Synthetic resins or natural rubbers -- part of the class 520 ser – Powdered coating composition
Reexamination Certificate
1998-05-11
2001-02-27
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Powdered coating composition
C525S042000, C525S043000, C525S044000, C428S482000
Reexamination Certificate
active
06194525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to powder coating compositions including unsaturated polyester resins and methods of using the same.
BACKGROUND OF THE INVENTION
Previously known thermosetting powdercoating compositions utilizing unsaturated polyester resins and reactive polymerization initiators have suffered from problems arising from the reactive nature of the ingredients, in particular, problems of premature curing. Generally, all ingredients required for curing the composition have to be contained and uniformly distributed in the powder coating composition when it is applied to an article, which may include a mold, on the surface of which the coating is to be formed. To obtain the requisite uniform distribution of the ingredients, the powder must be thoroughly mixed. Melt mixing, followed by granulation of the mixture, has long been a preferred method of mixing. However, melt mixing has had to be carefully carried out in order to avoid premature curing of thermally labile resins used in the powder coating compositions. As a result of efforts to avoid the problem of premature curing of the powder coating, the mixing was frequently incomplete, resulting in non-uniform distribution of the ingredients and poor quality coatings.
Three temperatures are important for powder coating compositions and powder components thereof. The first of these is referred to as the glass transition temperature (Tg) or melting point (mp) of the powder. In addition to determining the stability of the powder to fusion, this temperature also contributes to and affects significantly the second important temperature, which is referred to as the melt process temperature. Generally, the melt process temperature should be sufficiently above the Tg of the mixture so that the viscosity will be optimal to achieve good mixing. The melt process temperature, in turn, sets limits upon the third important temperature for thermosetting powder coating compositions, which is the cure temperature. The cure temperature should be sufficiently above the melt processing temperature so that cure does not begin during the melt processing or mixing step of the process.
Thus, the three important temperatures are intimately interrelated. A reasonable temperature increment should be maintained between each of these temperatures, but particularly between the melt processing temperature and the cure temperature. As a result of these relationships between the three important temperatures, attempts to reduce the cure temperature generally result in reducing the increments between the three temperatures or in forcing the lowering of the other two temperatures. Of course, reducing the temperature increment between the melt process temperature and the cure temperature is not desirable because the mixture may begin to cure while it is being mixed. Lowering of each of the three temperatures in order to maintain the temperature increments is also not desirable because a drop in the glass transition or melt temperature of the mixture results in a powder with a decreased resistance to fusion, sintering or blocking at ambient temperatures encountered in the normal handling of powder coating compositions.
U.S. Pat. No. 4,075,261, issued Feb. 21, 1978 to Fujiyoshi et al. (“Fujiyoshi”) discloses a powder coating composition comprising (1) an unsaturated polyester which is prepared by reacting terephthalic acid or its lower alkyl ester and an &agr;-olefinic dicarboxylic acid and optionally an organic acid having at least three carboxy groups in the molecule or its functional derivative, and an aliphatic or alicyclic glycol; and (2) an organic peroxide and a molecular crosslinking or bridging agent. Fujiyoshi teaches mixing the composition in a conventional manner, i.e., homogeneously compounding in a mixer, roll mill or kneader, followed by grinding to the desired small particle size.
U.S. Pat. No. 4,873,274, issued Oct. 10, 1989 to Cummings et al. (“Cummings”) discloses an unsaturated polyester resin coating powder composition consisting essentially of at least one unsaturated polyester resin; at least one copolymerizable second resin; and an initiator which comprises 1,1′-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, or which contains a small proportion of a fast initiator and a relatively large proportion of a slow initiator.
U.S. Pat. No. 5,593,730, issued Jan. 14, 1997 to Satgurunathan et al. (“Satgurunathan”) discloses a powder coating composition which comprises a hybrid polymer system in which granular form of a polymer A formable from monomer(s) by aqueous suspension polymerization and a polymer B, different to A, which polymer system has been obtained using a process which comprises dissolving polymer B in monomeric material to be used in the formation of polymer A, and polymer A and polymer B bear functional groups for imparting curability to the hybrid polymer system.
The present invention solves the problem of uniformly and completely mixing together the components of a thermosetting powder coating composition prior to actual use of the powder to form a coating while avoiding premature curing of the composition.
SUMMARY OF THE INVENTION
The present invention provides a powder coating composition comprising a low-temperature physical mixture of a powder (A) comprising a first unsaturated polyester resin and a free radical initiator, and a powder (B) comprising a polymerization promoter. The present invention further provides methods of making and using the powder coating composition. The compositions and processes of this invention provide a powder coating composition which cures at a lower temperature and more rapidly than conventional powder coating compositions and processes which advantageously employ the powder coating compositions of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fast, low temperature curable powder coatings are achieved in this invention through the use of a physical mixing of two or more powders having different compositions. The compositions of the powders are selected such that each powder contains an ingredient which is needed for curing but is absent from the other powder. This separation allows preparation of the individual powder compositions in a heated state (such as by melt mixing) without the initiation of the cure reaction. The powdered components containing the active ingredients, after melt-mixing, can then be physically mixed to form a homogenous powder coating composition in a low-temperature dry, non-molten state, at temperatures below the activation temperature for curing. The physically mixed powders for the powder coating composition may be packaged for later use. The powder coating composition in use is applied to a substrate for forming a coating on the substrate by curing at an elevated temperature. Upon heating, the active ingredients of the powders react together resulting in a rapid cure at a relatively low temperature. The low temperature cure which is achievable with this two-component powder coating composition would not be possible if the active components had been combined in the melt state, in which they would immediately react and cause premature cure of the powder coating composition.
In this invention, we have discovered a novel composition and a novel process which can be used with the composition to achieve a significant reduction in powder coating cure temperatures while retaining (1) an economically short cure time, (2) the standard melt processing temperatures and (3) the stability of the powder at ambient temperatures. These benefits have been achieved by using a process in which standard melt-mixing equipment is used to prepare two separate powders. Each of these powders contains an insufficient quantity of the active cure ingredients to cause cure at the usual melt-mixing and processing temperatures employed, so that the individual powders do not cure prematurely during processing of the powders. Separation of the active cure ingredients in this manner allows the ingredients for each of the powders to be processed in standard me
Brand Douglas E.
Drabeck Gerald W.
Ortiz Carlos E.
Sahni Atam P.
Scheibelhoffer Anthony S.
Ferro Corporation
Rankin, Hill Porter & Clark LLP
Wu David W.
Zalukaeva Tanya
LandOfFree
Powder coating composition comprising unsaturated polyesters... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Powder coating composition comprising unsaturated polyesters..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Powder coating composition comprising unsaturated polyesters... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2564090