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...
Patent
1995-12-22
1998-05-19
Reddick, Judy M.
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...
524367, 524369, C08K 506
Patent
active
057537380
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the use of specific alkoxy ethoxyethanols as cosolvent in aqueous resin formulations.
It is well known that some resins used for water-based coatings are largely incompatible with water, and that the compatibility with water can be improved by the addition of an organic solvent known as a "coupling solvent". The nature of the coupling solvent used can affect the performance of the formulated coating in several ways.
The "coupling power" of the solvent relates to how good the solvent is at increasing the solubility of the resin in water. A solvent good in this respect can, among other benefits, increase the range of humidity and/or temperature at which the coating may be successfully applied. A simple measure of the "coupling power" of the solvent may be obtained by adding water to a 30:70 by weight mixture of coupling solvent and n-heptane at room temperature, where the heptane acts as a model for an oleophilic resin. At some point as water addition is increased, the mixture moves from a single, homogeneous phase to a mixture of two phases. The amount of water added before the appearance of the second phase is an indication of the coupling power of the solvent. The objective is to maximise the amount of water that can be added to the coupling solvent before the second phase appears.
The rheology of a coating formulation is partly determined by the composition and phase behaviour of the water/resin/coupling solvent ternary mixture. A good coupling solvent can influence the rheology such that, eg, the process of formulating the coating is simplified by minimising viscosity variations when a solution of the resin in the coupling solvent is diluted with water. Effectively, it is believed that the coupling solvent associates preferentially with the organic phase rather than the aqueous phase. A good solvent can also improve the performance of the coating when applied to a substrate by, eg, reducing sagging and curtaining effects. Desirable rheological behaviour is related to the composition of the ternary mixture such that, when two liquid phases coexist, one of the phases should be very largely comprised of water. This behaviour is easily determined using a model system with n-heptane and carrying out the test to measure coupling power as described above. When just sufficient water is added so that a second phase begins to appear as signified by the formation of small droplets, these droplets are largely comprised of water whereas the larger organic phase comprises mainly n-heptane and the coupling solvent (shown as notation (d) in the Table below); the behaviour would be considered undesirable if two phases are formed which are comparable in volume and one of the phases is largely comprised of n-heptane (shown as notation (nd) in the Table below).
A coupling solvent for use in coatings should have a higher boiling point than water such that the coupling solvent allows a film of the coating applied on a substrate to dry as a continuous phase, ie the water evaporates faster than the solvent.
Hitherto, among high-boiling (200.degree.-350.degree. C.) coupling solvents, 2-(2-butoxyethoxy)ethanol (hereafter "BDGE"), which boils at 231.degree. C., has been the most commonly used monoalkyl diglycol ether coupling solvent, whilst hexyl glycol ether, which boils at 208.degree. C. has also been used. It has now been found that specific ethers of diethylene glycol perform just as well if not better than these solvents when used as coupling solvents in aqueous resin formulations in respect of their phase behaviour and/or their coupling power.
Accordingly, the present invention is an aqueous resin formulation comprising as cosolvent an alkoxy ethoxyethanol characterised in that, the alkoxy ethoxyethanol: 200.degree. to 350.degree. C. and respectively, either until more than 2.5% wt/wt of water is added, and/or, least 1.5% wt/wt of water, said droplets having >50% wt/wt of water.
Specific examples of the compounds which represent the cosolvents of the present invention include: ub.2.OH sub.2.OH
REFERENCES:
patent: 3446764 (1969-05-01), Phillips et al.
patent: 4460734 (1984-07-01), Owens et al.
patent: 4523922 (1985-06-01), Ong et al.
patent: 5374305 (1994-12-01), Glancy et al.
Chapman Richard George
Goodwin Stephen Paul
Hazel Nicholas John
Lucy Andrew Richard
Stewart Nevin John
BP Chemicals Limited
Reddick Judy M.
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