Coating processes – With post-treatment of coating or coating material – Coating material recirculation or regeneration
Reexamination Certificate
1999-09-02
2001-06-26
Dawson, Robert (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Coating material recirculation or regeneration
C521S040000, C523S423000
Reexamination Certificate
active
06251483
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a recyclable cold curing aqueous coating composition and a method for recycling an excess of the aqueous coating composition after applying to an article. Particularly, the present invention relates to a recyclable cold curing aqueous coating composition having a specified formulation, which shows excellent water resistance and corrosion resistance, and a method comprising the steps of collecting the aqueous coating composition in a coating booth by using a collecting solution, filtering the collected coating composition to separate into a concentrated coating composition and a filtrate, and subsequently adjusting the each for recycle use.
BACKGROUND OF THE INVENTION
Aqueous coating compositions having corrosion resistance are generally used as a primer for automobile parts, industrial machines, agricultural machines and the like. When the aqueous coating compositions are applied on a workpiece having poor heat resistance or high heat capacity, the coating compositions have to be dried and cured at a temperature of not more than 80° C. and therefore are generally called as cold curing aqueous coating compositions.
When the cold curing aqueous coating compositions are subjected to spray coating in a coating booth, much amount of paint dust that has not been deposited on a substrate is present. The spray dust is dissolved and dispersed into a booth aqueous solution (that may be called as a collecting solution, hereinafter) in the coating booth to collect. An amount of the collected spray dust in the above way is very large, and if it is disposed by itself, it is waste of paint as well as environmental pollution.
Many efforts to recycle the spray dust collected in the collecting solution have been made, and for example a recycle method is proposed in Japanese Patent Kokai Publication Sho 49 (1974)-51324. The method disclosed in the Japanese Publication comprises collecting the spray dust of the aqueous coating composition with water as a collecting solution to obtain a diluted solution of the aqueous coating composition, filtering the diluted solution through a reverse osmosis membrane or an ultrafiltration membrane, and concentrating and collecting the filtered composition. The concentrated coating composition is then subjected to an adjustment of non-volatile content to a level capable of recycle use. Herein, the “non-volatile” components mean components which are not volatilized away in the aqueous coating composition, including film-forming aqueous resin (such as aqueous alkyd resin and aqueous acrylic resin), pigment and the like.
The method as described in the Kokai Publication, however, has a problem that when filtering and concentrating the diluted solution of the aqueous coating composition with an ultrafiltration membrane, etc., an aqueous solution separated as a filtrate is produced with a very large amount. The collected coating components are reusable, but the aqueous filtrate is generally disposed away. There is a proposal that the aqueous filtrate is returned to the coating booth as the collecting solution and used again for collecting the spray dust.
However, both of the concentrated coating composition and the aqueous filtrate separated from the diluted solution of the aqueous coating composition involve many disadvantages when reusing. For example, since the concentrated coating composition has a reduced volatile content and less amounts of neutralizing amine and solvent, the hydration stability of the resin contained therein decreases, and therefore, an aggregation or separation of the aqueous coating composition may occur. The aqueous filtrate may also aggregate or separate the aqueous coating composition in recycle use.
In order to eliminate the above disadvantages, a method for improving the hydration stability of the resin in recycle use by increasing the hydrophilic property of the resin contained in the original aqueous coating composition is proposed. On applying the above proposal, however, film performances of the coating formed from the aqueous coating composition, such as corrosive resistance, water resistance, and the like, may deteriorate.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a recyclable cold curing aqueous coating composition having excellent water resistance and corrosive resistance, which improves the efficiency of filtration and concentration of the aqueous coating composition collected with a collecting solution for recycle use (which is called as a diluted solution of the aqueous coating composition hereinafter), without separation and aggregation of the resin or pigments.
Another object of the present invention is to provide a method for recycling the recyclable cold curing aqueous coating composition, wherein a dielectric constant of the collecting solution is controlled to obtain good recyclable properties for a long period.
Accordingly, the present invention provides a recyclable cold curing aqueous coating composition, comprising:
(a) an oxidative-polymerizable, modified epoxy resin with an acid value of 25 to 60, comprising 20 to 70 percents by weight of an epoxy resin based on the total weight of said modified epoxy resin, of which a particle size is not more than 200 nm in an aqueous medium;
(b) an anticorrosive pigment and/or an ampholytic metal oxide; and
(c) a drier.
The present invention further provides a method for recycling a recyclable cold curing aqueous coating composition, which comprises the following steps:
i) collecting the cold curing aqueous coating composition which has not been coated on an article in a coating booth by using a collecting solution;
ii) filtering and concentrating the collected coating composition to separate into a concentrated coating composition and a filtrate; and
iii) recycling the concentrated coating composition to be used as the recyclable cold curing aqueous coating composition, and recycling the filtrate to be used as the collecting solution, wherein said recyclable cold curing aqueous coating composition comprising:
(a) an oxidative-polymerizable, modified epoxy resin with an acid value of 25 to 60, comprising 20 to 70 percents by weight of an epoxy resin based on the total weight of said modified epoxy resin, of which a particle size is not more than 200 nm in an aqueous medium;
(b) an anticorrosive pigment and/or an ampholytic metal oxide; and
(c) a drier, said collecting solution having a dielectric constant of 20 to 70.
Most preferably, in the method for recycling a recyclable cold curing aqueous coating composition as mentioned above, the filtering and concentrating step ii) may be conducted in an ultrafiltration unit.
According to the present invention, the cold curing aqueous coating composition which is recyclable for a long period can be provided by using a certain oxidative-polymerizable, modified epoxy resin.
The present invention provides the cold curing aqueous coating composition which can be repeatedly used for a long period by specifying a resin composition, as well as controlling the dielectric constant of the collecting solution.
REFERENCES CLOSE TO THE PRESENT INVENTION
The Japanese Patent Kokai Publication Hei 6 (1994)-136296, of which the Applicant is the same as one of Applicants of the present application, describes a method for recycling an anti-corrosive aqueous coating composition, which comprises the steps of: controlling an electric conductivity of the aqueous coating composition, filtering a diluted solution of the aqueous coating composition collected with water after coating, and then adjusting the electric conductivity of the filtered coating composition to reuse. The Japanese Kokai Publication describes that the anti-corrosive aqueous coating composition comprises an epoxy resin and a pigment (e.g. a colorant, a filler or an anti-corrosive pigment), but does not disclose that the aqueous coating composition comprises an oxidative-polymerizable, modified epoxy resin as described in the present invention. The aqueous coating composition as described in the Japa
Hibi Susumu
Sueyoshi Junichi
Watanabe Masakazu
Yamauchi Masahiro
Aylward D.
Dawson Robert
Nippon Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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