Crosslinkable coating compositions

Details Crosslinkable coating compositions Crosslinkable coating compositions

2001-08-27

2003-08-26

Hampton-Hightower, P. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S050000, C524S501000, C524S507000, C524S839000, C524S840000, C524S591000

Reexamination Certificate

active

06610784

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to aqueous-based autoxidisably crosslinkable coating compositions, their preparation and use in forming films and coatings.
BACKGROUND OF THE INVENTION
Autoxidisably crosslinkable polymers are polymers which crosslink on exposure to oxygen. It is known that polymers which contain unsaturated fatty acid residues undergo crosslinking by autoxidation. The unsaturation in polymers from such groups imparts latent crosslinkability so that when a coating composition thereof is dried in air (often in conjunction with a drier salt) the composition undergoes crosslinking, thereby improving its properties such as mechanical properties (improved hardness and durability) and chemical resistance. A further advantage of coatings containing unsaturated fatty acid residues is an improved glossy appearance. EP 379007, EP 0017199 and EP 647655 all describe a one component emulsion which contain autoxidisable polymers with carboxylic acids groups to provide water dispersibility.
However disadvantages of autoxidisably crosslinkable polymers containing unsaturated fatty acid residues are that the curing process is slow (typically taking a period of days) and that yellowing of the coating occurs in time.
It is known in, for example, U.S. Pat. No. 4,198,811 and WO97/26303 to blend autoxidisably crosslinkable polymers with acrylic polymer dispersions to reduce yellowing and in some cases cost, however the performance of the resulting coatings, in particular the mechanical properties and the resistance to chemicals is greatly reduced.
BRIEF SUMMARY OF THE INVENTION
We have surprisingly found that compositions of autoxidisably crosslinkable polymers containing unsaturated fatty acid residues with a polymer which is not autoxidisably crosslinkable, but has certain other crosslinking means, not only reduces the cure time and yellowing of coatings derived from such a composition, but also that the performance of such a composition in other respects (such as the mechanical properties and chemical resistance) is not vitiated and is comparable to an improvement to the performance of the autoxidisable crosslinkable polymer containing unsaturated fatty acid residues alone.
According to present invention there is provided an aqueous crosslinkable coating composition comprising as aqueous dispersed components:
i) at least one autoxidisably crosslinkable organic polymer containing unsaturated fatty acid residues, and
ii) at least one vinyl polymer which is not autoxidisably crosslinkable and bears carbonyl functional groups, and wherein said composition has present therein carbonyl-reactive amine and/or hydrazine functional groups which impart crosslinkability to component (ii).
DETAILED DESCRIPTION OF THE INVENTION
For the sake of clarity by a carbonyl functionality in this specification (unless specified otherwise) is meant the carbonyl functionality of a ketone or aldehyde group. Such carbonyl functional groups in a vinyl polymer are normally chain-pendant and/or terminal groups.
By a hydrazine functional group is meant a carbonyl-reactive functional group of formula —NHNH
2
and also a carbonyl-reactive hydrazone group derived from such a group by reaction with a monoketone or monoaldehyde of at least two carbon atoms. It will become apparent that such functional groups are usually part of larger groups, such as those of formulae, —R—C(═O)—NH—NH
2
, —R—C(═O)—NH—N═C<, —R—NH—C(═O)NH—NH
2
, —R—NH—C(═O)—NH—N═C<, and —R—NH—NH
2
where R is optionally substituted alkylene, optionally substituted alicyclic, or optionally substituted aryl.
By an amine functional group is meant a carbonyl-reactive group of formula —NH
2
and carbonyl-reactive groups derived from such groups. Examples of amine functional groups include R—NH
2
, R—O—NH
2
, R—O—N═C<, —R—NH—C(═O)—O—N═C< and —R—NH—C(═O)—O—NH
2
where R is as described above.
By an autoxidisably crosslinkable polymer is meant a polymer which crosslinks on exposure to oxygen from air by virtue of containing unsaturated fatty acid residues.
By a not autoxidisably crosslinkable polymer is meant a polymer not containing unsaturated fatty acid residues.
For the purpose of this invention an “aqueous dispersion” of a polymer(s) means a dispersion of polymer(s) in a liquid carrier medium of which water is the principle component (at least 50 weight %, more usually at least 80 weight %, of the carrier medium). Minor amounts of organic liquids may optionally be present. The dispersion will typically comprise colloidally dispersed particles of the polymer(s), i.e. will typically be in the form of an aqeuous latex(ices).
Preferably the autoxidisably crosslinkable organic polymer containing unsaturated fatty acid residues is a polyurethane polymer. Other suitable polymers include alkyds which may be self-emulsifiable, water-based or emulsified alkyds.
In the invention composition, the carbonyl-reactive amine and/or hydrazine functional groups impart crosslinkability to the vinyl polymer(s) of component (ii) by virtue of the latter bearing carbonyl functional groups. It is nevertheless within the scope of the invention, albeit less preferred, for such amine and/or hydrazine functional groups to also impart crosslinkability to the polymer(s) of component (i) if this polymer(s) also bears carbonyl-functional groups—as is possible, but less preferred.
The disposition of the amine and/or hydrazine functional groups in the invention composition to impart crosslinkability as defined may be realised in various ways. More preferably hydrazine functional groups are used in the invention composition.
In a preferred embodiment, the carbonyl-reactive amine and/or hydrazine functional groups are present in the composition by virtue of being provided by added discrete compounds bearing 2 or more amine groups, hereinafter called polyamines, or 2 or more hydrazine functional groups, hereinafter called polyhydrazines. By “discrete” is meant that such compounds are exclusive of the polymers of components (i) and (ii). Preferably the polyamines or polyhydrazines are diamines or triamines (i.e. having 2 or 3 amine groups) or dihydrazines (i.e. having 2 hydrazine functional groups).
The presence of such a polyamine or polyhydrazine will impart crosslinkability to the vinyl polymer(s) of component (ii). However, if the polymer(s) of component (i) also bears carbonyl functional groups (as is possible as discussed above), such a polyamine or polyhydrazine will also impart crosslinkability to this polymer(s) of component (i) by reaction with the carbonyl functional groups thereof, i.e. in addition to crosslinkability by autoxidisation.
It is, furthermore, also possible for amine and/or hydrazine functional groups to be borne on the polymer(s) of component (i), i.e. the autoxidisably crosslinkable organic polymer containing unsaturated fatty acid residues could also bear carbonyl-reactive amine or hydrazine groups, thereby allowing the organic polymer(s) to undergo crosslinking by reaction with the carbonyl functional groups of the vinyl polymer(s) as well as crosslinking by autoxidation.
As discussed above, the polymer of component (i) in this embodiment may itself also bear carbonyl functional groups, and in such a case crosslinkability could also be provided by reaction between the polymer-based amine or hydrazine groups of the polymer(s) of component (i) and the polymer-based carbonyl functional groups of the polymer(s) of component (i) (in addition to that by reaction with the polymer-based carbonyl functional groups of the vinyl polymer(s) of component (ii)).
In a yet further embodiment, the not autoxidisably crosslinkable vinyl polymer(s) of component (ii) may in addition to bearing carbonyl functional groups also bear carbonyl-reactive amine or hydrazine groups. In such a case, crosslinkability could be provide by reaction between these polymer-based carbonyl functional groups and polymer-based amine or hydrazine groups of the vinyl polymer(s) of component (ii) (if present).
It is apparent fr

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