JP2007030307A - Transparent sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent sheet in which hard coat layers are formed on an acrylic resin substrate and which is excellent in scratch resistance and impact resistance and suppresses the occurrence of warpage. <P>SOLUTION: The transparent sheet has the acrylic resin substrate and the hard coat layers formed on the first and second surfaces of the substrate. The hard coat layers formed on the first and second surfaces of the substrate are different in hardness. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transparent sheet having a hard coat layer formed on both front and back surfaces of a base material made of an acrylic resin, and more particularly to a transparent sheet having both excellent scratch resistance and impact resistance.

  An acrylic resin is a high molecular compound containing polymers such as acrylic acid, methacrylic acid, and derivatives thereof, and is excellent in transparency, for example, has higher transparency than inorganic glass. In addition, acrylic resin is excellent in oil resistance, weather resistance, and processability, so it is currently used in various fields. For example, transparent cases such as water tanks, signboards, automobile tail lamps, and mobile phone liquid crystals. It is used for applications such as light guide plates for panels and liquid crystal displays (LCD).

  However, since the resin base material made of acrylic resin has a lower hardness than, for example, a glass plate, the surface of the base material is likely to be scratched or scratched, resulting in inferior scratch resistance or wear resistance. . Therefore, conventionally, in order to improve the scratch resistance and the like of the acrylic resin base material, it is common to form a hard coat layer on one or both of the front surface (first surface) and the back surface (second surface) of the base material. Has been done.

  Examples of the invention relating to the formation of the hard coat layer on the first surface and the second surface of such an acrylic resin substrate include, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-224839) and Patent Document 2 (Japanese Patent Laid-Open No. 2002-2002) No. 249711), Patent Document 3 (Japanese Patent No. 3090676), Patent Document 4 (Japanese Patent Laid-Open No. 8-99327), and the like are known.

  For example, Patent Document 1 discloses a hard coat paint (hard coat agent) containing methyl (meth) acrylate, silica fine particles, and a high molecular weight pigment dispersant containing aliphatic hydroxycarboxylic acid as constituent components. Yes. By using the hard coat agent described in Patent Document 1 and forming a hard coat layer on a resin molded body such as an acrylic plate, a molded body having excellent transparency and scratch resistance (for example, a resin sheet or the like) ) Can get. Here, “(meth) acrylate” means acrylate or methacrylate.

  Patent Document 2 discloses (A) a hydrolyzate of organoalkoxysilane and / or its as a hard coat composition (that is, a hard coat agent) for forming a hard coat layer on a synthetic resin molded article. A hard coating agent containing a condensate, (B) a colloidal metal oxide, (C) water, and (D) a hydrophilic organic solvent is disclosed. Conventionally, when a hard coat layer is formed on a synthetic resin molded product using an inorganic hard coat agent, the formed hard coat layer is prone to cracking and has poor bonding properties with the resin molded product. was there. However, by forming a hard coat layer using the hard coat agent of Patent Document 2, not only the wear resistance of the resin molded product is improved, but also a resin excellent in bondability, moisture resistance, and weather resistance. It is said that a molded product can be obtained.

  Furthermore, the said patent document 3 is disclosing the method of forming a silicon-type hard-coat layer on the surface of a plastic base material. In the method described in Patent Document 3, when a silicon-based hard coat layer is formed on the surface of a plastic substrate, the amount of light of 300 nm or less accounts for 45% or more of the amount of ultraviolet light of 400 nm or less on the surface of the plastic substrate. It is characterized in that a hard coat layer is formed after irradiation with ultraviolet energy from a light source and further treatment with an organic solvent or an aqueous alkali solution.

  In Patent Document 3, as a plastic substrate for forming a hard coat layer, for example, transparent thermoplastics such as polymethyl methacrylate, polycarbonate, and polystyrene, and transparent heat such as urethane (meth) acrylate and epoxy (meth) acrylate are used. It is said that curable plastic can be used.

  According to Patent Document 3, by irradiating ultraviolet rays before forming a silicon-based hard coat layer, the plastic substrate surface is activated without causing yellowing of the plastic substrate. The bond with the hard coat layer can be strengthened. Moreover, it is said that the water resistance and weather resistance which were excellent in the hard-coat layer can be provided by performing the process by the organic solvent or aqueous alkali solution after the ultraviolet irradiation. Therefore, it is said that the bondability, water resistance, and weather resistance of the silicon-based hard coat layer can be improved by forming a hard coat layer on the plastic substrate using the method of Patent Document 3.

  On the other hand, Patent Document 4 describes an invention relating to a method of forming a hard coat layer on a plastic substrate. In the method described in Patent Document 4, first, a resin material (hard coating agent) is applied to the surface of an original substrate that has been subjected to processing (for example, flattening, unevenness, etc.) in a state where the surface is to be transferred. A plastic substrate is laminated via Next, the resin material interposed between the original substrate and the plastic substrate is cured by ultraviolet irradiation or the like. Thereafter, the plastic substrate is peeled off from the original substrate together with the cured resin material. Thereby, the plastic substrate which has the hard-coat layer by which the outer surface was planarized or uneven | corrugated can be obtained.

  By forming the hard coat layer in this manner, it is possible to realize flattening or unevenness of the substrate surface, which is conventionally possible with a glass substrate but impossible with a plastic substrate. Therefore, for example, a thin and lightweight plastic substrate can be applied to an STN (super twisted nematic) element or the like, and a liquid crystal cell with a very small thickness can be formed with high accuracy.

In Patent Document 4, as a hard coating agent, a polyol polyacrylate such as pentaerythritol tetraacrylate, a reactive oligomer such as a urethane acrylate oligomer, a reactive diluent such as cyclohexyl acrylate, and a photopolymerization such as benzoin. It is preferable to use an ultraviolet curable paint comprising an initiator.
JP 2004-224839 A JP 2002-249711 A Japanese Patent No. 3090676 JP-A-8-99327

  However, when a resin sheet is formed by forming a hard coat layer on a substrate made of acrylic resin, etc., the scratch resistance on the surface of the resin sheet can be improved, but the impact resistance of the resin sheet is decreased. It is generally known. In particular, when the hardness of the hard coat layer is increased to improve the scratch resistance, the higher the hardness of the hard coat layer, the more markedly the impact resistance of the resin sheet is lowered, and the resin sheet is cracked or damaged. There was a problem that it was likely to occur.

  On the other hand, as a means for improving the scratch resistance on the surface of the acrylic resin sheet and suppressing the decrease in impact resistance, for example, a hard coat layer is provided only on one surface serving as the outer surface of the acrylic resin sheet in order to eliminate the above problems. It is conceivable to form. However, in this case, since the hard coat layer shrinks when the hard coat layer is formed (when the hard coat agent is cured), residual stress is generated on the surface of the acrylic resin substrate on which the hard coat layer is formed. End up. The shrinkage of the hard coat layer increases as the hardness of the hard coat layer increases.

  Furthermore, it is known that acrylic resin extends due to water absorption (saturated water absorption 2%). However, when a hard coat layer is formed only on one side of the acrylic resin sheet, water absorption is achieved between the front and back surfaces of the resin sheet. There will be a difference. For this reason, on the front and back surfaces of the resin sheet, there arises a problem that the amount of expansion and contraction due to water absorption is different. That is, when the hard coat layer is formed only on one side of the acrylic resin sheet, the resin sheet is caused by the residual stress generated when the hard coat layer is formed or the difference in the amount of expansion and contraction due to the difference in water absorption between the front and back surfaces. There was a problem that warpage occurred in itself and the yield was lowered.

  The present invention has been made to solve the conventional problems, and a specific object thereof is a transparent resin sheet in which a hard coat layer is formed on a base material made of an acrylic resin, and is scratch-resistant. An object of the present invention is to provide a transparent sheet that is excellent in heat resistance and impact resistance and also suppresses the occurrence of warpage.

  In order to achieve the above object, the transparent sheet provided by the present invention is formed on a base material made of an acrylic resin and both the first surface and the second surface of the base material as a basic configuration. A transparent sheet provided with a hard coat layer, wherein the hard coat layer formed on the first surface and the second surface of the base material has a hardness difference, and is the main feature. .

  Moreover, in the transparent sheet according to the present invention, the hard coat layer formed on the first surface and the second surface of the base material includes a polyacrylate, a reactive oligomer, a diluent, and a photopolymerization catalyst. Hard coat agent, hydrolyzate of organoalkoxysilane and / or condensate thereof comprising coating agent, methyl acrylate or methyl methacrylate, metal oxide, and high molecular weight pigment dispersant containing aliphatic hydroxycarboxylic acid as constituent components And one or more hard coat agents selected from among a hard coat agent containing a metal oxide and a hard coat agent containing an organosilicon compound and / or a hydrolyzate thereof. be able to.

  Furthermore, in the transparent sheet of the present invention, the pencil hardness of the hard coat layer formed on the first surface is preferably 2H or more and 7H or less, and the pencil hardness of the hard coat layer formed on the second surface is The hard coat layer formed on the first surface preferably has a hardness difference that is lower than the pencil hardness and does not cause the substrate to warp.

  Furthermore, it is preferable that the hardness difference between the hard coat layers formed on the first surface and the second surface of the substrate is 1H or more and 4H or less in pencil hardness.

  Moreover, it is preferable that the film thickness of the hard-coat layer formed in the said 1st surface and the 2nd surface is 1 micrometer or more and 30 micrometers or less.

  In the transparent sheet according to the present invention, the hard coat layers formed on both the first surface and the second surface of the base material made of acrylic resin have a difference in hardness. The inventors of the present invention have intensively studied and studied in order to obtain a resin sheet having both scratch resistance and impact resistance. As a result, considering the following knowledge, it was found that it is sufficient to provide a hardness difference between the two hard coat layers disposed on both sides of the acrylic resin substrate, and the transparent sheet of the present invention was completed. I came to let you.

That is, when a hard coat layer is formed on an acrylic resin substrate, the scratch resistance can be increased as the hardness of the hard coat layer formed on the substrate increases.
Further, for example, when a resin sheet provided with a hard coat layer on both sides is attached to a product and used, when an impact is applied to the resin sheet, generally from one surface (first surface) side of the resin sheet Shock is given. For this reason, compressive stress is generated on one surface (first surface) of the resin sheet to which an impact is applied, and tensile stress is generated on the other surface (second surface) of the resin sheet.

  Furthermore, although the hard coat layer is strong against compressive stress, it is weak against tensile stress. In particular, the higher the hardness of the hard coat layer, the lower the strength against tensile stress. For this reason, the hard coat layer does not easily crack or break even when a compressive stress is applied, but when a tensile stress is applied, the higher the hardness, the more likely the crack or break occurs.

  From the above, the transparent sheet of the present invention increases the hardness of the first hard coat layer formed on the first surface serving as the outer surface, and the second hard coat formed on the second surface serving as the other surface. The hardness of the layer is relatively lower than that of the hard coat layer on the first surface, and a hardness difference is provided between the first and second hard coat layers.

  The transparent sheet of the present invention having such a configuration can improve the scratch resistance of the sheet since the hardness of the first hard coat layer serving as the outer surface is high. Further, even if an impact is applied from the outer surface of the transparent sheet, a compressive stress is generated in the first hard coat layer, so that the first hard coat layer is not cracked or damaged.

  On the other hand, in this case, tensile stress is generated in the second hard coat layer, but the hardness of the second hard coat layer is lower than that of the first hard coat layer. For this reason, for example, compared with the case where the hard coat layer having the same high hardness as the first face is formed on the second face of the resin base material as in the prior art, the second hard coat layer is cracked or damaged. Can be suppressed.

  That is, the transparent sheet of the present invention combines scratch resistance and impact resistance, which has been difficult to achieve with a conventional resin sheet in which hard coat layers having the same hardness are formed on both sides of a base material. An excellent effect can be obtained. Furthermore, since the transparent sheet of the present invention has hard coat layers formed on both sides of the sheet, it becomes a high-quality transparent resin sheet with suppressed warpage.

  The hard coat layer in the transparent sheet of the present invention can be formed using the hard coat agent as described above. This makes it possible to stably form a hard coat layer on an acrylic resin substrate, as well as scratch resistance and impact resistance, as well as transparency, bondability between the acrylic resin substrate and the hard coat layer, and water resistance. In addition, a resin sheet having excellent weather resistance can be obtained.

  Furthermore, in the transparent sheet of the present invention, the pencil hardness of the hard coat layer formed on the first surface can be 2H or more and 7H or less. By forming the hard coat layer having such pencil hardness on the first surface of the base material, a transparent sheet having excellent scratch resistance is obtained. Further, the pencil hardness of the hard coat layer formed on the second surface is lower than the pencil hardness of the hard coat layer formed on the first surface, and warps the substrate with respect to the hard coat layer formed on the first surface. Such as a pencil hardness of 1H or more and 4H or less. Thereby, it is possible to obtain a high-quality transparent sheet that is extremely excellent in impact resistance and has no warping.

  Furthermore, the transparent sheet of the present invention can form a hard coat layer having a film thickness of 1 μm or more and 30 μm or less on the first surface and the second surface of the substrate. Thereby, it is possible to obtain a transparent sheet in which a hard coat layer having a desired hardness is stably formed without causing cracks or the like.

Hereinafter, the transparency sheet concerning the present invention is explained in detail, referring to drawings. Here, FIG. 1 is a schematic diagram schematically showing the configuration of the transparent sheet in the present embodiment.
As shown in FIG. 1, the transparent sheet 1 in the present embodiment includes a base material 2 made of an acrylic resin, and a first hard coat layer 3 formed on the first surface of the acrylic resin base material 2. And a second hard coat layer 4 formed on the second surface of the acrylic resin substrate 2. The first hard coat layer 3 and the second hard coat layer 4 have a predetermined hardness difference. In the present embodiment, the first surface of the acrylic resin substrate 2 refers to the surface that receives an impact when using the transparent sheet, and the second surface refers to the opposite surface. ing. Hereinafter, each component of the transparency sheet | seat 1 is demonstrated more concretely.

As said acrylic resin base material 2, the acrylic base material which has transparency currently generally used can be used. Specifically, a substrate made of the following synthetic resin can be used. That is, as the material of the acrylic resin substrate 2, polymethyl methacrylate, polycyclohexyl methacrylate, methyl methacrylate-cyclohexyl methacrylate copolymer, styrene-acrylonitrile copolymer, methyl methacrylate / styrene copolymer, poly (tricyclo [ 5.2.1.0 ^2,6 ] decan-8-yl methacrylate), methyl methacrylate-tricyclo [5.2.1.0 ^2,6 ] decan-8-yl methacrylate copolymer, methyl methacrylate-isovol. Nyl methacrylate copolymer, transparent thermoplastics such as methyl methacrylate-phenyl methacrylate copolymer, urethane (meth) acrylate, epoxy (meth) acrylate, polyester (meth) acrylate, etc. and monofunctional or polyfunctional (meth) Acry It includes plastics such as a copolymer of over bets.

  Further, the acrylic resin substrate 2 can be constituted by containing the above-described polymer as a main component and further containing a rubber-containing polymer (acrylic rubber). This rubber-containing polymer is obtained by polymerizing a mixture of an acrylic acid alkyl ester, another copolymerizable vinyl monomer, and a copolymerizable crosslinkable monomer to produce an elastic copolymer. It can be obtained by polymerizing a methacrylic acid ester and a vinyl monomer copolymerizable therewith or a mixture thereof in at least one stage.

  In this case, examples of the copolymerizable crosslinking monomer include ethylene glycol dimethacrylate, butanediol dimethacrylate, allyl acrylate, allyl methacrylate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, Examples include diallyl maleate, trimethylol triacrylate, and allyl cinnamate, and these can be used alone or in combination of two or more.

  In addition, it is preferable to include such a rubber-containing polymer in the acrylic resin substrate 2 so that the ratio of the elastic copolymer is 5 to 18% by weight. Thereby, since the acrylic resin base material 2 itself can be given elasticity, the strength against impact in the transparent sheet 1 can be further increased.

  Moreover, the shape, dimension, etc. of such an acrylic resin base material 2 are not specifically limited, and can be arbitrarily changed according to the usage form of the transparent sheet 1, for example, an acrylic resin base material. The thickness of 2 is 0.1 mm or more and 3 mm or less, preferably 0.2 mm or more and 0.9 mm or less. Thereby, the transparency sheet | seat 1 of this embodiment can be provided suitably for uses, such as liquid crystal panels, such as a mobile telephone which is illustrated below, for example.

  On the other hand, the first and second hard coat layers 3 and 4 formed on the first surface and the second surface of the acrylic resin substrate 2 are formed so as to have a difference in hardness. The material and forming method of the first and second hard coat layers 3 and 4 are not particularly limited, but can be preferably formed by using, for example, the following hard coat agent.

  For example, as a hard coat agent used for forming the hard coat layers 3 and 4, a hard coat agent containing polyacrylate, a reactive oligomer, a diluent, and a photopolymerization catalyst, methyl acrylate or methyl methacrylate, and a metal oxide And a hard coat agent comprising a high molecular weight pigment dispersant comprising an aliphatic hydroxycarboxylic acid as a constituent, a hydrolyzate of organoalkoxysilane and / or a condensate thereof, and a metal oxide, and In addition, a hard coat agent containing an organosilicon compound and / or a hydrolyzate thereof can be used. These hard coat agents can be used alone or in combination of two or more to form a hard coat layer.

  The hard coat agent will be described more specifically. When a hard coat agent containing a polyacrylate, a reactive oligomer, a diluent, and a photopolymerization catalyst is used, the polyacrylate may be pentaerythritol tetraacrylate. Polyacrylates of polyols such as dipentaerythritol hexaacrylate, glycerol triacrylate, butanediol diacrylate, and bisphenol A diacrylate can be used. Moreover, as said reactive oligomer, reactive oligomers, such as a urethane acrylate oligomer, an epoxy acrylate oligomer, and an ester acrylate oligomer, can be used. Further, as the diluent, reactive diluents such as cyclohexyl acrylate, furfuryl acrylate, and 2-ethylhexyl acrylate, and as the photopolymerization catalyst, benzoin, benzoin methyl ether, benzoin isobutyl ether, 2.2-dimethoxy- Photopolymerization initiators such as 2-phenylacetophenone, methyl-o-benzoylbenzoate, and p-isopropylphenyl-2-hydroxy-2-propylketone can be used.

  In addition, when using a hard coating agent containing methyl acrylate or methyl methacrylate, a metal oxide, and a high molecular weight pigment dispersant containing aliphatic hydroxycarboxylic acid as constituents, for example, the content of methyl (meth) acrylate In addition to the above, the binder component includes ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di ( (Meth) acrylate, polypropylene glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, pentaglycerol tri (meth) acrylate, penta Erythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hydroxypenta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and the like can be contained.

  Moreover, as said metal oxide, metal oxides, such as a silica, an alumina, a zirconia, can be used. By including such a metal oxide in (meth) acrylate or the like, the hardness of the hard coat layer can be easily increased. In particular, by using silica as the metal oxide, a hard coat layer with better transparency can be formed. Furthermore, the dispersant contains an aliphatic hydroxycarboxylic acid as a constituent component. By using such a dispersant, it is possible to disperse the silica fine particles without agglomeration by showing affinity for (meth) acrylate as a dispersion medium. As the aliphatic hydroxycarboxylic acid in such a dispersant, hydroxystearic acid, hydroxypalmitic acid, hydroxynanodecanoic acid, and hydroxyarachidic acid are preferably used, and hydroxystearic acid is particularly preferably used.

  Furthermore, when a hard coat agent containing a hydrolyzate of organoalkoxysilane and / or its condensate and a metal oxide is used, examples of the organoalkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, Propoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxy Alkyl group-containing organoalkoxysilanes such as silane, pentyltriethoxysilane, octyltriethoxysilane, decyltriethoxysilane, 2-norbornenetriethoxysilane, phenyltrimethoxysilane, Rutriethoxysilane, phenyltripropoxysilane, phenyltributoxysilane, phenyltriacetoxysilane, benzyltriethoxysilane, phenyl of the above phenyl group-containing alkoxysilane is methyl group, ethyl group, n-propyl group, isopropyl group, t-butyl A phenyl group-containing organoalkoxysilane such as an organoalkoxysilane having a substituent such as a group or a halogen group can be used alone or in combination of two or more.

  Moreover, the said metal oxide can be used in the state of the colloid solution disperse | distributed to hydrophilic solvents, such as water or alcohol, for example. Specific examples of such colloidal metal oxides include colloidal silica, colloidal antimony, colloidal alumina, colloidal zirconia, iron oxide / titanium oxide / silica composite sol, and the like. Among these, it is preferable to use colloidal silica.

  Furthermore, when a hard coat agent containing an organosilicon compound and / or a hydrolyzate thereof is used, examples of the organosilicon compound include methyl silicate, ethyl silicate, methyl triethoxy silane, ethyl triethoxy silane, vinyl triethoxy silane. , Phenyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, glycidoxymethyltrimethoxysilane, glycidoxytriethoxysilane, α-glycidoxyethyltriethoxysilane, β-glycyl Use dialkoxysilanes or diacyloxysilanes and / or hydrolysates thereof, such as sidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane Door can be.

  In the transparent sheet of the present embodiment, the hard coat agent as described above is applied to the first surface and the second surface of the acrylic resin substrate 2 and cured, so that a hard coat is formed on each surface. A layer can be formed. In this case, the method of applying the hard coat agent to the acrylic resin substrate 2 and the method of curing are not particularly limited, and conventionally known application methods and curing methods can be used. For example, when a hard coat agent is applied to the substrate 2, a bar coater, a die coater, a blade coater, a spin coater, a roll coater, a gravure coater, a flow coater, spraying, screen printing or the like can be used.

  And after apply | coating a hard-coat agent to the acrylic resin base material 2, a hard-coat agent is hardened by irradiating ionizing radiation (an ultraviolet ray or an electron beam) by heat-processing, or irradiating ionizing radiation (an ultraviolet ray or an electron beam). Can be made. Thereby, the 1st hard-coat layer 3 and the 2nd hard-coat layer 4 can be formed on the 1st surface and 2nd surface of the acrylic resin base material 2, respectively.

  In this embodiment, in addition to the method of applying a hard coat agent to an acrylic resin substrate and curing it as described above, for example, using the method described in Patent Document 4, the hard coat layer It is also possible to form. That is, an acrylic resin base material is laminated on the surface of a glass substrate on which a predetermined processing has been performed via a hard coat agent, and the hard coat agent is cured. Thereafter, the acrylic resin base material is peeled from the glass substrate together with the hard coat agent (hard coat layer) that has been cured. By performing such a process on both sides of the acrylic resin substrate, the hard coat layers 3 and 4 can be formed on the first surface and the second surface of the acrylic resin substrate 2, respectively.

  At this time, the film thickness of the first and second hard coat layers 3 and 4 to be formed is preferably 1 μm or more and 30 μm or less. By setting the thickness of the hard coat layer to 1 μm or more, the hard coat layer can be stably formed with a desired hardness, and a hard coat layer excellent in oxygen barrier properties and the like can be obtained. On the other hand, if the thickness of the hard coat layer is thicker than 30 μm, the hard coat layer is likely to be incompletely cured and cracks are likely to occur.

  Further, as described above, the transparent sheet 1 of the present embodiment is configured by giving a predetermined hardness difference to the hardness of the first and second hard coat layers 3 and 4. For example, the first hard coat layer 3 is formed to have a pencil hardness of 2H or more and 7H or less. Thereby, since the 1st hard-coat layer 3 used as the outer surface of the transparent sheet 1 becomes high hardness, the abrasion resistance in the transparent sheet 1 can be improved.

  On the other hand, the second hard coat layer 4 is lower than the pencil hardness of the first hard coat layer 3 and does not cause the acrylic resin substrate 2 to warp with respect to the first hard coat layer 3. It is formed to have a hardness difference. Thereby, the intensity | strength with respect to the tensile stress of the 2nd hard-coat layer 4 can be raised, and the impact resistance in the transparent sheet 1 can be improved.

  At this time, in order to prevent the acrylic resin base material 2 from being warped, the hardness difference provided between the first hard coat layer 3 and the second hard coat layer 4 is set to an acrylic resin base material. 2 varies depending on the thickness, hygroscopicity, etc., for example, the pencil hardness may be 1H or more and 4H or less. With such a hardness difference, the substrate 2 is not warped. That is, the second hard coat layer 4 is preferably formed to have a pencil hardness of 1H or more and 4H or less in order to stably obtain two effects of improving impact resistance and preventing warpage. For example, the transparent sheet 1 of the present embodiment is configured such that the pencil hardness of the first hard coat layer 3 is 4H, and the pencil hardness of the second hard coat layer 4 is 3H. Can do.

  In this embodiment, the method for controlling the hardness of the first and second hard coat layers 3 and 4 is not particularly limited. For example, the composition of the hard coat agent applied to the acrylic resin substrate 2 is changed. In addition, the hardness can be easily controlled by changing the thickness of the hard coat layer to be formed.

  As described above, the transparent sheet 1 in the present embodiment is a high-quality resin sheet that has high transparency, does not warp, and has both excellent scratch resistance and excellent impact resistance. . Such a transparent sheet 1 is, for example, a liquid crystal panel for a mobile phone, a cover for the panel, an L.P. C. D. It can be suitably used for applications such as covers and OHP panels. In addition, the present invention can be applied to in-vehicle use. C. D. It can also be used for panels, car stereo nameplates, back monitor CCD camera protective covers, and the like.

Hereinafter, the transparent sheet of the present invention will be described more specifically with reference to examples and comparative examples.
<Sample preparation>
(Example)
As an acrylic resin substrate, an impact-resistant acrylic plate containing about 15% by weight of an elastic copolymer is prepared, and hard coating is performed on both surfaces of the acrylic plate using the glass transfer method described in Patent Document 4 above. A layer was formed. That is, after each glass plate was placed on both sides of the impact-resistant acrylic plate via a predetermined hard coat agent, the hard coat agent was cured by irradiating ultraviolet rays from both outer sides of the glass plate.

  At this time, as a hard coating agent applied to the acrylic plate, polyacrylate (pentaerythritol tetraacrylate), reactive oligomer (urethane acrylate oligomer), diluent (cyclohexyl acrylate), and photopolymerization catalyst (benzoin) are included. The hard coat agent containing was used. The hard coat agent applied to the first surface of the acrylic plate and the hard coat agent applied to the second surface have different compositions, and the first surface of the acrylic plate has a pencil hardness of 4H. The composition of the hard coat agent was adjusted so that the second hard coat layer having a pencil hardness of 3H was formed on the second surface.

  After the hard coating agent is cured by irradiating with ultraviolet rays, the first hard coat layer and the second hard coat layer are formed on the impact-resistant acrylic plate by peeling off the glass plates placed on both sides of the acrylic plate. A transparent sheet on which was formed was prepared. When the thickness of the hard coat layer in the obtained transparent sheet was measured, the film thicknesses of the first and second hard coat layers were both 5 μm. Moreover, when the transparent sheet was observed visually, generation | occurrence | production of curvature in the transparent sheet was not confirmed. A plurality of such transparent sheets were prepared and used as samples in the examples.

(Comparative Example 1)
As a sample of Comparative Example 1, a plurality of transparent sheets were prepared in which a hard coat layer having the same pencil hardness was formed on both sides of an impact-resistant acrylic plate. That is, by preparing the same impact-resistant acrylic plate as in the previous example, and forming a hard coat layer having the same pencil hardness of 4H on both sides of the impact-resistant acrylic plate using a glass transfer method, A transparent sheet was prepared. When the thickness of the hard coat layer of the obtained transparent sheet was measured, the thicknesses of the first and second hard coat layers were both 5 μm.

(Comparative Example 2)
As a sample of Comparative Example 2, the impact-resistant acrylic plate prepared in Example and Comparative Example 1 was used as it was (no hard coat layer formed).

(Comparative Example 3)
As a sample of Comparative Example 3, a cast acrylic plate containing no elastic copolymer was prepared, and hard coat layers having the same pencil hardness of 6H were formed on both surfaces of the cast acrylic plate using a glass transfer method. Thus, a transparent sheet was produced. It was 5 micrometers when the thickness of the hard-coat layer of this obtained transparency sheet | seat was measured.

<Sample evaluation>
1. Measurement of Pencil Hardness Pencil hardness was measured based on JIS-D-0202 for each of the samples of Examples and Comparative Examples 1-3.

2. Evaluation of scratch resistance In order to evaluate the scratch resistance in each of the samples of Examples and Comparative Examples 1 to 3, the surface of each sample (the sample of the example) while applying a load of 500 g with # 0000 steel wool. The surface of the first hard coat layer was reciprocated 10 times. Thereafter, it was visually observed whether or not scratches had occurred on the surface of each sample where the steel wool was reciprocated.

3. Evaluation of impact resistance The Izod impact strength of each of the samples of Examples and Comparative Examples 1 to 3 was measured based on ASTM D256. Furthermore, in order to evaluate the impact resistance of each sample, the falling ball impact strength by the cone dropping method was measured. The falling ball impact strength was evaluated for impact resistance by dropping a 40 g cone from above the transparent sheet and comparing the height at which the cone was dropped when the transparent sheet was damaged.
For each sample of Examples and Comparative Examples 1 to 3, the results of the above pencil hardness measurement, scratch resistance evaluation, and impact resistance evaluation, and the base material and thickness are shown in the following table. 1 is shown collectively.

  As shown in Table 1 above, as a result of the evaluation of scratch resistance, the sample of the example serving as the transparent sheet of the present invention had no scratches caused by steel wool. On the other hand, countless scratches were observed in the sample of Comparative Example 2 in which the hard coat layer was not formed. That is, it was revealed that the transparent sheet of the present invention is excellent in scratch resistance.

  Further, comparing the sample of the example and the sample of comparative example 1, the sample of the example has a falling ball impact strength (impact resistance) twice or more that of the sample of comparative example 1. Became clear. Furthermore, it can be confirmed from the comparison between the sample of Example and the samples of Comparative Examples 1 and 3 that the impact resistance is further improved by containing an elastic copolymer. From the above results, it was confirmed that the transparent sheet of the present invention is a high-quality resin sheet having both scratch resistance and impact resistance, which were difficult to obtain conventionally.

  The transparent sheet of the present invention can be suitably used for applications requiring transparency, scratch resistance, and impact resistance, such as liquid crystal panels for mobile phones and panel covers.

It is a schematic diagram which shows typically the structure of the transparent sheet which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent sheet 2 Acrylic resin base material 3 1st hard-coat layer 4 2nd hard-coat layer

Claims (5)

A transparent sheet comprising a base material made of an acrylic resin and hard coat layers formed on both the first surface and the second surface of the base material,
The transparency sheet | seat characterized by the hard-coat layer formed in the 1st surface and the 2nd surface of the said base material having a hardness difference. The hard coat layer formed on the first surface and the second surface of the base material,
A hard coat agent comprising polyacrylate, a reactive oligomer, a diluent, and a photopolymerization catalyst;
A hard coat agent comprising methyl acrylate or methyl methacrylate, a metal oxide, and a high molecular weight pigment dispersant comprising an aliphatic hydroxycarboxylic acid as a constituent component;
A hard coat agent comprising a hydrolyzate of organoalkoxysilane and / or a condensate thereof, and a metal oxide; and
A hard coat agent containing an organosilicon compound and / or a hydrolyzate thereof,
The transparent sheet according to claim 1, wherein the transparent sheet is formed using one or two or more hard coat agents selected from among the above. The pencil hardness of the hard coat layer formed on the first surface is 2H or more and 7H or less,
The pencil hardness of the hard coat layer formed on the second surface is lower than the pencil hardness of the hard coat layer formed on the first surface, and has a hardness difference that does not cause the substrate to warp. Become,
The transparent sheet according to claim 1, wherein the sheet is transparent.   The transparency sheet according to any one of claims 1 to 3, wherein the hardness difference between the hard coat layers formed on the first surface and the second surface of the base material is 1H or more and 4H or less in pencil hardness. .   The thickness of the hard-coat layer formed in the said 1st surface and the 2nd surface is 1 micrometer or more and 30 micrometers or less, The transparent sheet in any one of Claims 1-4 characterized by the above-mentioned.

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