Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-06-02
2001-02-06
Szekely, Peter A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C522S042000, C524S108000, C524S110000, C524S361000, C524S362000, C524S363000, C524S364000, C524S365000, C525S438000
Reexamination Certificate
active
06184279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coating compositions with at least one curable film forming resin that result in cured coating films on substrates having good appearance from reduced defects like popping or gassing while allowing for a reduced tendency to discolor.
Various coating compositions involve curing of the film forming resins of the coating in a variety of ways ranging from self curing through evaporation of a carrier or solvent or reaction by such environmental factors like atmospheric water vapor to curing through the presence of one or more curing agents in the coating composition. The latter can be radiation curing like ultraviolet light curing and/or addition of crosslinking agents to crosslink with the film forming resin. With many of the aforementioned curing mechanisms or from application methods, the potential may exist for the latent evolution of gas, vapor or air during the curing of the coating. For instance with powder type coating compositions the spraying of the powder can result in entrapped air in the formed coating that could not adequately escape before curing. Such evolution can result in defects of the cured film from the gassing or popping or release of such gas, vapor and/or air.
For some powder coatings, several U.S. Pat. Nos. 4,801,680; 5,461,089; 5,635,548 and 5,248,400 (Franks, et al.) have disclosed the use of benzoin as an additive or modifier. The art has indicated that in some powder coatings the benzoin performs a degassing or antipopping or air release function, when used in an amount from 0.5 to 3 weight percent. Several patent documents have noted a discoloration problem particularly in hydroxyalkylamide cured polyester powder systems when benzoin is used as a degassing agent. Discoveries were made that wax type and thermoplastic polymer type degassing agents in U.S. Pat. No. 5,342,893 (Wilkinson, et al.) and EP 0471409 (DSM) gave reduced discoloration when used in place of benzoin.
Solid particulate coating formulations referred to in the industry as “powder coatings” are finding increasing use in painting metal substrates both as primer coatings and as top or clear coats of the base coat and clear coat composite coatings. The automotive industry provides corrosion protection and decorative appearance for motor vehicles by multilayered coating or paint composites on the various types of surfaces of motor vehicles. The finishing layers of this composite usually include the popular base coat clear coat composites. The base coat is a pigmented layer and the clear coat is a nonpigmented or only slightly pigmented layer that is applied separately to the base coat and cured to some degree with the base coat. To provide improved coating composites for motor vehicles, the industry continuously seeks improvements from an environmental standpoint without sacrificing surface appearance and/or performance properties. Using powder coating compositions as clear coats as well as for other coating layers in multilayered composite coatings would provide an environmentally acceptable coating composition. The powder clear coats are becoming more widely used for their advantages in application from their lower organic solvent emissions. These coatings typically have very low levels of volatile solvents, i.e., on the order of two percent or slightly higher but generally much less than other paint systems. Such compositions serving as solutions of environmental acceptable technology can not increase problems such as surface appearance defects like popping, gassing and the like and increased likelihood of non-compensatible discoloration of the coating.
An object of the present invention is to provide liquid and/or powder coating compositions with one or more curable resins or polymers that result in cured coatings having reduced appearance or surface defects from air, gas or solvent release from the coating while curing and particularly while also resulting in a cured coating with reduced yellowing.
SUMMARY OF THE INVENTION
In accordance with the present invention, coating compositions have at least one liquid or particulate curable film forming resinous material, and an effective degassing amount of a material having the structure:
wherein R and R′ are the same or different groups of primary alkyl groups with 1 to 6 carbon atoms including methyl groups or an aromatic group containing one or more heteroatoms either internal or external to the aromatic ring and dimer derivatives of Structure I compounds. The effective amount for degassing is usually in the range from about 0.01 to about 5 percent by weight based on the weight of total resin solids of the coating composition.
When the curable coating composition with the curable film-forming resinous material and the material of Structure I and/or dimers thereof is a liquid, a carrier may be used. The carrier can make the coating composition a solvent-borne or water-borne coating composition. Also, other additional components usually found in curable coating compositions can be present in amounts usually used by those skilled in the art. For chemical curing through crosslinking of a crosslinking agent with the curable film forming resinous material an appropriate crosslinking agent is present in the coating composition for crosslinking reaction with the resinous material. These amounts of the other additional components and film-forming resinous material provide most of the solids for the coating composition producing a cured coating. Also the liquid or powder coating composition of the present invention can be used as a single coating layer in coating substrates such as appliances and the like or as a coating layer in a multiple coating composite. Examples of the latter include those coating composites used in motor vehicle manufacturing and refinish coating operations which can include: liquid or powder primer coatings, primer surfacer coatings, pigmented or unpigmented formulations as well as pigmented formulations as the basecoat or in unpigmented formulations as the clearcoat in basecoat or colorcoat and clearcoat composite coatings.
DETAILED DESCRIPTION OF THE INVENTION
In the following description of the specification and claims unless otherwise expressly indicated to the contrary the following terms have the indicated meanings.
The use of numerical values in ranges for temperature, pressure, pH, and amounts of and molecular weight values of materials, whether number average molecular weight (“Mn”) or weight average molecular weight (“Mw”), amounts expressed in equivalents and equivalent ratios, and other reaction and operational conditions are stated as approximations as though the minimum and maximum values within the stated ranges were both preceded by the word “about”. In this manner small variations above and below, the stated ranges can be used to achieve substantially the same results as values within the ranges. Also, the disclosure of these ranges is intended as a continuous range including every value between the minimum and maximum values.
Also for molecular weights whether Mn or Mw, these quantities are those determinable from gel permeation chromatography using polystyrene as standards as is well known to those skilled in the art. An example is that discussed in U.S. Pat. No. 4,739,019 at column 4, lines 2-45. For this reference to a U.S. patent and for other references to issued U.S. patents and published patent applications in the following disclosure for the specifically stated information therein, that information is considered as incorporated by reference herein.
By the term “film-forming”, it is meant that an at least near continuous film, except perhaps for a few if any pin hole type marks, can be formed on at least a horizontal surface from either 1) the particulate polymeric material of a powder coating upon at least melting and curing at elevated temperature, or 2) the polymeric material dispersed or solubilized in a solvent or carrier upon drying or evaporation of the solvent or carrier and/or curing of the polymeric material.
Also by the term “
Anderson Lawrence G.
Barkac Karen A.
Rechenberg Karen S.
Altman Deborah M.
Chirgott Paul S.
PPG Industries Ohio Inc.
Stachel Kenneth J.
Szekely Peter A.
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