Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2000-09-26
2002-05-28
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S081000, C252S182220, C560S026000, C560S115000
Reexamination Certificate
active
06395860
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to curable coating compositions. More specifically, the invention concerns coating compositions including polyisocyanate crosslinkers.
BACKGROUND OF THE INVENTION
Curable, or thermosettable, coating compositions are widely used in the coatings art, particularly for topcoats in the automotive and industrial coatings industry. Coating compositions including melamine crosslinkers provide good resistance to scratch and mar, but coatings cured with melamine crosslinkers have poorer resistance to environmental etch. “Environmental etch” is a term applied to a kind of exposure degradation that is characterized by spots or marks on or in the finish of the coating that often cannot be rubbed out. On the other hand, isocyanate-functional crosslinking agents provide excellent resistance to environmental etch but are less desirable because of poorer scratch and mar and higher viscosity.
The average degree of functionality of the polyisocyanate crosslinkers is of considerable importance in the production of high-quality coatings. In general, the higher the average functionality, the higher the crosslink density that develops in the coating during cure and the higher its resistance to environmental etch. Typical polyisocyanates crosslinkers used in coating compositions are biurets, isocyanurates, and oligomers of diisocyanates that provide about three isocyanate groups for crosslinking. These polyisocyanates provide excellent resistance to environmental etch in cured coatings, but the coatings do not have the desired scratch and mar resistance.
Schmalstieg et al., U.S. Pat. No. 5,096,994, discloses polyisocyanates prepared by reacting a monoisocyanatocarboxylic acid chloride with a silylated polyol. The dendrimers disclosed reportedly offer increased solids content over isocyanurate-based coating compositions, but the synthesis results in a chlorinated by-product that must be removed. Residual chlorine in the reaction product or as a by-product impurity is problematic in coating compositions for a number of reasons, and so special steps must be taken in preparing the polyisocyanates of the '994 patent, including using an excess of the silylated polyol and carefully removing all of the chlorinated by-product. In addition, the monomers used for this preparation of the Schmalstieg polyisocyanates are expensive to prepare.
Hult et al., U.S. Pat. No. 5,418,301, describes preparing a dendritic polyester by reacting an initiator molecule with at least one hydroxyl group with a chain extender molecule having a carboxylic acid group and two hydroxyl groups. Optionally, the terminal hydroxyl groups of the dendrite can be reacted with a chain stopper, such as a monofunctional carboxylic acid or a diisocyanate or oligomer of a diisocyanate, which further extends the dendritic polyester. For example, the '301 patent provides an example in which the hydroxyl-functional dendritic polyester was used to prepare a polyurethane having no free isocyanate groups. The '301 patent does not describe preparing polyisocyanates.
It would be advantageous to have a polyisocyanate crosslinking agent that in addition to the environmental etch resistance available from polyisocyanate crosslinkers, provide improved scratch and mar resistance of the coating without dramatically increasing the viscosity of the coating composition. It would also be advantageous to prepare a polyisocyanate crosslinking agent from less expensive materials and materials more readily available in the coating industry.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide polyisocyanate compounds with increased functionality useful as crosslinking agents in coating compositions. Coating compositions based on the polyisocyanate compound crosslinkers of the invention exhibit marked improvement in scratch and mar resistance.
The polyisocyanate ester compound is a branched material having at least two ester linkages, at least four urethane linkages further from the center of the compound compared to the ester linkages, and at least one terminal isocyanate group for each urethane linkage, which isocyanate group may be blocked. The polyisocyanate compound is prepared first by reacting a polyol compound having at least two hydroxyl groups with a carboxylic acid compound having one carboxylic acid group and at least two hydroxyl groups to form a hydroxyl-functional ester product. The hydroxyl-functional ester product may have more than one ester linkage on average for each hydroxyl group of the polyol compound by reacting more than one carboxylic acid equivalent of the carboxylic acid compound, based on equivalents of hydroxyl of the polyol compound. The reaction of the excess may be carried out in one step, with all of the carboxylic acid compound introduced into the reactor initially. Alternatively may be carried out in a stepwise manner, for example by initially reacting one equivalent of carboxylic acid per polyol hydroxyl equivalent until the reaction is substantially complete and then reacting an additional amount of the carboxylic acid compound with the initial ester product to form the ester product of the first stage.
The hydroxyl-functional ester product is then reacted with a diisocyanate compound in which the isocyanate groups have different reactivities. The reaction with the diisocyanate compound is carried out under conditions so that only one of the isocyanate groups is reactive with the hydroxyl groups of the ester product of the first stage. Because each of the isocyanate is monofunctional under the reaction conditions, the product avoids building viscosity. In this way, a highly-functional isocyanate crosslinker can be used for the coating composition without the increase in viscosity experienced with polyisocyanate crosslinkers of the prior art. The polyisocyanate crosslinkers of the invention are prepared from materials that are relatively inexpensive compared with the isocyanatocarboxylic acid chloride/silylated polyol synthesis of the prior art and are prepared in a reaction that does not result in chlorinated products or impurities. The coating compositions prepared from the polyisocyanate crosslinkers of the invention have reduced volatile organic content and produce coatings with improved resistance to scratch and mar.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a poly-functional isocyanate compound. The compound may be formed through the esterification of a polyol with a monocarboxylic acid compound having at least two hydroxyl groups to form a hydroxyl-functional ester compound, followed by reaction of the hydroxyl groups of the ester compound with a diisocyanate compound in which the isocyanate groups have different reactivities to provide a polyisocyanate ester compound having a ester linkages closest to the polyol core with urethane linkages further from the core than the ester linkages. Preferably, there are from about two to about six ester linkages between any two urethane linkages.
The polyol is a compound that has at least two hydroxyl groups. The preferred polyol will have more than two hydroxyl groups, and preferably will have from about 3 to about 8 hydroxyl groups. The polyol may be an aliphatic, cycloaliphatic, or aromatic diol, triol, tetrol, or a sugar or sugar alcohol and may contain from two to about eight hydroxyl groups. Polyhydroxy-functional polymers are not polyol compounds according to the invention; “compound” refers to non-polymeric materials.
Examples of suitable diol compounds include, without limitation, 1,3-propanediol, 1,2-ethanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, dimethylolpropane, neopentyl glycol, 2-propyl-2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 2,2,4-trimethylpentane-1,3-diol, trimethylhexane-1,6-diol, 2-methyl-1,3-propanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cycloaliphatic diols such as cyclohexane dimethanol, 3-diox
Gupta Manoj K.
Ramesh Swaminathan
BASF Corporation
Budde Anna M.
Gorr Rachel
LandOfFree
Clearcoat composition with improved scratch and mar resistance does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Clearcoat composition with improved scratch and mar resistance, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Clearcoat composition with improved scratch and mar resistance will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2904168