JP7261844B2 - Polarizing plate and liquid crystal display device - Google Patents

Description

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

2. Description of the Related Art In recent years, liquid crystal display devices (LCDs) have been widely used due to their thinness, light weight, and low power consumption. A liquid crystal display device has a liquid crystal panel member in which polarizing plates are attached to both sides of a liquid crystal cell with an adhesive, and display is performed by controlling light from a backlight member with the liquid crystal panel member. Here, the polarizing plate is composed of a polarizing element and protective films laminated on both sides thereof. A cellulose acylate film is mainly used as the protective film.

There is no end to the demand for further reduction in thickness and weight and cost reduction for such LCDs. As a proposal to meet these demands, among the polarizing plate protective films, the cellulose acylate film located on the outside when laminated to the LCD is replaced with a stretched polyethylene terephthalate film (hereinafter also referred to as a PET film), which is inexpensive and has excellent mechanical strength. ) has been attempted to replace

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

To address this problem, for example, in Patent Document 2, a stretched PET film is used as the outer protective film of the polarizing plate bonded to the back side of the liquid crystal cell, and a high haze prevention film is used as the protective film on the viewing side of the polarizing plate on the viewing side. A technique for reducing oblique iridescent unevenness by providing a glare layer is disclosed. However, even with this method, oblique iridescent unevenness is not sufficiently improved, and by laminating a high haze antiglare layer on the viewing side, there is a problem that the entire display screen, especially black display, looks whitish. can't In order to prevent whitishness of black display, it is essential to use a low-haze antiglare layer or a clear hard coat layer on the viewing side.

In Patent Document 3, in a liquid crystal display device using a white light emitting diode as a backlight light 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 a protective film for the emitted light It is described that the rainbow unevenness can be suppressed by using a polyester film having an in-plane retardation of 3000 to 30000 nm as a protective film on the exit light side of the polarizing plate (also referred to as the viewing side polarizing plate) arranged on the side. there is

However, although such polyester films are on the market, they are more expensive than general-purpose PET films, and are not suitable for cost reduction purposes. Furthermore, it is difficult to reduce the film thickness in order to obtain a high in-plane retardation as described above, and it is not suitable for thin and light applications.

JP 2010-107892 A JP 2009-109993 A International publication WO2011/162198 pamphlet

In view of the circumstances as described above, the problem of the present invention, that is, the problem to be solved by the present invention is to solve the problem of using a general-purpose PET film as a polarizing plate protective film in a liquid crystal display device equipped with the film, particularly a black display. In order to prevent whitishness, even if a surface film having a low haze antiglare layer or a clear hard coat layer is used on the viewing side, a polarizing plate with good visibility without problems such as oblique rainbow unevenness can be produced at a low cost. It is an object of the present invention to provide a polarizing plate with good visibility that can be manufactured in a single step, and further to provide a liquid crystal display device with good visibility on which such a polarizing plate is mounted.

The inventors of the present invention focused on the back-side polarizing plate of the two polarizing plates attached to both sides of the liquid crystal cell, and as a result of repeated extensive studies, it was found that the conventional polarizing plate manufacturing method was used to protect the polarizing plate. As a film, a stretched polyester film is used as a base material, a light scattering film having a specific light scattering layer is used, and a light scattering layer of the light scattering film and a polarizing element are bonded to each other, while using a general-purpose stretched PET. The present inventors have found that even if a low-haze film is used as the protective film for the polarizing plate on the viewing side, it is possible to inexpensively produce a polarizing plate having good visibility without iridescent unevenness, thereby completing the present invention.

The problem to be solved by the present invention can be solved by a polarizing plate having the following structure. That is, a polarizing element (P) in which iodine is adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a polyester resin-based stretched film is used as a base material on one surface of the polarizing element (P), and a light scattering layer (DL) is provided. A polarizing plate in which a light scattering film layer (DF) on the polarizing element side is laminated via an adhesive layer (AL1),
The light scattering layer (DL) is
1) an internal haze of 50 to 95%;
2) The surface unevenness has an arithmetic mean roughness Ra of 0 to 0.30 μm based on JIS B0601
A polarizing plate characterized by:

According to the present invention, it is possible to inexpensively provide a polarizing plate free from oblique iridescent unevenness in a liquid crystal display device equipped with a general-purpose PET film. 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 in which iodine is adsorbed and oriented in the polyvinyl alcohol (hereinafter also referred to as PVA) resin layer of the present invention. Such a polarizing element is generally formed by using a PVA-based resin film, dyeing the PVA-based resin film with iodine, and uniaxially stretching the film.

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

The manufacturing method of the polarizing element is not particularly limited, but there is a method in which a polyvinyl alcohol-based resin film wound in advance in a roll is sent out and then stretched, dyed, cross-linked, etc., and a polyvinyl alcohol-based resin and a resin substrate for stretching are used. A typical method includes a step of producing a laminate of the above and stretching the laminate. Any of these methods can be used in the present invention. Methods for manufacturing these polarizing elements are described in paragraphs [0109] to [0128] of JP-A-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, even more preferably 5 to 25 μm.

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

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

The polyester resin-based stretched film of the present invention can be produced according to a general method for producing a polyester film. For example, a polyester resin is melted and a non-oriented polyester film extruded into a sheet is stretched in the longitudinal direction using the speed difference between rolls at a temperature above the glass transition temperature, and then stretched in the transverse direction by a tenter. , and heat treatment.

The polyester film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but a biaxially stretched film is generally more preferable because of its higher mechanical strength. The uniaxially stretched film manufacturing method includes a method of performing heat treatment after stretching in either the longitudinal direction or the lateral direction using a tenter, in contrast to the stretching method described above.
The in-plane retardation Re of the polyester film thus obtained is usually 500 to 3000 nm.

The thickness of the polyester film of the present invention is preferably 5 to 200 μm, more preferably 10 to 100 μm, even more preferably 20 to 80 μm.

In the present invention, it is preferable that one side of the film of the present invention has an easy-adhesion layer mainly composed of a polyester resin, a polyurethane resin, or a polyacrylic resin, in order to improve adhesion to the light-scattering layer.

Commercially available stretched PET films with an easy-adhesion layer include "Cosmo Shine" (registered trademark) manufactured by Toyobo Co., Ltd. and "Lumirror" (registered trademark) manufactured by Toray Industries, Inc. Such a film can also be preferably used in the present invention.

(Light scattering layer)
A light scattering layer is laminated on the stretched polyester film. The light scattering layer has a light scattering agent and a binder. The light-scattering layer contains a light-scattering agent in a dispersed state to scatter the light passing through the polyester film, thereby preventing oblique iridescent unevenness.

Light-scattering agents are particles that have the property of scattering light rays, and are roughly divided into inorganic fillers and organic fillers. Inorganic fillers include, for example, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or mixtures thereof. Specific materials for the organic filler include, for example, acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, polyacrylonitrile, and silicone resin. Among them, highly transparent acrylic resins are preferred, and polymethyl methacrylate (PMMA) is particularly preferred.

The shape of the light scattering agent is not particularly limited. beads are preferred.

When an organic filler is used as the light scattering agent, the average particle size of the light scattering agent is preferably 0.5 to 6 μm, more preferably 1 to 6 μm, even more preferably 1 to 5 μm. If the light scattering agent has a thickness of less than 0.5 μm, a sufficient light scattering effect cannot be obtained. Conversely, if the thickness is 6 μm or more, the surface unevenness becomes large, and there is a possibility that the adhesiveness to the polarizing element is lowered.

When an organic filler is used as the light-scattering agent, the amount of the light-scattering agent (the amount in terms of solid content per 100 parts by mass of the polymer content in the polymer composition, which is the material for forming the binder) is preferably 5 to 100 parts by mass. , more preferably 10 to 70 parts by mass, more preferably 20 to 50 parts by mass. If the blending amount of the light scattering agent is less than the above lower limit, the light scattering properties may be insufficient. Conversely, if the blending amount of the light scattering agent exceeds the above upper limit, there is a risk that the surface unevenness will increase and adhesion to the polarizing element will not be successful.

The binder includes thermosetting resins and active energy ray-curable resins. The composition for forming the binder may also include, for example, fine inorganic fillers, curing agents, plasticizers, dispersants, various leveling agents, antistatic agents, ultraviolet absorbers, antioxidants, viscosity modifiers, Lubricants, light stabilizers, solvents and the like may be appropriately blended.

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

Examples of the polyol include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under conditions of excess hydroxyl groups, and the like, and these may be used alone or in combination of two or more. Can be mixed and used. 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, (Meth)acrylic polyols obtained from such monomers are particularly preferred. Specific examples and preferred aspects of polyols are described in paragraphs [0050] to [0057] of JP-A-2013-117695, and can be suitably used in the present invention as well.

When a polyol is used as the binder, it may contain at least one selected from polyfunctional isocyanate compounds, melamine compounds and aminoplast resins among compounds having two or more functional groups that react with the hydroxyl groups of the polyol. As a result, the polyol of the matrix resin of the binder is bound by a crosslinked structure, and storage stability, stain resistance, flexibility, weather resistance, storage stability and the like are improved.
Among the above compounds, polyfunctional isocyanates are particularly preferred in the present invention. As a combination with the base polymer, a combination of (meth)acrylic polyol and polyfunctional isocyanate is particularly preferred.
Specific examples of the compound having two or more functional groups that react with the hydroxyl groups of the polyol, preferred embodiments, etc. are described in paragraphs [0071] to [0078] of JP-A-2013-117695, and in the present invention, can also be suitably used.

Examples of the active energy ray-curable resin include ultraviolet-curable resins that are crosslinked and cured by irradiation with ultraviolet rays, electron beam-curable resins that are crosslinked and cured by irradiation with electron beams, and the like, and polymerizable monomers. and polymerizable oligomers. Among them, as the active energy ray-curable resin, a (meth)acrylic, urethane or (meth)acrylic urethane ultraviolet curable resin is preferable.

As the polymerizable monomer, a (meth)acrylate monomer having a radically polymerizable unsaturated group in the molecule is preferably used, and among them, polyfunctional (meth)acrylate is preferable. Polyfunctional (meth) acrylates and preferred embodiments are described in paragraphs [0026] to [0032] of JP-A-2013-228720, and can be suitably used in the present invention as well.

When an ultraviolet curable resin is used 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, examples include benzophenone, benzyl, Michler's ketone, and 2-chlorothioxanthone. , 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-hydroxycyclohexylphenyl ketone, 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. Polymerizable oligomers having a cationic 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, these compounds may be used individually, or may be used in combination.
Specific examples, preferred embodiments, commercial products, etc. of the photopolymerization initiator can be referred to in paragraphs [0064] to [0067] of JP-A-2014-170130.

<Optical Properties of Light Scattering Layer>
The haze value (internal haze value) of the light scattering layer in the invention is 50 to 95%, preferably 60 to 92%, particularly preferably 70 to 90%. Within this range, oblique 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, more preferably 0.05 to 0.05 μm. 22 μm is particularly preferred. By controlling the thickness within this range, good adhesiveness to the polarizing element can be obtained.

<Thickness of light scattering layer>
The thickness of the light scattering layer in the invention is preferably 3 to 30 μm, more preferably 5 to 20 μm, particularly preferably 6 to 15 μm. By controlling the content 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 composition for the light-scattering layer is not particularly limited, and various known methods are employed. As specific lamination means, for example, coating using a gravure coating method, a roll coating method, a bar coating method, a blade coating method, a spray coating method, or the like is adopted. Among them, the gravure coating method is most preferable because the polymer composition of the beads can be coated thinly and evenly. In such a gravure coating method, the number of gravure lines is preferably 70 or more and 100 or less, and the number of revolutions is preferably 80 or more and 120 or less, in consideration of the formability of the light scattering layer.

(Back side of light scattering film)
It is also a preferred embodiment that the back surface of the light-scattering film (the surface of the substrate on which the light-scattering layer is not laminated) is laminated with an anti-sticking layer or a light-diffusing layer having surface irregularities and a haze of 10% or more. is.
A prism sheet is often installed under the rear-side polarizing plate for the purpose of condensing light. This prism sheet may interfere with pixels and cause moire. By laminating a light diffusion layer on the back surface of the light scattering film as described above, it is possible to impart a moiré prevention effect, which is preferable. In some cases, a diffusion sheet is installed to prevent moire caused by a prism sheet. However, by laminating a light diffusion layer on the back surface of the light scattering film, the diffusion sheet can be omitted, and the thickness of the image display device can be reduced. This is preferable from the viewpoint of cost reduction.

[Layer structure of polarizing plate]
The polarizing plate of the present invention may be a polarizing plate having a protective film on only one surface of the polarizing element or a polarizing plate having protective films on both surfaces 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/polarizer anti-sticking layer/polyester film/light scattering layer/adhesive layer/polarizer light diffusion layer/polyester film/light scattering layer/adhesive layer/polarizer polyester film/ Light scattering layer/adhesive layer/polarizing element/adhesive layer/protective film anti-sticking layer/polyester film/light scattering layer/adhesive layer/polarizing element/protective film light diffusing layer/polyester film/light scattering layer/adhesive Layer/polarizer/protective film

[Another protective film]
When the polarizing plate of the present invention has protective films on both sides, the other protective film may be a cellulose acylate film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, ) A film such as an acrylic polymer film can be used, but when laminating using a water-based adhesive such as a PVA adhesive, a cellulose acylate film or (meth)acrylic polymer is used in terms of moisture permeability. Any film is preferable, and a cellulose acylate film is particularly preferable.

The film 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 be reduced and the processability will be poor. A suitable film thickness is 5 to 100 μm, preferably 10 to 80 μm, more preferably 15 to 70 μm.

Also, from the viewpoint of optical compensation, it is preferable that there is no excess birefringence. Examples of cellulose acylate films satisfying such conditions include Fujitac ZRD (manufactured by Fuji Film Co., Ltd.), which can be preferably used in the present invention.

[Method for preparing polarizing plate]
Next, a method for producing the polarizing plate of the present invention will be described.

(Lamination of polarizing element (P) and light scattering film (DF))
The polarizing plate of the present invention can be produced by laminating one surface of the polarizing element (P) and the light scattering layer (DL) surface of the light scattering film (DF) via the adhesive layer (AL1). Any appropriate 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 type, or the like can be used.
The same adhesive used for bonding the light scattering film (DF) can also be used for bonding the other surface of the polarizing element (P) and the protective film layer (PF2).

As the active energy ray-curable adhesive, any appropriate adhesive can be used as long as it is an adhesive that can be cured by irradiation with an active energy ray. Examples of active energy ray-curable adhesives include ultraviolet-curable adhesives and electron beam-curable adhesives. Specific examples of curing types of active energy ray-curable adhesives include radical curing, cationic curing, anionic curing, and combinations thereof (for example, hybrids of radical curing and cationic curing).

As the active energy ray-curable adhesive, for example, an adhesive containing a compound (for example, a monomer and/or an oligomer) having a radically polymerizable group such as a (meth)acrylate group or a (meth)acrylamide group as a curing component. is mentioned.
Specific examples of the active energy ray-curable adhesive and its curing method are described, for example, in JP-A-2012-144690.

Any appropriate water-based adhesive may be employed as the water-based adhesive. Among them, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100-5500, more preferably 1000-4500, 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 adhesion.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the adhesiveness between the PVA-based resin layer and the protective film can be excellent, and the durability can be excellent. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by any method. The acetoacetyl group modification degree of the acetoacetyl group-containing PVA resin is typically 0.1 mol % or more, preferably about 0.1 mol % to 4 mol %.

The resin concentration of the water-based adhesive is preferably 0.1 wt % to 15 wt %, more preferably 0.5 wt % to 10 wt %.
The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer having a desired thickness is obtained after curing or after 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, most preferably 0.01 μm to 1 μm.

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

In the case where the polarizing plate of the present invention has protective films on both sides of the polarizing element, the protective films may be laminated on one side or both sides at the same time, but both sides are preferably laminated at the same time.

[Liquid crystal display device]
The liquid crystal display device of the present invention comprises a liquid crystal cell, a polarizing plate of the present invention arranged on the backlight side of the liquid crystal cell (back side polarizing plate), and a polarizing plate arranged on the viewing side (viewing side polarizing plate). characterized by comprising In the liquid crystal display device of the present invention, the viewing side polarizing plate is not particularly limited, 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%. 0 to 5% is particularly preferred. By controlling the haze of the viewer side protective film within this range, it is possible to achieve both oblique iridescent unevenness prevention and black tightness.

(Composition of a general liquid crystal display device)
A liquid crystal display device comprises a liquid crystal cell holding a liquid crystal between two electrode substrates, two polarizing plates disposed on both sides of the cell, and optionally between the liquid crystal cell and the polarizing plates. It has a structure in which at least one optical compensation film is arranged. The polarizing plate of the present invention can be used as the rear polarizing plate of the two polarizing plates.
A liquid crystal layer of a liquid crystal cell is usually formed by enclosing a liquid crystal in a space formed by sandwiching a spacer between two substrates. A transparent electrode layer is formed on a substrate as a transparent film containing a conductive material. The liquid crystal cell may further have a gas barrier layer, a hard coat layer or an undercoat layer (used for adhering the transparent electrode layer). These layers are typically provided on a substrate. The substrates of liquid crystal cells generally have 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 of various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroelectric Liquid Crystal), OCB (Optical Compensatory Bend), STN (Super Twisted Vendor) ally aligned), Various display modes have been proposed, such as ECB (Electrically Controlled Birefringence) and HAN (Hybrid Aligned Nematic). Further, a display mode in which the above display mode is divided in orientation has also been proposed. The polarizing plate of the present invention is effective in liquid crystal display devices of any display mode. Also, it can be used in any of transmissive, reflective, and transflective liquid crystal display devices.

When the polarizing plate of the present invention is adhered to the back surface of the IPS mode liquid crystal cell, light leakage when viewed from an oblique direction during black display is suppressed, which is particularly preferable.

The present invention will be specifically described based on examples below. The materials, reagents, amounts and ratios of substances, operations, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Accordingly, the present invention is limited and not restricted to the following examples.

[Preparation of light scattering film]
(Preparation of polyester resin stretched film substrate)
A biaxially stretched PET film with an easily adhesive layer having a film thickness of about 38 μm was obtained in the same manner as in WO2011/162198 [0076] (Comparative Example 1). This film had an in-plane retardation Re of 1178 nm and a haze of 0.2%.

(Lamination of light scattering layer)
As a light scattering polymer composition containing a light scattering agent and a binder, a polymer composition consisting of 43 parts of acrylic polyol (base polymer), 21 parts of PMMA particles having an average particle size of 2 μm, 6 parts of an isocyanate curing agent, and a solvent is used. board. The number of parts indicating the blending amount of each composition is the mass ratio in terms of solid content. A light-scattering film 1 was obtained by laminating 10 g/m ² (solid content conversion) of the polymer composition for light-scattering layer on the surface of the base material layer by a gravure coating method.

The light diffusion layer was evaluated according to the following [Evaluation method for light scattering layer]. The light scattering layer had an internal haze of 80% and an arithmetic mean roughness Ra of 0.16 μm.

Light-scattering films 2 to 9 were prepared by changing the size of the light-scattering agent particles, the amount of the light-scattering agent particles, and the thickness of the light-scattering layer with respect to the light-scattering film 1, and evaluated in the same manner as the light-scattering film 1. Table 1 shows the results.

Light-scattering film 10 was prepared in the same manner as light-scattering film 1 except that polyester polyol was used as the base polymer instead of acrylic polyol, and was evaluated in the same manner as light-scattering film 1. Table 1 shows the results.

Light-scattering film 11 was prepared in the same manner as light-scattering film 1 except that the cross-linking agent was changed from polyfunctional isocyanate to a melamine compound, and was evaluated in the same manner as light-scattering film 1. Table 1 shows the results.

[Evaluation method of light scattering layer]
(1-1) Haze [1] The total haze value (H) of the obtained light diffusion film is measured according to JIS-K7136: A haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used.
[2] The light-scattering polymer composition was applied to the surface of the light-scattering film by using a bar coater to smooth the surface at about 2 g/m ² (in terms of solid content) to prepare a film from which the surface haze was removed. This film was measured in the same manner as above to obtain an internal haze value (Hin).

(1-2) Surface shape of light scattering layer (arithmetic mean roughness Ra)
Measured according to JIS-B0601 (1994, 2001) using a surfcoder MODEL SE-3500 manufactured by Kosaka Laboratory Co., Ltd.

[Preparation of polarizing plate]
Next, a polarizing plate is produced using the light diffusion films 1 to 11 produced above and a biaxially stretched PET film having no light scattering layer laminated thereon.

(Fabrication of polarizing element)
A PVA film having an average degree of polymerization of 2400 and a degree of saponification of 99.9 mol % and a thickness of 40 μm was immersed in hot water at 25° C. for 120 seconds to swell. Then, the PVA film was dyed while being immersed in an aqueous solution of 0.6% by weight of iodine/potassium iodide (weight ratio=2/3) 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 prepare a polarizing element with a film thickness of 15 μm.

(Preparation of Adhesive for Polarizing Plate)
A modified PVA-based resin containing an acetoacetyl group (Gohsenex Z-410, manufactured by Nippon Synthetic Chemical Co., Ltd.) was dissolved in water to prepare an aqueous solution A adjusted to a solid concentration of 3%. Then, maleic acid was added to the aqueous solution A so as to be 0.5% by weight, and then glyoxal was added as a cross-linking agent. The amount of glyoxal added was 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 a polarizing plate.

(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 in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at 55° C. for 2 minutes, and then the film was removed. After washing with water, the film was 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 neutralize the film. Then, water was removed by an air knife three times, and after water was removed, the film was dried by staying in a drying zone at 70° C. for 15 seconds to prepare a saponified film.

(Preparation of polarizing plate)
After corona-treating the surface of the light-scattering layer of the light-scattering film prepared above, 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 adhesive layer had a thickness of 150 nm after drying.
Next, the light-scattering film and the cellulose acylate film having the above-mentioned adhesive applied to both sides of the polarizing element were laminated by a roll machine, and then dried at 60° C. for 10 minutes to obtain the polarizing plate 1 according to the present invention. .

Polarizing Plates 2 to 11 were produced by changing the type of the light scattering film and the bonding surface of the polarizing element to the polarizing plate 1 as shown in Table 2, and evaluated according to the following evaluation methods. Table 2 shows the results. In the polarizing plate 12, the light scattering film 1 was bonded to the polarizing element on the opposite side of the light scattering layer laminated surface. The polarizing plates 12 and 13 have only outer protective films and no inner protective films. Moreover, the polarizing plates 11 and 13 used biaxially stretched PET without a light scattering layer as an outer protective film instead of the light scattering film.

[Evaluation method of polarizing plate]
(2-1) Oblique rainbow unevenness A backlight with a white LED as a light source is prepared, and the polarizing plate prepared above is placed on it so that the ZRD40 side is on the backlight side. Observation was made in all directions at 45 degrees, and rainbow unevenness was evaluated in 6 stages according to the following criteria.
⊚: Rainbow unevenness is not seen at all at a polar angle of 60 degrees and at a polar angle of 45 degrees.
Good: Rainbow unevenness can be recognized at a polar angle of 60 degrees, but is hardly visible. At a polar angle of 45 degrees, no rainbow unevenness is visible.
Δ: Rainbow unevenness can be recognized at a polar angle of 60 degrees, but is not noticeable. At a polar angle of 45 degrees, no rainbow unevenness is visible.
x: Rainbow unevenness appears thin at a polar angle of 60 degrees. Rainbow unevenness is not visible when the polar angle is 45 degrees.
XX: Rainbow unevenness is clearly visible. Rainbow unevenness can be recognized when the polar angle is 45 degrees.
XXX: Rainbow unevenness is clearly visible. It is clearly visible even at a polar angle of 45 degrees.

(2-2) Adhesiveness Adhesiveness by manual peeling was evaluated according to the following criteria.
⊚: No peeling at all.
◯: Peeling occurs, but strong force is required.
x: Easily peeled off.

※偏光板１２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／保護フィルム

*The polarizing plate 12 is laminated with the light scattering film on the opposite side to the polarizing element. The configuration is as follows.
Light scattering layer/Polyester film/Adhesive layer/Polarizing element/Protective film

The results shown in Table 2 reveal the following.
1. When a general-purpose stretched PET film is used as the polarizing plate protective film, oblique iridescent unevenness occurs.
2. By providing a light scattering layer having an internal haze of 50 to 95% between the stretched PET and the polarizing element, oblique iridescent unevenness can be prevented.
3. The same oblique iridescent unevenness prevention effect can be obtained regardless of the presence or absence of the inner protective film.
4. When the light scattering layer is provided outside the polarizing plate, there is no effect of preventing iridescent unevenness.
5. If the surface Ra of the light scattering layer is 0.30 μm or less, the adhesiveness to the polarizing element is good, but if it exceeds 0.30 μm, sufficient adhesiveness may not be obtained.
6. If particles having an average particle diameter of more than 5 μm are used, Ra may exceed 0.30, and sufficient adhesion may not be obtained.
7. If a polyol other than an acrylic polyol is used as the basic polymer, or if a compound having two or more functional groups that react with the hydroxyl groups of the polyol other than the polyfunctional isocyanate is used as the cross-linking agent, the adhesive strength may decrease.

[Fabrication of liquid crystal display device]
LG Display monitor (32MP58HQ: white LED sidelight type backlight) is disassembled, the backlight side polarizing plate attached to the liquid crystal cell is peeled off, and polarizing plates 1 to 13 are laminated with a light scattering film instead. The non-bonded side was adhered to the liquid crystal cell via an adhesive, and assembled again to produce image display devices 1 to 13. It was evaluated according to the following evaluation methods. Table 3 shows the results.
In the image display device 9, since the polarizing plate was peeled off when the adhesive was attached, the oblique iridescent unevenness could not be evaluated.

[Evaluation method of polarizing plate]
(3-1) Oblique rainbow unevenness The monitor was set to display white, and the screen was obliquely observed in all directions at polar angles of 60 degrees and 45 degrees.
⊚: Rainbow unevenness is not seen at all at a polar angle of 60 degrees and at a polar angle of 45 degrees.
Good: Rainbow unevenness can be recognized at a polar angle of 60 degrees, but is hardly visible. At a polar angle of 45 degrees, no rainbow unevenness is visible.
Δ: Rainbow unevenness can be recognized at a polar angle of 60 degrees, but is not noticeable. At a polar angle of 45 degrees, no rainbow unevenness is visible.
x: Rainbow unevenness appears thin at a polar angle of 60 degrees. Rainbow unevenness is not visible when the polar angle is 45 degrees.
XX: Rainbow unevenness is clearly visible. Rainbow unevenness can be recognized when the polar angle is 45 degrees.
XXX: Rainbow unevenness is clearly visible. It is clearly visible even at a polar angle of 45 degrees.

The results shown in Table 3 clearly show the following.
1. When a general-purpose stretched PET film is used as the polarizing plate protective film, oblique iridescent unevenness occurs.
2. By providing a light scattering layer having an internal haze of 50 to 95% between the stretched PET and the polarizing element, oblique iridescent unevenness can be prevented.
3. The same oblique iridescent unevenness prevention effect can be obtained regardless of the presence or absence of the inner protective film.
4. When the light scattering layer is provided outside the polarizing plate, there is no effect of preventing iridescent unevenness.

Next, the relationship between white blurring (whitishness at the time of black display) and oblique iridescent unevenness prevention and superiority of the present invention when using a conventional high-haze antiglare film will be described.

(Preparation of low haze antiglare film)
A low haze antiglare 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 antiglare film was 3%.

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

(Preparation of viewing side polarizing plate)
The low haze antiglare film and the high haze antiglare film were saponified according to the above (Saponification of cellulose acylate film). Next, polarizing plate 21 was prepared by replacing the light scattering film with a saponified low haze antiglare film, and polarizing plate 22 was prepared by replacing the light scattering film with a high haze antiglare film. In any polarizing plate, the surface of the antiglare film bonded to the polarizing element is the surface on which the antiglare layer is not laminated.

[Fabrication of liquid crystal display device]
Disassemble the LG Display monitor (32MP58HQ: equipped with a white LED sidelight type backlight), peel off the backlight side polarizing plate attached to the liquid crystal cell, and replace the polarizing plate 1 or polarizing plate 13 according to Table 4. , The inner protective film side is attached to the liquid crystal cell via an adhesive, the polarizing plate on the viewing side is peeled off, and polarizing plate 21 or polarizing plate 22 is attached instead, and the side on which the antiglare layer film is not laminated is attached. They were combined and reassembled to produce image display devices 21-23. The black tight feeling was evaluated by the following evaluation method, and the oblique iridescent unevenness was evaluated by the same method as for the image display devices 1 to 15. Table 4 shows the results.

(3-2) Feeling of tight blackness The panel was driven in black display in a general household environment (about 200 Lx) where TVs are generally used, and the feeling of jet blackness was visually confirmed according to the following criteria.
A: The degree of blackness is very good.
B: Good degree of blackness.
C: Slightly whitish, but within the allowable range.
D: Whiteness is conspicuous.

The results shown in Table 4 reveal the following.
1. When a back polarizing plate using a general-purpose stretched PET film as a protective film is combined with a high-haze antiglare film on the viewing side, oblique iridescent unevenness can be reduced, but this is not sufficient. .
2. By using the polarizing plate of the present invention, both iridescent unevenness and blackness can be achieved, which is preferable.

Claims (9)

A polarizing plate set used in a liquid crystal display device having a liquid crystal cell,
Equipped with a viewing-side polarizing plate and a back-side polarizing plate,
The viewer-side polarizing plate includes a viewer-side protective film and a polarizing element ,
The haze of the viewing side protective film is 0 to 5%,
The back-side polarizing plate includes a polarizing element (P) formed by adsorbing and aligning iodine in a polyvinyl alcohol-based resin layer, and a polyester resin-based stretched film on one surface of the polarizing element (P) as a base material, which scatters light. A polarizing plate in which a light scattering film layer (DF) having a layer (DL) on the polarizing element side is laminated via an adhesive layer (AL1),
The light scattering layer (DL) is
1) an internal haze of 50 to 95%;
2) The surface unevenness has an arithmetic mean roughness Ra of 0 to 0.30 μm based on JIS B0601,
In the liquid crystal display device, the viewing-side polarizing plate is arranged on the viewing side of the liquid crystal cell so that the polarizing element and the viewing-side protective film are positioned in this order from the side closer to the liquid crystal cell,
In the liquid crystal display device, the back-side polarizing plate is arranged on the backlight side of the liquid crystal cell so that the polarizing element and the light scattering film layer are positioned in this order from the side closer to the liquid crystal cell. A set of polarizing plates characterized by: 2. The set of polarizing plates according to claim 1, wherein a protective film layer (PF2) is further laminated on the other surface of the polarizing element (P) via an adhesive layer (AL2). 3. The set of polarizing plates according to claim 1, wherein the stretched film has an in-plane retardation Re of 500 to 3000 nm. 4. 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 set of polarizing plates according to claim 4, wherein the binder is a curable binder containing (meth)acrylic polyol and polyfunctional isocyanate. 5. The set of polarizing plates according to claim 4, wherein the binder is an active energy ray-curable resin. 7. The set of polarizing plates according to claim 1, wherein the adhesive layer (AL1 or AL2) is a PVA-based adhesive layer or an active energy ray-curable adhesive layer. 3. The set of polarizing plates according to claim 2, wherein the protective film layer (PF2) is a cellulose acylate film having a thickness of 5 to 100 μm. A liquid crystal display device equipped with the set of polarizing plates according to any one of claims 1 to 8.