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...
Reexamination Certificate
1999-02-22
2001-05-01
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...
C524S823000, C524S215000, C524S272000, C526S080000, C526S142000, C526S307000, C526S319000
Reexamination Certificate
active
06225401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to processes for preparing filterable, deodorized, highly concentrated, aqueous dispersions of pressure-sensitive adhesive, based on copolymers of esters of acrylic and/or methacrylic acid, to products thus prepared and to their use.
2. Description of the Background
Polymer dispersions which are used in the adhesives industry for producing articles having contact adhesion are required to meet stringent quality criteria. Thus it must be possible to reproduce their properties within relatively narrow tolerances in order to enable them to be processed further without problems. In general, the processing of aqueous dispersions is more economic and more environment-friendly than that of systems which include organic solvents, since it does away with the need for complex equipment to recover the organic solvents. Highly concentrated aqueous dispersions of pressure-sensitive adhesive go a step further in terms of economy and environmental compatibility in that less water has to be evaporated in the course of their processing and, consequently, less energy is used than in the processing of aqueous dispersions having a lower polymer content. The transportation of highly concentrated dispersions, moreover, is more efficient than that of dispersions of lower concentration. For the processing of the aqueous polymer dispersions to form everyday products, the dispersions must be substantially free from volatile components. Volatile components are, in particular, unreactive monomers and saturated constituents in the monomers used, it being of course impossible to remove the latter by the polymerization reaction. To remove the volatile components, the polymer dispersions are treated—subsequent to their preparation—with steam (deodorization). For deodorization the polymer dispersions must be of sufficient stability, since otherwise the deodorization procedure is accompanied by the agglomeration of material and the formation of coagulum, reducing the solids content of the dispersions. This coagulation occurs with particular readiness in the case of highly concentrated polymer dispersions. Dispersions containing coagulum are not easy to filter, and before being used further as highly concentrated pressure-sensitive adhesive dispersions they require particularly laborious techniques for the removal of the coagulum.
There has been no lack of efforts to prepare highly concentrated aqueous polymer dispersions with solids contents or polymer contents of more than 65% by weight. For instance, EP-A 0 065 253 describes a process for preparing highly concentrated aqueous polyacrylate dispersions by the technique known as monomer emulsion feed polymerization, the resulting polymer dispersions being used for dressing leather. It is indicated that filterable polymer dispersions are obtained only when use is also made of a specific emulsifier, a dialkyl sulfosuccinate having 8 to 18 C atoms in the alkyls. However, there is great fluctuation in the properties of the resulting highly concentrated polymer dispersions, such as in their viscosities.
EP-B 0 037 923 likewise describes a process for preparing highly concentrated aqueous polyacrylate dispersions by the monomer emulsion feed polymerization technique, although the reproduction of the resulting dispersions does not meet the current quality requirements on account of the fact that marked fluctuations in properties occur here as well. Moreover, the highly concentrated aqueous polymer dispersions obtained are of only limited stability on deodorization. Furthermore, the process involves undesirable restrictions in terms of selection of monomers, content of minimum amounts of inhibitor, and the composition of the aqueous phase of the initial charge to the polymerization reactor, which are disadvantageous.
SUMMARY OF THE INVENTION
It is an object of the present invention to prepare filterable and deodorizable, highly concentrated, aqueous dispersions of pressure-sensitive adhesive with a highly reproducible set of properties by a process which does not have the disadvantageous restrictions of the prior art processes described above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
We have found that this object can be achieved by a process for producing readily filterable and deodorizable, highly concentrated, aqueous dispersions of pressure-sensitive adhesive, having readily reproducible properties, on the basis of copolymers of esters of acrylic and/or methacrylic acid, the copolymers having glass transition temperatures of not more than 0° C., by emulsion polymerization in the presence of customary emulsifiers and free-radical polymerization initiators in accordance with the monomer emulsion feed polymerization technique, in which the monomer emulsion is run in a feed stream into the polymerization reactor, which comprises conducting the emulsion polymerization of a monomer mixture comprising (A) at least 50% by weight of the overall monomer amount of at least one ester of acrylic and/or methacrylic acid with alcohols of 1 to 18 C atoms and (B) other olefinically unsaturated monomers (comonomers)
a) in the presence of less than 50 ppm of polymerization inhibitor, based on the amount of monomers, by the monomer emulsion feed polymerization technique, such that
b) the aqueous initial charge to the polymerization reactor is heated at from 30 to 110° C., and
c) from 1 to 10% by weight of the amount of the monomer emulsion added in the feed stream is added to this initial charge over the course of ¼ to 1 hour from the beginning of the feed and at an increasing rate (amount per unit time), and
d) then the remainder of the monomer emulsion is run in continuously and conventionally in accordance with the extent of polymerization of the monomers.
In accordance with the novel process, the preparation of the aqueous pressure-sensitive adhesive dispersions by emulsion polymerization of the monomers by the monomer emulsion feed polymerization technique takes place by initially charging an aqueous phase to the polymerization reactor, with or without the addition of auxiliaries, and then running in the monomer emulsion to be polymerized. The aqueous initial charge, which generally comprises from about 10 to 50 and, in particular, from 25 to 50% by weight of the overall amount of water of the initial charge plus the feed stream, preferably contains—in dissolved form before the beginning of the feed operation—at least one water-soluble salt, in particular in an amount of from about 1 to 7% by weight based on the initial charge. The salts, which in particular are inorganic salts, are usually polyelectrolytes as are also used as buffer substances, such as mixtures of primary, secondary and tertiary alkali metal phosphates or ammonium phosphates and, in particular, sodium pyrophosphate. Examples of other suitable salts are sodium chloride, sodium bicarbonate, calcium sulfate, magnesium phosphate, ammonium chloride and sodium sulfate. A suitable salt of an organic compound is the sodium salt of ethylenediaminetetraacetic acid. Before beginning the feed of the monomer emulsion, the aqueous initial charge is heated to a temperature in the range of, in general, from 30 to 110° C., in particular from 70 to 95° C.
The novel process takes place preferably in the presence of from 0.01 to 5 and, in particular, from 0.05 to 2% by weight, based on the amount of monomers, of a reducing agent, which can be added to the aqueous initial charge and/or to the monomer emulsion feed. The addition of the reducing agent to the initial charge (or to the emulsion feed) can be left out in some cases, especially when the target K values are relatively low. Suitable reducing agents are organic and inorganic compounds such as ascorbic acid, acetone bisulfite, reducing agents based on sulfinic acid, such as the sodium salt of hydroxymethanesulfinic acid, sodium bisulfite or complexed polyvalent metal ions, such as those of iron or of vanadium, for example iron(II) ammonium sulfate. Organic reducing agents, and especiall
Auchter Gerhard
Aydin Oral
Fussl Rudiger
Rehmer Gerd
Stanger Bernd
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
Zalukaeva Tanya
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