Background Art Generally, paint compositions have been used for coating surfaces of solid articles to form solid films and thus protect the surfaces of the articles by means of the solid films.

It is preferred that paint compositions be rapidly dried and cured, although they are in a gel-like flowable state before application to surfaces of articles. In addition to such conventional use of paint compositions for preventing corrosion of surfaces, they are also used for decoration purposes. Therefore, paint compositions are now widely used for a variety of articles made of various kinds of synthetic resins, metal and glass.

As one of the resource materials that make our life more convenient, many kinds of synthetic resins have been developed with the development of petrochemical industry.

Due to their unique and advantageous properties, such as relative low-weight, inexpensiveness and easy processability, as compared with glass or metal materials, synthetic resins are applied in a wide range of products which are used and frequently encountered in our daily life, such as electric home appliances, automotive parts, electronic parts, building materials, aircraft parts and cosmetic cases. Such synthetic resin products are coated with various kinds of paints for the purpose of surface protection and decoration.

Metal products, as another resource material useful in our daily life, are coated with paints for the purpose of anti-corrosion or electrical insulation. Glassware is another article which needs paint coatings to give colors or decorate its surface.

However, synthetic resin and metal products have some limitations on selection of paints with which they are coated due to their material or surface properties. UV curable paints are known to be most suitable for coating metal or plastic materials since they have

incomparably high productivity and green advantages in that they discharge extremely a small amount of VOC (Volatile Organic Compound) into the atmosphere.

As prior arts for UV curable paint compositions, UV curable paint compositions containing UV curable oligomers are disclosed in Korean Patent Nos. 103647 and 89390; U. S. Patent Nos. 3,782, 961,3, 829,531, 3,874, 905,3, 891,523, 3,895, 171,3, 899,611, 3,912, 516,3, 932,356, 4,301, 209 and 139,886. All of these paint compositions according to the prior arts have been proposed as being used for molded articles made of various synthetic resins.

In view of the processability, molded articles made of synthetic resins such as acrylonitrile-butadiene-styrene copolymer (ABS), polycarbonate (PC), polybutylene terephthalate (PBT), carbon fiber, unsaturated polyester (FRP), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) can be suitably coated with UV curable paint compositions.

However, conventional paint compositions containing UV curable oligomers cannot be recoated and cannot impart divers colors to the coatings made thereof, while they can impart hardness, durability, chemical resistance, and abrasion resistance to synthetic resinous molded articles coated therewith. Further, conventional UV curable paint compositions show limitations on the crosslinking degree of the film, and consequently, unsatisfactory curing properties such as chemical resistance, which is caused by weak adhesiveness to the metal materials to which the composition is applied. This low adhesiveness of the conventional UV curable paint compositions is also true for glass materials, resulting in failure in forming a firm paint film on the surface of glass.

Particularly, if pigments are contained in conventional UV curable paint compositions, they hinder transmission of UV light to produce wrinkles in a final paint film. For this reason, pigments have been only limitedly contained in conventional UV curable paint compositions. Therefore, various colors could not have been imparted in conventional UV curable paint compositions, which conclusively give a limitation to the essential properties of paints.

Detailed Description of the Invention Object of the Invention As discussed above, conventional UV curable paint compositions have failed to give good UV curability, adhesiveness and chemical resistance when applied to synthetic resinous molded articles and metal products. Particularly, when pigments are blended therein, the compositions will experience partial absorbance of UV light, and thereby poor curing and coating, which leads to failure in imparting various colors in practical use.

The failure of conventional paint compositions in imparting various colors to the coatings can be considered as being critically disadvantageous in that aesthetic sense and diverse designs are now greatly needed for synthetic resinous products or articles.

Additionally, conventional UV curable paint compositions have another disadvantage associated with waste of resources in that they can hardly recoat, and consequently, reproduce the coated articles with an acceptable percent defective.

Therefore, an object of the present invention is to improve a conventional UV curable paint composition, which aims at enhancing a drying property of a paint film when applied to plastics, metals, glass and the like, and enhancing UV curability even when various color pigments are blended in the composition.

Another object of the present invention is to provide a UV curable paint film composition having improved curing properties such as recoatability and chemical resistance, when applied to articles made of plastics, metals, glass and the like.

Preferred Embodiments for Carrying out the Invention The present invention relates to a UV curable paint composition, and provides a UV curable paint composition that has various applicable colors and superior UV curability and recoatability.

The UV curable paint composition of the present invention for achieving the above objects comprises 30 to 95 parts by weight of conventional UV curable composition with UV curable oligomer, UV curable monomer, photoinitiator and photosensitizer ; and 5 to 70 parts by weight of one or two or more cellulose-modified resins selected from a group

consisting of cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose propionate, cellulose-modified urethane acrylate, and nitrocellulose. The UV curable paint composition of the present invention may comprise up to 20 parts by weight of pigment or other additives in the same manner as a conventional UV curable paint composition.

The paint composition of the present invention comprises 30 to 95 parts by weight of a conventional UV curable paint composition and 5 to 70 parts by weight of cellulose- modified resins. Any conventional UV curable oligomers, UV curable monomers, photoinitiators or photosensitizers can be used in the UV curable paint composition of the present invention. Since the present invention is to improve the drying property and recoatability of a conventional UV curable paint composition, the UV curable composition of the present invention comprises these conventional components.

The UV curable oligomer used in the present invention may be selected from a group consisting of urethane acrylate oligomers, epoxy acrylate oligomers, polyester acrylate oligomers and combinations thereof. If two oligomers are selected, they are mixed in a ratio of 3: 1 to 1: 3.

The UV curable monomer used in the present invention may be selected from a group consisting of multi-functional monomers such as dipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylol propane triacrylate, ethoxylated trimethylol propane triacrylate, ethoxylated trimethylol propane methacrylate, propoxylated trimethylol propane triacrylate and propoxylated trimethylol propane trimethacrylate ; mono-functional monomers such as 2-ethylhexyl acrylate, octyldecyl acrylate, stearyl acrylate, behenyl acrylate, tridecyl methacrylate, nonylphenolethoxylate monoacrylate, 0-carboxyethyl acrylate, isobonyl acrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, 4-butylcyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, ethoxyethoxyethyl acrylate and ethoxylated monoacrylate; bi-functional monomers such as 1, 6-hexanediol diacrylate, triphenylglycol diacrylate, butanediol diacrylate, 1,3-butyleneglycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentylglycol diacrylate, ethyleneglycol dimethacrylate, diethyleneglycol diacrylate, diethyleneglycol dimethacrylate, tetraethyleneglycol diacrylate,

tetraethyleneglycol dimethacrylate, triethyleneglycol diacrylate, triethyleneglycol dimethacrylate, polyethyleneglycol diacrylate, polyethyleneglycol dimethacrylate, dipropyleneglycol diacrylate and ethoxylated. neopentylglycol diacrylate ; and combinations thereof.

A conventional polymerization initiator that is activated by UV light can be used as the photoinitiator. Particularly, the photoinitiator used in the present invention may be selected from a group consisting of 2-hydroxy such as benzophenone, benzyl dimethylketal, acetophenone, anthraquinone, thioxanthone, acyl phosphine oxide, amino alkylphenone, hydroxy allcylphenone, dialkoxy acetophenone and benzyl ketal type; ketones such as 1,2-diphenyl ethanone, 2-ethoxy-1, 2-diphenyl ethanone, di-isopropyl-1, 2-phenyl ethanone, 2-butoxy-1, 2-diphenyl ethanone, 2-isobutoxy-1,2-diphenyl ethanone, 2, 2-dimethoxy-1, 2- diphenylethanone, 2, 2-dibutoxy-1-phenyl ethanone, 1-hydroxy cyclohexyl phenyl ketone, dimethoxy hydroxy acetophenone, 1- (4-isopropylphenyl)-2-hydroxy-2-methyl propanone, 2-methyl-l- [4- (methylthio) phenyl]-2-morpholino propanone and 2-benzyl-2- dimethylamino-1- (4-morpholinophenyl)-butanone ; 3, 6-bis-2-methyl- ?--morpholino (propanoyl) -butylcarbazole and bis (2,4, 6-trimethyl benzoyl) -phenylphosphine oxide; and combinations thereof.

When a pigment is used, the photoinitiator used in the present invention is preferably a photoinitiator that is more responsive at a long wavelength band than a short wavelength band. The term"short wavelength"used herein means a relatively short wavelength within UV band, for example ranging from about 200 to 300 nm, while the term"long wavelength"means a relatively long wavelength within UV band, for example, ranging from about 400 to 500 nm.

The paint composition according to the present invention may contain a photosensitizer in order to increase the curing rate. A photosensitizer will efficiently increase the activity of UV-activated polymerization initiator to enhance UV-activated curing of the paint composition. The photosensitizer used in the present invention may be selected from a group consisting of methyldiethanolamine, triethanolamine, ethyl-4- (dimethylamino) benzoate, 2-normal-butoxyethyl-4- (dimethylamino) benzoate, isoacryl-4- (dimethylamino) benzoate, 2- (dimethylamino) ethylbenzoate, 1- (4-dimethylaminophenyl)-

ethanone and additionally unsaturated copolymerized tertiary amine oligomer, copolymerized amine acrylate oligomer ; and combinations thereof.

The paint composition according to the present invention may contain a leveling agent as an additive. Silicone or acrylic compounds may be used as a leveling agent.

The paint composition according to the present invention may also contain a flatting agent if necessary, in a case where half-glossy or non-glossy products are required.

The paint composition according to the present invention comprises 5 to 70 parts by weight of a cellulose-modified resin based on the total amount of the composition.

The cellulose-modified resin used in the present invention comprises one or more compounds selected from a group consisting of cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose propionate, cellulose-modified urethane acrylate and nitrocellulose resin.

The cellulose-modified urethane acrylate resin used in the present invention can be synthesized by the reaction of isocyanate materials as follows. The isocyanate materials to be used may include isocyanate isophorone diisocyanate (3-isocyanatomethyl-3, 5, 5- trimethyl cyclohexyl isocyanate), 4,4-dicyclohexyl methane-diisocyanate, trimethyl- hexamethylene-diisocyanate, 1, 6-hexamethylene diisocyanate, 2,2, 4-trimethyl-1, 6- hexamethylene diisocyanate, octadecylene diisocyanate, 1, 4-cyclohexylene diisocyanate, 2,4-toluene diisocyanate, 2, 6-toluene diisocyanate and oligomers thereof. In particular, the isocyanate oligomers can be selected from a group consisting of a Biuret form of the diisocyanates, an isocyanurate form of tri-functional triisocyanates or composite forms thereof.

In the present invention, the cellulose-modified resin is used for remarkably enhancing a drying property, UV curability and chemical resistance of the film, as compared with conventional dry resins. It is also used for preventing static electricity and improving the drying rate of the film. Thus, when the paint composition of the present invention is used, the percent defective due to dust adhesion during the coating process will greatly reduce. When the paint composition of the present invention is used for coating, there is an advantage in that a percent defective caused by dust adhesion in the coating process for paint film formation can be greatly reduced. This means that a newly

developed product according to the present invention has a greatly reduced percent defective by means of the cellulose-modified resin, as compared with the fact that the conventional UV curable paint has a high percent defective due to a large amount of adhering dust caused by static electricity, thereby resulting in many defective products in a practical coating process.

If the cellulose-modified resin is used in an amount of less than 5 parts by weight, the paint composition of the present invention will not exhibit as sufficient performance as mentioned above. If the cellulose-modified resin is used in an amount of more than 70 parts by weight, the workability of the composition will undesirably decrease. Therefore, the cellulose-modified resin is preferably used in a range of about 7 to 50 parts by weight, more preferably, about 10 to 30 parts by weight.

In consideration of the curing property of a final product, the cellulose-modified resin preferably has a molecular weight of 10,000 to 70,000. When the cellulose- modified resin has a molecular weight of less than 10,000, the UV curability and drying property become inferior. When the molecular weight is higher than 70, 000, it shows poor recoatability and workability.

The UV curable paint composition of the present invention may additionally comprise 0.1 to 20 parts by weight of a pigment, based on the total amount of the composition, to produce a colored paint composition. The composition will not be suitable for a colored paint at a pigment concentration of less than 0.1 parts by weight, while the physical property of the paint is deteriorated at a pigment concentration of more than 20 parts by weight. The pigment used in the present invention can be selected from metallic pigments such as aluminum paste, mica, inorganic pigments, organic pigments, extender pigments, anti-corrosive pigments and the like, all of which is used in conventional paints and can be used alone or in combination. Particularly, when metallic colors are desired, an organic-coated aluminum paste is suitable and desirable since it improves various physical properties, such as adhesiveness, acid resistance, alkali resistance and weather resistance. Additionally, the colored UV curable paint having such a pigment can provide an excellent metallic or mica color and appearance with ideal arrangement of the particles in the film.

The present invention can advantageously improve the recoatability and curing property of transparent paint films, as well as the UV curability, workability and curing properties of colored UV curable paints, by appropriately combining a conventional UV curable oligomer and monomer-containing paint compositions with a cellulose-modified resin.

The UV curable paint composition of the present invention can be prepared by a general method for preparing a paint composition, i. e. by weighing and mixing 30 to 95 parts by weight of conventional UV curable paint composition comprising a UV curable oligomer, a UV curable monomer, a photoinitiator and a photosensitizer, and 5 to 70 parts by weight of cellulose-modified resin; adding a pigment, other additives and a solvent thereto, if necessary; and then stirring and milling the mixture.

The UV curable paint composition of the present invention can be subjected to a coating process by a conventional method. That is, the UV curable paint composition may be sprayed onto the surfaces of plastic molded articles, metal products or glass articles, or otherwise coated by dipping or roll coating process, depending on the material and shape of the products to be coated, and film thickness as required.

The UV curable paint composition of the present invention may also contain an appropriate amount of volatile solvent to obtain suitable viscosity that is differently required by a coating method selected. A solvent is used to facilitate the coating process and to provide a smoother appearance. Solvents suitable for this purpose include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, esters, ethers and alcohols, and non-toxic organic solvents such as odorless mineral spirit coping with VOC regulations and may be used alone or in combinations. Varnish and solvent may also be used in a weight ratio of 5: 1 to 1: 5 in the UV curable paint composition according to the present invention. Other additives such as defoaming agent may also be employed for any known properties.

Advantages of the Invention As described above, the UV curable paint composition of the present invention provides an excellent recoatability, UV curability especially in colored paints, adhesiveness,

weather resistance, chemical resistance, abrasion resistance and hardness. The UV curable paint composition of the present invention shows better productivity, chemical resistance, hardness and abrasion resistance than two-liquid urethane paints, epoxy paints and thermally drying paints.

Further, the UV curable paint composition of the present invention still has the same degree of UV curability even when the composition contains a pigment. Thus, the UV curable paint composition of the present invention can express various colors, which overcomes the disadvantage of the conventional paint compositions having a limitation in providing a colored film.

EXAMPLES The present invention will now be described in more detail by way of preferred examples. However, it should be understood that the following examples are provided to better explain the scope and spirit of the present invention and thus not intended to limit the present invention thereto.

Preparation Example 1: Preparation of cellulose-modified resin To a 4-neck round flask equipped with a condenser, a stirrer and a thermometer were charged 1 equivalent of isophorone diisocyanate (IPDI, Olin, USA), a catalyst, a polymerization inhibitor and 200mL of toluene. Temperature was elevated to 40 PC with N2 purging. 0.4 equivalent weight of cellulose acetate butyrate (CAB553-1, Eastmann, USA) was placed in a dropping tube and a catalyst was added. They were added dropwise for 1 hour and reacted for 6 hours while maintaining the temperature at 45°C.

The primary reaction was ended with the determination of % NCO by wet analysis. 0.7 equivalent weight of hydroxy ethyl acetate (2-HEA, Nippon Shokubai K. K. , Japan) was subsequently added dropwise for 1 hour. The reaction was maintained at a temperature of 60 PC and terminated when % NCO had reached to 0 as determined by wet analysis to give cellulose-modified urethane acrylate resin as required.

Example 1 300 parts of cellulose-modified urethane acrylate resin prepared in Preparation Example 1,200 parts of urethane acrylate resin (EB284, SK UCB Co. , Ltd. , Korea), 200<BR> parts of pentaerythritol tetraacrylate (PETA, Miwon Commercial Co. , Ltd. , Korea), 150<BR> parts of 1,6 hexanediol diacrylate (HDDA, Miwon Commercial Co., Ltd. , Korea), 30 parts of photoinitiator (D1173, Ciba-Geigy), 25 parts of photoinitiator (Micure BP, Miwon Commercial Co. , Ltd. Korea), 80 parts of photosensitizer (EBECRYL P 115, SK UCB<BR> Co. , Ltd. , Korea) and 15 parts of leveling agent (BYK306, BYK-Chemie) were mixed and stirred to prepare a UV curable paint composition with a viscosity of 300 cps at 25 C.

The UV curable paint composition thus obtained was tested according to the following conditions for the comparison of physical properties (see Table 1 for the test results).

Example 2 300 parts of cellulose acetate butyrate resin (Eastmann, USA), 200 parts of urethane acrylate resin (SK UCB Co. , Ltd. , Korea), 100 parts of dipentaerythritol hexaacrylate (EM263, Eternal, Taiwan), 250 parts of trimethylol propane triacrylate (Miramer M300, Miwon Commercial Co. , Ltd. , Korea), 50 parts of photoinitiator (Irl84, Ciba-Geigy), 5 parts of photoinitiator, acryl phosphine-type (DAROCURE TPO, Ciba- Geigy), 10 parts of leveling agent (BYK306, BYK-Chemie) and 85 parts of pigment (Blue) were mixed and stirred to prepare a UV curable paint composition with a viscosity of 300 cps at 25°C.

The UV curable paint composition thus obtained was tested according to the following conditions for the comparison of physical properties (see Table 1 for the test results).

Example 3 300 parts of cellulose acetate propionate resin (Eastmann, USA), 200 parts of epoxy acrylate resin (Eternal, Taiwan), 100 parts of pentaerythritol tetraacrylate (PETA,

Miwon Commercial Co. , Ltd. , Korea), 300 parts of hexanediol diacrylate (Miramer M200,<BR> Miwon Commercial Co. , Ltd. , Korea), 20 parts of photoinitiator (ESACURE TZT,<BR> Lamberti, Italy), 25 parts of photoinitiator (Micure BK-6, Miwon Commercial Co. , Ltd., Korea), 50 parts of photosensitizer (ETERCURE 6420, Eternal, Taiwan) and 5 parts of leveling agent (BYK306, BYK-Chemie) were mixed and stirred to prepare a UV curable paint composition with viscosity of 330 cps at 25 °C.

The UV curable paint composition thus obtained was tested according to the following conditions for the comparison of physical properties (see Table 1 for the test results).

Comparative Example 1 500 parts of urethane acrylate resin, 350 parts of 1,6 hexanediol diacrylate (HDDA, Miwon Commercial Co. , Ltd., Korea), 55 parts of photoinitiator (D1173, Ciba-Geigy), 85<BR> parts of photosensitizer (EBECRYL P115, SK UCB Co. , Ltd. , Korea) and 10 parts of leveling agent (EBECRYL350, SK UCB Co., Ltd., Korea) were mixed and stirred to prepare a UV curable paint composition with viscosity of 300 cps at 25 °C.

The UV curable paint composition thus obtained was tested according to the following conditions for the comparison of physical properties (see Table 1 for the test results).

Comparative Example 2 450 parts of urethane acrylate resin, 50 parts of acrylic resin (NEOCRYL B728), 350 parts of 1,6 hexanediol diacrylate (HDDA, Miwon Commercial Co. , Ltd. , Korea), 50 parts of photoinitiator (D1173, Ciba-Geigy), 50 parts of photosensitizer (EBECRYL PI 15, SK UCB Co. , Ltd. , Korea), 10 parts of leveling agent (EBECRYL350, SK UCB Co. , Ltd., Korea) and 40 parts of pigment were mixed and stirred to prepare a UV curable paint composition with viscosity of 300 cps at 25 °C.

The UV curable paint composition thus obtained was tested according to the following conditions for the comparison of physical properties (see Table 1 for the test results).

Comparative test on physical properties of UV curable paint compositions The paint compositions prepared in Examples 1 through 3 and Comparative Examples 1 through 3 were used to compare the physical properties of the UV curable paint composition of the present invention and conventional UV curable paint composition.

The comparative test was conducted on a polycarbonate (PC) molded article.

The compositions were diluted 50% by weight with a solvent mixture of methylethylketone (MEK) and xylene (1: 1 w/w), and applied with a spray applicator onto the in thickness of 101lu. The applied composition was freed of the solvent to dryness for 2 min at 50 PC and cured at the curing energy of 800mJ/cm'using a UV curing apparatus (UV Irradiation Apparatus: American Ultraviolet, USA). The physical properties of the cured compositions were compared as follows: Results are shown in Table 1 below.

Table 1 Comparison of physical properties of Examples and Comparative Examples Com. Com. Physical property Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 W-Curillgl @ @ 0 @ X Recoatability*2) g) Q 0 X X Adhesiveness*2) 100/100 100/100 100/100 100/100 20/100 Weather resistance*3) 0 0 0 A A Alcohol A A O X A Chemical resistance*4) resistance Brine ouzo resistance*5) Abrasion resistance (mg) *6) 3 7 5 9 15 Hardness*7) 2H H H H F X Note (> : excellent, O : good, A : slightly poor, X: poor

X Test conditions *1) : The cured film was observed if it is tack-free or not using the Curability Measuring Lux Meter (IL390B), after passing through the UV curing apparatus.

*2): Determined according to JIS D0202 (Cross-Cut, Tape Test) *3): Observed for discoloration (yellowing) after exposure to sunlight for 7 days.

*4): Observed for the state of the film after 24h-dipping in 50% aqueous ethanol solution at the room temperature.

*5): Observed for the state of the film after 24h-dipping in 5% aqueous sodium chloride solution at the room temperature.

*6): Determined using the Dual Abraser (Model 505, Teledyne Taber, USA), at CS- 10, 1000g Load, 1000 times *7): Pencil hardness by Uni-Pencil (Mitsubishi) As can be seen from Table 1, the UV curable paint composition of the present invention shows an excellent recoatability, UV curability, adhesiveness, weather resistance, chemical resistance, abrasion resistance and hardness both in the absence and presence (Ex.

2) of a pigment, as compared to the conventional UV curable paint composition.

Industrial Applicability As described above, the UV curable paint composition of the present invention can be advantageously employed in coating plastic molded articles, metal and glass products.

Further, the UV curable paint composition of the present invention has a good recoatability and overcomes the problem of the conventional paint compositions in association with recoating the composition.

Therefore, the UV curable paint composition of the present invention can be suitably used for plastic electric home appliances/communication products, metal surface of automotive parts and the like, and color coated glass products, requiring various colors, and particularly for double coating with a still-good coating performance.

Although the UV curable paint composition of the present invention has been

specifically explained with reference to the preferred embodiments, the present invention is to be defined and limited only by the appended claims, not by the preferred embodiments.

Therefore, those skilled in the art will appreciate that various changes and modifications can be made without departing from the scope and spirit of the present invention, and all such changes and modifications fall within the scope of the invention defined by the appended claims.