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
1998-05-21
2003-03-25
Egwim, Kelechi (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...
C524S017000, C524S025000, C524S056000, C524S556000, C526S075000, C526S203000
Reexamination Certificate
active
06538057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to adhesives comprising an aqueous polymer dispersion obtainable by free-radical copolymerization in the presence of at least one protective colloid based on a prepolymer, to processes for their preparation and to their use.
2. Description of the Background
Packaging materials made from paper, board or card, such as folding boxes, are produced, and paper labels attached to nonabsorbent substrates, especially to hollow structures made from glass, plastic or metal, such as bottles or glasses, using adhesives which are referred to in general as packaging adhesives. Systems which are widespread as packaging adhesives are those comprising a polymer dispersion or a blend of a polymer dispersion with other active adhesive constituents.
Kleb- und Dichtstoffe, Vol. 40, 6/96, p. 22 f. describes, in general terms, dispersion adhesives in the paper and packaging industry. Accordingly, monomers considered for preparing the disperse phase which forms the adhesive substance are, for example, vinyl acetate, ethylene, vinyl propionate, acrylates, and dibutyl maleate. In addition to the chemical structure of the polymer dispersion and, in particular, the particle size distribution, the nature and amount of the emulsifiers and protective colloids have a decisive influence on the adhesive properties. Since the components used to stabilize the polymer dispersion are also incorporated into the adhesive film, they influence the properties of this film, for example its water resistance. A further important property of the resulting films, especially when the adhesive is used in the application of transparent labels such as printed polymer films, for example, is its transparency. Below a temperature—the white point or minimum film-forming temperature—which is characteristic for every polymer dispersion white layers are obtained instead of transparent films, with film labels losing their transparency especially at the unprinted areas and the visual color saturation of the printed image on the label suffering an overall loss in depth and brilliance.
The adhesives systems employed for the wet labeling of bottles are predominantly those based on an acrylate dispersion which is used either alone or as a blend with natural substances of high viscosity, such as starch or casein. A disadvantage of the known packaging adhesives based on acrylate dispersions is that these dispersions generally form films which exhibit marked clouding.
An essential requirement for an adhesive system to be used for the labeling of hollow articles is the formation of a film with high adhesion and low cohesion. For optimum deployment on the customary machines for the wet labeling of bottles it is necessary for the adhesive used to have a high viscosity at low shear rates, for example a viscosity in a range from about 2000 to 10,000 mPa·s at 25 s
−1
.
Particular requirements are imposed, furthermore, on adhesives to be used for the production or labeling of packaging which comes into contact with foods. Important properties then, in addition to those mentioned above, are the toxicological acceptability of the adhesive and the exclusion of factors which impair taste and odor. In addition to the toxicological aspects regarding the foods to be packaged, further particular requirements are imposed on the ingredients of the dispersions to be used in packaging adhesives in respect of any possible irritation to, and/or harm to the health of, the personnel entrusted with processing. For instance, some dispersions employed for the preparation of adhesives include butenol as polymerization regulator, which is not entirely acceptable from a toxicological standpoint.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide new adhesives suitable for the production and labeling of packaging. As well as good performance properties, such as high tack, low cohesion and high viscosity at low shear rates, these adhesives should in particular form a clear, transparent film in order to avoid the abovementioned disadvantages in connection with wet labeling using transparent films.
Furthermore, the dispersions employed.should as far as possible include no components regarded as toxicologically unacceptable.
We have found that this object is achieved, surprisingly, if an aqueous polymer dispersion obtainable by free-radical copolymerization in the presence of a particular protective colloid, based on a prepolymer, is employed in adhesives.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention thus provides an adhesive comprising:
a) from 5.0 to 95.0% by weight of an adhesive dispersion having a viscosity in the range from 2000 to 10,000 mPa·s, which comprises
a1) an aqueous polymer dispersion which is obtainable by free-radical polymerization of a mixture M which comprises at least one ethylenically unsaturated monomer A to give a polymer P in the presence of at least one protective colloid based on a water-soluble prepolymer which comprises at least one water-soluble monomer B, and further additives if desired,
a2) if desired, a base selected from the group consisting of alkali metal hydroxides, ammonia and volatile organic amines,
a3) if desired, a completely water-miscible organic solvent,
and, if desired, further additives;
b) from 0 to 90.0% by weight of a polysaccharide and/or a protein and/or a protein degradation product;
c) from 0 to 95.0% by weight of at least one filler;
d) from 0 to 10.0% by weight of at least one emulsifier;
e) from 0 to 30.0% by weight of further additives;
f) water to 100% by weight.
Component a)
a1):
The monomer mixture M used to prepared the polymers P contains from 50 to 100% by weight, preferably 60.to 99.9% by weight, of at least one free-radically polymerizable, ethylenically unsaturated monomer A (principal monomer) and from 0 to 50% by weight, if desired from 0.1 to 40% by weight, of at least one comonomer C and also, depending on the polymerization process, if desired, at least one water-soluble monomer B in the amounts described below.
Suitable monomers A are esters of &agr;,&bgr;-monoethylenically. unsaturated C
3
-C
6
mono- and dicarboxylic acids with alkanols having preferably 1 to 12 carbons, particularly preferably 1 to 8 carbons and, in particular, 1 to 4 carbons, for example esters of acrylic and/or methacrylic acid with methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and 2-ethylhexanol, esters of vinyl alcohol with C
1
-C
20
monocarboxylic acids, for example vinyl formate, acetate, propionate, n-butyrate, laurate and stearate, and vinyl esters of highly branched, saturated monocarboxylic acids having C
9
, C
10
and C
11
side chains (Versatic acids), vinylaromatic compounds, such as styrene, &agr;-methylstyrene, p-methylstyrene, &agr;-n-butylstyrene, p-n-butylstyrene, p-n-decylstyrene, o-chlorostyrene or vinyltoluene, and mixtures thereof.
Suitable comonomers C are, for example, vinyl halides and vinylidene halides, for example vinyl chloride and vinylidene chloride, &agr;,&bgr;-ethylenically unsaturated nitriles, for example acrylonitrile and methacrylonitrile, C
2
-C
6
monoolefins, for example ethylene and propylene, and nonaromatic hydrocarbons having 2 to 8 carbons and at, least 2 conjugated olefinic double bonds, for example butadiene, isoprene and chloroprene, and also mixtures thereof.
Further suitable comonomers C are crosslinking monomers, which in addition to their ethylenically unsaturated double bond have an epoxy, hydroxyl, N-methylol or carbonyl function or two nonconjugated, ethylenically unsaturated double bonds. The monomer mixture M can contain from 0 to 40% by weight, preferably from 0 to 20% by weight and, with particular preference, from 0.2 to 15% by weight of these crosslinking monomers. The crosslinking reaction preferably takes place not until during the drying of the polymers, and can be accelerated by heat treatment and, if desired, by adding catalysts, for example proton donors, such as maleic acid, diammonium hydrogenphosphate or ammoniu
Hartz Oliver
Langhauser Georg
Schumacher Karl-Heinz
Urban Dieter
Wildburg Gerald
BASF - Aktiengesellschaft
Egwim Kelechi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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