Lamination adhesives

Details Lamination adhesives Lamination adhesives

1999-06-01

2002-04-23

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S520000

Reexamination Certificate

active

06376094

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polymers composed of
from 5 to 95% by weight of a mixture of at least one C
2
-C
4
-alkyl acrylate and at least one C
6
-C
12
-alkyl acrylate (monomers a),
from 5 to 30% by weight of ethylenically unsaturated compounds having a glass transition temperature of above 0° C. and containing no functional groups other than the ethylenically unsaturated group (monomers b),
from 0 to 10% by weight of ethylenically unsaturated compounds a having at least one acid group or acid anhydride group (monomers c), and
from 0 to 60% by weight of further ethylenically unsaturated (compounds (monomers d),
the amounts by weight being based on the polymer.
The invention relates additionally to the use of the polymers as adhesives, especially as laminating adhesives, in other words for producing laminates.
2. Description of the Background
The use of aqueous polymer dispersions as adhesives for producing laminates, in other words as laminating adhesives, is known from EP-A-622 434 or WO 92/12213, for example.
In practice, laminating adhesives have to meet a large number of different requirements. For example, laminating adhesives are required to be universally applicable; in other words, they should be equally suitable for the bonding of different polymer films, for example of polyethylene (PE), oriented polypropylene (OPP), polyamide (PA) or polyethylene terephthalate (PETP), with one another and for bonding polymer films with paper or else, in particular, with aluminum foils or metallized polymer films.
The laminating adhesives should have good adhesion to substrates and, after laminating, should bring about high strength of the resulting film laminates.
Since the film laminates are often transparent, the laminating adhesives must also be free from fine coagulum as well as being resistant to ageing and stable to light and exhibiting little foaming.
Processing in the laminating units requires high stability to shearing and good flow properties. Moreover, aqueous systems are desirable in principle to avoid solvent wastes and solvent emissions.
A particular requirement is for high immediate strength of the laminates produced. A high immediate strength (peel strength, measured directly after the production of the laminate) offers the advantage that the film laminate can be subjected rapidly to further processing. This further processing may be the production of a triple laminate starting from the dual laminate, or further operations on the laminate (cutting, punching, folding, sealing).
The aqueous polymer dispersions known to date do not go far enough toward meeting the requirements placed on laminating adhesives. In particular, the immediate strength of the film laminates is too low.
SUMMARY OF THE INVENTION
It is an object of the present invention to remedy this situation.
We have found that this object is achieved by the polymer defined above and by the use thereof, or of the aqueous dispersion of the polymer, as an adhesive for producing laminates—a laminating adhesive.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel polymer is composed of the monomers a) to d) defined at the outset.
The monomers a) comprise a mixture of at least one C
2
-C
4
-alkyl acrylate and at least one C
6
-C
12
-alkyl acrylate.
The C
2
-C
4
-alkyl acrylate is especially n-butyl acrylate or ethyl acrylate. n-Butyl acrylate is particularly preferred.
Examples of suitable C
6
-C
12
-alkyl acrylates are n-hexyl, 2-ethylhexyl, octyl, decyl and dodecyl acrylate.
Preference is given to C
8
-alkyl acrylates, especially 2-ethylhexyl acrylate.
The proportion of the C
2
-C
4
-alkyl acrylate is preferably from 10 to 90% by weight, with particular preference from 20 to 75% by weight and, with very particular preference, from 30 to 70% by weight, and the proportion of the C
6
-C
12
-alkyl acrylates is preferably from 90 to 10% by weight, with particular preference from 25 to 80% by weight and, with very particular preference, from 30 to 70% by weight, these figures by weight being based in each case on the overall amount of the monomers a).
Monomers a) have a glass transition temperature of below 0° C.
Monomers b) are monomers which other than the ethylenically unsaturated group have no functional group, in other words no hydroxyl, acid, acid anhydride, nitro, epoxy or primary, secondary or tertiary amino group. Monomers b), or more accurately the homopolymers of the monomers b), have a glass transition temperature of above 0° C., preferably above 15° C.
The glass transition temperature of the polymer can be determined by conventional methods such as differential thermal analysis (DTA) or differential scanning calorimetry (DSC) (see for example ASTM 3418/82, midpoint temperature).
Examples of possible monomers b) are C
l
-C
20
-alkyl (meth)acrylates, vinyl esters of carboxylic acids with up to 20 carbons, vinylaromatic compounds of up to 20 carbons, ethylenically unsaturated nitrites, and vinyl halides, provided they have the glass transition temperature stated above.
Particularly suitable alkyl (meth)acrylates are methyl methacrylate, methyl acrylate, n-butyl methacrylate and tert-butyl acrylate.
Methyl acrylate, methyl methacrylate and butyl methacrylate are preferred.
Examples of vinyl esters of C
1
-C
20
carboxylic acids are vinyl laurate, stearate, propionate and 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 ethylenically unsaturated compounds substituted by chlorine, fluorine or bromine, preferably vinyl chloride and vinylidene chloride.
Monomers c) are, for example, ethylenically unsaturated monomers having carboxyl groups, such as (meth)acrylic acid, maleic acid, ethylenically unsaturated acid anhydrides or monoesters, such as maleic anhydride or maleic or fumaric monoester, present in the polymer. Monomers having sulfo or sulfonate groups are not mandatory constituents of the novel polymer.
The further monomers, d), can be of any desired type. Preferably, mention may be made, for example, of C
1
-C
10
-hydroxyalkyl (meth)acrylates, or monomers listed under monomers b), having a glass transition temperature of below 0° C.
The novel polymer consists preferably of
from 65 to 95
% by weight
of monomers a)
from 5 to 25
% by weight
of monomers b)
from 0 to 10
% by weight
of monomers c)
from 0 to 10
% by weight
of monomers d)
and with particular preference of
from 65 to 92.5
% by weight
of monomers a)
from 5 to 25
% by weight
of monomers b)
from 2.5 to 10
% by weight
of monomers c)
from 0 to 10
% by weight
of monomers d).
The glass transition temperature of the polymer can be determined by the DTA or DSC methods referred to above.
The glass transition temperature of the polymer is preferably below 60° C. and in particular is from −50 to +60° C., with particular preference from −30 to +40° C. and, with very particular preference, from −30 to +20° C.
The polymer is prepared preferably by emulsion polymerization, and is therefore an emulsion polymer.
Alternatively, preparation can take place by solution polymerization and subsequent dispersion in water.
In the case of emulsion polymerization use is made of ionic and/or nonionic emulsifiers and/or protective colloids, or stabilizers, as surface-active compounds.
A detailed description of suitable protective colloids is given in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1, Makromolekulare Stoffe, Georg-Thieme Verlag, Stuttgart, 1961, pp. 411 to 420. Suitable emulsifiers include anionic, cationic and nonionic emulsifiers. Emulsifiers are preferably employed exclusively as accompanying surface-active substances; their molecular weights, in contrast to the protective colloids, are usually below 2000 g/mol. Where mixtures of surface-active substances are used the individual components must of course be compatible; in case o

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