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
2003-02-28
2004-07-06
Niland, Patrick D. (Department: 1714)
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...
C427S372200, C427S385500, C524S502000, C524S507000, C524S515000, C524S522000, C524S523000
Reexamination Certificate
active
06759472
ABSTRACT:
The present invention relates to aqueous polymer dispersions comprising alkyds and vinyl polymers, a process for making such dispersions and the use of such dispersions for coatings.
The term alkyd is used to describe unsaturated fatty acid residue containing esters which are prepared from the reaction of a polyhydric alcohol, a polybasic acid and a drying oil. The unsaturation in the ester polyol imparts latent crosslinkability so that when a coating composition thereof is dried in the air, often in conjunction with a drier salt, the coating material undergoes crosslinking (autoxidation) and thereby improving its properties, for example its chemical resistance, hardness and durability. Alkyds however, due to the unsaturated fatty acid residues may be water-insoluble and therefore not easy to disperse in water, and furthermore alkyds are known to have a slow physical drying time. Vinyl polymers, on the other hand, are not known to suffer from such drawbacks.
Vinyl polymer dispersions are commonly used as aqueous polymer dispersions for coatings, however coatings derived from vinyl polymer dispersions tend to have poor gloss, poor filling and insufficient wood wetting and often require coalescing solvents to aid film formation. Alkyds, however, are known not to have such disadvantages.
Thus, it could be expected that a mixture of an alkyd dispersion and a vinyl polymer dispersion would improve the negative effects mentioned above of both the alkyd and the vinyl polymer on resultant coatings. Tijs Nabuurs and Anton German, Progress in Organic Coatings, Vol: 27, pages 163-172 (1996) discuss that a mixture of alkyd and vinyl polymers can exist as a blend of a vinyl polymer dispersion and an alkyd dispersion, however although the dispersions are blended, the alkyd and vinyl polymers still exist in distinct particles or phases. U.S. Pat. No. 3,919,145 and 4,108,811 describe water based compositions prepared by blending an oxidatively curable oil or an alkyd modified polyurethane with an acrylic or vinyl acetate latex.
A more effective way to form an intimate dispersion could be expected to be by forming the vinyl polymer in-situ, i.e. where all of the vinyl monomers are polymerised in the presence of the alkyd dispersion. U.S. Pat. No. 4,413,073 discloses the preparation of a film forming polymer from a dispersion comprising individual particles of preformed polymer and monomers where the monomers are polymerised in the presence of an amphiphatic compound. S.Wang et al, Journal of Applied Polymer Science, Vol 60, pages 2069-2076 (1996) discuss the emulsion and mini-emulsion copolymerisation of acrylic monomers in the presence of an alkyd.
It has been found, however that a disadvantage with such an approach is that unsaturation (due to the unsaturated fatty acid residues) in an alkyd tends to impair conversion of vinyl monomer to vinyl polymer and this effect becomes more pronounced as the level of unsaturation in the alkyd increases. A possible explanation given for the reduction of vinyl monomer conversion is that the unsaturated sites on the alkyd capture free radicals and therefore slow down the vinyl polymerisation which of course proceeds by a free radical initiated mechanism. Furthermore, the unsaturated site on the alkyd is partially or even entirely lost, resulting in the partial or total loss of the autoxidation properties of the alkyd.
We have discovered stable aqueous dispersions of alkyds and vinyl polymers, which overcome the problems discussed above.
Thus, according to a first embodiment of the present invention there is provided an aqueous dispersion comprising:
(i) alkyd;
(ii) vinyl polymer I
(iii) vinyl polymer II; and
(iv) liquid medium
wherein said vinyl polymer I is pre-formed prior to incorporation into the aqueous dispersion and wherein said vinyl polymer II is prepared in the presence of the alkyd and vinyl polymer I.
Preferably the vinyl polymer I and the alkyd are each pre-formed prior to incorporation into the aqueous dispersion. Surprisingly, in spite of the alkyd and vinyl polymer I being preformed, and therefore apparently consisting of a mixture of distinct particles or phases, the improvements resulting from such polymer types is not impaired.
According to a second embodiment of the present invention there is also provided a process for preparing an aqueous dispersion according to the present invention comprising combining:
(a) alkyd;
(b) olefinically unsaturated monomer(s);
(c) vinyl polymer I; and
(d) liquid medium;
at a temperature in the range of from 0 to 85° C., followed by polymerisation of the olefinically unsaturated monomer(s) to form a vinyl polymer II.
For the purposes of this invention an “aqueous dispersion” means a dispersion of the alkyd and vinyl polymers I and II in a liquid medium comprising at least 50% by weight, more usually at least 80% by weight of water. Minor amounts of organic liquid(s) may be present if desired or required. Furthermore the term “dispersion” is intended to additionally embrace emulsions, suspensions or solutions, the exact nature of the dispersion depending on the components used.
We have found that the aqueous dispersion of the invention does not suffer from impaired autoxidation properties of the alkyd and a higher solids level is attainable in the aqueous polymer dispersion as compared to the corresponding blends. Furthermore low or no volatile organic compounds are required to aid dispersion of the alkyd, as the dispersion of the alkyd in water is enabled not only by the nature of the alkyd but also by the presence of the olefinically unsaturated monomer(s) which are used as a reactive diluent and reduce the viscosity of the alkyd without contributing to the levels of volatile organic compounds (due to the subsequent polymerisation thereof to a polymer), and thus any requirement for additional solvent may be minimised.
Not wishing to be bound by a theory, it is believed that the alkyd may act as a non-volatile coalescing agent and that the majority of the olefinically unsaturated monomer(s) used to make vinyl polymer II diffuse from dispersed alkyd particles, through the water phase into the pre-formed dispersed vinyl polymer I particles (due to the better compatibility of the olefinically unsaturated monomer(s) with the vinyl polymer I than with the alkyd) where they swell the dispersed vinyl polymer I particles. Any free radical polymerisation of the olefinically unsaturated monomer(s) then does not result in the loss of the unsaturation in the alkyd since the free radical polymerisation predominantly occurs in the vinyl polymer I particles.
The alkyd may be any known in the art and for the purposes of this specification the term alkyd includes derivatives thereof such as uralkyds. General processes for preparing alkyds are disclosed in U.S. Pat. No. 4,108,811 and in “Alkyd Resin Technology”, T C Patton, 1962, Publisher John Wiley & Sons Inc.
Alkyd polyols are preferably prepared by the direct reaction of a triglyceride oil with for example a N,N-dialkanolamine, usually in the presence of a strong base such as sodium methoxide. Suitable triglyceride oils include but are not limited to soyabean oil, palm oil, linseed oil, tung oil, rapeseed oil, sunflower oil, dehydrated caster oil, tall oil and safflower oil.
Uralkyds may be prepared by reacting alkyds having isocyanate-reactive groups with polyisocyanates and optionally other components having isocyanate-reactive groups. Isocyanate-reactive groups are defined as groups which will react with an isocyanate group (—NCO) and examples include —OH, —NH
2
, —NH—, and —SH. Preferred isocyanate-reactive groups are —OH. Other components include but are not limited to polyamines and polyols, for example polyols having water-dispersing groups, as described below.
Examples of suitable polyisocyanate(s), (normally diisocyanate(s)) include aliphatic and cycloaliphatic polyisocyanates such as ethylene diisocyanate, 1,6-hexamethylene diisocyanate HDI, isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, 4,4′-dicyclohexylmethane dissocyanate, cyclopentyl
Overbeek Gerardus Cornelis
Scheerder Jurgen
Steenwinkel Pablo
Tennebroek Ronald
Avecia BV
Morgan & Lewis & Bockius, LLP
Niland Patrick D.
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