JP2010054913A - Protection film for image display device, polarizing plate, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection film having excellent adhesion durability between a polyester film and a hard coat layer to environmental light in the protection film for an image display device wherein the hard coat layer is formed on the surface of the polyester film. <P>SOLUTION: The polyester film having 60 to 75° contact angle to water on at least one surface thereof is used and a hard coat film obtained by forming the hard coat layer on the surface of the polyester film is used as the protection film for the image display device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a protective film for an image display device in which a hard coat layer is formed on the surface of a polyester film, and a polarizing plate and an image display device using the protective film.

  A protective film with high hardness performance to prevent scratches on the display surface of image display devices such as liquid crystal displays, plasma display panels, cathode ray tube (CRT) displays, and organic electroluminescence (EL) displays A layer is generally provided. In addition, since visibility is lost when external light is reflected on the display surface of the image display device, TVs and personal computers that emphasize image quality, video cameras and digital cameras used outdoors with strong external light, and reflected light are used. In mobile phones that display images, the protective film layer may be provided with a function to prevent reflection of external light. An anti-glare processing technique is used in which incident light is scattered by forming the image to blur the reflected image. In particular, the latter antiglare treatment technique is relatively inexpensive and is preferably used for applications such as large monitors and personal computers.

  In addition, for large screen image display device applications, such as wall-mounted television applications, there is a growing need for further thinning and light weight of image display devices. Thus, there is a demand for a function for reinforcing the strength of the image display element, and a reduction in the thickness of the protective film itself. As a protective film that meets these requirements, it is excellent in mechanical strength and cost, so that a polyester film, particularly a polyethylene terephthalate film is used as a base film, and a hard coat layer is formed on the surface thereof. Although it can be considered, the polyester film is generally inert and has poor adhesion, so that there is a problem in that the polyester film easily peels off from the hard coat layer. In order to solve such a problem, for example, Patent Document 1 proposes that an easy-adhesive primer layer of a predetermined methacrylate copolymer is provided on the surface of a polyester film. Patent Document 2 proposes forming an easy-adhesive coating film mainly composed of an acrylic resin having a crosslinkable functional group and a silane coupling agent on the surface of a polyester film.

Japanese Examined Patent Publication No. 3-62551 JP-A-5-316678

  In the above conventional protective film, when used in an image display device, particularly a liquid crystal display device, the adhesion between the polyester film and the hard coat layer is caused by exposure to ambient light, particularly ultraviolet rays therein. However, it may decrease in a short period of time. Accordingly, an object of the present invention is a protective film for an image display device in which a hard coat layer is formed on the surface of a polyester film, and a protective film having excellent adhesion durability between the polyester film and the hard coat layer against environmental light. It is to provide.

  As a result of intensive studies, the present inventors adopted a polyester film having a water contact angle of at least one surface in a specific range, and forming a hard coat layer on the surface, thereby achieving the above object. The present invention has been completed. That is, the present invention is a protective film for an image display device in which a hard coat layer is formed on at least one surface of a polyester film, and the water contact angle of the surface on which the hard coat layer of the polyester film is formed is 60. Provided is a protective film characterized by an angle of ˜75 °.

  Further, according to the present invention, there is provided a polarizing plate obtained by laminating the protective film having a hard coat layer formed on one surface of a polyester film and a polarizing film, the polarizing film being a protective film polyester film A polarizing plate disposed on the side is provided, and further includes the protective film or the polarizing plate and an image display element, and the protective film or the polarizing plate has a hard coat layer side facing outside, and the visual display of the image display device is provided. An image display device arranged on the side is also provided.

  The protective film of the present invention has high durability against environmental light in terms of adhesion between the polyester film as the base film and the hard coat layer formed on the surface thereof. Moreover, the polarizing plate which combined this protective film of this invention with the polarizing film also expresses the same effect. And since the image display apparatus of this invention which has arrange | positioned the protective film or polarizing plate of this invention has high durability with respect to environmental light, since the polyester film is used as the base film of a protective film, the intensity | strength of an image display element Is reinforced, and warping of the image display element can be prevented.

<Protective film>
The protective film of the present invention is a protective film used for image display device use, particularly for display surface protection, wherein a polyester film is used as a base film, and a hard coat layer is formed on at least one surface thereof. It is. And at least the surface on which the hard coat layer is formed of both surfaces of the polyester film has a water contact angle of 60 ° to 75 °.

<Polyester film>
The polyester film used as the base film is a film mainly composed of polyester, and may be a single layer film mainly composed of polyester or a multilayer film having a layer mainly composed of polyester. Also good. Moreover, the surface treatment may be performed on both surfaces or one surface of these single layer films or multilayer films, and this surface treatment is performed by corona treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation, or the like. Modification may be sufficient, and thin film formation by application | coating, vapor deposition, etc. of a polymer, a metal, etc. may be sufficient. The weight ratio of polyester in the entire polyester film is usually 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more.

  Examples of the polyester include polyethylene terephthalate, polyethylene isophthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, and 1,4-cyclohexanedimethylene terephthalate, and two or more of them may be used as necessary. . Of these, polyethylene terephthalate is preferably used.

  Polyethylene terephthalate is a polyester having a structural unit derived from terephthalic acid as a dicarboxylic acid component and a structural unit derived from ethylene glycol as a diol component, and 80 mol% or more of all repeating units are preferably ethylene terephthalate. The structural unit derived from other copolymerization components may be included. Other copolymer components include isophthalic acid, p-β-oxyethoxybenzoic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid , Dicarboxylic acid components such as sebacic acid, 5-sodium sulfoisophthalic acid, 1,4-dicarboxycyclohexane, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, bisphenol A ethylene oxide adduct, polyethylene glycol And diol components such as polypropylene glycol and polytetramethylene glycol. These dicarboxylic acid components and diol components can be used in combination of two or more if necessary. It is also possible to use an oxycarboxylic acid such as p-oxybenzoic acid in combination with the carboxylic acid component or diol component. As another copolymer component, a dicarboxylic acid component and / or a diol component containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be used. Polyethylene terephthalate can be produced by a direct polymerization method in which terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid and / or other diol are directly reacted, dimethyl ester of terephthalic acid and ethylene glycol, and necessary Depending on the above, any production method such as a so-called transesterification method in which a dimethyl ester of another dicarboxylic acid and / or another diol is transesterified can be applied.

  The polyester may be blended with known additives as necessary. Examples thereof include a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistant agent, and an impact resistance improving agent. Is mentioned. However, when a polyester film is used as a base film for an antiglare film, transparency is generally required, so it is preferable to keep the additive amount to a minimum.

  Moreover, in order to give haze to a polyester film, you may mix | blend inorganic fine particles or organic fine particles with polyester. Inorganic fine particles include calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica, glass, talc, mica, white carbon, magnesium oxide, zinc oxide, and other inorganic particles, and these inorganic particles are surface treated with fatty acids. What has been applied can be cited as a representative one. The organic fine particles include melamine beads (refractive index 1.57), polymethyl methacrylate beads (refractive index 1.49), methyl methacrylate / styrene copolymer resin beads (refractive index 1.50 to 1.59). ), Polycarbonate beads (refractive index 1.55), polyethylene beads (refractive index 1.53), polyvinyl chloride beads (refractive index 1.46), silicone resin beads (refractive index 1.46) and the like are used. be able to.

  The polyester film is preferably uniaxially stretched or biaxially stretched (the polyester film thus uniaxially stretched or biaxially stretched is hereinafter also simply referred to as “stretched polyester film”). The stretched polyester film is a film excellent in mechanical properties, solvent resistance, scratch resistance, cost, etc., and a protective film using such a polyester film is excellent in mechanical strength, etc., and has a reduced thickness. Can be planned.

  A stretched polyester film can be produced by forming the polyester into a film and performing a uniaxial stretching process or a biaxial stretching process. By performing the stretching treatment, a polyester film having high mechanical strength can be obtained. The method for producing the stretched polyester film is arbitrary, and is not particularly limited. For example, as a uniaxially stretched polyester film, a non-oriented film obtained by melting polyester and extruding it into a sheet shape is used. A method of performing heat setting treatment after transverse stretching with a tenter at the above temperature can be mentioned. In addition, in the biaxially stretched polyester film, the polyester is melted, and the non-oriented film extruded and formed into a sheet is subjected to heat setting treatment after longitudinal stretching with a tenter at a temperature equal to or higher than the glass transition temperature, and then lateral stretching. A method of performing heat setting treatment can be mentioned. In this case, the stretching temperature is usually 80 to 130 ° C., preferably 90 to 120 ° C., and the stretching ratio is usually 2.5 to 6 times, preferably 3 to 5.5 times. When the draw ratio is low, the polyester film tends not to exhibit sufficient transparency.

  In order to reduce the distortion of the orientation main axis, it is desirable to relax the polyester film before performing the heat setting after stretching. The temperature during the relaxation treatment is usually 90 to 200 ° C, preferably 120 to 180 ° C. The amount of relaxation varies depending on the stretching conditions, and it is preferable to set the amount of relaxation and the temperature during the relaxation treatment so that the thermal shrinkage rate at 150 ° C. of the polyester film after the relaxation treatment is 2% or less.

  The heat setting treatment temperature can be 180 to 250 ° C., preferably 200 to 245 ° C. In the heat setting treatment, it is preferable to first perform a heat treatment at a constant length and then perform a relaxation treatment in the width direction in order to reduce the distortion of the orientation main axis and improve the strength such as heat resistance. The amount of relaxation in this case is preferably adjusted so that the thermal shrinkage rate at 150 ° C. of the polyester film after the relaxation treatment is 1 to 10%, more preferably 2 to 5%. The maximum value of the distortion of the orientation main axis of the stretched polyester film used in the present invention is usually 10 degrees or less, preferably 8 degrees or less, and more preferably 5 degrees or less. When the maximum value of the orientation main axis is larger than 10 degrees, the coloring defect tends to increase when bonded to the liquid crystal display screen. In addition, the “maximum value of the distortion of the orientation main axis” of the stretched polyester film can be measured by, for example, a retardation film inspection apparatus RETS system manufactured by Otsuka Electronics Co., Ltd.

  The in-plane retardation value R of the stretched polyester film is preferably 1000 nm or more, and more preferably 3000 nm or more. When the in-plane retardation value R is less than 1000 nm, coloring from the front tends to be conspicuous. The in-plane retardation value R of the stretched polyester film is represented by the following formula (1).

R = (n _a −n _b ) × d (1)

Here, n _a is the refractive index in the in-plane slow axis direction of the polyester film, n _b is the refractive index in the in-plane fast axis of the stretched polyester film (the direction perpendicular to the plane slow axis direction) And d is the thickness of the stretched polyester film.

  The thickness of the polyester film thus obtained is preferably 20 to 100 μm, and more preferably 30 to 50 μm. When the thickness of the polyester film is less than 20 μm, handling tends to be difficult, and when the thickness exceeds 100 μm, the merit of thinning tends to be reduced.

  In the present invention, the polyester film as described above is selected from those having a water contact angle of 60 ° to 75 ° on at least one surface, and a hard coat layer is formed on the surface. The protective film of the present invention is produced. By forming the hard coat layer on the surface of the polyester film having a specific contact angle with water as described above, it is possible to improve the durability of adhesion between the polyester film and the hard coat layer with respect to ambient light. The water contact angle is preferably 65 ° to 75 °, more preferably 70 ° to 75 °. In addition, when the water contact angles on both surfaces of the polyester film are both 60 ° to 75 °, the values of the water contact angles on both surfaces may be the same or different from each other, The hard coat layer may be formed on both surfaces or only on one surface. In order to set the water contact angle of the surface of the polyester film to 60 ° to 75 °, depending on the material and surface condition of the polyester film, the type and conditions of the surface treatment as described above are appropriately selected. It is good to apply.

<Hard coat layer>
As a material for forming the hard coat layer, an ultraviolet curable resin, a thermosetting resin, an electron beam curable resin, or the like can be used, but an ultraviolet curable resin is preferably used from the viewpoint of productivity, hardness, and the like. Is done. A commercially available product can be used as the ultraviolet curable resin. For example, one or more polyfunctional acrylates such as trimethylolpropane triacrylate and pentaerythritol tetraacrylate, and “Irgacure 907”, “Irgacure 184” (above, manufactured by Ciba Specialty Chemicals), “ A mixture with a photopolymerization initiator such as “Lucirin TPO” (manufactured by BASF) can be used as an ultraviolet curable resin.

  By using the hard coat layer as an anti-glare hard coat layer having fine irregularities on the surface, the obtained protective film can be used as an anti-glare film for preventing reflection of external light. In order to make the hard coat layer an antiglare hard coat layer, it is also possible to form a surface uneven shape by dispersing filler inside the hard coat layer. It is also possible to form. For example, when an anti-glare hard coat layer is formed using an ultraviolet curable resin, after the filler is dispersed in the ultraviolet curable resin, the resin composition may be applied to a polyester film and irradiated with ultraviolet rays. The ultraviolet curable resin may be applied to the polyester resin film, and the ultraviolet ray may be irradiated in a state where the coating film is in close contact with the uneven surface of the mold. The thickness of the hard coat layer is usually 2 μm or more and 20 μm or less. In addition, when forming a hard-coat layer on both surfaces of a polyester film, both hard-coat layers may mutually be the same in composition and thickness, for example, one hard-coat layer is different. An antiglare hard coat layer may be used, and the other hard coat layer may be a so-called clear hard coat layer having no antiglare property.

<Low reflective film>
A surface of the hard coat layer may have a low reflection film. By providing a low reflection film on the outermost surface, reflection of external light due to reflection can be reduced. The low reflection film can be formed by providing a layer of a low refractive index material having a lower refractive index on the hard coat layer. Specific examples of such a low refractive index material include lithium fluoride (LiF), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), cryolite (3NaF · AlF ₃ or Na ₃ AlF _6). ) And other inorganic low-reflective materials containing acrylic resin, epoxy resin, etc .; fluorine-based or silicone-based organic compounds, thermoplastic resins, thermosetting resins, UV-curable resins, etc. An organic low reflection material can be mentioned.

  The thickness of such a low reflection film is usually 0.01 to 0.2 μm, preferably 0.08 to 0.12 μm.

<Polarizing plate>
Since the protective film of the present invention is excellent in adhesion durability between the polyester film and the hard coat layer with respect to ambient light, and is excellent in mechanical strength, it can be used as a protective film for the polarizing film. It becomes the polarizing plate which is excellent in the adhesion durability of the polyester film with respect to the hard coat layer, and excellent in mechanical strength. That is, in many cases, the polarizing plate is generally in the form of a protective film bonded to at least one surface of a polarizing film made of a polyvinyl alcohol-based resin film adsorbed and oriented with iodine or a dichroic dye. The protective film of the present invention is used as a protective film, preferably one protective film. In this case, as the protective film of the present invention, one in which the hard coat layer is formed on one surface of the polyester film is usually used, and the hard coat layer is an antiglare hard coat layer. Some are preferably used. And it is good to bond a polarizing film and the protective film of this invention so that a polarizing film may be arrange | positioned on the opposite side to the hard-coat layer side of the protective film, ie, the polyester film side. In this case, the other surface of the polarizing film may be in a state where nothing is laminated, the protective film of the present invention or another protective film may be laminated, and for bonding to the image display element. An adhesive layer may be formed. Moreover, on the protective film of the polarizing plate formed by laminating a protective film on at least one surface of the polarizing film, the protective film of the present invention is on the side opposite to the hard coat layer side, that is, on the side of the polyester film side. It can also be pasted together to make a polarizing plate. Furthermore, in the polarizing plate in which a protective film is bonded to at least one surface, after the specific polyester film is bonded to the polarizing film as the protective film, the hard coat layer is formed on the polyester film. It can also be set as a polarizing plate. In addition, the polarizing film and the protective film of this invention may be bonded together so that it may contact | connect directly, and may be bonded via another film.

<Image display device>
The image display device of the present invention comprises the protective film of the present invention or the polarizing plate of the present invention and an image display element. Here, the image display element is typically a liquid crystal panel having a liquid crystal cell in which liquid crystal is sealed between upper and lower substrates and displaying an image by changing the alignment state of the liquid crystal by applying a voltage. The protective film of the present invention or the polarizing plate of the present invention can also be applied to various known displays such as display panels, CRT displays, and organic EL displays. In the image display device of the present invention, the protective film or the polarizing plate is disposed on the visual recognition side with respect to the image display element with the hard coat layer side facing outside. The protective film may be directly bonded to the surface of the image display element. When the liquid crystal panel is used as the image display element, for example, as described above, the protective film is bonded to the surface of the liquid crystal panel via the polarizing film. You can also. As described above, when the protective film of the present invention is applied to an image display device, the adhesion durability between the polyester film and the hard coat layer with respect to environmental light is excellent, and an image display is performed as compared with the case where a conventional protective film is used. The strength of the element is reinforced and the warp of the image display element can be prevented.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. The measuring method of the water contact angle on the surface of the polyester film used in each example and the evaluation method of the adhesion of the protective film obtained in each example are as follows.

<Contact angle of water on the surface of the polyester film>
The polyester film is bonded to a glass substrate using an adhesive on the surface opposite to the surface whose water contact angle is to be measured, and a contact angle meter (image processing type contact angle meter FACE manufactured by Kyowa Interface Science Co., Ltd.) The polyester film bonded to the glass substrate was set on the CA-X type so that the polyester film was on the upper surface, and 1 picoliter of pure water was dropped to measure the contact angle. At this time, it was confirmed that the measurement sample was not tilted.

<Adhesiveness of protective film>
(1) Initial adhesion The protective film is cut out to 3 cm × 3 cm, and is bonded to a glass substrate with an adhesive on the surface opposite to the hard coat layer side. The hard coat surface is 1 mm × with a cutter knife. Cuts were made so that 1 mm squares were 10 × 10. At this time, care was taken so that the cut reached the interface between the hard coat layer and the polyester film, and the cut did not go deep inside the polyester film. The cellophane tape was affixed to the 10 × 10 grids thus produced, and the adhesiveness was evaluated by peeling the hard coat layer. At the time of peeling, the cellophane tape was drawn so that the angle of drawing was 45 °. In this way, the tape peeling test by the cross-hatch method was performed three times.

(2) Durability of adhesion A protective film is cut out to 3 cm × 3 cm, and is bonded to a glass substrate using an adhesive on the surface opposite to the hard coat layer side, and an ultraviolet ray long life carbon arc conforming to JIS B7751. Using a lamp (UV Auto Fade Meter U48SB manufactured by Suga Test Instruments Co., Ltd.), a weather resistance acceleration test based on JIS A1415 was performed. At that time, ultraviolet rays were irradiated from the hard coat layer side, and the irradiation time was 96 hours. About the protective film after a test, the tape peeling test by the cross hatch method similar to said (1) was performed 3 times, and what does not generate | occur | produce peeling at all was set as (circle), and what generate | occur | produced even slight peeling was set as x.

<Example 1>
As the polyester film, a polyethylene terephthalate film (Lumirror U34 manufactured by Toray Industries, Inc.) having a water contact angle of 74 ° on both surfaces is used, and pentaerythritol triacrylate and polyfunctional urethanized acrylate are provided on one surface thereof. A hard coat layer was formed by applying an ultraviolet curable resin composition containing (the reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate) as a main component and curing it with ultraviolet rays. The protective film thus obtained was evaluated for adhesion, and the results are shown in Table 1. The water contact angle on the hard coat layer surface was measured and found to be 86 °.

<Comparative Example 1>
As the polyester film, a polyethylene terephthalate film (Teijin DuPont Teijin Tetron Film O3PF8W manufactured by Teijin DuPont Co., Ltd.) having a water contact angle on both surfaces of 59 ° was used, and the same method as in Example 1 was used. A hard coat layer was formed. The protective film thus obtained was evaluated for adhesion, and the results are shown in Table 1.

<Comparative example 2>
A polyethylene terephthalate film (E5100 manufactured by Toyobo Co., Ltd.) having a water contact angle of 79 ° on one surface and a water contact angle of 58 ° on the other surface is used as the polyester film. A hard coat layer was formed on the surface having a contact angle of 79 ° in the same manner as in Example 1. The protective film thus obtained was evaluated for adhesion, and the results are shown in Table 1.

Claims (7)

  A protective film for an image display device in which a hard coat layer is formed on at least one surface of a polyester film, and a water contact angle of a surface on which the hard coat layer of the polyester film is formed is 60 ° to 75 °. A protective film characterized by being.   The protective film according to claim 1, wherein a surface treatment is applied to a surface on which a hard coat layer of the polyester film is formed.   The protective film according to claim 1 or 2, wherein the polyester film is a polyethylene terephthalate film.   The protective film according to claim 1, wherein the hard coat layer is an antiglare hard coat layer.   The protective film according to claim 1, wherein a hard coat layer is formed on one surface of the polyester film.   It is a polarizing plate formed by bonding the protective film according to claim 5 and a polarizing film, wherein the polarizing film is disposed on the polyester film side of the protective film.   The protective film according to any one of claims 1 to 5 or the polarizing plate according to claim 6 and an image display element, wherein the protective film or the polarizing plate has the hard coat layer side outside, and the image display element. An image display device arranged on the viewing side.