JP2014197116A - Liquid crystal display device, polarizing plate, and polarizer protection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a liquid crystal display device which offers good visibility and can be suitably made thinner; a polarizing plate suitable for the same; and a polarizer protection film constituting the polarizing plate.SOLUTION: A liquid crystal display device includes a backlight unit, a liquid crystal cell, and a polarizing plate located on each side of the liquid crystal cell. Each of the two polarizing plates has a polarizer protection film laminated on each surface thereof, of which at least one is a polyethylene naphthalate film having a retardation of 3,000-30,000 nm and a ΔNxy of no less than 0.15.

Description

  The present invention relates to a liquid crystal display device having good visibility and suitable for thinning, a polarizing plate suitable for the liquid crystal display device, and a polarizer protective film constituting the polarizing plate.

  A liquid crystal display device has polarizing plates on both sides of a liquid crystal cell, and displays an image or the like by a backlight having a light source such as a cold cathode fluorescent lamp (hereinafter referred to as CCFL) or a light emitting diode (hereinafter referred to as LED). Device.

  The polarizing plate is composed of a film called a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. In general, the polarizer protective film is composed of a triacetyl cellulose (hereinafter referred to as TAC) film.

  In recent years, with the thinning of LCDs, there has been a demand for thinner polarizing plates. Thereby, it was desired to reduce the thickness of the polarizer protective film, but when the polarizer protective film is a TAC film, sufficient mechanical strength cannot be obtained, and there is a problem such as being easily permeable to moisture. Due to its high price, an inexpensive alternative material has been strongly desired.

  In response to the above problems, it has been proposed to use a polyester film as an alternative material. (Patent Documents 1 to 4)

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A Japanese Patent No. 4926661

  Polyester film is promising as an alternative material because of its high mechanical strength and low moisture permeability compared to TAC film. However, the effect of optical anisotropy is likely to be manifested by thinning, and in a liquid crystal display device. There has been a problem that color unevenness and the like are easily recognized when observed from an oblique direction with respect to the vertical direction of the display surface.

  With respect to the above problems, Patent Documents 1 to 3 have taken measures to reduce optical anisotropy by using a copolyester as the polyester, but have not yet solved color unevenness.

  As shown in Patent Document 4, the pioneer intensively studied, and as a result, focused on the birefringence of the polyester film and the emission spectrum of the backlight, and came to elucidate the generation mechanism. That is, CCFL and LED are white light composed of a plurality of wavelengths, and when the white light passes through the polyester film, the phase difference (hereinafter referred to as retardation) with respect to each wavelength due to the birefringence of the polyester film. It was found that the intensity of light of each wavelength changes due to interference, and this is recognized as color unevenness. And it discovered that said subject could be improved by using combining the specific backlight light source and the polyester film which has a specific retardation.

  However, there have been cases where it has not been possible to fully meet the demand for further thinning of the polarizer protective film.

  As a result of intensive studies based on the invention disclosed in Patent Document 4, the present inventor obtained a film that can be adapted for further thinning of the polarizer protective film when a polyethylene naphthalate film is used. It was found that this problem can be solved. Based on such knowledge, the present inventors have repeated further studies and completed the present invention.

The representative present invention is as follows.
Item 1.
A backlight, a liquid crystal cell, and two polarizing plates disposed on both sides of the liquid crystal cell;
Each of the two polarizing plates has a polarizer protective film laminated on both sides of the polarizer,
At least one of the polarizer protective films is a polyethylene naphthalate film,
The polyethylene naphthalate film has a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more.
Liquid crystal display device.
Item 2.
Item 2. The liquid crystal display device according to item 1, wherein the polyethylene naphthalate film has a thickness of 100 µm or less.
Item 3.
Item 3. The liquid crystal display device according to item 1 or 2, wherein a ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the polyethylene naphthalate film is 0.2 or more and 1.2 or less.
Item 4.
A polarizing plate for a liquid crystal display device, wherein a polyethylene naphthalate film having a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more is disposed on at least one surface of the polarizer.
Item 5.
Item 5. The polarizing plate according to Item 4, wherein the polyethylene naphthalate film has a thickness of 100 µm or less.
Item 6.
A polarizer protective film for a liquid crystal display device comprising a polyethylene naphthalate film having a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more.
Item 7.
Item 7. The polarizer protective film for a liquid crystal display device according to item 6, having a thickness of 100 μm or less.

  The liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention can ensure visibility without color unevenness even when the display surface of the liquid crystal display device is observed from an oblique direction. Moreover, the polarizing plate and the polarizer protective film of the present invention have a mechanical strength suitable for thinning. Therefore, according to the present invention, it is possible to provide a liquid crystal display device that is excellent in visibility and thinner.

  The liquid crystal display device of the present invention is a device in which polarizing plates are arranged on both surfaces of a liquid crystal cell, and an image or the like is displayed by a backlight using CCFL, LED or the like as a light source. The polarizing plate is composed of a film called a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. The liquid crystal display device may appropriately include, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like as other constituent members.

  The configuration of the backlight may be an edge light method using a light guide plate or a reflection plate as a constituent member, or may be a direct type, but in the present invention, it is a continuous light source for a liquid crystal display device. It is preferable to use a white light source having a broad emission spectrum.

“Continuous and broad emission spectrum” means an emission spectrum in which there is no wavelength region where the light intensity becomes zero in the wavelength region of at least 450 to 650 nm, preferably in the visible light region. The visible light region is, for example, a wavelength region of 400 to 760 nm, and may be 360 to 760 nm, 400 to 830 nm, or 360 to 830 nm.

As a white light source having a continuous and broad emission spectrum, for example, a white light emitting diode (white LED) can be exemplified. The white LED includes a phosphor type (that is, an element that emits white light by combining an LED emitting blue light or ultraviolet light using a compound semiconductor and a phosphor) and an organic light-emitting diode (OLED). Etc. In addition, phosphors include yellow phosphors of yttrium, aluminum, and garnet, and yellow phosphors of terbium, aluminum, and garnet. Blue LEDs using compound semiconductors and yttrium, aluminum, and garnet yellow phosphors A white LED composed of a light emitting element in combination with the above has a continuous and broad emission spectrum and is excellent in luminous efficiency, and thus energy saving can be expected.

  A fluorescent tube such as CCFL widely used as a conventional backlight light source has a peak at a specific wavelength and has a discontinuous emission spectrum, so that the effects of the present invention may not be sufficiently obtained. is necessary.

  The polarizing plate of the present invention comprises a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. At least one of the polarizer protective films preferably has a specific retardation. As a resin constituting such a polarizer protective film, a resin in which a cyclic monomer that can be expected to have a high refractive index is arranged on the main chain and / or side difference is considered. Therefore, it is preferable to use polyethylene naphthalate having a naphthalene ring as an acid component, which has a large intrinsic birefringence and a large retardation even when the film is thin.

  The polyethylene naphthalate film used as the polarizer protective film preferably has a retardation of 3,000 to 30,000 nm. When the retardation is less than 3,000 nm, when used as a polarizer protective film, strong color unevenness occurs when observed from an oblique direction, and good visibility cannot be ensured. The lower limit of the preferred retardation is 4,500 nm, the next preferred lower limit is 5,000 nm, the more preferred lower limit is 6,000 nm, the still more preferred lower limit is 8,000 nm, and the still more preferred lower limit is 10,000 nm.

  On the other hand, the upper limit of retardation is 30,000 nm. Even if a film having a higher retardation is used, the effect of improving the visibility is not substantially obtained, and the thickness of the film is considerably increased, so that the handleability as an industrial material is lowered. is there.

  The retardation described above can be obtained by measuring the refractive index and thickness in the biaxial direction, or can be obtained using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments). .

  The polyethylene naphthalate film having the specific retardation can be used as an arbitrary polarizer protective film in a liquid crystal display device. Preferably, the polyethylene naphthalate film is a polarizer protective film on the light source side of a polarizing plate (hereinafter also referred to as “light source side polarizing plate”) disposed on the light source side of the liquid crystal, or on the viewing side of the liquid crystal cell. It is preferable to be used as a viewing-side polarizer protective film for a polarizing plate (hereinafter also referred to as “viewing-side polarizing plate”). More preferably, the polyethylene naphthalate film is a polarizer protective film disposed on the viewing side of the viewing side polarizing plate. When the polyethylene naphthalate film is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed.

  On the other hand, it is preferable to use a film having no retardation such as a TAC film, an acrylic film, or a norbornene resin film as the polarizer protective film not using the polyethylene naphthalate film having the specific retardation. For example, a film having no such retardation can be used as a viewing-side polarizer protective film constituting the light source-side polarizing plate and / or a light source-side polarizer protecting film constituting the viewing-side polarizing plate.

  Polyethylene naphthalate has an effect of absorbing light having a wavelength of 380 nm, which degrades iodine compound molecules constituting the polarizer. Therefore, it is preferable to use a polyethylene naphthalate film as a polarizer protective film also from this viewpoint.

  Such a polyethylene naphthalate has problems in terms of film forming stability and fracture resistance when the intrinsic viscosity is low, and therefore the intrinsic viscosity is preferably 0.55 dl / g or more, and more preferably, 0.1%. 60 dl / g or more. On the other hand, when the intrinsic viscosity is high, a problem arises from the viewpoint of extrudability and the like.

  In order to facilitate the stretching described later, addition of polyester resin monomers and copolymerization of polyethylene naphthalate with polyethylene naphthalate do not hinder the effects of the present invention and do not impair the transparency. Is possible.

  The polyethylene naphthalate film used as a polarizer protective film desirably has a light transmittance of 380 nm at a wavelength of 20% or less, more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less. . In order to control the light transmittance at 380 nm of the polyethylene naphthalate film in this way, an ultraviolet absorber can be added to the polyethylene naphthalate within a range not impeding the effects of the present invention. Further, for example, inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants, anti-gelling agents, and A surfactant or the like can also be added to polyethylene naphthalate as long as the effects of the present invention are not impaired and the transparency is not impaired.

  A polyethylene naphthalate film having a specific retardation can be obtained by any method. For example, polyethylene terephthalate is melt extruded at a temperature higher than its melting point, which is basically 1.0 to 3.5 times in the machine direction (MD) and / or 3 in the cross direction (TD). After stretching by 0.0 to 6.0 times, heat treatment is performed mainly for the purpose of dimensional stability and the like, and a polyethylene naphthalate film suitable for a polarizer protective film can be obtained. In addition, polyethylene naphthalate mixed with additives, particles, and the like within a range that does not impair the performance during extrusion is a known method such as a combining adapter method, a multi-slot method, or a multi-manifold method, for example, A / B It is also possible to have a laminated structure such as a two-type two-layer configuration, a two-type three-layer configuration of B / A / B configuration, and a three-type three-layer configuration of C / A / B.

  Furthermore, the polarizer protective film has an easy-adhesion layer mainly composed of at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin on at least one surface in order to improve the adhesion to the polarizer. Is preferred. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer.

  The coating liquid for the easy-adhesion layer formed on the polarizer protective film is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. As these coating liquids, water-soluble or water-dispersible properties disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191 and Japanese Patent No. 4150982 are disclosed. Examples thereof include a copolymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

  The easy adhesion layer formed on the polarizer protective film is a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, The known methods such as these can be applied alone or in combination.

  The polyethylene naphthalate film can be obtained according to a general method for producing a polymer film. For example, after polyethylene naphthalate is melted and an unoriented sheet is obtained by extrusion, MD stretching using a difference in roll speed and TD stretching by a tenter are performed alone at a temperature equal to or higher than the glass transition temperature of polyethylene naphthalate. Or the method of performing heat processing after performing in combination can be illustrated.

  The method for producing the polyethylene naphthalate film is not limited to the above-described method, but in the case of a biaxially stretched film, color unevenness is observed when observed obliquely with respect to a direction perpendicular to the surface of the polarizer protective film. From the viewpoint of eliminating color unevenness, simple uniaxial TD stretching is preferable, and MD relaxation is more preferable simultaneously with TD stretching. Although simple uniaxial MD stretching is possible, there are problems such as easy stretching unevenness, and attention is required.

  Specifically, in general, a facility called a simultaneous biaxial stretching machine is used, and a method of performing heat treatment after simultaneously performing TD stretching and MD stretching or a method of performing MD relaxation simultaneously with TD stretching and then performing heat treatment. A method can be exemplified. In this case, it is preferable that the MD relaxation magnification is 0.5 to 0.9 times, more preferably 0.65 to 0.8 times, taking into account the thickness unevenness. By setting the MD relaxation magnification in this way, the thermal shrinkage rate of the film can be suppressed.

  On the other hand, from the viewpoint of eliminating color unevenness, if the uniaxial symmetry is increased, the mechanical strength in the direction perpendicular to the axis may be lowered, so care must be taken.

  As shown in Patent Document 4, the pioneer maintains the mechanical strength of the protective film by controlling the ratio of the retardation of the polarizer protective film and the retardation in the thickness direction to be within a specific range, It has been found that the occurrence of color unevenness is suppressed. The retardation in the thickness direction is an average retardation (Rth) obtained by multiplying the two birefringences ΔNxz and ΔNyz by the film thickness d when the film is viewed from the cross section in the thickness direction. In addition, the retardation described so far is a retardation when viewed from the surface direction of the film, and is a retardation (Re) obtained by multiplying the birefringence ΔNxy by the film thickness d.

  ΔNxy is a birefringence generated by light incident on the film surface (xy plane) when the vertical direction of the polyethylene naphthalate film is the x-axis and the horizontal direction is the y-axis, and the refractive index in the x-axis direction. And the difference in refractive index in the y-axis direction (ΔNxy = | Nx−Ny |). The higher the birefringence ΔNxy is, the larger the retardation that can be obtained even with a thin film. However, when the birefringence ΔNxy is too high, the ratio of retardation and thickness direction retardation (Re / Rth) described later increases. Therefore, the birefringence ΔNxy needs to be set from the viewpoint of mechanical strength, and is preferably less than 0.3, more preferably less than 0.27, still more preferably less than 0.25, and even more preferably less than 0.24. . On the other hand, if the birefringence index ΔNxy is low, it is necessary to increase the film thickness in order to increase the retardation. Therefore, the birefringence index ΔNxy is preferably 0.15 or more, more preferably 0.16 or more, and even more preferably. Is 0.17 or more, more preferably 0.18 or more, and particularly preferably 0.20 or more.

  In polyethylene terephthalate film, it is technically difficult to adjust the birefringence ΔNxy to 0.15 or more and the ratio of retardation to thickness direction retardation (Re / Rth) to be in the range of 0.2 to 0.12. is there. With polyethylene naphthalate, the birefringence ΔNxy and the ratio of retardation to thickness direction retardation (Re / Rth) can be adjusted to the above range relatively easily, so that even a thin film can increase the retardation. In addition, a polarizer protective film excellent in mechanical strength can be obtained.

  From the optical viewpoint, the ratio of retardation of the polyethylene naphthalate film to the retardation in the thickness direction (Re / Rth) is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. . The larger the ratio (Re / Rth), the more the birefringence becomes isotropic, and the occurrence of color unevenness due to observation from an oblique direction is less likely to occur.

  On the other hand, the ratio of the retardation of the polyethylene naphthalate film to the thickness direction retardation (Re / Rth) is preferably 1.2 or less, more preferably 1.0 or less, from the viewpoint of mechanical strength. In a film having perfect uniaxial symmetry, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2.0. The larger the uniaxial symmetry, the stronger the uniaxial symmetry, and the direction perpendicular to the axis. The mechanical strength of is reduced.

  Examples of the method for controlling the retardation of the polyethylene naphthalate film of the present invention include stretching during film production as described above. Specifically, adjustment is preferable depending on the molecular weight of the resin, the added stretching aid, and the monomer, but the stretching temperature is set in the range of −10 ° C. to + 50 ° C. with the glass transition temperature (Tg) as a guide. It is preferable to increase the stretching temperature as the stretching proceeds. When the stretching temperature is low, breakage frequently occurs, and when the stretching temperature is high, uneven thickness or whitening may occur.

  The total draw ratio (= MD draw ratio x TD draw ratio) is set in the range of 3.0 times to 10.0 times, and when stretching in multiple stages, if the stretch ratio is increased in the initial stage, it will break. It is preferable that the stretching ratio in the latter half becomes higher than the initial stretching ratio.

  When MD stretching is performed, when the MD stretching ratio is carried out alone, the vicinity is preferably 3.5 times, and when TD stretching is used in combination, 1.5 to 2.5 times is preferable.

  The TD stretching ratio in TD stretching is preferably 3.0 to 6.0 times, and more preferably 3.5 to 5.0 times. Further, MD relaxation can be performed simultaneously with TD stretching, and depending on the TD stretching ratio, the relaxation ratio is preferably 0.5 to 0.9 times, more preferably 0.65 to 0.8 times. By this method, it is preferable to control so that the ratio of the retardation to the retardation in the thickness direction falls within a specific range.

  The heat treatment is preferably adjusted by the molecular weight of the resin, the added stretching aid, the monomer, and the stretching ratio, and the processing temperature is based on the glass transition temperature (Tg) and the melting point (Tm). It is preferable to set the temperature in the range of Tg + 50 ° C. or higher to Tm−30 ° C., and particularly control so that the heat shrinkage rate does not increase. Specifically, in both MD and TD, the heat shrinkage rate is preferably 2% or less, more preferably 1.5% or less, still more preferably 1.0% or less, and still more preferably. It is 0.8% or less, and particularly preferably 0.5% or less. By performing MD relaxation during the heat treatment, it is possible to further reduce the thermal shrinkage rate more efficiently. The thermal shrinkage rate can be measured in accordance with JIS C 2318 “Electric polyethylene terephthalate film (dimensional change)” as shown in Examples described later.

  If the heat shrinkage ratio is large, the film shrinks significantly when the heat treatment is performed in the post-processing step such as during the production of a polarizing plate, or when the liquid crystal display device is used at a high temperature for a long time. There is a risk that distortion of characteristics occurs, flatness is deteriorated, wrinkles, curls, etc. occur.

  In addition, the thickness unevenness also affects retardation and retardation in the thickness direction, so it is preferably 5.0% or less, more preferably 4.5% or less, and more preferably 4.0% or less. Further preferred. Thickness unevenness can be controlled by adjusting the above stretching conditions and heat treatment conditions.

  In order to meet the demand for thinner polarizing plates and image display devices, the thickness of the polyethylene naphthalate film is preferably 15 to 100 μm, more preferably 15 to 60 μm, and still more preferably 15 to 30 μm.

  For the viewing-side polarizing plate, it is preferable to use a polarizer protective film coated with various functional layers on the surface for the purpose of preventing reflection, suppressing glare, and suppressing scratches.

  Examples of the functional layer laminated at an arbitrary position on the viewing side of the polarizer protective film include, for example, a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and charging. One or more selected from the group consisting of a prevention layer, a silicone layer, an adhesive layer, an antifouling layer, a water repellent layer, a blue cut layer, and the like can be used.

  When providing various functional layers, it is preferable to have an easy-adhesion layer on the surface of the polarizer protective film. In that case, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the functional layer and the refractive index of the polarizer protective film. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

(Hard coat layer)
The hard coat layer may be a layer having hardness and transparency, and is usually formed of various curable resins such as an ionizing radiation curable resin cured by ultraviolet rays or an electron beam, and a thermosetting resin cured by heat. Is used. In order to appropriately add flexibility and other physical properties to these curable resins, thermoplastic resins and the like may be added as appropriate. Among the curable resins, ionizing radiation curable resins are typical and preferable in that an excellent hard coating film can be obtained.

  As the ionizing radiation curable resin, conventionally known resins can be appropriately employed. As the ionizing radiation curable resin, a radical polymerizable compound having an ethylenic double bond, a cationic polymerizable compound such as an epoxy compound, and the like are typically used. These compounds are used as monomers, oligomers, prepolymers, and the like. Can be used alone or in appropriate combination of two or more. Typical compounds are various (meth) acrylate compounds that are radical polymerizable compounds. Among the (meth) acrylate compounds, compounds used at a relatively low molecular weight include, for example, polyester (meth) acrylate, polyether (meth) acrylate, acrylic (meth) acrylate, epoxy (meth) acrylate, urethane (meth) ) Acrylate, etc.

  Examples of the monomer include monofunctional monomers such as ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, N-vinylpyrrolidone; or, for example, trimethylolpropane tri (meth) acrylate, tripropylene glycol di (Meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, etc. These polyfunctional monomers are also used as appropriate. (Meth) acrylate means acrylate or methacrylate.

  When the ionizing radiation curable resin is cured with an electron beam, a photopolymerization initiator is unnecessary, but when it is cured with ultraviolet rays, a known photopolymerization initiator is used. For example, in the case of a radical polymerization system, acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, or the like can be used alone or in combination as a photopolymerization initiator. In the case of a cationic polymerization system, an aromatic diazonium salt, aromatic sulfonium salt, aromatic iodonium salt, metatheron compound, benzoin sulfonate, or the like can be used alone or in combination as a photopolymerization initiator.

  The thickness of the hard coat layer may be an appropriate thickness, for example, 0.1 to 100 μm, but usually 1 to 30 μm. The hard coat layer can be formed by appropriately adopting various known coating methods.

  A thermoplastic resin, a thermosetting resin, or the like can be appropriately added to the ionizing radiation curable resin for the purpose of adjusting the physical properties as appropriate. Examples of the thermoplastic resin or thermosetting resin include an acrylic resin, a urethane resin, and a polyester resin, respectively.

  In order to impart light resistance to the hard coat layer and prevent discoloration, strength deterioration, cracking, and the like due to ultraviolet rays contained in sunlight, it is also preferable to add an ultraviolet absorber in the ionizing radiation curable resin. When an ultraviolet absorber is added, the ionizing radiation curable resin is preferably cured with an electron beam in order to reliably prevent the ultraviolet coater from inhibiting the curing of the hard coat layer. Examples of the ultraviolet absorber include organic ultraviolet absorbers such as benzotriazole compounds and benzophenone compounds, or inorganic ultraviolet absorbers such as fine particles of zinc oxide, titanium oxide, and cerium oxide having a particle size of 0.2 μm or less, What is necessary is just to select and use from well-known things. The addition amount of the ultraviolet absorber is about 0.01 to 5% by mass in the ionizing radiation curable resin composition. In order to further improve the light resistance, it is preferable to add a radical scavenger such as a hindered amine radical scavenger in combination with an ultraviolet absorber. In addition, the electron beam irradiation has an acceleration voltage of 70 kV to 1 MV and an irradiation dose of about 5 to 100 kGy (0.5 to 10 Mrad).

(Anti-glare layer)
It is one of the preferred embodiments that an antiglare layer is provided on the most visible side of the image display device.
As the antiglare layer, a conventionally known layer may be appropriately employed, and it is generally formed as a layer in which an antiglare agent is dispersed in a resin. As the antiglare agent, inorganic or organic fine particles are used. These fine particles have a spherical shape, an elliptical shape, or the like. The fine particles are preferably transparent. Examples of such fine particles include silica beads as inorganic fine particles and resin beads as organic fine particles. Examples of the resin beads include styrene beads, melamine beads, acrylic beads, acrylic-styrene beads, polycarbonate beads, polyethylene beads, and benzoguanamine-formaldehyde beads. The fine particles are usually added in an amount of 2 to 30 parts by mass, preferably about 10 to 25 parts by mass with respect to 100 parts by mass of the resin.

  The above resin for dispersing and holding the antiglare agent is preferably as hard as possible as in the hard coat layer. Therefore, as the resin, for example, a curable resin such as an ionizing radiation curable resin or a thermosetting resin described in the hard coat layer can be used.

  The thickness of the antiglare layer may be an appropriate thickness, and is usually about 1 to 20 μm. The antiglare layer can be formed by appropriately adopting various known coating methods. In addition, it is preferable to add well-known anti-settling agents such as silica to the coating liquid for forming the anti-glare layer in order to prevent precipitation of the anti-glare agent.

(Antireflection layer)
It is also one of preferable modes that an antireflection layer is provided on the outermost surface side of the image display device and the interface of each film with air.
As the antireflection layer, a conventionally known layer may be appropriately employed. In general, the antireflection layer is composed of at least a low refractive index layer, and a low refractive index layer and a high refractive index layer (having a higher refractive index than the low refractive index layer) are alternately stacked adjacent to each other and the surface side has a low refractive index. It consists of multiple layers as the rate layer. Each thickness of the low-refractive index layer and the high-refractive index layer may be an appropriate thickness according to the application, and is about 0.1 μm when adjacent layers are stacked, and about 0.1 to 1 μm when the low-refractive index layer alone is used. It is preferable.

  As a low refractive index layer, a layer containing a low refractive index material such as silica or magnesium fluoride in a resin, a layer of a low refractive index resin such as a fluorine-based resin, or a low refractive index material in a low refractive index resin A thin film formed by a thin film forming method (for example, physical or chemical vapor deposition such as vapor deposition, sputtering, CVD, or the like), an oxidation layer, or a layer made of a low refractive index material such as silica or magnesium fluoride. Examples thereof include a film formed by a sol-gel method in which a silicon oxide gel film is formed from a silicon sol solution, or a layer in which void-containing fine particles are contained in a resin as a low refractive index substance.

  The void-containing fine particles are fine particles containing gas inside, fine particles having a porous structure containing gas, etc., and with respect to the original refractive index of the fine particle solid portion, It means fine particles whose refractive index is apparently lowered. Examples of such void-containing fine particles include silica fine particles disclosed in JP-A No. 2001-233611. Examples of the void-containing fine particles include hollow polymer fine particles disclosed in JP-A No. 2002-805031, in addition to inorganic substances such as silica. The particle diameter of the void-containing fine particles is, for example, about 5 to 300 nm.

  As the high refractive index layer, a layer containing a high refractive index material such as titanium oxide, zirconium oxide or zinc oxide in a resin, a layer of a high refractive index resin such as a fluorine-free resin, or a high refractive index material is highly refracted. A layer formed of a high-refractive-index material such as titanium oxide, zirconium oxide, or zinc oxide in a thin film forming method (for example, vapor deposition, sputtering, CVD, etc., physical or chemical vapor deposition) Method).

(Anti-fouling layer)
As the antifouling layer, a conventionally known layer may be appropriately employed. Generally, in the resin, a silicon compound such as silicone oil or silicone resin; a fluorine compound such as fluorine surfactant or fluorine resin. It can be formed by a known coating method using a paint containing a stain-proofing agent such as wax. The thickness of the antifouling layer may be set appropriately, and can usually be about 1 to 10 μm.

(Antistatic layer)
As the antistatic layer, a conventionally known layer may be employed as appropriate, and it is generally formed as a layer containing an antistatic layer in a resin. As the antistatic layer, an organic or inorganic compound is used. For example, examples of the antistatic layer of an organic compound include a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, a nonionic antistatic agent, and an organometallic antistatic agent. The inhibitor is used not only as a low molecular compound but also as a high molecular compound. As the antistatic agent, conductive polymers such as polythiophene and polyaniline are also used. Further, as the antistatic agent, for example, conductive fine particles made of a metal oxide are used. The particle diameter of the conductive fine particles is, for example, about 0.1 nm to 0.1 μm in average particle diameter in terms of transparency. Examples of the metal oxide include ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , ITO (indium doped tin oxide), In ₂ O ₃ , Al ₂ O ₃ , ATO (antimony doped tin oxide), AZO (aluminum doped zinc oxide) etc. are mentioned.

  Examples of the resin containing the antistatic layer include curable resins such as ionizing radiation curable resins and thermosetting resins as described in the hard coat layer. When the layer is formed as a layer and the surface strength of the antistatic layer itself is unnecessary, a thermoplastic resin or the like is also used. The thickness of the antistatic layer may be set appropriately, and is usually about 0.01 to 5 μm. The antistatic layer can be formed by appropriately adopting various known coating methods.

  As the liquid crystal cell, any liquid crystal cell that can be used in a liquid crystal display device can be appropriately selected and used, and the method and structure thereof are not particularly limited. For example, a liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be appropriately selected and used. Therefore, the liquid crystal cell can be used by appropriately selecting a known liquid crystal material and a liquid crystal made of a liquid crystal material that can be developed in the future. In one embodiment, a preferred liquid crystal cell is a transmissive liquid crystal cell.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

  Evaluation in the examples and evaluation of physical properties were performed according to the following methods.

(1) Thickness (d)
The thickness (d) was determined in accordance with JIS K 7130 “Method for measuring thickness of plastic film and sheet (Method A)”.

(2) Refractive index (Nx, Ny, Nz)
According to JIS K 7142 “Plastic Refractive Index Measurement Method (Method A)”, the longitudinal direction (MD) refractive index (Nx), the lateral direction (TD) refractive index (Ny), and the thickness direction refractive index. (Nz) was determined.

(3) Birefringence (ΔNxy), retardation (Re)
Retardation refers to the refractive index (Nx) in each axial direction of the film with respect to the thickness direction (z-axis) and the two axial directions (x-axis and y-axis) that are orthogonal to and perpendicular to the film surface. , Ny, Nz) is a phase difference represented by the product of birefringence and film thickness d. Here, the in-plane retardation that is the product of the birefringence index Nxy and the thickness d caused by light incident on the film surface (xy plane) with MD as the x axis and TD as the y axis is referred to as retardation (Re). , Each was obtained from the following equation. In general, the unit of retardation is nm.
ΔNxy = | Nx−Ny |
Re = ΔNxy × d

(4) Thickness direction retardation (Rth)
Thickness direction retardation refers to the thickness direction (z axis) and two axial directions (x axis and y axis) that are orthogonal to the film surface and perpendicular to each other. The resulting retardation is shown, and here, the product of the average of two birefringences in the xz plane and the yz plane and the film thickness d was obtained from the following equation. In general, the unit is nm.
Rth = (| Nx−Nz | + | Ny−Nz |) / 2 × d

(5) Intrinsic viscosity (IV)
For the viscosity number obtained in accordance with JIS K 7367-5 "Plastics-Determination of viscosity of diluted solution using capillary viscometer-Part 5: Thermoplastic polyester (TP) homopolymer and copolymer" Under the following measurement conditions, the value when the mass concentration (c) = 0 was set as the intrinsic viscosity (IV) from the relationship of the viscosity number to the mass concentration (c) of the solution.
Solvent: phenol / 1,1,2,2-tetrachloroethane = 60/40 (wt%)
Tube: Ubbelohde viscosity tube Temperature: 30 ± 0.1 (° C)

(6) Glass transition temperature (Tg), melting point (Tm)
The midpoint glass transition temperature obtained from the DSC curve of differential scanning calorimetry (DSC) in accordance with JIS K 7121 “Plastic transition temperature measurement method” is the glass transition temperature (Tg), and the melting peak temperature is the melting point (Tm). did.

(7) Color unevenness observation The film of the Example and comparative example produced by the method described later on one side of a commercially available polarizer, the absorption axis of the polarizer and the orientation axis of the film (the higher of Nx and Ny) are perpendicular to each other. It stuck so that it might become, and the polarizing plate was produced by sticking the commercially available TAC film on the opposite surface. This is replaced with a polarizing plate on the viewing side of a commercially available liquid crystal display device having a liquid crystal cell sandwiched between polarizing plates having white LEDs as backlight and two TAC films as polarizer protective films. Or it installed so that it might become a film of a comparative example. Visual observation was performed from the front side and the oblique direction of the liquid crystal display device thus obtained, and the occurrence of color unevenness was determined as follows.
◎: Color unevenness is not observed when observed from any direction
○: When observed from an oblique direction, some uneven color unevenness can be observed.
×: Color unevenness can be clearly observed when observed from an oblique direction.

(8) Tear Strength Based on JIS K 7128 “Plastic Film and Sheet Tear Test Method (Method B)”, the lower value of the Elmendorf tear strength, which is a value converted into 16 sheets for MD and TD. Was determined as follows.
○: Tear strength is 50 mN or more
X: Tear strength is less than 50 mN

(9) Shrinkage rate (SH)
Based on JIS C 2318 “Polyethylene terephthalate film for electrical use (dimensional change)”, the dimensional change rate before and after heating at 150 ° C. was determined as the shrinkage rate for MD and TD.

(Production Example 1-Polyethylene naphthalate)
To a mixture of dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol, manganese acetate tetrahydrate salt, antimony trioxide and trimethyl phosphoric acid are added as catalysts, and the ester exchange reaction is carried out while gradually raising the temperature. I did it. The polycondensation reaction was continued at 290 ° C. under reduced pressure, and the polycondensation reaction was terminated using the stirring torque as a guide. Thereafter, the cooled and solidified material in a cooling state in a strand state was cut into pellets, and further dried under reduced pressure to obtain polyethylene naphthalate. The physical properties were as follows.
IV: 0.60 dl / g
Tm: 265 ° C
Tg: 124 ° C

(Production Example 2-Adhesiveness Modification Solution)
With respect to all components of dicarboxylic acid, 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol% of sodium 5-sulfonatoisophthalate and 50 mol% of neopentyl glycol with respect to all components of glycol A water-dispersible sulfonic acid metal base-containing copolymer polyester resin was obtained by a transesterification reaction and a polycondensation reaction by a conventional method. Next, an adhesive property modification liquid was obtained in which this and the agglomerated silica particles were dispersed in a solution in which water, isopropyl alcohol, n-butyl cellosolve, and nonionic surfactant were mixed.

<Example 1>
Using an extruder, polyethylene naphthalate was melted at about 300 ° C. and melt extruded from the slit. An unstretched sheet obtained by cooling and solidifying a chill roll having a surface temperature of about 60 ° C. by an electrostatic application method using a roll speed difference, a preheating roll having a set temperature of 110 ° C. and a roll immediately before stretching having a set temperature of 130 ° C. And a cooling roll with a set temperature of 50 ° C. was passed, and uniaxial stretching of MD was performed 3.5 times. After that, the adhesive reforming solution is applied on both sides by a reverse roll coating method so that the coating amount after drying is 0.08 g / m ² , and heat treatment at 180 ° C. is performed with a tenter having a draw ratio of 1.0. A film having a thickness of about 15 μm was obtained. In addition, no breakage occurred during the process, and no abnormality such as whitening was observed in the film. In the color unevenness observation, it was only possible to observe an extremely thin color unevenness.

<Comparative Example 1>
In the same manner as in Example 1, the MD was uniaxially stretched 2.5 times to obtain a film having a thickness of 15 μm. In addition, although the fracture | rupture etc. did not generate | occur | produce in the process, the whitening substantially parallel to TD was recognized. In the color unevenness observation, the color unevenness was clearly observed.

<Example 2>
In the same manner as in Example 1, the MD was uniaxially stretched 4.0 times to obtain a film having a thickness of 15 μm. In addition, although the fracture occurred frequently in the tenter during the process, no whitening was observed for those that passed the process. Further, in the color unevenness observation, the color unevenness could not be confirmed.

The results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1.

  In the table, “MDx” indicates the draw ratio in the longitudinal direction. “TDx” indicates the stretching ratio in the transverse direction. “Total magnification” indicates the total stretching ratio (= MD stretching ratio × TD stretching ratio). Same in the table below.

  In MD stretching, if the magnification is appropriate, it can be used as a polarizer protective film. If the magnification is low, problems such as whitening and color unevenness occur, and if the magnification is high, breakage and the like are confirmed. did it. On the other hand, the range of magnifications that can be set is narrow, but this is presumed to be because the film is constrained in the TD and thickness directions, so that the molecular orientation changes greatly with a slight change in magnification. Therefore, it is in the direction to eliminate by widening the stretching section of the roll, or by performing in multiple stages, but there are concerns about the occurrence of thickness unevenness and distortion, and film scratches due to the roll, so care must be taken. .

<Example 3>
Using an extruder, polyethylene naphthalate was melted at about 300 ° C. and melt extruded from the slit. An unstretched sheet that has been cooled and solidified on a chill roll having a surface temperature of about 60 ° C. by an electrostatic application method is 0.08 g / m ² after drying the adhesive modification liquid on both sides by a reverse roll coating method. It applied so that it might become. Then, after drying at 80 ° C., a heat treatment at 180 ° C. was performed continuously with TD stretching using a tenter having a stretching ratio of 3.5 times and a stretching temperature of 140 ° C. to obtain a film having a thickness of about 15 μm. In addition, breakage etc. did not occur so much during the process, and abnormalities such as whitening were not recognized in the film. In the color unevenness observation, it was only possible to observe an extremely thin color unevenness.

<Example 4>
In the same manner as in Example 3, the film was uniaxially stretched 6.0 times to TD to obtain a film having a thickness of 15 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. In the color unevenness observation, it was only possible to observe an extremely thin color unevenness.

<Comparative example 2>
In the same manner as in Example 3, TD was uniaxially stretched 3.0 times to obtain a film having a thickness of 15 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. In the color unevenness observation, the color unevenness was clearly observed.

The results of Examples 3 and 4 and Comparative Example 2 are shown in Table 2.

  In TD stretching, it can be confirmed that there is a possibility that it can be used as a polarizer protective film if the stretching ratio is a certain level or more, and it has been confirmed that problems such as whitening and color unevenness occur when the magnification is low.

<Example 5>
In the same manner as in Example 2, TD was uniaxially stretched 3.5 times to obtain a film having a thickness of 30 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 6>
In the same manner as in Example 3, the TD was uniaxially stretched 6.0 times to obtain a film having a thickness of 30 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 7>
In the same manner as in Example 3, TD was uniaxially stretched 2.5 times to obtain a film having a thickness of 30 μm. In the tenter during the process, breakage occurred frequently, and whitening was observed in the film. In addition, in the color unevenness observation, a very thin color unevenness can be observed.

<Example 8>
In the same manner as in Example 3, TD was uniaxially stretched 3.5 times to obtain a film having a thickness of 50 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 9>
In the same manner as in Example 3, the film was uniaxially stretched 6.0 times to TD to obtain a film having a thickness of 50 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 10>
In the same manner as in Example 3, TD was uniaxially stretched 2.5 times to obtain a film having a thickness of 50 μm. In the tenter during the process, breakage occurred frequently, and whitening was observed in the film. In addition, in the color unevenness observation, a very thin color unevenness can be observed.

<Example 11>
In the same manner as in Example 3, TD was uniaxially stretched 3.5 times to obtain a film having a thickness of 100 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 12>
In the same manner as in Example 3, the film was uniaxially stretched 6.0 times to TD to obtain a film having a thickness of 100 μm. In the tenter in the process, no breakage occurred, and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 13>
In the same manner as in Example 3, TD was uniaxially stretched 2.5 times to obtain a film having a thickness of 100 μm. In the tenter in the process, breakage occurred and whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

The results of Examples 5 to 13 are shown in Table 3.

  In TD stretching, if the stretching ratio is a certain value or more, it can be confirmed that the film can be used as a polarizer protective film, and the tendency was not changed even when the thickness was increased. In particular, regarding the fracture, it is assumed that the tendency did not change even when the thickness was increased, because a high stress was locally generated due to the thickness unevenness, and the fracture propagated starting from this.

<Example 14>
Using an extruder, polyethylene naphthalate was melted at about 300 ° C. and melt extruded from the slit. An unstretched sheet that has been cooled and solidified on a chill roll having a surface temperature of about 60 ° C. by an electrostatic application method is 0.08 g / m ² after drying the adhesive modification liquid on both sides by a reverse roll coating method. It applied so that it might become. After drying at 80 ° C., the film is stretched 2.0 times to MD and 5.0 times to TD at the same time with a tenter with a stretching temperature of 140 ° C., and then heat-treated at 180 ° C. to give a film with a thickness of about 15 μm. Got. In addition, breakage etc. did not occur so much during the process, and abnormalities such as whitening were not recognized in the film. In the color unevenness observation, it was only possible to observe an extremely thin color unevenness.

<Comparative Example 3>
A film having a thickness of 15 μm was obtained in the same manner as in Example 14 except that MD was stretched 2.5 times. In the tenter in the process, there was no breakage and no whitening was observed in the film. However, in the color unevenness observation, the color unevenness was clearly observed.

<Example 15>
A film having a thickness of 100 μm was obtained in the same manner as in Example 14. In the tenter in the process, there was no breakage and no whitening was observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Comparative example 4>
A film having a thickness of 100 μm was obtained in the same manner as in Example 14 except that MD was stretched 2.5 times. In the tenter in the process, there was no breakage and no whitening was observed in the film. However, in the color unevenness observation, the color unevenness was clearly observed.

  Table 4 shows the results of Examples 14 and 15 and Comparative Examples 3 and 4.

  In MD stretching and TD stretching, if the draw ratio is within the range of the present invention, it can be confirmed that there is a possibility that it can be used as a polarizer protective film.

<Example 16>
Using an extruder, polyethylene naphthalate was melted at about 300 ° C. and melt extruded from the slit. An unstretched sheet that has been cooled and solidified on a chill roll having a surface temperature of about 60 ° C. by an electrostatic application method is 0.08 g / m ² after drying the adhesive modification liquid on both sides by a reverse roll coating method. It applied so that it might become. After drying at 80 ° C., the film is stretched 3.0 times to TD with a tenter with a stretching temperature of 140 ° C. At the same time, the MD is relaxed 0.7 times and further heat-treated at 180 ° C. A film of about 15 μm was obtained. During the process, breakage and the like did not occur so much, and abnormalities such as whitening were not observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 17>
A film having a thickness of about 15 μm was obtained in the same manner as in Example 16 except that the film was stretched 6.0 times in TD and simultaneously 0.9 times relaxed in MD. During the process, breakage and the like did not occur so much, and abnormalities such as whitening were not observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

<Example 18>
A film having a thickness of about 15 μm was obtained in the same manner as in Example 16 except that the film was stretched 6.0 times in TD and simultaneously relaxed in MD by 0.7 times. During the process, breakage and the like did not occur so much, and abnormalities such as whitening were not observed in the film. Further, in the color unevenness observation, the color unevenness could not be confirmed.

  The results of Examples 16 to 18 are shown in Table 4.

  In Table 4, “MDR” indicates the MD relaxation ratio during TD stretching. As shown in Table 4, it was confirmed that by relaxing the MD simultaneously with the TD stretching, a thin film having a low thermal shrinkage and little color unevenness can be obtained.

  By using the liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention, it is possible to contribute to the thinning and cost reduction of the display device without reducing the visibility due to color unevenness, Industrial applicability is extremely high.

Claims (7)

A backlight, a liquid crystal cell, and two polarizing plates disposed on both sides of the liquid crystal cell;
Each of the two polarizing plates has a polarizer protective film laminated on both sides of the polarizer,
At least one of the polarizer protective films is a polyethylene naphthalate film,
The polyethylene naphthalate film has a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more.
Liquid crystal display device. The liquid crystal display device according to claim 1, wherein the polyethylene naphthalate film has a thickness of 100 μm or less. The liquid crystal display device according to claim 1 or 2, wherein a ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the polyethylene naphthalate film is 0.2 or more and 1.2 or less. A polarizing plate for a liquid crystal display device, wherein a polyethylene naphthalate film having a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more is disposed on at least one surface of the polarizer. The polarizing plate according to claim 4, wherein the polyethylene naphthalate film has a thickness of 100 μm or less. A polarizer protective film for a liquid crystal display device comprising a polyethylene naphthalate film having a retardation of 3,000 to 30,000 nm and a ΔNxy of 0.15 or more. The polarizer protective film for a liquid crystal display device according to claim 6, wherein the thickness is 100 μm or less.