JP4867690B2 - Liquid crystal display and polarizing plate set - Google Patents

Description

  The present invention relates to a liquid crystal display device in which light leakage of a display screen hardly occurs even after being placed in a humid environment for a long period of time, and a set of polarizing plates useful for the liquid crystal display device.

  The polarizing plate usually has a configuration in which a protective layer made of a transparent resin is laminated on one or both sides of a polarizer made of a polyvinyl alcohol resin to which a dichroic dye is adsorbed and oriented via an adhesive. As the protective layer, a triacetyl cellulose film is generally used, but many attempts have been made to replace the protective layer with another resin, or to provide a phase difference in the protective layer. These polarizing plates are further bonded to a liquid crystal cell with an adhesive via another optical functional film such as a retardation film, if necessary, and become a component of a liquid crystal display device.

  Since the polarizer and the protective film, which are constituent elements of the polarizing plate, are made of resin, they expand and contract when exposed to high temperature and high humidity conditions. When expansion or contraction occurs in this way, stress is generated in the protective film, causing a phenomenon called `` frame unevenness '' in which white light leakage occurs at the edges and four corners of the liquid crystal panel due to the phase difference shifting. It has been. As represented by large-sized televisions, for which demand has increased remarkably in recent years, such a frame unevenness phenomenon has become a major problem as the size of liquid crystal display devices has increased.

  In addition, a cellulose resin film having a phase difference, which has come to be used as a protective film for a polarizer, has a large dimensional change with respect to environmental changes, a large photoelastic coefficient, and a high hygroscopicity. For example, frame unevenness is likely to occur. Therefore, there is a demand for measures to eliminate the frame unevenness.

  On the other hand, with the rapid spread of liquid crystal display devices in recent years, it has been required to show high display quality under various environments. For example, when the liquid crystal display device is placed in a high humidity environment for a long time and then moved to a low humidity environment, problems such as round light leakage appearing at the four corners of the display screen of the liquid crystal panel have emerged, and improvements have been made. It has been demanded.

  Various proposals have been made regarding the suppression of light leakage as described above. For example, in JP 2006-235485 A (Patent Document 1), when a polarizing plate is bonded to a liquid crystal cell, the polarizing plate is maintained at 10 ° C. or lower and bonded to a liquid crystal cell of 20 ° C. or higher. It describes that the occurrence of light leakage can be prevented. Japanese Patent Laid-Open No. 2006-30457 (Patent Document 2) describes that unevenness under high humidity can be reduced by defining the relaxation elastic modulus of a polarizing plate to which a protective film is bonded. .

  However, the measures proposed in these patent documents apply to actual production, such as making the production and storage process of the polarizing plate complicated and requiring the physical properties of the protective film to be greatly restricted. There are many problems to do.

  In recent years, the protective film for the polarizing plate is also replaced with another resin from the conventional cellulose resin film. For example, in JP-A-2002-174729 (Patent Document 3), a protective film made of an amorphous polyolefin-based resin (cyclic olefin-based resin) is bonded to one surface of a polyvinyl alcohol-based polarizer. It is described that a protective film made of a different resin is bonded to the surface to form a polarizing plate.

JP 2006-235485 A JP 2006-30457 A JP 2002-174729 A

  An object of the present invention is to provide a liquid crystal display device that is less likely to cause light leakage on a display screen even after being placed in a high humidity environment for a long time and then moved to a normal environment with low humidity. Another object of the present invention is to provide a set of polarizing plates suitably used for such a liquid crystal display device.

  The present inventor has conducted intensive research to solve such a problem, and as a result, the problem of light leakage is that of the light exit side polarizing plate that has been exposed to a high humidity environment for a long time and absorbed an excessive amount of moisture. It has been clarified that the polarizer and the protective film are caused by shrinkage stress when the moisture is released in a low humidity environment. Specifically, this shrinkage stress causes the liquid crystal cell to bend and the four corners of the liquid crystal cell are pressed against the frame of the panel, causing a shift in the phase difference in the liquid crystal cell surface and causing light leakage as described above. is there.

  In order to suppress such a phenomenon, the present inventor, as a liquid crystal cell side protective layer of the light emitting side polarizing plate of the liquid crystal display device, a polymer film having low hygroscopicity and less dimensional change due to environmental changes, specifically, It has been found that it is preferable to dispose a cyclic olefin resin film having a saturated water absorption of less than 0.05% by weight. Furthermore, when a cellulose acetate-based resin film is disposed as the liquid crystal cell side protective layer of the light incident side polarizing plate, this polarizing plate configuration cancels out the curvature of the cell to some extent, and further prevents light leakage. I found it.

Therefore, according to the present invention, the backlight, the light incident side polarizing plate, the liquid crystal cell, and the light emitting side polarizing plate are arranged in this order, and each of the light incident side polarizing plate and the light emitting side polarizing plate is a polarizer. It has a laminated structure sandwiching both sides of the transparent protective layer, at least a transparent protective layer positioned on the liquid crystal cell side of the light-emitting side polarizing plate, the retarded the refractive index in the in-plane slow axis direction n _x, in a plane phase The refractive index in the direction perpendicular to the axis (that is, the in-plane fast axis direction) is n _y , the refractive index in the thickness direction is n _z , the thickness is d, and the following formulas (1) and (2) are satisfied, and saturated water absorption The transparent protective layer, which is composed of a cyclic olefin resin film having a rate of less than 0.05% by weight and is located at least on the liquid crystal cell side of the light incident side polarizing plate, also satisfies the following formulas (1) and (2). A liquid crystal display device composed of a cellulose resin film is provided. .

_{(N x -n y) × d} ≧ 30nm (1)
_nx > _ny > _nz (2)

  Further, according to the present invention, there is also provided a set of polarizing plates disposed on both surfaces of the liquid crystal cell, the polarizing plate set having a laminated structure in which both surfaces of the polarizer are sandwiched between transparent protective layers, and at least liquid crystal A light emitting side polarizing plate, wherein the transparent protective layer disposed on the cell side is composed of a cyclic olefin-based resin film satisfying the formulas (1) and (2) and having a saturated water absorption of less than 0.05% by weight And a laminated structure in which both surfaces of the polarizer are sandwiched between transparent protective layers, and at least the transparent protective layer disposed on the liquid crystal cell side is composed of a cellulose acetate-based resin film satisfying the above formulas (1) and (2) The light incident side polarizing plate.

  Even when the liquid crystal display device of the present invention is moved from a high-humidity environment to a low-humidity environment, light leakage from the screen due to deformation of the polarizer protective layer and curvature of the panel is unlikely to occur, and the display quality is good. It will be a thing. The set of polarizing plates of the present invention is useful for providing such a liquid crystal display device.

  Hereinafter, the present invention will be described in detail. An example of a basic layer structure of the liquid crystal display device according to the present invention is shown in a schematic cross-sectional view in FIG. The liquid crystal display device of the present invention includes a backlight 10, a light incident side polarizing plate 20, a liquid crystal cell 40 and a light emitting side polarizing plate 30. The light incident side polarizing plate 20 has a laminated structure in which both surfaces of a polarizer 21 made of polyvinyl alcohol resin are sandwiched between transparent protective layers 23 and 24, and the light emitting side polarizing plate 30 is also made of polyvinyl alcohol resin. The polarizer 31 has a laminated structure in which both surfaces of the polarizer 31 are sandwiched between transparent protective layers 33 and 34.

  And in this invention, the resin film which satisfy | fills said Formula (1) and (2) simultaneously as the transparent protective layers 23 and 33 located in the liquid crystal cell 40 side of both polarizing plates 20 and 30 is employ | adopted. The transparent protective layer 33 located on the liquid crystal cell side of the light exit side polarizing plate 30 is composed of a cyclic olefin resin film having a saturated water absorption of less than 0.05% by weight, and the liquid crystal cell of the light incident side polarizing plate 20 is used. The transparent protective layer 23 located on the side is composed of a cellulose acetate resin film.

In general, the film exhibiting optical anisotropy, in-plane retardation R ₀ and the thickness direction retardation R _th is provided with a refractive index of the three axial directions as defined above n _x, n _y and n _z, thickness d Is defined by the following equations (3) and (4).

_{R 0 = (n x -n y} ) × d (3)
R _th = [(n _x + _ny ) / 2−n _z ] × d (4)

The equation (1) means that the in-plane retardation R ₀ is 30 nm or more, as can be seen from the above equation (3). The Formula (2), three axial directions of a refractive index n _x, of n _y and n _z, the refractive index in the in-plane slow axis n _x is the largest, the smallest refractive index n _z in the thickness direction That is, biaxial orientation.

The transparent protective layer 23 located on the liquid crystal cell side of the light incident side polarizing plate 20 and the transparent protective layer 33 located on the liquid crystal cell side of the light emitting side polarizing plate 30 have an in-plane retardation R ₀ of 30 nm or more. It is preferable that the value does not become too large. Specifically, the in-plane retardation R ₀ is preferably 100 nm or less. When R ₀ is 30 nm or less, the viewing angle compensation of the polarization axis is insufficient, light leakage from the oblique angle in black display increases, and the color change also increases. On the other hand, if R ₀ becomes too large, the viewing angle is over-compensated, adversely affecting light loss and color change. In addition, each thickness direction retardation R _th is relatively large, and is preferably set to a value larger than the in-plane retardation R ₀ , specifically, from the range of about 70 to 300 nm. It is preferable to select according to the characteristics of the cell. Similarly to R ₀ , when R _th is too small, viewing angle compensation of the liquid crystal layer is insufficient, and conversely, when R _th is too large, over compensation is achieved.

As described above, as the transparent protective layers 23 and 33 positioned on the liquid crystal cell side of the light incident side polarizing plate 20 and the light emitting side polarizing plate 30, respectively, the in-plane retardation R ₀ is 30 nm or more and biaxially oriented. By adopting the film, the viewing angle of the polarizer can be compensated, and light leakage and color change when the black display state is viewed from an oblique direction can be suppressed. In addition, since the liquid crystal cell side transparent protective layer 33 of the light emitting side polarizing plate 30 is made of a cyclic olefin resin film, the liquid crystal display device is stored for a long time in a high humidity environment and then moved to a low humidity environment. This prevents light from leaking through the display screen, which is likely to occur. The suppression of light leakage when moving from such a high-humidity environment to a low-humidity environment is achieved by applying a cyclic olefin-based resin film having a low saturated water absorption rate, specifically less than 0.05% by weight, to the light emitting side polarizing plate 30 The liquid crystal cell side transparent protective layer 33 is achieved. On the other hand, the liquid crystal cell side transparent protective layer 23 of the light incident side polarizing plate 20 is formed of a cellulose acetate-based resin film, thereby realizing further suppression of light leakage.

  Here, the saturated water absorption is a value obtained by the method specified in ASTM D570, and is obtained by immersing a dried test piece in water at a constant temperature for a time until the mass increase due to water absorption is saturated. It is expressed as a percentage of the mass (saturated water absorption) of the test piece increased by water immersion with respect to the mass of the previous test piece. Usually, it is measured by immersing in water at 23 ° C. for 24 hours. Sufficient saturated water absorption is reached after 24 hours of immersion. In the cyclic olefin resin, if the amount of polar groups introduced increases, the saturated water absorption tends to increase, so use a film of a cyclic olefin resin in which the amount of polar groups is small or no polar groups are introduced. It is preferable.

The cyclic olefin-based resin film constituting the liquid crystal cell side transparent protective layer of the light emitting side polarizing plate 30 also has a low photoelastic coefficient, for example, 7 × 10 ⁻¹³ cm ² / dyne or less, and is dimensioned to environmental changes. In addition to excellent stability, the change in phase difference due to heat is small. In the light emission side polarizing plate 30, at least the transparent protective layer 33 located on the liquid crystal cell side is composed of a cyclic olefin resin film that satisfies the above conditions, but the transparent protective layer 34 located on the opposite side (viewing side) The transparent protective layer 33 on the liquid crystal cell side may be made of the same type of resin, or may be made of a different type of resin. Even when the viewing-side transparent protective layer 34 is composed of the same kind of resin as the liquid crystal cell-side transparent protective layer 33, the transparent protective layer 34 needs to satisfy the relationship of the above formulas (1) and (2). Is not necessarily.

  Further, with respect to the light incident side polarizing plate 20, the transparent protective layer 23 located on the liquid crystal cell side is composed of a cellulose acetate-based resin film that satisfies the above conditions, but the transparent protective layer located on the opposite side (backlight side). 24 may be made of the same kind of resin as the transparent protective layer 23 on the liquid crystal cell side, or may be made of a different kind of resin. Even when the backlight-side transparent protective layer 24 is made of the same kind of resin as the liquid crystal cell-side transparent protective layer 23, the transparent protective layer 24 needs to satisfy the relationship of the above formulas (1) and (2). There is not necessarily sex.

  The cyclic olefin resin constituting at least the liquid crystal cell side transparent protective layer 33 of the light emitting side polarizing plate 30 is a thermoplastic resin having a monomer unit made of cyclic olefin such as norbornene and polycyclic norbornene monomer. Yes, it can be a hydrogenated product of a ring-opening copolymer of the above-mentioned cyclic olefin or a ring-opening copolymer using two or more kinds of cyclic olefins, and an aromatic compound having a cyclic olefin and a chain olefin or a vinyl group And an addition copolymer. Moreover, a small amount of polar groups may be introduced as long as the saturated water absorption rate is satisfied.

  In the case of a copolymer of a cyclic olefin and a chain olefin or an aromatic compound having a vinyl group, examples of the chain olefin include ethylene and propylene, and examples of the aromatic compound having a vinyl group Examples thereof include styrene, α-methylstyrene, and nuclear alkyl-substituted styrene. In such a copolymer, the unit of the monomer comprising the cyclic olefin may be 50 mol% or less, for example, about 15 to 50 mol%. In particular, when a terpolymer of a cyclic olefin, a chain olefin, and an aromatic compound having a vinyl group is used, the monomer unit composed of the cyclic olefin can have a relatively small amount. In such a terpolymer, the unit of monomer composed of a chain olefin is usually about 5 to 80 mol%, and the unit of monomer composed of an aromatic compound having a vinyl group is usually about 5 to 80 mol%.

  Among the commercially available thermoplastic cyclic olefin-based resins that have a low saturated water absorption rate when used as a film, “Topas” sold by Ticona, Germany, and ZEON CORPORATION. There are “ZEONOR” and “ZEONEX” and “Apel” sold by Mitsui Chemicals, Inc. (all are trade names). Such a cyclic olefin-based resin is formed into a film, and a known film forming method such as a solvent casting method or a melt extrusion method is appropriately used for forming the film. Formed cyclic olefin resin films are also commercially available, such as “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd., “ZEONOR FILM” sold by OPTES CO., LTD. (Both are trade names).

  The cyclic olefin-based resin film can be given an arbitrary retardation value by stretching. In general, stretching is performed continuously while unwinding the film from the roll, and the film is stretched in a heating furnace in the roll traveling direction or in a direction perpendicular to the traveling direction. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cyclic olefin resin to the glass transition temperature + 100 ° C. is usually employed. The draw ratio is usually about 1.1 to 6 times, preferably 1.1 to 3.5 times. Prior to bonding with the polarizer, the cyclic olefin-based resin film is preferably subjected to a surface activation treatment such as corona treatment on the bonding surface in order to enhance the adhesion to the cyclic olefin resin film.

  The cellulose acetate-based resin constituting at least the liquid crystal cell-side transparent protective layer 23 of the light incident side polarizing plate 20 is one in which at least a part of cellulose is esterified. For example, triacetyl cellulose, diacetyl cellulose, cellulose Examples include acetate propionate. Examples of commercially available triacetyl cellulose films include “Fujitack Film” (available in various grades) sold by Fuji Film Co., Ltd., “KC8UX2M” and “KC8UY” sold by Konica Minolta Opto Co., Ltd. Etc. (both are trade names).

  A cellulose acetate-based resin film can also be given an arbitrary retardation value by stretching. The cellulose acetate-based resin film in which retardation is expressed has characteristics such as low birefringence and wavelength dispersion characteristics such as “reverse wavelength dispersion” in which the retardation value decreases as the wavelength becomes shorter. In the present invention, as at least the liquid crystal cell side transparent protective layer 23 of the light incident side polarizing plate 20, a cellulose acetate-based resin film satisfying the above formulas (1) and (2) is adopted. Cellulose acetate-based resin films with biaxial orientation retardation developed by stretching are also commercially available. For example, “KC4FR-T” and “KC8UCR-5” sold by Konica Minolta Opto Etc. (both are trade names). The cellulose acetate-based resin film is usually subjected to saponification treatment in order to improve the adhesion with the polarizer. As the saponification treatment, a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide can be employed.

  Although the thickness of the cyclic olefin-based resin film and the cellulose acetate-based resin film is preferably thinner, if it is too thin, the strength decreases and the processability is inferior, whereas if it is too thick, the transparency decreases, Problems such as an increase in the weight of the polarizing plate occur. Therefore, an appropriate thickness of these films is, for example, about 5 to 200 μm, and preferably 20 to 100 μm. In particular, the cellulose acetate-based resin film disposed as the liquid crystal cell side transparent protective layer 23 of the light incident side polarizing plate 20 is 20 to 20 in consideration of the influence on the phase difference caused by the stress generated by the heat of the backlight. The thickness is more preferably 60 μm, ideally 35 to 45 μm.

  As described above, the transparent protective layer 24 located on the opposite side (backlight side) of the light incident side polarizing plate 20 to the liquid crystal cell and the opposite side (viewing side) of the light emitting side polarizing plate 30 to the liquid crystal cell. The transparent protective layer 34 positioned may be made of the same type of resin as the transparent protective layers 23 and 33 on the liquid crystal cell side, or may be made of a different resin. Further, the refractive index characteristic is not particularly limited. Each of the transparent protective layers 24 and 34 located on the opposite side of the liquid crystal cell is practically composed of a transparent resin film having an in-plane retardation of almost zero, and in particular, a cellulose acetate-based resin film, particularly triacetyl cellulose. It is preferable to comprise.

The viewing-side transparent protective layer 34 of the light emitting side polarizing plate 30 can be provided with a surface treatment layer such as a hard coat layer, an antiglare layer, an antireflection layer, or an antistatic layer. It is more preferable to provide such a surface treatment layer and to make the water vapor transmission rate of the transparent protective layer 1,000 g / m ² · 24 hours or less in order to reduce light leakage. Here, the hard coat layer is a layer provided to improve the scratch resistance of the surface, the antiglare layer is a layer provided to prevent reflection of external light and glare, and the antireflection layer is The layer is provided to prevent reflection of external light, and the antistatic layer is a layer provided to prevent generation of static electricity.

  The hard coat layer can be provided by, for example, a method of applying an ultraviolet curable hard coat resin and irradiating the hard coat resin with ultraviolet rays to cure the hard coat resin. The anti-glare layer is, for example, a method in which an ultraviolet curable resin to which a filler is added is applied and then cured by irradiating with ultraviolet rays to reveal the irregularities based on the filler. In such a state, it can be provided by, for example, a method in which ultraviolet rays are irradiated and cured to reveal irregularities. The antireflection layer can be provided by a method of depositing a metal oxide or the like in a single layer or a plurality of layers. The antistatic layer can be provided by a method in which an ultraviolet curable resin containing an antistatic agent is applied and irradiated with ultraviolet rays to be cured.

  Cellulose acetate-based resin films, especially triacetylcellulose films, are easy to provide such a surface treatment layer, and therefore, the transparent protective layer 34 positioned on the viewing side of the light exit side polarizing plate 30 is formed of cellulose acetate-based resin. It is preferable also from this aspect to comprise a film.

  Polarizers 21 and 31 constituting polarizing plates 20 and 30 transmit linearly polarized light having a vibration vector in a certain direction out of light perpendicularly incident on the film surface, and linearly polarized light having a vibration vector in a direction orthogonal to the polarized light. For example, a film obtained by adsorbing and orienting a dichroic dye such as iodine or a dichroic organic dye on a polyvinyl alcohol-based resin film is used. Such a polarizer can be produced by a known method. Specifically, it can be obtained by subjecting a polyvinyl alcohol resin film to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment. The thickness of the polarizer is about 5 to 40 μm. The polarizer and the transparent protective layer sandwiching both surfaces thereof are usually laminated via an adhesive. As the adhesive used for bonding the polarizer and the transparent protective layer, any adhesive can be used in consideration of the respective adhesiveness. An aqueous solution of a polyvinyl alcohol-based resin is one of preferred adhesives, and this aqueous solution preferably further contains a curing agent such as a water-soluble epoxy resin or a polyvalent aldehyde.

  After laminating the polarizer and the protective film, a drying process is performed. The drying process is performed, for example, by blowing hot air, and the temperature at that time is appropriately selected from the range of about 40 to 100 ° C., preferably 60 to 100 ° C. The drying time is about 20 to 1,200 seconds. In the polarizing plate in which at least one transparent protective layer is composed of a cyclic olefin-based resin film, after drying, it is further cured at room temperature or slightly higher temperature, for example, at a temperature of about 20 to 50 ° C. for about 12 to 600 hours. Is preferred. The temperature at the time of curing is generally set lower than the temperature adopted at the time of drying.

  The polarizers 21 and 31 in the light incident side polarizing plate 20 and the light emitting side polarizing plate 30 each have an absorption axis in the plane. Among the transparent protective layers laminated thereon, at least the transparent protective layers 23 and 33 located on the liquid crystal cell side exhibit refractive index anisotropy as is apparent from the above definition, and therefore, in-plane slow phase. There are axes and fast axes. The slow axis and the fast axis are orthogonal to each other in the plane. The polarizer 21 and the liquid crystal cell side transparent protective layer 23 constituting the light incident side polarizing plate 20 and the polarizer 31 and the liquid crystal cell side transparent protective layer 33 constituting the light emitting side polarizing plate 30 are the absorption axes of the polarizer. And the in-plane slow axis of the liquid crystal cell-side transparent protective layer may be arranged so as to have a substantially parallel relationship or a substantially orthogonal relationship. In particular, it is preferable in terms of productivity to arrange the two so as to be substantially orthogonal. That is, in the present invention, the film showing biaxial orientation to the extent defined as the liquid crystal cell-side transparent protective layers 23, 33 is preferably produced by a stretching operation mainly composed of transverse stretching, in which case the slow axis is Since it becomes the width direction of the roll film, the absorption axis of the polarizer and the slow phase of the transparent protective layer are bonded by roll-to-roll bonding with the polarizer whose longitudinal direction (flow direction) is the absorption axis. The axis is orthogonal. Further, the light incident side polarizing plate 20 and the light emitting side polarizing plate 30 are usually arranged so that their absorption axes are orthogonal to each other.

  The polarizing plate thus obtained usually has a pressure-sensitive adhesive layer formed on one side or both sides thereof. In the present invention, at least the side to be bonded to the liquid crystal cell, that is, the transparent protective layer 33 made of a cyclic olefin resin film having a phase difference, and the transparent protective layer 23 made of a cellulose acetate type resin film having a phase difference. A pressure-sensitive adhesive layer is formed on each outer side. The thickness of the pressure-sensitive adhesive layer is usually about 5 to 100 μm, preferably 5 to 40 μm. If the pressure-sensitive adhesive layer is too thin, the tackiness is lowered, and if it is too thick, problems such as the pressure-sensitive adhesive protruding easily occur.

  The pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer is usually based on an acrylic resin, styrene resin, silicone resin, or the like, to which a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added, and It consists of a composition to which a silane coupling agent or the like is added if necessary.

  In the polarizing plate constituting the liquid crystal display device of the present invention, another optical functional film may be attached to the surface of the transparent protective layer. As the optical functional film, for example, a film composed of a functional layer such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer as described above, or a property opposite to that of a certain kind of polarized light is transmitted. A reflective polarizing separation film that reflects polarized light, a reflective film having a reflective function on the surface, a transflective film having both a reflective function and a transmissive function, and the like. A commercially available product equivalent to a reflective polarized light separation film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties is sold by the US 3M Company (Sumitomo 3M Co., Ltd. in Japan). “DBEF” (trade name) and the like.

  The backlight 10 may be widely used in general liquid crystal display devices. For example, a sidelight that is composed of a light guide plate and a light source disposed on the side of the light guide, and once the light from the light source is taken into the light guide plate, the light is uniformly emitted to the front side. A direct-type backlight that consists of a mold backlight and a diffuser plate and a light source placed behind it, and diffuses the light from the light source uniformly with the diffuser plate and emits it to the front side. And so on.

  The liquid crystal cell 40 is a device in which a liquid crystal is sealed between two transparent substrates in order to switch the amount of transmitted light, and has a function of changing the alignment state of the liquid crystal by applying a voltage. It may be widely used. The liquid crystal cell 40 typically includes at least a pair of transparent substrates disposed opposite to each other, a transparent electrode provided on each surface of the substrates, and a liquid crystal layer sealed between the electrodes. Have Depending on the alignment state of the liquid crystal layer enclosed in the liquid crystal cell and the alignment state of the liquid crystal layer when a voltage is applied between the electrodes, for example, a twisted nematic (TN) mode or a vertical alignment (VA) mode is used. There are various types.

  The configuration of the present invention is particularly effective for a vertical alignment mode liquid crystal cell. In the vertical alignment mode, rod-like liquid crystal molecules having positive or negative dielectric anisotropy are enclosed in a cell, and the major axis of the liquid crystal molecules is aligned substantially perpendicular to the substrate in the absence of voltage application. The major axis of liquid crystal molecules rotates in a direction parallel to the substrate by applying a voltage, thereby switching the amount of transmitted light. If the light incident side polarizing plate 20 and the light emitting side polarizing plate 30 are arranged so that their absorption axes are orthogonal to the vertical alignment mode liquid crystal cell, display is performed in a normally black mode.

  The set of polarizing plates according to the present invention is a combination of the light emitting side polarizing plate 30 and the light incident side polarizing plate 20 described above with reference to FIG. Since the description so far applies to each configuration as it is, repeated description will be omitted.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further in detail, this invention is not limited by these examples.

The polarizer protective films used in the examples and comparative examples are as follows, and are denoted by respective symbols below. The thickness, the in-plane retardation R _0, thickness direction retardation R _th and water absorption are manufacturer nominal value, slow axis direction refractive indices n _x in the plane, the fast axis direction in-plane refractive index n _y, and The thickness direction refractive index _nz is a value obtained with a phase difference measuring device “KOBRA-21ADH” manufactured by Oji Scientific Instruments. Note that R ₀ and R _th were actually measured using “KOBRA-21ADH”, but almost the same results as the following values were obtained. Further, n _x, n _y, wherein the n _z and thickness formula (3) and a value obtained by equation (4), but may not necessarily match the following R ₀ and R _th, which is triaxial The main factors are that the refractive indices _nx , _ny and _nz in the direction are kept to the fourth decimal place.

(A) Norbornene-based resin film with in-plane retardation COP: trade name “Zeonor film”, obtained from Optes Co., Ltd.
Thickness 73 μm, R ₀ = 55 nm, R _th = 124 nm,
_{n x = 1.5310, n y =} 1.5302, n z = 1.5288,
Water absorption less than 0.01% by weight.

(B) Cellulose acetate-based resin film with in-plane retardation RAC: trade name “KC4FR-T”, obtained from Konica Minolta Opto,
40 μm thickness, R ₀ = 45 nm, R _th = 125 nm,
n _x = 1.4785, n _y = 1.4775, n _z = 1.4750.

(C) Triacetylcellulose film with in-plane retardation of almost zero TAC1: Trade name “Fujitac Film”, obtained from FUJIFILM Corporation
Thickness 80μm.
TAC2: Trade name “KC8UX2M”, obtained from Konica Minolta Opto,
Thickness 80μm.

[Example 1]
(A) Production of light emission side polarizing plate An antiglare layer made of an acrylic ultraviolet curable resin was provided on one surface of a triacetylcellulose film TAC1 subjected to surface saponification treatment. Separately, a TAC1 saponification surface provided with the above antiglare layer was provided on one side of a polarizer having iodine adsorbed and oriented on a polyvinyl alcohol film, and the other side of the polarizer was subjected to corona treatment. The norbornene-based resin film COP was bonded via an adhesive made of an aqueous solution of a polyvinyl alcohol resin, respectively, to produce a light emission side polarizing plate. The COP was arranged so that its in-plane slow axis was perpendicular to the absorption axis of the polarizer.

(B) Production of light incident side polarizing plate Similarly, a cellulose acetate-based resin film RAC that has been subjected to surface saponification treatment on one side of a polarizer in which iodine is adsorbed and oriented on a polyvinyl alcohol film is used in addition to the polarizer. The surface was bonded with a triacetylcellulose film TAC2 that had been subjected to surface saponification treatment via an adhesive made of an aqueous solution of a polyvinyl alcohol resin to produce a light incident side polarizing plate. The RAC was arranged so that its in-plane slow axis was perpendicular to the absorption axis of the polarizer.

(C) Production and Evaluation of Liquid Crystal Display Device The light emitting side polarizing plate was peeled off from the vertical alignment mode liquid crystal display device “Aquos” (diagonal dimension 26 inches = about 66 cm) manufactured by Sharp Corporation. The polarizing plate produced in (a) was attached via an acrylic adhesive in the same axial direction as the original polarizing plate so that the norbornene-based resin film COP was on the liquid crystal cell side. Also, the light incident side polarizing plate is peeled off. Instead, the polarizing plate prepared in (b) above is an acrylic adhesive in the same axial direction as the original polarizing plate so that the cellulose acetate-based resin film RAC is on the liquid crystal cell side. Pasted through the agent.

  This display device was placed under humid heat conditions at a temperature of 60 ° C. and a relative humidity of 95% for 24 hours, then taken out in a normal temperature and normal humidity environment at a temperature of 23 ° C. and a relative humidity of 60%, and the black display screen was visually observed. Evaluation was made over time. As a result, a slight light omission began to be observed 1 hour after lighting, but the light omission completely disappeared after 10 hours.

[Comparative Example 1]
(A) Production of light exit side polarizing plate Triacetyl cellulose in which the same antiglare layer as used in (a) of Example 1 was provided on one side of a polarizer having iodine adsorbed and oriented on a polyvinyl alcohol film. The saponification treatment surface of the film TAC1 is bonded to the other surface of the polarizer with a cellulose acetate resin film RAC subjected to surface saponification treatment via an adhesive made of an aqueous solution of a polyvinyl alcohol resin. A light incident side polarizing plate was prepared. The RAC was arranged so that its in-plane slow axis was perpendicular to the absorption axis of the polarizer.

(B) Production of light incident side polarizing plate A polarizing plate produced in the same manner as in (b) of Example 1 was used as a light incident side polarizing plate.

(C) Production and Evaluation of Liquid Crystal Display Device The polarizing plate produced in (a) above was attached as a light output side polarizing plate so that its RAC was on the liquid crystal cell side, and the polarizing plate produced in (b) above was prepared. A liquid crystal display device was fabricated in the same manner as in Example 1 (c) except that the RAC was attached as a light incident side polarizing plate so that the RAC was on the liquid crystal cell side. The display device was subjected to the same wet heat test as that in Example 1 (c), and then taken out in a room temperature environment for evaluation. As a result, very strong light leakage began to be observed 1 hour after lighting, and the light leakage was clearly observed even after 10 hours.

[Comparative Example 2]
(A) Production of Light Emission Side Polarizing Plate A polarizing plate produced in the same manner as (a) of Comparative Example 1 was used as a light emission side polarizing plate.

(B) Production of light incident side polarizing plate Corona-treated norbornene resin film COP is applied to one side of a polarizer having iodine adsorbed and oriented on a polyvinyl alcohol film, and the other side of the polarizer. The surface saponification-treated triacetyl cellulose film TAC2 was bonded via an adhesive made of an aqueous solution of a polyvinyl alcohol resin, respectively, to produce a light incident side polarizing plate. The COP was arranged so that its in-plane slow axis was perpendicular to the absorption axis of the polarizer.

(C) Production and Evaluation of Liquid Crystal Display Device The polarizing plate produced in (a) above was attached as a light output side polarizing plate so that its RAC was on the liquid crystal cell side, and the polarizing plate produced in (b) above was prepared. A liquid crystal display device was produced in the same manner as in Example 1 (c) except that the COP was attached as a light incident side polarizing plate so that it was on the liquid crystal cell side. The display device was subjected to a wet heat test similar to that in Example 1 (c), and then taken out in a normal temperature and normal humidity environment for evaluation. As a result, strong light omission began to be observed 1 hour after lighting, and the light omission was clearly observed even after 10 hours.

  Table 1 summarizes the outline of the layer configuration and the test results in the above Examples and Comparative Examples.

  As can be seen from Table 1, the transparent protective layer located on the liquid crystal cell side of the light emitting side polarizing plate satisfies the relationship of the above formulas (1) and (2) and has a saturated water absorption of 0.05% by weight. A cellulose acetate resin film that employs a cyclic olefin resin film that is less than or equal to the liquid crystal cell side of the light incident side polarizing plate and that also satisfies the relationship of the above formulas (1) and (2). In the case of Example 1 employed, even when the product was placed in a high temperature and high humidity environment for a long time and then taken out in a normal temperature and normal humidity environment, the occurrence of light leakage was small and good visibility was obtained.

It is a cross-sectional schematic diagram which shows the example of the fundamental layer structure of the liquid crystal display device which concerns on this invention.

Explanation of symbols

10 …… Backlight,
20. Light incident side polarizing plate,
21 …… Polarizer,
23, 24 ... Transparent protective layer,
30: Light exit side polarizing plate,
31 ... Polarizer,
33, 34 ... Transparent protective layer,
40: Liquid crystal cell.

Claims (8)

A liquid crystal display device in which a backlight, a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate are arranged in this order,
Each of the light incident side polarizing plate and the light emitting side polarizing plate has a laminated structure in which both sides of a polarizer made of polyvinyl alcohol resin are sandwiched between transparent protective layers,
Transparent protective layer positioned on at least the liquid crystal cell side of the light-emitting side polarizing plate, in-plane slow axis direction of the refractive index n _x, the refractive index in a direction perpendicular to the slow axis in the plane n _y, the thickness direction Where n _{z is} the refractive index and d is the thickness, the following formulas (1) and (2)
_{(N x -n y) × d} ≧ 30nm (1)
_nx > _ny > _nz (2)
And is composed of a cyclic olefin-based resin film having a saturated water absorption of less than 0.05% by weight,
The transparent protective layer located at least on the liquid crystal cell side of the light incident side polarizing plate is composed of a cellulose acetate-based resin film satisfying the above formulas (1) and (2).   The liquid crystal display device according to claim 1, wherein the cellulose acetate-based resin film constituting the liquid crystal cell side transparent protective layer of the light incident side polarizing plate has a thickness of 20 to 60 µm.   The transparent protective layer positioned on the backlight side of the light incident side polarizing plate and the transparent protective layer positioned on the viewing side of the light emitting side polarizing plate are both composed of a cellulose acetate-based resin film. Liquid crystal display device.   The transparent protective layer located in the visual recognition side of the light emission side polarizing plate has a surface treatment layer selected from a hard coat layer, an antiglare layer, an antireflection layer and an antistatic layer. Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the liquid crystal cell is in a vertical alignment mode. A set of polarizing plates arranged on both sides of the liquid crystal cell,
It has a laminated structure sandwiching both sides of a polarizer comprising a polyvinyl alcohol-based resin in the transparent protective layer, at least a transparent protective layer disposed on the liquid crystal cell side, the refractive index in the in-plane slow axis direction n _x, surface the the refractive index in the direction orthogonal to the slow axis in the inner n _y, the refractive index in the thickness direction n _z, the thickness as d, the following formula (1) and (2)
_{(N x -n y) × d} ≧ 30nm (1)
_nx > _ny > _nz (2)
And a light emitting side polarizing plate composed of a cyclic olefin resin film having a saturated water absorption of less than 0.05% by weight, and a laminate in which both sides of a polarizer composed of a polyvinyl alcohol resin are sandwiched between transparent protective layers The transparent protective layer having a structure and disposed at least on the liquid crystal cell side is composed of a light incident side polarizing plate composed of a cellulose acetate-based resin film satisfying the formulas (1) and (2). A set of polarizing plates.   Located on the opposite side of the transparent protective layer disposed on the liquid crystal cell side of the light exit side polarizing plate and the transparent protective layer disposed on the liquid crystal cell side of the light incident side polarizing plate. The set of polarizing plates according to claim 6, wherein the transparent protective layer is composed of a cellulose acetate-based resin film.   The transparent protective layer located opposite to the transparent protective layer disposed on the liquid crystal cell side of the light exit side polarizing plate is a surface treatment layer selected from a hard coat layer, an antiglare layer, an antireflection layer and an antistatic layer. A set of polarizing plates according to claim 6 or 7.

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