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
2001-01-12
2004-06-01
Moore, Margaret G. (Department: 1712)
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...
C525S103000
Reexamination Certificate
active
06743854
ABSTRACT:
This application claims priority of European Patent Application No. 00300192.2 filed on Jan. 12, 2000.
FIELD OF THE INVENTION
The present invention relates to a coating composition fast curing at ambient temperature (touch dry in less than 2 hours at 25° C.) with a high solids content (>70% by weight) and a low VOC (<250 grams solvent per liter of the composition, g/l) which can be used in durable protective coatings.
BACKGROUND OF THE INVENTION
There has been increased concern in recent years about the release of volatile solvents into the atmosphere, and there has been a consequent need to reduce the volatile organic solvent content of coating, sealant, and adhesive compositions. This has not been easy for coating compositions, which require a relatively low viscosity of below 20 Poise for application by the usual methods of spray, roller or brush, and particularly not for coating compositions which have to be applied and cure rapidly at ambient temperature, for example coatings for large structures such as ships, bridges, buildings, industrial plants, and oil rigs.
Coating compositions generally need to contain a polymer to confer film-forming properties, but any polymer used needs to be of sufficient molecular weight to give the required low viscosity, particularly after pigmentation as a paint. Such low-viscosity polymers often require long curing times to develop satisfactory mechanical properties, especially when cured at low temperature.
In WO 98/04594 a process is disclosed for the preparation of a curable polymer composition by polymerisation of a functional olefinically unsaturated monomer in the presence of a reactive diluent which is a liquid organic compound of viscosity less than 2 Pa.s (20 Poise) having at least one functional group which is substantially non-reactive with the functional olefinically unsaturated monomer and which is capable of reacting with a curing agent to form a polymer network. The major drawback of this technology is that this low-viscous coating material results in a low final film T
g
and moderate durability.
In WO 96/16109 and WO 98/32792 an epoxy-polysiloxane coating composition is disclosed that is prepared by combining water, a polysiloxane, a difunctional aminosilane hardener, optionally an organooxysilane, and a non-aromatic epoxy resin. The maximum amount of solvent added to these compositions is approximately 420 g/l. The compositions are intended to be used as protective coatings for primed or galvanised steel, aluminium, concrete, and other substrates at a dry film thickness in the range of 25 &mgr;m to about two millimetres. Whilst these compositions are employed as durable topcoats, their gloss and colour retention properties when exposed to natural or accelerated test conditions (UV-A, UV-B) are not as expected for polysiloxane based compositions. This strongly affects the appearance of a coated substrate.
U.S. Pat. No. 4,446,259 discloses a coating composition having a liquid carrier and a binder which is a blend of an olefinically unsaturated polymer containing glycidyl groups and a crosslinkable polysiloxane having attached to the silicone atoms of its backbone alkyl, phenyl, and hydroxyl groups. These compositions are used as ambient temperature curing protective coatings. The major drawback of these compositions is the presence of a relatively large amount of organic solvent in the composition.
EP 0 822 240 discloses a coating resin composition comprising a silica-dispersed oligomer solution of an organosilane, an acrylic resin, and a curing catalyst. The coating resin compositions on average have a solid content in the range of 40-50% by weight. Consequently, these coating compositions have a VOC well above 250 g/l.
WO 97/22728 discloses a heat-resistant powder coating composition comprising at least one glycidyl-functional polyacrylic polymer and at least one hydroxyl-functional polysiloxane. This composition is cured at temperatures greater than about 250° C. This high-curing temperature renders the composition unsuitable for use in the coating of large structures such as ships, bridges, etc. Further, this coating composition is not curable unless the coated surface is heated.
SUMMARY OF THE INVENTION
The present invention provides a solution to the drawbacks associated with the above-mentioned prior art. The ambient temperature curing coating composition according to the present invention comprises:
a linear or branched polysiloxane having the formula
wherein each R1 is independently selected from the group consisting of alkyl, aryl, alkoxy groups having up to six carbon atoms, reactive glycidoxy groups, and OSi(OR3)
3
groups, wherein each R3 independently has the same meaning as R1, each R2 is selected from the group consisting of hydrogen and alkyl and aryl groups having up to six carbon atoms, and wherein n is selected so that the molecular weight of the polysiloxanes is in the range of from 200 to about 5,000, preferably 500-2,000,
a glycidyl-functional acrylic polymer, and
a hardener.
DETAILED DESCRIPTION OF THE INVENTION
It is preferred that R1 and R2 comprise groups having fewer than six carbon atoms to facilitate rapid hydrolysis of the polysiloxane, which reaction is driven by the volatility of the alcohol analogue product of the hydrolysis. R1 and R2 groups having more than six carbon atoms tend to impair the hydrolysis of the polysiloxane due to the relatively low volatility of each alcohol analogue. Preference is given to the use of alkoxysilyl-functional polysiloxane. Methoxy-, ethoxy-, and silanol-functional polysiloxanes having molecular weights in the range of about 400 to about 2000 are preferred for formulating coating compositions according to present invention. Methoxy-, ethoxy-, and silanol-functional polysiloxanes having molecular weights of less than 400 would produce a coating composition that would be brittle and offer poor impact resistance. Any liquid methoxy-, ethoxy-, and silanol-functional polysiloxane with a molecular weight above 400 can be used, though it is preferred to use polysiloxanes with a molecular weight of less than 2000, as they enable the production of compositions that require few if any additional solvents to achieve application viscosity, i.e. which can be used without adding solvent in excess of current volatile organic content (VOC) requirements. In general, a high-molecular weight polysiloxane can be used without violating VOC requirements by mixing it with a reactive or non-reactive diluent. However, normally this will affect film properties.
Suitable polysiloxanes that can be used in the composition according to the present invention include: DC 3037 and DC 3074 (both ex Dow Corning), or SY 231, SY 550, and MSE 100 (all ex Wacker)
The glycidyl-functional acrylic polymer can be prepared by copolymerizing one or more olefinically unsaturated monomers with a glycidyl-functional olefinically unsaturated monomer.
Examples of ethylenically unsaturated monomers which can be copolymerised with such a glycidyl-functional olefinically unsaturated monomer are acrylic esters such as butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-hexyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl methacrylate or acrylate, cyclohexyl (meth)acrylate, 2,2,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, acrylonitrile, methacrylonitrile, trimethoxysilyl propyl(meth)acrylate, and vinyl compounds such as styrene, vinyl acetate or vinyl chloride, wherein the notation (meth)acrylate means acrylate or methacrylate.
The glycidyl-functional olefinically unsaturated monomer in general can be any one of the above-mentioned olefinically unsaturated monomers functionalised with one or more epoxide groups. Glycidyl methacrylate is one of the preferred monomers in the preparation of the glycidyl-functional acrylic polymer.
To prepare a coating composition with a low VOC, the glycidyl-functional acrylic polymer can be prepared, for example, by free radical polymerisation or any other reaction in the presence of
Nixon Steve Alister
Yeats Keith
International Coatings Limited
McGillycuddy Joan M.
Moore Margaret G.
Parker Lainie E.
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