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
2001-06-12
2003-06-17
Cain, Edward J. (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...
C524S588000
Reexamination Certificate
active
06579932
ABSTRACT:
This application is the national phase of International Patent Application No. PCT/EP99/08158, filed on Oct. 20, 1999, and which claims priority of European Patent Application No. 98203590.9, filed Oct. 26, 1998.
This invention relates to aqueous coating compositions and more particularly to aqueous coating compositions comprising a mixture of different polyurethane dispersions.
Aqueous coating compositions comprising a polyurethane dispersion are well-known for the production of film coatings on various substrates such as wood, metal, fabrics, and plastics. These may be useful for the provision of, for example, protective coatings, since polyurethane resins possess very desirable properties such as good chemical resistance, abrasion resistance, toughness, adhesion, and durability.
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous coating composition comprising: 5-95 wt. % of at least one polyurethane/acrylate hybrid dispersion and 95-5 wt. % of at least one dispersion of a polyurethane resin with oxidatively drying groups.
SUMMARY OF THE INVENTION
The weight percentages are based on the weight of total solid polyurethane resins present. The aqueous coating composition may comprise a mixture of different polyurethane/acrylate hybrid dispersions and/or a mixture of dispersions of different polyurethane resins with oxidatively drying groups.
It has been found that the use of a mixture of a polyurethane/acrylate hybrid dispersion and a dispersion of a polyurethane resin with oxidatively drying groups in aqueous coating compositions provides synergistic properties which cannot be obtained when using one of the polyurethane resin dispersions. Such properties are, for example, levelling, open time, and processability. Other properties such as scratch resistance and hardness remain at a very good level. Furthermore, coating compositions with a low VOC can be provided, as required by the present environmental laws.
In Tennebroek et al.,
European Coatings Journal
, 1997, No. 11, pp. 1016-1021, an evaluation is provided of coating compositions comprising either a polyurethane/acrylate hybrid dispersion or a dispersion of a polyurethane resin with oxidatively drying groups. In Bell et al.,
Paint
&
Ink International
, September/October 1996, pp. 6-10, an evaluation is provided of coating compositions comprising a dispersion of a polyurethane resin with oxidatively drying groups for application on wood surfaces. EP-A-0 332 326 discloses coating compositions comprising polyurethane/acrylate hybrid dispersions. None of the above-mentioned publications teaches or suggests the possibility of combining a polyurethane/acrylate hybrid dispersion with a dispersion of a polyurethane resin with oxidatively drying groups, nor are the synergistic effects obtained by this combination recognised.
Preferably, the aqueous coating composition comprises: 40-90 wt. % of at least one polyurethane/acrylate hybrid dispersion and 10-60 wt. % of at least one dispersion of a polyurethane resin with oxidatively drying groups.
The aqueous coating composition preferably has a VOC of 350 g/l or less, more preferably a VOC of 50 to 350 g/l, most preferably a VOC of 100 to 300 g/l, measured according to ASTM 3960-92.
A polyurethane/acrylate hybrid dispersion is defined as an aqueous dispersion comprising at least one polyurethane resin and at least one vinyl polymer. A vinyl polymer in this specification is meant to be a polymer obtained by the free radical addition polymerisation of at least one olefinically unsaturated monomer.
The polyurethane/acrylate hybrid dispersion may be formed by subjecting one or more vinyl monomers to free radical polymerisation conditions in the presence of a dispersion of an already chain-extended polyurethane resin using conventional techniques. Thus, free radical initiators may be added to a mixture of polyurethane dispersion and vinyl monomer or, alternatively, monomer may be added gradually to a polyurethane dispersion containing initiator.
In another variant of the preparation of polyurethane/acrylate hybrid dispersions a solution is formed of an isocyanate-terminated prepolymer in at least one vinyl monomer. The solution is then emulsified in an aqueous medium and the isocyanate-terminated prepolymer is chain extended. Subsequently, either vinyl monomer can be added and the polymerisation thereof initiated or the polymerisation of the vinyl monomer can be initiated and further vinyl monomer can be added during polymerisation.
Conventional free radical initiators may be used such as hydrogen peroxide, t-butyl hydroperoxide, persulphates such as NH
4
persulphate, K persulphate, and Na persulphate. The amount generally is 0.05 to 3 wt. %, based on the weight of total vinyl monomers charged. Other suitable free radical initiators for such variants include mixtures such as a combination of t-butyl hydroperoxide, isoascorbic acid, and Fe.EDTA.
The weight ratio of polyurethane resin to vinyl resin in the composition is suitably in a range of 9:1 to 1:9, more preferably 5:1 to 1:5.
Preferably, the polyurethane/acrylate hybrid dispersion comprises hydrazine- (or hydrazone-) functional groups and carbonyl-functional groups to provide a self-crosslinking reaction. The hydrazine- (or hydrazone-) functional groups and carbonyl-functional groups may be present as chain pendant groups in the polyurethane or the polyacrylate or both, or they may be present as separate compounds in the polyurethane/acrylate hybrid dispersion. For the sake of clarity, in this specification (unless specified otherwise) by a carbonyl functionality is meant the carbonyl functionality of a ketone or aldehyde group. Also, by a hydrazine-functional group is meant the functional group of formula —NHNH
2
. A hydrazone-functional group is a group derived from such a hydrazine group by reaction with a monoketone or monoaldehyde containing at least 2 carbon atoms. It is preferred that the hydrazine- (or hydrazone-) functional groups and carbonyl-functional groups are present in an equivalent ratio of 1:20 to 20:1, more preferably 1:10 to 10:1.
As is well-known, polyurethane resins generally are made by reacting an organic polyisocyanate with an organic compound containing isocyanate-reactive groups, particularly a macro polyol, optionally with the inclusion of a low-molecular weight organic polyol. A favoured route to their formation involves the formation of an isocyanate-terminated polyurethane prepolymer followed by chain extension with an active hydrogen-containing compound.
The isocyanate-terminated prepolymer preparation reaction takes place under substantially anhydrous conditions at a temperature between about 30 and about 130° C. until the reaction between the isocyanate groups and the isocyanate-reactive groups is substantially complete. During the production of the isocyanate-terminated prepolymer the reactants generally are used in proportions corresponding to a ratio of isocyanate groups to isocyanate-reactive groups of from about 1.1:1 to about 6:1, preferably from about 1.5:1 to 3:1. If desired, catalysts such as dibutyl tin dilaurate or stannous octoate may be used to assist prepolymer formation. A non-reactive organic solvent may optionally be added before or after prepolymer formation to control the viscosity. Suitable solvents which may be used include acetone, methylethyl ketone, dimethyl formamide, ethylene carbonate, propylene carbonate, diglyme, N-methyl pyrrolidone (NMP), ethyl acetate, ethylene and propylene glycol diacetates, alkyl ethers of ethylene and propylene glycol diacetates, alkyl ethers of ethylene and propylene glycol monoacetates, toluene, xylene, and sterically hindered alcohols such as t-butanol and diacetone alcohol. The preferred solvents are water-miscible solvents such as N-methyl pyrrolidone (NMP), dimethyl sulphoxide, and dialkyl ethers of glycol acetates or mixtures of N-methyl pyrrolidone (NMP) and methylethyl ketone.
The chain extension can be conducted at elevated, reduced or ambient temperatures. Convenient temperatures are from about 5 to 95° C. or, m
Geurink Petrus Johannes Arnoldus
Schipper Katinka
Verbiest Rudolf
Akzo Nobel N.V.
Burke Michelle J.
Cain Edward J.
Parker Lainie E.
Vickrey David H.
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