JP2011033751A - Protective cover for liquid crystal display - Google Patents

Abstract

The present invention relates to a protective cover for a liquid crystal display device, and in order to prevent the display from becoming difficult to see even when the liquid crystal display device is observed while wearing polarized glasses, a liquid crystal is provided on the protective cover itself of the liquid crystal display device. By giving the function of converting linearly polarized light from the display into circularly polarized light or elliptically polarized light, it is thinner and lighter than using films having these two types of functions, and also has excellent scratch resistance. A protective cover for a liquid crystal display device is provided.
A protective cover for a liquid crystal display for protecting a display screen of a liquid crystal display device having a polarizing plate on the observation side, the liquid crystal display having a polymethyl methacrylate resin layer on at least one side of a polycarbonate resin layer A protective cover for liquid crystal displays that changes linearly polarized light emitted from the device into circularly polarized light or elliptically polarized light.
[Selection figure] None

Description

  The present invention relates to a protective cover for a liquid crystal display that protects a liquid crystal display device, and the liquid crystal display protective cover does not become difficult to see even when the liquid crystal display device is observed while wearing polarized glasses.

  Liquid crystal display devices are mobile devices such as mobile phones, PDAs, AV devices, game machines, digital cameras, watches, mobile navigation, car navigation, fish finder, etc. due to their thin, lightweight and low power consumption features. Widely used in equipment installed on the body.

  As described above, portable information devices using a liquid crystal display device have been increasingly used not only indoors but also outdoors.

  Sunglasses are increasingly worn outdoors, especially in the summer, but so-called polarized sunglasses with polarization characteristics reduce glare and glare from reflected light on watersides, golf course grass, road surfaces, buildings, etc. It is becoming more and more used. Polarized sunglasses are usually designed to reduce the S wave and transmit the P wave as its polarization characteristics. Usually, the polarized light component contained in the reflected light has many S wave components, and by blocking this, the glare in the reflected light is reduced, so that what is desired to be observed is made easy to see.

  When observing a liquid crystal display with polarized sunglasses having such characteristics, the polarization transmission axis of the polarizing film installed on the display surface side of the liquid crystal display panel is orthogonal to the polarization transmission axis of the polarized sunglasses. In such a case, the display becomes dark and difficult to see. As described above, as the application field in which the liquid crystal display device is used is expanded and the number of people wearing polarized sunglasses increases, there has been a strong demand for a solution to this problem.

  As a method for solving such a problem, Patent Document 1 discloses that a linearly polarized light which is attached to the front surface of a liquid crystal panel and has an axis inclined by a predetermined angle with the direction of the linearly polarized light of the liquid crystal panel is rotated. A liquid crystal display device characterized in that means for polarizing the polarization direction of display light emitted from the display screen into circularly polarized light or elliptically polarized light is disclosed in Patent Document 2. In addition, as a method of solving this problem, various methods are described in Patent Documents 3-10.

  Further, since the protective cover of the liquid crystal panel is required to have transparency, weather resistance, surface hardness, etc., acrylic resin has been mainly used conventionally, and in many cases has been hard-coated. Portable information devices that use liquid crystal display devices are required not only to improve functionality but also to be lighter and thinner, and thin materials that are thin enough to protect the surface of the liquid crystal display are also required. Is coming. As a result, polycarbonate resin is processed into a sheet shape as a material that is hard to break even if it is made thinner, and it is hard coated to be used as a protective cover for liquid crystal displays. However, since the elastic modulus of the polycarbonate resin itself is low and the hardness is not sufficient, there is a problem that the hardness is insufficient even when the hard coat processing is performed.

Japanese Patent Laid-Open No. 1-204092 Japanese Patent Laid-Open No. 10-10523 Japanese Patent Laid-Open No. 10-10522 Japanese Patent Laid-Open No. 10-49082 JP 2000-19325 A JP 2002-350821 A JP 2004-170875 A JP 2005-148119 A JP 2005-157082 A JP 2008-83307 A

  The present invention relates to a protective cover for a liquid crystal display device, and in order to prevent the display from becoming difficult to see even when the liquid crystal display device is observed while wearing polarized glasses, a liquid crystal is attached to the protective cover itself of the liquid crystal display device. By giving the function of converting linearly polarized light from the display into circularly polarized light or elliptically polarized light, it is thinner and lighter than using films having these two types of functions, and also has excellent scratch resistance. Another object of the present invention is to provide a protective cover for a liquid crystal display device.

The present inventors have found that the above object can be achieved by processing a polycarbonate resin and a polymethyl methacrylate resin using a multi-manifold type multilayer die to form a protective cover for a liquid crystal display. The present invention has been completed based on these findings, and has been completed. The present invention provides the following protective cover for a liquid crystal display.
Item 1. A protective cover for a liquid crystal display for protecting a display screen of a liquid crystal display device provided with a polarizing plate on the observation side, having a polymethyl methacrylate resin layer on at least one surface of the polycarbonate resin layer, and emitting from the liquid crystal display device A protective cover for liquid crystal displays that changes linearly polarized light into circularly or elliptically polarized light.
Item 2. Item 2. The protective cover for a liquid crystal display according to Item 1, which is a multilayer synthetic resin sheet obtained by processing polycarbonate resin and polymethylmethacrylate resin using a multi-manifold type multilayer die.
Item 3. Item 3. The protective cover for liquid crystal display according to item 1 or 2, wherein the retardation is λ / 4.
Item 4. Item 4. The protective cover for liquid crystal display according to any one of Items 1 to 3, wherein a hard coat treatment is applied to at least one of the surfaces of the polymethyl methacrylate resin layer.

  The protective cover for a liquid crystal display of the present invention has a function of converting linearly polarized light from the liquid crystal display into circularly polarized light or elliptically polarized light in the protective cover of the liquid crystal display device itself, so that the liquid crystal display device can be observed while wearing the polarizing glasses. However, the display does not become dark and difficult to see. In addition, the protective cover for liquid crystal display of the present invention is thinner and lighter than using a film having a function of protecting a liquid crystal display device and a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. Can do. Furthermore, the protective cover for a liquid crystal display of the present invention is excellent in scratch resistance.

  Hereinafter, the protective cover for liquid crystal display of the present invention will be described in detail.

Protective cover for liquid crystal display The protective cover for liquid crystal display of the present invention is a protective cover for liquid crystal display for protecting the display screen of a liquid crystal display device having a polarizing plate on the observation side, and is provided on at least one surface of the polycarbonate resin layer. It has a polymethyl methacrylate resin layer and is characterized in that linearly polarized light emitted from the liquid crystal display device is changed to circularly polarized light or elliptically polarized light.

  By converting the linearly polarized light emitted from the liquid crystal display into circularly polarized light or elliptically polarized light, even if the liquid crystal display device is observed while wearing the polarizing glasses, the display becomes dark and does not become difficult to see.

  In the protective cover for a liquid crystal display of the present invention, it is preferable that at least one of the surfaces of the polymethyl methacrylate resin layer is subjected to a hard coat treatment.

  The liquid crystal display device using the protective cover for liquid crystal display of the present invention is any liquid crystal display device (TN liquid crystal, STN liquid crystal, TFT liquid crystal, etc.) as long as it has a polarizing plate on the observation side. However, it is particularly effective for IPS-driven TFT liquid crystal.

  A method of changing linearly polarized light emitted from the liquid crystal display device to circularly polarized light or elliptically polarized light will be described below. By arranging the protective cover for liquid crystal display so that the direction of linear polarization coming out of the liquid crystal display panel is 45 ° with respect to the fast axis and slow axis of the protective cover for liquid crystal display which is a quarter wave plate The emitted light can be converted into circularly polarized light. Even if the linear polarization direction is 45 ° with respect to the fast axis and slow axis of the protective cover for liquid crystal display, if the tilt angle is greater than 0 ° and less than 90 °, Any protective cover for liquid crystal displays that can convert light into elliptically polarized light is not limited to those with a retardation of λ / 4 (quarter wave plate), but any type of retardation protective cover for liquid crystal displays. It may be.

  Specific examples of the layer structure of the protective cover for a liquid crystal display of the present invention include a polycarbonate resin layer as a PC layer, a polymethyl methacrylate resin layer as a PMMA layer, and a hard coat layer as an HC layer. PC layer / PMMA layer, PMMA Layer / PC layer / PMMA layer, PC layer / PMMA layer / HC layer, PMMA layer / PC layer / PMMA layer / HC layer, HC layer / PMMA layer / PC layer / PMMA layer / HC layer. In addition, other layers can be added to these layer structures as long as the effects of the present invention are achieved.

  The thickness of the protective cover for a liquid crystal display of the present invention can be appropriately selected as necessary, but it is preferably about 110 to 2200 μm, more preferably about 220 to 1370 μm.

-Polycarbonate resin layer Polycarbonate resin is suitably used as the base material for the protective cover for liquid crystal display of the present invention in that it is difficult to break even if it is thin, transparency, processing characteristics, market availability, etc. It is done.

  The thickness of the polycarbonate resin layer is preferably 100 to 2000 μm, more preferably 200 to 1200 μm.

  The polycarbonate resin has high transparency, and the total light transmittance (JIS K7105) measured in the form of a sheet having a thickness of 3 mm is preferably 80% or more, more preferably 85 to 89%.

  As the polycarbonate resin, a polymer derived from a divalent phenolic compound typified by bisphenol A is used. The method for producing the polycarbonate resin is not particularly limited, and any one produced by any of the phosgene method, the transesterification method, and the solid phase polymerization method can be used. There is no particular limitation on the molecular weight.

  Moreover, you may contain various additives, such as a general heat stabilizer used for polycarbonate resin, a ultraviolet absorber, a light-resistant stabilizer, a mold release agent, a lubricant, and an antistatic agent.

-Polymethylmethacrylate resin layer The polymethylmethacrylate resin layer in this invention aims at preventing the damage | wound of the protective cover for liquid crystal displays of this invention.

  The polymethyl methacrylate resin layer is formed on one side or both sides of the polycarbonate resin layer. The thickness of the polymethyl methacrylate resin layer is preferably 10 to 100 μm, more preferably 20 to 70 μm. When the thickness of the polymethyl methacrylate resin layer increases, warpage due to moisture absorption tends to occur, and thus it is necessary to limit the thickness to a sufficient level in order to exhibit sufficient hardness. Here, the thickness of the polymethyl methacrylate resin layer means the thickness of one side when the polymethyl methacrylate resin layer is on both sides of the polycarbonate resin layer.

  The polymethyl methacrylate resin in the present invention has a core-shell structure (multilayer polymer particles) in which a core layer made of a rubber-like polymer (crosslinked elastic polymer) is covered with a shell layer of a glass-like polymer (thermoplastic polymer). It is also possible to disperse the fine particles (see, for example, Japanese Patent Publication No. 62-41241). Further, the polymethyl methacrylate resin layer may contain various additives such as a general heat stabilizer, ultraviolet absorber, light stabilizer, mold release agent, lubricant, and antistatic agent.

  The methacrylic resin in the present invention has high transparency, and the total light transmittance (JIS K7105) measured in the form of a sheet having a thickness of 3 mm is preferably 85% or more, and more preferably 90 to 93%.

Hard coat layer In general, an inorganic hard coat layer, an organic hard coat layer, an organic inorganic hard coat layer (also referred to as a hybrid system), a silicone hard coat layer, and the like can be used as the hard coat layer in the present invention.

The inorganic hard coat layer is made of, for example, SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ or the like, and the layer is formed by vacuum deposition, sputtering, or the like on the acrylic resin layer.

  Examples of the organic hard coat layer include a type in which a melamine type, alkyd type, urethane type and acrylic resin paint is heat-cured, a type in which a polyfunctional acrylic resin paint is UV-cured, and the like.

  Examples of the organic / inorganic hard coat layer include those in which a photopolymerization reactive functional group is introduced on the surface of silica ultrafine particles and uniformly dispersed in the organic component of the ultraviolet curable hard coat material. Ultraviolet curable hard coat components and photosensitive groups of inorganic ultrafine particles undergo a polymerization reaction, resulting in the formation of a network-like crosslinked coating film in which ultrafine silica particles mediated by chemical bonds are uniformly dispersed in an organic matrix, etc. Is mentioned.

  Examples of the silicone hard coat layer include polycondensation of partial hydrolysates such as carbon functional alkoxysilane, alkyltrialkoxysilane, and tetraalkoxysilane, and those in which colloidal silica is blended.

  In the present invention, as described above, a reaction type hard coat film containing alkoxysilane, which is said to be silane-based, can also be used, but in terms of productivity, it is a reactive crosslinking type of various organic compounds that are said to be organic-based. It is desirable to use a hard coat film or an organic / inorganic hard coat layer (also called a hybrid system).

  In particular, by using a scratch-resistant organic hard coat film or organic / inorganic hard coat layer (also called a hybrid system) that is cured by irradiating ultraviolet rays, the display faceplate can be stably displayed with high productivity. A transparent multilayer sheet can be produced.

  Since the protective cover for a liquid crystal display of the present invention is used in an environment from a low temperature to a high temperature, it is necessary to determine the thickness of the hard coat layer in consideration of the expansion and contraction of the sheet due to a temperature change. In order to follow the expansion and contraction of the sheet due to temperature change, it is desirable that the thickness of the hard coat layer is thin, but the hardness of the sheet surface tends to decrease. On the other hand, if the thickness of the hard coat layer is large, curing shrinkage due to UV curing increases and cracks may occur. For this reason, the thickness of the hard coat layer in the protective cover for liquid crystal display is preferably about 1 to 20 μm, particularly about 3 to 12 μm, thereby satisfying both hardness and durability. Here, when there are two hard coat layers, the thickness of the hard coat layer means the thickness of one layer.

Method for Producing Liquid Crystal Display Protective Cover The liquid crystal display protective cover of the present invention is obtained by processing a polycarbonate resin and a polymethylmethacrylate resin using a multi-manifold type multilayer die.

  The multi-manifold type multilayer die is a method in which a laminated sheet is formed by extruding from a sheet-shaped die after being integrated inside a sheet extrusion die. It is possible to minimize variations in the thicknesses of the layers without interposing foreign matters between the bonding surfaces at the time of bonding.

  In the process of sheet extrusion, control either one of molten resin temperature, draw ratio from die to calendar roll, rotation ratio of each calendar roll, rotation ratio of calendar roll and take-up roll, or a combination of these. Thus, the retardation of the manufactured protective cover for liquid crystal display can be adjusted. For example, by performing such control so that the retardation approaches λ / 4, the protective cover for a liquid crystal display of the present invention having the retardation of λ / 4 can be obtained.

  The hard coat treatment on at least one of the surfaces of the polymethyl methacrylate resin layer of the present invention can be performed by a known method.

  That is, for the hard coat treatment, it is possible to use various coating materials that contain a crosslinking monomer and are cured by irradiation with ionizing radiation, and various coating materials that are cured by causing polymerization or condensation reaction by heating. . As for the method of coating the polymethyl methacrylate resin layer, a known method such as a dip coating method, various roll coating methods, a flow coating method, a rod coating method, a blade coating method, a spray coating method, a die coating method, a gravure roll coating method, etc. You can choose from the methods.

  Examples and the like will be given below to explain the present invention in more detail. However, the present invention is not limited to these experimental examples.

[Test method]
Specifically, the surface damage property test in Examples and Comparative Examples was performed as follows.

The surface of the sheet was reciprocated 10 times while pressing steel wool # 0000 with a load of 500 g / cm ² , and then the degree of scratching was determined as follows.

Less than 10 scratches occurred; ○
11 to 50 scratches occurred;
Countless scratches occurred; ×
[Example 1]
Extruder (main single-screw extruder made by Tanabe Plastics, extruder screw diameter φ40mm L / D = 32, sub-single screw extruder made by Plastic Giken, extruder screw diameter φ25mm L / D = 24) and multi-manifold die Into the main extruder, polycarbonate resin (manufacturer: Sumitomo Dow Co., Ltd., varieties: Caliber 301-15) and polymethylmethacrylate resin (manufacturer: Mitsubishi Rayon Co., Ltd., varieties: Acripet VH) are introduced into the sub-cylinder. Then, the main extruder is extruded at a cylinder temperature of 270 ° C. and a screw rotation speed of 60 rpm, the sub-extruder is extruded at a cylinder temperature of 260 ° C. and a screw rotation speed of 30 rpm, and the draw ratio at which the resin discharged from the die is drawn down to a three-roll device is adjusted. At the same time, the sheet coming out from the three-roll apparatus was taken up by a take-up machine while slowly cooling the sheet. By adjusting the speed ratio between the three-roll device and the take-up machine, a sheet was prepared so that the overall retardation was λ / 4. As described above, a two-layer 0.5 mm sheet composed of a polycarbonate resin layer having a retardation of λ / 4 of about 430 μm and a polymethyl methacrylate resin layer of 70 μm was obtained.

  On the polymethylmethacrylate resin layer of this two-layer sheet, UV-curable hard coat paint made of polyfunctional acrylic resin (Nippon Synthetic Chemical Industry Co., Ltd. UV-1700B 9 g, Shin-Nakamura Chemical Co., Ltd. A-LEN -10 1 g) was used to form a hard coat layer of about 4 μm by a roll coating method.

[Comparative Example 1]
Extruder (main single-screw extruder made by Tanabe Plastics, extruder screw diameter φ40mm L / D = 32, sub single-screw extruder made by Pla Giken, extruder screw diameter φ25mm L / D = 24) and a multi-manifold die, polycarbonate resin (manufacturer: Sumitomo Dow Co., Ltd., product type: Caliber 301-15) in the main extruder, and polymethyl methacrylate resin (manufacturer: Mitsubishi Rayon Co., Ltd., product type) in the secondary cylinder. Acrypet VH) is charged, the main extruder is extruded at a cylinder temperature of 290 ° C and a screw speed of 60 rpm, the auxiliary extruder is extruded at a cylinder temperature of 260 ° C and a screw speed of 30 rpm, and the resin discharged from the die is fed into a three-roll device. The sheet was taken out by a take-up machine while the sheet coming out of the three-roll apparatus was gradually cooled. The sheet was made by setting the take-up machine speed to be slower than the three-roll machine. As described above, two 0.5 mm sheets each comprising a polycarbonate resin layer of about 430 μm and a polymethyl methacrylate resin layer of 70 μm, each having a retardation of almost 0, were obtained. On this polymethyl methacrylate resin layer layer, a hard coat layer of about 4 μm was formed by a roll coat method using an ultraviolet curable hard coat paint (Nippon Synthetic Chemical Industry Co., Ltd. UV-1700B) made of a polyfunctional acrylic resin.

  The hard-coated two-layer sheet comprising the polycarbonate resin and the polymethylmethacrylate resin obtained in Example 1 and Comparative Example 1 is 45 degrees in the longitudinal direction and 90 degrees in the longitudinal direction with respect to the extrusion direction. The sample sheet was cut out in the horizontal direction and the sample sheet was taken out.

Table 1 shows the result of observing the screen display with this sample sheet attached on an IPS-driven liquid crystal display and wearing polarized sunglasses.

  From the above results, the protective cover for the liquid crystal display of the present invention does not become dark and difficult to see even when the liquid crystal display device is observed while wearing the polarized sunglasses. Are better.

[Example 2]
Extruder (Toshiba Machine's main single screw extruder, extruder screw diameter φ90mm L / D = 32, Toshiba Machine's sub single screw extruder, extruder screw diameter φ50mm L / D = 32) and multi-manifold die Used, polycarbonate resin (manufacturer: Sumitomo Dow Co., Ltd., varieties: Caliber 301-15) is introduced into the main extruder, and polymethyl methacrylate resin (manufacturer: Mitsubishi Rayon Co., Ltd., varieties: Acripet VH) is introduced into the sub-cylinder. The main extruder is extruded at a cylinder temperature of 300 ° C, the sub-extruder is extruded at a cylinder temperature of 270 ° C, and the resin discharged from the die is a horizontal three roll device (roll temperature, first roll: 130 ° C, second roll: 120 ° C The third roll (150 ° C.) was cooled into a sheet, and the sheet coming out of the three-roll apparatus was taken out by a take-up machine while gradually cooling the sheet. By adjusting the speed ratio between the rolls of the three-roll apparatus and the speed ratio between the three-roll machine and the take-up machine, a sheet was prepared so that the retardation was λ / 4 as a whole. As described above, a 0.5 mm sheet having two layers composed of a polycarbonate resin layer having a retardation of λ / 4 of about 430 μm and a polymethyl methacrylate resin layer of 70 μm was obtained.

  On the polymethylmethacrylate resin layer of this two-layer sheet, UV-curable hard coat paint made of polyfunctional acrylic resin (Nippon Synthetic Chemical Industry Co., Ltd. UV-1700B 9 g, Shin-Nakamura Chemical Co., Ltd. A-LEN -10 1 g) was used to form a hard coat layer of about 4 μm by roll coating.

[Comparative Example 2]
As in Example 2, an extruder (Toshiba Machine's main single screw extruder, extruder screw diameter φ90 mm L / D = 32, Toshiba Machine's subsidiary single screw extruder, extruder screw diameter φ50 mm L / D = 32 ) And multi-manifold die, polycarbonate resin (manufacturer: Sumitomo Dow Co., Ltd., varieties: Caliber 301-15) in the main extruder, and polymethyl methacrylate resin (manufacturer: Mitsubishi Rayon Co., Ltd., varieties: Acrylic) in the secondary cylinder Pet VH) is injected, the main extruder is extruded at a cylinder temperature of 300 ° C, the sub-extruder is extruded at a cylinder temperature of 270 ° C, and the resin discharged from the die is a horizontal three roll device (roll temperature, first roll: 130 ° C, The second roll (120 ° C., the third roll; 150 ° C.) was cooled into a sheet shape, and the sheet coming out of the three-roll apparatus was slowly cooled, and the sheet was taken up by a take-up machine. By adjusting the speed ratio between the rolls of this three-roll apparatus and the speed ratio between the three-roll machine and the take-up machine, a sheet was made so that the retardation was almost zero as a whole. As described above, a 0.5 mm sheet having two layers consisting of about 430 μm of the polycarbonate resin layer having substantially no retardation and 70 μm of the polymethyl methacrylate resin layer was obtained.

  On the polymethylmethacrylate resin layer of this two-layer sheet, UV-curable hard coat paint made of polyfunctional acrylic resin (Nippon Synthetic Chemical Industry Co., Ltd. UV-1700B 9 g, Shin-Nakamura Chemical Co., Ltd. A-LEN -10 1 g) was used to form a hard coat layer of about 4 μm by roll coating.

  The hard-coated two-layer sheet comprising the polycarbonate resin and the polymethylmethacrylate resin obtained in Example 2 and Comparative Example 2 is oriented at 45 degrees in the longitudinal direction and 90 degrees in the longitudinal direction. The sample sheet was cut out in the horizontal direction and the sample sheet was taken out.

  Table 2 shows the results of observing the screen display with this sample sheet attached on an IPS-driven liquid crystal display and wearing polarized sunglasses.

  From the above results, the protective cover for the liquid crystal display of the present invention does not become dark and difficult to see even when the liquid crystal display device is observed while wearing the polarized sunglasses. Are better.

Claims (4)

  A protective cover for a liquid crystal display for protecting a display screen of a liquid crystal display device provided with a polarizing plate on the observation side, having a polymethyl methacrylate resin layer on at least one surface of the polycarbonate resin layer, and emitting from the liquid crystal display device A protective cover for liquid crystal displays that changes linearly polarized light into circularly or elliptically polarized light.   The protective cover for a liquid crystal display according to claim 1, which is a multilayer synthetic resin sheet obtained by processing a polycarbonate resin and a polymethyl methacrylate resin using a multi-manifold type multilayer die.   The protective cover for a liquid crystal display according to claim 1 or 2, wherein the retardation is λ / 4.   The protective cover for a liquid crystal display according to any one of claims 1 to 3, wherein a hard coat treatment is applied to at least one of the surfaces of the polymethyl methacrylate resin layer.