Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-06-21
2004-01-27
Chen, Vivian (Department: 1773)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S437000, C525S441000, C525S443000, C427S407100, C428S480000, C428S482000
Reexamination Certificate
active
06683137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an intermediate coating composition which not only allows shortening a period of baking but also has an excellent appearance and good adhesion thereof to a top coating film, a method for forming multilayered coating films, and multilayered coating films.
2. Description of Related Art
Multilayered coating films have been conventionally formed on metallic base materials to be coated to provide corrosion-resistance as well as excellent appearance. In the automobile coating, one method comprises applying a thermosetting intermediate coating and baking it, successively applying a thermosetting top coat base coating on said baked intermediate coating without baking the top coat base coating, and applying a thermosetting top coat clear coating by wet-on-wet, and then simultaneously curing the top coat base coating and top clear coating. In another method, a thermosetting top coat solid coating is applied to said baked intermediate coating film and cured by baking.
Furthermore, in the automobile line for coating, in spite of requests for minimizing the baking period as much as possible to improve efficiency of the coating process, most of the automobile line for intermediate coating has been operated at 140° C. for 30 minute at present.
Although development of an intermediate coating has been in progress which is durable to the automobile line for intermediate coating under baking conditions at 140° C. for 15 minute, coating conditions unfavorably affect the appearance of coating film and adhesion to the top coating.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an intermediate coating composition, a method for forming multilayered coating films and multilayered coating films, wherein, by specifying the acid value and cross linking agent of said intermediate coating resin, multilayered coating films can have an excellent appearance and good adhesion to the top coating under brief baking conditions. Moreover, said intermediate coating composition is capable of retaining the storage stability, so that the coating process can be shortened.
In view of the aforementioned problems, the present inventors have actively pursued studies to achieve the present invention as follows:
1. An intermediate coating composition comprising a high-acid-value polyester resin, low-acid-value polyester resin, melamine resin containing imino groupsand pigment, wherein the ratio (AV
1
/AV
2
) of the acid value of a high-acid-value polyester resin (AV
1
) to that (AV
2
) of a low-acid-value polyester resin is in the range of 1.25-5.0.
2. The intermediate coating composition being free of an acid catalyst for promoting reaction of said melamine resin with said high-acid-value polyester resin and said low-acid-value polyester resin.
3. The intermediate coating composition, wherein the weight ratio (P1/P2) of said high-acid-value polyester resin (P1) to said low-acid-value polyester resin (P2) is as follows: P1/P2=30/70-90/10.
4. The intermediate coating composition wherein said high-acid-value polyester resin has a number-average molecular weight in the range of 2,000-4,000, hydroxyl group value in the range of 90-120, and acid value in the range of 15-40.
5. The intermediate coating composition wherein said high-acid-value polyester resin is a lactone-modified polyester resin, the lactone content in said lactone-modified polyester resin being in the range of 10-30 percent by weight as converted to solid portions.
6. The intermediate coating composition wherein said low-acid-value polyester resin has a number-average molecular weight in the range of 2,000-4,000, a hydroxyl group value in the range of 90-120, and an acid value in the range of 5-12.
7. The intermediate coating composition wherein said melamine resin containing an imino group is a methyl/butyl mixed alkylated melamine resin containing high imino-groups, methylated melamine resin containing high imino groups or butylated melamine resin containing high imino groups.
8. The intermediate coating composition wherein the melamine resin contains 50-100 percent by solid weight of a methyl/butyl mixed alkylated melamine resin containing high imino-groups.
9. A method for forming multilayered coating films, comprising the steps of:
forming the intermediate coating composition on an undercoated base material; and
forming a top coating.
10. Multilayered coating films obtained by said method for forming multilayered coating films.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the present invention will be described below in more detail.
Intermediate Coating Composition
One embodiment of an intermediate coating composition according to the present invention is an intermediate coating composition comprising a high-acid-value polyester resin, a low-acid-value polyester resin, a melamine resin containing an imino group and a pigment, wherein a ratio (AV
1
/AV
2
) of the acid value (AV
1
) of the high-acid-value polyester resin to the acid value (AV
2
) of the low-acid-value polyester resin is adjusted to be in the range of 1.25-5 so as to minimize a baking period in the automobile line for intermediate coating and to provide an excellent appearance and adhesion to the top coating on the intermediate coating. In the following, specific construction as well as operation and effects of the intermediate coating composition will be described.
A resin which is a condensation product of polyalcohol with polycarboxylic acid is used as the polyester resin. The resin also includes an alkyd resin obtained by adding components for providing fatty acid residues derived from natural drying oil or semi-drying oil. These resins contain free hydroxyl and carboxyl groups in a predetermined proportion which allow reactions with a standard cross-linking agent.
Polyalcohols suitable for manufacturing polyester resins include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, tripentaerythritol, hexanetriol and condensation products of trimethylolpropane and ethylene oxide or propylene oxide.
Appropriate carboxylic acids include succinic acid (or anhydride thereof), adipic acid, azelaic acid, sebacic acid, maleic acid (or anhydride thereof), fumaric acid, mucoic acid, itaconic acid, phthalic acid (or anhydride thereof), isophthalic acid, terephthalic acid, trimellitic acid (or anhydride thereof) and pyromellitic acid (or anhydride thereof), also including fatty acids derived from natural drying oils or semi-drying oils such as linseed oil, soybean oil, tall oil, dehydrated castor oil, fish oil and tung oil, and those derived from safflower oil, sunflower oil and cottonseed oil. Usually, oil length of such alkyd resins does not preferably exceed 50%. For the purpose of providing plasticity on polyesters, monofunctional saturated carboxylic acids may be further combined therewith. Examples of these carboxylic acids may include C
4
-C
20
saturated fatty acids, benzoic acids, p-tertiary butyl benzoate and abietic acid.
An intermediate coating composition of the present invention is characterized in that the acid values of polyester resins thereof are set to have a specific ratio between the high-acid-value polyester resin (P1) and the low-acid-value polyester resin (P2) present in the composition, and the acid values can be controlled by adjusting an amount of terminal carboxyl groups.
The specific ratio is a ratio (AV
1
/AV
2
) of the acid value (AV
1
) of the high-acid-value polyester resin (P1) to the acid value (AV
2
) of the low-acid-value polyester resin (P2), being in the range of 1.25-5. When this ratio is less than 1.25, curing becomes insufficient. In contrast, when the ratio exceeds 5, appearance of intermediate coating and adhesiveness thereof to a top coating become insufficient because of excessive curing. Preferably, the ratio is in the range of 1.5-3.5.
The high-acid-value polyester resin (P1) preferably has a number-ave
Kida Masuo
Tanaka Yasuo
Chen Vivian
Nippon Paint Co. Ltd.
Pennie & Edmonds LLP
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