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
2002-08-28
2004-05-04
Wu, David W. (Department: 1713)
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...
C524S512000, C524S502000, C524S507000, C524S542000, C524S592000, C524S590000, C524S602000, C522S092000, C522S094000, C522S100000, C522S109000, C522S112000
Reexamination Certificate
active
06730733
ABSTRACT:
The present invention relates to certain dual-cure polymer compositions, their use in coating, and coatings derived therefrom.
There is an ongoing demand to provide aqueous polymer compositions suitable for coatings which have an excellent balance of properties, such as for example good dispersion stability of the components of the compositions, good chemical and solvent resistance of coatings formed from the compositions, and a combination of facile film formation (i.e. low minimum film forming temperature MFT, preferably ambient temperature or below) as well as good hardness and blocking resistance in coatings formed from the composition at low or no coalescent aid requirement in the composition (these being organic solvents or plasticisers which assist film formation but may be undesirable for environmental reasons).
We have now discovered certain aqueous compositions having such an excellent balance of properties as mentioned above.
According to the present invention there is provided an aqueous polymer composition suitable for coating which comprises the following components dispersed in water:
(1) a combination of an acrylic polymer(s) A and an acrylic polymer(s) B where polymer(s) A has a Tg of not more than 30° C. and polymer(s) B has a Tg of at least 35° C., more preferably at least 45° C., which is at least 25° C. higher than the Tg of polymer A, and wherein one or both of polymers A and B bear crosslinker functional groups capable of imparting ambient-temperature crosslinkability to component (1) in a coating formed from the composition via the formation of non-radically-formed covalent bonds; and
(2) a self-dispersible, ionically stabilised polymer having olefinically unsaturated bond functionality capable of imparting radiation-curability thereto in a coating formed from the composition.
There is also provided according to the invention a method of coating a substrate using an aqueous polymer composition as defined above.
There is further provided according to the invention a coating obtainable or derived from an aqueous composition as defined above.
There is further provided according to the invention a substrate having a coating obtainable or derived from an aqueous composition as defined above.
Aqueous polymer dispersions for coatings which comprise two polymers of differing Tg, one having a Tg of not more than 10° C. and the other having a Tg>25° C., and also a multi functional material having at least two ethylenically unsaturated groups which can each participate in a free-radical initiated addition polymerisation, are known from EP-A-0736573. The dispersions are said to be curable by heat or radiation. In addition, the polymers of differing Tg may bear groups for grafting or crosslinking purposes, although these are not employed in the worked examples. The multifunctional material is said at page 4 lines 30 to 32 to be either not emulsified or emulsified in the water of the polymer dispersion, and in the latter case it may be emulsified with the aid of surfactants such as those used in aqueous emulsion polymerisation. While it is further stated at page 4 lines 7 to 12 that the multifunctional compounds may incorporate internal hydrophilic components to facilitate such emulsification (although this is not exemplified in a worked example), the earlier-stated requirement to also employ external surfactant when emulsification is required is not said to be negated, so the multi-functional compound of EP-A-0736573 even when containing internal hydrophilic components is not self-dispersible as defined in this specification (see later). We have found that the aqueous compositions of the present invention surprisingly provide improved properties in comparison to the type of composition taught in EP-A-0736573, and in particular improved resistance to blocking of coatings made from the compositions, both before and after radiation curing, and improved dispersion stability.
For the purposes of this invention, by an “aqueous polymer composition” is meant a dispersion of polymers of components (1) and (2) in a liquid carrier medium of which water is the principal component (at least 50 weight %, more usually at least 80 weight %). Minor amounts of organic liquids may optionally be present although it is preferred that the aqueous composition is substantially solvent-free, by which is meant that the composition contains less than 5 wt % of organic solvent(s) based on total polymer solids, more preferably less than 2 wt %, and most preferably no solvent at all. (In this specification organic plasticisers are intended to be within the scope of the term “solvent”; these, like coalescent solvents, are also used in the art to decrease MFT although strictly speaking they are not solvents).
The invention composition will typically comprise colloidally dispersed particles of the polymers of components (1) and (2), i.e. will typically be in the form of an aqueous polymer latex.
The MFT of the invention composition is preferably less than 35° C., and is particular ambient temperature or below. By ambient temperature is meant herein a temperature within the range 10 to 25° C.
The crosslinker functional groups of the acrylic polymer(s) of component (1) are usually chain-pendant and/or terminal. The groups on the polymer of component (2), which provide radiation curability are olefinically unsaturated bonds and are usually chain-pendant and/or terminal, but may also be in-chain.
The aqueous invention composition may be termed a “dual-cure” composition because the polymers of components (1) and (2) are crosslinkable, after forming a film from the composition, by different crosslinking mechanisms, as will now be explained (although, as will also be explained, in some embodiments of the invention, the polymer of component (2) takes part in the crosslinking of the polymer(s) of component (1) as well as crosslinking by a different crosslinking mechanism).
In component (1), one or both of acrylic polymers A and B bear crosslinker functional groups, i.e. groups which can impart ambient-temperature crosslinkability to this component via the formation of non-radically-formed covalent bonds, by which we mean herein covalent bonds which are formed other than by a free-radical addition mechanism (auto-oxidation being considered as forming bonds by a free radical mechanism for the purposes of this invention, ie such bond formation being excluded from the scope of the invention) or by an anionic or cationic addition polymerisation mechanism. (However, crosslinking by coordinate bond formation as e.g. by lone electron pair donation from groups such as carboxyl groups (oxygen atoms thereof) to acceptor shells of metal ions of appropriate metal compounds is intended to be within the scope of the term non-radically-formed covalent bonds). To form such bonds, such crosslinker groups must undergo reaction with other groups borne by compounds already present in the composition or which are subsequently added thereto. (In the case of coordinate bond formation the lone pair of atoms of crosslinker groups coordinate to acceptor metal ion shells of already present or subsequently added metal compounds).
In the most preferred embodiment of the invention (embodiment X for future reference), one or both of polymers A and B carry crosslinker groups and the composition contains, or is subsequently mixed with, an external crosslinking agent having 2 or more groups (or in the case of coordinate bond formation, an acceptor metal ion shell—see eg EP-A-6547 and U.S. Pat. No. 2,904,526) which are reactable with the crosslinker groups on polymers A and/or B to form the crosslinking covalent bonds. By “external” is meant that the crosslinking agent is exclusive of the polymers of components (1) and (2) (i.e. is not provided by any of these polymers).
For the achievement of ambient-temperature crosslinkability in embodiment X it is preferred that the crosslinker groups on the polymers A and/or B are carbonyl groups (by which is meant, unless otherwise specified, the carbonyl functionality of a ketone or aldehyde group)
Nabuurs Tijs
Overbeek Gerardus Cornelis
Steenwinkel Pablo
Tennebroek Ronald
Avecia Limited
Morgan & Lewis & Bockius, LLP
Sastri Satya B
Wu David W.
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