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
1996-07-02
1997-07-01
Cain, Edward J.
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...
C08L 3104
Patent
active
056439938
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an aqueous polymer dispersion containing structured particles, which is intended in particular for the production of solvent-less paints, to a process for its production, and to its application to solventless paint formulations.
Latex-based paint compositions containing opacifying pigments, such as titanium dioxide, and non-opacifying pigments have been known for a long time. When an aqueous polymer emulsion is applied to a substrate, and after the water has evaporated, a film appears on the surface of the said substrate owing to the coalescence of the polymer which is present in the emulsion.
In order to obtain a homogeneous film, the forces of coalescence must exceed the resistance of the polymer particles to deformation and to viscoelasticity. The viscoelastic nature of the polymer particles, consequently, is the major factor determining the tendency of the latex to form a film.
It is established art to use a plasticizer in order to modify the viscoelasticity of a polymer latex. The plasticizers may be solids with a low melting point (for example dibutyl or dioctyl phthalate) or else solvents having a high boiling point. In a general manner, they increase the elongation and the elasticity but reduce the breaking strength of the resin in which they are incorporated. Despite being less volatile than the solvents, they are nevertheless in possession of a characteristic odour.
It is also known to use solvents (of the glycol type, for example), sometimes called coalescence agents, in order to modify the viscoelastic nature of the polymer. These are volatile plasticizers in that they facilitate the elastic deformation of the particles of the latex.
The result of using plasticizers and coalescence agents in latex films is a greater degree of coalescence within an extended temperature range, and up until now it has been thought that their presence was essential to good film formation.
Moreover, it is known to classify paints according to their gloss, measuredly reflection of light at a given angle, for example in accordance with the standard DIN 53778 (Part 1), into: 85.degree.. angle of 60.degree..
The properties expected of a paint are good applicability, good binding power, the absence of cracks even at low temperature (5.degree. C.), the absence of a tacky or sticky nature, good resistance to wet abrasion (washability) and, finally, a degree of reflection of light which is suited to one or other of the above categories. According to which one of these categories it belongs to, the pigment volume concentration of the paint is very different: from 70% to 95%, approximately, for a matt paint, and only from 20% to 40%, approximately, for a semi-gloss paint. Likewise, washability is a property which is easily obtained in semi-matt and semi-gloss paints because of the high proportion of latex in the latter. In contrast, in matt paints which usually contain only from 10% to 15%, approximately, by weight of latex polymer, satisfactory washability can only be obtained by careful selection of the nature of the latex polymer.
Moreover, it is well known that the paint industry causes a certain number of problems with regard to ecology and to respect for the environment, which result from the chemical composition of the paint and, in particular, from the presence in this composition of volatile organic substances such as the coalescence agents.
These problems are, in particular, those brought about by the toxicity of these organic substances when the paint is produced and applied, and by the destruction of the ozone layer of the atmosphere when these substances evaporate during application.
Aqueous polymer dispersions comprising non-homogeneous or structured particles obtained, in general, by the technique of overpolymerization, carried out in at least two polymerization steps, are well known. Examples of such structured particles, of varied morphology, have been described by J. C. Daniel in Macromol. Chem., Suppl 10/11, pages 359 to 390 (1985) and are designated, in particular, using th
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patent: 4107120 (1978-08-01), Plamondon et al.
patent: 4868016 (1989-09-01), Lorah et al.
patent: 5185387 (1993-02-01), Klesse et al.
Daniel, J.C., Makromol. Chem. Suppl. 10/11, pp. 359-90 (1985) (English abstract only).
Okubo, M., et al., Production of Anomalously Shaped Carboxylated Polymer Particles by Seeded Emulsion Polymerization, Colloid and Polymer Science, 265: 876-881 (1987).
Cain Edward J.
Cray Valley S.A.
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