Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-11
2001-06-12
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C165S133000, C165S134100, C165SDIG005, C525S057000, C525S192000, C525S199000, C525S200000, C525S205000, C525S212000, C525S217000, C525S218000, C525S222000, C525S223000, C525S227000, C525S230000, C525S916000, C525S060000
Reexamination Certificate
active
06245854
ABSTRACT:
TECHNICAL FIELD
This invention relates to hydrophilic fluorocarbon-containing coating compositions, and in particular, to a hydrophilic fluorocarbon-containing coating composition for application to metallic surfaces, such as heat exchangers.
BACKGROUND ART
A typical heat exchanger comprises a plurality of parallel, spaced apart fins defining air flow passages. The fins are typically made of aluminum and aluminum alloys due to the excellent heat conductance properties of aluminum. The heat exchanger fins are designed to have surface areas which are as large as possible, and spaces between the fins which are as narrow as possible without increasing the resistance to air flow between the fins, in order to increase the heat radiation or cooling effect.
As a result, particularly when the heat exchanger is used for cooling, moisture from warm air passing through the heat exchanger condenses on the cold fin surfaces and, if those surfaces are hydrophobic, beads of water accumulate to block the narrow passages between adjacent heat exchanger fins. The increased resistance to air flow operates to reduce the efficiency of the heat exchangers.
In order to help prevent the accumulation of water between heat exchanger fins, the surfaces of the heat exchanger fins have been coated with hydrophilic coatings so that a thin film of water coating the surface can readily slide off the surface of the heat exchanger fins, a phenomenon known as “sheeting off”, to prevent blockage of the narrow passages between the adjacent heat exchanger fins.
The hydrophilic coatings which have been employed to date have included chromates and silicates. These hydrophilic coatings have some undesirable characteristics which include, being toxic, producing an unpleasant odor, and having relatively weak corrosion resistance due to relatively poor adhesion to surfaces and high surface coating porosity which can allow corrosive materials to permeate and react with metal surfaces.
Accordingly, it would be desirable to provide a hydrophilic coating composition which produces coatings which are non-toxic, do not produce an unpleasant odor and have improved corrosion resistance.
Also, the coatings should be less than, or equal to, about 5 microns, uniform and essentially free of gaps and/or holes. Thus, it would be desirable to provide coatings which are thin, uniform and essentially free of gaps and/or holes.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a coating composition which produces coatings which are non-toxic, do not produce unpleasant odors and have improved corrosion resistance.
For carrying out the above, and other objects, the present invention provides a hydrophilic coating composition for hydrophilically coating a metallic surface. The hydrophilic coating composition comprises a fluorocarbon-containing hydrophilic polymer comprising units of a hydrophilic monomer and units of a fluorocarbon-containing hydrophobic comonomer. The coating composition produces hydrophilic coatings on metallic surfaces having a contact angle below about 50°. Preferably, the fluorocarbon-containing hydrophilic polymer comprises mostly units of hydrophilic monomers and very few units of hydrophobic comonomers, with the comonomers containing hydrophobic units to make associative domain between macro-molecules.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention comprises a hydrophilic coating composition for producing hydrophilic coatings on metallic surfaces, such as aluminum, steel, titanium, copper, nickel, and their alloys. The metallic surfaces for which the hydrophilic coating composition of the present invention are useable with any metallic surface which may benefit from a hydrophilic coating. The coating composition of the present invention are particularly well suited for use with heat exchangers for automobile cooling systems, and as such will be described herein for application to heat exchangers, but in doing so is not intended to limit their use to automotive heat exchangers.
The hydrophilic coating composition of the present invention minimally comprises, based on the weight of the coating composition, from about 0.05 to about 10 weight percent fluorocarbon-containing hydrophilic polymer (FHP), from about 1 to about 20 weight percent water soluble polymer, from about 1 to about 5 weight percent curing agent, and from about 5 to about 98 weight percent water. More preferably, the hydrophilic coating composition comprises, based on the weight of the coating composition, from about 0.1 to about 3 weight percent fluorocarbon-containing hydrophilic polymer, from about 1 to about 5 weight percent water soluble polymer, from about 1 to about 3 weight percent curing agent, and from about 89 to about 98 weight percent water. Most preferably, the hydrophilic coating composition comprises, based on the weight of the hydrophilic coating composition, about 0.5 weight percent fluorocarbon-containing hydrophilic polymer, about 2.5 weight percent water soluble polymer, about 1 weight percent curing agent, and about 96 weight percent water. Optionally, the hydrophilic coating composition may also contain up to about 2 weight percent, based on the weight of the coating composition, of antimicrobial agent.
The fluorocarbon-containing hydrophilic polymer preferably has a molecular weight of between about 50,000 to about 6,000,000, more preferably from about 300,000 to about 2,000,000, and most preferably from about 500,000 to about 1,000,000. The fluorocarbon-containing hydrophilic polymer can be either a copolymer or a terpolymer.
The fluorocarbon-containing hydrophilic polymer comprises units of hydrophilic monomer and units of hydrophobic comonomer. The units of hydrophobic comonomer are preferably present in the fluorocarbon-containing hydrophilic polymer in an amount which is sufficient to impart a hydrophilic surface on the metallic surface when the hydrophilic coatings are formed thereon.
A hydrophilic surface is defined for the purpose of the present invention as one having a contact angle of less than about 50° when measured in accordance with ASTM NO. D-724. The hydrophilic coating composition of the present invention, when coated on metallic surfaces, preferably imparts a contact angle as determined by ASTM No. D-724 of less than about 40°, more preferably less than about 20°, and most preferably less than about 10°.
To provide a hydrophilic surface, the units of hydrophobic comonomer are preferably present in the hydrophilic polymer in an amount of less than about 10 mole percent, more preferably in an amount of about 0.01-5 mole percent, and most preferably in an amount of about 0.01 to 1.0 mole percent. Preferably, the backbone of the fluorocarbon-containing hydrophilic polymer essentially comprises the hydrophilic monomer units, and the hydrophobic comonomer units essentially comprise side- and/or end-chains of the polymer. The hydrophobic side- and/or end-chains are believed to have intermolecular interactions between fluorocarbon groups in the polymer solution. It is believed, without wishing to be bound to any particular theory, that anymore than about 10 mole percent of hydrophobic comonomer will result in undissolved fluorocarbon-containing hydrophilic polymer and the fluorocarbon-containing polymer possessing a hydrophobic characteristic.
The hydrophilic monomers used in forming the fluorocarbon-containing hydrophilic polymer of the present invention can be any suitable hydrophilic monomer, such as vinyl monomers. Examples of suitable vinyl monomers include vinyl alcohol, polyvinyl acetate, vinyl pyrrolidone, and acrylamide.
The hydrophilic monomer is preferably represented by the general formula (I).
where R
1
=H or CH
3
and
In an alternative embodiment, the hydrophilic monomer could be a co-monomer of vinyl monomer and an ionic monomer. Preferred ionic monomers include, but are not limited to, sodium 2-acylamilido 2-methyl propane sulfonate, which is an anionic monomer available from Aldrich Chemical Company under the name NaAmps, and acryloyloxyethyl trimethyl a
Farah Riad A.
Obioha Chimere N.
Schuetzle Dennis
Zhang Yun-xiang
Egwim K. C.
Shelton Larry I.
Visteon Global Technologies Inc.
Wu David W.
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