Crosslinkable coating compositions

Details Crosslinkable coating compositions Crosslinkable coating compositions

2001-09-20

2003-04-29

Seidleck, James J. (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...

C525S217000, C525S221000, C428S522000, C428S423100, C428S500000

Reexamination Certificate

active

06555625

ABSTRACT:

The present invention relates to aqueous-based autoxidisably crosslinkable coating compositions, their preparation and use in forming films and coatings.
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 one component emulsions which contain antoxidisable polymers having carboxylic acid functional groups to provide water dispersability.
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 in U.S. Pat. No. 4,108,811 and WO 97/26303, 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. U.S. Pat. No. 5,559,192 discloses a composition containing an autoxidisable polymer and an acetoacetate functional vinyl polymer however the acetoacetate functional groups do not take part in any crosslinking of the composition.
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 acetoacetyl functional groups, and
wherein said composition has present therein acetoacetyl-reactive amine and/or hydrazine functional groups which impart crosslinkability to component (ii).
By an acetoacetyl functional group in this specification is meant a group having the formula:
where the methyl group may optionally be mono, di or tri-substituted (for example so as to provide therewith a higher alkyl group of 2 to 10 carbon atoms, usually 2 to 4 carbon atoms) and the methylene group may optionally be monosubstituted (usually by alkyl of 1 to 4 carbon atoms, particularly methyl). The methyl group could also, in principle, be replaced by other groups such as a cyclic phenyl group, or an optionally substituted heterocyclic group, and the use of such alternative groups are also considered to provide acetoacetyl functional groups for the purpose of this specification. A polymer-bound acetoacetyl functional group will normally be provided in the environment of an acetoacetate grouping of formula:
or an acetoacetamide grouping of formula:
or a 1,3 diketone grouping of formula:
where R
1
is hydrogen or a monovalent hydrocarbyl radical such as an (optionally substituted) alkyl, aryl, aralkyl or alkaryl radical (usually of 1 to 10, particularly 1 to 6 carbon atoms) and R
2
is a divalent hydrocarbyl radical such as an (optionally substituted) alkylene, arylene, aralkylene or alkarylene radical (usually of 1 to 20, particularly 1 to 10 carbon atoms).
Suitable optional substituents for the groups represented by R
1
and R
2
and for the methyl or methylene groups of Formulae (1) to (4) may be selected from —CN, C
1-4
-alkoxy, phenyl, halogen such as —F, —Cl and —Br and C
1-4
-alkyl.
It is preferred, however, that the acetoacetyl functional group is provided by an acetoacetate or acetoacetamide group, and more preferably by an acetoacetate group.
By a hydrazine functional group is meant an acetoacetyl-reactive functional group of formula —NHNH
2
and also an acetoacetyl-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 an acetoacetyl-reactive group of formula —NH
2
, —NH— and acetoacetyl-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 purposes of this invention an “aqueous dispersion” of a polymer(s) means a dispersion of a polymer(s) in a liquid carrier medium of which water is the principle component (at least 50 weight %, more usually at least 80 weight %, or 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 aqueous 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 acetoacetyl-reactive amine and/or hydrazine functional groups impart crosslinkability to the vinyl polymer(s) of component (ii) by virtue of the latter bearing acetoacetyl 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 acetoacetyl-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 amine functional groups are used in the invention composition.
In a preferred embodiment, the acetoacetyl-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 acetoacetyl functional groups (as is possible as discussed above), such a polyamine or polyhydr

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