Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-27
2004-04-27
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S458000, C526S201000, C526S224000, C526S227000, C526S318440
Reexamination Certificate
active
06727327
ABSTRACT:
The present invention relates to aqueous polymer dispersions and to their use in aqueous adhesive formulations for producing laminates.
The use of aqueous polymer dispersions as adhesives and in aqueous adhesive formulations is known to the skilled worker. They have the advantage over solvent-based adhesives that it is possible in principle to avoid solvent waste and solvent emissions.
In practice, adhesives for producing laminates, which are also referred to as laminating adhesives, have to meet a large number of different requirements. For example, laminating adhesives are desired to be universally applicable; in other words, they should be equally suitable for the bonding of different polymer films made, for example, from polyethylene (PE), oriented polypropylene (OPP), polyamide (PA) or polyethylene terephthalate (PETP) with one another, with aluminum foils or metallized polymer films, and for bonding polymer films with paper.
The laminating adhesives should have good substrate adhesion and after lamination should bring about a high and durable level of strength in the resulting laminates (film composites). Furthermore, a high level of instant strength of the film composite is desirable in order to permit rapid further processing, especially in the case of multi-ply laminates. Processing in the laminating units, furthermore, requires the dispersions to be of high shear stability and have good flow properties.
The aqueous polymer dispersions available commercially to date still do not go far enough toward meeting the requirements to which laminating adhesives are subject.
Wo 92/12213 and EP-A 622 434 disclose laminating adhesives based on aqueous polymer dispersions comprising in copolymerized form both at least one ethylenically unsaturated carboxylic acid and at least one ethylenically unsaturated sulfonic acid. Because of this acid combination, such adhesives lead to comparatively high laminate strength. Ethylenically unsaturated sulfonic acids, however, are comparatively expensive and in many countries do not have approval under food law, so that replacement of these monomers in polymers for laminating adhesives is desirable.
DE-A 196 49 383 and the application DE 197 38 185.5, whose priority date is earlier than that of the present specification, describe aqueous polymer dispersions based on alkyl acrylates and their use as laminating adhesives. The adhesives described result in good instant strength of the laminates.
The application DE 19816742, whose priority date is earlier than that of the present specification, discloses aqueous laminating adhesive formulations whose polymers carry anhydride groups. For optimum bonding, amino-containing crosslinkers must be added to the dispersions during formulation. Two-component adhesive formulations of this kind (2K systems) are of course more awkward to prepare than those consisting of the polymer dispersion as the only adhesive component (1K systems). Furthermore, 2K systems are often not sufficiently stable on storage.
It is an object of the present invention to provide aqueous polymer dispersions which, as laminating adhesives, bring about improved laminate strength relative to the prior art without the need for crosslinkers or monomers containing sulfonic acid groups.
We have found that this object is achieved and that aqueous polymer dispersions composed essentially of n-butyl acrylate lead to particularly stable laminates having good permanent and instant strength if the polymers are prepared in the presence of small amounts of a polymerization regulator.
The present invention accordingly provides aqueous polymer dispersions comprising at least one particulate polymer P having a glass transition temperature T
g
of less than 0° C. Whiz is composed of ethylenically unsaturated monomers M including:
i. from 60 to 94.9% by weight, preferably from 75 to 89.5% by weight, of n-butyl acrylate as monomer M1,
ii. from 5 to 39.9% by weight, preferably from 10 to 24.5% by weight, of at least one monomer M2 selected from esters of methacrylic acid with C
1
to C
4
alkanols, tert-butyl acrylate, and vinylaromatic monomers, and
iii.from 0.1 to 5% by weight, preferably from 0.5 to 2% by weight, of at least one monomer M3 selected from ethylenically unsaturated compounds having at least one acid group,
the propportions of said monomers M1to M3 being based on 100% by weight of monomers M,
obtainable by free-radical aqueous emulsion polymerization of monomers M in the presence of at least 0.01% by weight, based on the weight of the monomers M, of at least one molecular weight regulator. The present invention also provides for the use of such polymer dispersions in adhesive formulations for producing laminates, and the corresponding laminating adhesives.
Among the polymer P dispersions of the invention, preference is given to those obtainable by polymerizing the monomers M in the presence of at least 0.05% by weight and not more than 0.5% by weight, preferably in the presence of from 0.1 to 0.5% by weight, in particular from 0.15 to 0.4 and especially from 0.2 to 0.3% by weight, based on 100 parts by weight of the monomers M to be polymerized, of at least one molecular weight regulator. It is supposed that even small amounts of molecular weight regulators suppress the polymer crosslinking reactions that always take place to a, minor extent in the course of free-radical, addition polymerization. In general, the K value of the polymers P in the latex obtained does not exceed a value of 90 (K value according to Fikentscher determined in a 1% by weight solution of the polymer in tetrahydrofurane.
Typical molecular weight regulators are organic sulfur compounds, halogenated hydrocarbons, silanes, allyl alcohols, and aldehydes. Molecular weight regulators given preference in accordance with the invention are compounds having at least one thiol group such as thioglycolic acid, ethyl thioglycolate, mercaptoethanol, mercaptopropyltrimethoxysilane, and linear or branched alkyl mercaptans such as tert-butyl mercaptan and tert-dodecyl mercaptan. The regulator is added to the polymerization vessel preferably continuously during the polymerization of the monomers M. Preferably, both the major amount of the monomers M to be polymerized and the major amount of the molecular weight regulator are supplied continuously to the polymerization reaction. The molecular weight regulator is preferably supplied continuously to the polymerization reaction in the form of a separate, preferably aqueous solution or together with the monomers, e.g., in an aqueous monomer emulsion.
The vinylaromatic monomers specified as monomers M2 include styrene, a-methylstyrene, ortho-chlorostyrene, and vinyltoluene. The esters of methacrylic acid with C
1
-C
4
alkanols include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and tert-butyl methacrylate.
Preferred monomers M2 are methyl methacrylate and styrene.
Monomers M3 include monomers which contain at least one acidic group and the anhydrides and salts of such monomers. Monomers M3 include &agr;,&bgr;-monoethylenically unsaturated mono- and dicarboxylic acids, monbesters of &agr;,&bgr;-monoethylenically unsaturated dicarboxylic acids, the anhydrides of said &agr;,&bgr;-monoethylenically unsaturated carboxylic acids, and also ethylenically unsaturated sulfonic acids, phosphonic acids or dihydrogen phosphates and the water-soluble salts thereof, e.g., their alkali metal salts. Preferred monomers M3 are &agr;,&bgr;-monoethylenically unsaturated C
3
-C
8
carboxylic, acids and C
4
-C
8
dicarboxylic acids, examples being itaconic acid, crotonic acid, vinylacetic acid, acrylamidoglycolic acid, acrylic acid and methacrylic acid, and also the anhydrides thereof. Particularly preferred monomers M3 are acrylic acid and methacrylic acid.
In addition to the abovementioned monomers M1to M3 the monomers M may also include further, auxiliary monomers. Examples of these include neutral or nonionic, modifying monomers M4 of increased solubility in water, e.g., the amides or the N-
Centner Alexander
Gerst Matthias
Schumacher Karl-Heinz
BASF - Aktiengesellschaft
Egwim Kelechi C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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