Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-09-01
2003-09-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S261000, C524S267000, C524S388000
Reexamination Certificate
active
06613826
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Technical Field
The present invention relates to an aqueous coating composition which can improve poor appearance caused when plastic materials are directly coated with the composition by a high-volume-low-pressure (HVLP) gun, namely, which gives good sprayability.
B. Background Art
Plastic materials utilized for automotive interior parts include polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), poly(phenylene oxide) (PPO) and polycarbonate (PC). In recent years, polyolefin materials are getting often used in view of cost and recyclability.
Until now, these plastic materials were coated with organic solvent type paints or aqueous paints by spray guns, such as a HVLP gun and a conventional air-spray gun.
Among these conventional coating methods, the combination of the aqueous paint and the HVLP gun is regarded as important in recent years because of environmental conservation and reducing cost.
However, water is evaporated a little when the aqueous paint is sprayed. Then, the viscosity rises a little after spray-coating and the aqueous paint is easily sagged. Therefore, the viscosity of the paint should be determined higher. However, a high viscosity paint is difficult to atomize. Particularly, bubbles occur by use of a low-pressure-atomizing-type paint and causes poor appearance.
Therefore, a low viscosity paint is used at the sacrifice of sagging performance, or an air-spray gun having good atomizability is used at the sacrifice of transfer efficiency inevitably.
SUMMARY OF THE INVENTION
A. Object of the Invention
An object of the present invention is to provide: a high viscosity aqueous coating composition, which can be coated onto plastic materials such as polyolefin materials by a HVLP gun, and which has excellent sagging performance and can obtain a coating film with good appearance.
B. Disclosure of the Invention
The present inventors made various experiments to solve the above-mentioned problems. As a result, they found the following two phenomena as mechanisms which cause the poor appearance.
That is to say, as is mentioned in the above way, the first phenomenon is that small bubbles generated due to bad atomizability remain on coating film surfaces in the drying step, and therefore, rough appearance is obtained. The second phenomenon is in the following. The plastic material is a material having lower surface tension. However, the high viscosity aqueous paint has higher surface tension. Therefore, the wettability is insufficient, and large bubbles are formed on the interface between the plastic material and the aqueous paint. When the bubbles become flat in the drying step, pin holes and blotchy appearance occur on coating film surfaces.
The present inventors further made various experiments. As a result, they found that an acetylene diol defoamer is effective to the small bubbles, and a silicone wetting agent is effective to the large bubbles. Then, they confirmed that the above-mentioned problems are solved by combining these two kinds of additives and blending them in a specific amount respectively, and they completed the present invention.
Accordingly, an aqueous coating composition, according to the present invention, comprises an acetylene diol defoamer and a silicone wetting agent in addition to a film-formable component, wherein the nonvolatile solid content of the acetylene diol defoamer is in the range of 0.25 to 1.0 weight % of the entirety of the aqueous coating composition, and the nonvolatile solid content of the silicone wetting agent is in the range of 0.75 to 2.0 weight % of the entirety of the aqueous coating composition.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous coating composition, according to the present invention, comprises a film-formable component, an acetylene diol defoamer, and a silicone wetting agent as essential components, and can further comprise an organic solvent as a promoter for forming coating films, and other additives such as colorants if necessary.
Hereinafter, these and other components are explained in detail.
[Essential Components Comprised in Coating Composition]
(Film-formable Component)
The film-formable component is not especially limited to the kind if the component is a film-formable resin. This resin is ordinary used as a form of emulsion including this resin (resin emulsion).
These resin emulsions are not especially limited, but examples thereof include an emulsion including a polypropylene chloride resin and/or a water-insoluble acrylic resin.
The polypropylene chloride resin is not especially limited, but example thereof includes a polypropylene derivative comprising a polypropylene chloride moiety and a maleic anhydride moiety as bonded to this propylene chloride moiety.
Examples of the water-insoluble acrylic resin include resins obtained by homopolymerizing or copolymerizing acrylic monomers having a hydroxyl group, acrylic monomers having a carboxyl group, or acrylic monomers having an ester group.
The water-insoluble acrylic resin may be modified by the above polypropylene chloride resin.
The emulsification of the above resins is carried out by conventional methods for producing emulsions as used for paints.
(Acetylene Diol Defoamer)
The acetylene diol defoamer prevents surface flatness defect from being caused by small bubbles which are formed when being coated with a high viscosity paint by a HVLP spray gun.
Examples of the acetylene diol defoamer include Sufinol 104 (made by Air Products), and Dinol 604 (made by Air Products).
(Silicone Wetting Agent)
The silicone wetting agent prevents surface flatness from being damaged by large bubbles which are formed on the interface between the plastic material and the aqueous coating composition according to the present invention.
Examples of silicone wetting agent include Coatosil 1211 (made by Witco Corporation), Polyflow KL-245 (made by Kyoeisha Chemical Co., Ltd.). These silicone wetting agents include dimethylpolysiloxane, and blocked or grafted polymers of alkylene glycols as effective components.
[Aqueous Coating Composition]
In the present invention, the nonvolatile solid content of the acetylene diol defoamer is in the range of 0.25 to 1.0 weight %, preferably 0.35 to 0.75 weight %, more preferably 0.35 to 0.5 weight %, of the entirety of the aqueous coating composition. In case where the nonvolatile solid content of the acetylene diol defoamer is less than 0.25 weight %, the surface flatness is lowered because of the small bubbles. On the other hand, in where the nonvolatile solid content of the acetylene diol defoamer is more than 1.0 weight %, the sagging performance is lowered and the finishing state of coating film surfaces is deteriorated.
In the present invention, the nonvolatile solid content of the silicone wetting agent is in the range of 0.75 to 2.0 weight %, preferably 0.75 to 1.5 weight %, more preferably 0.75 to 1.0 weight %, of the entirety of the aqueous coating composition. In case where the nonvolatile solid content of the silicone wetting agent is less than 0.75 weight %, the surface flatness is lowered because of the large bubbles, and the poor condition such as blotchy appearance is caused. On the other hand, in case where the nonvolatile solid content of the silicone wetting agent is more than 2.0 weight %, the tack remains on the coating film surfaces, and the finishing state of the coating film surfaces is deteriorated.
In the present invention, the content of the film-formable component is not especially limited, but is determined in consideration of the adhesion and economy.
In the aqueous coating composition according to the present invention, other resins may fitly be combined just as a film-formable component in order to raise the toughness of cured coating films.
Water-soluble acrylic resins are the most preferable of the above other aqueous resins, but emulsions of resins other than the water-soluble acrylic resins, such as pol
Fritcher Jesse
Kim Juhan
Makarewicz Jeffrey
Haugen Law Firm PLLP
Rajguru U. K.
Seidleck James J.
Toyota Technical Center U.S.A., Inc.
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