WO2018008522A1 - Optical member and liquid crystal display device - Google Patents

Abstract

Provided is an optical member which makes it possible, at low cost, to prevent reductions to visibility that occur when a liquid crystal display device having a protective cover is viewed through polarized sunglasses. This optical member is provided with a polarizing film and a protective cover. The in-plane retardation of the protective cover is at least 1000 nm, and the angle formed by the slow axis of the protective cover and the absorption axis of the polarizing film is 40° to 50°.

Description

Optical member and liquid crystal display device

The present invention relates to an optical member and a liquid crystal display device having the optical member.

サ ン グ ラ ス Sunglasses with polarization characteristics (polarized sunglasses) are used to reduce glare in an environment with strong sunlight. However, when the liquid crystal display device is viewed with the polarized sunglasses on, the display light of the liquid crystal display device is absorbed by the polarized sunglasses depending on the posture of the viewer, and the visibility decreases.

In Patent Document 1, a white light emitting diode is used as a backlight of a liquid crystal display device, and a polymer film having a retardation of 3000 to 30000 nm is provided on the viewer side of the polarizer. A visibility improving method is described in which the angle formed with the slow axis is about 45 °. According to the visibility improvement method of patent document 1, it is supposed that the visibility when a screen is observed through polarized sunglasses can be improved.

JP 2011-215646 A

For example, in a liquid crystal display device mounted on a car navigation system, the display panel is covered with a transparent protective cover such as plastic. When the polymer film used in the visibility improving method of Patent Document 1 is applied to a liquid crystal display device for a car navigation system, the luminance is reduced due to the optical characteristics of the protective cover, or rainbow unevenness occurs. Problems may occur. Moreover, in the visibility improving method of Patent Document 1, it is necessary to use a polymer film having a high retardation, which increases costs as compared with a conventional liquid crystal display device.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical member that can suppress a decrease in visibility when a liquid crystal display device with a protective cover is visually recognized through polarized sunglasses. It is to provide.

The optical member of the present invention includes a polarizing film and a protective cover, the protective cover has an in-plane retardation of 1000 nm or more, and an angle formed by the slow axis of the protective cover and the absorption axis of the polarizing film is 40. ° to 50 °.
In one embodiment, the in-plane phase difference of the protective cover is 7000 nm or more.
In one embodiment, the thickness of the protective cover is 1000 μm or more.
In one embodiment, when the bending strength of the protective cover according to ASTM-D790 bending test method is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), S × T The value is 400 or more.
In one embodiment, an adhesive is filled between the protective cover and the polarizing film.
In one embodiment, an antireflection film is laminated on the side of the protective cover opposite to the polarizing film.
The liquid crystal display device of the present invention includes the optical member.

According to the present invention, it is possible to suppress a reduction in visibility when viewing a liquid crystal display device with a protective cover through polarized sunglasses at low cost.

It is sectional drawing of the optical member which concerns on one Embodiment of this invention. It is sectional drawing of the optical member of another embodiment of this invention. It is sectional drawing of the optical member of another embodiment of this invention.

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

(Definition of terms and symbols)
In the present specification, the “in-plane retardation” is an in-plane retardation of a layer (film) measured with light having a wavelength of 550 nm at 23 ° C., and a thickness of the layer (film) is defined as d (nm). Is obtained by the equation: Re = (nx−ny) × d. Here, “nx” is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), and “ny” is the direction orthogonal to the slow axis in the plane (that is, the fast phase). (Nz direction), and “nz” is the refractive index in the thickness direction.

A. Optical Member FIG. 1 is a cross-sectional view of an optical member according to one embodiment of the present invention. As shown in FIG. 1, the optical member 10 has a laminated structure of a polarizing film 1 and a protective cover 2. The in-plane retardation of the protective cover 2 is 1000 nm or more, and the angle formed by the slow axis of the protective cover 2 and the absorption axis of the polarizing film 1 is 40 ° to 50 °. The optical member 10 of the present invention can be mounted on a liquid crystal display device. By providing the optical member 10 on the viewer side of the liquid crystal cell of the liquid crystal display device, the visibility when the display screen of the liquid crystal display device is observed through polarized sunglasses can be improved. Specifically, a decrease in front luminance and a change in hue (color shift) according to the viewing angle can be suppressed.

FIG. 2 is a cross-sectional view of an optical member according to another embodiment of the present invention. The optical member 11 shown in FIG. 2 has a structure in which the polarizing film 1 and the protective cover 2 are bonded together via an interlayer filling adhesive 3. FIG. 3 is a cross-sectional view of an optical member according to still another embodiment of the present invention. As in the optical member 12 shown in FIG. 3, the antireflection film 4 may be provided on the viewer side of the protective cover 2. As the antireflection film 4, an antireflection film usually used in the industry can be employed. For example, a layer made of a medium refractive index material, a layer made of a high refractive index material, and a layer made of a low refractive index material. Can be employed.

B. Polarizing film The polarizing film 1 has a laminated structure of a polarizer and a protective layer. Specifically, in the laminated structure of the polarizing film 1 and the protective cover 2, a protective layer (not shown) can be provided on the protective cover 2 side of the polarizer. Further, another protective layer (not shown: hereinafter also referred to as an inner protective layer) may be provided on the opposite side of the polarizer from the protective cover 2.

B-1. Polarizer Any appropriate polarizer may be adopted as the polarizer. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers. Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and ethylene / vinyl acetate copolymer partially saponified films. In addition, there may be mentioned polyene-based oriented films such as those subjected to dyeing treatment and stretching treatment with dichroic substances such as iodine and dichroic dyes, PVA dehydrated products and polyvinyl chloride dehydrochlorinated products. Preferably, a polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching is used because of excellent optical properties.

The dyeing with iodine is performed, for example, by immersing a PVA film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or may be performed while dyeing. Moreover, you may dye | stain after extending | stretching. If necessary, the PVA film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment and the like. For example, by immersing the PVA film in water and washing it before dyeing, not only can the surface of the PVA film be cleaned of dirt and anti-blocking agents, but the PVA film can be swollen to cause uneven staining. Can be prevented.

As a specific example of a polarizer obtained by using a laminate, a laminate of a resin substrate and a PVA resin layer (PVA resin film) laminated on the resin substrate, or a resin substrate and the resin Examples thereof include a polarizer obtained by using a laminate with a PVA resin layer applied and formed on a substrate. For example, a polarizer obtained by using a laminate of a resin base material and a PVA resin layer applied and formed on the resin base material may be obtained by, for example, applying a PVA resin solution to a resin base material and drying it. A PVA-based resin layer is formed thereon to obtain a laminate of a resin base material and a PVA-based resin layer; the laminate is stretched and dyed to make the PVA-based resin layer a polarizer; obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, the stretching may further include, if necessary, stretching the laminate in the air at a high temperature (for example, 95 ° C. or higher) before stretching in the aqueous boric acid solution. The obtained resin base material / polarizer laminate may be used as it is (that is, the resin base material may be used as a protective layer of the polarizer), and the resin base material is peeled from the resin base material / polarizer laminate. Any appropriate protective layer according to the purpose may be laminated on the release surface. Details of a method for manufacturing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. This publication is incorporated herein by reference in its entirety.

The thickness of the polarizer is typically 1 μm to 80 μm. The upper limit of the thickness of the polarizer is preferably 50 μm, more preferably 35 μm, and particularly preferably 30 μm. The lower limit of the thickness of the polarizer is preferably 1 μm, more preferably 3 μm. When the thickness of the polarizer is in such a range, curling during heating can be satisfactorily suppressed, and good appearance durability during heating can be obtained.

B-2. Protective layer The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Further, a polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

The protective layer may be subjected to surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment as necessary. Further / or, if necessary, the protective layer may be treated to improve visibility when viewed through polarized sunglasses (typically, an (elliptical) circular polarization function is added, an ultra-high phase difference is applied. Granting). By performing such processing, it is possible to improve the visibility when the display screen of the liquid crystal display device on which the optical member 10 is mounted is viewed through the polarized sunglasses.

The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. In addition, when the surface treatment is performed, the thickness of the protective layer is a thickness including the thickness of the surface treatment layer.

The inner protective layer is preferably optically isotropic. In this specification, “optically isotropic” means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is −10 nm to +10 nm. Say. The inner protective layer can be composed of any suitable material as long as it is optically isotropic. The material can be appropriately selected from the materials described above with respect to the protective layer, for example.

The thickness of the inner protective layer is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 15 μm to 95 μm.

C. Protective cover
The protective cover 2 is made of a transparent plastic material having birefringence. The in-plane retardation of the protective cover 2 is preferably 1000 nm or more, more preferably 3000 nm or more, still more preferably 5000 nm or more, and particularly preferably 7000 nm or more. The upper limit of the in-plane retardation of the protective cover 2 is 30000 nm, for example. Thereby, the change (color shift) of the hue according to the viewing angle at the time of visually recognizing the liquid crystal display device which mounts the optical member 10 through polarized sunglasses can be suppressed.

The angle formed between the slow axis of the protective cover 2 and the absorption axis of the polarizing film 1 is preferably 40 ° to 50 °, more preferably 42 ° to 48 °, and particularly preferably about 45 °. Thereby, the fall of front luminance at the time of visually recognizing the liquid crystal display device which mounts optical member 10 through polarization sunglasses can be controlled.

The thickness of the protective cover 2 is preferably 1000 μm or more, more preferably 2000 μm or more. By setting the thickness of the protective cover 2 to 1000 μm or more, the mechanical strength necessary for protecting the liquid crystal cell can be realized when the optical member 10 is provided on the viewer side of the liquid crystal cell of the liquid crystal display device. it can. Moreover, it is preferable that the thickness of the protective cover 2 is 4000 micrometers or less. Thereby, while being able to make a liquid crystal display device compact, the protective cover 2 can be applied also to a liquid crystal display device with a touch panel.

When the bending strength of the protective cover is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the value of S × T indicating the strength of the protective cover is preferably 400 or more. Preferably it is 500 or more, More preferably, it is 600 or more. On the other hand, the upper limit value of S × T is preferably 4000, and more preferably 2000. The bending strength of the protective cover can be measured according to the bending test method of ASTM-D790.

Any appropriate material can be adopted as the material constituting the protective cover 2. As the material, polycarbonate resin, polymethyl methacrylate resin, or the like can be used. The protective cover 2 may be bonded to the polarizing film 1 without leaving a gap as shown in FIG. 1, or may be provided with a gap between the protective cover 2 and the polarizing film 1.

In one embodiment, the angle formed between the slow axis of the protective cover 2 and the absorption axis of the polarizing film 1 is 40 ° to 50 °, and the in-plane retardation of the protective cover 2 is 1000 nm or more. Thereby, by providing the optical member 10 on the viewer side of the liquid crystal cell of the liquid crystal display device, the visibility is lowered when the liquid crystal display device is viewed through the polarized sunglasses without requiring any other high retardation film. Can be suppressed. Specifically, a decrease in front luminance and a change in hue (color shift) according to the viewing angle can be suppressed.

D. Interlayer Filling Adhesive Any appropriate pressure sensitive adhesive can be adopted as the interlayer filling adhesive 3. For example, the interlayer filling pressure-sensitive adhesive 3 may be an acrylic pressure-sensitive adhesive containing an acrylic polymer. The content of the acrylic polymer in the interlayer filling pressure-sensitive adhesive 3 is not particularly limited, but is preferably 96% to 100% by weight, more preferably 98% to 100% by weight from the viewpoint of odor. The acrylic polymer preferably has (meth) acrylic acid alkyl ester and / or (meth) acrylic acid alkoxyalkyl ester having a linear or branched alkyl group as an essential monomer component (monomer component). It is a structured acrylic polymer.

The specific constitution of the interlayer filling adhesive 3 is preferably 84 to 94% by weight of 2-ethylhexyl acrylate (2EHA), acrylic acid based on the total amount (100% by weight) of monomer components constituting the acrylic polymer. This is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer composed of a monomer component containing 5 to 15% by weight of (AA) and 0.03 to 0.15% by weight of dipentaerythritol hexaacrylate (DPHA). Further, as another specific constitution of the interlayer filling pressure-sensitive adhesive 3, preferably, 84 to 94% by weight of isooctyl acrylate (i-OA) with respect to the total amount (100% by weight) of monomer components constituting the acrylic polymer. An acrylic pressure-sensitive adhesive layer containing an acrylic polymer composed of a monomer component containing 5 to 15% by weight of acrylic acid (AA) and 0.03 to 0.15% by weight of dipentaerythritol hexaacrylate (DPHA) .

The thickness of the interlayer filling adhesive 3 is preferably 25 μm to 500 μm, more preferably 75 μm to 350 μm. The interlayer filling pressure-sensitive adhesive 3 has a 180 ° peel-off adhesive strength (referred to as “adhesive strength (23 ° C.)”) at 23 ° C. with respect to the protective cover 2 of preferably 5 N / 20 mm or more, more preferably 8 N / 20 mm or more. It is. By setting the adhesive force (23 ° C.) to 5 N / 20 mm or more, generation of delay bubbles (bubbles appearing at the interface with the protective cover) is suppressed. The adhesive strength (23 ° C.) is measured by performing a 180 ° peel test (according to JIS Z0237 (2000), tensile speed: 300 mm / min) using a protective cover as an adherend at 23 ° C. Can do.

Details of such an interlayer filling pressure-sensitive adhesive are described as a pressure-sensitive adhesive layer in, for example, Japanese Patent Application Laid-Open No. 2012-153788. This publication is incorporated herein by reference in its entirety.

E. Liquid Crystal Display Device The optical members described in the items A to D can be applied to a liquid crystal display device. Therefore, the present invention includes a liquid crystal display device using such an optical member. A liquid crystal display device according to an embodiment of the present invention includes a liquid crystal cell and the optical member according to any of the above items A to D disposed on the viewing side of the liquid crystal cell. The optical member is disposed so that the polarizing film is on the liquid crystal cell side.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

<Example 1>
1. Production of Polarizing Plate A polyvinyl alcohol film having a thickness of 80 μm was stretched up to 3 times while being dyed for 1 minute in an iodine solution of 0.3% concentration at 30 ° C. between rolls having different speed ratios. Thereafter, the total draw ratio was stretched to 6 times while being immersed in an aqueous solution containing 60% at 4% concentration of boric acid and 10% concentration of potassium iodide for 0.5 minutes. Next, after washing by immersing in an aqueous solution containing potassium iodide at 30 ° C. and 1.5% concentration for 10 seconds, drying was performed at 50 ° C. for 4 minutes to obtain a polarizer. A polarizing plate (polarizing film) was prepared by bonding a saponified 80 μm thick triacetyl cellulose film on both surfaces of the polarizer with a polyvinyl alcohol adhesive.

2. Production of optical member As a protective cover, an in-plane retardation is 7605 nm, and a plastic cover (product name “HMR551T”, manufactured by Mitsubishi Gas Chemical Co., Ltd.) having a thickness of 1450 μm made of a laminated structure of polycarbonate resin and polymethyl methacrylate resin is used. Using. The angle θ between the slow axis of the plastic cover and the absorption axis of the polarizing plate is 45 ° through the interlayer filling adhesive (product name “CS9864” manufactured by Nitto Denko Corporation) between the plastic cover and the polarizing plate. The optical member was obtained by pasting together.
When the bending strength of the protective cover measured according to the bending test method of ASTM-D790 is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the strength of the protective cover (S × T ) Was 1377.

<Comparative Example 1>
An optical member in the same manner as in Example 1 except that a plastic cover (product name “NF2000”, manufactured by Mitsubishi Gas Chemical Co., Inc.) having a thickness of 1500 μm and made of polycarbonate resin is used as the protective cover. Got.
When the bending strength of the protective cover measured according to the bending test method of ASTM-D790 is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the strength of the protective cover (S × T ) Was 1425.

<Comparative example 2>
An optical member was obtained in the same manner as in Example 1 except that a plastic cover (product name “PC1151” manufactured by Teijin Ltd.) with a thickness of 2000 μm made of polycarbonate resin was used as the protective cover. It was.
When the bending strength of the protective cover measured according to the bending test method of ASTM-D790 is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the strength of the protective cover (S × T ) Was 1900.

<Comparative Example 3>
Example 1 except that a plastic cover (product name “MR200” manufactured by Mitsubishi Rayon Co., Ltd.) having a thickness of 1500 μm made of polymethyl methacrylate resin was used as the protective cover. Thus, an optical member was obtained.
When the bending strength of the protective cover measured according to the bending test method of ASTM-D790 is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the strength of the protective cover (S × T ) Was 1425.

<Comparative example 4>
As a protective cover, an in-plane retardation of 112.4 nm and a plastic cover with a thickness of 1500 μm made of a laminated structure of polymethyl methacrylate resin / polycarbonate resin / polymethyl methacrylate resin (product name “MT3LTR” manufactured by Kuraray Co., Ltd.) An optical member was obtained in the same manner as in Example 1 except that was used.
When the bending strength of the protective cover measured according to the bending test method of ASTM-D790 is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the strength of the protective cover (S × T ) Was 1425.

<Comparative Example 5>
An optical member was obtained in the same manner as in Example 1 except that the plastic cover and the polarizing plate were bonded so that the angle θ formed by the slow axis of the plastic cover and the absorption axis of the polarizing plate was 0 °. .

<Comparative Example 6>
An optical member was obtained in the same manner as in Comparative Example 1 except that the plastic cover and the polarizing plate were bonded so that the angle θ formed by the slow axis of the plastic cover and the absorption axis of the polarizing plate was 0 °. .

<Comparative Example 7>
An optical member was obtained in the same manner as in Comparative Example 2 except that the plastic cover and the polarizing plate were bonded together so that the angle θ formed by the slow axis of the plastic cover and the absorption axis of the polarizing plate was 0 °. .

<Comparative Example 8>
An optical member was obtained in the same manner as in Comparative Example 3 except that the plastic cover and the polarizing plate were bonded to each other so that the angle θ formed by the slow axis of the plastic cover and the absorption axis of the polarizing plate was 0 °. .

<Comparative Example 9>
An optical member was obtained in the same manner as in Comparative Example 4 except that the plastic cover and the polarizing plate were bonded so that the angle θ formed by the slow axis of the plastic cover and the absorption axis of the polarizing plate was 0 °. .

For the optical members of Example 1 and Comparative Examples 1 to 9, the front luminance and the color shift when the liquid crystal display device including each optical member was observed through polarized sunglasses were evaluated as follows.

(1) Front luminance measurement method ITEC's LED surface light source “LPDC1-1150NCW-1R6” is placed on the back side (polarizing plate side) of the optical member, and the polarizing plate assuming polarizing sunglasses is placed on the front side of the optical member (plastic The brightness of the light source was measured through the optical member and the polarizing plate using a conoscope (manufactured by AUTRONIC MELCHERS Co., Ltd.) (unit: cd / m ² ). In addition, the polarizing plate was arrange | positioned so that the absorption axis of the polarizer might be orthogonal to the absorption axis of the polarizer of an optical member.
(2) Color shift measurement method A light source, an optical member, and a polarizing plate are arranged in the same manner as the measurement of front luminance, and a conoscope (manufactured by AUTRONIC MELCHERS Co., Ltd.) is used in a polar angle direction of 0 ° to 60 °. Hue, x value, and y value at azimuth angles of 0 ° to 360 ° were measured. As the color shift amount (Δxy value), the x value and y value at two arbitrary points are (x _A , y _A ) and (x _B , y _B ), and the following formula: {(x _A −x _B ) ² + The maximum value of (y _A -y _B ) ² } ^1/2 was taken as the Δxy value. In addition, the polarizing plate was arrange | positioned so that the absorption axis of the polarizer might be orthogonal to the absorption axis of the polarizer of an optical member.

Table 1 shows the measurement results of the front luminance and color shift of the optical members of Example 1 and Comparative Examples 1 to 4, and Table 2 shows the measurement results of the front luminance and color shift of the optical members of Comparative Examples 5 to 9. Tables 1 and 2 show an xy chromaticity diagram (horizontal axis: x value, vertical axis: y value) and a color shift amount (Δxy value) as measurement results of the color shift.

The optical member of the present invention is suitable for a liquid crystal display device mounted on a mobile phone, a portable information terminal, a digital camera, a video camera, a portable game machine, a car navigation system, a copy machine, a printer, a fax machine, a watch, a microwave oven, a car, etc. Used for.

DESCRIPTION OF SYMBOLS 1 Polarizing film 2 Protective cover 3 Interlayer filling adhesive 4 Antireflection film 10, 11, 12 Optical member

Claims (7)

1. A polarizing film and a protective cover;
   The in-plane retardation of the protective cover is 1000 nm or more,
   An optical member, wherein an angle formed by a slow axis of the protective cover and an absorption axis of the polarizing film is 40 ° to 50 °.
2. The optical member according to claim 1, wherein an in-plane retardation of the protective cover is 7000 nm or more.
3. The optical member according to claim 1 or 2, wherein the protective cover has a thickness of 1000 µm or more.
4. When the bending strength of the protective cover according to ASTM-D790 bending test method is S (kgf / cm ² ) and the thickness of the protective cover is T (mm), the value of S × T is 400 or more. The optical member according to any one of claims 1 to 3.
5. The optical member according to any one of claims 1 to 4, wherein an adhesive is filled between the protective cover and the polarizing film.
6. The optical member according to any one of claims 1 to 5, wherein an antireflection film is laminated on the side of the protective cover opposite to the polarizing film.
7. A liquid crystal display device comprising the optical member according to any one of claims 1 to 6.

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