Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-01-25
2004-05-25
Metznaier, Daniel S. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C106S287220, C106S287240, C106S287250, C528S093000, C528S112000, C528S113000, C528S119000, C528S121000, C528S176000, C528S183000
Reexamination Certificate
active
06740359
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates coating compositions suitable for use in automotive refinish applications and more particularly related to fast dry ambient temperature curable coating compositions.
BACKGROUND OF THE INVENTION
A number of clear and pigmented coating compositions are utilized in various coatings, such as, for example, primers, basecoats and clearcoats used in automotive refinish coatings, which are generally solvent based. In repairing damage, such as dents and scratches to autobodies, the original coating in and around the damaged area is typically sanded or ground out by mechanical means. Some times the original coating is stripped off from a portion or off the entire autobody to expose the substrate (e.g., bare metal) underneath. After repairing the damage, the repaired surface is coated, typically in portable or permanent low cost painting enclosures vented to the atmosphere to remove the organic solvents from the freshly applied paint coatings in an environmentally safe manner. Generally, the drying and curing of the freshly applied paint takes place within these enclosures. Furthermore, it is preferable to conduct the foregoing drying and curing steps within the enclosure to prevent the wet paint from collecting dirt in the air or other contaminants.
As these paint enclosures take up significant floor space of typical small autobody paint repair shops, these shops prefer to dry and cure these paints as rapidly as possible. More expensive enclosures are frequently provided with heat sources, such as conventional heat or infra red lamps located inside the enclosure to cure the freshly applied paint at accelerated rates. Therefore, to provide more cost effective utilization of shop floor space and to minimize fire hazards resulting from wet coatings from solvent based coating compositions, there exists a continuing need for fast curing coating formulations which cure under ambient conditions while still providing outstanding performance characteristics such as solvent resistance. Several attempts have been made to address the aforedescribed problem. U.S. Pat. No. 5,332,785 discloses a coating composition based on a polyepoxide containing acetoacetate groups and a polyamine in the form of the corresponding aldimine or ketimine. However, a need still exits for fast drying coating compositions that have sufficient sandability in shorter dry times.
STATEMENT OF THE INVENTION
The present invention is directed to a coating composition comprising:
a binder component comprising:
(i) an epoxy resin having at least one acetoacetate functionality and at least one epoxy group, and
one or more reactive components provided with at least two acetoacetate functionalities, said reactive component being selected from the group consisting of a structured reactive diluent, an acrylic polymer, a polyester, and a combination thereof; and
(ii) a crosslinking component selected from the group consisting of a polyamine, a blocked polyamine and a mixture thereof, wherein said polyamine has an average of at least two amine functionalities per polyamine molecule and wherein said blocked polyamine has an average of at least two imine functionalities per molecule.
The present invention is further directed to a method of producing a coating on a substrate comprising:
mixing a binder component with a crosslinking component of a coating composition to form a pot mix,
wherein said binder component comprises:
(i) an epoxy resin having at least one acetoacetate functionality and at least one epoxy group, and
(ii) one or more reactive components provided with at least two acetoacetate functionalities, said reactive component being selected from the group consisting of a structured reactive diluent, an acrylic polymer, a polyester, and a combination thereof; and wherein said crosslinking component selected from the group consisting of a polyamine, a blocked polyamine and a mixture thereof, wherein said polyamine has an average of at least two amine functionalities per polyamine molecule and wherein said blocked polyamine has an average of at least two imine functionalities per molecule;
applying a layer of said pot mix over a substrate surface; and
curing said layer under ambient conditions to form said coating on said substrate.
Optionally in some coating applications, it may be preferable to incorporate within the curable composition an organosilane material for enhanced performance and adhesion properties.
Optionally, the coating can be used in low VOC applications.
The ratio of the number of equivalents of primary/secondary amino groups or a combination thereof of polyamine or blocked polyamine to the number of equivalents of total acetoacetate is between 0.3 to 2.5.
The acetoacetate containing epoxy resin is present in the range of 5 to 90 weight percent, preferably in the range of 15 to 70 and most preferably in the range of 15 to 60 weight percent of total binder component solids.
The other acetoacetate containing binder component (structured reactive diluent and/or polymer) is present in the range of 5 to 90 weight percent, preferably in the range of 15 to 70 weight percent and most preferably in the range of 15 to 60 weight percent of total binder component solids.
The coating composition includes in the range of 10 to 90 percent of the crosslinking component, preferably in the range of 15 to 70 weight percent and most preferably in the range of 15 to 60 weight percent of total binder solids. Polyketimine is the preferred.
“Low VOC coating composition” means a coating composition that has in the range of 0.6 to 0.3, preferably 0.21 to 0.25 kilograms of organic solvent per liter (1.3 to 2.5, preferably 1.8 to 2.1 pounds of organic solvent per gallon) of the composition, as determined under the procedures provided in ASTM D3960.
Ambient cure conditions is defined as the temperature range of 12° C. to 45° C. (55° F. to 110° F.) and a humidity range of 15% to 90% that is present in the spraying area. This does not refer to the temperature and humidity of the spray line.
The present invention is an ambient cure coating composition (also usable at higher bake temperatures) with the following advantages:
a) Fast dry times especially with low VOC coating compositions. Dry time is defined as the minimum time required to wet sand a pigmented tack free coating, typically of the order of 15 minutes.
b) Reduced time to dry sand especially in low VOC coating compositions. This is the minimum time needed to dry sand following application of the coating over the substrate. Typically of the order of 1 hour.
c) Superior solvent resistance and resistance to water or moisture.
Acetoacetate Containing Epoxy Resins
The acetoacetate containing epoxy resins are obtained by reacting hydroxyl containing polyepoxide either completely or partially with acetoacetic acid derivatives. The reaction of hydroxyl groups with acetoacetic acid derivatives such as t-butylacetoacetate or ethylacetoacetate is carried out as a transesterification reaction. U.S. Pat. No. 5,332,785 provides more details, which is incorporated herein by reference. A more detailed treatment on this subject can be found in a paper by Witzman et al Journal of Coatings Technology, Vol 62, No. 789, 1990.
The acetoacetate containing epoxy resin is present in the range of 5 to 90 weight percent, preferably in the range of 15 to 70 and most preferably in the range of 15 to 60 weight percent of total binder component solids.
The weight average molecular weight of the hydroxyl containing polyepoxy resins as determined by GPC using polystyrene standards is in the range of 100 to 30,000, preferably in the range of 100 to 15,000, more preferably in the range of 100 to 10,000. The polyepoxy resins have hydroxyl numbers in the range of 20 to 1800, preferably in the range of 50 to 1500 and most preferably in the range of 100 to 1000. The Tg of the hydroxyl containing polyepoxy resins are in the range of −60° C. to 150° C., preferably in the range of −40° C. to 100° C., more preferably in the range of −30° C. to 80
Corcoran Patrick H.
Kumar Uday
Rodrigues Cesar A.
Desmukh Sudhir G.
E. I. du Pont de Nemours and Company
Metznaier Daniel S.
Robertson Jeffrey B.
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