Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-29
2001-09-18
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S407000, C523S408000, C523S410000, C524S501000, C524S802000
Reexamination Certificate
active
06291554
ABSTRACT:
BACKGROUND OF THE INVENTION
Epoxy resins have been widely used in the field of bonding, packaging, coating etc. Typically, epoxy resins are used in the type of “two-part”, or called “A/B Part” type. Upon application, the main ingredient of the epoxy resin (Part A) and the curing agent (Part B) are admixed in a proper ratio in accordance with the epoxide equivalent weight (EEW) of the epoxy resin to the equivalent weight of the curing agent, and then cured. The application properties of the epoxy resins include curing rate which depends on the EEW thereof, the chemical structure and reactivity of the curing agents and the ratio between Parts A and B. Particularly, dosing the exact and accurate amounts of the epoxy resins and the curing agents is the most difficult step to control, especially, when the factors of equipment and manual-operation in the workplace are taken into account. These bothersome problems often arise when two-part type epoxy resins are used. Further, epoxy resins with high EEW (>250) are in solid form at ambient temperature and accordingly, need to be formulated into liquid solution with solvents such that the cross-linking agent can be admixed homogeneously. Thus the use of solvent cannot be eliminated under this circumstance. In particular, the emission of the solvents from epoxy resin coating composition result in not only the economic loss but also the damages to the environment protection, safety and hygiene.
At present, the aqueous epoxy resin emulsions are prepared by adding emulsifiers to conventional solvent-type epoxy resins and adding water to emulsify the resulting mixture. However, emulsification exerted by the emulsifiers added is limited by the critical micelle concentration of the aqueous epoxy resin emulsions and therefore, aggregation will occur in the emulsions under the situation where the emulsions are arbitrarily diluted with water or are blended with other aqueous resins. As a result of the foregoing, such aqueous epoxy resin emulsions obtained thorough emulsification with emulsifiers are not widely accepted in this field.
It is therefore a worldwide trend to replace the conventional solvent type resins with aqueous resins.
SUMMARY OF THE INVENTION
The present application provides an self-emulsified aqueous epoxy resin dispersion. The present dispersion is prepared by reacting a commercial epoxy resin with a dicarboxylic acid anhydride whereby the secondary hydroxy group of the epoxy resin are esterified with the dicarboxylic acid anhydride, while resulting in introducing a carboxyl group into the epoxy resin, adding a tertiary amine to the resultant carboxyl-containing epoxy resin in an amount at least stoichiometrically required to react with said carboxyl groups, such that the carboxyl groups in the epoxy resin are converted into the hydrophilic tertiary amine carboxylate groups, adding water to the reaction product, whereby self-emulsifying the epoxy resin. The present invention also provides a single-pack double curable aqueous resin system which comprises an aqueous resin containing an epoxy group and a tertiary amine carboxylate group, and as a cross-linking agent a polyaziridine in an aqueous medium. Upon application in coating, free carboxyl groups are liberated from the tertiary amine carboxylate groups of the aqueous epoxy resin through the action of carbon dioxide in the atmosphere and react with the reacting group, that is, ethylenimine groups of the polyaziridine, as a cross-linking agent, under common curing condition to form hydrophobic aminoester groups among the aqueous resin molecules. The amino groups in the resultant aminoester groups further react with the terminal epoxy groups of the epoxy resin to run second cross-linking reaction via ring-opining thereby completing a double curing in the aqueous epoxy resin. Furthermore, aqueous resins containing both carboxyl and epoxy groups or only carboxyl group such as aqueous acrylate resin and polyurethane (PU) resin can be cured by making use of this curing system. Also provided is a single-pack curable hybrid resin which is prepared by blending a mixture of the self-emulsified aqueous epoxy resin according to the present invention and the commercial aqueous resin mentioned above in various ratios with a polyaziridine as a cross-linking agent.
REFERENCES:
patent: 3862914 (1975-01-01), Anderson et al.
patent: 4179440 (1979-12-01), Martinez
patent: 5439952 (1995-08-01), Lum et al.
Chen Kan-Nan
Chen Tsorng-Wen
Lin Yun-Shan
Yeh Jen-Taut
Aylward D.
Beyer Weaver & Thomas LLP
Chinese Petroleum Corp.
Dawson Robert
LandOfFree
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