Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-05-05
2003-03-11
Yoon, Tae H. (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C523S201000, C524S504000, C428S500000
Reexamination Certificate
active
06531185
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of surface treatment and in particular to hydrophobic thermoplastic films for surface coatings and more particularly to films obtained by low-temperature drying of a latex containing neither volatile organic compounds nor coalescents.
BACKGROUND OF THE INVENTION
In the context of the invention, the term “latex” should be understood to mean an aqueous dispersion of polymer particles which can be obtained by the emulsion polymerization of one or more monomers.
Many latices are intended for the building, paper, textile and leather industries and are used in the surface treatments of various materials, particularly as paints, varnishes, adhesives and mastics. More generally, such latices are required to have a minimum film-forming temperature, called hereafter MFT, as low as possible. The MFT is the lowest temperature at which the particles form a continuous film after the water has been evaporated.
When the polymers constituting the particles dispersed in a latex have a relatively low glass transition temperature, denoted by T
g
, it is easy for the latex to form a film at room temperature but the films obtained are tacky and their mechanical integrity is poor. On the other hand, if the polymers have a high T
g
the films will be of better quality but film formation at room temperature would require the addition of a coalescents. The latter is generally a volatile organic compound which evaporates during application and film formation, as described in U.S. Pat. No. 4,455,402 and U.S. Pat. No. 5,021,469.
For obvious environmental—friendliness and cost-reduction reasons, it is desirable to develop containing neither volatile organic compounds nor coalescents, having a relatively low MFT and able to give films at low temperature which have no surface tack and are of good mechanical quality.
To achieve this objective, EP 466,409 proposes a solution based on a mixture of two latices, one having a low T
g
, generally called a “soft” latex which providing film formation and the other having a high T
g
generally called a “hard” latex providing mechanical integrity. EP 609,756 describes a latex, prepared in two steps, having a “soft” core with a T
g
ranging from −5° C. to −55° C. and a “hard” shell with a T
g
of less than 50° C.
Likewise, FR 2,090,483 describes a latex, obtained by two-step polymerization, consisting of 35 to 50% of a polymer, obtained in the first step, having a T
g
of less than 10° C. and of 50 to 65% of a polymer, obtained in the second step, having a T
g
of greater than 60° C., the first-step polymer being crosslinked and fastened to the second.
REFERENCES:
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patent: 5403894 (1995-04-01), Tsai et al.
patent: 5424341 (1995-06-01), Ogoe et al.
patent: 5500457 (1996-03-01), Manisha et al.
patent: 5631323 (1997-05-01), Güntherberg et al.
patent: 41 39 382 (1992-06-01), None
patent: 0 522 791 (1993-01-01), None
patent: 2 729 150 (1996-07-01), None
Domingues Dos Santos Fabrice
Drujon Xavier
Fabre Pascale
Leibler Ludwik
Meunier Gilles
Elf Atochem S.A.
Smith , Gambrell & Russell, LLP
Yoon Tae H.
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