JP2007108242A - White color sheet for liquid crystal backlight reflection plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white color sheet which can be used for a liquid crystal backlight reflection plate, is excellent in flexibility and has a high reflectance. <P>SOLUTION: A polymerizable acrylic composition comprising a heat-polymerizable acrylic coating material which is prepared by mixing a (meth)acrylic mixture of (meth)acrylic polymer 2 to 50 pts.mass and (meth)acrylic monomer 98 to 50 pts.mass including isobonyl (meth)acrylate 30 to 97 mass% with heat radical polymerization initiator 0.1 to 5 pts.mass, cross-linking agent 0.1 to 20 pts.mass, plasticizer having molecular weight of 500 or more 1 to 20 pts.mass and titanium oxide pigment 40 to 120 pts.mass and is adjusted to have a viscosity of 1 to 100 Pa s is applied onto a substrate. The coated film thus formed provides the white color sheet for liquid crystal backlight reflection plate which has a total reflectance of ≥94% in the color tone measurement according to JIS Z8722 and a diffusion reflectance deprived of regular reflection light of ≥91%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a white sheet that is used in a liquid crystal backlight reflector and is suitable for forming a coating film that increases the effective efficiency of emitted light.

  In the liquid crystal display, a reflector is disposed on the back surface of the liquid crystal screen to prevent escape of screen light. For a reflector that requires a high light reflectance, a white film having a high reflectance is used. A study of diverting a technique related to a lamp shade for a lighting fixture that requires a similar high light reflectance to a surface light source reflector is also underway. As a typical high light reflection material, there is a reflection material such as an Ag vapor deposition film in which a metal vapor deposition film is deposited on a substrate surface to form a mirror surface. Although a vapor deposition film has a high specular reflectance, it does not easily cause diffuse reflection, and the amount of light directed to a display surface such as a liquid crystal decreases.

As a reflective material in place of an Ag vapor deposition film, a thermoplastic polyester foam containing fine bubbles (Patent Document 1), a reflector (Patent Document 2) on which a resin coating film in which silica aerogel is dispersed is formed, with a specular reflection strength. On the other hand, a surface light source reflector (Patent Document 3) having a large scattering reflection intensity is known.
Japanese Patent No. 2925745 JP-A-11-29745 Japanese Patent Laid-Open No. 4-296619

  Reflective materials and reflective films that have increased reflectivity by foaming resin promote reflection at the interface between the membrane resin and the microbubbles, which have significantly different refractive indexes, and have high reflectivity regardless of the presence of white pigments such as titanium oxide. Presents a face. However, it is necessary to increase the film thickness in order to improve the reflectance. In general, the reflective film is prepared by dissolving and extruding a film of polyester or the like and then drawing fine bubbles inside the film by a method of stretching uniaxially or biaxially. The reflectivity increases as the film becomes thicker, but the cost is high and the productivity is low, and the film thickness is about 150 to 200 μm.

  Further, since the reflector on the back of the liquid crystal display screen is irradiated with illumination light from a fluorescent tube or LED, it is always irradiated with ultraviolet rays that are contained in the illumination light in a small amount. Reflective materials and reflective films that have a high reflectance with foamed resin do not contain pigments such as titanium oxide pigments that are also effective in shielding ultraviolet rays, so the resin itself deteriorates due to ultraviolet rays. Discoloration proceeds and total reflection and diffuse reflection decrease.

  The reflectance is affected by the film thickness and the coating film structure. Therefore, the present inventors investigated and examined the influence of the film thickness and the coating film structure on the reflectance with the aim of total reflectance: 94% or more and diffuse reflectance: 91% or more. As a result, a (meth) acrylic polymer and an acrylic mixture of (meth) acrylic monomers containing isobornyl (meth) acrylate are blended with a plasticizer, and a film is formed from a paint blended with titanium oxide with less impurities. As a result, it was found that even with one coat, a white sheet having a reflectance required for a liquid crystal backlight reflecting material which is free from defects such as wrinkles and rough skin, can be thickened, and has excellent ultraviolet resistance is formed. The present invention has been completed on the basis of such knowledge, and a coating film prepared from a heat-polymerizable acrylic paint in which a (meth) acrylic polymer and a (meth) acrylic monomer are blended at a specific ratio. An object of the present invention is to provide a white sheet for a liquid crystal backlight reflector, which improves the utilization efficiency of illumination light by using a surface layer coating film, and does not decrease the reflectance even after long-term use.

  The white sheet of the present invention is a single layer coat. This coating film is formed by polymerizing and curing a heat-polymerizable acrylic paint, can be easily thickened to a thickness of 100 μm or more, hardly deteriorates even under ultraviolet irradiation, and has a high reflectance suitable as a liquid crystal backlight reflector. Present. The heat-polymerization acrylic mixture paint used for this coating film is (meth) acrylic polymer: 2 to 50 parts by mass, (meth) acrylic monomer containing 30 to 97% by mass of isobornyl (meth) acrylate: 98 to 50 parts by weight of (meth) acrylic mixture, thermal radical polymerization initiator: 0.1 to 5 parts by weight, cross-linking agent: 0.1 to 20 parts by weight, plasticizer with molecular weight of 500 or more: 1 to 20 parts by weight Parts, titanium oxide pigment: 40 to 120 parts by mass, and the viscosity is adjusted to 1 to 100 Pa · s. As the thermal radical polymerization initiator, there is a peroxide polymerization initiator, and a titanium oxide pigment in which impurities such as metals and metal oxides are regulated to 0.1% by mass or less is preferable.

[Preparation of thermal polymerization acrylic paint]
The thermal polymerization type acrylic paint uses, as a base resin, an acrylic mixture obtained by mixing a (meth) acrylic polymer and a (meth) acrylic monomer containing azobornyl (meth) acrylate. The mixing ratio of the (meth) acrylic polymer and the (meth) acrylic monomer is selected in the range of 2:98 to 50:50 (mass ratio). If the amount of the (meth) acrylic polymer is too small, the volatilization amount becomes excessive at the time of curing, and the smoothness of the coating film is liable to be impaired. On the other hand, when the amount of the (meth) acrylic polymer is too large, the viscosity of the paint is increased, and problems are likely to occur during coating. The (meth) acrylic monomer contains 30 to 97% by mass (preferably 30 to 85% by mass) of isobornyl (meth) acrylate. If content of isobornyl (meth) acrylate is less than 30 mass%, the stickiness of a coating film will rise and coating workability will fall. On the other hand, when the compound exceeds 97% by mass of isobornyl (meth) acrylate, the glass transition temperature Tg of the coating film rises, and there is a concern that workability and impact resistance may be lowered.

  The (meth) acrylic monomer is a compound having at least one of an acryloyl group and a methacryloyl group in the molecule, and is a (meth) acrylic acid alkyl ester, a (meth) acrylic acid ester of an alicyclic alcohol, Acrylic acid aryl esters, alkoxyalkyl (meth) acrylates, functional group-containing monomers and the like are used alone or in combination of two or more. (Meth) acrylic acid alkyl esters include methyl (meth) acrylate, hexyl (meth) acrylate, (meth) acrylate-2-ethylhexyl, octyl (meth) acrylate, decyl (meth) acrylate, (meth ) Dodecyl acrylate, stearyl (meth) acrylate, and the like.

  (Meth) acrylic acid esters of alicyclic alcohols include cyclohexyl (meth) acrylate, and aryl esters of acrylic acid include phenyl (meth) acrylate, isobornyl (meth) acrylate, and benzyl (meth) acrylate. . Examples of the alkoxyalkyl (meth) acrylate include methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, and the like. Functional group-containing monomers such as alkoxyalkyl (meth) acrylate, glycidyl ether (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and (meth) acrylic acid can also be used. In addition, (meth) acrylic acid is a term including both acrylic and methacrylic.

  In the (meth) acrylic mixture, a compound having another polymerizable unsaturated group copolymerizable with the (meth) acrylic monomer may be mixed. Examples of compounds having other polymerizable unsaturated groups that can be copolymerized include unsaturated carboxylic acids such as itaconic acid, crotonic acid, maleic acid, fumaric acid, (meth) acrylamide, N-methylol (meth) acrylamide, N- Amide group-containing vinyl monomers such as methoxy (meth) acrylamide and N-butoxy (meth) acrylamide, organosilicon group-containing vinyl monomers such as vinyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane, styrene, methyl There are aromatic vinyl monomers such as styrene, (meth) acrylonitrile and the like.

  Furthermore, di (meth) acrylic acid ester of ethylene glycol, di (meth) acrylic acid ester of diethylene glycol, di (meth) acrylic acid ester of triethylene glycol, di (meth) acrylic acid ester of propylene glycol, dipropylene glycol Di (meth) acrylic esters of (poly) alkylene glycols such as di (meth) acrylic esters, trimethylolpropane tri (meth) acrylic esters, pentaerythritol tetra (meth) acrylic esters, dipentaerythritol hexa ( You may mix the monomer which has 2 or more of polymerizable unsaturated groups in a molecule | numerator, such as polyvalent (meth) acrylic acid ester, such as (meth) acrylic acid ester, and divinyl monomers, such as divinylbenzene. A monomer having two or more polymerizable unsaturated groups in the molecule has the same effect as a crosslinking agent described later.

The (meth) acrylic polymer can be prepared by polymerization methods such as bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc., but considering the mixing with the (meth) acrylic monomer mixture component, the bulk polymerization method The solution polymerization method is preferable, and the bulk polymerization method that does not require the volatilization of the solvent is particularly preferable. When the main component of the monomer constituting the (meth) acrylic polymer component is the same as the (meth) acrylic monomer, partial polymerization is preferably performed by a bulk polymerization method. As the partial polymerization, the method described in Patent Document 4 can be employed. When partial polymerization is used, a polymerization initiator component, a crosslinking agent component, and the like are mixed into the partial polymer. This (meth) acrylic monomer is a compound obtained by polymerizing a monomer having one or more (meth) acryloyl groups in the molecule, and has a weight average molecular weight measured by gel permeation chromatography (GPC). there preferable polymer in the range of ¹⁰ 3 to 10 ^6.
JP 2000-313704 A

  For the polymerization of the (meth) acrylic monomer, a peroxide-based or azo-based thermal radical polymerization initiator can be used, but a peroxide-based thermal polymerization initiator is preferably used. The thermal polymerization initiators may be used alone or in combination of two or more, and a decomposition accelerator such as cobalt naphthenate or dimethylaniline may be used in combination. A polymerization initiator is mix | blended in the ratio of 0.1-5 mass parts (preferably 0.3-3 mass parts) with respect to 100 mass parts of acrylic mixtures. When the blending amount of the polymerization initiator is small, it takes time to cure and the volatile matter increases, which is not effective. On the other hand, when an excessive amount of the polymerization initiator is blended, a large amount of bubbles are generated during the reaction, and coating film defects such as peeling and rough skin are likely to occur.

  Peroxide-based thermal polymerization initiators include isobutyl peroxide, cumyl peroxyneodecanate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tertiary butyl peroxyneodecanate, 3, 5 , 5-trimethylhexanol peroxide, lauryl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, benzoyl peroxide, t -Butyl peroxymaleic acid, t-butyl peroxybenzoate, etc. are mentioned. Among these, a thermal polymerization initiator having a 10-hour half-life temperature of 35 to 100 ° C. is preferable.

  Furthermore, a crosslinking agent is mix | blended in the ratio of 0.1-20 mass parts (preferably 0.5-10 mass parts) with respect to 100 mass parts of acrylic mixtures. If the blending amount of the cross-linking agent is small, the strength of the coating film is lowered. On the contrary, if the amount is too large, the flexibility of the coating film is lost and foaming is caused. Crosslinking agents include isocyanate-based, epoxy-based, aziridine-based, metal chelate-based, melamine resin-based, silane coupling agent-based, and the like, which are added to the acrylic mixture alone or in combination of two or more.

  Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate and the like, and these isocyanate monomers. Examples include an isocyanate compound added with methylolpropane, an isocyanurate, a burette type compound, a polyether polyol, a polyester polyol, an acrylic polyol, a polybutadiene polyol, a polyisoprene polyol, and a urethane prepolymer type isocyanate. However, the use of hexamethylene diisocyanate, isophorone diisocyanate, or the like is preferable to tolylene diisocyanate, diphenylmethane diisocyanate, or the like, which tends to cause yellowing of the coating film.

  As epoxy-based crosslinking agents, ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ', N'-tetraglycidyl-m-xylylenediamine, N, N, N', N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N, N-diglycidylaminophenylglycidyl ether, N, N-diglycidyl toluidine, N, N-diglycidyl aniline and the like can be mentioned.

  Examples of the aziridine-based crosslinking agent include trimethylolpropane tri-β-aziridinylpropionate, trimethylolpropane tri-β- (2-methylaziridine) propionate, tetramethylolmethane tri-β-aziridinylpropionate, etc. Is mentioned. Examples of the metal chelate crosslinking agent include aluminum isopropylate, diisopropoxybisacetylacetone titanate, aluminum triethylacetoacetate and the like. Examples of the melamine resin-based crosslinking agent include methylated melamine resin, butylated melamine resin, and benzoguanamine resin. Examples of the silane coupling agent-based crosslinking agent include glycidoxypropyltrimethoxysilane, aminopropyltrimethoxysilane, and chloropropyltrimethoxysilane.

The acrylic mixture is blended with a plasticizer having a molecular weight of 500 or more in order to prevent cracks generated in the coating film due to the impact applied during processing. When using a thermal polymerization type acrylic paint (Patent Document 5) in which a thermal radical polymerization initiator and a crosslinking agent are blended with an acrylic mixture of (meth) acrylic monomer and (meth) acrylic polymer, vinyl chloride sol A coating film without bubbles is formed with the same film thickness as when paint is used, but cracking of the coating film occurs occasionally when the obtained coated metal sheet is processed into a product shape by press molding with a high processing speed. Is done. Generation | occurrence | production of the coating-film crack by impact is suppressed by mix | blending the plasticizer of molecular weight 500 or more in the ratio of 1-20 mass parts. The sticking resistance and flex resistance of the coating film are not impaired by the blending of the plasticizer. The effect of the plasticizer formulation on the suppression of impact cracking of the coating film is presumed as follows.
JP 2003-171579 A

  Even when the plasticizer is not added, even if the glass transition temperature Tg of the coating film is lower than the processing temperature, there is a limit to the deformation of the acrylic resin in press molding or the like where the processing speed is high, and the coating film does not follow the deformation. Cracking occurs. On the other hand, in a system in which a plasticizer is blended, a plasticizer enters between the molecules of the (meth) acrylic polymer, and slipping easily occurs between the molecules of the (meth) acrylic polymer. Deformation also occurs in the layer part. As a result, even if an impact is applied at the time of processing, the coating sufficiently follows the deformation of the substrate without cracking.

  The impact resistance of the coating can be improved to some extent even when a plasticizer such as dioctyl phthalate (DOP) having a molecular weight of less than 500, which is generally used in vinyl chloride sol paints and acrylic sol paints, is used. However, a plasticizer having a small molecular weight has a weak binding force to the (meth) acrylic polymer and moves relatively freely in the coating film, so that it bleeds out and the coating film surface tends to be sticky. Although the compatibility with the (meth) acrylic polymer decreases as the molecular weight of the plasticizer increases, it does not easily move in the coating film as the molecular weight increases, and a large sticking suppression effect is obtained.

  When 1 to 20 parts by mass of a plasticizer having a molecular weight of 500 or more is added, the glass transition temperature Tg of the coating film is -20 to 60 ° C in order to balance the coating properties such as stickiness resistance, workability, and impact resistance. (Preferably 0 to 40 ° C.) When the glass transition temperature Tg of the coating film is lower than −20 ° C., the sticking resistance of the coating film decreases, and conversely, when the glass transition temperature Tg exceeds 60 ° C., the workability and impact resistance of the coating film are likely to deteriorate.

  As the plasticizer, a plasticizer having three or more ester bonds in one molecule is suitable. Specific examples include trimellitic acid derivatives, fatty acid derivatives such as pentaerythritol fatty acid esters, phosphoric acid derivatives, polyester plasticizers, and acrylic low-molecular monomers mainly composed of acrylic monomers. Plasticizers may be used alone or in combination of two or more. The blending ratio of the plasticizer with respect to the acrylic mixture is selected in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the acrylic mixture. The effect of the plasticizer on the flexibility of the coating film is observed at a blending amount of 1 part by mass or more. However, when an excessive amount of the plasticizer is blended, the coating film tends to be sticky.

  This acrylic mixture is blended with a titanium oxide pigment effective for improving the reflectance. Since titanium oxide pigments vary in whiteness depending on the production method, it is necessary to select titanium oxide with high whiteness in order to improve reflectivity. Impurities of heavy metals and metal oxides mixed during the purification of titanium oxide have an adverse effect on whiteness, and coloring with Fe, Cr, Cu, Mn, V, Nb, etc. is particularly harmful. Therefore, it is preferable that the impurities of heavy metals and metal oxides be regulated to 0.1% by mass or less as impurities.

  Impurities: Titanium oxide pigments of 0.1% by mass or less can be prepared by surface-treating rutile titanium oxide preferably made by a chlorine method with alumina, silica, zirconia, titania, organic matter or the like. The particle diameter of the titanium oxide pigment effective for improving the reflectance is preferably in the range of 0.2 to 0.3 μm (more preferably 0.25 to 0.3 μm). Examples of the chlorinated titanium oxide pigment include Taipur R900, R920 (manufactured by DuPont), Taipaque CR50, CR58, CR67 (manufactured by Ishihara Sangyo) and the like.

  The mixing ratio of the titanium oxide pigment to the acrylic mixture is selected in the range of 40 to 120 parts by mass with respect to 100 parts by mass of the acrylic mixture. Necessary total reflectance: 94% or more, diffuse reflectance: 91% or more can be achieved by blending 40 parts by mass or more of titanium oxide pigment, but excessive blending of titanium oxide increases the viscosity of the paint and makes the film surface beautiful. It is difficult to obtain a coating film having, and this is also a cause of reducing workability.

  As other pigments, extender pigments such as calcium carbonate, clay, talc, barium sulfate, aluminum oxide, and magnesium oxide can be added as long as the coating properties such as reflectance and processability are not lowered. Additives such as fillers, antioxidants, flame retardants, and UV absorbers are also blended into the thermal polymerization acrylic paint as necessary. The viscosity of the heat-polymerizable acrylic paint blended with each component is adjusted in the range of 1 to 100 Pa · s (preferably 2 to 50 Pa · s). When the viscosity is too low, a uniform coating film cannot be obtained due to the flow after application and is hardened. When the viscosity is too high, streaks or the like are generated at the time of application, and bubbles are difficult to escape from the coating film.

As a support to which the thermal polymerization type acrylic paint of the present invention is applied, not only release paper (separator) that has been conventionally used, but also metal foil, various resin films that have not been subjected to release treatment, and the like can be used. . If no peeling process, the surface of the support was subjected to corona discharge treatment, 30 dyn / cm ² or more (preferably 36 dyn / cm ² or higher) With surface tension of a thermal polymerization type acrylic coating is good and support Adhesion can be obtained. In order to cast the heat-polymerizable acrylic paint on the support, it may be applied using a roll coater, curtain coater, die coater, knife coater, Mayer coater or the like. The coating amount on the support is preferably set so that a dry film thickness of 100 μm or more is formed. When the dry film thickness is less than 100 μm, radicals generated by the decomposition of the polymerization initiator are combined with oxygen in the air and disappear, which tends to cause insufficient polymerization and curing. In order to increase the reflectance, a film thickness of 100 μm or more is necessary. Since the baking conditions are selected in the range of heating temperature: 100 to 150 ° C. and heating time: 30 to 900 seconds, the support must be selected and used as a resin film that does not soften under the baking conditions.

-Preparation of coating composition-
2-ethylhexyl acrylate (2-EHA): 95 parts by mass, 2-hydroxyethyl acrylate (2-HEA): 5 parts by mass A copolymer having a weight average molecular weight of 5 × 10 ⁵ and an acrylic polymer A did. Acrylic polymer A, 2-EHA, 2-HEA, isobornyl acrylate (manufactured by Osaka Organic Chemical Industry) is blended to form an acrylic mixture, and hexamethylene diisocyanate-based isocyanate crosslinking agent (TPA100: manufactured by Asahi Kasei Chemicals), organic A plurality of coating compositions were prepared by adding a peroxide (Perocta O: manufactured by NOF Corporation), a plasticizer, and a titanium oxide pigment at various ratios.

  The prepared coating composition is shown in Table 1. In any coating composition, the blending amounts of the crosslinking agent and the organic peroxide were fixed to 3 parts by mass and 1.0 part by mass, respectively. Test No. As the plasticizer of No. 7, a dipentaerythritol plasticizer (D-600: manufactured by Mitsubishi Chemical Corporation) having a number average molecular weight of 943 was used. However, in other coating compositions, Test No. was omitted. . Except for 23, a polyester plasticizer having a number average molecular weight of 2000 (W-2050: manufactured by Dainippon Ink & Chemicals, Inc.) was used. The titanium oxide pigment is an impurity produced by the sulfuric acid method: Test No. 1 using about 0.15% by mass of titanium oxide. Except for 24, a titanium oxide pigment (CR58: manufactured by Ishihara Sangyo Co., Ltd.) having an impurity of 0.001% by mass or less manufactured by a chlorine method was used.

-Application and baking-
A predetermined amount of the coating composition shown in Table 1 was applied onto a 100 μm thick polyethylene terephthalate (PET) separator subjected to double-sided peeling treatment, and then a coating film having a dry film thickness of 160 μm was formed by heating at 120 ° C. for 10 minutes.
-Performance evaluation of sheet-
A test piece was cut out from each sheet, the reflectance was measured, and the stickiness, flexibility, and ultraviolet resistance of the coating film were investigated.
[Measurement of reflectance]
Using a spectrocolorimeter (CM3700d light source C) used for measuring the object color according to JIS Z 8722, the reflectance at a wavelength of 650 nm was measured as the total reflectance. Further, the reflectance at a wavelength of 650 nm from which regular reflection light was removed was measured as diffuse reflectance.

[Stickyness evaluation test]
The surface of the coating film was touched with a finger, the coating film with tack was evaluated as x, and the coating film without tack was evaluated as ◯.
[Flexibility test]
A sample with a sheet width of 10 mm and a length of 150 mm is wrapped around a SUS tube having an outer diameter of 26 mm and a thickness of 2 mm, and fixed at a temperature of 20 ° C. and a humidity of 65% (standard state described in JIS Z 8703). After leaving it to stand for 24 hours, the sheet in which no cracks or breakage occurred was evaluated as “◯”, and the sheet in which cracks or breakage occurred was evaluated as “X”.
[Ultraviolet irradiation test]
Ultraviolet light intensity: 100 mW / cm ² UV lamp was used for 24 hours in an environment of temperature: 63 ° C. and humidity: 50%. The UV resistance was evaluated by making the film ○ and yellowing the coating film.

  As can be seen from the survey results in Table 2, the coating film formed from the thermal polymerization type acrylic paint containing isobornyl (meth) acrylate, plasticizer and titanium oxide has no stickiness and excellent flexibility. Both the total reflectance and the diffuse reflectance were 95% or more. As the blending amount of isobornyl (meth) acrylate was increased, the glass transition temperature Tg of the resin was increased, the coating film was hardened, and fine cracks were generated in the flexibility test. On the other hand, when the amount of isobornyl (meth) acrylate was small, the glass transition temperature Tg was lowered, and the coating film became sticky. If the glass transition temperature Tg was adjusted to the range of −20 to 60 ° C., there was no problem. Test No. in which the glass transition temperature Tg is out of the proper range. 17-22, and test No. using a coating composition containing no plasticizer. No. 23 was inferior in stickiness resistance and flexibility. In addition, Test No. using a titanium oxide pigment prepared by the sulfuric acid method was used. 24, the total reflectance and diffuse reflectance did not reach the specified values.

  For comparison, a foamed PET film that is commercially available as a white film having a high light reflectance was used and subjected to a similar test to investigate the reflectance, flexibility, UV resistance, and the like. For the white film, Toray E60L (film thickness: 188 μm) and Teijin DuPont Films UX-188 (film thickness: 188 μm) were used. As can be seen from the results of the investigation in Table 3, the conventional foamed PET film showed high values for both total reflectance and diffuse reflectance, but when used for a liquid crystal backlight reflector because of poor UV resistance. The color change of the coating film progressed over time, and the total reflectance and diffuse reflectance decreased.

As explained above, (meth) acrylic monomer, (meth) acrylic polymer acrylic mixture containing isobornyl (meth) acrylate, plasticizer, titanium oxide, thermal radical polymerization initiator, crosslinking The white sheet formed from the heat-polymerized acrylic paint blended with the agent is free of bubbles and rough skin even if it is thickened because the generation of bubbles is suppressed during film formation, and it is easy to increase the thickness to 100 μm or more. Excellent flexibility, high reflectance of 94% or higher total reflection, 91% or higher diffuse reflectance. When a white sheet is used as a reflective material for a liquid crystal display by utilizing the remarkably high reflectance of the white sheet, illumination light can be used efficiently for image display, and a member suitable for a liquid crystal display that requires a clear image display is provided. can get. White sheet with excellent flexibility and high reflectivity is used not only as a reflective material for liquid crystal displays but also as a reflective material incorporated in lighting fixtures, internal lighting advertising signs, interior lighting for store displays, vending machines, etc. it can.

Claims (5)

  (Meth) acrylic polymer: 2 to 50 parts by mass, (meth) acrylic acid isobornyl: 30 to 97% by mass of (meth) acrylic monomer: 98 to 50 parts by mass of (meth) acrylic mixture, Thermal radical polymerization initiator: 0.1 to 5 parts by mass, crosslinking agent: 0.1 to 20 parts by mass, plasticizer having a molecular weight of 500 or more: 1 to 20 parts by mass, titanium oxide pigment: 40 to 120 parts by mass Viscosity: A coating-type acrylic composition comprising a heat-polymerization-type acrylic paint adjusted to 1 to 100 Pa · s, coated on a support, and formed into a coating film, all in color measurement according to JIS Z8722 A white sheet for a liquid crystal backlight reflector, having a reflectance of 94% or more and a diffuse reflectance of 91% or more after removing regular reflection light.   The white sheet for a liquid crystal backlight reflector according to claim 1, wherein a metal and a metal oxide contained as impurities in the titanium oxide pigment are regulated to 0.1% by mass or less.   The white sheet for a liquid crystal backlight reflector according to claim 1, wherein the thermal radical polymerization initiator is a peroxide polymerization initiator.   The white sheet for a liquid crystal backlight reflector according to claim 1, wherein the white sheet has a glass transition temperature Tg of -20 to 60 ° C. The white sheet for a liquid crystal backlight reflector according to claim 1, wherein the thickness of the white sheet is 100 µm or more.