Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-01-05
2002-04-09
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S400000, C523S402000, C523S414000
Reexamination Certificate
active
06369134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cationic electrodeposition coating composition which contains a plasticizer, and in particular to a cationic electrodeposition coating composition which contains a propylene oxide oligomer as a plasticizer.
2. Description of the Related Art
The level of awareness of environmental issues has increased of late, and along with it unprecedented efforts have been made to reduce the amount of organic solvents released into the atmosphere. Although cationic electrodeposition coatings contain water as a medium, and are thus aqueous in nature, they contain volatile organic compounds (VOCs) nonetheless.
Typical cationic electrodeposition coatings contain butyl cellosolve, hexyl cellosolve or another organic solvent as a plasticizer, to ensure a smooth coating film. However, as noted in the foregoing, the inclusion of these organic solvents is not preferable from an environmental standpoint. In an attempt to resolve such drawbacks, Japanese Patent Application Laid-open No. 1-69678 teaches that polypropylene glycol with a molecular weight of 1500 to 6000 can be added as a plasticizer. The polypropylene glycol which has been added migrates to the surface and be able to impart of smoothness therein. However, the propylene oxide repeating units therein contained have a low solubility parameter, and therefore if intermediate and top coats are formed on the resulting cationic electrodeposition coating film, poor adhesion results.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cationic electrodeposition coating composition which contains a plasticizer and a reduced VOC content, without having to sacrifice the good adhesion with intermediate and top coats.
The cationic electrodeposition coating composition of the present invention contains a cationic group-containing epoxy modified base resin, a blocked isocyanate curing agent and a plasticizer, wherein the plasticizer is a propylene oxide oligomer with an average molecular weight of 200 to 1500, contains a primary hydroxyl group on repeating terminals of the propylene oxide, and contains one or two primary hydroxyl groups and/or primary amino groups in the molecule.
The propylene oxide oligomer referred to in the foregoing can be represented by:
HX—CH
2
—A—Y—(CH(CH
3
)CH
2
O)nH
(where X is an oxygen atom or NH; A is a hydrocarbon group with 1 to 11 carbons which may be branched or which may have interposed oxygen atoms; Y is an oxygen atom, NH or N—A—CH
2
—XH (with A and X being the same as described above) and n is 3 to 22). An amount of plasticizer contained in such a configuration can be 2 to 15 wt % per the total solid content weight of the cationic group-containing epoxy modified base resin and blocked isocyanate curing agent.
In addition, the present invention also provides an article which is coated by the electrodeposition coating composition as mentioned above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cationic electrodeposition coating composition of the present invention contains a cationic group-containing epoxy modified base resin, a blocked isocyanate curing agent and a plasticizer.
The plasticizer contained in the cationic electrodeposition coating composition of the present invention is a propylene oxide oligomer having an average molecular weight of 200 to 1500, which contains a primary hydroxyl group on the repeating terminals of the propylene oxide and which contains one or two primary hydroxyl groups and/or primary amino groups in the molecule. If the average molecular weight falls outside the aforedescribed range, smoothness is not imparted to the coating film. A preferable average molecular weight is 600 to 1000.
The propylene oxide oligomer can be represented by:
HX—CH
2
—A—Y—(CH(CH
3
)CH
2
O)nH.
In the above expression, X is an oxygen atom or NH. Since X bonds with the hydrogen atom and the CH2, the aforedescribed plasticizer is to contain primary hydroxyl groups in the molecule when X is an oxygen atom and primary amino groups when X is NH.
A is a hydrocarbon group with 1 to 11 carbons which may be branched, or which may have interposed oxygen atoms. Y is an oxygen atom, NH or N—A—CH
2
—XH (with A and X being the same as earlier described). As is described in the following, the plasticizer contained in the cationic electrodeposition coating composition of the present invention is obtained by addition reacting propylene oxide with a starting substance selected from among diols which contain a primary hydroxyl group, amino alcohols which contain primary hydroxyl groups and primary amino groups, diamines which contain primary amino groups and polyamines which contain primary amino groups and secondary amino groups, and therefore the A is a structure obtained by removing a single methylene group from a hydrocarbon moiety which may contain the oxygen atoms and which constitutes the starting material, and the Y is a structure obtained by removing an active hydrogen from the primary hydroxyl groups, primary amino groups or secondary amino groups, with which the addition reaction is initiated.
For example, with ethylene glycols, in which the starting substance is a diol which contains primary hydroxyl groups, X and Y are oxygen atoms and A is a methylene group. With ethanolamines, in which the starting substance is an amino alcohol which contains primary hydroxyl groups and primary amino groups, X is NH, A is a methylene group and Y is an oxygen atom. With ethylene diamines, in which the starting substance is a polyamine which contains primary amino groups and secondary amino groups, X is NH, A is a methylene group and Y is N—A—CH2—XH (with A and X being the same as earlier described).
The n in the expression represents the number of repeating units in the propylene oxide. The propylene oxide repetition enables the viscosity to be reduced and the smoothness of the cationic electrodeposition coating film to be improved. A number from 3 to 22 can be taken for n, depending on the average molecular weight range and the configuration of the aforedescribed HX—CH
2
—A—Y. The plasticizer contained in the cationic electrodeposition coating composition of the present invention is a propylene oxide oligomer and therefore the value of the n does not necessarily have to be an integer.
The plasticizer contained in the cationic electrodeposition coating composition of the present invention contains a primary hydroxyl group on the repeating terminals of the propylene oxide. The primary hydroxyl group together with one or two primary hydroxyl groups and/or primary amino groups contained in the molecule contribute the curing reactivity in the cationic electrodeposition coating composition, and inhibit decrease of the corrosion resistance that is brought about by the addition of the plasticizer to be controlled.
The plasticizer can be obtained by conducting a ring-opening addition reaction in the presence of a catalyst between the propylene oxide and a starting substance comprising diols which contain primary hydroxyl groups, amino alcohols which contain primary hydroxyl groups and primary amino groups, diamines which contain primary amino groups and polyamines which contain primary amino groups and secondary amino groups. Examples of the primary hydroxyl group-containing diols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propane diol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 1,8-nonane diol, 1,10-decane diol and 1,12-dodecane diol.
Examples of the primary hydroxyl group- and primary amino group-containing amino alcohols include ethanol amine, hydroxyethylene hydrazine, 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, 2-(2-aminoethoxy)ethanol, 3-amino-1,2-propane diol, serinol, 2-amino-2-ethyl-1,3-propane diol, 2-amino-2-ethyl-1,3-propane diol, and 1,3-diamino-2-hydroxy propane.
Examples of the primary amino group-containing diamine include ethylene diamine, diaminopropane, diamino butane, diamino pentane, hexane diamine, diaminopentane, diamino
Ando Makoto
Shirakawa Shinsuke
Takegawa Masahiro
Yamada Mitsuo
Cain Edward J.
Nippon Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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