Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1996-12-20
2003-02-25
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S075000, C528S053000, C528S055000, C522S090000, C526S301000, C427S375000, C252S182180, C560S025000, C560S115000, C560S118000, C560S158000
Reexamination Certificate
active
06525161
ABSTRACT:
This invention is concerned with improvements relating to powder coating compositions and methods of coating substrates using such compositions.
Powder coating is a well-established process, basically comprising the application of a powdered fusible material to a substrate, heating of the powder in contact with the substrate to cause the powder to melt and reflow, and cooling the resultant melt to form a solid coating on the substrate. The coating material may simply comprise a film-forming thermoplastic material or may comprise a reactive material, e.g. an epoxy resin together with a curing agent therefore, so that during the course of melting and reflowing reaction occurs to cure the material in situ on the substrate. In any event, powder coating materials are generally such that they have to be melted and reflowed at relatively high temperatures, e.g. 150° C. or more. As a result, powder coating processes are generally not suitable for the coating of heat-sensitive materials such as wood or plastics material. In order to coat such materials, it would be necessary to have a product which had a relatively low melting temperature, e.g. below about 120° C., whilst at the same time being solid at ambient temperature, which material could subsequently be cured in situ on the substrate during the melting/reflowing stage or, afterwards.
U.S. Pat. No. 4,093,674 discloses a thermosetting powder coating composition comprising a solid resin having a Tg from 5° to 150° C. and free hydroxyl groups and a solid polyisocyanate compound, with a molar ratio of isocyanate groups in the latter to active hydrogen in the former of 0.2 to 2. Among examples of the solid resin are the polymers of hydroxyalkylacrylates preferably with Mn from 1,000 to 30,000. This powder coating composition is said to provide advantages over isocyanate crosslinking-type urethane resins wherein all the isocyanate groups are previously blocked with a phenol or an alcohol.
G.B.-A-1,590,413 discloses a urethane resin having at least 2 terminal ethylenically unsaturated groups and comprising the reaction product of at least one isocyanate-functional prepolymer and at least one unsatured monomer having a single isocyanate-reactive-hydrogen-containing group, said isocyanate-functional prepolymer being the reaction product of (i) at least one diisocyanate and (ii) a mixture of at least 2 polyols (at least 30 mole % being polymeric and at most 70 mole % being monomeric in the said mixture) in an NCO:OH ratio of at least 2.3. This urethane resin is mixed with similar unsaturated materials derived from polymeric polyols, with the unreacted excess of diisocyanate and with a reactive diluent which at the end produces flowable and fluid compositions with viscosities of about 4.5 Pa.s. No mention of powder coating may be found in this document.
U.S. Pat. No. 4,500,696 discloses powder surface coatings comprising polyols and a polyisocyanate component comprising blocked adducts of aliphatic diisocyanates. They involve no unsaturated alcohol.
U.S. Pat. No. 5,089,586 discloses acrylate-free water-dispersible allyl urethanes prepared from a polyglycol or its reaction product with an unsaturated dicarboxylic acid, a hydroxyallyl compound (preferably an allyl ether) and a diisocyanate.
International Application WO-93/19132 discloses mixtures, in a binder composition for powder coatings, of an unsaturated polyester and an oligomer having a plurality of allyl ether groups and having further urethane groups.
EP-A-0 410 242 relates to a powder coating composition which comprises the reaction product of one or more organic polyisocyanates with one or more monovalent alcohols containing (meth)acryloyl groups, and one or more compounds which are free from (meth)acryloyl groups and contain at least two isocyanate-reactive groups.
FR-A-2 091 106 relates to a process for preparing a polymer having C=C double bonds, capable of being polymerized, comprising a polyisocyanate which allows to bind an ester which contains polymerizable C=C double bonds and which has active H, to a matter containing several H.
GB-1 443 715 refers to a copolymerizable fluid composition comprising a photocopolymerizable ethylenically unsaturated liquid monomer, a photosensitizer and a photopolymerizable divinylurethane monomer prepared from xylylene diisocyanate, (meth)acrylic esters having a hydroxyl group and di-, tri-, tetra-, penta- or hexavalent alcohol.
U.S. Pat. No. 4,078,015 concerns a copolymerizable composition including a polymerizable acrylic diurethane and a polymerizable polyacrylic polyurethane which is the reaction product of an organic diisocyanate, a &bgr;-hydroxy alkyl ester of an acrylic acid, and a diol.
It has now been found, in accordance with the present invention, that useful solid ethylenically unsaturated materials, having relatively low melting point and suitable for use in powder coating compositions may be prepared by reacting a diisocyanate with one or more monohydric alcohols, optionally in combination with a monomeric polyol such as a dihydric alcohol.
According to one embodiment of the invention, therefore, there is provided a powder coating composition comprising a powdered solid ethylenically unsaturated material having a melting point from about 60° to 120° C. obtained by reacting a polyisocyanate with an at least stoechiometric amount of an alcoholic component comprising
at least two monovalent alcohols, some of them bearing an ethylenic unsaturation derived from acrylic acid or methacrylic acid, and optionally
at least a monomeric polyol.
Said monomeric polyol can be a dihydric aliphatic alcohol or a dihydric polyalkylene glycol.
In accordance with a preferred embodiment of the invention the polyisocyanate is reacted with an at least stoichiometric amount of :
(i) a monohydric alcohol component, or
(ii) a monohydric alcohol component followed by another different monohydric alcohol component, or
(iii)a monohydric alcohol component, followed by a dihydric alcohol component, followed by a monohydric alcohol component, or
(iv) a dihydric alcohol component, followed by a monohydric alcohol component alone or in admixture with a dihydric alcohol component,
the monohydric alcohol component(s) comprising a monohydric aliphatic alcohol or an etherified or esterified dihydric aliphatic alcohol or dihydric polyalkylene glycol, at least a part of which bearing an ethylenic unsaturation derived from acrylic acid or methacrylic acid and the dihydric alcohol component comprising a dihydric aliphatic alcohol or a dihydric polyalkylene glycol and being preferably used in an amount not more than 50%, preferably not more than 25%, of the stoichiometric amount of hydroxyl groups required to react with the isocyanate groups on the polyisocyanate.
As noted above, it is a requirement of the present invention that the material obtained (hereinafter simply referred to as an “oligourethane”, “urethane acrylate” or “oligomer”) have a melting point of from 60 to 120° C. (the term “melting point” as used herein means the melting point as determined by the ring and ball method).
It is also most often preferred that the powdered solid material of the invention have a viscosity in the range from 0.1 Pa.s to 2.5 Pa.s.
Suitable polyisocyanates for use in the preparation of the oligourehanes include toluene diisocyanate, diphenylmethane-4,4′-diisocyanate, hexamethylene-1,6-diisocyanate, napthylene-1,5-diisocyanate, 3,3,′-dimethoxy-4,4,′-biphenyldiisocyanate, 3,3′-dimethyl-4,4,′-biphenyldiisocyanatei phenylene diisocyanate, 4,4′-biphenyldiisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate and tetramethylene xylene diisocyanate.
A wide variety of monohydric aliphatic alcohols may be used to produce the oligourethanes, e.g. C
1
to C
22
alcohols. Typical etherified dihydric alcoholic materials which may be used as monohydric alcoholic component include propylene glycol methyl ether, dipropylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, tripropylene glycol buty
Cray Valley Iberica
Fein Michael B.
Gorr Rachel
O'Connor Cozen
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