Metal salt crosslinked adhesives

Details Metal salt crosslinked adhesives Metal salt crosslinked adhesives

1999-08-25

2003-02-25

Gallagher, John J. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C524S556000, C526S317100

Reexamination Certificate

active

06524427

ABSTRACT:

The invention relates to adhesives comprising as binder an aqueous dispersion of a polymer formed from free-radically polymerizable compounds (monomers), wherein from 0.1 to 20% by weight of the monomers, based on the overall amount of the monomers, are ethylenically unsaturated acids at least 20 mol % of whose acid groups are present as a salt of at least divalent metals.
The invention relates in particular to the use of said adhesives in gloss film lamination.
The use of aqueous dispersions of crosslinkable polymers as adhesives, or as binders in adhesives, is known. EP A 644 902 describes aqueous polymer dispersions of this kind which comprise hydroxylamines or oxime ethers as crosslinkers. The polymers crosslink with the hydroxylamines or oxime ethers at room temperature following removal of the dispersion water.
The above crosslinking systems require a specific polymer structure: in particular, monomers with carbonyl groups are necessary for the crosslinking reaction.
There is a general desire for alternative crosslinking systems comprising simple and readily available monomers and crosslinkers. The new crosslinking systems of this kind would have to meet a series of requirements. In particular, aqueous polymer dispersions already containing the crosslinker would have to be stable on storage so that one-component systems were possible (with the crosslinker not added until shortly before subsequent application). The crosslinking reaction should take place without an increase in temperature.
Adhesives are required to have good sticking properties and, in particular, very good adhesion and cohesion. In the context of their use in gloss film lamination, important factors are good adhesion to the substrates (transparent polymer films and paper or card) and high elasticity of the resultant laminates.
When the film composites are intended to be partially transparent, the adhesives must also be free from fine coagulum and must be aging resistant, light stable and low-foaming.
Processing in the laminating units imposes the requirements of high shear stability and good flow properties.
In particular, there is a desire for a high level of immediate strength in the composites produced. Such immediate strength (peel strength measured directly following the production of the composite) offers the advantage that the film composite can quickly be processed further. This further processing may, for example, be in the form of further operations on the laminate (cutting, punching, folding, sealing).
Aqueous polymer dispersions which comprise carboxylates of divalent metals are already known, for example, from EP 442 370 and DE 1051436.
It is an object of the present invention to provide adhesives which are based on crosslinkable polymers and meet the above requirements.
We have found that this object is achieved by the adhesives defined at the outset and by their use in gloss film lamination.
The adhesives of the invention preferably comprise a polymer composed of
a) from 20 to 99.9% by weight, preferably from 60 to 99.5% by weight and, with particular preference, from 80 to 99.5% by weight of at least one principal monomer
b) from 0.1 to 20% by weight, preferably from 0.5 to 10% by weight and, with particular preference, from 0.5 to 5% by weight of an ethylenically unsaturated acid at least 20 mol % of whose acid groups are present in the form of a salt of at least divalent metals
c) from 0 to 70% by weight, preferably from 0 to 35% by weight and, with particular preference, from 0 to 15% by weight of further monomers (monomers c).
Principal monomers a) are selected from C
1
-C
20
-alkyl (meth)acrylates, vinyl esters of carboxylic acids having up to 20 carbon atoms, vinylaromatic compounds having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of C
1
-C
10
alcohols, aliphatic hydrocarbons with 2 to 8 carbon atoms and 1 or 2 double bonds, or mixtures of these monomers.
Examples are C
1
-C
10
-alkyl (meth)acrylates, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2 ethylhexyl acrylate.
Mixtures of the alkyl (meth)acrylates are also suitable in particular.
Examples of vinyl esters of carboxylic acids with 1 to 20 carbon atoms are vinyl laurate, stearate, propionate, acetate, and Versatic acid vinyl ester.
Suitable vinylaromatic compounds are vinyltoluene, &agr;- and p-methylstyrene, &agr;-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, and, preferably, styrene. Examples of nitriles are acrylonitrile and methacrylonitrile.
The vinyl halides are chloro-, fluoro- or bromo-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.
Examples of vinyl ethers are vinyl methyl ether and vinyl isobutyl ether. Preference is given to vinyl ethers of C
1
-C
4
alcohols.
As hydrocarbons having 2 to 8 carbon atoms and two olefinic double bonds mention may be made of butadiene, isoprene and chloroprene.
Suitable monomers a) are preferably C
1
-C
10
-alkyl acrylates and methacrylates, especially C
1
-C
8
-alkyl acrylates and methacrylates, with particular preference being given in each case to the acrylates.
Very particular preference is given to methyl acrylate, ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, octyl acrylate and 2-ethylhexyl acrylate, and to mixtures of these monomers, as monomers a).
With particular preference, the polymer contains at least 5% by weight, preferably at least 15% by weight, of methyl or ethyl acrylate and at least 5% by weight, preferably at least 15% by weight, of n-butyl acrylate. The amounts by weight are based on the polymer.
Monomers b) comprise, for example, monomers having carboxylic acid, sulfonic acid or phosphonic acid groups. Carboxylic acid groups are preferred. Examples that may be mentioned are acrylic, methacrylic, itaconic, maleic and fumaric acid.
Examples of further monomers, c), are hydroxyl-containing monomers, especially C
1
-C
10
-hydroxyalkyl (meth)acrylates, and also (meth)acrylamide.
Phenyloxyethyl glycol monomer (meth)acrylate, glycidyl acrylate, glycidyl methacrylate, and amino (meth)acrylates such as 2 aminoethyl (meth)acrylate may additionally be mentioned as further monomers c).
Monomers c) which in addition to the double bond carry further functional groups, such as isocyanate, amino, hydroxyl, amido or glycidyl, may, for example, improve the adhesion to substrates.
Preferably, at least 40 mol %, with particular preference at least 70 mol % and, with very particular preference, 100 mol % of the acid groups of the acids b) are present in the form of a salt of at least divalent metals.
The metals are, for example, divalent or trivalent metals, preferably divalent metals, and especially Ca, Mg, Zn or Mn.
With particular preference the metal is Ca.
Converting the acid groups to the salts can be done by adding basic compounds of the metals, in particular by means of the hydroxyl compounds. A suitable example is Ca(OH)
2
.
Converting the acid groups into the salt groups can be done even before the polymerization is conducted or else during or after the polymerization of the monomers.
Preferably, conversion to the salt groups takes place following polymerization, by adding the basic metal compounds to the resultant aqueous polymer dispersion.
The glass transition temperature of the polymer obtained from the monomers a) to c) is preferably below 60° C., in particular from −50 to +60° C., with particular preference from −30 to +40° C., and, with very particular preference, from −30 to +20° C.
The glass transition temperature of the polymer can be determined by customary methods, such as differential thermal analysis or differential scanning calorimetry (see e.g. ASTM 3418/82, midpoint temperature).
The polymer is prepared preferably by emulsion polymerization and in that case is an emulsion addition polymer.
Alternatively, preparation can take place by solution polymerization with subsequent dispersion in water.
In the case of emulsion polymerization, ionic and/or nonionic emulsifiers and/or protecti

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