Polymer dispersions as an additive in building materials

Details Polymer dispersions as an additive in building materials Polymer dispersions as an additive in building materials

2003-03-10

2004-10-26

Wu, David W. (Department: 1713)

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...

C524S555000, C524S556000, C524S558000, C524S560000, C524S570000, C524S571000, C524S002000

Reexamination Certificate

active

06809148

ABSTRACT:

The present invention relates to polymer dispersions comprising at least one copolymer which contains, as polymerized monomers,
a) from 25 to 70% by weight of at least one conjugated aliphatic diene,
b) from 25 to 70% by weight of at least one vinylaromatic monomer,
c) from 2.5 to 15% by weight of at least one monoester of a C
2
-C
10
-alkanediol with acrylic acid or methacrylic acid or
c′) from 0.1 to 10% by weight of at least one alkylpolyethylene glycol (meth)acrylate of the formula (I)
where R
1
is hydrogen or methyl, R
2
is C
1
-C
4
-alkyl and n is an integer from 1 to 100, or
c″) from 2 to 15% by weight of a mixture of the monoester c) and the alkylpolyethylene glycol (meth)acrylate c′),
d) from 0 to 1.0% by weight of ethylenically unsaturated monomers which have at least one acid group, or salts thereof,
e) from 0 to 5.0% by weight of ethylenically unsaturated nitriles and
f) from 0 to 1.0% by weight of amides of &agr;,&bgr;-ethylenically unsaturated mono- and dicarboxylic acids.
The present invention furthermore relates to the use of the novel polymer dispersions as an additive in building materials and a process for improving the mechanical strength, elasticity and processibility of building materials.
Hydraulic binders are understood as meaning mineral substances which are processed together with water and, if required, additives and conventional assistants to give a material which is plastic in the moist state and solidifies to a stone-like material after a certain time when left to stand in the air or in the water, if required with exposure to elevated temperatures. Examples of hydraulic binders are cement, gypsum, lime and clay.
The use of polymer dispersions or the polymer powders or polymer granules obtainable from these for improving the properties of building materials based on hydraulic binders is known in principle. Polymer dispersions for use with hydraulic binders have, as a rule, a high proportion of polar and/or ionic auxiliary monomers, such as (meth)acrylic acid and (meth)acrylamide, and a high content of emulsifiers. These measures are intended to improve the stability of the dispersions in the presence of the hydraulic binders since the high electrolyte content of the hydraulic binders leads to considerable destabilization of disperse systems.
In order to increase the mechanical strength of building materials based on hydraulic binders in the hardened state, polymer dispersions whose polymers have a high glass transition temperature (T
g
) are frequently used. Thus, EP-A-537 411 describes the use of polymer dispersions having a T
g
>+30° C. as an additive for cement. The additive is intended to improve the strength of cement-bound materials and to prolong the open time.
Building materials based on hydraulic binders which contain such polymer dispersions are comparatively brittle and exhibit in particular poor low-temperature flexibility. This is presumably due to the fact that, owing to the high T
g
of the polymer, no film formation of the latex particles in the building materials takes place.
In order to reduce the brittleness and to increase the low-temperature flexibility of hardened building materials based on hydraulic binders, polymer dispersions which contain polymers having a low T
g
are therefore used. Thus, AT-359 904 describes the use of polymer dispersions having a T
g
of −70 to −8° C. as an additive for cement-containing building materials. By adding from 3 to 35% by weight of such dispersions, mortars which have high low-temperature flexibility after hardening are said to be obtained. However, the addition of these dispersions leads to building materials having low strength.
JP-A 53134823 discloses a polymer dispersion which comprises, inter alia, conjugated dienes, monomers, such as styrene, acrylonitrile and esters of acrylic acid or of methacrylic acid, and unsaturated esters of carboxylic acids having hydroxyl groups. The polymer dispersions described there are said to be employed for modifying cement-containing systems which are preferably used as non-bleeding underwater concretes. From 8 to 40 parts by weight of the polymer dispersion are used per 100 parts by weight of cement. The compositions mentioned in this application are all prepared using an amount of initiator which does not exceed 0.125 mol %, based on the monomers. Owing to the relatively small amount of initiator and the relatively large amount of acid, the compositions claimed there are only poorly processible in particular in cement-containing sealing slurries.
The prior application DE-A 10040825.7 relates to the use of ammonia-free polymer dispersions as an additive in building materials based on hydraulic binders. The polymer dispersions described there comprise, as monomers, inter alia from 40 to 80% by weight of an ester of acrylic acid, from 10 to 40% by weight of a vinylaromatic monomer and from 2 to 15% by weight of a monoester of a C
2
-C
10
-alkanediol with acrylic acid or methacrylic acid. Such polymer dispersions have in particular high shear stability and electrolyte stability and, as additives in building materials, lead to improved mechanical properties of these building materials in the hardened state. For some applications, in particular for seals, the polymer dispersions laid open there exhibit relatively high water absorption and insufficient water tightness.
It is an object of the present invention to remedy the disadvantages described and to provide improved polymer dispersions which, inter alia, have high hydrolysis stability and water tightness and, when added to building materials based on hydraulic binders, lead to improved mechanical properties of the building materials in the hardened state, in particular to increased tensile strength and elongation at break. Furthermore, the improved polymer dispersions should be readily processible and flexible.
We have found that this object is achieved by novel polymer dispersions comprising at least one copolymer which contains, as polymerized monomers,
a) from 25 to 70% by weight of at least one conjugated aliphatic diene,
b) from 25 to 70% by weight of at least one vinylaromatic monomer,
c) from 2.5 to 15% by weight of at least one monoester of a C
2
-C
10
-alkanediol with acrylic acid or methacrylic acid or
c′) from 0.1 to 10% by weight of at least one alkylpolyethylene glycol (meth)acrylate of the formula (I)
where R
1
is hydrogen or methyl, R
2
is C
1
-C
4
-alkyl and n is an integer from 1 to 100, or
c″) from 2 to 15% by weight of a mixture of the monoester c) and the alkylpolyethylene glycol (meth)acrylate c′),
d) from 0 to 1.0% by weight of ethylenically unsaturated monomers which have at least one acid group, or salts thereof,
e) from 0 to 5.0% by weight of ethylenically unsaturated nitrites and
f) from 0 to 1.0% by weight of amides of &agr;,&bgr;-ethylenically unsaturated mono- and dicarboxylic acids.
The present invention furthermore relates to the use of the above-defined, aqueous polymer dispersions as an additive in building materials based on hydraulic binders. The copolymer contained in the novel polymer dispersions acts as a film-forming component. In the context of this invention, building materials based on hydraulic binders are both the hydraulic binders themselves and building materials which contain at least 5, in particular 10, particularly preferably at least 25, % by weight of at least one hydraulic binder. The use in building materials which contain cement as a binder is preferred.
The building materials based on hydraulic binders are generally converted into a processible form, generally into the form of liquid or plastically deformable materials, in general by adding water (mixing water) and, if required, conventional mineral and/or nonmineral additives. As a rule, these materials harden in the course of time when left to stand. Typical building materials based on hydraulic binders which are processed in this manner are cement, mortar, renders, tile adhesives, mineral sealing slurries, concrete and the like. The

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