Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-07-19
2003-11-11
Chang, Ceila (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
Reexamination Certificate
active
06646153
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to novel reactive urethane compounds, their synthesis and end-uses particularly in automotive coatings with improved chemical resistance and mechanical properties. In a preferred embodiment, the invention relates to automotive paint compositions having hydroxy functional binders and a cross-linking agent such as melamine, urea or benzoguanamine formaldehyde resins (so called aminoplast resins) and/or blocked polyisocyanates (when the curing temperature is relatively high, i.e., above 80° C.) in a one-pack formulation or polyisocyanates (when the crosslinking needs to take place at lower temperatures) in 2-pack formulations.
Acrylic polyols are typically used in topcoat formulation because of the outstanding durability. However,the mechanical properties like chip resistance and scratch resistance are poor. Polyester polyols do give better mechanical properties but are poor for chemical resistance, specifically acid etch resistance. Polyurethane polyols combine excellent chemical and mechanical properties with very good durability.
U.S. Pat. Nos. 4,485,228 and 4,540,766 describe high solids coating systems based on low molecular weight polyester urethane polyols. More particularly U.S. Pat. No. 4,485,228 describes compositions crosslinked with polyisocyanates in a 2-pack system while U.S. Pat. No. 4,540,766 describes 1-pack systems crosslinked with polyisocyanates. In those patents the polyester urethane polyols are prepared by a stoichiometric excess of a polyester polyol with a polyisocyanate to avoid high molecular weight build-up during the synthesis.
U.S. Pat. No. 4,543,405 refers to low molecular weight polyurethane polyols which are prepared from a polyisocyanate with a large excess of a polyol. This excess of polyol is, after the reaction has completed, distilled-off. In related U.S. Pat. Nos. 4,540,771 and 4,605,724 the polyester polyols for the polyurethane polyols are produced from polycarboxylic acids or lactone with low molecular weight polyol, wherein the excess polyol is also removed by distillation. The disadvantage of the procedure in above mentioned references is the distillation step which is not economic.
EP 0 661 316 and EP 0 866 082 relate to reactive urea/urethane compounds, the process for preparation and coatings based on those compounds which are prepared from the reaction of a polyisocyanate with a secondary amine containing one or two hydroxyl groups. The advantage of this process is the fact that the reaction of the isocyanate group preferentially goes with the secondary amine group to form low molecular weight hydroxyfunctional urethane-urea adducts. The disadvantage is that urea groups have a strong hydrogen bonding character which leads to limited solubility and relatively high solution viscosity. U.S. Pat. No. 5,130,405 and U.S. Pat. No. 5,175,227 are directed to high solids coating compositions containing polyurethane oligomers derived from the reaction of symmetrical and unsymmetrical 1,3-diols and polyisocyanates. Such compounds do have very low molecular weight with high hydroxyl values. Low molecular weight oligomers with high hydroxyl values act as strong slow solvents and many times negatively influence the appearance of automotive clear coats. EP 0 767 230, EP 0 767 187, EP 0 767 226, EP 0 767 228, EP 0 767 231, EP 0 767 229, EP 0 767 232 and EP 0 767 227 all relate to curable coating compositions having carbamate functional groups for crosslinking purposes. The carbamate functional groups can be represented by
—O—CO—NH—R
wherein R is hydrogen or alkyl, preferably Cl -C4 alkyl and more preferably hydrogen. Primary carbarnates (R=hydrogen) negatively influence solution viscosity due to strong hydrogen bonding and secondary carbamates need specific catalysis to react with amino resins.
U.S. Pat. No. 4,820,830 relates to hydroxyalkyl carbamates prepared by reacting cyclic carbonates with diamines. Such hydroxyalkyl carbamates have many times limited solubility and compatibility due to high secondary carbamate content. U.S. Pat. No. 4,883,854 describes polyurethanes derived from hydroxyalkyl carbamates which are synthesized from polyamines with at least two amine groups and cyclic carbonates. There is no teaching on the reaction products of mono secondary amines with cyclic carbonates to form the hydroxyl functional carbamates and the further use in the synthesis of branched hydroxyl functional oligomers with controlled molecular weight distribution. U.S. Pat. No. 4,542,173 relates to self-crosslinkable binders containing at least to hydroxyalkyl carbamate groups with a secondary carbamate group. U.S. Pat. No. 5,175,231 relates to urethane oligomers with an amine functional group.
It is therefore desirable to find a method for preparing highly branched hydroxy functional urethane adducts with a controlled molecular weight distribution and essentially free from primary carbamate and urea groups. Such compounds would provide coating compositions with a good combination of low solution viscosity (low VOC), excellent chemical resistance, mechanical properties and outdoor durability.
SUMMARY OF THE INVENTION
Hydroxy functional urethane compounds comprising the reaction product of:
a) a hydroxy functional urethane intermediate containing a tertiary carbamate group prepared by reaction of a cyclic 5-ring carbonate with a beta-hydroxy functional, secondary amine, said intermediate represented by the formula:
wherein
R
1
and R
2
=hydrogen, alkyl, cycloalkyl or a residue R
6
—O— or R
6
—CO—O— with R
6
;
R
6
=an alkyl, cycloalkyl or benzylic group having up to 18 carbon atoms;
R
4
and R
5
=hydrogen or alkyl group containing eventually a hydroxyl group; and
R
3
=alkyl, cycloalkyl or benzylic group eventually containing an ether linkage and/or a hydroxyl group, or HO—CH(R
1
)—CH(R
2
)— with
b) a compound with at least 2 isocyanate groups.
Such hydroxy functional urethanes can be used in automotive coatings to improve the mechanical properties and chemical resistance of such coatings.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to novel hydroxyl functional binders which comprise the reaction product of polyisocyanates with a tertiary carbamate having at least two hydroxyl groups. The coating compositions based on those binders offer improved mechanical properties and chemical resistance. The tertiary carbamate with at least two hydroxyl groups can be represented as:
wherein
R
1
and R
2
=hydrogen, alkyl, cycloalkyl or a residue R
6
—O— or R
6
—CO—O— with R
6
;
R
6
=an alkyl, cycloalkyl or benzylic group having up to 18 carbon atoms;
R
4
and R
5
=hydrogen or alkyl group containing eventually a hydroxyl group; and
R
3
=alkyl, cycloalkyl or benzylic group eventually containing an ether linkage and/or a hydroxyl group, or HO—CH(R
1
)—CH(R
2
)—
In particularly preferred embodiments, R
1
is CH
3
or H; R
2
is H, R
3
is HO—CH(CH
2
)—CH
2
— or CH
3
(CH
2
)
3
—; R
4
is H; and R
5
is H, CH
3
, or C
2
H
5
.
Such carbamates can be prepared by the reaction of a secondary amine with a cyclic 5-ring carbonate. Examples of 5-ring carbonates include ethylene carbonate, propylene carbonate, butylene carbonate and glycerine carbonate. Examples of secondary amines are alkyl, benzyl and cycloalkyl-ethanolamines and alkyl-propanol amines as methyl ethanolamine, n-butyl aminoethanol, hexyl aminoethanol, benzyl aminoethanol, cyclohexyl aminoethanol, methyl propanolamine, n-butyl propanolamine, cyclohexyl propanolamine and benzyl propanolamine.
Such compounds are typically prepared by reaction of cyclic oxides as ethyleneoxide or propyleneoxide with a primary amine. Examples of bis-hydroxyl functional secondary amines are diethanolamine and diisopropanolamine. Secondary amines can also be prepared from the reaction of primary amines with other cyclic three-member oxides as n-butyleneoxide, cyclohexeneoxide, i-butyleneoxide and derivatives as monoepoxy ethers and monoepoxy esters. Examples of monoepoxy esters are glycidyl esters
Chang Ceila
E. I. du Pont de Nemours and Company
Lerman Bart E.
Oh Taylor V.
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