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
2002-04-26
2004-09-21
Cain, Edward J. (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...
C524S376000, C524S377000, C524S378000
Reexamination Certificate
active
06794434
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the use of surfactants as plasticizers in water-based polymer coating compositions to reduce or eliminate the need for conventional cosolvents and to reduce the overall volatile organic compounds (VOC's) of the coating composition.
BACKGROUND OF THE INVENTION
Both legislative and marketplace developments are pushing for reduced volatile organic emissions in a variety of industries. In an increasing number of industries, aqueous coating compositions continue to replace solvent-based coating compositions in efforts to significantly reduce volatile organic emissions. A variety of paints, inks, sealants and adhesives, for example, which were previously formulated with organic solvents are now formulated as aqueous compositions. Emissions from coatings compositions commonly result from volatile organic compounds (VOC's) in the compositions. The amounts of VOC's in a coating composition are expressed in grams per liter (g/l).
While the move from organic solvent-based to aqueous compositions brings environmental, safety and health benefits, aqueous coating compositions must still meet or exceed the performance standards expected from solvent-based coating compositions. The coatings or films must form at ambient temperatures (35° to 160° F.), yet have good performance properties after curing. For example, a coating composition should exhibit good print and block resistance and yield good adhesion and tensile properties. Once cured, most applications require that the coating be unaffected by environmental conditions such as water, humidity, and end-use temperature fluctuations.
Aqueous coating compositions may contain upwards of ten to twenty components which are generally identified by their function. For example, in addition to a resin or resins (also called latexes or binders), an aqueous coating composition may have pigments, extenders, antisettling agents, dispersants, surfactants (such as wetting agents, defoamers, and antifoamer), rheology modifiers, coalescing solvents, plasticizers, water, glycols, catalysts, biocides, crosslinkers, and colorants. Glycols are components added for freeze-thaw resistance, wet edge properties and as aids in low temperature coalescence. Representative glycols used for these purposes include ethylene glycol and propylene glycol. Because the glycols generally evaporate at ambient conditions, they contribute to VOC's found in aqueous coating formulations. A typical contribution to VOC's by glycols would be 100 to 200 grams per liter. Glycols are one of the first components aqueous coating manufacturers seek to decrease or eliminate in an effort to reduce emissions. However, the resulting coating may then suffer in the desired properties of low temperature coalescence, freeze/thaw resistance and wet edge.
Cosolvents (also known as coalescing solvents) are commonly employed in aqueous compositions to aid in film formation (or knitting-together) of hard latex particles. This hardness can be measured in terms of the starting film-formation temperature or of the glass transition temperature of the manufactured latex solid. As drying occurs, the cosolvents evaporate from the coating and the glass transition temperature of the coating approaches that of the starting resin. The addition of cosolvents enables the coating to behave like a softer film-forming material during drying and then perform as a harder, resistant film after drying. Examples of cosolvents include aliphatic and aromatic hydrocarbons and oxygenated solvents, such as alcohols, ketones and glycol ethers A typical amount of cosolvent ranges from 50 to 300 or more grams per liter of coating composition. Coating compositions based on cosolvents are described, for example, in
Paint Handbook,
1-12 to 1-24 (Harold B. Crawford & Beatrice E. Eckes eds., 1981), incorporated here by reference. Because cosolvents present in the coating formulation contribute considerably to VOC's content and tend to contribute odor to the coating, cosolvents are becoming more undesirable in aqueous coatings. However, in many aqueous coating systems, the elimination of the cosolvent(s) result in either lack of film formation or such poor film formation that the coating has poor appearance and poor resistance properties. In some cases, plasticizers may be added to the aqueous coating formulation to replace some or all of the cosolvents. Typically, plasticizers are organic compounds that do not significantly evaporate at ambient conditions but remain in the coating. Examples of typical plasticizers would be chemicals from the phthalate, adipate, and benzoate families. They soften the polymer and are used to impart flexibility to an otherwise hard and brittle polymer. However, plasticizers, especially at high levels, can have deleterious effects on coating performance properties. Because the coating remains soft, it can have poor block and print resistance, poor stain resistance and a tacky feel.
Many of the components discussed above used to formulate waterborne coatings have small amounts of volatile compounds present along with the components. Some examples are the solvents that colorants are dispersed in, the solvents that catalysts are dispersed in, and even the glycols or solvents that are present in many commercial surfactants, biocides, defoamers, or rheology modifiers. For example, the low level of VOC calculated for the formulation used in Examples 1-6 below (11 g/l) arises from a particular component; the solvents present in the cobalt catalyst employed.
Surfactants are commonly used in coating formulations to improve wetting of the substrate by the coating, and wetting of the pigment by the resin. They can also improve formulating latitude by preventing shocking of the coating composition as various components are added and can increase the service life of the coating by increasing shelf stability. Typically, low levels of surfactants are used to accomplish these goals and mixtures of surfactants may be employed to impart one or more of the properties listed above. Surfactants are not generally volatile materials under ambient conditions and remain in the coating during the drying process. However, at the low concentrations typically used, little effect on polymer hardness or coating performance is observed. If too much surfactant is used in the aqueous coating composition, the wet coating could exhibit excessive foaming and poor thickening efficiency with thickeners while the cured coating could have problems with water sensitivity, poor exterior durability and poor block, stain and print resistance. Thus, surfactants are typically used in the lowest amounts necessary to achieve their beneficial properties while avoiding any detrimental effects.
A discussed above, a need exists to reduce or eliminate VOC's from aqueous coating compositions without effecting wet coating or end-use performance properties. The invention answers that need.
SUMMARY OF THE INVENTION
It has been discovered that surfactants can be employed at levels similar to those used by conventional cosolvents and function as a plasticizers in the coating, thus eliminating the need for conventional cosolvents and eliminate the VOC's associated with the cosolvents. Preferred surfactants of the invention can be used to plasticize the coating, aid in low temperature film formation and contribute to the typical properties associated with surfactants in coatings while not contributing deleteriously to the final balance of properties in the finished coating.
The invention relates to an improved water-based polymer coating composition comprising a polymer resin, water and surfactant. As an improvement over previous water-based polymer coating compositions an anionic and/or nonionic surfactant is present in an amount effective to plasticize the coating formed from the composition. A water-based polymer coating composition of the invention is also substantially free from cosolvents. The invention also relates to a method of coating a substrate and a substrate which h
Collins Martha Jean
Martin Richard Alvin
Stockl Rebecca Reid
Cain Edward J.
Eastman Chemical Company
Nixon & Peabody LLP
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