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
1999-12-23
2002-03-19
Boykin, Terressa M. (Department: 1711)
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
active
06359067
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermosetting powder coating composition, and more specifically, it relates to a thermosetting powder coating composition which has excellent coating characteristics (impact resistance, chipping resistance, adhesive properties, weathering resistance and the like) and excellent coating appearance and which can particularly provide a baked coating film suitable for the use of automobile coating.
BACKGROUND ART
[Research development trend and expectation of a powder coating composition in the technical field of a coating composition from the viewpoints of ecology and the like]
Heretofore, solvent type coating compositions have been used for the coating of materials, and for use in the fields of automobiles and the like in which a severe quality is required, coating compositions which can meet various requirements have been developed and used. In recent years, in the technical field of the coating compositions, the change of from the solvent type coating composition to a powder type coating composition (hereinafter referred to as “the powder coating composition”) has been expected from the viewpoints of local and global environmental protection, labor safety hygiene environmental improvement, the prevention of fire and explosion, the saving of resources, and the like.
As the expectation of the high function and diversification of the powder coating composition increases in accordance with historical and social demand, it becomes required that the powder coating composition possesses such high coating film performances (e.g., impact resistance and acid rain resistance) as to be equal to those of the solvent type coating composition.
However, the performances of a coating film which are required for the powder coating composition become more and more strict, but it is not always recognized that the powder compositions which can completely meet such requirements are on the market.
[Technical Background of Usual Powder Coating Compositions]
Typical examples of conventional powder coating compositions include epoxy resin and polyester resin powder coating compositions mainly comprising bisphenol A. In these coating compositions, however, weathering resistance is insufficient, and what is worse, the resistance to acid rain which is nowadays particularly noticeable is also insufficient. In consequence, these coating compositions are unsatisfactory in an outdoor use such as the coating of automobile bodies.
In order to overcome these drawbacks, an acrylic powder coating composition has been suggested in Japanese Patent Publication No. 38617/1973, whereby the weathering resistance has been remarkably improved. However, in points of impact resistance and chipping resistance, this acrylic powder coating composition is inferior to the conventional polyester-based powder coating composition. That is to say, the powder type coating composition which can simultaneously meet all of the weathering resistance, the impact resistance and the chipping resistance is not always considered to be on the market.
As understood from the above, the powder coating composition which can simultaneously satisfy the weathering resistance and the impact resistance is desired from the market, and research and development have been intensively conducted with the intention of putting such a coating composition to practical use.
[Technical background regarding the improvement of the impact resistance of the coating film of the acrylic powder coating composition]
In the course of the development regarding the acrylic powder coating composition, there have been disclosed techniques of improving low-temperature setting properties and re-coat properties in, for example, (1) Japanese Patent Application Laid-Open No. 112743/1993 in which a dibasic acid or the like is mixed, and (2) Japanese Patent Application Laid-Open No. 165463/1988 in which an alkyl titanate is mixed. In both the techniques, however, the impact resistance is merely mentioned as a secondary effect, and its effect is not always sufficient. Next, both the techniques (1) and (2) will be described.
(1) Japanese Patent Application Laid-Open No. 112743/1993
There is herein disclosed a technique of obtaining a powder type coating composition having the excellent setting properties. That is to say, the publication discloses a powder type coating composition which comprises (A) a copolymer having a glycidyl group, (B) an aliphatic or an alicyclic dibasic acid, its anhydride or a polyol-modified anhydride of the dibasic acid, and (C) if necessary, a pigment and other additives. This copolymer (A) has a number-average molecular weight (Mn) of 1,000 to 10,000 and a glass transition temperature of 30 to 90° C. Such a copolymer can be obtained from (a) at least 20% by weight of glycidyl acrylate or glycidyl methacrylate, (b) 35 to 50% by weight of styrene, (c) 10 to 45% by weight of one or more alkyl esters of an aliphatic unsaturated monocarboxylic acid or dicarboxylic acid, and (d) 0 to 50% by weight of one or more unsaturated other olefin monomers.
(2) Japanese Patent Application Laid-Open No. 165463/1988
In this publication, there is disclosed a thermosetting acrylic powder coating composition which contains a specific glycidyl group functional acrylic resin, an aliphatic dibasic acid (anhydride) and an alkyl titanate compound as main components and which can be molten and set at a low temperature and which can provide a coating film having excellent hardness, impact resistance, flexing resistance and the like. That is to say, there is herein disclosed a thermosetting acrylic powder coating composition mainly comprising (A) a glycidyl group functional acrylic resin obtained by copolymerizing an alkyl ester having 1 to 14 carbon atoms of (meth)acrylic acid and a glycidyl ester of (meth)acrylic acid as the main components, (B) an aliphatic dibasic acid (preferably adipic acid, sebacic acid, decanedicarboxylic acid, muconic acid or the like) or its acid anhydride, and (C) an alkyl titanate compound (e.g., tetrapentadecyl titanate) represented by Ti(OR)
4
(wherein R is an alkyl group having 15 to 20 carbon atoms).
The present inventors have intensively investigated coating films on the surfaces of bodies and chassis of vehicles such as automobiles against which gravel and pebbles hit at a high relative velocity during running and which are exposed to the sunlight outdoors without any shelter or severe weather conditions, and as a result, in the best mode of this technique, it has been confirmed that the impact resistance is excellent but the chipping resistance as well as the appearance and the weathering resistance of the coating films are poor. That is to say, this powder coating composition is not always suitable for the above-mentioned use application.
[Technical background regarding the improvement of the impact resistance of the coating film of a coating composition including a thermoplastic elastomer]
With regard to the improvement of the impact resistance of the coating film of the coating composition including a thermoplastic elastomer, for example, the following techniques (1) to (3) are disclosed. However, it is difficult to apply these techniques to thermosetting powder coating compositions and acrylic thermosetting powder coating compositions.
(1) Japanese Patent Publication Nos. 74367/1992 and 17721/1995
In these publications, there is disclosed a resin composition for a coating composition obtained by polymerizing a vinyl monomer (B) including 50% by weight or more of an acrylic ester or a methacrylic ester having an alkyl group of 1 to 8 carbon atoms or a cyclohexyl group in an inert solvent in which a hydrogenated compound of a styrene-butadiene-styrene block copolymer or a hydrogenated compound (A) of a styrene-butadiene-styrene block copolymer graft-modified with maleic acid or its acid anhydride is dissolved [a weight ratio (A/B)=2/8 to 7/3]. This resin composition for the coating composition is considered to be excellent in weathering resist
Kikuta Yoshio
Matsumoto Tsuyoshi
Miyawaki Takahisa
Mizoguchi Mitsuyuki
Sakayama Hiroyuki
Boykin Terressa M.
Burns Doane Swecker & Mathis L.L.P.
Mitsui Chemicals Inc.
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