BACKGROUND A coating process is usually applied to the surface of a car in order to protect the surface and to provide a desired color and a fine external appearance. The coating process is a process in which paint, which is a resin composition, is applied to the surface of a car and spread thereon, so that it is cured to form a continuous resin coated film having a uniform thickness. A resin coated film, formed on the surface of an object by a coating process, is referred to as a coated film.

If any functional deficiency in paint (e. g. , intervention of foam and adherence of dusts) occur during the coating process, the coated film that results has problems in uniformity, continuity and surface smoothness, resulting in defects (e. g. , traces of cloudiness, recessed portions, and scratches). Moreover, after the formation of the coated film, the uniformity, continuity and smoothness of the coated film may be impaired due to

friction and collision of the car body with another object. If there is any defective portion on the coated surface, the appearance of the car body is impaired, resulting in degradation in the value of the car, etc. Therefore, it is necessary to repair this defective portion.

When a defective portion of the coated film surface is repaired, the defective portion has defects removed and the polished portion is again coated, if necessary, so that a process for restoring the defect-removed portion or the recoated portion to the same appearance as the peripheral portion, is carried out. In general, in this process, the texture adjustment, polishing and finishing processes are carried out sequentially on the coated film surface.

The texture adjusting process of the coated film surface refers to a process in which, with respect to the repairing portion, the structure of the texture (e. g. , orange peel) is adjusted to the same degree as the peripheral portion. In this case, the repairing portion is abraded by using an abrasive article having abrasive particles of 5 to 10 um in size (JIS #1500 to #3000), or abraded with a comparatively hard pad or buff using a compound having fine particles with a particle size of 10 to 20 um. The polishing process is a process for making the abrasion scratches caused by the texture adjustment smaller. In this case, a compound including ultra-fine particles (e. g., having a particle size of 5 to 10 um) and a comparatively soft pad and buff are used. The finishing process is a process for making the abrasion scratches smaller until they become invisible. In this case, a compound including super-fine particles (e. g. , having a particle size of 2 to 3 um) and a comparatively soft pad and sponge buff are used.

As described above, most of the repairing processes of the coated film are abrading processes using abrasive grains. Here, the abrasive grains are made of a metal oxide and diamond, and have extremely high hardness as compared to the coated film. Therefore, abrasion scratches are always caused on the coated film surface when such abrasive grains are used. In other words, the above-mentioned restoring processes of the coated surface appearance are processes in which the particle size of abrasive grains is gradually reduced so as to make the abrasion scratches on the coated film gradually smaller, and consequently to make them invisible to the unaided eye.

In the case when the abrasion scratches are made smaller in a finishing process, the irregular cycle of abrasion scratches sometimes approaches the same degree as the wavelength of light. Moreover, in the case when the abrasive grains are regularly moved by using a single action sanding machine and a single polisher, etc. in the finishing process, the finished surface has periodic striped irregularities with a period having the same degree as the wavelength of light. When light is directed thereto, and reflected therefrom, light interference is caused due to a difference in light paths, resulting in a phenomenon in which the finished surface has the appearance of rainbow colors. This phenomenon is generally referred to as "aurora marks." When aurora marks occur on the finished surface of a coated film, further polishing processes must be carried out to remove these marks. In order to remove the aurora marks, it is necessary to make the abrasion scratches irregular, for example, by moving a polishing pad in a complicated manner. For this reason, processes in which polishing is carried out little-

by-little using a double action sanding machine, etc. , are utilized. These processes require special skill, extra time and labor.

Moreover, even if the aurora marks are removed, small abrasion scratches still exist. Therefore, the finishing method of the surface of a coated film using abrasive grains has a limitation for making the coated film surface glossy.

SUMMARY The present invention provides a finishing method for the surface of a coated film that makes the surface sufficiently glossy without causing aurora marks. The present invention also provides a finishing agent for use in such a finishing method.

In one aspect the present invention provides a finishing method for a coated film surface comprising the steps of : (a) applying a finishing agent to a surface of a coated film ; (b) polishing the coated film surface to which the finishing agent has been applied ; wherein the finishing agent is an aqueous composition comprising water, a petrolic solvent, and plastic particles.

In another aspect the present invention provides a finishing agent comprising water, a petrolic solvent, and plastic particles. In a specific embodiment, the finishing agent comprises : (a) 100 parts by weight of water, (b) 1 o 50 parts by weight of petrolic solvent ; and (c) 1 to 50 parts by weight of plastic particles. In another specific embodiment, the plastic particles have a hardness that is not greater than the hardness of the coated film. In another specific embodiment, the plastic particles are spherical and have an average particle size of 5 to 500 um.

DETAILED DESCRIPTION The finishing agent for the surface of a coated film of the present invention is an aqueous composition that comprises water, a petrolic solvent and plastic particles.

Petrolic solvent With respect to the petrolic solvent, materials that are superior in swelling and lubricating the coated film are preferred. By these properties, the coated film is softened, and the plastic particles are improved in degree of moving freedom. Consequently, the adjusting ability of the surface structure of the coated film (e. g. , orange peel) is enhanced and performance of the finishing agent is improved.

With respect to the coated film, in general, resins such as acryl melamine resin, aminoalkyd resin and urethane resin are used. The coated film generally has a hardness of H to 2H (JIS (1979, K5400) ) prior to being swelled by the petrolic solvent. In contrast, after being swelled by the petrolic solvent, the coated film preferably has a hardness of approximately B from the viewpoint of acceleration of the polishing process.

In general, the polishing process for finishing the surface of a coated film is carried out for 1 to 5 minutes under an ambient temperature of 25°C to 60°C. Therefore, the petrolic solvent needs to have low volatility so as not to be dried during the process. Therefore, the petrolic solvent preferably has an initial boiling point of not less than 100°C, more preferably, not less than 130°C.

It is preferred that the petrolic solvent can be wiped off easily using a cloth and does not remain inside the coated film even in the case of being

adhered to the coated film surface.

The petrolic solvent is a solvent that is obtained by fractional distillation of petroleum. The preferred petrolic solvents are hydrocarbon compounds having boiling points of 100°C to 350°C, and mixtures thereof.

Particularly preferred are aromatic hydrocarbons, naphthenic hydrocarbons, and paraffinic hydrocarbons having 3 to 22 carbon atoms, preferably 7 to 13 carbon atoms, and mixtures thereof.

The aromatic hydrocarbon has an aromatic ring making it effective to swell the coated film. However, aromatic hydrocarbons having more than two aromatic rings may be toxic : Therefore, when aromatic hydrocarbon are used, those having three or less aromatic rings in sequence are preferred.

The aromatic hydrocarbon preferably has an aniline point (a mixture aniline point) of 50° C to 100° C, preferably 60° C to 90° C. If the aniline point is too low, the coated film may be damaged.

In addition, from the viewpoint of health and safety of a worker, or in consideration of effects to the environment, aromatic hydrocarbons that are low in odor, are not irritating to skin, and ones that have a high ignition point are preferred. Specifically, paraffinic hydrocarbons having 7 to 13 carbon atoms are preferred.

The petrolic solvent is preferably contained in the finishing agent in an amount of 1 to 50 parts by weight, more preferably, 1 to 30 parts by weight, and most preferably, 3 to 10 parts by weight with respect to 100 parts by weight of water. If the petrolic solvent is present in an amount of less than 1 part by weight, the coated film is not sufficiently swelled and the structure adjusting effect on the coated film surface is not sufficiently

obtained. If the petrolic solvent is present in an amount of more than 50 parts by weight, the coated film becomes too soft, resulting in degradation in the finished state of the coated film surface.

Plastic particles Conventionally, with respect to components used for adjusting the structure of the surface of a coated film, abrasive grains have been typically used. However, the abrasive grains abrade the coated film resulting in abrasion scratches forming on the finished surface of the coated film. The abrasion scratches may cause aurora marks and degradation of gloss. In the finishing agent of the present invention, plastic particles that are softer than abrasive grains are used so that the structure of the coated film surface is adjusted while preventing the formation of abrasion scratches.

The plastic particles preferably have a hardness that is not greater than the hardness of the coated film. If the hardness of the plastic particles is greater than the hardness of the coated film, the structure of the coated surface may be disturbed, or the appearance and the gloss of the finished surface may become poor due to generation of abrasion scratches.

Usually, the hardness of the coated film is 90 to 95 in durometer A hardness. Therefore, the hardness of the plastic particles is preferably a value that is less than the hardness of the coated film by not less than 2 units in durometer A hardness, for example, 80 to 90 if the coated film is 90 to 95.

Although not particularly limited, the shape of the plastic particles is preferably spherical. This is because the spherical shape is effective for adjusting the surface structure of the coated film without causing abrasion scratches on the coated film surface. The particles have an average particle

size of preferably 5 um to 500 um, more preferably 20 um to 100 um. If the average particle size is less than 5 um, the force to be applied to the structure of the coated film surface becomes insufficient. If the average particle size is more than 500 um, the particles do not effectively enter the inside of the structure of the coated film.

The material of the plastic particles may be properly selected from resins having an appropriate hardness. Examples include polymers such as poly (meth) acrylate, polystyrene, polyolefin, phenol resins, epoxy resins, acrylonitrile-butadiene-styrene resins, high-density polyethylene resins, urea resins, polyester resins, polyvinyl chloride, polyamide and polycarbonate. Crosslinked polymer particles are preferably used in order to improve the solvent-resistant property.

The particles may be surface modified, for example, with a metal coating or a functional group adding process. The surface of the particles may be smooth or have voids formed thereon. Commercially available plastic particles may be used. For example, plastic particles available under the trade designation"CHEMISNOW"manufactured by Soken Kagaku K. K. , etc. may be used. In particular, preferable plastic particles are crosslinked poly (meth) acrylate, polyethylene and polyurethane.

The plastic particles are contained in the finishing agent in an amount of preferably 1 to 50 parts by weight, more preferably 10 to 20 parts by weight with respect to 100 parts by weight of water. If the plastic particles are included in an amount of less than 1 part by weight, the finishing agent becomes insufficient to adjust the structure of the coated film surface. If the plastic particles are included in an amount of more than 50 parts by weight, the structure of the coated film surface may be

disturbed.

Abrasive Grains In order to enhance the adjusting effect on the structure of the coated film surface, abrasive grains may be contained in the finishing agent of the present invention. With respect to the abrasive grains, those materials that are hard, good in cutting property, and less likely to cause deep scratches on the abrasion surface when used as free abrasive grains are preferred.

Preferred abrasive grains have an average grain size of 10 nm to 50 um, more preferably 1 um to 10 um. Preferably, the grain size distribution should be narrowed so as not to cause unwanted scratches.

The material of the abrasive grains is preferably selected from aluminum oxide, silica, aluminum silicate, talc, kaolin, clay and a mixture thereof. In particular, preferable abrasive grains are alumina particles.

The abrasive grains are preferably contained in the finishing agent in an amount not more than 60 parts by weight, more preferably not more than 30 parts by weight, and most preferably not more than 15 parts by weight with respect to 100 parts by weight of water. If the content of the abrasive grains is more than 60 parts by weight, aurora marks may be caused, resulting in degradation in gloss on the finished surface of the coated film.

Dispersant A dispersant is optionally contained so as to prevent the plastic particles and abrasive grains from aggregating in the finishing agent.

Since the finishing agent comprises water, a petrolic solvent, plastic particles, abrasive grains, etc. , it is necessary for the dispersant to disperse the plastic particles and abrasive grains in an emulsion medium.

With respect to the dispersant, a water-soluble surfactant is generally used. Specific examples include polycarboxylic acid and salts thereof, and polyaminoamide and acid esters thereof, etc.

The dispersant is preferably contained in the finishing agent in an amount of 0.5 to 5 parts by weight with respect to 100 parts by weight of water. If the dispersant is blended in an amount of less than 0.5 parts by weight, the plastic particles and the abrasive grains tends to aggregate in the finishing agent. If the content of dispersant is more than 5 parts by weight, the dispersing property of the plastic particles and abrasive grains is not improved and the dispersant tends to remain on the finished surface of the coated film.

Lustering agent In order to make the finished surface of the coated film finer and to add gloss, a lustering agent may be added to the finishing agent. With this arrangement, this finishing agent is also appropriate for use as a countermeasure against"hazing"of the coated film. Since the lustering agent serves as a component that is allowed to reside on the coated film surface after a repairing process to fill fine scratches, the agent preferably give no adverse effects to hydrophilic and oil repellent functions of the coated film.

Hydrophilic silicones or hydrophilic waxes may be used as the lustering agent. Specific examples include polyether modified silicone, hydrophilic aminosilicone, hydrophilic epoxy silicone, glycerol, hydrogenated castor oil and derivatives thereof, amide compounds, etc.

In particular, hydrophilic aminosilicones, made from block copolymer between polyether and amino modified silicone, are preferably used since

the hydrophilic aminosilicone remains on the surface of the coated film and exerts effects for maintaining gloss and hydrophilic property of the coated film.

The amount of lustering agent is properly adjusted based on the required finishing of the coated film surface after a repairing process. In general, the lustering agent is contained in an amount of not more than 10 parts by weight, preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of water. Even when the lustering agent comprises more than 10 parts by weight, there is not much additional improvement in the surface of the coated film.

Other additives In order to increase and adjust the viscosity of the finishing agent, a condensing agent may be added. When the viscosity of the finishing agent is too low, the finishing agent tends to flow down along the vertical surface of a car, making it difficult for the worker to carry out the polishing process.

Therefore, the condensing agent is used so as to adjust the viscosity of the finishing agent.

Examples of typical condensing agents include heavy metal soap such as water-bearing aluminum silicate, dimethyl dioctadecyl salt of montmorillonite clay, alkali-soluble acrylic polymer emulsion, colloidal silica and lead oleate, zinc oleate, zinc stearate and aluminum stearate. A preferable condensing agent used in the present invention is an alkali- soluble acrylic polymer emulsion.

An emulsifier may optionally be employed. The emulsifier is a compound that reduces interfacial tension between the dispersion phase and the dispersion medium, and makes emulsification easily and stable.

Examples of emulsifiers include soap. In addition, a thixotropic agent may be employed. The thixotropic agent is a colloid solution that transforms from a gel-form to a sol-form to provide flowability when an external force is applied. When left to stand, the thixotripic agent reverts to a gel-form.

Examples of the thixotropic agent include inorganic substances such as anhydrous aluminium silicate, clay, and mica fine powder, and organic substances such as fatty acid derivative and hydrogenized castor oil.

In order to prevent bacteria from growing in the finishing agent, a stabilizer and a preserving agent may be used. Typical examples include methyl paraben, ethyl paraben, propyl paraben, butyl paraben, potassium sorbate, sorbic acid and o-phenyl phenol.

Pigments, dyes and perfumes may be added to the finishing agent of the present invention if necessary.

Preparation of finishing agent The finishing agent can be prepared by mixing the above-mentioned components with water. Tap water, distilled water, or deionized water may be used. Deionized water is preferred because ions and other substances that would accelerate the growth of bacteria in the finishing agent have been removed.

The order of addition of the materials to prepare the finishing agent is, for example, water, additives, petrolic solvent, dispersant, abrasive grains and/or plastic particles. The mixture is continuously stirred while adding the various components. Thereafter, the finishing agent is mixed with a high shear mixer until it has been formed into a uniform dispersant.

Finishing method of coated film surface In the finishing method of the present invention, first, a coating

process is carried out over a subject to be coated (e. g. , a metal panel). After the coated film has been sufficiently dried and cured, texture adjusting and polishing processes are carried out in the conventional manner. Next, the finishing agent is applied to the coated film surface and the surface is polished. The polishing process is carried out using a comparatively soft pad and a sponge buff. A single action sanding machine, a single polisher, and the like, may be used as a polishing tool.

When the polishing tool is used, the pad and the buff are secured to the tool. With respect to the pad and buffing tool, for example, those manufactured by 3M Company (St. Paul, MN) may be used.

Next, the buff is placed in contact with the coated film surface on which the finishing agent has been applied. The tool is then turned on and pressure is applied against the tool during the polishing process. The polishing time is generally 3 to 30 seconds. The polishing process may be carried out multiple times with pressure being increased or decreased.

Finally, any residual finishing agent on the finished surface is removed by washing with water or wiping with a woven fabric, non-woven fabric or ultra-thin fiber cloth of 0.1 to 0.5 denier. The polishing process may be repeated to provide a finer surface finish.

EXAMPLES The following examples further illustrate the present invention but should not be construed to limit the present invention. In the examples, "parts"represent"parts by weight"unless otherwise defined.

Example 1 Ion exchanged water, dispersant, and an antiseptic agent were weighed, and were uniformly mixed. Polymethyl methacrylate (PMMA) particles (durometer A hardness of 86) were added to the mixture, and it was stirred to form uniform dispersion. A petrolic solvent was added to the dispersion and this was emulsified uniformly with stirring speed being gradually increased to obtain a finishing agent. Table 1 shows the composition of the finishing agent.

Table 1 Composition Weight % Ion exchange water 60 Petrolic solvent 23 PMMA particles 11 Other additives 6 Total 100 Onto a bond steel plate of 380 mm x 250 mm having a thickness of 0.8 mm was applied a top coating composition"SPERIO 2K (10: 1) SUPER BLACK"manufactured by Nippon Paint Co. , Ltd. by using a spray gun so that a dry thickness of 20 to 30 um was achieved. The coated film was dried to touch, and was further dried and cured for 24 hours at 60°C to obtain a test piece.

The coated surface of the test pieces was polished by using a wet sanding finish disk"#2000 PAPER"manufactured by Sumitomo 3M Co., Ltd. and a finishing sander"53. 05" manufactured by 3M Company, and this was sufficiently polished by using a fine particles compound"DYNAMITE CUT"manufactured by Sumitomo 3M Co. , Ltd and an electric single polisher manufactured by Hitachi, Ltd.

To the polished surface of the coated film was applied 4 g of super- fine particles compound"HARD I-L5982"manufactured by Sumitomo 3M Co. , Ltd. , and a polishing process was carried out for 30 seconds by using an electric single polisher manufactured by Hitachi, Ltd. being equipped with 5760 separate wool buff. The residual compound on the polished surface was wiped with a cloth. Next, 4 g of the finishing agent that had been prepared was applied to the polished surface of the coated film and the surface was polished for 30 seconds by using an electric single polisher manufactured by Hitachi, Ltd. being equipped with 5763 separate sponge buff. The residual compound on the polished surface was wiped with a cloth.

The state of the finished surface of the coated film was evaluated as to the following items. Table 2 shows the results of the tests.

Gloss The 20° gloss of the finished surface was measured.

Abrasion scratches Ra and Rmax of the finished surface were measured using a surface roughness measuring device"SURFCORDER SE-30D"manufactured by "Kosaka Kenkyusho K. K.", Aurora marks Light was applied onto the finished surface, the surface was observed in some directions at a shallow angle near the surface. The presence or absence of aurora marks was determined. When no aurora marks were observed, the finishing agent was evaluated as"O". When aurora marks were observed, the finishing agent was evaluated as"X".

Examples 2 to 6 The finishing agent was prepared according to the same manner as described in Example 1 except that the average particle size of the PMMA particles was altered. Then the finishing agent was tested, and evaluated.

Table 2 shows the results.

Comparative Example 1 The finishing agent was prepared according to the same manner as described in Example 1 except that aluminum oxide particles (average particle size of 2 um) were used in place of the PMMA particles. Then the finishing agent was tested, and evaluated. Table 2 shows the results.

Table 2 Example No. 1 2 3 4 5 6 C. Ex. 1 PMMA particle 8 15 20 50 90 100 A1203 size (m) (2 um) Gloss (20-gloss) 80.2 83.7 84.5 83.6 83.8 84. 0 81.7 Abrasion Ra 0.004 0. 003 0.0028 0.0031 0.0039 0.0040 0.0047 scratches Lqmax 0.0372 0. 025 0. 0308 0. 0350 0.0418 0.0560 0.0425 (um) Aurora marks O O O O O O X Example 7 A super-fine particles compound"HARD II-L5985"manufactured by Sumitomo 3M Co. , Ltd. was provided. This compound comprised about 10% by weight of aluminum oxide particles having an average particle size of 2 um. To this compound was added PMMA particles having an average particle size of 90 um, and this was stirred using a high shearing mixer until an uniform dispersion was formed. Thus, a finishing agent was prepared.

The resulting finishing agent was tested and evaluated according to

the same manner as in Example 1. Table 3 shows the results.

Examples 8 to 12 The finishing agent was prepared according to the same manner as described in Example 7 except that the plastic particles was altered in the content and the materials. Then the finishing agent was tested, and evaluated. Table 3 shows the results.

Comparative Example 2 The same procedures as described in Example 7 was carried out except that super-fine particles compound"HARD II-L5985"manufactured by Sumitomo 3M was used. Table 3 shows the results.

Table 3 Example No. 7 8 9 10 Plastic Amount of addition 30 10 3 1 particles (parts) 4 90 um Material PMMA PMMA PMMA PMMA Hardness 86 86 86 86 Gloss (20° gloss) 81.3 80.7 81.1 81.5 Abrasion scratches Ra 0. 018 0.0025 0.0018 0.0022 (um) Rmax 0. 0312 0.0433 0.0427 0. 0414 Aurora marks O O O X Table 3 (Continued) Example N D. 11 12 C. Ex. 2 Plastic Amount of 10 10 0 particles addition (parts) # 90 um Material Polyethylene Polyurethane - Hardness 65 (Shore D) 88 - Gloss (20° gloss) 80 79.5 80. 17 Abrasion scratches Ra 0.0019 0.0019 0.0035 (um) Rmax 0. 0304 0. 0035 0. 06 Aurora marks O O X

Although aurora marks were generated on the finished coated film surface of Comparative Examples, no aurora marks were generated on the finished coated film surface of the Examples. Moreover, as compared to the Comparative Examples, the finished coated film surface of the Examples had a higher level of gloss with fewer abrasion scratches.

The plastic particles made it possible to provide a superior finished coated film surface even though they had a lower hardness and larger particle size as compared to alumina abrasive grains. It is believed that the plastic particles exert a function of compressing the coated film rather than abrading the coated film. This function makes it possible to improve the gloss without forming new abrasion scratches on the coated film surface.

Various modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing description with departing from the scope and spirit of the invention.