Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-09-08
1999-02-16
Mullis, Jeffrey C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525244, 525262, C08F27902, C09D15104, C09J15104
Patent
active
058721894
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to water-redispersible powders of film-forming polymers with a "core/shell" structure.
More particularly, the film-forming polymers are prepared by aqueous emulsion polymerization of monomers containing ethylenic unsaturation.
Redispersible powders of the above type, which are generally obtained by spray-drying polymer latices, are already known. These powders have a great commercial advantage because they can be marketed as they are to the various users who redisperse them in water to prepare formulations which are suitable for the conventional uses of latices, namely especially the preparation of paper-coating compositions, paint compositions, adhesive coatings (pressure-sensitive adhesives, tiling adhesives) and additives to hydraulic binders of the mortar or concrete type.
It is understood that the sale of such powders which can be redispersed by the user into a pseudo- or neolatex has, when compared with the sale of the initial latex, the immense advantage of not comprising water, which generally constitutes at least 50% of the weight of the latex, and this entails considerable savings in transport and handling.
However, such powders must exhibit the following properties to be marketable: produce a neolatex of narrow particle size which is suitable for the targeted application, targeted in the case of the present invention, the additive resulting from the redispersible powder must be compatible with the hydraulic binder, must allow the hydraulic binder to set solid without delaying the setting process and must impart to the coatings, comprising the binder containing the additive, a correct adhesiveness to the usual substrates even in the moist state, as well as good mechanical properties.
The present invention proposes a redispersible powder exhibiting all of the desired properties indicated above in the conventional applications of latices and more particularly in coating compositions and compositions of additives for a hydraulic binder, in particular for Portland cement.
It relates, in fact, to a water-redispersible powder based on film-forming polymers which are substantially insoluble and which are prepared by aqueous emulsion polymerization of monomers containing ethylenic unsaturation and with a "core/shell" structure comprising a hydrophobic core based on a polymer exhibiting a Tg (glass transition temperature) of between -30.degree. and +25.degree. C., preferably between -10.degree. and 20.degree. C., and a hydrophilic shell based on a polymer exhibiting a Tg higher than 55.degree. C., preferably higher than +90.degree. C., characterized in that the shell is bonded to the core by covalent bonds resulting from the reaction of an agent for grafting the shell onto the ethylenic unsaturations remaining in the core, and is substantially insoluble in an alkaline medium.
The present invention also relates to a process for the preparation of a redispersible powder in accordance with the invention, and to the use of the said powder.
The powder according to the invention is composed of particles based on film-forming polymers which are water-insoluble, exhibiting a core/shell structure. These particles with a core/shell structure consist of a core made up of a hydrophobic and soft polymer, that is to say exhibiting a Tg of between -30.degree. and +25.degree. C., preferably between -10.degree. and +20.degree. C., which contains remaining ethylenic unsaturations, and of a core based on a hydrophilic, hard polymer exhibiting a Tg higher than 55.degree. C., preferably higher than 90.degree. C. The shell is bonded to the core by covalent bonds resulting from the reaction of an agent for grafting the shell onto the ethylenic unsaturations remaining in the core.
The glass transition temperature is determined by the differential thermal analysis method.
Such particles of substantially water-insoluble core/shell polymers are generally prepared from a polymer latex by a two-stage polymerization process such as, for example, that described in Patent U.S. Pat. No. 4,876,313, cited as r
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patent: 4937280 (1990-06-01), Biglione
patent: 5403894 (1995-04-01), Tsai et al.
patent: 5500286 (1996-03-01), Someya et al.
Honey Chemical Ind, Derwent AN 91-055066, abstracting JP 3006269, Jan. 1991 .
Bett Bill
Richard Joel
Mullis Jeffrey C.
Rhone-Poulenc Chimie
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