WO2006121228A1

WO2006121228A1 - Coating method of metal sheet using japanese lacquer mixture

Info

Publication number: WO2006121228A1
Application number: PCT/KR2005/001771
Authority: WO
Inventors: Hyung-Chul Kim
Original assignee: Han-Kook National Corp.
Priority date: 2005-05-09
Filing date: 2005-06-10
Publication date: 2006-11-16

Abstract

Disclosed is a method of coating a metal sheet with a Japanese lacquer mixture. Specifically, this invention provides a method of coating a metal sheet with a Japanese lacquer mixture, including pretreating the surface of a metal sheet, subjecting the metal sheet to a printing process such as offset printing or silk screen printing, drying the printed metal sheet, coating the metal sheet with a filtered Japanese lacquer mixture, and drying the coated metal sheet. According to this invention, the metal sheet coating method adopts a printing process, and thus the metal sheet, variously printed, is coated with lacquer, such that a Japanese lacquered metal sheet having various colors and patterns can be produced on an industrial scale. Further, since the metal sheet is excellent with respect to the absorption of harmful electromagnetic waves, far infrared emissivity, and durability, it may be variously applied to mobile phones, notebook computers, automobile interior materials, construction materials, etc.

Description

COATING METHOD OF METAL SHEET USING

JAPANESE LACQUER MIXTURE

[Technical Field]

The present invention relates to a method of coating a metal sheet with a Japanese lacquer mixture, and more particularly, to a method of coating a metal sheet with a Japanese lacquer mixture, comprising pretreating the surface of a metal sheet, subjecting the metal sheet to a printing process such as offset printing or silk screen printing, drying the printed metal sheet, coating the metal sheet with a filtered Japanese lacquer mixture, and drying the coated metal sheet.

[Background Art]

In general, raw Japanese lacquer or Japanese lacquer collected from the lacquer tree is known to be composed mainly of urushiol, with small amounts of rubber, nitrogen-containing material, and water. Japanese lacquer, which is a kind of natural resin, has been used in a large amount in a manner such that it is mainly applied on wood to produce articles for living, such as wardrobes, vessels, spoons, chopsticks, and tables, in

Korea, China and Japan for thousands of years. Further, it is also known that Japanese lacquer has advantages such as high flame resistance, heat resistance, rot resistance, insect resistance, and electric insulation properties, and as well, the preservative quality thereof is good.

Recently, various attempts to apply Japanese lacquer to a synthetic polymer (Korean Patent Laid-open Publication No. 2000- 0024493) and to a ceramic and metal container (Korean Patent

Laid-open Publication No. 2002-0072903), in addition to the wood products, have been made.

However, the use of the Japanese lacquer which is applied to coating while making keeping variously printed patterns clear has not yet been disclosed. Moreover, since the uncured Japanese lacquer coating causes an allergic reaction in the human body, general users are reluctant to employ such lacquer. For these reasons, Japanese lacquer has numerous difficulties in use. In addition, the Japanese lacquer coating begins to cure from its surface contacted with moisture and oxygen, and has very low oxygen permeability and moisture permeability. Thus, in order to cure the inner portion of the coating, there is the need for a UV drying process or a process of repeatedly applying and curing of Japanese lacquer, which is complicated. Thereby, while the production cost increases, economic benefits are negated, and consequently, it is difficult to realize industrial production of lacquer products.

[Disclosure]

[Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a method of coating a metal sheet with a mixture of Japanese lacquer and varnish, in order to produce a metal sheet that has various colors, a Japanese lacquer coating, and excellent far infrared emission and electromagnetic wave-blocking effects using a printing process, on an industrial scale.

Another object of the present invention is to provide a method of coating a metal sheet with a mixture of Japanese lacquer and lacquer, in order to produce a metal sheet that has various glosses and colors and high hardness using a printing process, on an industrial scale.

[Technical Solution]

In order to solve the aforementioned technical problems, a method of coating a metal sheet with a Japanese lacquer mixture is comprised of pretreating a surface of a metal sheet, subjecting the metal sheet to printing, including offset printing or silk screen printing, drying the printed metal sheet, coating the metal sheet with a mixture of filtered Japanese lacquer and varnish and drying the coated metal sheet. Then, it is desirable that the method further includes coating the coated and dried metal sheet using lacquer containing PMMA (polymethyl methacrylate) and MMA (methyl methacrylate) and then drying it. Hereinafter, a detailed description will be given of the present invention.

The metal sheet used in the present invention is formed of a metal, such as titanium steel, stainless steel, aluminum, or an aluminum alloy. In particular, aluminum is preferable. The metal sheet is surface polished and water washed, and thus has a thickness of 0.3-2 mm. The surface of the metal sheet is pretreated using a physical process, a chemical process or a primer process. Examples of the physical process include sand blast, shot blast, dry-ice blast, hairline, vibration, etc., and examples of the chemical process include aluminum deposition, anodizing, electrocoloring, and alkali degreasing for final washing in all tests.

The primer treatment is used in the case where inorganic material such as plastic is difficult to adhere to the metal sheet, and is also used for silk screen printing for a heater or various decorations and marks. Such a pretreatment process functions to increase adhesion upon printing and corrosion resistance. In the present invention, the anodizing treatment is preferably used in order to prevent the oxidation of the material through chromate treatment.

The pretreated metal sheet is subjected to printing such as offset printing or silk screen printing to print a desired design pattern on the metal sheet in advance. Shortly after the printing process, a drying process is conducted at 150~200^°Cfor

30-90 min.

The metal sheet thus printed and dried is coated with Japanese lacquer in a manner such that a mixture of Japanese lacquer and varnish is prepared and then applied on the metal sheet .

As such, in the present invention, lacquer native to Korea, China, Japan or Southeast Asia may be used without limitation. Further, although such lacquer may have a composition varying with the production area, it may be independently applied. The Japanese lacquer used in the present invention is filtered with filter paper, after which 95~98 wt% of the filtered Japanese lacquer is mixed with 2-5 wt% of varnish, thus obtaining the mixture. The mixture of Japanese lacquer and varnish thus prepared is preferably applied though silk screen printing, but the present invention is not limited to such a printing process. Shortly after the application of the mixture of Japanese lacquer and varnish, a drying process is conducted at 130-180 ^°C for 30-90 min. In order to enhance gloss and weather resistance, the method of the present invention preferably further comprises coating the Japanese lacquered metal sheet thus dried using lacquer containing PMMA (polymethyl methacrylate) and MMA

(methyl methacrylate) and then drying it. In such a case, the PMMA is acryl resin including MMA as a main monomer, and the admixture containing PMMA and MMA is used in an amount of 95~99 wt% based on the total weight of the lacquer, in which the PMMA and MMA are preferably admixed at 5-8: 5-2. In particular, a ratio of PMMA and MMA of 6:4 is most preferable, in the interest of high transparency and desirable properties .

The lacquer admixture is preferably applied through silk screen printing, but the present invention is not limited to such a printing process. After the application of the lacquer admixture, a drying process is conducted at 80-120 ^°C for 30-90 min. In the present invention, the drying process is conducted under temperature conditions optimal to prevent cracking or peeling of the Japanese lacquer coating upon curing. As shown in FIG. 2, the metal sheet thus produced comprises a metal sheet 10, a pretreated anodized layer 20, a design printed layer 30, a Japanese lacquered layer 40, and a lacquered layer 50, which are sequentially formed upwards.

Also, the present invention provides a method of coating a metal sheet with a Japanese lacquer mixture comprising pretreating a surface of a metal sheet, subjecting the metal sheet to printing, including offset printing or silk screen printing, drying the printed metal sheet, coating the metal sheet with a mixture of filtered Japanese lacquer and varnish and drying the coated metal sheet.

In addition, a series of processes of pretreating the surface of a metal sheet, subjecting the metal sheet to printing such as offset printing or silk screen printing, and drying the printed metal sheet is conducted as above.

The printed and dried metal sheet is coated with a mixture of Japanese lacquer and a lacquer admixture. As such, the Japanese lacquer, which is filtered using filter paper, is used in an amount of 20-80 wt% and the lacquer admixture is used in an amount of 80~20 wt% to prepare the mixture. When the amount of Japanese lacquer is incresed and the amount of lacquer is decreased, the surface gloss is decreased and the color is darkened. On the other hand, when the amount of Japanese lacquer is decreased and the amount of lacquer is incresed, the surface gloss is increased and the color is brightened. In this way, it is possible to perform the coating treatment in order to realize various glosses and colors according to the preferences of the consumer .

In this case, it is preferred that the Japanese lacquer be added with 5 wt% of varnish. The mixture of the Japanese lacquer and the lacquer admixture is preferably applied through silk screen printing, but the present invention is not limited to such a printing process.

The lacquer admixture containing the PMMA and the MMA is used in an amount of 20-80 wt% based on the total weight of the mixture to be applied, in which the PMMA and MMA are preferably admixed at a ratio of 5-8: 5-2. In particular, a ratio of PMMA to MMA of 6:4 is most preferable in the interest of high transparency and desirable properties.

Shortly after the application of the mixture of the Japanese lacquer and the lacquer admixture, a drying process is conducted at 130~180°C for 30-90 min. In the present invention, the drying process is conducted at a temperature that is optimal for preventing cracking or peeling of the Japanese lacquer coating upon curing.

As shown in FIG. β, the metal sheet thus produced comprises a metal sheet 10, a pretreated anodized layer 20, a design printed layer 30, and a layer 40'of the mixture of Japanese lacquer and lacquer, which are sequentially formed upwards.

[Advantageous Effects]

According to the present invention, since the metal sheet coating method adopts a printing process and the metal sheet, variously printed, is coated with Japanese lacquer, the Japanese lacquered metal sheet having various colors and patterns can be simply produced on an industrial scale. Further, since such a metal sheet is superior with respect to the absorption of harmful electromagnetic waves, far infrared emissivity, and durability, it can be variously applied to mobile phones, notebook computers, automobile interior materials, construction

materials, etc.

[Description of Drawings]

FIG. 1 is a flowchart showing the process of coating a metal sheet with a mixture of Japanese lacquer and varnish, according to the present invention;

FIG. 2 is a sectional view showing the metal sheet coated with the mixture of Japanese lacquer and varnish, produced according to the process of the present invention; FIG. 3 is a photograph showing an aluminum sheet coated with the mixture of Japanese lacquer and varnish, produced according to the process of the present invention;

FIG. 4 is a photograph showing an aluminum sheet obtained by further applying lacquer on the Japanese lacquered aluminum sheet of FIG. 3;

FIG. 5 is a flowchart showing the process of coating a metal sheet with a mixture of Japanese lacquer and lacquer, according to the present invention;

FIG. 6 is a sectional view showing the metal sheet coated with the mixture of Japanese lacquer and lacquer, produced according to the process of the present invention; and

FIG. 7 is a photograph showing an aluminum sheet coated with the mixture of Japanese lacquer and lacquer, produced according to the process of the present invention. [Mode for Invention]

A better understanding of the present invention may be obtained through the following examples, test examples and tables which are set forth to illustrate, but are not to be construed as the limit of the present invention. Example 1

Coating of Metal Sheet with Japanese Lacquer FIG. 1 illustrates the process of coating the metal sheet according to the present invention. Specifically, an aluminum sheet (H-26, available from Alcoa) having a weight of 0.25-0.30 kg and a thickness of 0.5 mm was surface polished and water washed. Thereafter, the aluminum sheet was subjected to surface cleaning using a degreasing agent and then pretreated with 2 kg of an acidic chromate solution diluted with water to form a 1.5~2.5 mm thick anodized film.

A predetermined design pattern was printed on the aluminum sheet through offset printing, after which the aluminum sheet was dried in a box oven (available from Taeyang Electronic Company) at 180 ^°C for 1 hour. Raw Japanese lacquer native to China was filtered with filter paper and was then mixed with 5 wt% of varnish based on the total weight of the filtered Japanese lacquer to prepare a Japanese lacquer mixture, which was then applied to a thickness of 1.5-2.5 mm on the printed aluminum sheet through silk screen printing. Subsequently, the sheet was dried in a box oven at 160 °C for 1 hour (FIG. 3) .

Example 2

Coating of Japanese Lacquered Metal Sheet with Lacquer On the Japanese lacquered aluminum sheet of Example 1, lacquer (plexβ788, available from ROHM), containing PMMA and MMA admixed at 6:4, was applied through silk screen printing. Thereafter, the aluminum sheet was dried in a box oven at 100 "C for 1 hour, thus producing a lacquered aluminum sheet (FIG. 4) . Example 3

Coating of Metal Sheet with Mixture of Japanese Lacquer and Lacquer

FIG. 5 illustrates the process of coating the metal sheet according to the other example of the present invention. Specifically, an aluminum sheet (H-26, available from Alcoa) having a weight of 0.25~0.30 kg and a thickness of 0.5 mm was surface polished and water washed. Thereafter, the aluminum sheet was subjected to surface cleaning using a degreasing agent and then pretreated with 2 kg of an acidic chromate solution diluted with water in order to form a 1.5-2.5 mm thick anodized film.

Subsequently, the aluminum sheet was printed with a predetermined design pattern through offset printing and was then dried in a box oven (available from Taeyang Elctronic Company) at 180 °C for 1 hour.

Raw Japanese lacquer native to China was filtered with 300 mesh sized filter paper and was then mixed with 5 wt% of varnish based on the total weight of the filtered Japanese lacquer to prepare a Japanese lacquer mixture, which was then further mixed with lacquer (plexβ788, available from ROHM), containing PMMA and MMA admixed at 6:4, at varying weight ratios as shown in

Table 1 below, thus preparing a mixture of Japanese lacquer and lacquer. Subsequently, the mixture thus prepared was applied to a thickness of 1.5~2.5 mm on the printed aluminum sheet through silk screen printing. Then, the sheet was dried in a box oven at

160 °C for 1 hour, thus obtaining an aluminum sheet coated with the mixture of Japanese lacquer and lacquer (FIG. 7) .

[Table l]

As a result, as seen in FIG. 7, it has been confirmed that the color of the sheet is darkened as the amount of Japanese lacquer is increased (A: 20 wt% of Japanese lacquer + 80 wt% of lacquer admixture, B: 30 wt% of Japanese lacquer + 70 wt% of lacquer admixture, and C: 50 wt% of Japanese lacquer + 50 wt% of lacquer admixture) . Test Example 1

Measurement of Hardness and Gloss

The thickness of the Japanese lacquer coating, hardness and gloss of the aluminum sheet of each of Examples 1 to 3 were measured. The hardness was evaluated using a pencil according to JIS D 0202.8.10, and the gloss was evaluated at an incident angle of

60^° using a glossmeter, available from BYK. The results are

shown in Table 2 below.

[Table 2]

As is apparent from Table 2, a sheet having high hardness and gloss can be produced even though the Japanese lacquer coating is thin. Moreover, when the amount of lacquer admixture is increased, the gloss is enhanced.

Test Example 2

Test of Specific Absorption Rate

A mobile phone case was manufactured by the present inventors using the aluminum sheet of Example 1. Such a mobile phone case and commercially available mobile phone cases of manufacturers A and B were measured with respect to a specific absorption rate for evaluating the absorption of electromagnetic waves under conditions given in Table 3 below by Hyundai Calibration & Certification Technologies Co. Ltd.

[Table 3]

[Table 4]

As is apparent from FIG. 4, the three mobile phone cases exhibit the specific absorption rate of 1.6 W/kg or less, satisfying the standard for exposure to electromagnetic waves. In particular, of these mobile phone cases, the mobile phone case manufactured using the aluminum sheet of Example 1 can be seen to have a superior specific absorption rate of 0.0961.

Test Example 3

Test of Far Infrared Emissivity

The emissivity of far infrared rays emitted from the aluminum sheet of Example 1 was measured by Korea Institute of Far Infrared Applied Estimation.

Specifically, the emissivity of the aluminum sheet was determined at 37 °C using an FT-IR spectrometer, compared to that of a black body. The results are given in Table 5 below

[Table 5]

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims .

[industrial Applicability]

As described hereinbefore, the present invention provides a method of coating a metal sheet with a Japanese lacquer mixture. According to the present invention, the metal sheet coating method adopts a printing process, and thus the metal sheet, variously printed, is coated with lacquer, such that the Japanese lacquered metal sheet having various colors and patterns can be produced on an industrial scale. Further, since the metal sheet produced using the method of the present invention is excellent with respect to the absorption of harmful electromagnetic waves, far infrared emissivity, and durability, it can be variously applied to mobile phones, notebook computers, automobile interior materials, construction materials, etc.

Claims

[CLAIMS]

[Claim l]

A method of coating a metal sheet with a Japanese lacquer

mixture, comprising: pretreating a surface of a metal sheet; subjecting the metal sheet to printing, including offset printing or silk screen printing; drying the printed metal sheet; coating the metal sheet with a mixture of filtered Japanese lacquer and varnish; and drying the coated metal sheet.

[Claim 2]

The method according to claim 1, wherein the mixture of the Japanese lacquer and the varnish comprises 95~98 wt% of Japanese lacquer and 2~5 wt% of varnish, based on total weight of the mixture .

[Claim 3]

The method according to claim 1 or 2, further comprising coating the coated and dried metal sheet using lacquer containing PMMA (polymethyl methacrylate) and MMA (methyl methacrylate) and then drying it.

[Claim 4]

The method according to claim 3, wherein the lacquer comprises the PMMA and the MMA admixed at 5-8: 5-2. [Claim 5]

A method of coating a metal sheet with a Japanese lacquer mixture, comprising: pretreating a surface of a metal sheet; subjecting the metal sheet to printing, including offset printing or silk screen printing; drying the printed metal sheet; coating the metal sheet with a mixture of filtered Japanese lacquer and lacquer; and drying the coated metal sheet.

[Claim β]

The method according to claim 5, wherein the mixture of the Japanese lacquer and the lacquer comprises 20-80 wt% of Japanese lacquer and 80-20 wt% of lacquer, based on total weight of the mixture.

[Claim 7]

The method according to claim 5 or β, the lacquer contains PMMA (polymethyl methacrylate) and MMA (methyl methacrylate) and the PMMA and the MMA admixed at 5-8:5-2.