Coating composition

Abstract: A coating composition comprising plate-like iron oxide particles having an average particle diameter of from 0.5 to 5.0 µm, a lamellar thickness of from 500 to 5000nm and a plate ratio (the ratio of the average particle diameter to the lamellar thickness) of from 50 : 1 to 500 : 1; at least one pigment selected from the group consisting of a coloring pigment, a mica pigment and a metal powder pigment; a film-forming polymer; and an organic solvent.

Description: The present invention relates to a coating composition suitable for protecting the bodies of for example, automobiles and at the same time displaying a soft and bright ornamental texture. For finish coating of automobiles and bicycles, solid colour coating and metallic coating are mainly adopted. Inorganic pigments such as titanium dioxide pigments and iron oxide pigments, and organic pigments having excellent weather resistance such as copper phthalocyanine pigments, quinacridone pigments and perylene pigments, are usually used for solid colour coating. For metallic coating, a metal powder such as aluminium powder and mica are used together with, for example, the above-described organic pigments so as to display a bright texture. A coating film formed by using such a metallic coating is required to have a sufficient durability for protecting the substrate and an ornamental property (beautiful appearance). As the above-described metallic coatings, a metallic coating obtained by mixing ordinary iron oxide with a metal powder such as aluminium powder or mica is usable. However, such a coating containing ordinary iron oxide cannot produce a coated product having a characteristic bright texture, because it does not produce the phenomenon of light interference. The above-described metallic coatings have a durability which is almost sufficient to meet market demand, but the aesthetic appearance on the object which is coated is not satisfactory as regards a soft and bright texture. As a result of studies undertaken by the present inventors to overcome the above-mentioned defects, it has been found that plate-like iron oxide particles having an average particle diameter of from 0.5 to 5.0 µm, a lamellar thickness of from 5 to 50 nm (50 to 500Å) and a plate ratio (the ratio of particle diameter to thickness) of from 50 : 1 to 500 : 1 show a phenomenon of light interference, and that by applying a coating composition obtained by mixing these particles with a coloured pigment, a coated product having a soft and bright texture which is different from the texture produced by a conventional coating containing a metal powder or a mica is obtained. On the basis of these findings, the present invention has been achieved. Accordingly the present invention provides a coating composition comprising plate-like iron oxide particles having an average particle diameter of from 0.5 to 5.0 µm, a lamellar thickness of from 5 to 50 nm (50 to 500Å) and a plate ratio (the ratio of the average particle diameter to the lamellar thickness) of from 50 : 1 to 500 : 1; at least one pigment selected from the group consisting of a colouring pigment, a mica pigment and a metal powder pigment; a film-forming polymer; and an organic solvent. The present invention also provides on article coated with a coating composition as defined above. As the plate-like iron oxide particles, plate-like hematite particles may be exemplified. Such plate-like hematite particles are described in U.S. Patent Application No. 07/466,132 filed on January 19, 1990 and EP-A- 306224. The plate-like hematite particles are obtained by autoclaving an alkaline suspension of iron (III) hydroxide oxide particles, FeO x ·Fe₂O₃ (0 ≦ × ≦ 1) particles or a ferric salt, the alkaline suspension having a pH of not less than 9 and containing 0.1 to 15.0 mol of a water-soluble salt based on 1 mol of Fe and a Si-containing compound in an amount of 1.5 to 20.0 mol%, expressed as Si, based on the total amount of Fe in the alkaline suspension. The iron (III) oxide hydroxide particles may have any particle form such as an acicular form and a spindle form that is obtainable by a conventional reaction method. It is possible to use a wet-cake obtained by washing a reaction mother liquor containing iron (III) oxide hydroxide with water, a dried wet-cake thereof or the reaction mother liquid. The FeO x ·Fe₂O₃ (0 ≦ × ≦ 1) particles which are usable are, for example, a wet-cake obtained by washing with water a reaction mother liquor containing particulate or cubic magnetite particles obtained by the reaction of a ferrous salt and an aqueous alkaline solution, a dried wet-cake thereof or the reaction mother liquid, and acicular or spindle FeO x ·Fe₂O₃ (0 ≦ × ≦ 1) particles obtained by reducing or further oxidizing, if necessary, the above-mentioned acicular spindle iron (III) oxide hydroxide particles. As the ferric salt, ferric chloride, ferric sulfide, ferric nitrate, for example, are usable. The pH of the alkaline suspension is not less than 9, preferably not less than 12. If the pH is less than 9, acicular iron (III) oxide hydroxide particles or FeO x ·Fe₂O₃ (0 ≦ × ≦ 1) particles are disadvantageously mixed into the plate-like hematite particles. The autoclaving is carried out by using an autoclave at a temperature of ordinarily 150 to 330°C, preferably 200 to 300°C, more preferably 250 to 300°C, for 2 to 6 hours. It is a general tendency that the higher the alkali concentration, the lower the reaction temperature for producing plate-like hematite particles. If the temperature is lower than 150°C, the suspension contains iron (III) oxide hydroxide, FeO x ·Fe₂O₃ (0 ≦ × ≦ 1) or a ferric salt as it is, thereby producing no plate-like hematite particles. If the temperature is higher than 330°C, the production of plate-like hematite particles is possible, but when the safety of the autoclave is taken into consideration, the upper limit of the temperature is 330°C. As the water-soluble salt, sulfates, nitrates, chlorides and acetates of alkaline metals may be exemplified. The amount of water-soluble salt added is 0.1 to 15.0 mol, preferably 0.5 to 10.0 mol, more preferably 3.0 to 5.0 mol, based on 1 mol of Fe. By the synergistic effect of the coexistence of the water-soluble salt and the Si-containing compound, the plate-like hematite particles have a very thin thickness, particularly of from 5 to 50 nm (50 to 500Å) and a relatively large plate ratio, particularly of from 50 : 1 to 500 : 1. If the water-soluble salt is added in an amount of less than 0.1 mol, the thickness and plate ratio of the plate-like hematite particles produced becomes unfavorable. In particular, since the thickness of the plate-like hematite particles becomes more than 50 nm (500Å), the plate ratio becomes less than 50 : 1 and the hue and chroma of the particles becomes low, and it is difficult to obtain the target plate-like hematite particles. Even if the water-soluble salt is added in an amount of more than 15 mol, it is possible to obtain the target plate-like hematite particles, but the addition of more water-soluble salt than necessary is pointless. Examples of the Si-containing compound are the silicates of potassium and sodium, and colloidal silica. The Si-containing compound is added so that 1.5 to 20.0 mol%, preferably 5.0 to 15.0 mol%, expressed as Si, is contained in the alkaline suspension based on the total amount of Fe. If the amount of the Si-containing compound added is less than 1.5 mol%, expressed as Si, based on the total amount of Fe, the thickness of the plate-like hematite particles becomes more than 50nm (500Å) and, hence, the plate ratio becomes small, so that the plate-like hematite particles take on a red-purple to black purple colour. On the other hand, if it is more than 20 mol%, expressed as Si, based on the total amount of Fe, the thickness of the plate-like hematite particles becomes smaller than 50Å on the basis of the synergistic effect of the water-soluble salt and Si-containing compound, and as a result destruction of the particle form is apt to aise. The water-soluble salt and the Si-containing compound exert an influence on the particle form (for example the plate ratio and the lamellar thickness) and the surface property of the plate-like hematite particles produced. It is, therefore, necessary to add the water-soluble salt and the Si-containing compound before the reaction producing the plate-like hematite particles. The water-soluble salt may be added before, simultaneously with, or after the addition of the Si-containing compound. The average particle diameter and plate ratio of the plate-like hematite particles is apt to increase in proportion to the amount of water-soluble salt added. In a coating composition of the present invention, the amount of the plate-like iron oxide particles used is 0.02 to 90 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the coating composition. If it is less than 0.02 parts by weight, the coating composition cannot display a sufficient bright texture. If it is more than 90 parts by weight, the physical properties of the coating film tend to lower. The pigment(s) used are at least one selected from a colouring pigment, a metal powder pigment and a mica pigment. The colouring pigment is one which is used for ordinary coating such as a quinacridone pigment, perylene pigment, copper phthalocyanine pigment, anthraquinone pigment, metal complex pigment, transparent iron oxide pigment or carbon black. As the metal powder pigment, aluminium powder pigments, stainless steel powder pigments and copper powder pigments are for example, usable. Among these, aluminium powder pigments are preferably used. As a mica pigment, a wide range of known mica pigments are usable, such as transparent pearl mica, coloured mica and interfered mica. As the film-forming polymer used in the present invention, acrylic resins, acryl melamine resins, vinyl chloride-vinyl acetate copolymers, alkyd resins, polyesters, polyurethanes and amino resins, which are polymers conventionally used in the field of coating, may be exemplified. However, the polymer used in the present invention is not restricted to these resins. The amount of film-forming polymer in the present invention is about 20 to 60 parts by weight, preferably 30 to 40 parts by weight, based on 100 parts by weight of the coating composition. A conventionally well known organic solvent for coatings is used as an organic solvent in which the film-forming polymer is dissolved or dispersed. For example, toluene, xylene, butyl acetate, ethyl acetate, methyl acetate, acetone, methylethyl ketone, methylisobutyl ketone, methanol, ethanol, butanol and cyclohexane are usable. The amount of organic solvent used is 10 to 90 parts by weight, preferably 30 to 70 parts by weight, based on 100 parts by weight of the coating composition. The amount of the pigment(s) used is 0.1 to 2000 parts by weight, preferably 3 to 1000 parts by weight, based on 100 parts by weight of plate-like iron oxide particles, and 0.1 to 90 parts by weight, preferably 0.1 to 60 parts by weight, based on 100 parts by weight of the coating composition. If it is less than 0.1 parts by weight based on 100 part by weight of plate-like iron oxide particles, it is difficult to fully display a bright texture. On the other hand, if it is more than 2000 parts by weight based on 100 part by weight of plate-like iron oxide particles, the bright texture of the plate-like iron oxide particles is impaired. The colouring pigment, mica pigment and metal powder pigment may be used singly or in the form of a mixture. The amount of the colouring pigment is not more than 60 parts by weight, preferably 0.1 to 30 parts by weight, based on 100 parts by weight of the coating composition. The amount of the mica pigment is not more than 30 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the coating composition. The amount of the metal powder pigment is not more than 30 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the coating composition. A filler, antistatic agent, stabilizer, antioxidant or ultraviolet absorber, for example, may be added to the coating composition of the present invention, if necessary. In order to form the coating composition of the present invention the plate-like iron oxide particles and at least one pigment selected from the group consisting of a colouring pigment, a mica pigment and a metal powder pigment are mixed with a solution of a film-forming polymer in an organic solvent in, for example, a said mill or a high-speed mixer. The thus-obtained coating composition is applied on a a base plate such as a metal plate, glass plate, ceramic plate, plastic plate or enamel plate, a base plate coated by electrodeposition, an undercoated base plate or a second-coated base plate, by a spray coating method, flow coating method or roll coating method, and dried to form a coloured coat layer. A clear coating agent prepared by dissolving or dispersing a resin similar to the film-forming polymer in an organic solvent is applied on the coloured coating layer as a base coat layer, dried ordinarily and heat-treated to form a coating film. To prepare a coating composition of the present invention, it is preferable to prepare a base coatings by mixing the plate-like iron oxide particles, colouring pigment and metal powder pigment with a solution of a film-forming polymer in an organic solvent respectively, and mixing predetermined amounts of the respective base coatings. According to the present invention, it is possible to form a coating film having a sufficiently bright texture. By forming a coloured base-coat layer by applying a coating composition of the present invention onto a base plate such as a metal plate, and further by forming a clear coat layer thereon, it is possible to obtain a coating film having a soft texture, a bright texture and an excellent directional property which cannot be obtained from a conventional metallic coating film. Thus, a coating composition of the present invention is optimum as a protecting and ornamenting coating applied to an object such as an automobile or a bicycle. EXAMPLES The present invention is further described in the following Examples. "Parts" and "%" in the Examples and Comparative Examples mean "parts by weight" and "% by weight", respectively. PRODUCTION EXAMPLE 1 An alkaline suspension of pH 13.8 which was obtained by mixing 0.2 mol of α-FeOOH (major axis: 1.0 µm, BET specific surface area 50.2 m²/g), 0.6 mol of NaNO₃ (which is equivalent to 3 mol on the basis of 1 mol of Fe), 4.21 g of water-glass No. 3 (SiO₂ : 28.55 wt%, containing 10 mol% of Si on the basis of the total amount of Fe) and 1.0 mol of NaOH was heated to 280°C in an autoclave. This temperature was maintained for 2 hours while mechanically stirring the suspension, thereby producing a yellowish brown precipitate. After the mixture was cooled to room temperature, the yellowish brown precipitate was filtered out. The precipitate was thoroughly washed with water and then dried. The particles obtained were hematite particles as shown from the X-ray diffraction pattern. The average particle diameter was 2.5 µm, the thickness was 240Å and the plate ratio was 104 : 1, as was clear from an electron micrograph thereof. PRODUCTION EXAMPLE 2 An alkaline suspension of pH 13.8 which was obtained by mixing 0.2 mol of α-FeOOH (major axis: 1.0 µm, BET specific surface area 50.2 m²/g), 0.8 mol of NaNO₃ (which is equivalent to 4 mol on the basis of 1 mol of Fe), 3.37 g of water-glass No. 3 (SiO₂ : 28.55 wt%, containing 8 mol% of Si on the basis of the total amount of Fe) and 1.0 mol of NaOH was heated to 280°C in an autoclave. This temperature was maintained for 2 hours while mechanically stirring the suspension, thereby producing a yellowish brown precipitate. After the mixture was cooled to room temperature, the yellowish brown precipitate was filtered out. The precipitate was thoroughly washed with water and then dried. The particles obtained were hematite particles, as shown from the X-ray diffraction pattern. The average particle diameter was 2.4 µm, the thickness was 350Å and the plate ratio was 69 : 1, as was clear from an electron micrograph thereof. Example 1 (Mixture A) (Mixture B) Mixtures A and B were respectively dispersed by a sand mill. 90 parts of Mixture A and 10 parts of Mixture B were uniformly mixed to obtain a coating composition (containing 15.3 parts by weight of plate-like hematite particles and 1.7 parts by weight of the quinacridone pigment based on 100 parts by weight of the coating composition). Example 2 (Mixture C) Mixture C was dispersed by a sand mill. 5 parts of Mixture C and 95 parts of Mixture A in Example 1 were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of plate-like hematite particles and 0.3 part by weight of carbon black based on 100 parts by weight of the coating composition). Example 3 (Mixture D) (Mixture E) Mixtures D and E were respectively dispersed by a sand mill. 95 parts of Mixture D and 5 parts of Mixture E were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of plate-like hematite particles and 0.9 part by weight of copper phthalocyanine blue based on 100 parts by weight of the coating composition). Example 4 (Mixture F) Mixture F was dispersed by a high-speed mixer. 50 parts of Mixture F and 50 parts of Mixture A in Example 1 were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of plate-like hematite particles and 8.5 parts by weight of the aluminium pigment based on 100 parts by weight of the coating composition). Example 5 (Mixture G) Mixture G was dispersed by a high-speed mixer. 50 parts of Mixture G and 50 parts of Compound D in Example 3 were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of plate-like hematite particles and 8.5 parts by weight of the mica pigment based on 100 parts by weight of the coating composition). Example 6 Mixture A 70 parts Mixture B 20 parts Mixture G 10 parts Mixtures A, B and G were uniformly mixed to obtain a coating composition (containing 11.9 parts by weight of plate-like hematite particles, 3.4 parts by weight of the quinacridone pigment and 1.7 parts by weight of the mica pigment based on 100 parts by weight of the coating composition). Example 7 Mixture A 50 parts Mixture E 10 parts Mixture F 40 parts Mixtures A, E and F were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of plate-like hematite particles, 1.7 parts by weight of copper phthalocyanine blue and 6.8 parts by weight of the aluminium pigment based on 100 parts by weight of the coating composition). Comparative Example 1 (Mixture H) Mixture H was dispersed by a sand mill. 90 parts of Mixture H and 10 parts of Mixture B in Example 1 were uniformly mixed to obtain a coating composition (containing 15.3 parts by weight of granular hematite particles and 1.7 parts by weight of the quinacridone pigment based on 100 parts by weight of the coating composition). Comparative Example 2 (Mixture I) Mixture I was dispersed by a sand mill. 90 parts of Mixture I and 10 parts of Mixture B in Example 1 were uniformly mixed to obtain a coating composition (containing 15.3 parts by weight of spindle-shaped hematite particles and 1.7 parts by weight of the quinacridone pigment based on 100 parts by weight of the coating composition). Comparative Example 3 Mixture H 95 parts Mixture C 5 parts Mixtures H and C were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of granular hematite particles, 0.9 parts by weight of carbon black based on 100 parts by weight of the coating composition). Comparative Example 4 Mixture H 95 parts Mixture E 5 parts Mixtures H and E were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of granular hematite particles, 0.9 part by weight of copper phthalocyanine blue based on 100 parts by weight of the coating composition). Comparative Example 5 Mixture I 95 parts Mixture E 5 parts Mixtures I and E were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of spindle-shaped hematite particles, 0.9 parts by weight of copper phthalocyanine blue based on 100 parts by weight of the coating composition). Comparative Example 6 Mixture I 95 parts Mixture C 5 parts Mixtures I and C were uniformly mixed to obtain a coating composition (containing 16.2 parts by weight of spindle-shaped hematite particles, 0.9 parts by weight of carbon black based on 100 parts by weight of the coating composition). Comparative Example 7 (Mixture J) Mixture J was dispersed by a sand mill. 50 parts of Mixture J and 50 parts of Mixture F in Example 4 were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of plate-like hematite particles and 8.5 parts by weight of the aluminium pigment based on 100 parts by weight of the coating composition). Comparative Example 8 Mixture I 50 parts Mixture F 50 parts Mixtures I and F were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of spindle-shaped hematite particles and 8.5 parts by weight of the aluminium pigment based on 100 parts by weight of the coating composition). Comparative Example 9 Mixture H 50 parts Mixture G 50 parts Mixtures H and G were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of. plate-like hematite particles and 8.5 parts by weight of the mica pigment based on 100 parts by weight of the coating composition). Comparative Example 10 Mixture I 50 parts Mixture G 50 parts Mixtures I and G were uniformly mixed to obtain a coating composition (containing 8.5 parts by weight of spindle-shaped hematite particles and 8.5 parts by weight of the mica pigment based on 100 parts by weight of the coating composition). The coating compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 10 were diluted with a thinner to a viscosity suitable for spraying (15 sec by Ford cup No. 4), and sprayed on a steel panel having an irregular surface by an air spray gun. After the obtained panel was dried for 10 minutes, the resultant panel was subjected to clear coating (acryl melamine) by an air spray gun. After the obtained panel was dried at room temperature for 15 minutes, it was cured by baking at 140°C for 30 minutes. The aesthetic appearance of each panel obtained was evaluated. The results are shown in Table 1. Aesthetic appearance was evaluated in five stages ranging from 5 meaning best to 1 meaning worst. L*₄₅/L*₋₄₅ is the ratio of the lightness of acceptance angles +45° and -45°, at where the incidence light is -70°. In this case, the line perpendicular to the paint film surface is regarded as 0°. This L*₄₅/L*₋₄₅ value shows the difference of lightness when the paint film is projected to the light at different angle, the so called down-flop effect. The measurement was made by a gonio-photometer colour measurement system GCMS-3 sold by Murakami Color Research. The larger value of L*₄₅/L*₋₄₅ means the more effect of down-flop, and in the case of L*₄₅/L*₋₄₅≒ l, the down-flop effect is negligible. It is necessary for the purpose of the present invention that L*₄₅/L*₋₄₅ ≧ 1.5. The bright texture is expressed by a sensory value in proportion to the quantity of reflected light at a positive angle to incident light, in other words, what is called a glittering appearance. It is necessary for the purpose of the present invention that the evaluation of the bright texture is not less than 3. The directional property means the difference of colour tone between the reflected light at positive angle and negative angle, when the incident light comes at a certain negative angle, in other words, it is called the "flip-flop" effect. It is necessary for the purpose of the present invention that the evaluation of the directional property is not less than 3. The soft texture is the sensory value which is related to the distribution of positive reflected light. The softer the texture is, the wider is the half width of the distribution of positive reflected light. This is the sensory value of the denseness of what is called a glittering appearance. It is necessary for the purpose of the present invention that the evaluation of the soft texture is not less than 3.

Claims: A coating composition comprising plate-like iron oxide particles having an average particle diameter of from 0.5 to 5.0 µm, a lamellar thickness of from 5 to 50 nm and a plate ratio (the ratio of the average particle diameter to the lamellar thickness) of from 50 : 1 to 500 : 1; at least one pigment selected from the group consisting of a colouring pigment, a mica pigment and a metal powder pigment; a film-forming polymer; and an organic solvent. A coating composition according to claim 1, wherein the amount of said film-forming polymer is from 30 to 40 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to claim 1 or 2, wherein the amount of said organic solvent is from 30 to 70 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to claim 1, 2 or 3 wherein the amount of said plate-like iron oxide particles is from 1 to 50 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to any one of the preceding claims, wherein the amount of the pigment is from 0.1 to 60 parts by weight based on 100 parts by weight of said coating composition and from 3 to 1,000 parts by weight based on 100 parts by weight of said plate-like iron oxide particles. A coating composition according to any one of the preceding claims, wherein the amount of the colouring pigment is from 0.1 to 30 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to any one of the preceding claims, wherein the amount of the mica pigment is from 1 to 15 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to any one of the preceding claims, wherein the amount of the metal powder pigment is from 1 to 15 parts by weight based on 100 parts by weight of said coating composition. A coating composition according to any one of the preceding claims, wherein said plate-like iron oxide particles are plate-like hematite particles. An article coated with a coating composition as defined in any one of claims 1 to 9.

Inventors: HORIISHI NANAO, KATAMOTO TSUTOMU, MATSUZAKI SATORU, OKURA KEN, HORIISHI, NANAO, KATAMOTO, TSUTOMU, MATSUZAKI, SATORU, OKURA, KEN
Applicants: DAINICHISEIKA COLOR CHEM, TODA KOGYO CORP, DAINICHISEIKA COLOR & CHEMICALS MFG. CO. LTD., TODA KOGYO CORP.
Application year: 1990
Main classification: C09D7
IPC codes: C09D5, C09D7, C09C1