nx=ny. Typically, another retardation layer 50 and a conductive layer or an isotropic substrate 60 with a conductive layer are provided in this order from the retardation layer 20 side. Typically, the other retardation layer 50 and the conductive layer or the isotropic substrate with conductive layer 60 are any layers provided as needed, and either or both of them may be omitted. For convenience, the phase difference layer 20 may be referred to as a 1 st phase difference layer, and the other phase difference layer 50 may be referred to as a 2 nd phase difference layer. In the case of providing a conductive layer or an isotropic substrate with a conductive layer, the polarizing plate with a phase difference layer can be applied to a so-called in-plane type input display device in which a touch sensor is introduced between an image display unit (for example, an organic EL unit) and the 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 layer shown in fig. 1 and 2, or may have a laminated structure of the 1 st alignment layer 21 and the 2 nd alignment layer 22 shown in fig. 3.
The above embodiments may be appropriately combined, or the constituent elements in the above embodiments may be obviously modified by 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 on the polarizing plate 102 with a retardation layer of fig. 3. For example, the structure of the isotropic base material 60 having a conductive layer provided outside the 2 nd retardation layer 50 may be replaced with an optically equivalent structure (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 characteristics (for example, refractive index characteristics, in-plane retardation, nz coefficient, photoelastic coefficient), thickness, arrangement position, and the like of the other retardation layer can be appropriately set according to the purpose.
The polarizing plate with a retardation layer of the present invention may be in the form of a sheet or a long sheet. In the present specification, "elongated" means an elongated shape having a length sufficiently long with respect to a width, and includes, for example, an elongated shape having a length of 10 times or more, preferably 20 times or more, with respect to a width. The long polarizing plate with the retardation layer may be wound into a roll.
In actual use, an adhesive layer (not shown) may be provided on the opposite side of the retardation layer from 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 on the surface of the 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 the retardation layer is preferably 60 μm or less, more preferably 55 μm or less, further preferably 50 μm or less, particularly preferably 40 μm or less. The lower limit of the total thickness may be 28 μm, for example. 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 bending durability. Such a polarizing plate with a retardation layer can be particularly suitably used for a curved image display device and/or a bendable or bendable image display device. The total thickness of the polarizing plate with the retardation layer means the total thickness of all layers constituting the polarizing plate with the retardation layer except for an 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 the retardation layer does not include the thickness of an adhesive layer for adhering the polarizing plate with the retardation layer to an adjacent member such as an image display unit and a release film temporarily attachable to the surface thereof).
The polarizing plate with a retardation layer according to the embodiment of the present invention has a unit weight of, for example, 6.5mg/cm 2 Hereinafter, it is preferably 2.0mg/cm 2 ～6.0mg/cm 2 More preferably 3.0mg/cm 2 ～5.5mg/cm 2 Further preferably 3.5mg/cm 2 ～5.0mg/cm 2 . When the display panel is thin, the panel is slightly deformed by the weight of the polarizing plate with the retardation layer, and there is a concern that display failure occurs, but the display panel has a thickness of 6.5mg/cm 2 The polarizing plate with a retardation layer having a unit weight as described below can prevent such panel deformation. In addition, the polarizing plate with the retardation layer having the above unit weight has good handleability even when it is thinned, andcan exhibit very excellent flexibility and bending durability.
Hereinafter, the constituent elements of the polarizing plate with a retardation layer will be described in more detail.
B. Polarizing plate
B-1 polarizing film
As described above, the thickness of the polarizing film 11 is 8 μm or less, the transmittance of the monomer is 48% or more, and the degree of polarization is 85% or more. In general, there is a trade-off relationship between the transmittance of the monomer and the absorbance, and if the transmittance of the monomer is increased, the absorbance is decreased, and if the absorbance is increased, the transmittance of the monomer is decreased. Therefore, it has been difficult to put a thin polarizing film satisfying optical characteristics such as a single body transmittance of 48% or more and a polarization degree of 85% or more into practical use. The use of a thin polarizing film having excellent optical characteristics such as a single body transmittance of 48% or more and a polarization degree of 85% or more, and suppressed variation in optical characteristics, is one of the features of the present invention.
The thickness of the polarizing film is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm.
The polarizing film preferably exhibits absorption dichroism at any one of wavelengths 380nm to 780 nm. The monomer transmittance of the polarizing film is preferably 50% or less. The polarization degree of the polarizing film is preferably 86% or more, more preferably 87% or more, and further preferably 88% or more. On the other hand, the degree of polarization is preferably 92% or less. The above-mentioned monomer transmittance is typically a Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting for visibility. The polarization degree is typically determined based on 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 of 8 μm or less is typically measured using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (refractive index of surface: 1.53) and a protective film (refractive index: 1.50) as a measurement target. According to a polarizing filmThe refractive index of the surface of the protective film and/or the refractive index of the surface in contact with the air interface of the protective film may change the reflectance of the interface of each layer, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film having a refractive index of not 1.50 is used, the measured value of the transmittance 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 uses the reflectance R of polarized light parallel to the transmission axis in the interface between the protective film and the air layer 1 (transmission axis reflectivity) is represented by the following formula.
C＝R 1 －R 0
R 0 ＝((1.50－1) 2 /(1.50+1) 2 )×(T 1 /100)
R 1 ＝((n 1 －1) 2 /(n 1 +1) 2 )×(T 1 /100)
Wherein R is 0 Is the transmission axis reflectivity in the case of using a protective film with a refractive index of 1.50, n 1 Is the refractive index of the protective film used, T 1 Is the transmittance of the polarizing film. For example, when a base material having a surface refractive index of 1.53 (cycloolefin film, hard coat film, or the like) is used as the protective film, the correction amount C is about 0.2%. In this case, the transmittance obtained by measurement can be converted into a transmittance when a protective film having a surface refractive index of 1.50 is used by adding 0.2% to the transmittance. Based on the calculation based on the above formula, the transmittance T of the polarizing film is set to 1 The amount of change in correction value C at 2% change is 0.03% or less, and the effect of the transmittance of the polarizing film on the value of correction value C is limited. In addition, in the case where the protective film has absorption other than surface reflection, correction may be appropriately performed according to the absorption amount.
In one embodiment, the width of the polarizing plate with the retardation layer is 1000mm or more, and thus the width of the polarizing film is also 1000mm or more. In this case, the difference (D1) between the maximum value and the minimum value of the monomer transmittance in the position of the polarizing film in the width direction is preferably 1% or less, more preferably 0.8% or less, still more preferably Is selected to be less than 0.6%. The smaller D1 is, the more preferable, and 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 characteristics can be industrially produced. In another embodiment, the polarizing film is at 50cm 2 The difference (D2) between the maximum value and the minimum value of the monomer transmittance in the region (a) is preferably 0.5% or less, more preferably 0.25% or less, and still more preferably 0.15% or less. The smaller D2 is more preferable, and the lower limit of D2 may be, for example, 0.01%. When D2 is within the above range, uneven brightness in the display screen can be suppressed when the polarizing plate with the 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 by using the laminate include a polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed on the resin base material. A polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed on the resin base material, can be produced by the following method: for example, a PVA-based resin solution is applied to a resin substrate, dried, and a PVA-based resin layer is formed on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; the laminate was stretched and dyed, and the PVA-based resin layer was formed into a polarizing film. In the present embodiment, stretching typically includes stretching the laminate by immersing the laminate in an aqueous boric acid solution. Further, the stretching may further include stretching the laminate in a gas atmosphere at a high temperature (for example, 95 ℃ or higher) before stretching in an aqueous boric acid solution, as needed. The resulting laminate of the resin substrate and the polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizing film), and the resin substrate may be peeled off from the laminate of the resin substrate and the polarizing film, and any appropriate protective layer according to the purpose may be laminated on the peeled surface. Details of such a method for producing a polarizing film are described in, for example, japanese patent application laid-open No. 2012-73580. The entire disclosure of this publication may be incorporated into this specification by reference.
The manufacturing method of the 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 substrate to form a laminate; and sequentially performing auxiliary stretching treatment in a gas atmosphere, dyeing treatment, stretching treatment in an aqueous solution, and drying shrinkage treatment for shrinking the laminate by more than 2% in the width direction by heating while conveying the laminate in the length direction. Thus, a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, a degree of polarization of 85% or more, excellent optical characteristics, and suppressed variation in optical characteristics can be provided. That is, by introducing the auxiliary stretching, even when PVA is coated on the thermoplastic resin, crystallinity of PVA can be improved, and high optical characteristics can be achieved. Further, by simultaneously improving the orientation of PVA in advance, problems such as lowering and dissolution of the orientation of PVA can be prevented when immersed in water in the subsequent dyeing step and stretching step, and high optical characteristics can be achieved. In addition, when the PVA-based resin layer is immersed in a liquid, disturbance of orientation and decrease of orientation of polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical characteristics of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and 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 the protective layers of the polarizing film, respectively. Specific examples of the material that is the main component of the film include cellulose resins such as cellulose Triacetate (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth) acrylic resins, and transparent resins such as acetates. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, ultraviolet curable resins, and the like can be mentioned. In addition, for example, a vitreous polymer such as a siloxane polymer can be mentioned. In addition, a polymer film described in Japanese patent application laid-open No. 2001-343529 (WO 01/37007) can also 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-mentioned resin composition.
As will be described later, the polarizing plate with a retardation layer of the present invention is typically disposed on the visible side of an image display device, and the 1 st protective layer 12 is typically disposed on the visible side. Therefore, the 1 st protective layer 12 may be subjected to a surface treatment such as a hard coat treatment, an antireflection treatment, an anti-sticking treatment, and an antiglare treatment, as necessary. In addition, when the visibility is performed by polarized sunglasses, the 1 st protective layer 12 may be subjected to a treatment for improving visibility (typically, an (elliptical) polarization function, or an ultra-high phase difference) as needed. By performing such a treatment, even when the display screen is visually recognized through a polarized lens such as polarized sunglasses, excellent visibility can be achieved. Therefore, the polarizing plate with the retardation layer can be applied to an image display device that can be used outdoors.
The 1 st protective layer preferably has a thickness of 5 μm to 80. Mu.m, more preferably 10 μm to 40. Mu.m, still more preferably 10 μm to 30. Mu.m. In the case of performing the surface treatment, the thickness of the outer protective layer is a thickness including the thickness of the surface treatment layer.
In one embodiment, the 2 nd protective layer 13 is preferably optically isotropic. In the present specification, "optically isotropic" means that the in-plane retardation Re (550) is from 0nm to 10nm and the retardation Rth (550) in the thickness direction is from-10 nm to +10nm. 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 150nm. The thickness of the 2 nd protective layer is preferably 5 μm to 80. Mu.m, more preferably 10 μm to 40. Mu.m, still more preferably 10 μm to 30. Mu.m. From the viewpoint of thickness reduction and weight reduction, the 2 nd protective layer is preferably omitted.
B-3 method for producing polarizing film
The polarizing film may be manufactured by a method comprising the steps of: for example, a laminate is produced by forming a polyvinyl alcohol resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol resin (PVA-based resin) on one side of a long thermoplastic resin substrate; and sequentially performing auxiliary stretching treatment in a gas atmosphere, dyeing treatment, stretching treatment in an aqueous solution, and drying shrinkage treatment for shrinking the laminate by more than 2% in the width direction by heating while conveying the laminate in the length direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed by a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The shrinkage ratio of the laminate in the width direction by the drying shrinkage treatment is preferably 2% or more. According to such a production method, the polarizing film described in item B-1 above can be obtained. In particular, a laminate including a PVA-based resin layer containing a halide is produced, and the laminate is stretched in multiple stages including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and the stretched laminate is heated by a heating roller, whereby a polarizing film having excellent optical characteristics (typically, a single body transmittance and a degree of polarization) and suppressed in variation in optical characteristics can be obtained. Specifically, by using a heating roller in the drying shrinkage treatment step, the entire laminate can be uniformly shrunk while the laminate is 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 the variation in the optical characteristics (particularly, the transmittance of the monomer) of the polarizing film can be suppressed.
B-3-1 production of laminate
As a method for producing a laminate of the thermoplastic resin base material and the PVA-based resin layer, any suitable method can be used. It is preferable that 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 relative to 100 parts by weight of the PVA-based resin.
As a coating method of the coating liquid, any suitable method can be employed. Examples include: roll coating, spin coating, wire bar coating, dip coating, die coating, spray coating, knife 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. Mu.m, more preferably 3 to 20. Mu.m.
Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like), and an easy-to-adhere layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.
B-3-1-1. Thermoplastic resin substrate
The thickness of the thermoplastic resin substrate is preferably 20 μm to 300. Mu.m, more preferably 50 μm to 200. Mu.m. When the particle size is less than 20. Mu.m, it may be difficult to form a PVA based resin layer. If the particle size exceeds 300. Mu.m, for example, in the stretching treatment in an aqueous solution described later, the thermoplastic resin substrate may take a long time to absorb water, and the stretching may require an excessive load.
The water absorption rate of the thermoplastic resin base material is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin base material absorbs water, and the water functions as a plasticizer, thereby plasticizing the resin. 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 rate of the thermoplastic resin base material is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent defects such as a significant decrease in dimensional stability of the thermoplastic resin base material at the time of production, and deterioration in appearance of the resulting polarizing film. In addition, the substrate is prevented from breaking when stretched in an aqueous solution, and the PVA based resin layer is prevented from peeling from the thermoplastic resin substrate. The water absorption of the thermoplastic resin base material can be adjusted by introducing a modifying group into the constituent material, for example. The water absorption was 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 base material, crystallization of the PVA-based resin layer can be suppressed, and stretchability of the laminate can be sufficiently ensured. In addition, considering plasticization of the thermoplastic resin base material with water and satisfactory stretching in an aqueous solution, it is more preferably 100 ℃ or less, and still more preferably 90 ℃ or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60℃or higher. By using such a thermoplastic resin base material, it is possible to prevent the thermoplastic resin base material from being deformed (for example, to generate irregularities, looseness, wrinkles, and the like) and the like when the PVA-based resin-containing coating liquid is coated and dried, and thus it is possible to produce a laminate satisfactorily. In addition, the stretching of the PVA-based resin layer can be performed well at an appropriate temperature (for example, about 60 ℃). The glass transition temperature of the thermoplastic resin base material can be adjusted by, for example, using a crystallization material in which a modifying group is introduced into a constituent material and heating the material. The glass transition temperature (Tg) is a value obtained in accordance with JIS K7121.
As the constituent material of the thermoplastic resin base material, any suitable thermoplastic resin may 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, polyamide resins, polycarbonate resins, copolymer resins thereof, and the like. Of these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferable.
In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (hardly crystallized) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acid and copolymers further containing cyclohexanedimethanol and diethylene glycol as diol.
In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate-based resin having isophthalic acid units. This is because the thermoplastic resin base material has excellent stretchability and can suppress crystallization during stretching. This is considered to be because a large bending can be imparted to the main chain by introducing isophthalic acid units. The polyethylene terephthalate resin has terephthalic acid units and ethylene glycol units. The content of isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all the repeating units. This is because a thermoplastic resin base material having very excellent stretchability can be obtained. On the other hand, the content of isophthalic acid units is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all the repeating units. By setting the content ratio as described above, the crystallinity can be favorably improved in the drying shrinkage treatment described later.
The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin substrate may be stretched in the cross direction. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate to be described later. In the present specification, "orthogonal" means that the elements are substantially orthogonal. Here, "substantially orthogonal" is intended to include a case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.
The stretching temperature of the thermoplastic resin substrate is preferably Tg-10 to tg+50℃withrespect to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin base material is preferably 1.5 to 3.0 times.
As the stretching method of the thermoplastic resin substrate, any suitable method can be employed. Specifically, the stretching may be fixed-end stretching or free-end stretching. The stretching mode may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or may be performed in multiple stages. In the case of performing in multiple stages, the stretching ratio is a product of stretching ratios in the respective stages.
B-3-1-2. Coating solution
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 diols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone, or two or more may be used in combination. Among these, water is preferable. The PVA based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. In such a resin concentration, a uniform coating film can be formed to adhere to the thermoplastic resin substrate. The halide content in the coating liquid is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.
Additives may be blended into the coating liquid. Examples of the additive include: plasticizers, surfactants, and the like. Examples of the plasticizer include: polyhydric alcohols such as ethylene glycol and glycerol. Examples of the surfactant include: nonionic surfactants. These additives are used for the purpose of further improving the uniformity, dyeing property, and stretchability of the resulting PVA-based resin layer.
As the PVA-based resin, any suitable resin may be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be cited. The 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 saponification degree can be determined in accordance with JIS K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing film excellent in durability can be obtained. If the saponification degree is too high, gelation may occur.
The average polymerization degree of the PVA-based resin may be appropriately selected according to purposes. 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 K6726-1994.
As the above-mentioned halide, any suitable halide may be used. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferable.
The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA-based resin. When the amount of the halide exceeds 20 parts by weight based on 100 parts by weight of the PVA-based resin, the halide may ooze out, and the finally obtained polarizing film may be clouded.
In general, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is improved by stretching the PVA-based resin layer, but if the PVA-based resin layer after stretching is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disturbed and the orientation may be reduced. 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 degree of orientation 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, stretching of a PVA film monomer in an aqueous boric acid solution is usually performed at 60 ℃, whereas stretching of a laminate of an a-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of about 70 ℃, in which case the orientation of PVA at the initial stage of stretching is reduced at a stage before the stretching in an aqueous solution is increased. In contrast, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate in an aqueous boric acid solution at a high temperature in air (auxiliary stretching), crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disorder of orientation of polyvinyl alcohol molecules and decrease of orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical characteristics of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and 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 method of 2-stage stretching in which dry stretching (auxiliary stretching) is combined with stretching in an aqueous boric acid solution is selected. By introducing the auxiliary stretching as in the 2-stage stretching, the stretching can be performed while suppressing crystallization of the thermoplastic resin base material, and the problem of the decrease in stretchability due to excessive crystallization of the thermoplastic resin base material in the subsequent stretching in the aqueous boric acid solution can be solved, and the laminate can be stretched at a higher magnification. In addition, when the PVA-based resin is coated on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the coating temperature as compared with the case of coating the PVA-based resin on a metal drum in general, and as a result, there is a problem that crystallization of the PVA-based resin is relatively lowered, and sufficient optical characteristics cannot be obtained. In contrast, by introducing the auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin, crystallinity of the PVA-based resin can be improved, and high optical characteristics can be realized. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, when immersed in water in the subsequent dyeing step and 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 achieved.
The stretching method of the auxiliary stretching in the gas atmosphere may be fixed-end stretching (for example, stretching using a tenter), or free-end stretching (for example, stretching the laminate in one direction by passing it between rolls having different circumferential speeds), and the free-end stretching may be positively employed in order to obtain high optical characteristics. In one embodiment, the stretching treatment in the gas atmosphere includes one stepAnd a heated roll stretching step of stretching the laminate by a circumferential speed difference between heated rolls while conveying the laminate in the longitudinal direction thereof. The stretching treatment in the gas atmosphere typically includes a region stretching process and a heated roller stretching process. The order of the region stretching step and the heat roller stretching step is not limited, and the region stretching step may be performed first, or the heat roller stretching step may be performed first. The zone stretching process may be omitted. In one embodiment, the zone stretching step and the heated roll stretching step are performed sequentially. In another embodiment, the film end is gripped in a tenter stretching machine, and the distance between tenters is stretched in the conveying direction (the distance between the tenters is stretched to a stretching ratio). At this time, the distance of the tenter in the width direction (the direction perpendicular to the conveying direction) is arbitrarily set close to the set. It is preferable that the stretching ratio in the conveying direction be set so as to be closer to the free end. In the case of free end stretching, the shrinkage in the width direction= (1/stretch ratio) 1/2 To calculate.
The auxiliary stretching in the gas atmosphere may be performed in one stage or may be performed in multiple stages. In the case of performing in multiple stages, the stretching ratio is the product of stretching ratios in the respective stages. The stretching direction in the auxiliary stretching in the gas atmosphere is preferably substantially the same as the stretching direction in the stretching in the aqueous solution.
The stretching ratio in the auxiliary stretching in the gas atmosphere is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of combining auxiliary stretching in a gas atmosphere and stretching in an aqueous solution is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more, relative to the original length of the laminate. In the present specification, "maximum stretch ratio" means a stretch ratio immediately before the laminate breaks, and additionally, a stretch ratio at which the laminate breaks is confirmed, and "maximum stretch ratio" means a value smaller than this by 0.2.
The stretching temperature of the auxiliary stretching in the gas atmosphere may be set to any appropriate value depending on the material forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature of the thermoplastic resin substrateThe glass transition temperature (Tg) of the thermoplastic resin substrate is more preferably not less than +10℃, 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-based resin can be suppressed, and defects caused by the crystallization (e.g., inhibition of orientation of the PVA-based resin layer due to stretching) can be suppressed. The crystallization index of the PVA-based 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 ATR method using a fourier transform infrared spectrophotometer. Specifically, the polarized light was measured as measurement light, and 1141cm of the obtained spectrum was used -1 1440cm -1 The crystallization index was calculated by the following formula.
Crystallization index= (I) C /I R )
Wherein, the liquid crystal display device comprises a liquid crystal display device,
I C : when the measurement light is incident and measured at 1141cm -1 Strength of (2)
I R : when the measurement light is incident and measured at 1440cm -1 Is a strength of (a) is a strength of (b).
B-3-3 insolubilization treatment
If necessary, the insolubilization treatment is performed after the auxiliary stretching treatment in a gas atmosphere and before the stretching treatment in an aqueous solution and dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the PVA can be prevented from being lowered in orientation when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight based on 100 parts by weight of water. The temperature of the insoluble bath (boric acid aqueous solution) is preferably 20 to 50 ℃.
B-3-4 dyeing treatment
The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, iodine is adsorbed to the PVA-based resin layer. Examples of the adsorption method include: a method in which a PVA-based resin layer (laminate) is immersed in a staining solution containing iodine; a method of applying the dyeing liquid to the PVA-based resin layer; and a method of spraying the dyeing liquid on the PVA-based resin layer. A method of immersing the laminate in a dyeing liquid (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 to be blended is preferably 0.05 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add 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. Among these, potassium iodide is preferable. The amount of the iodide to be blended is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, based on 100 parts by weight of water. In order to suppress dissolution of the PVA-based resin, the 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, 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, immersion time) can be set so that the final polarizing film has a monomer transmittance of 48% or more and a degree of polarization of 85% or more. As such dyeing conditions, an aqueous iodine solution is preferably used as the dyeing solution, and the ratio of the iodine content to the potassium iodide content in the aqueous iodine solution is preferably 1:5 to 1:20. The ratio of iodine to potassium iodide content in the aqueous iodine 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 laminate is immersed in the treatment bath containing boric acid (typically, the insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath, and 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 the dyeing property as described above, the upper limit of the boric acid concentration of the dyeing bath is adjusted so as to be preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and further preferably 0.5 part by weight, relative to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath in which boric acid is previously mixed. This reduces the ratio of change in boric acid concentration when boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid to be previously mixed in the dyeing bath (i.e., the amount of boric acid not originating 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 in the subsequent stretching in an aqueous solution, the decrease in the orientation of PVA when immersed in high-temperature water can be prevented. The concentration of the aqueous boric acid solution is preferably 1 to 5 parts by weight based on 100 parts by weight of water. In the case of performing the crosslinking treatment after the dyeing treatment, it is preferable to further add an iodide. By adding iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The amount of iodide to be blended is preferably 1 to 5 parts by weight based on 100 parts by weight of water. Specific examples of iodides are 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. According to the stretching treatment in an aqueous solution, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80 ℃) of the thermoplastic resin base material and the PVA-based resin layer, and stretching can be performed at a high magnification while suppressing crystallization of the PVA-based resin layer. As a result, a polarizing film having excellent optical characteristics can be produced.
Any suitable method may be used for stretching the laminate. Specifically, the stretching may be performed at a fixed end or at a free end (for example, a method in which a laminate is uniaxially stretched by passing the laminate between rolls having different peripheral speeds). The free end stretch is preferably selected. Stretching of the laminate may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate to be described later is the product of the stretching ratios in the respective stages.
The stretching in the aqueous solution is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in the aqueous boric acid solution). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding tension applied during stretching and water resistance insoluble in water. Specifically, boric acid can form a tetrahydroxyboric acid anion in an aqueous solution and crosslink with the PVA-based resin by hydrogen bonding. As a result, the PVA-based resin layer can be given rigidity and water resistance, and stretched well, and a polarizing film having excellent optical characteristics can be produced.
The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight, relative to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. It is also possible to use an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like other than boric acid or borate in a solvent.
Preferably, iodide is blended in the stretching bath (boric acid aqueous solution). By adding iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodides are described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 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 ℃. If the temperature is such, the PVA-based resin layer can be stretched at a high rate while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher from the viewpoint of forming a PVA-based resin layer. In this case, when the stretching temperature is lower than 40 ℃, there is a concern that the thermoplastic resin base material may not be stretched well even if plasticization 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 there is a concern that excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.
The stretching ratio by stretching in an aqueous solution is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretch ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to 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 stretching ratio can be achieved by using an aqueous stretching method (stretching in an aqueous boric acid solution).
B-3-7 drying shrinkage treatment
The drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or may be performed by heating a conveying roller (using a so-called heating roller) (heating roller drying method). Preferably both are utilized. By drying with the heating roller, the heating curl of the laminate can be effectively suppressed, and a polarizing film excellent in appearance can be produced. Specifically, by drying the laminate while the laminate is in a state of being brought along the heated roller, crystallization of the thermoplastic resin base material can be efficiently promoted, and the crystallinity can be increased, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material increases, and the PVA-based resin layer is allowed to shrink due to drying, thereby suppressing curling. Further, since the laminate can be dried while being kept flat by using the heating roller, not only curling but also the occurrence of 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 ratio of the laminate in the width direction by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roller, the laminate can be continuously contracted 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 treatment. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveyance rollers R1 to R6 are disposed so as to alternately continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but the conveyance 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, for example.
The drying condition can be controlled by adjusting the heating temperature of the conveying 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 satisfactorily increased, curling can be satisfactorily suppressed, and an optical laminate excellent in durability can be produced. The temperature of the heating roller may be measured by a contact thermometer. In the illustrated example, 6 conveying rollers are provided, but there is no particular limitation as long as the number of conveying rollers is plural. The number of the conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.
The heating roller may be provided in a heating furnace (for example, an oven) or may be provided in a normal manufacturing line (in a room temperature environment). Preferably, the air blower is provided in a heating furnace provided with an air blowing mechanism. By using the drying by the heating roller and the hot air drying in combination, abrupt 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 to 300 seconds. The wind speed of the hot air 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 mini-blade type digital anemometer.
B-3-8. Other treatments
The washing treatment is preferably performed after the stretching treatment in the aqueous solution and before the drying shrinkage treatment. The above-mentioned washing 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 a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be greatly increased 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 the retardation layer can be further thinned and lightened. In the present specification, the term "alignment fixing layer" means a layer in which a liquid crystal compound is aligned in a predetermined direction in a layer and the alignment state thereof is fixed. The term "alignment layer" as used hereinafter is a concept including an alignment cured layer obtained by curing a liquid crystal monomer. In the present embodiment, the rod-like liquid crystal compound is typically aligned (uniformly aligned) in a state of being aligned along the slow axis direction of the retardation layer.
Examples of the liquid crystal compound include: a liquid crystal compound whose liquid crystal phase is a nematic phase (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 solvolysis or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.
In the case where 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 thereby fixed. 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, for example, a temperature change peculiar to the liquid crystalline compound. As a result, the 1 st retardation layer is a retardation layer which is not affected by temperature changes 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 is preferably in the range of 40 to 120 ℃, more preferably 50 to 100 ℃, and most preferably 60 to 90 ℃.
As the liquid crystal monomer, any suitable liquid crystal monomer may be used. For example, the polymerizable mesogenic compounds described in Japanese patent application laid-open No. 2002-533742 (WO 00/37585), EP358208 (US 5211877), EP66137 (US 4388453), WO93/22397, EP0261712, DE19504224, DE4408171, GB2280445 and the like can be used. Specific examples of such a polymerizable mesogenic compound include, for example, a product name LC242 from BASF, a product name E7 from Merck, and a product name LC-Silicon-CC 3767 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: an alignment treatment is performed on the surface of a given substrate, a coating liquid containing a liquid crystal compound is applied to the surface, the liquid crystal compound is aligned in a direction corresponding to the alignment treatment, and the alignment state is fixed. 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 polarizer 10. In another embodiment, the substrate may be the 2 nd protective layer 13. In this case, the transfer step is omitted, and the alignment layer (1 st retardation layer) can be formed and then laminated successively by roll-to-roll, so that productivity can be further improved.
As the above-mentioned orientation treatment, any suitable orientation 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 a rubbing treatment and a stretching treatment. Specific examples of the physical alignment treatment include a magnetic field alignment treatment and an electric field alignment treatment. Specific examples of the chemical alignment treatment include a tilt vapor deposition method and a photo-alignment treatment. The process conditions of the various orientation processes may employ any suitable conditions according to purposes.
The alignment of the liquid crystal compound may be performed as follows: the treatment is performed at a temperature at which a liquid crystal phase is exhibited, depending on the kind of the liquid crystal compound. By performing such a 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 a polymerization treatment or a crosslinking treatment as described above.
Specific examples of the liquid crystal compound and the method for forming the alignment layer are described in Japanese patent application laid-open No. 2006-163343. The description of this publication is incorporated by reference into this specification.
As another example of the alignment fixing layer, a mode in which a discotic liquid crystal compound is aligned in any of a homeotropic alignment, a hybrid alignment, and an oblique alignment is cited. In the discotic liquid crystal compound, the discotic liquid crystal compound is typically oriented substantially perpendicularly to the film surface of the 1 st retardation layer. The substantially perpendicular discotic liquid crystal compound means that the average value of the angle formed by the film surface and the discotic surface of the discotic liquid crystal compound is preferably 70 ° to 90 °, more preferably 80 ° to 90 °, and even 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 parent nucleus such as benzene, 1,3, 5-triazine, calixarene, or the like is arranged at the center of a molecule, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group, or the like is substituted radially as a side chain thereof. Typical examples of discotic liquid crystals include benzene derivatives, benzophenanthrene derivatives, trimeric indene derivatives, phthalocyanine derivatives, cyclohexane derivatives described in c.Destrade et al, mol.Cryst.Liq.Cryst.71, p.111 (1981), angew.chem.96, p.70 (1984), J.M.Lehn et al, J.chem.Soc.chem.Commun.,1794 (1985), J.Zhang et al, J.am.chem.Soc.116, p.2655 (1994), and azacrown ethers and phenylacetylene. As other specific examples of the discotic liquid crystal compound, there are mentioned, for example: japanese patent application laid-open No. 2006-133652, japanese patent application laid-open No. 2007-108732, and Japanese patent application laid-open No. 2010-244038. The descriptions of the above documents and publications are incorporated by reference into the present specification.
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 the alignment-fixing layer of the liquid crystal compound, the thickness thereof is preferably 0.5 μm to 7 μm, more preferably 1 μm to 5 μm. By using the liquid crystal compound, an in-plane retardation equivalent to that of the resin film can be achieved at a significantly thinner thickness than the resin film.
Typically, the refractive index characteristics of the 1 st retardation layer show a relationship of nx > ny=nz. The 1 st retardation layer is typically provided for imparting an antireflection property to the polarizing plate, and can function as a λ/4 plate when the 1 st retardation layer is a single layer of the alignment layer. 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 160nm. Here, "ny=nz" includes not only the case where ny is completely equal to nz but also the case where ny is substantially equal to nz. Therefore, ny > nz or ny < nz may be sometimes used within a range not to impair the effect 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. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.
The 1 st phase difference layer may exhibit an inverse dispersion wavelength characteristic in which a phase difference value becomes larger according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which a phase difference value becomes smaller according to the wavelength of the measurement light, and a flat wavelength dispersion characteristic in which a phase difference value hardly changes according to the wavelength of the measurement light. In one embodiment, the 1 st phase difference layer exhibits an inverse dispersive wavelength characteristic. In this case, re (450)/Re (550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a constitution, a very excellent antireflection characteristic can be achieved.
The angle θ between 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 within such a range, as described above, by setting the 1 st retardation layer to a λ/4 plate, 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, as shown in fig. 3, the 1 st retardation layer 20 may have a laminated structure of a 1 st orientation fixing layer 21 and a 2 nd orientation fixing layer 22. In this case, either one of the 1 st orientation fixing layer 21 and the 2 nd orientation fixing layer 22 may function as a λ/4 wave plate, and the other may function as a λ/2 wave plate. Therefore, the thicknesses of the 1 st orientation fixing layer 21 and the 2 nd orientation 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 orientation fixing layer 21 functions as a λ/2 wave plate and the 2 nd orientation fixing layer 22 functions as a λ/4 wave plate, the thickness of the 1 st orientation fixing layer 21 is, for example, 2.0 μm to 3.0 μm, and the thickness of the 2 nd orientation 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 orientation-fixing layer is preferably 200nm to 300nm, more preferably 230nm to 290nm, and still more preferably 250nm to 280nm. Regarding the orientation-fixing layer of the single layer, the in-plane phase difference Re (550) of the 2 nd orientation-fixing layer is as described above. The angle between the slow axis of the 1 st orientation-fixing layer and the absorption axis of the polarizing film is preferably 10 ° to 20 °, more preferably 12 ° to 18 °, and still more preferably about 15 °. The angle between the slow axis of the 2 nd orientation-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, a characteristic close to the ideal inverse wavelength dispersion characteristic can be obtained, and as a result, a very excellent antireflection characteristic can be realized. The liquid crystal compound constituting the 1 st alignment layer and the 2 nd alignment layer, the method for forming the 1 st alignment layer and the 2 nd alignment layer, the optical characteristics, and the like are as described above for the alignment layer of the single layer.
D. 2 nd phase difference layer
As described above, the 2 nd retardation layer may be a so-called negative C plate having refractive index characteristics showing a relationship of nz > nx=ny. By using the negative C plate as the 2 nd retardation layer, reflection in the oblique direction can be prevented well, and a wide viewing angle of the antireflection function can be achieved. In this case, the retardation Rth (550) in the thickness direction of the 2 nd retardation layer is preferably-50 nm to-300 nm, more preferably-70 nm to-250 nm, still more preferably-90 nm to-200 nm, particularly preferably-100 nm to-180 nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of the 2 nd retardation layer may be less than 10nm.
The 2 nd retardation layer having refractive index characteristics 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 liquid crystal material (liquid crystal compound) may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the method for forming the liquid crystal compound and the retardation layer include those described in [0020] to [0028] of JP-A-2002-333642 and a method for forming the retardation layer. In this case, the thickness of the 2 nd retardation layer is preferably 0.5 μm to 10. Mu.m, more preferably 0.5 μm to 8. Mu.m, still more preferably 0.5 μm to 5. Mu.m.
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 (e.g., vacuum evaporation, sputtering, CVD, ion plating, spraying, etc.). Examples of the metal oxide include: indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferable.
When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50nm or less, more preferably 35nm or less. The lower limit of the thickness of the conductive layer is preferably 10nm.
The conductive layer may be transferred from the above-described base material to the 1 st retardation layer (or the 2 nd retardation layer when the 2 nd retardation layer is present), and the conductive layer may be used alone as a constituent layer of the polarizing plate with a retardation layer, or a laminate with the base material (base material with a conductive layer) may be formed and laminated to the 1 st retardation layer (or the 2 nd retardation layer when the 2 nd retardation layer is present). Preferably, the substrate is optically isotropic, and therefore, the conductive layer can be used as an isotropic substrate with a conductive layer for a polarizing plate with a retardation layer.
As the optically isotropic substrate (isotropic substrate), any suitable isotropic substrate can be used. Examples of the material constituting the isotropic substrate include: a material having a main skeleton of a resin having no conjugated system, such as a norbornene resin or an olefin resin; materials having a cyclic structure such as a lactone ring or a glutarimide ring in the main chain of the acrylic resin, and the like. If such a material is used, when an isotropic substrate is formed, the retardation that is exhibited with the orientation of the molecular chains can be suppressed to a small level. The thickness of the isotropic substrate is preferably 50 μm or less, more preferably 35 μm or less. The lower limit of the thickness of the isotropic substrate is, for example, 20 μm.
The conductive layer and/or the conductive layer of the isotropic substrate with conductive layer may be patterned as desired. By patterning, the via portion and the insulating portion can be formed. As a result, an electrode can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. As the pattern forming method, any suitable method may be employed. Specific examples of the pattern formation method include a wet etching method and a screen printing method.
F. Image display device
The polarizing plate with a retardation layer according to any one of items A to E above 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). The 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 the retardation layer is laminated such that the retardation layer is on the image display unit (e.g., liquid crystal unit, organic EL unit, inorganic EL unit) side (such that the polarizing film is on the visible side). In one embodiment, the image display device may have a curved shape (substantially curved display screen), and/or be bendable or bendable. In such an image display device, the effect of the polarizing plate with a retardation layer of the present invention becomes remarkable.
Examples
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in examples and comparative examples are weight basis.
(1) Thickness of (L)
The thickness of 10 μm or less was measured using an interferometer film thickness meter (product name "MCPD-3000" manufactured by Otsuka electronics Co., ltd.). The thickness of more than 10 μm was measured using a digital micrometer (product name "KC-351C", manufactured by Anritsu Co., ltd.).
(2) Monomer transmittance and degree of polarization
For the laminate (polarizing plate) of the polarizing film/protective layer used in examples and comparative examples, the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc measured by an ultraviolet-visible spectrophotometer (V-7100 manufactured by japan spectroscopy co.) were used as Ts, tp, and Tc of the polarizing film, respectively. These Ts, tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) of JIS Z8701 and correcting the visibility. 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.
The polarization degree P is obtained from Tp and Tc obtained by the following equation.
Degree of polarization P (%) = { (Tp-Tc)/(tp+tc) } 1/2 ×100
The spectrophotometer may be used for equivalent measurement by using LPF-200 manufactured by Otsuka electronics Co., ltd. As an example, for samples 1 to 3 of the polarizing plates having the same structure as the following examples, the single transmittance Ts and the polarization degree P were obtained by measurement using V-7100 and LPF-200, and the measurement 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 when either spectrophotometer was used.
TABLE 1
In the case of using, for example, a polarizing plate having an Antiglare (AG) surface-treated adhesive having a diffusion property as a measurement target, different measurement results can be obtained depending on the spectrophotometers, and in this case, the difference between measurement values depending on the spectrophotometers can be compensated by performing numerical conversion based on measurement values obtained when the same polarizing plate is measured with each spectrophotometer.
(3) Deviation of optical characteristics of elongated 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 individual transmittance of the central portions of the 5 measurement samples was measured in the same manner as in (2) above. Next, the difference between the maximum value and the minimum value among the individual transmittance measured at each measurement position is calculated, and the value is set as the deviation of the optical characteristics of the long polarizing film.
(4) Deviation of optical characteristics of polarizing film in sheet form
From the polarizers used in examples and comparative examples, measurement samples of 100mm X100 mm were cut out, and a single sheet-like polarizer (50 cm 2 ) Is a deviation of the optical characteristics of (a). Specifically, the total of 5 positions of the center portion and the positions around 1.5cm to 2.0cm inward from the midpoints of the 4 sides of the measurement sample were measured as in (2) above. Next, the difference between the maximum value and the minimum value in the transmittance of the single body measured at each measurement position was calculated, and the difference was defined as the deviation in the optical characteristics of the single-sheet polarizing film.
(5) Warp of
The polarizing plates with retardation layers obtained in examples and comparative examples were cut out to a size of 110mm×60 mm. At this time, the polarizing film is cut so that the absorption axis direction of the polarizing film becomes the longitudinal direction. The cut polarizing plate with the retardation layer was bonded to a glass plate having a size of 120mm×70mm and a thickness of 0.2mm by an adhesive, and the resultant was used as a test sample. The test specimen was put into a heating oven maintained at 85℃for 24 hours, and the amount of warpage after taking out was measured. When the test specimen was left standing on a flat surface with the glass plate facing downward, the height of the highest portion from the flat surface was used as the warpage amount.
(6) Basis weight
The polarizing plates with retardation layers obtained in examples and comparative examples were cut to a given size, and the weight (mg) was divided by the area (cm) 2 ) The weight per unit area (unit weight) of the polarizing plate with the retardation layer was calculated from this.
(7) Bending resistance
The polarizing plates with retardation layers obtained in examples and comparative examples were cut out to have dimensions of 50mm×100 mm. At this time, the polarizing film is cut out so that the absorption axis direction of the polarizing film becomes the short side direction. The cut polarizing plate with the retardation layer was subjected to a bending test at 20℃and 50% RH using a bending tester (CL 09 type-D01, manufactured by Yuasa Co., ltd.) with a constant temperature and humidity chamber. Specifically, the polarizing plate with the retardation layer was repeatedly bent in a direction parallel to the absorption axis direction so that the retardation layer side was positioned outside, and the number of times of bending until cracks, peeling, film breakage, and the like, which were defects, were generated was measured, and evaluated on the basis of the following criteria (bending diameter: 2 mm. Phi.).
< evaluation criterion >)
Less than 1 ten thousand times: failure of
More than 1 ten thousand times and less than 3 ten thousand times: good grade (good)
More than 3 ten thousand times: excellent (excellent)
Example 1
1. Polarizing film production
As the thermoplastic resin base material, an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape, 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 based resin obtained by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410" manufactured by Nippon chemical industries 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 a PVA aqueous solution (coating liquid).
The PVA aqueous 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 resulting laminate was uniaxially stretched to 2.4 times the free end in the longitudinal direction (longitudinal direction) in an oven at 130℃between rolls having different peripheral speeds (auxiliary stretching treatment in a gas atmosphere).
Subsequently, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).
Next, in a dyeing bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃, the film was immersed for 60 seconds (dyeing treatment) while adjusting the concentration so that the monomer transmittance (Ts) of the finally obtained polarizing film became 48% or more.
Then, the resultant mixture was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40℃for 30 seconds (crosslinking treatment).
Then, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0 wt%) at a liquid temperature of 70 ℃ and uniaxially stretched (stretching treatment in an aqueous solution) between rolls having different peripheral speeds so that the total stretching ratio in the machine direction (longitudinal direction) became 5.5 times.
Then, the laminate was immersed in a washing bath (aqueous solution obtained by mixing 100 parts by weight of water with 4 parts by weight of potassium iodide) at a liquid temperature of 20 ℃ (washing treatment).
Then, the resultant was dried in an oven maintained at 90℃and then contacted with a SUS-made heating roller maintained at 75℃in surface temperature for about 2 seconds (drying shrinkage treatment). The shrinkage 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. Manufacture of polarizer
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 obtained polarizing film by an ultraviolet curable adhesive. Specifically, the cured adhesive was applied so that the total thickness of the cured adhesive became 1.0 μm, and bonded by a roll machine. Then, UV light is irradiated from the protective layer side to cure the adhesive. Then, after cutting both ends, the resin base material was peeled off to obtain a long polarizing plate (width: 1300 mm) having a configuration of a protective layer/polarizing film. The single body transmittance of the polarizing plate (substantially polarizing film) was 48.48%, and the polarization degree was 87.036%. The variation in the optical characteristics of the long polarizing film was 0.58%, and the variation in the optical characteristics of the single polarizing film was 0.14%.
3. Production of 1 st orientation fixing layer and 2 nd orientation fixing layer constituting phase difference 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: IRGACURE 907, manufactured by BASF) for the polymerizable liquid crystal compound in 40g of toluene.
[ chemical formula 1]
The surface of a polyethylene terephthalate (PET) film (thickness 38 μm) was rubbed with a rubbing cloth (rubbing cloth), and an orientation treatment was performed. When the polarizing plate was bonded, the orientation treatment direction was set to 15 ° with respect to the absorption axis direction of the polarizing film, as viewed from the visual side. The liquid crystal coating liquid was applied to the alignment-treated surface by a bar coater, and the liquid crystal compound was aligned by drying at 90℃for 2 minutes. Irradiating the thus-formed liquid crystal layer with 1mJ/cm using a metal halide lamp 2 The liquid crystal layer is 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 270nm. 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 visual side. The thickness of the liquid crystal alignment fixing layer B was 1.5 μm and the in-plane retardation Re (550) was 140nm. Further, 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 polarizing film surface of the polarizing plate obtained in the above 2 was sequentially transferred with the liquid crystal alignment fixing layer a and the liquid crystal alignment fixing layer B obtained in the above 3. At this time, transfer (bonding) was performed so that the angle between the absorption axis of the polarizing film and the slow axis of the alignment layer a became 15 ° and the angle between the absorption axis of the polarizing film and the slow axis of the alignment layer B became 75 °. The transfer (bonding) was performed using the ultraviolet curable adhesive (thickness 1.0 μm) used in the above 2. Thus, a polarizing plate with a retardation layer having a structure of a protective layer/an adhesive layer/a polarizing film/an adhesive layer/a retardation layer (1 st orientation fixing layer/adhesive layer/2 nd orientation fixing layer) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 52. Mu.m. The obtained polarizing plate with the retardation layer was subjected to the evaluations of (5) to (7) above. The warpage amount was 1.8mm.
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. Mu.m. The obtained polarizing plate with the retardation layer was subjected to the same evaluation as in example 1. The warpage amount was 1.5mm.
Example 3
A polarizing plate with a retardation layer was produced in the same manner as in example 1, except that a cellulose Triacetate (TAC) film having a thickness of 25 μm was used as the protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 37. Mu.m. The obtained polarizing plate with the retardation layer was subjected to the same evaluation as in example 1. The warpage amount was 1.3mm.
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 to 2.4 times in the transport direction between rolls having different circumferential speed ratios (swelling step) while being immersed in a swelling bath (water bath) at 20 ℃ for 30 seconds, and then was immersed in a dyeing bath at 30 ℃ (aqueous solution having an iodine concentration of 0.03 wt% and a potassium iodide concentration of 0.3 wt%) and dyed so that the final stretched monomer transmittance became a desired value, and was stretched to 3.7 times in the transport direction based on the original polyvinyl alcohol film (completely unstretched polyvinyl alcohol film in the transport direction) (dyeing step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film was 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 ℃ and stretched in the transport direction to 4.2 times based on the original polyvinyl alcohol film (crosslinking step). Further, the obtained polyvinyl alcohol film was immersed in a stretching bath (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 to 6.0 times in the transport direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a washing bath (aqueous solution having a potassium iodide concentration of 3.0 wt%) at 20℃for 5 seconds (washing step). The washed polyvinyl alcohol film was dried at 30℃for 2 minutes to prepare a polarizer (thickness: 12 μm).
2. Manufacture of polarizer
As the adhesive, an aqueous solution containing a polyvinyl alcohol resin having an acetoacetyl group (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, acetoacetylation rate: 5 mol%) and methylolmelamine in a weight ratio of 3:1 was used. A hard-coated cellulose Triacetate (TAC) film having a thickness of 25 μm was laminated on one surface of the polarizer obtained as described above using the adhesive and a TAC film having a thickness of 25 μm was laminated on the other surface of the polarizer using a roll laminator, and then the resultant was dried by heating in an oven (temperature: 60 ℃ for 5 minutes) to produce a polarizing plate having a configuration 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
The surface of the protective layer 2 of the polarizing plate obtained in the above 2 was successively transferred with the liquid crystal alignment fixing layer a and the liquid crystal alignment fixing layer B in the same manner as in example 1, to produce a polarizing plate with a retardation layer having a constitution of the 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). The total thickness of the obtained polarizing plate with a retardation layer was 68. Mu.m. The obtained polarizing plate with the retardation layer was subjected to the same evaluation as in example 1. The warpage amount was 4.2mm.
Comparative example 2
A polarizing film was produced in the same manner as in example 1, except that potassium iodide was not added to the PVA aqueous solution (coating liquid), the stretching ratio in the auxiliary stretching treatment in the gas atmosphere was set to 1.8 times, and a heating roller was not used in the drying shrinkage treatment, but the PVA-based resin layer was dissolved in the dyeing treatment and the stretching treatment in the aqueous solution, and the polarizing film could not be produced. Therefore, a polarizing plate with a retardation layer cannot be manufactured.
Comparative example 3
1. Manufacture of polarizer
A long polarizing plate (width: 1300 mm) having a structure of a protective layer/polarizing film 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. Fabrication of retardation film constituting retardation layer
2-1 polymerization of polyester carbonate resin
Polymerization was carried out using a batch polymerization apparatus consisting of 2 vertical reactors equipped with stirring blades and a reflux cooler controlled to 100 ℃. Bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl ] feed]29.60 parts by mass (0.046 mol) of methane, 29.21 parts by mass (0.200 mol) of Isosorbide (ISB), 42.28 parts by mass (0.139 mol) of Spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC) and 1.19X10 of calcium acetate 1 hydrate as a catalyst -2 Parts by mass (6.78X10) -5 mol). After the inside of the reactor was replaced with nitrogen under reduced pressure, the reactor was heated with a heat medium, and stirring was started at the time when the internal temperature reached 100 ℃. After 40 minutes from the start of the temperature increase, the internal temperature was brought to 220℃and the pressure was reduced while maintaining the temperature under control, and 13.3kPa was reached 90 minutes after the temperature was reached 220 ℃. The phenol vapor produced as a by-product of the polymerization reaction was introduced into a reflux cooler at 100℃and a certain amount of the monomer components contained in the phenol vapor was returned to the reactor, while the uncondensed phenol vapor was introduced into a condenser at 45℃and recovered. After nitrogen gas was introduced into the 1 st reactor and the pressure was temporarily returned to the atmospheric pressure, the oligomerization reaction liquid in the 1 st reactor was transferred to the 2 nd reactor. Then, the temperature rise and pressure reduction in the 2 nd reactor were started to reach an internal temperature of 240℃and a pressure of 0.2kPa in 50 minutes. Then, polymerization was carried out until a given stirring power was reached. At the moment of reaching a given power, the reaction vessel is led toAnd (3) introducing nitrogen, recovering the pressure, extruding the generated polyester carbonate resin into water, and cutting off the wire material to obtain the granules.
2-2 preparation of phase-difference film
The obtained polyester carbonate resin (pellets) were dried in vacuo at 80℃for 5 hours, and then a film-forming apparatus equipped with a single screw extruder (manufactured by Toshiba machine Co., ltd., cylinder set temperature: 250 ℃), a T-die (width: 200mm, set temperature: 250 ℃), chilled rolls (set temperature: 120 to 130 ℃) and a winder was used to prepare a long resin film having a thickness of 135. Mu.m. The obtained long resin film 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. Mu.m. The Re (550) of the obtained retardation film was 141nm, re (450)/Re (550) was 0.82, and the Nz coefficient was 1.12.
3. Production of polarizing plate with retardation layer
The polarizing film surface of the polarizing plate obtained in the above 1 was bonded to the retardation film obtained in the above 2 by an acrylic adhesive (thickness 5 μm). At this time, the polarizing film was bonded so that the absorption axis of the polarizing film and the slow axis of the retardation film became an angle of 45 °. Thus, a polarizing plate with a retardation layer having a structure of a protective layer, an adhesive layer, a polarizing film, an adhesive layer, and a retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89. Mu.m. The obtained polarizing plate with a retardation layer was subjected to the evaluations of (6) and (7).
Table 2 shows the structures of the polarizing plates with retardation layers obtained in examples 1 to 3 and comparative examples 1 and 3, and the evaluation results.
TABLE 2
[ evaluation ]
As is clear from table 2 and comparison between example 1 and comparative example 2, the polarizing plate with a retardation layer according to the example of the present invention is thin, can suppress warpage after a heating test, and is excellent in optical characteristics. In addition, the bending resistance is improved by setting the weight per unit area of the polarizing plate with the retardation layer to a predetermined value or less.
Industrial applicability
The polarizing plate with a retardation layer of the present invention is suitable for use as a circularly polarizing plate for liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

Claims (9)

1. A method for manufacturing a polarizing plate with a retardation layer,
the polarizing plate with a phase difference layer has a polarizing plate 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 [ mu ] m or less, a monomer transmittance of 48% or more, a degree of polarization of 85% or more,
the phase difference layer is an orientation fixing layer of a liquid crystal compound,
the manufacturing method includes manufacturing the polarizing film by a manufacturing method including:
forming a polyvinyl alcohol resin layer containing iodide or sodium chloride and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate; and
the laminate is sequentially subjected 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 to 10% in the width direction by heating while being conveyed in the longitudinal direction, wherein the drying shrinkage treatment is performed in a heating furnace using a heating roller, the total contact time between the laminate and the heating roller is 1 to 20 seconds, and the temperature of the heating roller is 65 to 100 ℃.
2. The method for producing a polarizing plate with a retardation layer according to claim 1, wherein the total thickness of the polarizing plate with a retardation layer is 60 μm or less.
3. The method for producing a polarizing plate with a retardation layer as claimed in claim 1, wherein,
the phase difference layer is a single layer of an orientation fixing layer of a liquid crystal compound,
re (550) of the retardation layer is 100nm to 190nm,
the slow axis of the retardation layer forms an angle of 40 DEG to 50 DEG with the absorption axis of the polarizing film.
4. The method for producing a polarizing plate with a retardation layer as claimed in claim 1, wherein,
the phase difference layer has a laminated structure of an alignment fixing layer of a 1 st liquid crystal compound and an alignment fixing layer of a 2 nd liquid crystal compound,
re (550) of the orientation-fixing layer of the 1 st liquid crystal compound is 200nm to 300nm, the angle between the slow axis and the absorption axis of the polarizing film is 10 DEG to 20 DEG,
re (550) of the orientation-fixing layer of the 2 nd liquid crystal compound is 100nm to 190nm, and an angle formed between a slow axis thereof and an absorption axis of the polarizing film is 70 DEG to 80 deg.
5. The method for producing a polarizing plate with a retardation layer as claimed in claim 1, wherein the polarizing film is at 50cm 2 The difference between the maximum value and the minimum value of the transmittance of the monomer in the region of (2) is 0.5% or less.
6. The method for producing a polarizing plate with a retardation layer according to claim 1, wherein the polarizing film has a width of 1000mm or more, and a difference between a maximum value and a minimum value of a single transmittance in a position of the polarizing film in a width direction is 0.1% or less.
7. The method for producing a polarizing plate with a retardation layer according to claim 1, wherein the polarizing film has a single body transmittance of 50% or less and a polarization degree of 92% or less.
8. The method for producing a polarizing plate with a retardation layer according to claim 1, further comprising a step of providing another retardation layer on the outer side of the retardation layer, wherein refractive index characteristics of the other retardation layer show a relationship of nz > nx=ny.
9. The method for producing a polarizing plate with a retardation layer according to claim 1, further comprising a step of providing a conductive layer or an isotropic substrate with a conductive layer on the outer side of the retardation layer.
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