Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-01-05
2002-06-25
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C204S489000, C204S505000, C204S506000, C523S404000, C523S406000, C523S414000, C523S415000, C523S417000
Reexamination Certificate
active
06410146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cationic electrodeposition coating composition. In particular, it relates to a cationic electrodeposition coating composition which contains a curing agent that has been blocked with a terminal primary OH-containing propylene glycol monoalkyl ether.
2. Description of the Related Art
Blocked isocyanate curing agents are generally used in cationic electrodeposition coatings. The blocked isocyanate curing agents are obtained by reacting a polyisocyanate compound with a blocking agent which is reacted with the isocyanate groups and stable at ambient temperature, but can regenerate free isocyanate groups when heated to a dissociation temperature or higher. The blocking agents contain an active hydrogen and can be suitably selected according to the type of polyisocyanate compound to be employed.
However, the increasing level of awareness of environmental issues of late have been accompanied in developed countries by efforts to regulate the amounts of hazardous atmospheric pollutants (HAPs). Since the blocked isocyanate curing agents release blocking agents into the atmosphere when heated, the blocked isocyanate curing agents also need to be considered as a substance under HAPs as blocked by a substance which is considered as a HAPs. For example, conventionally used cationic electrodeposition coating compositions contain diphenyl methane diisocyanates (MDI) which are blocked with E-caprolactam and butyl cellosolve. Since both of the blocking agents are HAPs substances, there is the concern that their use is banned through enforcement of the environmental regulatory standards.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cationic electrodeposition coating composition which contains a blocked isocyanate curing agent that has been blocked with a substance not recognised as a HAPs.
The cationic electrodeposition coating composition of the present invention contains an epoxy-modified base resin having a cationic group and a blocked isocyanate curing agent, wherein the blocked isocyanate curing agent is obtained by reacting a polyisocyanate compound with a terminal primary OH-containing propylene glycol monoalkyl ether as a blocking agent, as expressed by the formula RO(CH(CH
3
)CH
2
O)
n
H (where R is an alkyl group having 1 to 8 carbons, which may be branched, and n is 1 to 3). The polyisocyanate compound described above is e.g. diphenyl methane diisocyanate, and R in the formula for the propylene glycol monoalkyl ether is an n-butyl group and n is 1 to 2.
In addition, an article is coated using the cationic electrodeposition coating composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cationic electrodeposition coating composition of the present invention contains an epoxy modified base resin having a cationic group and a blocked isocyanate curing agent.
The blocked isocyanate curing agent contained in the cationic electrodeposition coating composition of the present invention is obtained by reacting a polyisocyanate compound with a terminal primary OH-containing propylene glycol monoalkyl ether as a blocking agent, as expressed by the formula RO(CH(CH
3
)CH
2
O)
n
H (where R is an alkyl group having 1 to 8 carbons, which may be branched, and n is 1 to 3).
Examples of the polyisocyanate compound include alkylene diisocyanate, such as trimethylene diisocyanate, trimethyl hexamethylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate; cycloalkylene diisocyanate, such as bis(isocyanatomethyl)cyclohexane, cyclopentane diisocyanate, cyclohexane diisocyanate, and isophorone diisocyanate; aromatic diisocyanate, such as tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, and diphenylether diisocyanate; aromatic/aliphatic diisocyanate, such as xylylene diisocyanate, and diisocyanate diethylbenzene; triisocyanate, such as triphenylmethane triisocyanate, triisocyanate benzene, and triisocyanate toluene; tetraisocyanate, such as diphenyl dimethyl methane tetraisocyanate; polymerized polyisocyanate, such as dimer or trimer of tolylene diisocyanate; and terminal isocyanate-containing compounds which are obtained by reacting the above polyisocyanate compounds with a low molecular active hydrogen-containing organic compound such as ethylene glycol, propylene glycol, diethylene glycol, trimethylol propane, hydrogenated bisphenol A, hexanetriol, glycerine, pentaerythritol, castor oil and triethanolamine; and the like.
On the other hand, the terminal primary OH-containing propylene glycol monoalkyl ether is a compound expressed by RO(CH(CH
3
)CH
2
O)
n
H. In the formula, R is an alkyl group having 1 to 8 carbons, which may be branched. Specific examples of alkyl groups include methyl groups, ethyl groups, n-propyl groups, isopropyl groups, n-butyl groups, isobutyl groups, t-butyl groups, amyl groups, hexyl groups, octyl groups and 2-ethylhexyl groups. The number n is 1 to 3, but does not have to be an integer. A preferable formula for the propylene glycol monoalkyl ether has R as an n-butyl group and n being a number between 1 and 2.
The reaction between the polyisocyanate compound and the terminal primary OH-containing propylene glycol monoalkyl ether can be conducted using a well-known method. For example, the polyisocyanate compound is dissolved in a solvent which does not contain active hydrogen, then adding thereto a terminal primary OH-containing propylene glycol monoalkyl ether in an amount corresponding to the NCO equivalent in the polyisocyanate compound, in the presence of a urethanizing catalyst such as a tin compound, then heating the mixture and causing the reaction to occur. The reaction can be confirmed as having finished when the isocyanate group absorption spectrum has disappeared in an IR absorption spectrum.
The cationic group-containing epoxy modified base resin, which is another component contained in the cationic electrodeposition coating composition of the present invention, is manufactured by opening the epoxy rings in the starting material epoxy resin by bringing about a reaction with a mixture of a primary amine, secondary amine, tertiary amine acid salt or other amine, a sulfide and an acid. The term “cationic group” in the present specification shall refer to a group which is cationic in itself or a group rendered cationic by an addition of an acid. A typical example of the starting raw material resin is a polyphenol polyglycidyl ether epoxy resin formed from a reaction between bisphenol A, bisphenol F, bisphenol S, phenol novolac, cresol novolac or other polycyclic phenol compound and epichlorohydrin. Another example of the starting raw material resin is an oxazolidone ring-containing epoxy resin as taught in Japanese Patent Application Laid-open No. 5-306327. This epoxy resin is obtained by a reaction between a diisocyanate compound or a bisurethane compound obtained by blocking the NCO groups in a diisocyanate compound with methanol, ethanol or other lower alcohol, and epoxy groups.
The epoxy resin which is the starting raw material can be used after employing a bifunctional polyester polyol, polyether polyol, bisphenol or dibasic carboxylic acid for chain extension, prior to the epoxy ring-opening reaction brought about by the amine or sulfide. Similarly, in order to adjust the molecular weight or amine equivalent, or to improve the heat flow property, some epoxy rings of the epoxy resin may be reacted with 2-ethyl hexanol, nonyl phenol, ethylene glycol mono-2-ethyl hexyl ether, propylene glycol mono-2-ethyl hexyl ether or other monohydroxy compound, prior to the epoxy ring-opening reaction.
Examples of amines which can be used when opening the epoxy rings and introducing the amino groups include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine acid salt, and N,N-dimethylethanolamine acid salt or other primary amine, secondary amine or tertiary amine acid salt. A ketimine blocked primary amino group-containin
Shirakawa Shinsuke
Tsutsui Keisuke
Yamada Mitsuo
Aylward D.
Nippon Paint Co. Ltd.
Wenderoth Lind & Ponack LLP
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