WO2006004324A1

WO2006004324A1 - Reflector plate for lcd backlight and method of producing same

Info

Publication number: WO2006004324A1
Application number: PCT/KR2005/001722
Authority: WO
Inventors: Jang Sub Chung; Bae Geun Lee; Tae Yeul Park
Original assignee: POHANG COATED STEEL CO Ltd
Current assignee: POHANG COATED STEEL CO Ltd
Priority date: 2004-06-21
Filing date: 2005-06-08
Publication date: 2006-01-12
Anticipated expiration: 2006-12-21
Also published as: KR20050120886A

Abstract

A reflector plate for LCD backlight is composed of a metal sheet such as an aluminum sheet or a stainless steel, a top coat coated on the metal sheet with a thickness of 3 to 25D, and a photo- reflective film adhesively bonded to the top coat. The top coat comprises a base resin selected from the group consisting of a thermoplastic vinyl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90°C and a thermoplastic acryl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120°C. Also provided is a method of producing such reflector plate in a continuous coating line.

Description

REFLECTOR PLATE FOR LCD BACKLIGHT AND METHOD

OF PRODUCING SAME

Technical Field

[1] The present invention generally relates to a reflector plate for LCD backlight and a method of producing the same, and more particularly, to a reflector plate for LCD backlight having enhanced adhesion strength to a photo-reflective film as well as excellent physical properties including workability and a method of producing such reflector plate through a continuous metal plate coating line in a cost-effective and efficient manner. Background Art

[2] Generally, reflector plates for a liquid crystal display (LCD) backlight are produced by way of adhesively bonding a high reflectance film to a metal plate, in which process it is important to conduct the film bonding operation while keeping the inherent re¬ flectivity of the film intact. It is also required that the film thus bonded has high adhesion strength and increased peeling resistance. In an effort to meet these re¬ quirements, a number of film bonding methods have been proposed in the past.

[3] Representative examples of the prior art methods include a method of disposing a double-faced adhesive sheet between a metal plate and a photo-reflective film and then applying pressure thereto to have the film bonded, and a method of placing a hot-melt substance such as ethylene vinyl acetate, polyamide or the like between a metal plate and a photo-reflective film and then applying heat thereto to cause the photo-reflective film to be bonded to the metal plate.

[4] Hot-melt substances are kept in a solid state under a normal temperature but will be transformed into a liquid as it is heated up to a given temperature. A myriad of such hot-melt substances are known, among which polyethylene vinyl acetate is most general and has been widely used in packaging boxes or cartons and bonding papers, woods, metals, garments and plastics. In the meantime, rubber-based hot-melt substances are utilized as a pressure sensitive adhesive that has a bonding ability at a normal temperature and exhibits excellent flexibility and tensile strength. Among these rubber-based hot-melt substances, polyamide is said to have higher heat resistance than other ones and has been used in manufacturing deflection coils for cathode ray tubes of television sets and other products that require increased thermal resistance. Polyurethane is a humidity-cured hot-melt adhesive which tends to react with moisture and become inseparable once completely cured by the moisture. Such a polyurethane adhesive is widely employed for the purpose of bonding woods, shoes, garments, car parts, etc.

[5] According to the prior art methods of producing a LCD backlight reflector plate that make use of a double-faced adhesive sheet or hot-melt adhesives, it is necessary to purchase a metal plate that has passed a pretreatment process and a coating process. And, in a separate factory, a photo-reflective film is bonded to the metal plate by feeding an adhesive sheet together with the photo-reflective film. However, the prior art methods pose a number of drawbacks in that it is cumbersome to separately purchase, transport and handle the materials needed, production processes are complicated as a whole, and a separate film bonding facility has to be provided in addition to the metal plate manufacturing factory. This means that the process for producing the reflector plate is less efficient and quite costly. Disclosure of Invention Technical Problem

[6] Taking the afore-mentioned problems inherent in the prior art methods into account, it is an object of the present invention to provide a reflector plate for LCD backlight that exhibits enhanced properties in terms of boding strength, heat resistance, workability and the like.

[7] Another object of the present invention is to provide a method of producing a reflector plate for LCD backlight that can produce a reflector plate for LCD backlight through a continuous coating line in a cost-effective and efficient manner without redu cing a reflectivity of a photo-reflective film.

[8] In accordance with one aspect of the invention, there is provided a reflector plate for LCD backlight, comprising: a metal sheet; a top coat coated on the metal sheet; and a photo-reflective film adhesively bonded to the top coat, wherein the top coat comprises a base resin selected from the group consisting of a thermoplastic vinyl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90⁰C and a thermoplastic acryl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120⁰C.

[9] In accordance with another aspect of the invention, there is provided a method of producing a reflector plate for LCD backlight, comprising the steps of: continuously supplying a metal sheet; pre-treating the metal sheet to enhance corrosion resistance and coat adhesiveness of the metal sheet; coating a top coat on the metal sheet, the top coat comprising a base resin selected from the group consisting of a thermoplastic vinyl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90⁰C and a ther¬ moplastic acryl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120⁰C; causing the top coat to run dry in an oven; and thermally bonding a photo-reflective film to the top coat while the top coat remain heated. Brief Description of the Drawings

[10] Fig. 1 is a cross-sectional view illustrating a reflector plate for LCD backlight produced in accordance with a preferred embodiment of the present invention. Best Mode for Carrying Out the Invention

[11] A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawing.

[12] Referring to Fig. 1, it can be seen that a reflector plate for LCD backlight according to the present invention is composed of a metal sheet 1, a bottom coat 2, an in¬ termediate coat 3 and a top coat 4, respectively coated on the metal sheet 1 one above atop, and a photo-reflective film 5 adhesively bonded to the top coat 4. Although three coated layers, i.e., the bottom coat 2, the intermediate coat 3 and the top coat 4, are shown in the drawing, the top coat 4 is essential but the bottom coat 2 and the in¬ termediate coat 3 may be optionally employed in the present invention.

[13] In view of the characteristics of a LCD backlight, it is preferred that the metal sheet

1 is made of aluminum or stainless steel and that a polyethylene terephthalate film is used as the photo-reflective film 5. The polyethylene terephthalate film itself is widely known in the art and may be properly adopted from the products of K.K. Toray, Japan, which are commercially available as model names #188E60V, #250E6SV, #188E60L and #250E60L, depending on the brilliance, reflectivity and thickness desired. De¬ scription will be offered later regarding paints for the bottom coat 2, the intermediate coat 3 and the top coat 4.

[14] In order to produce the reflector plate for LCD backlight according to the present invention, a metal sheet is supplied successively through a continuous coating line and is subjected to pre-treatments such as degreasing, water cleansing, chromate treatment and the like with a view to enhance corrosion resistance and coat adhesiveness. A top coat paint that has an excellent thermal bonding ability to a photo-reflective film is coated on the metal sheet at one time with a thickness of 3 to 25D by a roll coating process. The top coat paint thus coated is caused to run dry with a hot air in an oven for 20 to 150 seconds and the photo-reflective film is adhesively bonded to the top coat while the latter remains at an elevated temperature. The photo-reflective film is suc¬ cessively fed from a roll and a protective film will be laminated on the photo-reflective film to obtain a finished product.

[15] As an alternative embodiment, it may be contemplated that an intermediate coat paint is coated on the metal sheet with a thickness of 3 to 25D and a top coat paint that has an excellent thermal bonding ability to a photo-reflective film is coated on the in¬ termediate coat with a thickness of 3 to 25D. It is also possible that a bottom coat paint is coated on the metal sheet with a thickness of 3 to 25D, an intermediate coat paint is coated on the bottom coat with a thickness of 3 to 25D, and a top coat paint that has an excellent thermal bonding ability to a photo-reflective film is coated on the in¬ termediate coat with a thickness of 3 to 25D. In either case, the coated paints are dried with a hot air in an oven for 20 to 150 seconds and a photo-reflective film is adhesively bonded to the top coat before the latter is cooled down.

[16] Preferably, the intermediate coat paint is coated on the metal sheet with a thickness of 10 to 15D and the top coat paint is coated on the intermediate coat with a thickness of 3 to 8D. Alternatively, the bottom coat paint is coated on the metal sheet with a thickness of 4 to 5D, the intermediate coat paint is coated on the bottom coat with a thickness of 10 to 15D, and the top coat paint is coated on the intermediate coat with a thickness of 3 to 8D. The film is then adhesively bonded to the top coat.

[17] In the process of producing the inventive reflector plate, if the thickness of the top coat is less than 3D, the bonding strength of the top coat with respect to the film decreases sharply. A top coat whose thickness is greater than 25D may cause such coating defects as a popping and the like and is disadvantageous in the view point of economy.

[18] In the following, description will be given on paints for a bottom coat, an in¬ termediate coat and a top coat used in producing a reflector plate according to the present invention.

[19] Bottom coat paint is optionally employed for the purpose of enhancing close contact with the metal sheet. Examples of the bottom coat paint include an epoxy- based primer, a polyester-based primer, a urethane-based primer, an acryl-based primer and modified primers thereof. AU paints that are available for the bottom coat of a pre- coated metal may be put in use with no limitation.

[20] In addition to the intrinsic anti-corrosion property and the increased fixing property with the top coat and the metal sheet, the bottom coat paint is given an elongation ratio great enough to absorb the shocks occurring at the boundary between the top coat and the metal sheet, while preventing the cracks of the metal sheet, which may take place in the process of metalworking, from propagation to the intermediate coat and the top coat.

[21] All pigments usable for the pre-coated metal can be employed without any limitation as pigments for the bottom coat paint, examples of which include rust inhibiting pigments such as chromium-based rust inhibiting pigments and non- chromium-based rust inhibiting pigments (free from toxicity), organic pigments and inorganic pigments. The bottom coat paint may be a transparent one containing no pigment.

[22] Now, description will be shifted to intermediate coat paint. As the intermediate coat paint, all kinds of paints usable for the pre-coated metal can be employed, including a regular polyester-based (RPE) paint, a high polymer polyester-based (HPP) paint, a fluorine-based paint, a urethane-based paint, an epoxy-based paint, modified paints thereof and the like.

[23] In addition to the anti-corrosion property for the metal sheet against moisture and the increased bonding property with the top coat and the metal sheet, the intermediate coat paint is given an elongation ratio great enough to absorb the shocks occurring at the boundary between the bottom coat and the top coat, while preventing the cracks of the metal sheet, which may take place in the process of metalworking, from propagation to the top coat. Also the intermediate coat paint is composed to increase the fixing strength with the top coat, thus avoiding any reduction in the bonding strength of the photo-reflective film which would otherwise occur by the attack of moisture or heat.

[24] The intermediate coat paint is compounded as follows.

[25] It is preferred that the intermediate coat paint comprises polyester-based resin and modified resin thereof, as base binder resin, and polyisocyanate resin, a cross-linking agent.

[26] Preferably, the polyester-based resin has number average molecular weight of 2,000 to 30,000, OH value of 2 to 100, acid value of 0 to 50 and glass transition temperature of -20 to 80⁰C.

[27] If the number average molecular weight is less than 2,000, workability becomes de¬ teriorated, and if the number average molecular weight is greater than 30,000, solid content in the paint will be decreased, thereby making it difficult to increase the thickness of a coat. The dry ability of a coat will be reduced if the glass transition temperature is less than -20⁰C, while the coat will become tough and cracks may occur in the course of processing or by virtue of shocks, if the glass transition temperature is greater than 80⁰C. Furthermore, if the OH value is greater than 100 with the acid value above 50, workability and shock resistance will be reduced.

[28] Melamine may be used as the cross-linking agent in place of polyisocyanate, in which case a shortcoming exists in that heat resistance of the film is decreased at the end of bonding process.

[29] Examples of polyisocyanate compounds include hexamethylene diisocyanate

(HMDI), isophorone diisocyanate (IPDI), xylene diisocyanate, 2-, A-, 6-triisocyanate toluene and other similar compounds. For application to a pre-coated metal, use is made of polyisocyanate compounds whose radicals are thermally dissociated, when masked. [30] According to the present invention, the base resin of the intermediate coat, e.g., polyester resin or modified resin thereof are used in a range of 10 to 50wt% on the basis of the total paint composition. If the content of polyester resin or modified resin thereof is less than 10wt%, sharp reduction is shown in terms of workability. If the content of polyester resin or modified resin thereof is greater than 50wt%, it cannot be used for the paint due to solids contained in the resin itself.

[31] It is preferred in the instant invention that polyisocyanate should be used in a range of 2 to 15wt% on the basis of the total paint composition. If the content of poly¬ isocyanate is less than 2wt%, solvent resistance and hardness of a coat will be reduced sharply. Flexibility and shock resistance of a coat will be marred if the content of poly¬ isocyanate is less than 15wt%.

[32] A hardening agent is added to promote cross-linking reaction between polyester resin or modified resin thereof as a base resin and polyisocyanate as a cross-linking resin and enhance compactness of a coat. The hardening agent comprises amine-based catalyst, metal salt-based catalyst, naphthenic acid-based catalyst and the like. Examples of the amine-based catalyst include, among other things, triethyl amine, N,N-diethyl cyclohexyl amine, 2,6-diethyl morpholine, triethyl diamine, dimethyl aminoethyl adipate, diethyl ethanol amine and N,N-dimethyl benzyl amine. Examples of the metal salt-based catalyst include oleic acid potassium, tetra-2-ethyl-hexyl titanate, SnCl , FeCl and dibuthyl tin dilaurate (DBTDL). Examples of the naphthenic acid-based catalyst include Zn-naphthenate, Pb-naphthenate, Co-naphthenate and Ca- naphthenate.

[33] If the hardening agent is used in too small amount, a coat will be hardened insuf¬ ficiently depending on the working condition. Use of the hardening agent in too much amount increases the coat hardening speed to an unacceptable degree, which in turn creates popping or shrinkage on the coat in a coating process.

[34] All pigments usable for the pre-coated metal can be employed without any limitation as pigments for the intermediate coat paint, examples of which include rust inhibiting pigments such as chromium-based rust inhibiting pigments and non- chromium-based rust inhibiting pigments (free from toxicity), organic pigments and inorganic pigments. The intermediate coat paint may be a transparent one containing no pigment.

[35] A top coat paint will now be set forth in detail.

[36] As the top coat on which boding ability of the photo-reflective film depends, it is advantageous to use thermoplastic resin to thereby enhance the boding ability. Preferably, the top coat is produced through the use of vinyl-based resin, acryl-based resin and modified resin thereof.

[37] The top coat paint is compounded as follows. [38] Above all, the top coat paint comprises thermoplastic vinyl resin, thermoplastic acryl resin and modified resin thereof, as base binder resin. Preferably, the ther¬ moplastic vinyl resin has number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90⁰C.

[39] If the number average molecular weight is less than 10,000, bonding strength between the top coat and the photo-reflective film becomes deteriorated, and if the number average molecular weight is greater than 70,000, solid content in the top coat will be decreased, thereby making it difficult to increase the thickness of the top coat, which may be a culprit in reducing the bonding ability of the top coat to the photo- reflective film. Adhesiveness appears in place of bonding property, thus weakening the overall bonding strength, if the glass transition temperature is less than 30⁰C. The coat will become too tough and the bonding area may be broken away by virtue of shocks, if the glass transition temperature is greater than 90°C. Furthermore, if the OH value is greater than 100 with the acid value above 20, bonding strength as measured through a boiling water test will be reduced.

[40] It would be preferred that the thermoplastic acryl resin has number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120°C.

[41] If the number average molecular weight is less than 10,000, bonding strength between the top coat and the photo-reflective LCD film becomes deteriorated, and if the number average molecular weight is greater than 70,000, solid content in the top coat will be decreased, thereby making it difficult to increase the thickness of the top coat, which may be a culprit in reducing the bonding ability of the top coat to the photo-reflective film. Adhesiveness appears in place of bonding property, thus weakening the overall bonding strength, if the glass transition temperature is less than 10°C. The coat will become too tough and the bonding area may be broken away by virtue of shocks, if the glass transition temperature is greater than 120⁰C. Furthermore, if the OH value is greater than 100 with the acid value below 5 or above 20, bonding strength as measured through a boiling water test will be reduced.

[42] As used herein, the term "glass transition temperature" (Tg) denotes a value measured by differential thermal analysis (DTA) and the term "number average molecular weight" means a value obtained through gel permeation chromatography (GPC).

[43] According to the present invention, it would be preferred that the thermoplastic vinyl resin, the thermoplastic acryl resin or the modified resin thereof is used in a range of 5 to 50wt% on the basis of the total paint composition for the top coat. If the resin is contained less than 5wt%, solid content in the paint and viscosity will be decreased thus worsening the workability, and coat layer build-up property becomes deteriorated thereby making it difficult to produce a top coat with a specified thickness. If the resin is contained more than 50wt%, solid content in the paint and viscosity will be too high to be used as the top coat paint.

[44] All pigments usable for the pre-coated metal can be employed without any limitation as pigments for the top coat paint, examples of which include rust inhibiting pigments such as chromium-based rust inhibiting pigments and non-chromium-based rust inhibiting pigments (free from toxicity), organic pigments and inorganic pigments. The top coat paint may be a transparent one containing no pigment, which provides an effect of increasing the bonding strength between the film and the top coat.

[45] For the top coat containing acryl resin, all kinds of solvents usable for the pre- coated metal can be employed without any limitation. With respect to the top coat containing vinyl resin, it is preferable to use a ketone-based solvent that exhibits excellent solubility, although combined use of ketone-based and non-ketone-based solvents may be contemplated.

[46] In the top coat containing vinyl resin, it would be preferred that a heat resistant stabilizer is used to enhance the thermal stability of the vinyl resin.

[47] According to the present invention, bondability and workability are important features of the resin composition used. In order not to mar the bonding strength between the resin composition and the film, it is an essential factor to properly control the kind and amount of additives added to the resin composition. Examples of the additives available for this purpose include a polyester-based additive, an acryl-based additive, a vinyl-modified acryl-based additive and a silicon-based additive. Of these, the polyester-based additive is preferred because it does not reduce the bonding strength. The acryl-based additive, the vinyl-modified acryl-based additive and the silicon-based additive should preferably be excluded from use or used in a minimized amount because they tend to float up to a bonding surface and serve to reduce the bonding strength between the resin composition and the film.

[48] Although it would be preferable not to use the additives as noted above, they may be used to assure flatness of a coat or to suppress generation of bubbles in the coating process thus improving workability. If a need exists for use of the additives, the polyester-based additive is preferably used in an amount of 0-1.0wt%. The acryl-based additive, the vinyl-modified acryl-based additive and the silicon-based additive should preferably be used in a range of 0-0.2wt%.

[49] Use of the polyester-based additive in a greater amount than 1.0wt% or use of the acryl-based additive, the vinyl-modified acryl-based additive and the silicon-based additive in an amount exceeding 0.2wt% will decrease the bonding strength between the resin composition and the film.

[50] Now, the present invention will be described in greater detail through Examples and Comparative Examples which should be understood not to limit the scope of the invention.

[51] Example 1 [52] In a continuous coating line, the thermoplastic vinyl-based top coat paint composition as shown in Table 1 was once roll-coated on a 0.35mm-thick aluminum sheet to have a thickness of 5D and then dried with hot air for 20-150 seconds at a peak metal temperature (PMT) of 250°C to have a surface gloss ratio of 10-100%. A polyethylene terephthalate film of 193Din thickness was then bonded to the coating product, thus preparing a specimen with a top coat.

[53] Example 2 [54] A specimen with a top coat was prepared in the same manner as in Example 1 except that the thermoplastic acryl resin-based paint composition as shown in Table 1 is used as the top coat paint.

[55] Table 1

[56] Example 3 [57] A specimen with intermediate and top coats was prepared in the same manner as in Example 1 except that "FINECOAT BC. 7000" paint sold by Samwha Paint Industrial Co., Ltd., a Korean corporation, is used as intermediate coat paint and the ther¬ moplastic vinyl resin-based paint composition as shown in Table 1 is used as the top coat paint. In this Example, the intermediate coat paint was once coated with a thickness of 15Cl and dried at a peak metal temperature of 232°C, while the top coat paint was once coated with a thickness of 5D.

[58] Example 4 [59] A specimen with intermediate and top coats was prepared in the same manner as in Example 3 except that the thermoplastic acryl resin-based paint composition as shown in Table 1 is used as the top coat paint.

[60] It should be noted that, although "FINECOAT BC. 7000" paint of Samwha Paint Industrial Co., Ltd. was used as the intermediate coat paint in Examples 3 and 4, there occurs no difference in film bonding strength even if use is made of other color paints, which have been used for a pre-coated metal, including regular polyester (RPE)-based paint, high polymer polyester (HPP)-based paint, fluorine-based paint and urethane- based paint.

[61] Example 5 [62] A specimen with intermediate and top coats was prepared in the same manner as in Example 3 except that the thermoplastic vinyl resin-based paint composition as shown in Table 1 is used as the top coat paint and the paint composition as shown in Table 2 is used as the intermediate coat paint.

[63] Table 2

[64] Example 6 [65] A specimen with intermediate and top coats was prepared in the same manner as in Example 5 except that the thermoplastic acryl resin-based paint composition as shown in Table 1 is used as the top coat paint.

[66] Example 7 [67] A specimen with bottom, intermediate and top coats was prepared in the same manner as in Example 1 except that the bottom coat paint "FINECOAT LP PRIMER" (HPP/melamine-based paint for household electric appliances) sold by Samwha Paint Industrial Co., Ltd. is once coated with a thickness of 5D, the intermediate coat paint "FINECOAT BC. 6000" sold by Samwha Paint Industrial Co., Ltd. is once coated with a thickness of 15D, and the thermoplastic vinyl resin-based top coat paint composition as shown in Table 1 is once coated with a thickness of 5D. In this Example, the bottom coat paint was dried at a peak metal temperature of 224°C, while the intermediate coat paint was dried at a peak metal temperature of 232°C.

[68] Example 8

[69] A specimen with bottom, intermediate and top coats was prepared in the same manner as in Example 7 except that the thermoplastic acryl resin-based paint composition as shown in Table 1 is used as the top coat paint.

[70] It should be noted that, although "FINECOAT LP PRIMER" (HPP/melamine-based paint for household electric appliances) paint of Samwha Paint Industrial Co., Ltd. was used as the bottom coat paint in Examples 7 and 8, all kinds of rust inhibiting primers for a pre-coated metal used in the field of buildings and household electric appliances can be employed as the bottom coat paint because there occurs no difference in film bonding strength depending on the kinds of the bottom coat paint. Moreover, although "FINECOAT BC. 6000" paint of Samwha Paint Industrial Co., Ltd. was used as the in¬ termediate coat paint in Examples 7 and 8, there occurs no difference in film bonding strength even if use is made of other color paints, which have been used for a pre- coated metal, including regular polyester (RPE)-based paint, high polymer polyester (HPP)-based paint, fluorine-based paint and urethane-based paint.

[71] Example 9

[72] A specimen with bottom, intermediate and top coats was prepared by using the bottom coat paint "FINECOAT LP PRIMER" (HPP/melamine-based paint for household electric appliances) sold by Samwha Paint Industrial Co., Ltd., the in¬ termediate coat paint composition as shown in Table 2 and the thermoplastic vinyl resin-based top coat paint composition as shown in Table 1.

[73] Example 10

[74] A specimen with bottom, intermediate and top coats was prepared in the same manner as in Example 9 except that the thermoplastic acryl resin-based paint composition as shown in Table 1 is used as the top coat paint.

[75] It should be noted that, although "FINECOAT LP PRIMER" (HPP/melamine-based paint for household electric appliances) paint of Samwha Paint Industrial Co., Ltd. was used as the bottom coat paint in Examples 9 and 10, all kinds of rust inhibiting primers for a pre-coated metal used in the field of buildings and household electric appliances can be employed as the bottom coat paint because there occurs no difference in film bonding strength depending on the kinds of the bottom coat paint.

[76] Comparative Examples 1-4

[77] Specimens for comparison were prepared in the same manner as in Example 7 except that use is made of the bottom, intermediate and top coat paints as shown in Table 3 below.

[78] Table 3

[79] Note: 1) HPP/melamine-based PCM primer for household electric appliances sold by Samwha Paint Industrial Co., Ltd. under a trade name "FINECOAT LP PRIMER"; 2) PCM epoxy primer sold by Samwha Paint Industrial Co., Ltd. under a trade name "FINECOAT SP-7 PRIMER"; 3) Intermediate coat paint for bonding a PET film used by Pohang Coated Steel Co., Ltd. under the name "BB291S"; 4) Transparent coat paint for bonding a PET film used by Pohang Coated Steel Co., Ltd. under the name "BB290S"; and 5) PCM primer for household electric appliances sold by Samwha Paint Industrial Co., Ltd. under a trade name "FINECOAT SL. 4000 CLEAR".

[80] Test of Physical Properties [81] Physical properties of the specimens prepared in Examples 1-10 and Comparative Examples 1-4 were evaluated in the following test methods.

[82] (1) Initial Bonding Strength [83] A 5mm- wide "#" mark is scored on a film-bonded surface by means of a sharp- edged knife to conduct the 5mm Erichsen test. The degree of peeling-apart is evaluated by way of forcibly peeling off the planar part and the Erichsen part. The Erichsen test is carried out under the requirements of NCCA-II-23.

[84] (2) Bonding Strength Test through Scoring and Boiling Water Dipping [85] An "X" mark is scored on a film-bonded surface by means of a sharp-edged knife to conduct the Erichsen test, after which the specimens are dipped into boiling water for one hour. Creation of blisters and the degree of peeling-apart is evaluated for the planar part and the Erichsen part. The Erichsen test is carried out under the re¬ quirements of NCCA-II-23.

[86] (3) Heat Resistance [87] The film-bonded plate is maintained within an oven of 170°C for one hour and then the change of appearance is evaluated. [88] (4) Bonding Strength Test through Boiling Water Dipping and Scoring [89] The film-bonded plates are first dipped into boiling water for one hour and then an "X" mark is scored on a film-bonded surface by means of a sharp-edged knife to conduct the Erichsen test. The degree of peeling-apart is evaluated by way of forcibly peeling off the planar part and the Erichsen part. The Erichsen test is carried out under the requirements of NCCA-II-23.

[90] Results of Physical Property Test [91] Table 4

[92] Table 5

[93] Table 6

[94]

Industrial Applicability [95] As described in the foregoing, the present invention makes it possible that a reflector plate for LCD backlight having increased film bonding strength, enhanced heat resistance and excellent workability is produced through a continuous coating line in a cost-effective and efficient manner.

Claims

[1] A reflector plate for LCD backlight, comprising: a metal sheet; a top coat coated on the metal sheet; and a photo-reflective film adhesively bonded to the top coat, wherein the top coat comprises a base resin selected from the group consisting of a thermoplastic vinyl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90°C and a thermoplastic acryl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120°C.

[2] The reflector plate for LCD backlight as recited in claim 1, further comprising an intermediate coat lying between the metal sheet and the top coat, the intermediate coat selected from the group consisting of a polyester-based paint, a high polymer polyester-based paint, a fluorine-based paint, an urethane-based paint, an epoxy-based paint and modified paints thereof.

[3] The reflector plate for LCD backlight as recited in claim 1, further comprising an intermediate coat lying between the metal sheet and the top coat, the intermediate coat comprising as its base resin, a polyester-based resin with number average molecular weight of 2,000 to 30,000, OH value of 2 to 100, acid value of 0 to 50 and glass transition temperature of -20 to 80°C and modified resins thereof, and as its cross-linking agent, a polyisocyanate resin.

[4] The reflector plate for LCD backlight as recited in claim 2, further comprising a bottom coat lying between the metal sheet and the intermediate coat, the bottom coat selected from the group consisting of an epoxy-based primer, a polyester- based primer, an urethane-based primer, an acryl-based primer and modified primers thereof.

[5] The reflector plate for LCD backlight as recited in claim 3, further comprising a bottom coat lying between the metal sheet and the intermediate coat, the bottom coat selected from the group consisting of an epoxy-based primer, a polyester- based primer, an urethane-based primer, an acryl-based primer and modified primers thereof.

[6] The reflector plate for LCD backlight as recited in claim 1, wherein the photo- reflective film comprises a polyethylene terephthalate film.

[7] The reflector plate for LCD backlight as recited in claim 1, wherein the top coat further comprises a polyester-based additive.

[8] The reflector plate for LCD backlight as recited in claim 1, wherein the top coat has a thickness of 3 to 25D.

[9] The reflector plate for LCD backlight as recited in claim 1, wherein the base resin of the top coat is in a range of 5 to 50wt% on the basis of solid content weight of a paint for the top coat.

[10] The reflector plate for LCD backlight as recited in claim 3, wherein the in¬ termediate coat has a thickness of 3 to 25D.

[11] The reflector plate for LCD backlight as recited in claim 3, wherein the base resin of the intermediate coat is in a range of 10 to 50wt% on the basis of solid content weight of a paint for the intermediate coat.

[12] A method of producing a reflector plate for LCD backlight, comprising the steps of: continuously supplying a metal sheet; pre-treating the metal sheet to enhance corrosion resistance and coat ad¬ hesiveness of the metal sheet; coating a top coat on the metal sheet, the top coat comprising a base resin selected from the group consisting of a thermoplastic vinyl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 0 to 20 and glass transition temperature of 30 to 90°C and a thermoplastic acryl resin with number average molecular weight of 10,000 to 70,000, OH value of 0 to 100, acid value of 5 to 70 and glass transition temperature of 10 to 120⁰C; causing the top coat to run dry in an oven; and thermally bonding a photo-reflective film to the top coat while the top coat remain heated.

[13] The method as recited in claim 12, further comprising the step of coating an in¬ termediate coat between the metal sheet and the top coat, the intermediate coat selected from the group consisting of a polyester-based paint, a high polymer polyester-based paint, a fluorine-based paint, an urethane-based paint, an epoxy- based paint and modified paints thereof.

[14] The method as recited in claim 12, further comprising the step of coating an in¬ termediate coat between the metal sheet and the top coat, the intermediate coat comprising as its base resin, a polyester-based resin with number average molecular weight of 2,000 to 30,000, OH value of 2 to 100, acid value of 0 to 50 and glass transition temperature of -20 to 80°C and modified resins thereof, and as its cross-linking agent, a polyisocyanate resin.

[15] The method as recited in claim 13, further comprising the step of coating a bottom coat between the metal sheet and the intermediate coat, the bottom coat selected from the group consisting of an epoxy-based primer, a polyester-based primer, an urethane-based primer, an acryl-based primer and modified primers thereof. [16] The method as recited in claim 14, further comprising the step of coating a bottom coat between the metal sheet and the intermediate coat, the bottom coat selected from the group consisting of an epoxy-based primer, a polyester-based primer, an urethane-based primer, an acryl-based primer and modified primers thereof.