Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-12-10
2003-09-23
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S071000, C524S458000, C524S461000, C524S502000, C524S515000, C524S525000
Reexamination Certificate
active
06624207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous polymer dispersion comprising rubber particles and polymer particles having a reinforcing action, wherein the rubber particles are made up of
x % by weight of an aromatic monovinyl compound and
y % by weight of an aliphatic conjugated diene having from 4 to 9 carbon atoms
in copolymerized form, and
x is from 5 to 35 and
y is from 65 to 95,
and the polymer particles having a reinforcing action are made up of
from 50 to 90% by weight of a first, hard polymer phase A and
from 10 to 50% by weight of a second, soft polymer phase B, where
the polymer phase A has a glass transition temperature above 70° C. and comprises from 90 to 100% by weight of an aromatic monovinyl compound and up to 10% by weight of an aliphatic conjugated diene having from 4 to 9 carbon atoms in copolymerized form and
the polymer phase B comprises
x±≦3% by weight of the aromatic monovinyl compound used in the rubber particles and
y±≦3% by weight of the aliphatic conjugated diene having from 4 to 9 carbon atoms used in the rubber particles in copolymerized form.
The invention likewise relates to a process for preparing this polymer dispersion and to its use for producing latex foams and molded foam articles. In particular, the invention relates to the polymer particles having a reinforcing action used in the aqueous polymer dispersion and their preparation by means of free-radical-initiated aqueous emulsion polymerization.
2. Discussion of the Background
Latex foams and molded latex articles are produced according to the prior art from aqueous rubber dispersions by mechanical beating-in of air with addition of sulfur-crosslinking vulcanizers, gelled by addition of gelling agents and then vulcanized by heating to give a cellular, largely open-pored foam. The production of such latex foams and molded latex articles is described, for example, in DE-A 2150872 or DE-A 19757700. The rubber dispersions generally comprise reinforcing dispersions, i.e. aqueous dispersions of polymer particles having a reinforcing action. The type and amount of this reinforcing component have a strong influence on the property profile of the finished latex foam.
The latex foam is required to have a high elasticity, particularly in the use temperature range from 20 to 70° C., which must not be lost after prolonged compression and especially in continuous use. Accordingly, the compressive set (in accordance with ISO 1856) in this temperature range should be as small as possible and the recovery of the compressed molding should occur very quickly, i.e. the hysteresis (in accordance with DIN 53 577) should likewise be very small. Furthermore, the tensile strength and the maximum elongation to break (in accordance with ISO 1789) should be as high as possible. Likewise, the density of the foam should be as low as possible at a given indentation resistance of the foam (in accordance with ISO 2439A) so that the foam articles can be produced as economically as possible in respect of the amount of rubber dispersion which needs to be used.
Reinforcing polymer particles in the form of their aqueous polymer dispersion have been known for a long time for achieving a targeted increase in hardness, strength and elongation of latex foam. These are generally styrene/butadiene dispersions having a high styrene content up to 100% by weight. Reinforcing dispersions having a homogeneous structure, i.e. prepared in a single process step, have been described as disadvantageous in DE-A 1056364, since they do not meet the requirement for low compressive set values over a wide temperature range. According to this disclosure, better results are achieved by use of multistage grafted copolymer dispersions having a comparable overall composition which are prepared in a two-stage batch process. Such rubber dispersions and latex foam articles produced therefrom have a glass transition temperature of the reinforcing component which is within a relatively narrow temperature range in the stated interval from 20 to 70° C.
An embodiment of such a multiphase grafted copolymer dispersion which is improved in respect of significant points is described in EP-A 187 905. There, use is made, in particular, of semicontinuous feed stream addition processes to prepare polymer particles having different monomer compositions in the individual phases. The latex foams produced on the basis of these teachings have a balanced property combination with, in particular, low compressive set values in the entire temperature range from 20 to 70° C. The glass transition temperatures of the individual phases of the reinforcing component cover, according to this embodiment and in contrast to earlier teachings, a very wide range within the stated interval from 20 to 70° C. However, the moderate values of the fast elastic recovery of the latex foams produced according to these teachings, reflected in the relatively high hysteresis values, is not fully satisfactory.
EP-A 753 530 describes aqueous rubber dispersions comprising polymer particles having a reinforcing action which are said to comprise from 20 to 75% by weight of a hard polymer core, from 15 to 78% by weight of a soft outer phase and from 2 to 10% by weight of transition regions between these phases which have a copolymer composition between those of the hard and soft phases. It is important that the polymer particles having a reinforcing action are mixed in the form of their aqueous dispersion into the aqueous rubber dispersion only after the latter has been agglomerated.
Furthermore, it is known to those skilled in the art that the property profile of latex foams is generally improved in respect of the foam homogeneity if the agglomeration of the rubber dispersion is carried out in the presence of the polymer particles having a reinforcing action (coagglomeration). However, coagglomeration has hitherto been known only for freeze agglomeration (cf. U.S. Pat. No. 3,296,178, U.S. Pat. No. 3,673,133 and CA-B 961 588). However, freeze agglomeration requires a high outlay in terms of apparatus and has poor economics as a result of the high energy costs. Pressure agglomeration processes require far less outlay in terms of apparatus and are significantly cheaper. However, owing to rapid fouling and blocking of the apparatuses, pressure agglomeration processes cannot be used for the coagglomeration of rubber dispersions comprising the known reinforcing polymer particles.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide polymer particles having a reinforcing action for foamable rubber dispersions, which particles can be coagglomerated with the rubber dispersions by means of a pressure agglomeration process and make it possible to produce latex foams which have a property profile comparable to or better than the prior art.
We have found that this object is achieved by the above-described aqueous polymer dispersion, a process for preparing it and its use for producing latex foams and molded foam articles.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rubber particles present in the aqueous polymer dispersion comprise x % by weight of an aromatic monovinyl compound and y % by weight of an aliphatic conjugated diene having from 4 to 9 carbon atoms in copolymerized form.
Here, x is from 5 to 35, often from 10 to 30 and all values between these. x is frequently ≧7, ≧9, ≧11, ≧13, ≧15, ≧17, ≧19, ≧21, ≧23 and ≦33, ≦31, ≦29, ≦27, ≦25, ≦23, ≦9.
For the purposes of the present inventon, aromatic monovinyl compounds are monomers of the formula CH
2
═CR
1
R
2
, where R
1
is an aromatic unit having from 6 to 10 carbon atoms which may also bear further alkyl radicals and/or halogen substituents. R
2
is hydrogen or an alkyl radical having from 1 to 4 carbon atoms. Preferred aromatic monovinyl compounds are, for reasons of economics and availability, styrene, &agr;-methylstyrene and vinyltoluene, with particular preference being given to styrene. Of course, it is also
Balk Roelof
Graalmann Onno
van der Most Bernhard
BASF - Aktiengesellschaft
Mullis Jeffrey
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Aqueous polymer dispersion comprising rubber particles and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous polymer dispersion comprising rubber particles and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous polymer dispersion comprising rubber particles and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3063327