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
2001-07-19
2004-05-25
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...
C524S589000, C524S590000
Reexamination Certificate
active
06740705
ABSTRACT:
This invention relates to a process for making poly(urethane-urea)/addition polymer composite particles without the need to handle viscous materials and to a process for making optionally solvent-free aqueous dispersions of the composite particles. The composite particles have outer regions which contain poly(urethane-urea) optionally carrying some ionic carboxylate groups and inner regions which contain addition polymer. Commercial polyurethanes additionally contain important urea moieties and so the term “poly(urethane-urea)” is used in this specification to take account of that fact. Addition polymers are polymers (including copolymers) derivable from the free radical addition polymerisation of ethylenically unsaturated relatively hydrophobic monomers such as acrylic (including methacrylic) esters, vinyl esters, (usually vinyl carboxylates) or styrene. In addition the invention relates to and to aqueous coating compositions and adhesives formulations containing the composite particles. Nowadays, environmental concerns increasingly demand minimisation or preferably total avoidance of organic solvent in aqueous dispersions of particles of this type. Organic solvent free dispersions would be useful in adhesives formulations and in coating compositions for wood, concrete, plaster, glass fiber and plastics surfaces of the type found in buildings and metal surfaces of the type found in motor vehicles.
United States Patent Specification U.S. Pat. No. 4,644,030 (published in 1987) describes a technique for making poly(urethane/urea)/addition polymer composite particles in which a high molecular weight polyurethane prepolymer is first made by dissolving diol and di-isocyanate in addition polymerisable hydrophobic monomers acting as a hydrophobic volatile organic solvent whereupon the diol and di-isocyanate react together exothermically to form a viscous solution of high molecular weight prepolymer in the hydrophobic monomer. After formation of the prepolymer has been completed, the solution of prepolymer in hydrophobic monomer is dipersed as fine droplets in water. The prepolymer in the droplets is chain extended to make poly(urethane-urea) and the addition polymerisable monomers are subjected to addition polymerisation to make addition polymer and the two come together to form poly(urethane-urea) composite particles.
There are two problems with the technique of U.S. Pat. No. 4,644,030. The first is that the intrinsic viscosity of the prepolymer in the monomer is high and so either there will be difficulties in shearing the solution into fine droplets on dispersion into the water or this stage of the process will be limited to operation at high temperatures and/or low concentrations of prepolymer. Ideally, the viscosity of the prepolymer/monomer solution should be well below 1 Pascal-sec at room temperature (say 18° C.). The second problem is that the reaction between the diol and di-isocyanate is exothermic and so there is a risk that a premature addition polymerisation of the addition polymerisable monomers could be triggered in a local hot spot, especially if the solution has to be hot to keep its viscosity low.
A widely used commercial alternative process to that of U.S. Pat. No. 4,644,030 resorts to the use of solutions of prepolymer in hot potent unpolymerisable organic solvents which solvents of necessity have unpleasant characteristics. A typical commercial process employing potent solvents begins with a reaction of aliphatic di-isocyanates (even though they are more expensive than their aromatic analogues) with dimethylol propionic acid (which is also costly) to produce the polyurethane prepolymer dissolved in the organic solvent. The solvent must be aprotic so as to be inert to the isocyanate and it also has to be miscible with water which in practice leads to the choice of N-methyl pyrrolidone even though it is a skin and eye irritant. In addition, the process uses triethylamine as a neutralising base even
though it is pungent and malodorous and it also uses hydrazine as a chain extender even though it is carcinogenic. Use of all these substances needs specialist handling techniques and so the process cannot be performed in the conventional plants used in the production of polymer latexes by the addition polymerisation of ethylenically unsaturated monomers. Briefly a typical current process is as follows:
Aliphatic di-isocyanate monomers dissolved in N-methyl pyrrolidone are reacted in organic solvent with dimethylol propionic acid and usually other diols to form a low viscosity solution of polyurethane prepolymer carrying carboxylic acid groups. An approximate reaction scheme is shown in
FIG. 1
of the drawings where R represents a polymethylene chain (for example ethylene) and where any reactions involving diols other than dimethylol propionic acid have been omitted for simplicity.
The carboxylic acid groups are next neutralised by triethylamine so as to provide the ionic carboxylate groups needed for making a stable dispersion in water.
The neutralised solution is added to water with vigorous agitation whereupon the prepolymer particles become stably dispersed in the water/N-methyl pyrrolidone mixture.
Next the polyurethane prepolymer is chain extended in the presence of the water by adding a diamine (for example hydrazine) to the aqueous dispersion so as to produce urea moieties. An approximate reaction scheme is shown in
FIG. 2
of the drawings. Urea moieties usually improve the resistance to organic solvents and also improve the hardness of the poly(urethane-urea).
The product of the chain extension reaction is an aqueous dispersion of solvent-swollen poly(urethane-urea) particles in water containing unpleasant residual organic solvent. Therefore the low viscosity solution of prepolymer in the potent organic solvent is only obtained at the cost of an aqueous dispersion contaminated with the organic solvent.
In a last stage of the process, acrylic hydrophobic monomer is fed with vigorous stirring into the aqueous dispersion of swollen poly(urethane-urea) particles where it diffuses into the swollen particles. The diffused monomer is subjected to addition polymerisation initiated by free radicals (which also diffuse into the swollen particles) whereupon acrylic addition polymer is produced. The acrylic polymer is hydrophobic whereas the poly(urethane-urea) is hydrophilic owing to its ionic carboxylate and urea groups. This difference in hydrophobic/hydrophilic character causes the poly(urethane-urea) spontaneously to encapsulate the particles of acrylic polymer so forming a composite particle which has a core/shell structure and which is stably dispersed in water, albeit water contaminated with usually at least 3 wt % and often up to 10 wt % of unpleasant and environmentally undesirable residual organic liquid.
In order to be able to form stable aqueous dispersions, existing commercial particles need to have a large number of ionic carboxylate groups carried by their poly(urethane-urea) polymer. Usually this large number equates to a notional acid value of around 30 mgKOH/g polyurethane/urea content of the composite particles. By “notional acid value” is meant the acid value which the particles would have if their ionic carboxylate groups were converted to carboxylic acid groups. Such large numbers of ionic carboxylate groups are undesirable for two reasons. Firstly, they adversely alter the nature of the compositions into which the particles are formulated and in particular they may impart excessive water-sensitivity. Secondly, the large numbers of ionic carboxylate groups interact with the water and organic solvent in an aqueous dispersion to cause swelling of the particles and a consequent increased viscosity of the aqueous dispersion. For this reason, it is not possible to obtain useful aqueous dispersions of such particles containing more than at best 40 wt % of the highly carboxylated particles and usually the particle contents are only about 30 wt %.
The process uses aliphatic di-isocyanates even though most of their aromatic analogues are much cheaper. The
Cain Edward J.
Imperial Chemical Industries plc
Stachel Kenneth J.
LandOfFree
Process for making poly (urethane-urea)/addition polymer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for making poly (urethane-urea)/addition polymer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for making poly (urethane-urea)/addition polymer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3239947