Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-01-12
1997-06-10
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
524513, 524515, 524516, 524517, 524522, 525163, C08F 2000
Patent
active
056376561
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP94/00893 filed Jun. 02, 1994.
TECHNICAL FIELD
The present invention relates to an aqueous resin composition for outer surface coating of can, which gives a coating film of excellent resistance to pasteurization, excellent hardness and excellent processability and which generates, during the baking of the coating film, a reduced amount of a vapor or mist of low-molecular weight (low fuming) from the alkyl-etherified amino resin component.
BACKGROUND ART
In recent years, conventional solvent type coatings are being shifted to aqueous coatings in order to prevent the air pollution caused by the organic vapors emitted from said solvent type coatings.
Ordinary aqueous coatings for can comprise a film-forming resin and a crosslinking agent. As the crosslinking agent, there is mainly used an alkyl-etherified melamine resin or an alkyl-etherified benzoguanamine resin.
As these amino resins, there is used an alkyl-etherified amino resin containing a functional group such as imino group, methylol group or the like, or a completely alkyl-etherified amino resin. There is also used an amino resin containing a mononuclear component in a large amount, in order to allow the resulting aqueous coating to have sufficient water solubility.
When such an amino resin is used as the crosslinking agent, however, a vapor of low-molecular weight substance is emitted from the alkyl-etherified amino resin during the baking of the aqueous coating composition containing the amino resin, and reaches the inner wall of the curing oven and condenses; the condensate drops on the coated article; resultantly, there occur problems such as the deterioration of coated surface, the necessity of frequent cleaning of oven inside, and the like. Hence, an improvement therefor is desired.
There also remain, in some cases, a problem of the insufficient stability of coating caused by an alkyl-etherified amino resin of insufficient water solubility, and a problem of poor resistance to pasteurization, insufficient hardness and processability, caused by the high content of mononuclear component.
The techniques for making water-soluble a water-insoluble alkyl-etherified amino resin are disclosed in U.S. Pat. No. 3,464,946, U.S. Pat. No. 3,444,114, etc. When the resulting amino resin is used as a crosslinking agent for outer surface coating of can, however, the coating is not satisfactory in fuming during baking as well as in film properties such as resistance to pasteurization, hardness, processability and the like.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an aqueous resin composition for outer surface coating of can, which gives a coating film of excellent resistance to pasteurization, excellent hardness and excellent processability and which can greatly reduce fuming during the baking of coating film.
The present inventor made an extensive study in order to solve the above-mentioned problems. As a result, the present inventor found out that the molecular weight of an amino resin used as a crosslinking agent has a sufficient influence on the resistance to pasteurization and on the processability of coating film as well as on the fuming during baking. The present inventor also found out that when an amino resin is made water-soluble by treating with a hydroxycarboxylic acid and the resulting amino resin-oxycarboxylic acid condensate containing a lower amount of a mononuclear component is used as a crosslinking agent, the resulting aqueous coating retains excellent processability, gives a coating film of excellent hardness and resistance to pasteurization and reduces fuming during baking. The finding has led to the completion of the present invention.
The present invention provides an aqueous resin composition for outer surface coating of can, which is characterized by comprising 30-70 parts by weight of a crosslinking agent (A) which is obtained by subjecting an alkyl-etherified amino resin and a hydroxycarboxylic acid to co-condensation and which contains a mononuclear componen
REFERENCES:
patent: 3464946 (1969-09-01), Downing
patent: 4981885 (1991-01-01), Engel et al.
Michl Paul R.
Mitsui Cytec Ltd.
Rajguru U. K.
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