Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1997-12-05
2001-05-01
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S212000, C427S213340, C427S487000, C525S054200, C525S243000, C525S262000, C525S281000, C525S285000, C525S301000, C525S310000, C526S238230
Reexamination Certificate
active
06224981
ABSTRACT:
The present invention relates to water-redispersible powders based on film-forming polymers with a “core/shell” structure, the said film-forming polymers being 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:
they must be stable in storage,
they must be easily redispersible in water at ambient temperature and must produce a neolatex of narrow particle size which is suitable for the targeted application,
for the application as additive to hydraulic binders, more particularly 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 to 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,
they must be redispersible in a wide pH range,
they must exhibit a good redispersion in a medium containing multivalent, in particular alkaline, ions.
The objective of the present invention is to propose a redispersible powder exhibiting all of the desired properties indicated above, and a process for the preparation of this powder.
To this end, the invention relates first of all to a water-redispersible powder based on film-forming polymers which are substantially water-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 and 25° C., preferably between −10 and 20° C., and
a shell, the shell being 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,
characterized in that the shell is prepared by emulsion polymerization, on the core, of a mixture of monomers comprising:
at most 90%, preferably from 50 to 80% by weight of at least one monomer chosen from styrene and a C
1
-C
12
alkyl acrylate or methacrylate,
at most 50%, preferably from 15 to 40% by weight of at least one monomer carrying a saccharide group and exhibiting at least one ethylenic unsaturation, and
at most 10%, preferably at most 5% by weight of at least one grafting agent chosen from the (meth)allyl esters of (meth)acrylic acid, (meth)allyl esters of the mono- and diesters of maleic, fumaric and itaconic acids, and alkene derivatives of amides of acrylic and methacrylic acids, such as N-methallylmaleimide.
The invention also relates to a pseudolatex obtained by redispersion in water of a redispersible powder according to the invention.
The invention also relates to a process for the preparation of a powder according to the invention, which consists in carrying out the following stages:
the core is prepared by aqueous emulsion polymerization, then
a mixture of monomers is polymerized in aqueous emulsion on the core in the presence of a grafting agent and of an organophilic polymerization initiator, whereby the shell is formed, then
water is removed from the reaction mixture.
Finally, the invention relates to the use of the said pseudolatices and of the redispersible powders according to the invention as additives to hydraulic binders, adhesives, paper-coating compositions and paints.
The invention relates first of all to a water-redispersible powder based on film-forming polymers which are substantially water-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 and 25° C., preferably between −10 and 20° C., and
a shell, the shell being 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,
characterized in that the shell is prepared by emulsion polymerization, on the core particles, of a mixture of monomers comprising:
at most 90%, preferably from 50 to 80% by weight of at least one monomer chosen from styrene and a C
1
-C
12
alkyl acrylate or methacrylate,
at most 50%, preferably from 15 to 40% by weight of at least one monomer carrying a saccharide group and exhibiting at least one ethylenic unsaturation, and
at most 10%, preferably at most 5% by weight of at least one grafting agent chosen from the (meth)allyl esters of (meth)acrylic acid, (meth)allyl esters of the mono- and diesters of maleic, fumaric and itaconic acids, and alkene derivatives of amides of acrylic and methacrylic acids, such as N-methallylmaleimide.
The powder according to the invention is composed of particles based on water-insoluble film-forming polymers exhibiting a core/shell structure. These core/shell particles consist of a core formed by a hydrophobic and soft polymer, that is to say exhibit a Tg of between −30 and +25° C., preferably between −10 and +20° C., which comprises remaining ethylenic unsaturations, and of a shell based on a hard, hydrophilic polymer exhibiting a Tg higher than 55° C., preferably higher than 90° 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 core/shell polymers which are substantially insoluble in water are 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 reference, according to which, during a first stage, the core formed by a hydrophobic and soft polymer is prepared and, during a second stage, the shell formed by a hard and hydrophilic polymer is grafted onto the core.
In general the core is prepared by polymerization of a mixture of monomers comprising from 99.9 to 92% of at least one monomer chosen from styrene, butadiene and C
1
-C
12
alkyl acrylates and methacrylates and from 0.1 to 8% of at least one monomer chosen from a carboxylic acid containing ethylenic unsaturation, an ester of unsaturated carboxylic acid containing a hydroxyalkyl functional group or a monomer containing an amide functional group. The core is preferably prepared by polymerization of a mixture of monomers based on styrene and butadiene.
The more or less hydrophobic nature of the core can be adjusted with the carboxylic acid monomers containing ethylenic unsaturation, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, or a monomer ester of unsaturated carboxylic acid containing a hydroxalkyl functional group, like hydroxyethyl acrylate and hydroxypropyl acrylate or a monomer containing an amide functional group chosen, for example, from methylolacrylamide, acrylamide, methacrylamide and methylmethacrylamide.
A person skilled in the
Bett William
Richard Joel
Rhodia Chimi
Seugnet Jean-Louis
Thibodeau Paul
Zacharia Ramsey
LandOfFree
Water-redispersible powders of film-forming polymers having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Water-redispersible powders of film-forming polymers having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water-redispersible powders of film-forming polymers having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553682