JP2003306645A - Water-based coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based coating composition which scarcely increases the viscosity even in a high solid content concentration, has the excellent dispersion stability of a scaly glossy pigment, the good sagging resistance of a coated coating film under high humidity, and can form coating films having excellent metallic touches and smoothness, while the addition of a rheology-adjusting agent such as polymer fine particles has widely been carried out to enhance the solid content concentration of the water-based coating, but causes the increase of the viscosity, whereby it is difficult to obtain an excellent smooth coating film, and further while the scaly glossy pigment does not have sufficient dispersion stability and thereby has various defects such as the sagging of a coating film, when coated under high humidity. <P>SOLUTION: This water-based coating composition is characterized by adding a wax aqueous dispersion to the water-based coating. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION [0001] The present invention shows that even when the solid content is increased, almost no increase in viscosity is observed, and the dispersion stability of the scaly glittering pigment is excellent. The present invention relates to an aqueous coating composition which can form a coating film having excellent sagging resistance of a coating film under high humidity and excellent metallic feeling and smoothness. 2. Description of the Related Art In order to increase the solid content concentration of an aqueous paint, it is widely used to add a rheology modifier such as polymer fine particles, but when these are added, the viscosity increases. Therefore, it is difficult to obtain a coating film having excellent smoothness, and the dispersion stability of the flaky glittering pigment is not sufficient, and when applied under high humidity, the applied coating film tends to sag. Therefore, these improvements are desired. An object of the present invention is to eliminate the above-mentioned deficiencies. As a result of intensive studies, it has been found that the object can be achieved by incorporating an aqueous dispersion of wax into an aqueous paint. As a result, the present invention has been completed. Thus, according to the present invention, there is provided an aqueous coating composition (hereinafter referred to as "the present coating"), characterized in that the aqueous coating composition contains an aqueous dispersion of wax. DETAILED DESCRIPTION OF THE INVENTION In the present coating composition, an aqueous dispersion of wax is a liquid composition obtained by dispersing wax in water in the form of fine particles. The wax is a beeswax-like substance which is solid at room temperature and becomes a liquid having a relatively low viscosity when heated, and known waxes can be used in the present coating composition. Specifically, petroleum waxes such as paraffin wax and microcrystalline wax; plant waxes such as carnauba wax, candelilla wax, rice wax, and wood wax; animal waxes such as beeswax and spermaceti; montan wax, ozokerite, and ceresin Mineral wax such as polyethylene wax, Fischer-Tropsch wax, fatty acid amide wax, and synthetic wax such as hardened castor oil (caster wax). Of these waxes, the acid value is from 0 to 80.
Those containing mgKOH / mg, particularly 20 to 50 mgKOH / mg, and having a dropping point within the range of 50 to 160 ° C, particularly 60 to 120 ° C, are suitable. The acid value is the amount of carboxyl groups contained in the wax, and the dropping point is the temperature at which the wax is heated to become liquid and begin to drip. The latter can be measured according to JIS K2222.5.4. The wax can be neutralized with a basic compound such as an amine at the same time or before dispersing in water. An aqueous dispersion of wax can be easily obtained by adding wax to water and mechanically dispersing it uniformly. The ratio of water to wax is, based on the total weight of both, 20 to 99.9% water, especially 50 to 90%.
%, And the wax is suitably in the range of 0.1 to 80%, particularly 50 to 10%. Further, a dispersion resin, a surfactant and the like can be further added to the aqueous dispersion of the wax, if necessary. The present coating composition is an aqueous coating composition characterized by containing an aqueous dispersion of wax in an aqueous coating composition. More specifically, the coating composition is prepared by adding an aqueous dispersion of wax to an aqueous resin composition. It can be prepared, and can further contain a coloring pigment, an extender, an organic solvent, and the like, if necessary. As the aqueous resin composition, known coating resins which can be dissolved or dispersed in water can be used.
Specifically, an acrylic resin having a hydrophilic group such as a carboxyl group and a crosslinking functional group such as a hydroxyl group in one molecule,
One or more base resins selected from vinyl resins, polyester resins, urethane resins, and the like, and a crosslinking agent such as a hydrophobic or hydrophilic alkyl etherified melamine resin that reacts with these crosslinkable functional groups. Can be suitably used. The composition ratio of the base resin and the crosslinking agent is 50 to 90 based on the total amount of both components.
% By weight, especially 65 to 85% by weight, the latter being preferably in the range of 50 to 10% by weight, especially 35 to 15% by weight. [0010] Examples of the coloring pigments that can be blended as required include solid color pigments and metallic pigments. As solid color pigments, for example, white pigments such as titanium oxide, zinc white, lead white, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, antimony white; carbon black, acetylene black, lamp black, bone black, graphite, Black pigments such as iron black and aniline black; yellow pigments such as naphthol yellow S, Hansa yellow, pigment yellow L, benzidine yellow and permanent yellow; orange pigments such as chrome orange, chrome vermillion and permanent orange; iron oxide and amber Brown pigment; red pigment such as red iron red, permanent red, quinacridone red pigment; purple pigment such as cobalt purple, fast violet and methyl violet lake; blue such as ultramarine, navy blue, cobalt blue, phthalocyanine blue and indigo Pigments; chromium green, Pigment Green B, etc. green pigments such as phthalocyanine green and the like. The mixing ratio of the solid color pigment is 100 parts by weight (solid content) of the aqueous resin composition.
Per unit weight is preferably in the range of 1 to 200 parts by weight. The metallic pigment is a scaly pigment capable of imparting glittering glitter and light interference to a coating film. Examples of the metallic pigment include scaly aluminum, vapor-deposited aluminum, aluminum oxide, oxybismuth chloride ( For example, EngelhardAsia Pacific
Inc. Product name, "Mearlite Radia"
nt Pearl STL "," Mearlite R
adian Pearl SUQ ”,“ BBT ”(tentative name), mica, titanium oxide-coated mica, iron oxide-coated mica, mica-like iron oxide, and the like. The size of these metallic pigments is 1 to 30 μm in the longitudinal direction, and the thickness is 0.1 μm.
001 to 1 μm is preferred. The mixing ratio of the metallic pigment is 100 parts by weight (solid content) of the aqueous resin composition,
0.5 to 40 parts by weight are suitable. Examples of extenders include barita powder, precipitated barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, alumina white, gloss white, mica powder, and the like. . The coating composition of the present invention may further contain an antisettling agent, an electrostatic assistant, and the like. The present coating composition can be obtained by incorporating an aqueous dispersion of wax into the prepared aqueous coating composition or during the preparation of the aqueous coating composition. The mixing ratio of the wax aqueous dispersion can be arbitrarily selected according to the purpose, and is not particularly limited. For example, 1 to 20 parts by weight, based on 100 parts by weight (solid content) of the aqueous resin composition in the aqueous paint, Especially 5-10
A range of parts by weight is suitable. The paint thus obtained can be used as an intermediate paint or a top coat,
Solid color coatings, metallic coatings, etc. can be formed. The paint is applied directly to the outer panel of automobile bodies such as cars, trucks, motorcycles and buses made of metal or plastic, the outer panel of household electric appliances, etc. It is preferable to apply an undercoat paint such as a cationic electrodeposition paint beforehand to cure the coating film before applying. [0017] The paint of the present invention can be used for these coating materials (undercoat paint,
Further, an intermediate coating may be applied as appropriate), and the coating can be applied by electrostatic coating, airless spray, air spray, or the like. The coating thickness is 5 to 5 based on the cured coating.
A range of 60 μm, especially 10 to 45 μm, is suitable.
This coating is at 100-180 ° C, preferably at 120-1
The composition can be cured by heating at 60 ° C. for 10 to 40 minutes. Single paint film with this paint, clear paint film,
Solid color coatings, metallic coatings, etc. can be formed. After heat-curing the coating film of the present coating, or 6
In an uncured state obtained by preheating at 0 to 100 ° C. for about 3 to 10 minutes, a clear paint can be applied to the coated surface. The clear coating is preferably a thermosetting coating which forms a colorless transparent or colored transparent coating. More specifically, the clear coating contains a thermosetting resin composition and an organic solvent. , A metallic pigment, an ultraviolet absorber and the like. Examples of the thermosetting resin composition include an acrylic resin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and an epoxy group, a polyester resin, an alkyd resin, a fluororesin, a urethane resin, and a silicon-containing resin. Melamine resin, urea resin, (block) polyisocyanate compound, epoxy compound or resin, carboxyl group-containing compound or resin,
Examples of the composition include a crosslinking agent such as an acid anhydride, an alkoxysilane group-containing compound, or a resin. Specifically, the paint is electrostatically applied to an object to be coated,
Apply a film having a thickness of 5 to 30 μm, preferably 10 to 20 μm based on the cured coating film by an airless spray, an air spray, or the like, and heat-curing the coating film, or 6
A clear paint is applied to an uncured coating surface preheated at 0 to 100 ° C. for about 3 to 10 minutes based on the cured coating film.
0 μm, preferably 20-80 μm
Heating is performed at 00 to 180 ° C. for about 10 to 40 minutes to cure these coating films. [Effects of the Invention] By adding an aqueous dispersion of wax, almost no increase in viscosity is observed even when the solid content concentration of the water-based paint is increased, so that a coating film with excellent smoothness is formed even when a thick film is applied at a high concentration. It became possible. In addition, storage and transportation costs and the like can be reduced. 2. By incorporating an aqueous dispersion of wax, the dispersion stability of the scaly glittering pigment blended in the present coating composition was improved, and it was possible to reduce the occurrence of metallic unevenness and the like. 3. In addition, paint under high humidity (for example,
Even when applied at a humidity of 85% or more), the applied coating film is less likely to sag and a coating film having excellent smoothness can be formed. EXAMPLES Examples and comparative examples according to the present invention will be described below. All parts and percentages are based on parts by weight, the blending amounts are indicated by solids content, and the film thickness of the coating is for the cured coating. Example 1 75 parts of a hydroxyl group-containing acrylic resin (Note 1), 25 parts of a melamine resin (Note 2), "Alpaste 7679NS" (trade name, manufactured by Toyo Aluminum Co., Ltd., aluminum flake paper)
ST) 10 parts and 5 parts of an aqueous dispersion of wax (Note 3) were mixed and dispersed in deionized water to obtain a viscosity of 13 seconds / ford cup #
Adjusted to 4/20 ° C. (Note 1) Hydroxyl group-containing acrylic resin: methyl methacrylate 38 parts, ethyl acrylate 17 parts, n
A copolymer of a monomer component consisting of 10 parts of butyl acrylate, 7 parts of hydroxyethyl methacrylate, 20 parts of lauryl methacrylate and 8 parts of acrylic acid was neutralized with diethanolamine. Number average molecular weight 30,000. (Note 2) Melamine resin: Imino group type melamine resin, "Cymel 325" (trade name, manufactured by Mitsui Cytec Co., Ltd.). (Note 3) Aqueous dispersion of wax: 70 parts of water and 30 parts of polyethylene wax were stirred with a disper for 20 minutes, and both components were uniformly mixed and dispersed to obtain an aqueous dispersion. Comparative Example 1 75 parts of acrylic resin (Note 1), melamine resin (Note 2) 2
5 parts and "Alpaste 7679NS" 10 parts were mixed and dispersed in deionized water, and the viscosity was 13 seconds / Ford cup # 4 /
Adjusted to 20 ° C. Performance Test Results A cationic electrodeposition paint and an intermediate paint were applied, and the water-based paints obtained in Examples and Comparative Examples were applied to a steel sheet obtained by curing these coatings so as to have a thickness of 15 μm. 5 at 80 ° C
After preheating for about a minute, apply a clear coating (Note 4) on the uncured coating surface to a film thickness of 40 μm.
Both coatings were simultaneously cured by heating at 140 ° C. for 30 minutes. A performance test was performed on the obtained multilayer coating film, and the results are shown in Table 1. (Note 4) Clear paint: 50 parts of a carboxyl group-containing acrylic resin (Note 5), 50 parts of an epoxy group-containing acrylic resin (Note 6), “Tinuvin 900” (manufactured by Ciba-Geigy Co., trade name, ultraviolet absorber) 1 part, 2 parts of an equivalent blend of tetrabutylammonium bromide and monobutyl phosphoric acid, "BYK300" (trade name, manufactured by Big Hemi Co., Ltd.)
0.1 part of a surface conditioner was mixed and dispersed in an aromatic hydrocarbon-based solvent to adjust the viscosity to 20 sec / ford cup # 4/20 ° C. (Note 5) Carboxyl group-containing acrylic resin: methanol half ester of maleic anhydride 2
0 parts, 20 parts of 4-hydroxy n-butyl acrylate, n
A copolymer of a monomer component consisting of 40 parts of butyl acrylate and 20 parts of styrene. Number average molecular weight 3500, hydroxyl value 78 mgKOH / g, acid value 86 mgKOH / g. (Note 6) Epoxy group-containing acrylic resin: a monomer component comprising 30 parts of glycidyl methacrylate, 20 parts of 4-hydroxy n-butyl acrylate, 30 parts of n-butyl acrylate and 20 parts of styrene. Copolymer. The number average molecular weight is 3000, the epoxy group content is 2.12 mmol / g, and the hydroxyl value is 78 mgKOH / g. [Table 1] Test Method Smoothness: The smoothness of the surface of the multilayer coating film was visually evaluated. ○: good smoothness without unevenness, △: slight occurrence of unevenness,
X indicates that the smoothness is slightly inferior, and x indicates that the occurrence of unevenness is large and the smoothness is inferior. Flip-flop property (FF value): Measured using ALCOPE60 (trade name, manufactured by Kansai Paint Co., Ltd.). FF
The value indicates that the flip-flop property is stronger as the phenomenon that the metal feeling is stronger in the highlight part and the metal feeling is weaker in the shade part is more remarkable. The larger the value, the stronger the flip-flop property. Metallic unevenness: The result of visual observation of the uniform dispersibility of the metallic pigment in the multilayer coating film.は indicates that the metallic pigment is uniformly dispersed and no unevenness is observed at all, △ indicates that the metallic pigment is slightly inferior in dispersibility and slight unevenness is observed, and x indicates that the metallic pigment is inferior in dispersibility and uneven. This indicates that many occurrences are observed.

Claims (1)

Claims: 1. An aqueous paint composition comprising an aqueous dispersion of a wax in an aqueous paint.