Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-19
2003-03-18
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S213000, C524S188000, C524S431000, C524S904000, C556S420000, C427S387000
Reexamination Certificate
active
06534568
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to powder coating and adhesive formulations utilizing organosilane compounds, or their hydrolyzates or condensates, 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 coatings 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.
SUMMARY OF THE INVENTION
One aspect of the invention is a powder coating or adhesive formulation which includes as components thereof (A) at least one silane of the formula I:
or the hydrolyzates or condensates of such silane, where R
1
is a hydrocarbon, acyl, alkylsilyl or alkoxysilyl 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; Z is a direct bond or a divalent organic linking group; X is an m-valent organic group or H; and m is 1-20, and (B) at least one organic resin component.
One embodiment of the invention is a powder coating or adhesive formulation as described above where the silane has the formula:
wherein A and B are independently NH or O and R
1
, R
2
, R
3
, a and m are as previously defined. In some embodiments the silane is a carbamate compound of formula II, i.e. one of A and B is NH and the other is O.
Silane carbamate compounds of formula II having a melting point in the range of about 30° C. to about 170° C. make up a further aspect of the invention.
Silanes, useful in the present invention, can be prepared via many synthetic routes. For instance, a terminally unsaturated organic compound can be hydrosilylated to give a silane. Further chemical reactions can be carried out on silanes having organo functional groups. Silyl carbamates, useful in the invention can be prepared by reaction of polyol compounds with isocyanatopolyalkoxysilanes. Other carbamates, useful in the invention can be prepared by reaction of polyisocyanates with hydroxyalkylpolyalkoxy silanes. Such silyl carbamates can also be made by reaction of a polyisocyanate with a terminally unsaturated alcohol, and subsequent hydrosilation of the reaction product thereof. Silyl isocyanates can be oligomerized to: uretdiones, allophanates, biurets, isocyanurates. Silyl amines can be reacted with anhydrides to yield amides or with isocyanates to yield ureas.
Powder coatings or adhesives within the invention may be based on a conventional resin system. In such coatings the silane component of formula I function as property modifying and/or crosslinking additives. Silane compounds of formula I, where m is greater than 1, and especially those in which X is polymeric, may be used as the base crosslinking resin for the coating formulation.
The silane may be coupled with fillers or pigments. This is accomplished by means of a hydrolysis or condensation reaction mechanism in which the silane compound actually reacts with the filler or pigments. Powder coatings employing such treated fillers or pigments make up yet another aspect of the invention. Preferred such fillers or pigments are ones in which the silane has an alkyl, epoxy, acrylate, methacrylate, acid anhydride, polyether, hydroxyalkyl, or amine (especially primary or secondary amine) group, thereon or the silane is one of formula II. Novel TiO
2
fillers treated with silanes of formula II or of formula III
Q—R
3
—Si(OR
1
)
a
R
2
3−a
III
where Q is a monovalent organic group having at least one epoxide, amine, methacryl, acryl, acid anhydride or hydroxyalkyl functionality and R
1
, R
2
and R
3
, are as previously defined constitute a further aspect of the invention. Novel fillers and pigments treated with a silane of formula II, make up yet a further aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Powder coating systems may be based on an organic resin system including thermoplastic materials and thermosettable materials. The term “resin” is used in the art to refer to materials which are settable. Thermoplastic polymers are “resins” because they are settable from the melt form. Thermosetting materials generally are commonly referred to as resins regardless of their status as polymers, prepolymers or monomers. Herein, the term “resin” includes both thermoplastic polymers and thermosetting materials.
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 met
Barbera Bruce C.
Katz Lawrence E.
Petty Herbert E.
Su Shiu-Chin Huang
Waldman Bruce A.
Crompton Corporation
Dawson Robert
Dilworth Michael P.
Robertson Jeffrey B.
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