Technical Field
The present invention relates, in general, to a paint composition having high far-infrared radioactivity, antibiotic activity and solvent resistance, and a precoated metal sheet coated with such a paint composition. More particularly, the present invention relates to a paint composition for use in home appliances, which has high gloss, processability and storage stability, as well as high far-infrared radioactivity, antibiotic activity and solvent resistance, and a precoated metal sheet coated with the paint composition.
Background Art
Generally, solar light reaches the earth while electric and magnetic fields fluctuate, like a wave, and has heat, and thus, is called 'thermal rays'. Light is classified into X-rays, ultraviolet rays, visible light, infrared rays, etc., depending on particles, waves and frequencies of vibration, and X-rays are permeable, ultraviolet rays and visible light are reflexible, and infrared rays are absorbable. Of infrared rays, far-infrared rays have a longer wavelength than visible
light and thus are regarded as a sort of electromagnetic wave having a frequency of 1.5-1000 (Jin. Far-infrared rays which are light energy having a slightly longer wavelength of 5-25 um among infrared rays have been used for various purposes from far-infrared sauna to home appliances construction materials general living goods etc. because they have been determined to be beneficial to human beings in recent years.
To manifest biofunctions far-infrajred emissivity should be not less than 0.9. Further antibiotic activity is assayed by measuring the rate of bacterial reduction using Escherichia coli and Psaudomonas aeruginosa. In particular in the case of a precoated metal sheet for use in home appliances it should have high processability and gloss.
As a conventional technique concerned with a painr composition having far-infrared radioactivity Korean Patent Application No. 1997-18446 discloses the use of a material emitting far-infrared rays by impregnating zeolite with Zn and Ag. However the material used is expensive thus negating economic benefits and also the far-infrared emissivity is as low as 0. 90.
On the other hand the paint for prrecoated metal sheets used for construction materials need be hardly processed; it has larger amounts of fillers. Of the fillers silica is added in a relatively large amount of 10-15 pajrts by weight which has been used to decrease the alkalinity of conventional far-infrared emitting powder. However in trie case of the paint

for precoated metal sheets used for home appliances silica undesirably acts to retard the processability.
As the far-infrared emitting material jade and elvan (Korean Patent Application Nos. 1988-0001616 and 1995-0026761)
are representatively known. In Japanese Patent Laid-open Publication No. 2002-53812 a paint including apati-e torumaline and charcoal to emit far-infrared rays and anions is disclosed. However since the materials mentioned above are expensive and have a large particle size they are unsuitable for use in precoated metal sheets.
Japanese Patent Laid-open Publication No. 2003-171604 discloses an antibacterial coating material comprising a silicone resin and antibacterial photocatalytic powder. However such a rHir.~ is unsuitable for precoated --Enal sneers for home appliances due ro its low processability.
Korean Patent Application No. 1998-709300 discloses an anti-fouling silicone emulsion coating composition. However it is difficult to use such a composition in the fields requiring processability. In addition since silicone functions as a matting agent the above composition is unsuitable for use in highly glossy products.
Japanese Patent Application No. 1999-319848 discloses a method of forming a photocatalytic layer which has excellent alkali resistance and water resistance using a silicone modified acryl resin. However the use of silicone modified acryl resin results in decreased processability and gloss and the above resin is undesirable as a resin component for use in

precoated metal sheets.
U.S. Patent No. 6376559 discloses a method of preparing a coating composition comprising a dispersing component having an inorganic silica sol dispersed in a solvent. However the
solution system used in the above invention is unsuitable for a coating process.
Korean Patent Application No. 1997-702389 discloses a thermos etting composition having high anti-fouling characteristics weather resistance and chemical .resistance
using a ceramic component a coating finish method and a coated article and Korean Patent Application No. 2001-43214 discloses a urethane based coating resin composition having h±gh glcss weather resistance hardness and flexibility and a curing coating composition including the same. In addition U. S. Patent No. 6022919 discloses a coating composition comprising a resin produced by copolymerising monomers containing methacrylate ester OH group COOH group styrene and acrylonitrile. However the coating compositions as mentioned above do not exhibit far-infrared radioactivity (emission) antibiotic activity solvent resistance gloss processability and storage stability to the extent of being suitable for use in precoated metal sheets for home appliances.
Disclosure of the Invention
Accordingly the present invention has been made keeping in mind the above problems occurring in the related a-rt and an

object of the present invention is to provide a paint composition having high antibiotic activity far-infrared radioactivity and solvent resistance.
Another object of the present invention is to prrovide a
paint composition having high gloss processability and storage stability as well as high antibiotic activity far-infrared radioactivity and solvent resistance.
A further object of the present invention is to provide a precoated metal sheet coated with the paint composition having high antibiotic activity far-infrared radioactivity and solver.t resistance.
Yet another object of the present invention is ro provice a precoated metal sheet coated with the paint compositirn naving high gloss processability and srorage stability as well as high antibiotic activity far-infrared radioactivity and solvent resistance.
In order to accomplish the above objects according to one aspect of the present invention a paint composition is provided which comprises a thermosetting resin 9-60 parts by weight of ceramic powder and 0.2-4.0 parts by weight cf phosphoric acid based on 100 parts by weight of the thermosetting resin.
According to another aspect of the present invention a precoated metal sheet coated with the paint composition is provided.

Best Mode for Carrying Out the Invention
Hereinafter a detailed description will be given of the present invention.
According to the present invention a paint composition comprising ceramic powder is provided thus exhibiting high far-infrared radioactivity and antibiosis. Further phosphoric acid is used instead of silica to control the alkalinity. Thereby the problem of low processability due to conventional use of silica is overcome and solvent resistance and storage stability are increased. Moreover a silane compound and a curing catalyst are used to improve glos?; of the coated film and further harden the coared film.
The ceramic powder used in the present invention includes at least one alkali oxide selected from the group consisting of CaCOs ZnOf and Al23 powder which has high far—infrared radioactivity. In addition the ceramic powder may further include Al-Zn powder.
However since the ceramic powder has high alkalinity solvent resistance and storage stability of the paint are lowered. Also high gloss and high processability required for use in home appliances cannot be exhibited. In particular due to low solvent resistance the coated surface is discolored and damaged when being exposed to the solvent (methylethvlketone: hereinafter abbreviated as XMEK'). Such phenomena do not occur upon preparation of a paint for use in construction

materials. The reason is that the paint for precoated metal sheets for use in construction materials is not processed much and hence includes large amounts of fillers. Of the fillers silica having an acidic group is added in an amount of 10-15 parts by weight based on 100 parts by weight of the resin and functions to neutralize the alkalinity of the ceramic component in the paint. However the paint composition which is used for home appliances instead of for construction materials as in the present invention does not include silica. If silica is used in the present invention processability may be deteriorated.
Therefore with the aim of solving the problems caused zy the cerairdc pcwder the paint ccirpositior. for pr=c:-=~ed ~etsL sheets of the present invention includes ceramic powder and phosphoric acid mixed at a predetermined ratio whereby the alkalinity attributed to the ceramic component is reduced and the stability and solvent resistance of the paint can be improved. Further a silane compound and a curing catalyst are additionally used to increase the gloss and hardness of the coated film. The paint composition of the present invention which is to be used for metal sheets for home appliances preferably has a thermosetting resin having a higher molecular weight than a thermosetting resin conventionally used for construction materials. Commonly the thermosetting resin for construction materials has a molecular weight of 3000 to 4000. In the case of using the thermosetting resin having a molecular

weight of 3000-4000 processability becomes insufficient. Hence in the present invention the thermosetting resin which has a molecular weight of 10000 or more and preferably 10000-20000 is used to manifest processability required for home appliances.
As the thermosetting resin any resin may be used so long as it ' is usable for a paint for precoated metal sheets and includes polyester resin silicone modified polyester resin or acryl resin but is not limited thereto. Preferably a polyester resin or an acryl resin is used. The above resin is inexpensive and has high corrosion resistance and solvent resistance and thus can be preferably used. The resin may be used alone or in combination with other kinds of resins. However since every resin has different curing and processing conditions it is preferable that one kind of resin be used alone.
The ceramic powder Includes at least one selected from the group consisting of CaCO3 ZnO and powder and may further include Al-Zn powder. The ceramic powder which exhibits far-infrared radioactivity and antibiotic activity is used in an amount of 9-60 parts by weight preferably 15-30 parts by weight and more preferably 9-30 parts by weight based on 100 parts by weight of the thermosetting resin. If the ceramic powder is used in an amount less than 9 parts by weight far-infrared radioactivity and antibiosis are decreased. Meanwhile if the ceramic powder is used in an

amount exceeding 60 parts by weight although far-infrared radioactivity and antibiosis are increased processability and gloss are lowered and also solvent resistance is undesirably reduced.
Upon preparation of the paint two or three kinds of ceramic powder may be used. Based on 100 parts by weight of the thermosetting resin 3-20 parts by weight of CaCOs 3-20 parts by weight of ZnO and 3-20 parts by weight of AloOs preferably 5-10 parts by weight of CaCO3 5-10 parts by weight of ZnO and 5-10 parts by weight of Al2Os and more preferably 3-10 parts by weight of 3-10 parts by weight of ZnO and 3-10 parts by weight of AlaOa are used.
Further the Al— ceramic powder is additionallv used in an amount of 3-20 parrs by weigrn based on 100 parrs oy weight of the thermosetting resin. In the case where the Al-Zn ceramic powder is additionally included the Al-Zn ceramic powder and at least one ceramic powder selected from the group consisting of CaCC>3 ZnO and Al2Oa powder are mixed within their use ranges respectively so that their amounts total 9-60 parts by weight preferably 15-30 parts by weight and more preferably 9-30 parts by weight based on 100 parts by weight of the thermosetting resin.
The ceramic powder has a particle size of 1-20 fun and preferably 1-15 jim. Since the coated film is formed in a thickness of 5-25 f.im if the particle size is larger than the above thickness the ceramic powder protruding from the coated

film may negatively affect corrosion resistance and outer appearance.
In addition to decrease the alkalinity increased by using the .ceramic powder and increase the solvent resistance
phosphoric acid is mixed along with the "hermosetting resin and the ceramic powder. The use of phosphoric acid results in decreased alkalinity and increased solvent resistance. As well storage stability is improved.
Phosphoric acid is used in an amount of 0.2-4.0 parts by weight and preferably 0.5-2.0 parts by weight based on 100 parts by weight of the thermosetting resin. In the case where the ceramic powder is used in a small amount for example an amount less than 9 p=rts by weight based on 100 paris by weight of the thermosetting resin rne alkalinity can be sufficiently inhibited even though phosphoric acid is used in an amount less than 0.2 parts by weight. However in the case where an excessive amount of ceramic powder is used to increase the far-infrared radioactivity the above amount of phosphoric acid is insufficient to decrease the alkalinity of the ceramic powder. On the other hand if phosphoric acid exceeds 4.0 parts by weight acidity is too strong and thus the paint may be agglomerated resulting in lowered storage stability.
In addition the paint composition of the present invention further includes 0.01-1.0 parts by weight of the silane compound based on 100 parts by weight of the thermosetting resin if required. The silane compound

functions to harden the coated film and increase the gloss of the film. If the silane compound is used in an amount less than 0.01 parts by weight desirable properties caused by the addition of the silane compound are hardly manifested. Conversely if the amount of the silane compound exceeds 1.0 part by weight unreacted silane compound remains in the paint. After such a paint composition is applied on the metal sheet the resultant film has poor properties and the resin agglomerates thus reducing the sicrage stability.
The silane compound includes at least one selected from the group consisting of mercapte-propyl-trimethoxysilane 3-aminopropyltriethoxy silane 3-trimethcxysilylprcpyl methacrviate and 3-aminopropyltrimethoxy silane but is not limited rhere~o.
In addition the paint composition of the present invention further includes the curing catalyst so as to increase the gloss of the coated film and further harden the film if required. The curing catalyst functions to shorten the curing time of the film prolonged due to the addition of large amounts of ceramic powder and pigment. Thereby the coated film has high gloss and becomes harder.
The curing catalyst is used in an amount of 2-6 parts by weight based on 100 parts by weight of the thermosetting resin. If the curing catalyst is used in an amount less than 2 parts- by weight the curing time is hardly shortened. Meanwhile if the curing catalyst is used in an amount

exceeding 6 parts by weight the coated film is cured too fast that is the film is cured before it obtains a desired smoothness thus negating economic benefits. The curing catalyst includes dodecylbenzenesulfonic acid but is not limited thereto.
Moreover an additive such as a dispersing agent a leveling agent or a thickening agent which is generally added to a paint composition for precoated metal sheets is additionally used so that the total amount of each additive to be used satisfies 1.0-7.0 parts by weight based on 100 parts by weight of the thermosettin'g resin if required. The ~otal amount of the additive is not limited to an amount generally used in the art and may be appropriately used depending en the desired properties.
Moreover a coloring pigment which is generally added to a paint composition for precoated metal sheets is additionally used so as to exhibit hiding power of the coated filir. if required. The coloring pigment is used in an amount of 10-8C parts by weight based on 100 parts by weight of the thermosetting resin. If the above amount is less than 10 parts by weight the metal sheet has no hiding power. On the other hand the coloring pigment exceeding 80 parts by weight negatively affects processabilty and gloss.
The kinds and amounts of the additive such as dispersing agent leveling agent or thickening agent and the coloring pigment are generally known in the art and thus may be

appropriately selected by those skilled in the art when preparing the paint. The .kinds and amounts of the additive and the pigment are not particularly limited.
To control the viscosity of the paint composition to be
prepared thinner that is a solvent is used in an appropriate amount in which its amount is appropriately controlled in accordance with techniques generally used in the art. For example the viscosity is controlled so that the time required to discharge the paint composition from a ford cup §4 is 100-120 sec but is not limited thereto.
The paint composition of the present invention is prepared by uniformly dispersing the ceramic powder in the thermosetting resin at 1000-5000 rpm using a high speed distributer and then adding phosphoric acid serving tr ensure solvent resistance while decreasing the alkalinity ~o the thermosetting resin having ceramic powder dispersed therein. Subsequently the silane compound the curing catalyst and the additive are used to prepare the paint composition which is formed into a hard film having high gloss if required.
According to the present invention a precoatec metal sheet coated with such a paint composition is provided which exhibits high far-infrared radioactivity antibiotic activity solvent resistance gloss processability and storage stability.
As such the above coating method is not particularly limited in the present invention and the coated film is

manufactured by a top coating of applying the paint composition of the present invention to a dry film thickness of 5-25 j.tm preferably 15-20 jiin and more preferably 15 f.un on an iron steel material more specifically a zinc coated steel sheet that is typically pretreated and under coated and then drying it at 200-250°C. The paint composition of the present invention may be applied for example on steel sheets for home appliances.
If the coated film has a dry film thickness less than 5 pjn weather resistance and hiding power are decreased due to the very thin film. Meanwhile if the thickness exceeds 25 um the processability of the precoated metal sheet is somewhat decreased and preparation costs may increase. The dry film thickness is not limited thereto.
Also when the coated film is dried at a temperature
lower than 200°C the film does not dry and cross-link thus it is difficult to obtain desired properties of the film. On the other hand if the film is dried at a temperature exceeding 250°C the paint composition may be undesirably pyrolyzed.
The precoated metal sheet coated with the paint composition of the present invention can be employed in fields which require bio-effects having storage and maturation effects on food growth promotion effects on plants activation effects on water or the like for example the maintenance of food's freshness promotion of blood circulation etc.
A better understanding of the present invention may be

obtained through the following inventive examples and comparative examples which are set forth to illustrate but are not to be construed as the limit of the present invention.
Example
Each component constituting a paint composition shown in Table 1 below was mixed in an amount shown in Table 1 below to prepare paint compositions of Comparative Examples 2-10 and Inventive Examples 1-11. In Comparative Examples and Inventive Examples when preparing each paint composition ceramic powder was used in an amount shown in Table 1 below based on ICO carts by weight of z polyester resir. ar.d sufficiently stirred at 1000-5000 rpm so that tne ceramic powder was uniforrrily dispersed in the resin. Subsequently in cases of requiring the addition of phosphoric acid additives a silane compound and a curing catalyst they were added to the paint composition and sufficiently stirred at 1000-5000 rpm.
In Comparative Examples 2 and 3 a polyester resin having a molecular weight of about 3000 was used. In Comparative Example 4 and Inventive Examples 1 to 6 a polyester resin having a molecular weight of about 12000 was used. Also in Comparative Examples 5 to 10 and Inventive Examples 7 to 11 a polyester resin having a molecular weight of about 15000 was
used. The ceramic powder having a particle size of 15 Jim was used.

Further mercapto-propyl-trimethoxy silane and dodecylbenzenesulfonic acid were used as the silane compound and the curing catalyst respectively.
In Comparative Examples and Inventive Examples as the additives 1.5 parts by weight of a defoaming agent 0.4 parts by weight of a dispersing agent 0.3 parts by weight of a leveling agent and 80 parts by weight of titanium dioxide as a coloring pigment were used based on 100 parts by weight of the resin. Additionally thinner was used as a solvent to obtain the viscosity requiring about 100-120 sec when the paint composition was discharged from a ford cup #4. The used components were mixed while being stirred at a high speed of 1000-5000 rpm. The defoaming agenz the -dispersing agent and the leveling agent were purchased from BYK-CHEMIE GmbH Germany. BYK 051 and BYK 171 were used as the defoaming agent and the dispersing agent respectively and BYK 357 was used as the leveling agent.
A metal sheet having a size of 20x10 cm was coated with each of the paint compositions of Comparative Examples 2-10 and Inventive Examples 1-11. As such before coating the metal sheet had been pretreated with chromate at a thickness of about 1 urn and then under coated with epoxy anticorrosive paint at a thickness of about 5 Each of the paint compositions of Comparative Examples 2-10 and Inventive Examples 1-11 was applied to a dry film thickness of 15 pm. The coating method

was conducted using a bar coating process. The paint was dried at 232°C as an actual preparation temperature for 24 sec to manufacture a test sample. In Comparative Example 1 there was used a metal sheet for home appliances available from POCOS Co. Ltd. Kcrea which had been treated with chro~3te at a thickness of about 1 jam under coaled with epoxy at = thickness of about 5 join and then top coated with polyester at a thickness of about
Each test sample was measured for processability solvent resistance gloss storability antibiotic activity and far-infrared emissivity in accordance with the following procedures. The results are shown in Table 1 below.
1Processability was assayed in sucr. a way tha~ the test sample was bent at 180° to have 3t curved surfaces and thus whether cracks were generated at bended surfaces was confirmed. As the results the case where cracks were generated was determined to be ^poor' while the case where no cracks were generated was determined to be good' .
2 ) Solvent resistance was assayed in such a way that when the coated metal sheet was rubbed with a gauze dipped into MSK under a load of 1 kg the number of rubs was counted until the top coated surface was peeled off and thus the under coated surface was seen. As such a reciprocating rub was taken as one rub .

3) Gloss was assayed in such a way that surface gloss was
measured using a 60° glossmeter.
4) Storage stability was assayed in such a way that 30
days after the paint composition was prepared the state cf ~he
paint was observed with the naked eye. As the results ihe
case where the precipitate was not gelled was determined ~o be
Ngood' while the case where it was gelled was determined ~o be
poor'.
5) Antibiotic activity was assayed in such a way that
antibiotic activity of the metal sheet was tested in accordance
with a pressurization close adhesion method (KICM-EIK-1GC2• of
Korea Institute of Construction Materials. For ~est
Escherichia coli and Psaudomonas asruginosa were inoculated to
a standard test sample and a metal sheet test sample coated
with the paint composition including antibiotic radioactive
powder and then the inoculated samples were covered with
other non-inoculated metal sheet samples and cultured at 3"7°C
for 24 hours. The bacterial death rate was measured as a rate
of bacterial reduction.
6) Far-infrared emissivity was assayed in such a way that far-infrared emissivity of the precoated metal sheet was measured at a wavelength of 5-20 pm in accordance with a KS standard test method (KS L 2514 6.4) as test provision of far-

As is apparent from Table I a .conventional precosteci metal sheet of Comparative Example 1 exhibits low antibiosis having a rate of bacterial reduction less than 10% and has lew far-infrared emissivity of 0.86. In Comparative Examples 2 and 3 using the polyester resin having a molecular weight of 3000-4000 although an excessive amount of the ceramic powder is used silica is also used thus manifesting good solvent resistance and storability. However processability and high gloss required for home appliances are poor and thus conventional metal sheets cannot be used for home appliances.
In Comparative Examples 4-6 without the use of phosphoric acid CaCQ3 ZnO and AlaOa are used in larger amounts based on the polyester resin and thus far-infrared emissivity increases but solvent resistance decreases.
In Comparative Examples 7 to 10 properties unsuitable for use in home appliances are shown due to the use of larger amounts of ceramic powder in spite of using phosphoric acid.
In Inventive Examples having the -eramic pov.'der phosphoric acid silane and curing catalyst mixed at appropriate ratios processability solvent resistance gloss storability and far-infrared emissivity are exhibited ~o be high and as well higher antibiotic activity of 50-99.9% is manifested compared to conventional precoated metal sheets.
Industrial Applicability
As described above the present inver.tic-r. prcvices a paint composition including ceramic powder and phosphoric acid and a precoated metal sheet coated with the paint composition in which far-infrared radioactivity and antibiotic activity are excellent and as well the alkalinity of the ceramic powder is neutralized by phosphoric acid to increase the storage stability and solvent resistance. Further the silane compound and the curing catalyst are additionally used whereby gloss and processability are improved.
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 .

18. A precoated metal sheet coated with the paint composition as claimed in any one of claims 1 to 11, 12, 14 or-15 wherein the said paint composition is applied to the pre-coated metal sheet into a dry film thickness of 5-25 p m or wherein such precoated metal sheet coated with paint composition is used for home appliances.
19. A paint composition substantially as herein described with reference to the foregoing description, examples and the accompanying tables.