JP7430741B2 - Polarizing plate and image display device - Google Patents

Description

The present invention relates to a polarizing plate having a laminated light scattering film layer and a liquid crystal display device equipped with the polarizing plate.

In recent years, liquid crystal display devices (LCDs) have been widely used because they are thin, lightweight, and consume little power. A liquid crystal display device has a liquid crystal panel member in which polarizing plates are bonded to both sides of a liquid crystal cell using an adhesive, and displays are performed by controlling light from a backlight member with the liquid crystal panel member. Here, a polarizing plate consists of a polarizing element and a protective film laminated on both sides of the polarizing element.A typical polarizing element is made by dyeing a stretched polyvinyl alcohol (PVA) film with iodine or a dichroic dye. Cellulose acylate film is mainly used as the protective film.

There is no end to the demand for further thinner and lighter LCDs and cost reductions for such LCDs. As a proposal to meet these demands, we have proposed replacing the cellulose acylate film, which is located on the outside of the polarizing plate protective film when laminated to the LCD, with a stretched polyethylene terephthalate film (hereinafter also referred to as PET film), which is inexpensive and has excellent mechanical strength. ) is being attempted.

However, when cellulose acylate film is replaced with general-purpose PET film, rainbow-like unevenness (hereinafter simply referred to as "diagonal rainbow unevenness") becomes noticeable when viewed from an oblique direction, resulting in poor visibility. is widely known. (For example, Patent Document 1)

To solve this problem, for example, in Patent Document 2, a stretched PET film is used for the back side protective film of the polarizing plate bonded to the back side of the liquid crystal cell, and the viewing side protective film of the viewing side polarizing plate is used to prevent high haze. A method of reducing diagonal rainbow unevenness by using an anti-glare film having a glare layer has been disclosed. However, even with this method, the improvement of diagonal rainbow unevenness is not sufficient, and since the anti-glare layer with high haze is provided on the viewing side, indoor illumination light is scattered and reflected on the surface of the anti-glare layer, and the entire display screen, especially the black There is a problem in that the display looks whitish, resulting in a significant deterioration in image quality. In order to prevent whitishness of black display, it is essential to use a protective film (hereinafter also simply referred to as "low haze film") that has a low haze anti-glare layer or clear hard coat layer on the viewing side. .

Patent Document 3 discloses, in a liquid crystal display device using a white light emitting diode as a backlight source, a polarizing plate protective film on the incident side of a polarizing plate (also referred to as a "back side polarizing plate") disposed on the incident light side, or By using a polyester film with an in-plane retardation of 3000 to 30000 nm as the protective film on the exit light side of the polarizing plate placed on the exit light side (also referred to as the "viewing side polarizing plate"), the above diagonal rainbow unevenness is suppressed. It describes what you can do.

However, although polyester films having such high in-plane retardation are on the market, they are more expensive than general-purpose PET films, and therefore are not suitable for applications aimed at cost reduction. Furthermore, since the in-plane retardation is proportional to the thickness, it is difficult to reduce the film thickness in order to obtain the above-mentioned high in-plane retardation, and the film is not suitable for thinning and lightweight applications.
Further, in Patent Document 3, it is necessary to use a white light emitting diode with a broad emission spectrum as a backlight light source, but in recent years, attempts have been made to use a light source with a sharp emission spectrum in order to widen the color reproduction range. (for example, Patent Document 4), and the contents of Patent Document 3 are not suitable for such uses.

Japanese Patent Application Publication No. 2010-107892 Japanese Patent Application Publication No. 2009-109993 International publication WO2011/162198 pamphlet Japanese Patent Application Publication No. 2012-169271

In view of the above-mentioned circumstances, the problem of the present invention, that is, the problem that the present invention aims to solve, is to use a general-purpose PET film as a polarizing plate protective film, and to provide a liquid crystal display device equipped with the same, especially for white display of black display. Even if a surface film with a low haze anti-glare layer or a clear hard coat layer is used on the viewing side to prevent glare, there are no problems such as diagonal rainbow unevenness, visibility is good, and it is manufactured at low cost. It is an object of the present invention to provide a polarizing plate that can be used, and also to provide a liquid crystal display device with good visibility equipped with such a polarizing plate. Another object of the present invention is to provide a thin polarizing plate suitable for making liquid crystal display devices thinner.

Of the two polarizing plates bonded on both sides of a liquid crystal cell, the inventors of the present invention have made intensive studies focusing on the back side polarizing plate, and as a result, the back side polarizing plate has been As a protective film, a stretched polyester film is used as a base material, and a light scattering film having a specific light scattering layer is used, and the light scattering layer of the light scattering film and a polarizing element are laminated together, thereby making it possible to use general purpose stretched PET. While using the method, it was discovered that even if a low haze film is used as the viewing side protective film of the viewing side polarizing plate, a polarizing plate with no diagonal rainbow unevenness and good visibility can be produced at a low cost, leading to the completion of the present invention.

The problem to be solved by the present invention can be solved by a polarizing plate having the following configuration. That is, it includes a polarizing element (P) formed by adsorbing and orienting iodine to a polyvinyl alcohol resin layer, and a light scattering film layer (DF) has an adhesive layer (AL1) on one surface of the polarizing element (P). A polarizing plate laminated through the
The light scattering film layer (DF) has a polyester resin stretched film as a base material, and has a light scattering layer (DL) on the polarizing element (P) side,
The light scattering layer (DL) is
1) Internal haze is 50-95%,
2) A polarizing plate characterized in that the surface unevenness has an arithmetic mean roughness Ra of 0 to 0.30 μm based on JIS B0601.

Furthermore, preferably, a back layer (BL) having a specific surface unevenness is provided on the side of the polyester resin stretched film base material of the light scattering film layer (DF) on which the light scattering layer (DL) is not laminated. Furthermore, it is a laminated polarizing plate, and when this polarizing plate is placed on the back side (backlight side) of a liquid crystal cell, the diffusion sheet placed between the backlight and the back side polarizing plate can be omitted, and the image This can further contribute to making the display device thinner and reducing costs.

According to the present invention, while using a general-purpose PET film, a polarizing plate without diagonal rainbow unevenness can be provided at low cost in a liquid crystal display device equipped with the same. Furthermore, the polarizing plate of the present invention can provide a polarizing plate and a liquid crystal display device with good visibility while using general-purpose PET.

[Polarizing element]
A well-known polarizing element can be used as the polarizing element of the present invention in which iodine is adsorbed and oriented on a polyvinyl alcohol (hereinafter also referred to as PVA) resin layer. Such a polarizing element is generally formed by using a PVA resin film, dyeing the PVA resin film with iodine, and uniaxially stretching the PVA resin film.

As mentioned above, the PVA resin is generally obtained by saponifying polyvinyl acetate resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers that can be copolymerized with it, such as ethylene-vinyl acetate copolymers. Examples include merging. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the PVA resin is 1,000 to 10,000, preferably 1,500 to 5,000. This PVA-based resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

The method for manufacturing the polarizing element is not particularly limited, but there is a method in which a polyvinyl alcohol resin film that has been rolled in advance is sent out and subjected to stretching, dyeing, crosslinking, etc., and a method in which a polyvinyl alcohol resin and a resin base material for stretching are used. A typical method includes the steps of preparing a laminate and stretching the laminate. In the present invention, any of these methods can be used.
Methods for manufacturing these polarizing elements are described in paragraphs [0109] to [0128] of JP-A No. 2014-48497, and these methods can be used in the present invention.
The thickness of the polarizing element of the present invention is preferably 3 to 35 μm, more preferably 4 to 30 μm, and even more preferably 5 to 25 μm.

[Light scattering film layer]
Next, the light scattering film layer of the present invention will be explained. The base film of the light scattering film layer of the present invention is a stretched polyester resin film.

(Polyester resin stretched film)
The polyester resin used in the present invention is not particularly limited in structure. Preferably, the main component is a resin having a structure obtained by condensing an aromatic dicarboxylic acid and an aliphatic glycol, more preferably polyethylene terephthalate or polyethylene naphthalate, and particularly polyethylene terephthalate. preferable. Other copolymerization components may be included as long as they do not impede the effects of the present invention. Other polymers may be blended.
The polyester of the present invention can also contain additives such as antioxidants and ultraviolet absorbers, if necessary.

The polyester resin stretched film of the present invention can be manufactured according to a general polyester film manufacturing method. For example, a non-oriented polyester film made by melting a polyester resin and extruding it into a sheet is stretched vertically using a speed difference between rolls at a temperature above the glass transition temperature, and then stretched horizontally using a tenter. , a method of applying heat treatment.

The polyester resin-based stretched film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but generally a biaxially stretched film has higher mechanical strength and is more preferable. In addition to the above-mentioned stretching method, the uniaxially stretched film manufacturing method includes a method in which the film is stretched either in the longitudinal direction or in the lateral direction using a tenter, and then subjected to heat treatment. The in-plane retardation Re of the polyester resin stretched film thus obtained is usually 500 to 3000 nm.

The thickness of the stretched polyester resin film of the present invention is preferably 5 to 200 μm, more preferably 10 to 100 μm, and even more preferably 20 to 80 μm.
In the present invention, in order to improve the adhesion with the light scattering layer, it is preferable that the polyester resin stretched film of the present invention has an easy-to-adhesion layer mainly composed of polyester resin, polyurethane resin, polyacrylic resin, etc. on at least one side of the polyester resin stretched film of the present invention. preferable.

Examples of commercially available stretched PET films with an easily adhesive layer include "Cosmoshine" (registered trademark) manufactured by Toyobo Co., Ltd. and "Lumirror" (registered trademark) manufactured by Toray Industries. Such a film can also be preferably used in the present invention.

(light scattering layer)
The light scattering layer is laminated on the polyester resin stretched film. The light scattering layer has a light scattering agent and a binder. The light-scattering layer contains a light-scattering agent dispersed therein to scatter light that has passed through the polyester film, thereby preventing diagonal rainbow unevenness.

Light scattering agents are particles that have the property of scattering light rays, and are broadly classified into inorganic fillers and organic fillers. Examples of the inorganic filler include silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or mixtures thereof. Among these, silica particles are preferred in terms of refractive index.
Specific materials for the organic filler include, for example, acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, polyacrylonitrile, silicone resin, and the like. Among these, highly transparent acrylic resins are preferred, and polymethyl methacrylate (PMMA) or a copolymer of methyl methacrylate and styrene is particularly preferred.

The shape of the light scattering agent is not particularly limited, and examples thereof include spherical, cubic, needle-like, rod-like, spindle-like, plate-like, scale-like, and fibrous shapes, among which spherical shape has excellent light scattering properties. beads are preferred.
When an organic filler is used as the light scattering agent, the average particle diameter of the light scattering agent is preferably 0.5 to 6 μm, more preferably 1 to 6 μm, and even more preferably 1 to 5 μm. If the thickness of the light scattering agent is less than 0.5 μm, a sufficient light scattering effect cannot be obtained. On the other hand, if it is larger than 6 μm, the surface irregularities will become large and the adhesion to the polarizing element may deteriorate.

When an organic filler is used as a light-scattering agent, the amount of the light-scattering agent (in terms of solid content based on 100 parts by mass of the polymer in the polymer composition that is the material for forming the binder) is preferably 5 to 100 parts by mass. , more preferably 10 to 70 parts by weight, and even more preferably 20 to 50 parts by weight. If the amount of the light scattering agent is less than the above lower limit, the light scattering properties may be insufficient. On the other hand, if the amount of the light scattering agent exceeds the above upper limit, surface irregularities may become large and adhesion with the polarizing element may not be successful. In addition, when a permanent filler is used as a light scattering agent, the amount of the permanent filler is approximately the same as that of an organic filler.

Examples of the binder include thermosetting resins and active energy ray-curable resins. In addition, the composition for forming the binder may also include, for example, a fine inorganic filler with an average particle diameter of less than 0.5 μm, a curing agent, a plasticizer, a dispersant, various leveling agents, an antistatic agent, an ultraviolet absorber, Antioxidants, viscosity modifiers, lubricants, light stabilizers, solvents, etc. may be appropriately blended.

The base polymer of the thermosetting resin is not particularly limited, and examples include acrylic resin, urethane resin, polyester resin, fluorine resin, silicone resin, polyamide resin, polyimide resin, and epoxy resin. Examples include polymer resins, ultraviolet curable resins, thermosetting resins, photocurable resins, etc., and these polymers can be used alone or in combination of two or more. In particular, as the base polymer, polyols are preferred because they have high processability and can easily form a light-scattering layer by means such as coating. Further, the base polymer used for the binder itself is preferably transparent from the viewpoint of increasing light transmittance, and colorless and transparent is particularly preferred.

Examples of the above-mentioned polyols include polyols obtained by polymerizing monomer components containing hydroxyl group-containing unsaturated monomers, polyester polyols obtained under conditions with an excess of hydroxyl groups, and the like, which may be used alone or in combination of two or more. Can be used in combination. In the present invention, it is preferable that the main component is a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, and the unsaturated monomer is preferably a (meth)acrylic monomer, Particularly preferred are (meth)acrylic polyols obtained from such monomers. Specific examples and preferred embodiments of the polyol are described in paragraphs [0050] to [0057] of JP-A-2013-117695, and can be suitably used in the present invention as well.

When using a polyol as a binder, it is preferable to contain at least one compound selected from polyfunctional isocyanate compounds, melamine compounds, and aminoplast resins among compounds having two or more functional groups that react with the hydroxyl group of the polyol. As a result, the polyol of the matrix resin of the binder is bonded with a crosslinked structure, and storage stability, stain resistance, flexibility, weather resistance, storage stability, etc. are improved.
Among the above compounds, polyfunctional isocyanates are particularly preferred in the present invention. Furthermore, as a combination with the base polymer, a combination of (meth)acrylic polyol and polyfunctional isocyanate is particularly preferable.
Specific examples and preferred embodiments of compounds having two or more functional groups that react with the hydroxyl group of polyol are described in paragraphs [0071] to [0078] of JP-A No. 2013-117695, and in the present invention. can also be suitably used.

Examples of the above-mentioned active energy ray-curable resins include ultraviolet curable resins that are crosslinked and cured by irradiation with ultraviolet rays, and electron beam curable resins that are crosslinked and cured by irradiation with electron beams. and polymerizable oligomers. Among these, the active energy ray-curable resin is preferably a (meth)acrylic, urethane, or (meth)acrylic urethane-based ultraviolet curable resin.

As the polymerizable monomer, a (meth)acrylate monomer having a radically polymerizable unsaturated group in the molecule is preferably used, and polyfunctional (meth)acrylate is particularly preferred. Specific examples and preferred embodiments of polyfunctional (meth)acrylates are described in paragraphs [0026] to [0032] of JP-A No. 2013-228720, and they can be suitably used in the present invention as well. .

When using an ultraviolet curable resin as the active energy ray curable resin, it is desirable to add about 0.1 to 5 parts by mass of a photopolymerization initiator to 100 parts by mass of the resin. The photopolymerization initiator is not particularly limited, and for polymerizable monomers and polymerizable oligomers having a radically polymerizable unsaturated group in the molecule, for example, benzophenone, benzyl Michler's ketone, 2-chloro Thioxanthone, 2,4-diethylthioxanthone, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-Hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,1-[ 4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, bis(cyclopentadienyl)-bis[2,6-difluoro-3-(pyrrole-1) -yl)phenyl]titanium, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and the like. Further, examples of polymerizable oligomers having a cationically polymerizable functional group in the molecule include aromatic sulfonium salts, aromatic diazonium salts, aromatic iodonium salts, metallocene compounds, benzoinsulfonic acid esters, and the like. In addition, each of these compounds may be used alone, or a plurality of them may be used in combination.
For specific examples, preferred embodiments, commercial products, etc. of the photopolymerization initiator, the descriptions in paragraphs [0064] to [0067] of JP-A-2014-170130 can be referred to.

<Optical properties of light scattering layer>
The haze value (internal haze value) due to the inside of the light scattering layer in the present invention is 50 to 95%, preferably 55 to 92%, and particularly preferably 60 to 90%. Within this range, diagonal rainbow unevenness can be prevented.

<Surface shape of light scattering layer>
The surface shape of the light scattering layer in the present invention has a roughness parameter (arithmetic mean roughness Ra) according to JIS-B0601 of 0 to 0.30 μm, preferably 0 to 0.25 μm, and preferably 0.05 to 0. Particularly preferred is 22 μm. By controlling it within this range, good adhesion to the polarizing element can be obtained.

<Thickness of light scattering layer>
The thickness of the light scattering layer in the present invention is preferably 3 to 30 μm, more preferably 5 to 20 μm, and particularly preferably 6 to 15 μm. By controlling it within this range, the optical properties and surface shape of the light scattering layer described below can be appropriately controlled.

The means for laminating the light scattering layer is not particularly limited, and various known methods may be employed. As a specific laminating method, for example, coating using a gravure coating method, a roll coating method, a bar coating method, a blade coating method, a spray coating method, etc. is adopted. Among these, the most preferred is the gravure coating method, which allows a thin and even coating of a polymer composition containing beads. In such a gravure coating method, considering the formability of a light scattering layer, etc., the number of gravure lines is preferably 70 or more and 100 or less, and the rotation speed is preferably 80 or more and 120 or less.

(Back side of light scattering film layer)
The back surface of the light-scattering film layer (the surface of the base material on which the light-scattering layer is not laminated) has an anti-sticking layer or a light-diffusing layer with surface irregularities and a haze of 10% or more (in this application, "back layer"). ) is also preferably laminated.
A prism sheet is often installed under the back polarizing plate for the purpose of condensing light. This prism sheet may interfere with pixels and cause moiré. By further laminating a back layer having an uneven surface shape on the back surface of the light scattering film layer as described above, a moire prevention effect can be imparted, which is preferable. In addition, in order to prevent moire caused by the prism sheet, a diffusion sheet may be installed opposite the back polarizing plate, but a back layer having an uneven surface shape is further laminated on the back side of the light scattering film layer. This allows the above-mentioned diffusion sheet to be omitted, which is preferable from the viewpoint of making the image display device thinner and reducing costs.

(Back layer with surface unevenness)
Next, the "back layer having an uneven surface shape" that can be preferably used in the present invention will be explained. (Hereinafter, the "back layer having an uneven surface shape" will also be simply referred to as the "back layer.")
The back layer is laminated on the back surface of the light scattering film layer (the surface of the base material on which the light scattering layer is not laminated).

The back layer has a binder. Although the back layer may be formed using only a binder, it is preferable to contain a filler in order to obtain an appropriate surface unevenness. As the filler, those exemplified as the light scattering agent for the light scattering layer can be used.
Among these, spherical particles are preferred from the viewpoint of ease of controlling the surface shape, and spherical organic fillers are more preferred from the viewpoint of preventing scratches on the prism sheet.
Among the organic fillers, highly transparent acrylic resins are preferred, and polymethyl methacrylate (PMMA) or a copolymer of methyl methacrylate and styrene is particularly preferred.

When an organic filler is used in the back layer, the average particle size is preferably 1 to 20 μm, more preferably 2 to 15 μm, and even more preferably 3 to 12 μm. When the particle size is less than 1 μm, it is difficult to obtain sufficient surface roughness, and on the other hand, when it is larger than 20 μm, the back layer becomes thick.

As the binder for the back layer, those described in the light scattering layer described above can be preferably used. In addition, the amount of the organic filler (in terms of solid content based on 100 parts by weight of the polymer in the polymer composition that is the binder forming material) is preferably 5 to 100 parts by weight, more preferably 10 to 70 parts by weight, More preferably 20 to 50 parts by mass.
If the amount of the organic filler is less than the above lower limit, the surface roughness may become insufficient. On the other hand, if the amount of the organic filler exceeds the above upper limit, the fixation of the organic filler may become insufficient and the filler may fall off.

<Optical properties of back layer>
The haze value of the back layer in the present invention is 3 to 90%, preferably 10 to 80%, and particularly preferably 15 to 70%. Within this range, moiré caused by the prism can be prevented.
In addition, the haze of the back layer mentioned here means the haze value when only the back layer is laminated on the PET film base material without laminating the above-mentioned light scattering layer.

The internal haze value of the back layer can be controlled by the difference in refractive index between the binder and filler of the back layer. It is preferable that the back layer has substantially no internal haze, specifically preferably -1 to 1%. Coloring of light passing through the back layer can be suppressed.
Note that the internal haze of the back layer referred to here refers to a method in which only the back layer is laminated on a PET film base material without laminating the light scattering layer described above, and a binder liquid is further applied and cured on the surface of the back layer. It means the haze value of the back layer after smoothing. A specific method for measuring the internal haze value will be described in Examples below.

<Surface shape of back layer>
The surface shape of the back layer in the present invention has a roughness parameter (arithmetic mean roughness Ra) according to JIS-B0601 of preferably 0.05 to 1.50 μm, more preferably 0.08 to 1.20 μm, and 0.10 to 0. .90 μm is more preferred, and 0.10 to 0.60 μm is particularly preferred. By controlling within this range, it is possible to achieve both prevention of moire and front brightness.

<Thickness of back layer>
The thickness of the back layer in the present invention is preferably 3 to 20 μm, more preferably 5 to 17 μm, and particularly preferably 6 to 15 μm. By controlling it within this range, the optical properties and surface shape of the backing layer described below can be appropriately controlled.
The means for laminating the back layer is not particularly limited, and as with the light scattering layer, various known methods can be employed. Further, the light scattering layer and the back layer may be laminated in sequence in two steps, or the two layers may be laminated at the same time. In the case of laminating in two steps, there is no restriction on the order of lamination.

[Layer structure of polarizing plate]
The polarizing plate of the present invention may be a polarizing plate having a protective film on only one side of the polarizing element, or a polarizing plate having protective films on both sides of the polarizing element. In the present invention, the preferred layer structure of the polarizing plate is shown below.
Polyester film / light scattering layer / adhesive layer / polarizing element back layer with uneven surface / polyester film / light scattering layer / adhesive layer / polarizing element polyester film / light scattering layer / adhesive layer / polarizing element / adhesive layer / Protective film Back layer with surface irregularities / Polyester film / Light scattering layer / Adhesive layer / Polarizing element / Adhesive layer / Protective film

[Other protective film]
When the polarizing plate of the present invention has a protective film on both sides, the other protective film may be a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, or a film made of a cycloolefin resin such as norbornene. ) Films such as acrylic polymer films can be used; however, when laminating with a water-based adhesive such as PVA adhesive, cellulose acylate films or (meth)acrylic polymers are preferable in terms of moisture permeability. Any film is preferred, and cellulose acylate film is particularly preferred.

The thickness of the protective film at this time is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength will decrease and the processability will be poor. A suitable film thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.
In addition, the polarizing plate of the present invention can be used in liquid crystal cells with various display modes, as described below, but when the liquid crystal cell is in IPS mode, it may be necessary to have no extra birefringence from the viewpoint of optical compensation. preferable. An example of a cellulose acylate film that satisfies such conditions is Fujitac ZRD (manufactured by Fuji Film Co., Ltd.), which can be preferably used in the present invention.

[Method for manufacturing polarizing plate]
Next, a method for producing a polarizing plate of the present invention will be explained.
(Lamination of polarizing element (P) and light scattering film layer (DF))
The polarizing plate of the present invention can be produced by bonding one surface of the polarizing element (P) and the light scattering layer (DL) surface of the light scattering film layer (DF) via an adhesive layer (AL1). Any suitable adhesive can be used as the adhesive used in the present invention. Specifically, as the adhesive, a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, etc. can be used. Furthermore, the above adhesive used for adhering the light scattering film layer (DF) can be similarly used for adhesion between the other surface of the polarizing element (P) and the protective film layer (PF2).

As the active energy ray-curable adhesive, any suitable adhesive can be used as long as it can be cured by irradiation with active energy rays. Examples of active energy ray curable adhesives include ultraviolet ray curable adhesives and electron beam curable adhesives. Specific examples of the curable type of the active energy ray curable adhesive include a radical curable type, a cation curable type, an anion curable type, and a combination thereof (for example, a hybrid of a radical curable type and a cation curable type).

Examples of the active energy ray-curable adhesive include an adhesive containing a compound (for example, a monomer and/or oligomer) having a radically polymerizable group such as a (meth)acrylate group or a (meth)acrylamide group as a curing component. can be mentioned.
Specific examples of the active energy ray-curable adhesive and its curing method are described in, for example, JP-A No. 2012-144690.

Furthermore, any suitable water-based adhesive may be employed as the water-based adhesive. Among these, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA resin contained in the water-based adhesive is preferably about 100 to 5,500, more preferably 1,000 to 4,500 from the viewpoint of adhesiveness. The average degree of saponification is preferably about 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, from the viewpoint of adhesive properties.

The PVA resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the adhesiveness between the PVA resin layer and the protective film is excellent, and the durability is excellent. The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin and diketene by any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 20 mol%.

The resin concentration of the water-based adhesive is preferably 0.1% to 15% by weight, more preferably 0.5% to 10% by weight.
The thickness of the adhesive when applied may be set to any appropriate value. For example, settings are made so that an adhesive layer having a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

In the present invention, a layer formed with a PVA adhesive is referred to as a PVA adhesive layer, and a layer formed with an active energy ray curable adhesive is referred to as an active energy ray curable adhesive layer.
When adhering the polarizing element and the light-scattering film layer, in order to improve the adhesion between the polarizing element and the adhesive, and between the light-scattering layer and the adhesive, one or both of the polarizing element and the light-scattering layer must be coated in advance. Surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation, and primer coating treatment may be performed.

In the case where the polarizing plate of the present invention has a protective film on both sides of the polarizing element, the protective films may be laminated on one side at a time or both sides may be laminated at the same time, but it is preferable that both sides be laminated at the same time.
Further, it is preferable that the slow axis direction (the direction in which the in-plane refractive index is maximized) of the stretched polyester resin film and the absorption axis direction of the polarizing element are substantially parallel or substantially perpendicular to each other. If it deviates from the above, rainbow unevenness may be observed from the front when mounted on a liquid crystal display device.

[Liquid crystal display device]
The liquid crystal display device of the present invention includes a liquid crystal cell, a polarizing plate (rear side polarizing plate) of the present invention disposed on the backlight side of the liquid crystal cell, and a polarizing plate disposed on the viewing side (viewing side polarizing plate). It is characterized by containing. In the liquid crystal display device of the present invention, there is no particular restriction on the viewing side polarizing plate, but the haze of the viewing side protective film of the viewing side polarizing plate is preferably 0 to 10%, and more preferably 0 to 8%. Particularly preferred is 0 to 5%. By controlling the haze of the viewing side protective film within this range, it is possible to both prevent diagonal rainbow unevenness and reduce blackness.

(Composition of general liquid crystal display device)
A liquid crystal display device includes a liquid crystal cell in which a liquid crystal is supported between two electrode substrates, two polarizing plates placed on both sides of the cell, and, if necessary, a liquid crystal cell supporting a liquid crystal between the liquid crystal cell and the polarizing plate. It has a configuration in which at least one optical compensation film is disposed. The polarizing plate of the present invention can be used as a back polarizing plate of two polarizing plates.
The liquid crystal layer of a liquid crystal cell is usually formed by sealing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on the substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer, or an undercoat layer (used for adhesion of the transparent electrode layer). These layers are typically provided on a substrate. The substrate of a liquid crystal cell generally has a thickness of 50 μm to 2 mm.

(Type of liquid crystal display device)
The film of the present invention can be used in liquid crystal cells with various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-ferroelectric Liquid Crystal), O CB (Optically Compensatory Bend), STN (Super Twisted Nematic), VA (Vertically Aligned), Various display modes have been proposed, such as ECB (Electrically Controlled Birefringence) and HAN (Hybrid Aligned Nematic). Furthermore, a display mode in which the above display mode is divided into orientations has also been proposed. The polarizing plate of the present invention is effective in liquid crystal display devices of any display mode. Further, any of a transmissive type, a reflective type, and a semi-transmissive type liquid crystal display device can be used.

It is particularly preferable that the polarizing plate of the present invention is bonded to the back surface of the above-mentioned IPS mode liquid crystal cell, since light leakage when viewed from an oblique direction during black display is suppressed.

The present invention will be specifically described below based on Examples. The materials, reagents, amounts of substances, their proportions, operations, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to or limited to the following examples.

[Preparation of light scattering film]
(Preparation of polyester resin stretched film base material)
A biaxially stretched PET film in the form of a long roll with adhesive layers on both sides having a film thickness of approximately 38 μm was obtained in the same manner as in WO2011/162198 [0076] (Comparative Example 1). The in-plane retardation Re of this film was 1178 nm, the slow axis was in the width direction (perpendicular to the longitudinal direction), and the haze was 0.2%.

(Lamination of light scattering layer)
A light scattering polymer composition containing a light scattering agent and a binder includes 43 parts of acrylic polyol (base polymer), 21 parts of methyl methacrylate-styrene copolymer (refractive index: 1.52) particles with an average particle size of 3 μm, and isocyanate. A polymer composition consisting of 6 parts of a curing agent and a solvent was used. The number of parts indicating the amount of each composition is a mass ratio in terms of solid content. A light scattering film 1 was obtained by laminating 15 g/m ² (in terms of solid content) of a polymer composition for a light scattering layer on the surface of this base layer by gravure coating. At this time, the refractive index of the binder was 1.50.

The light scattering layer was evaluated according to the following [Evaluation method for light scattering layer]. The internal haze of the light scattering layer was 80%, and the arithmetic mean roughness Ra was 0.05 μm.
Light scattering films 2 to 6 were prepared from light scattering film 1 by changing the blending amount of light scattering agent particles and the thickness of the light scattering layer, and evaluated in the same manner as light scattering film 1. The results are shown in Table 1.

[Evaluation method of light scattering layer]
(1-1) Haze [1] Measure the total haze value (H) of the obtained light scattering film according to JIS-K7136: A haze meter NDH2000 manufactured by Nippon Denshoku Kogyo Co., Ltd. was used.
[2] A film obtained by removing the light scattering agent from the above light scattering polymer composition on the surface of the light scattering layer and smoothing the surface with a bar coater at about 2 g/m ² (solid content equivalent) to remove surface haze. Created. This film was measured in the same manner as above, and the internal haze value (Hin) was obtained from the difference from the haze value of the base film.

(1-2) Surface shape of light scattering layer (arithmetic mean roughness Ra)
It was measured using a surfcorder MODEL SE-3500 manufactured by Kosaka Institute Co., Ltd. in accordance with JIS-B0601 (1994, 2001).

(Preparation of light scattering film having only a back layer)
A polymer composition for the back layer containing an organic filler and a binder consists of 43 parts of acrylic polyol (base polymer), PMMA particles with an average particle size of 10 μm (refractive index: 1.50), 6 parts of an isocyanate curing agent, and a solvent. A polymer composition was used. The number of parts indicating the amount of each composition is a mass ratio in terms of solid content. The amount of PMMA particles added was appropriately adjusted so that the Ra (arithmetic mean roughness) after lamination would be the value shown in Table 1.

By laminating 7 g/m ² (in terms of solid content) of the polymer composition for the back layer using the gravure coating method on the biaxially stretched PET film with the easy-adhesion layer on which the light-scattering layer is not laminated, only the back layer can be formed. A light scattering film 21 having the following properties was obtained.
Light scattering films 22 to 25 were prepared in the same manner as light scattering film 21 by changing the amount of filler and the thickness of the back layer.

(Preparation of light scattering film having light scattering layer and back layer)
Light scattering films 11 to 14 were produced in the same manner except that the back layers of light scattering films 21 to 24 having only back layers were laminated on the surface of the light scattering film 2 on which the light scattering layer was not laminated.
Similarly, the light scattering films 15 to 17 were formed in the same manner except that the back layer of the light scattering film 22 having only the back layer was laminated on the surface of the light scattering films 4, 3, and 1 on which the light scattering layer was not laminated. Created.

[Evaluation method of back layer]
(2-1) Haze [1] Measure the total haze value (H) of the obtained light scattering film layer according to JIS-K7136: A haze meter NDH2000 manufactured by Nippon Denshoku Kogyo Co., Ltd. was used. The haze of the light scattering films 21 to 25 having only the back layer was measured, and the haze was defined as the haze of the back layer. For the haze of the back layer of a light scattering film layer having a light scattering layer and a back layer, the value of light scattering films 21 to 25 prepared with the same formulation was used as the haze of the back layer.
[2] The back layer of the light scattering films 21 to 25 having only a back layer is coated with the above-mentioned back layer polymer composition from which the light scattering agent has been removed using a bar coater at about 2 g/m ² (in terms of solid content). A film was prepared that was smoothed and had its surface haze removed. This film was measured in the same manner as above, and the internal haze value (Hin) of the back layer was obtained from the difference from the haze value of the base film. For the internal haze of the back layer of a light scattering film layer having a light scattering layer and a back layer, the internal value of light scattering films 21 to 25 prepared with the same recipe was taken as the internal haze of the back layer.

(2-2) Surface shape of back layer (arithmetic mean roughness Ra)
It was measured using a surfcorder MODEL SE-3500 manufactured by Kosaka Institute Co., Ltd. in accordance with JIS-B0601 (1994, 2001).

Note that in Table 1, light scattering films 1 to 6 have only a light scattering layer on one side of a polyester resin stretched film base material and do not have a back layer. The light scattering films 11 to 17 have a structure in which a polyester resin stretched film base material has a light scattering layer on one side and a back layer on the other side. Further, the light scattering films 21 to 25 have only a back layer on one side of a polyester resin stretched film base material and do not have a light scattering layer.
Further, the internal haze of the back layer of light scattering films 21 to 25 was all 0%.

[Preparation of polarizing plate]
Next, a polarizing plate is produced using the light scattering films 1 to 6, 11 to 17, 22, and 25 produced above and a biaxially stretched PET film on which no light scattering layer is laminated.

(Preparation of polarizing element)
A 40 μm thick PVA film with an average degree of polymerization of 2400 and a degree of saponification of 99.9 mol % was immersed in warm water at 25° C. for 120 seconds to swell. Next, the PVA film was dyed while being immersed in an aqueous solution of iodine/potassium iodide (weight ratio = 2/3) with a concentration of 0.6% by weight and stretched 2.1 times. Thereafter, the film was stretched in an acidic bath containing boric acid and potassium iodide at 60°C, washed with water, and dried to produce a polarizing element with a film thickness of 15 μm.

(Preparation of adhesive for polarizing plate)
An aqueous solution A was prepared by dissolving a modified PVA resin containing an acetoacetyl group (Gosenex Z-410, manufactured by Nippon Gosei Kagaku Co., Ltd.) in water and adjusting the solid content concentration to 3%. Next, maleic acid was added to the aqueous solution A in an amount of 0.5% by weight, and then glyoxal was added as a crosslinking agent. The amount of glyoxal added was set to 5 by weight when the weight of Z-410 was 100. Sodium hydroxide was added to this aqueous solution to adjust the pH to 2.5 to obtain an adhesive for polarizing plates.

(Saponification of cellulose acylate film)
A commercially available cellulose acylate film (Fujitac ZRD40, manufactured by Fuji Film Co., Ltd., film thickness 40 μm) was immersed for 2 minutes in a 1.5 mol/L NaOH aqueous solution (saponification solution) kept at 55°C. The film was washed with water, then immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a washing bath under running water for 30 seconds to make the film neutral. Then, draining with an air knife was repeated three times, and after removing the water, the film was dried by staying in a drying zone at 70° C. for 15 seconds to produce a saponified film.

(Preparation of polarizing plate)
After the surface of the light scattering layer of the light scattering film produced above was subjected to corona treatment, the above adhesive was applied so that the thickness of the adhesive layer after drying was 150 nm. The above adhesive was applied to one side of the saponified cellulose acylate film so that the thickness of the adhesive layer after drying was 150 nm.
Next, the light scattering film and the cellulose acylate film, each of which has the above-mentioned adhesive applied to both sides of the polarizing element, are combined using a roll laminating machine to combine the slow axis of the biaxially stretched PET film, which is the light scattering film base material, with the absorption of the polarizing element. After bonding so that the axes were perpendicular, the plates were dried at 60° C. for 10 minutes to obtain a polarizing plate 1 according to the present invention.

Polarizing plates 2 to 6, 11 to 17, and 21 to 27 were prepared by changing the type of light scattering film layer and the bonding surface with the polarizing element to polarizing plate 1 as shown in Table 2. In addition, the polarizing plate 21 was made by pasting the light scattering film 1 with a polarizing element on the opposite side to the light scattering layer lamination surface. Polarizing plates 22 and 23 are light-diffusing films having only a back layer and no light-diffusing layer, and were laminated with an easy-adhesive layer of a PET base material on the opposite side of the back layer and the polarizing element. The polarizing plates 25 to 27 have only an outer protective film and no inner protective film. In addition, for the polarizing plates 24 and 27, biaxially stretched PET without a light scattering layer laminated thereon was used as an outer protective film instead of the light scattering film layer.

[Fabrication of liquid crystal display device]
A monitor made by LG Display (32MP58HQ: equipped with a white LED edge-light type backlight, IPS mode liquid crystal cell: consisting of a light guide plate, a diffusion sheet, two prism sheets, and a diffusion sheet from the bottom) was disassembled and attached to the liquid crystal cell. Peel off the backlight side polarizing plate, and instead attach polarizing plates 1 to 6, 11 to 17, and 21 to 27 to the liquid crystal cell via an adhesive, with the side on which the light scattering film is not attached, The diffusion sheet placed opposite the uppermost back polarizing plate was removed and reassembled to produce image display devices 1 to 6, 11 to 17, and 21 to 27. Evaluation was made according to the following [Evaluation method for image display device]. The results are shown in Table 2.

[Evaluation method of image display device]
(3-1) Diagonal rainbow unevenness With the monitor set to white display, the screen was observed in all directions diagonally at polar angles of 60 degrees and 45 degrees, and rainbow unevenness was evaluated on a 6-grade scale according to the following criteria.
◎: No rainbow unevenness is visible at either the polar angle of 60 degrees or the polar angle of 45 degrees.
○: Rainbow unevenness can be somewhat recognized at a polar angle of 60 degrees, but it is hardly visible. No rainbow spots are visible at a polar angle of 45 degrees.
△: Rainbow unevenness can be recognized at a polar angle of 60 degrees, but it is not noticeable. No rainbow spots are visible at a polar angle of 45 degrees.
×: Rainbow unevenness appears faint at a polar angle of 60 degrees. Rainbow unevenness cannot be seen at a polar angle of 45 degrees.
XX: Rainbow unevenness is clearly visible. Rainbow unevenness can be recognized at a polar angle of 45 degrees.
×××: Rainbow unevenness is clearly visible. It is clearly visible even at a polar angle of 45 degrees.

(3-2) Moiré The monitor was set to white display, and the images were observed in all directions at a polar angle of 0 to 60 degrees, and the moiré was evaluated on a 6-grade scale according to the following criteria.
◎: No moire is visible in all directions.
○: Moiré is hardly visible in all directions.
△: Moire can be recognized in some areas, but it is not bothersome.
×: Moiré appears thin in some places.
XX: Moiré is clearly visible in some areas.
×××: Moiré is clearly visible throughout.

(3-3) Front brightness The monitor before disassembly and after lamination of the polarizing plates of the examples of the present invention and comparative examples was set to white display, the front brightness was measured, and the front brightness was graded into three levels according to the following criteria. evaluated.
○: Brightness is 95% or more compared to the brightness before decomposition.
Δ: Brightness is 90% or more and less than 95% of the brightness before decomposition.
×: Brightness is less than 90% of the brightness before decomposition.

※偏光板２１は光散乱フィルムを反対面で偏光素子と貼合。以下の構成となる。
光散乱層／ポリエステルフィルム／接着剤層／偏光素子／接着剤層／保護フィルム

*Polarizing plate 21 has a light scattering film attached to the polarizing element on the opposite side. The configuration is as follows.
Light scattering layer/polyester film/adhesive layer/polarizing element/adhesive layer/protective film

When the image display device shown in Table 1 was observed from the front (observation of "frontal rainbow unevenness") according to (3-1) diagonal rainbow unevenness in the previous period, no frontal rainbow unevenness was observed in any image display. Ta.

The following is clear from the results shown in Table 2.
1. When a general-purpose stretched PET film is used as a polarizing plate protective film, diagonal rainbow unevenness occurs.
2. By providing a light scattering layer with an internal haze of 50 to 95% between the stretched PET and the polarizing element, diagonal rainbow unevenness can be prevented.
3. The same diagonal rainbow unevenness prevention effect can be obtained regardless of the presence or absence of the inner protective film.
4. A light scattering layer provided outside the polarizing plate does not have the effect of preventing rainbow unevenness.
5. A material having a light scattering layer and a back layer having an uneven shape has a high moiré improvement effect.
6. In particular, those provided with a back layer having an uneven shape with an arithmetic mean roughness Ra of 0.10 to 0.90 μm have a high moiré reduction effect.
7. A structure in which there is no light scattering layer and only a back layer having an uneven shape has almost no effect of preventing rainbow unevenness.

Next, the relationship between white blur (whitishness during black display) and prevention of diagonal rainbow unevenness when a conventional high haze anti-glare film is used and the superiority of the present invention will be explained.

(Production of low haze anti-glare film)
A low haze anti-glare film was obtained according to Example 1 described in paragraphs [0120] to [0141] and [0156] of JP-A-2013-228720. The haze of the low haze anti-glare film was 3%.

(Production of high haze anti-glare film)
A high haze anti-glare film was obtained according to the anti-glare protective film (C) described in paragraphs [0074] to [0079] of JP-A-2009-109993. The haze of the high haze anti-glare film was 44%.

(Preparation of viewing side polarizing plate)
A low haze anti-glare film and a high haze anti-glare film were saponified according to the above (saponification of cellulose acylate film). Next, with respect to polarizing plate 1, polarizing plate 31 was produced by replacing the light scattering film layer with a saponified low haze anti-glare film, and polarizing plate 32 was produced by replacing the light scattering film layer with a high haze anti-glare film. In both polarizing plates, the surface of the anti-glare film that is bonded to the polarizing element is the surface on which the anti-glare layer is not laminated.

[Fabrication of liquid crystal display device]
Disassemble the LG Display monitor (32MP58HQ: equipped with a white LED sidelight type backlight, IPS mode liquid crystal cell), peel off the backlight side polarizing plate attached to the liquid crystal cell, and replace it with polarizing plate 12 according to Table 3. Alternatively, the inner protective film side of the polarizing plate 13 is pasted to the liquid crystal cell via an adhesive, the viewing side polarizing plate is peeled off, and the polarizing plate 31 or 32 is laminated with an anti-glare film instead. The opposite sides were bonded together, the diffusion sheet placed corresponding to the uppermost back side polarizing plate was removed, and reassembled to produce image display devices 31 to 33. The feeling of darkening was evaluated using the following evaluation method, and diagonal rainbow unevenness was evaluated using the same method as that used for image display device 1. The results are shown in Table 3.

(3-4) Feeling of jet blackness The panel was driven to display black in a typical home environment where a TV is used (approximately 200 Lx), and the feeling of jet blackness was visually confirmed using the following criteria.
A: The degree of black is very good.
B: Good level of black.
C: Some whitishness is felt, but it is within an acceptable range.
D: Noticeable whitishness.

The following is clear from the results shown in Table 3.
1. Although it is possible to reduce diagonal rainbow unevenness by combining a rear-side polarizing plate using a general-purpose stretched PET film as a protective film and a high haze anti-glare film on the viewing side, it is not sufficient to reduce the diagonal rainbow unevenness, and a new problem arises in which the black display becomes whitish. .
2. By using the polarizing plate of the present invention, it is possible to both prevent diagonal rainbow unevenness and achieve blackness (very good degree of blackness), which is preferable.

Claims (8)

A polarizing plate set used in a liquid crystal display device having a liquid crystal cell and a backlight,
comprising a viewing side polarizing plate placed on the viewing side of the liquid crystal cell, and a back side polarizing plate placed on the backlight side of the liquid crystal cell,
The viewing side polarizing plate includes a viewing side protective film,
The haze of the viewing side protective film is 0 to 5%,
The back side polarizing plate is
The polarizing element (P) includes a polarizing element (P) formed by adsorbing and aligning iodine to a polyvinyl alcohol resin layer, and a light scattering film is provided on the surface of the polarizing element (P) that becomes the backlight side when placed in the liquid crystal display device. A polarizing plate in which layers (DF) are laminated via an adhesive layer (AL1),
The light scattering film layer (DF) has a polyester resin stretched film as a base material, and has a light scattering layer (DL) on the polarizing element (P) side,
The light scattering layer (DL) is
1) Internal haze is 50-95%,
2) The surface unevenness has an arithmetic mean roughness Ra of 0 to 0.30 μm based on JIS B0601,
The light scattering film layer (DF) is further laminated with a back layer (BL) having an uneven surface shape on the side of the base material of the polyester resin stretched film on which the light scattering layer (DL) is not laminated. ,
A set of polarizing plates, wherein the surface unevenness of the back layer (BL) has an arithmetic mean roughness Ra of 0.10 to 1.50 μm based on JIS B0601. According to claim 1, in the back side polarizing plate, a protective film layer (PF2) is further laminated on the other surface of the polarizing element (P) via an adhesive layer (AL2). A set of polarizing plates. 3. The polarizing plate set according to claim 1, wherein the polyester resin stretched film has an in-plane retardation Re of 500 to 3000 nm. The polarizing plate set according to claim 1, wherein the light scattering layer (DL) is a layer in which particles having an average particle size of 0.5 to 6 μm are dispersed in a binder. 5. The polarizing plate set according to claim 4, wherein the binder is a curable binder containing a (meth)acrylic polyol and a polyfunctional isocyanate. 6. The polarizing plate set according to claim 1, wherein the back layer (BL) is a layer in which particles having an average particle size of 1 to 20 μm are dispersed in a binder. The polarizing plate set according to claim 1, wherein the back layer (BL) has a haze of 3 to 90%. 3. The polarizing plate set according to claim 2, wherein the adhesive layer (AL1 or AL2) is a PVA adhesive layer or an active energy ray-curable adhesive layer.