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
1999-03-15
2001-05-01
Yoon, Tae H. (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...
C524S504000, C524S535000, C524S802000, C528S492000
Reexamination Certificate
active
06225402
ABSTRACT:
The present invention relates to stable aqueous polymer dispersions for use in coatings for untreated polyolefinic substrates. More particularly, aqueous dispersions of acrylic modified chlorinated polyolefin (CPO) polymer are prepared by forming a polymer salt in a hydrophilic organic solvent and removing the hydrophilic organic solvent from the blend of water and the hydrophilic organic solvent.
BACKGROUND OF THE INVENTION
The use of polyolefin resins such as polypropylene has become widespread due to their desirable physical properties and their relatively low price. Polyolefinic materials are used extensively in the automobile industry for the manufacture of various external and internal automobile parts, such as bumpers, side mirror supports, interior panels and door handles. It is often desirable to apply a coating to the polyolefin substrate to achieve, for example, a protective and/or decorative coating.
Coating untreated polyolefin substrates is generally difficult because of poor adhesion of coatings to these types of substrates. Polypropylene possesses a low surface tension and low polarity. Hence, it is difficult to ensure that an applied coating will adhere effectively to the surface of a polypropylene substrate.
Two ways to obtain adhesion to polyolefinic substrates are through modifications of the substrate or through the use of adhesion promoting materials. Substrate pretreatment usually involves oxidizing the surface by methods such as flame treatment, gas plasma, corona discharge, UV radiation or chemical means. These processes usually have treatment uniformity problems or may adversely affect the substrate by increasing surface roughness or by overheating. Chlorinated polyolefins have been used as adhesion promoters. They are thought to adhere to the substrate via dispersive forces. The chlorine enhances the solubility in various solvents as well as promoting adhesion of the primer to topcoats by polar interactions.
Environmental concern over the use of organic solvents has become increasingly important to the coating industry. This concern not only extends to preservation of the environment for its own sake, but extends to public safety as to both living and working conditions. Volatile organic emissions resulting from coating compositions which are applied and used by industry and by the consuming public are not only often unpleasant, but also contribute to photochemical smog. Governments have established regulations setting forth guidelines relating to volatile organic compounds (VOCs) which may be released to the atmosphere. The U.S. Environmental Protection Agency (EPA) established guidelines limiting the amount of VOCs released to the atmosphere, such guidelines being scheduled for adoption or having been adopted by various states of the United States. Guidelines relating to VOCs, such as those of the EPA, and environmental concerns are particularly pertinent to the paint and coating industry which uses organic solvents that are emitted into the atmosphere.
Water-borne chlorinated polyolefin compositions have been developed that are useful as primers for coating polypropylene substrates. These types of compositions usually require the formation of CPO emulsions. These emulsions typically include maleinated CPO, surfactant, amine, water, and in some cases cosolvent. EP 774500 describes a blend of one of these emulsions with an acrylic resin and a crosslinker capable of reacting with the acrylic resin for providing a waterborne coating system for untreated polypropylene. This system is a blend and contains significant amounts of surfactant.
U.S. Pat. No. 5,637,409 describes an aqueous coating composition comprising a blend of surfactant, CPO, monomers, solvent, amine, and water. This dispersion is mixed with initiator and then applied to substrate. The polymerization of the monomers then takes place. This technique is in effect a two component system which contains the undesirable odor and necessary precautions associated with monomer handling. This type of system makes the production of a homogeneous defect-free film difficult.
SUMMARY OF THE INVENTION
The present invention is directed to stable aqueous dispersions of an acrylic modified chlorinated polyolefin and a process for their preparation. The aqueous dispersions of acrylic modified chlorinated polyolefin are effective for use as coatings on treated and untreated polyolefinic substrates. The aqueous dispersions of the invention have less than about 10 weight percent organic solvent, at least about 10 weight percent solids, and a viscosity of less than about 10 poise at about ambient temperature. The aqueous dispersions of the invention are effective for providing a coating with an adhesion of at least 4B as determined by ASTM method D3359.
In an important aspect of the invention, a chlorinated polyolefin having a weight average molecular weight of at least about 1000 is modified by grafting with an acrylic. A preformed acrylic polymer may be grafted onto the chlorinated polyolefin or acrylic monomers may be grafted and polymerized onto the chlorinated polyolefin. In an important aspect of the invention, the acrylic grafted onto the chlorinated polyolefin, whether it is a preformed acrylic polymer grafted onto the chlorinated polyolefin or the result of the grafting and polymerization of acrylic monomers onto the chlorinated polyolefin, has a weight average molecular weight of at least about 2000. The acrylic provides the acrylic modified chlorinated polyolefin with ionizable groups effective for allowing the acrylic modified chlorinated polyolefin to form a stable aqueous dispersion.
In accordance with the dispersion process of the invention, an acrylic modified chlorinated polyolefin polymer is synthesized in a organic solvent. The organic solvent may be a hydrophilic organic solvent, a hydrophobic organic solvent, or a mixture of hydrophobic organic solvent and hydrophilic organic solvent. In an important aspect of the invention, the organic solvent is a hydrophilic organic solvent and the hydrophilic solvent has a solubility in water of at least about 5 weight percent, at processing temperatures, based on the weight of the solvent and water mixture. The polymer which is formed in the organic solvent has an acid value of at least about 10, and has a solubility of at least about 25 weight percent in the organic solvent at processing temperatures, based on the weight of the polymer and solvent.
After the polymer is fully dissolved in the organic solvent the polymer may be neutralized by adding a neutralizer, by adding the polymer to water that already contains neutralizer, or by adding the polymer to water and then adding neutralizer to the polymer/water mixture. Depending on the type of ionizable groups present in the polymer it may be important that the polymer is neutralized before it is blended with water so that water dispersible neutralized ionizable groups are generally evenly distributed throughout the polymer.
In an important aspect of the invention, an amount of neutralizer is added effective for providing a dispersion of the polymer upon removal of the organic solvent. The neutralizer may be any salt-forming base compatible with the ionizable functional polymer such as sodium hydroxide or an amine. In a very important aspect the neutralizer is an amine type which includes ammonia, triethanol amine, dimethyl ethanol amine, diethylamine (DEA), triethylamine (TEA), 2-amino-2-methyl-1-propanol, and mixtures thereof. Not all of the ionizable groups on the polymers need to be reacted with the base (or neutralized).
After the formation of the polymer salt solution in the organic solvent, and mixing that solution with water to form a water/organic solvent/polymer salt blend, the organic solvent and possibly a portion of the water are removed or stripped from the blend at a duration, temperature and pressure effective for providing an aqueous dispersion having a resin mean particle size of not greater than about 15 microns, in an important aspect not greater than about 10 microns, and in a ver
Coad Michael Davis
O'Callaghan Kevin Jude
Riddick Wayne Taylor
Will, II Martin Joseph
Fitch Even Tabin & Flannery
McWhorter Technologies Inc.
Yoon Tae H.
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