Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2000-04-12
2001-11-20
Dawson, Robert (Department: 1712)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
C106S287130, C106S287140, C106S287250, C556S420000, C524S188000, C428S400000, C428S426000, C428S447000
Reexamination Certificate
active
06319311
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to powder coating and adhesive formulations utilizing silyl carbamates as crosslinkers and/or adhesion promoters.
BACKGROUND OF THE INVENTION
Powder coatings are an environmentally friendly system, making them a desirable alternative to conventional solvent borne coating systems. Overall, operating and material costs are such that powder coating competes favorably with the solvent and waterborne markets.
Although powder coating represent only a portion of the total market, as compared to solvent type systems, the technology has considerable advantages. Most notably, since powder coating lacks solvent, there are no VOC issues with which to be concerned. Further, since there is less waste generated, the powder coating technique has less impact on the environment.
Powder coating involves several steps, the most critical of which is the premixing of the ingredients. During this initial phase, the binder, together with the other additives are mixed thoroughly in the equipment. Inadequate premix in the first stage could lead to a non-homogenous composition of the coating and poor mechanical properties or surface defects in the final product. The resulting premix is then fed into an extruder. The molten material produced from the extruder is cooled and squeezed into easily breakable strips. The strips are then ready for grinding to a particular particle size range.
The most common method for the application of powder coatings is by electrostatic spraying. The basic principle of this method involves propelling the powder, via compressed air, through a spray gun where it becomes electrostatically charged. In addition to charging the powder the gun also serves to deposit the powder supplied by the feeder. When the electric field is removed, the charged particles are still held on the surface, attracted by charges on the substrate. The uncharged powder in the overspray is collected and reused.
Another commonly used method of powder coating is triboelectric spraying. This is similar to electrostatic spraying, except the particles are positively charged (electrostatically charged particles have a negative charge ). A new technique, that is being developed for flat surfaces, employs electromagnetic brush technology which enables efficient high speed application of very thin layers with no recycling.
Among the drawbacks of thermoset powder coating systems is the difficulty in making tough films from ingredients that are low in molecular weight and therefore able to flow easily under shear conditions. Since the application of the powder coating involves overspraying, specialized recovery equipment is also necessary to reclaim the unused powder. Substrates must also be able to withstand the powder coating cure temperatures which typically range between 150 and 190° C.
The silanes of the present invention advantageously can be used to improve the physical and chemical properties of thermoplastic powder coatings. These powder coating formulations do not require curing agents and can be applied via the aforementioned electrostatic or tribostatic spray techniques. However, most thermoplastic powder is applied by passing the heated substrate through a fluidized bed.
Silanes are known to be useful in liquid coatings. For example in WO 96/39468 sprayable liquid coating compositions are described which include a film-forming reactive silyl group-containing compound and polymer microparticles insoluble in the liquid coating composition. The silyl group-containing compound may be the 1:2 mole ratio adduct of cyclohexanedimethanol and isocyanatopropyltrimethoxysilane.
SUMMARY OF THE INVENTION
The invention pertains to powder coating formulations which include as a component thereof an alkoxy functionalized silane compound.
One aspect of the invention is a powder coating formulation which includes as a component thereof a silane carbamate of the formula:
where R
1
is a hydrocarbon or acyl group; R
2
is a monovalent hydrocarbon group; R
3
is alkylene, optionally interrupted with one or more ether oxygen atoms; a is 0 or 1; X is an m-valent organic group; m is 1-6; and, either A=NH and B=O, or A=O and B=NH.
Carbamates, useful in the invention, where A=NH and B=O, may be prepared by reaction of polyol compounds with isocyanatoalkyltrialkoxysilanes. Novel silane carbamates which may be obtained in this manner include carbamates so formed in which the polyol compound is a hydrocarbon diol. Linearly symmetrical diols such as 1,4-cyclohexanediol, 4,4′-isopropylidenedicyclohexanol and 1,4-cyclohexanedimethanol also produce preferred silane carbamate compounds of the invention.
Other carbamates, useful in the invention, where A=O and B=NH, may be prepared by reaction of polyisocyanates with hydroxyalkylpolyalkoxy silanes. Such silyl carbamates may also be made by reaction of a polyisocyanate with a terminally unsaturated alcohol, and subsequent hydrosilation. Novel silyl carbamates that can be obtained in this manner include carbamates so formed in which the diisocyanate has a hydrocarbon chain.
Formulations as described herein also may be employed as adhesives.
DETAILED DESCRIPTION OF THE INVENTION
Powder coating systems may be based on a number of thermosetting chemistries. Well known powder coating systems include polyurethane systems based on blocked polyisocyanates and polyols, especially polyester or poly(meth)acrylate polyols; acid functional acrylic or other acid functional polymers cured with epoxy functional curing agents; anhydride/epoxy systems; epoxy/polyol systems; hybrid systems employing epoxide resins and polyesters with both carboxyl and hydroxyl functionality; systems based on hydroxyalkylamides and acid functional polymers. Examples of suitable epoxy resins include bisphenol A-type polyepoxides, glycidyl methacrylate copolymers and epoxy-novolac resins. Typically the systems are designed to melt-flow and to cure concurrently in a single heating step, although in some cases a UV curing system may be employed to separate the film-forming melt flow stage from the curing stage.
Particular powder coating systems in which the inventive compounds are useful include polyester-urethane powder coatings in which hydroxyl-functional polyester resins are cured with polyisocyanates. The polyisocyanates are blocked internally or blocked with a blocking agent. The leading blocking agent is e-caprolactam. When the powder-coated part is heated, the e-caprolactam is volatilized, unblocking the isocyanates groups and leaving them free to react with the hydroxyl functionality on the polyester resin. The most common blocked-isocyanate is the caprolactam-blocked IPDI (isophoronediisocyanate) such as Hüls Vestagon B 1530. The polyisocyanates can be blocked internally by a self-condensation process to form uretdione. One such uretdione compound that is commercially available is Hüls Vestagon BF 1540 (an IPDI uretdione).
Typical hydroxyl-functional polyester resins used in polyester-polyurethane systems are derived from condensation polymerization of glycol, dicarboxylic acid and polyol (more than two hydroxyl groups in the monomer). Frequently used glycols are trimethylpentanediol and neopentyl glycol; polyols include trimethylolpropane and trimethylolethane. Dibasic acids include isophthalic acid and terephthalic acid. A standard method of preparation of hydroxyl-functional polyester resin for polyurethane powder coating with reaction details is given in the book of Oldering and Hayward [Oldering, P., and Hayward, G., in Resins for Surface Coatings, Vol. II, SITA Technology, London, 1987, p.137.]. Different patents describe methods for making hydroxyl functional polyester resin for polyurethane powder coatings with minor variations with respect to the acid value, hydroxyl value, functionality of the resin and the choice of the raw materials. The hydroxyl-functional polyester for powder coatings could have an acid number less than 10, a molecular weight of 2800-3200, a hydroxyl number of 84, and a
Katz Lawrence E.
Petty Hebert E.
Su Shiu-Chin Huang
Waldman Bruce A.
Dawson Robert
Dilworth Michael P.
Grandinetti Paul
OSi Specialties Inc.
Robertson Jeffrey B.
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