Cement compositions comprising redispersible polymer powders

Details Cement compositions comprising redispersible polymer powders Cement compositions comprising redispersible polymer powders

2000-08-17

2002-12-03

Szekely, Peter (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

Reexamination Certificate

active

06489381

ABSTRACT:

The present specification relates to cement-based compositions comprising per 100 parts by weight of cement from 1 to 500 parts by weight of a polymer built up from
a) 30-99.5% by weight of at least one alkyl ester of (meth)acrylic acid,
b) 0-70% by weight of at least one vinylaromatic,
c) 0.5-10% by weight of at least one alkyl polyethoxy(meth)-acrylate of the formula
where R
1
is a hydrogen atom or a methyl group, R
2
is a C
1
to C
4
alkyl group and n is an integer from 1 to 55,
d) 0-10% by weight of at least one ethylenically unsaturated mono- or dicarboxylic acid or anhydride, amide or hydroxyalkylamide thereof,
e) 0-10% by weight of acrylonitrile or methacrylonitrile, and
f) 0-50% by weight of further ethylenically unsaturated compounds other than a) to e).
The properties of hydraulic binders, especially cement, can be improved by adding synthetic polymers. The desire is to increase the flexibility of the binders resulting in improved crack bridging and, consequently, in improved freeze-thaw resistance. Further, polymer additives generally bring about reduced penetration of water and improved adhesion to different substrates.
Suitable polymers are those which are added to the cement in powder form and are present in aqueous dispersion after water has been added. The presence of cement, however, has a deleterious effect on the stability of the aqueous dispersion and results in the formation of coagulum. Therefore, the polymers are required to have very high electrolyte stability.
One possibility for increasing the electrolyte stability of polymer dispersions is copolymerization with surface-active monomers.
The use of polymer dispersions containing surface-active monomers in the polymer as an additive for cementitious materials is described in DE-A-2051569. Mention is made inter alia of esters of carboxylic acids with polyalkylene oxides.
JP-53126093 describes polymer dispersions which can contain ethoxylated (meth)acrylates. The degree of ethoxylation of the (meth)acrylate is from 4 to 30 and the end group on the ethylene oxide chain is a hydroxyl, methyl or alkylaryl group. Addition to cement is one of the uses referred to.
JP-10195312 likewise describes polymer dispersions which can contain hydroxyl-terminated, alkoxylated (meth)acrylates. The polymers are used as an additive for cement.
JP-08217808 describes polymer dispersions having multiphase latex particles, and mixtures thereof with cement. The shell of the latex particles consists of a copolymer containing from 0.05 to 70% of an ethoxylated (meth)acrylate. In the examples, polyethylene glycol monomethacrylate is used.
The use of the alkoxylated (meth)acrylic acid derivatives described above as comonomers results generally in adequate electrolyte stability of the polymers. A disadvantage in many cases, however, is the increased incidence of coagulum formation in the polymer dispersions. Increased coagulum formation makes it more difficult to filter and spray-dry the dispersions. A further disadvantage is an increase in viscosity which is associated with the use of alkoxylated (meth)acrylic acid derivatives and which often occurs after the polymers are added to the aqueous cement slurry. Finally, when relatively large amounts of alkoxylated (meth)acrylic acid derivatives are used, it is common to observe a severe reduction in the strength of the polymer-modified cement materials.
It is an object of the present invention to provide polymer-modified cement compositions in which the polymer has sufficient electrolyte stability. The polymer dispersion used as additive should have a very low coagulum fraction and should be readily convertible to powder form by spray drying. Further requirements are very good compatibility and processability with cement. The hardened polymer-cement formulations should combine high strength with adequate flexibility.
We have found that this object is achieved by the compositions defined above and their use.
The compositions of the invention contain per 100 parts by weight of cement from 1 to 500, preferably from 5 to 250, with particular preference from 10 to 150, parts by weight of the polymer defined in claim
1
.
The polymer contains preferably at least 0.8% by weight, with particular preference at least 1% by weight, of the ethoxylated monomer of the formula I (monomer c). In general, the polymer contains not more than 8% by weight, with particular preference not more than 5% by weight and with very particular preference not more than 4% by weight of the monomer c), based on the polymer.
Preferably, the polymer has the following composition:
a) 40-99% by weight, with particular preference from 50 to 98% by weight, of at least one alkyl ester of (meth)acrylic acid,
b) 0-65% by weight, with particular preference from 0 to 60% by weight, of at least one vinylaromatic,
c) 0.8-8% by weight, with particular preference from 1 to 5% by weight, of at least one alkyl polyethoxy(meth)acrylate of the formula I,
d) 0.1-5% by weight, with particular preference from 0.3 to 4% by weight, of at least one ethylenically unsaturated mono- or dicarboxylic acid,
e) 0-8% by weight, with particular preference from 0 to 6% by weight, of acrylonitrile or methacrylonitrile, and
f) 0-40% by weight, with particular preference from 0 to 30% by weight, of further ethylenically unsaturated compounds other than a) to e).
The alkyl esters of (meth)acrylic acid (monomers a) are preferably C
1
to C
18
, with particular preference C
1
to C
8
, alkyl (meth)acrylates, examples being methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. Particular preference is given to methyl methacrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.
The vinylaromatics (b) are especially &agr;-methylstyrene and styrene.
Preferred alkyl polyethoxy(meth)acrylates of the formula (I) (monomers c) are those in which R
2
is methyl and n is an integer from 5 to 50, with particular preference from 5 to 30.
Suitable ethylenically unsaturated mono- or dicarboxylic acids, anhydrides or amides (d) are, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, their amides such as acrylamide or methacrylamide or their hydroxyalkylamides such as methylol(meth)acrylamide. Acrylic acid and methacrylic acid are particularly preferred.
Examples of further monomers (f) are crosslinking monomers, such as divinylbenzene, &agr;-ethylstyrene, butanediol diacrylate, ethyldiglycol diacrylate, hexanediol diacrylate, ureidoethyl methacrylate, ureidoethyl methacrylamide, allyl methacrylate, 3-methacryloyloxypropyltrimethoxysilane, acetoacetoxyethyl methacrylate, diacetoneacrylamide, acrylamidoglycolic acid or methyl acrylamidoglycolate methyl ether. The proportion of crosslinking monomers, if used, is generally below 5% by weight.
The glass transition temperature of the polymer is preferably from −60 to 50° C., in particular from −60 to +30° C., with particular preference from −30 to +40° C.
The glass transition temperature of the polymer can be determined in accordance with customary methods such as differential thermal analysis or differential scanning calorimetry (cf., e.g., ASTM 3418/82, midpoint temperature).
The polymer is prepared preferably by emulsion polymerization and is therefore an emulsion polymer.
Alternatively, it can be prepared, for example, by solution polymerization with subsequent dispersion in water.
In the case of the emulsion polymerization, ionic and/or nonionic emulsifiers and/or protective colloids, and/or stabilizers, are used as surface-active compounds.
A detailed description of suitable protective colloids is given in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1, Makromolekulare Stoffe [Macromolecular Substances], Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411 to 420. Suitable emulsifiers include anionic, cationic and nonionic emulsifiers. Accompanying surface-active substances used are preferably exclusively emulsifiers, whose molecular weights, unli

Affiliated with

Also associated with

Rating

Cement compositions comprising redispersible polymer powders does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cement compositions comprising redispersible polymer powders, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cement compositions comprising redispersible polymer powders will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2916486