Adhesives containing polyvinyl alkyl ethers

Details Adhesives containing polyvinyl alkyl ethers Adhesives containing polyvinyl alkyl ethers

2002-01-28

2004-05-11

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S104000, C522S107000, C522S109000, C522S110000, C522S150000, C522S153000, C522S154000, C522S904000, C428S3550RA, C428S3550AC, C428S3550EN, C525S191000, C525S221000, C525S222000, C525S153000

Reexamination Certificate

active

06734222

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a mixture containing:
A) a polymer, which consists to an extent of at least 40 wt % of C
1
-C
18
alkyl (meth)acrylates (referred to below as polyacrylates) and
B) a homopolymer or copolymer of vinyl alkyl ether (referred to below as polyvinyl alkyl ether), which consists to an extent of at least 70 wt % of structural units of the following formula
in which X stands for a single bond or a C
1
-C
3
alkylene group and R for a C
1
-C
6
alkyl group.
The invention also relates to the use of said mixture as an adhesive or a hot-melt adhesive, particularly for the production of self-adherent articles incorporating flexible PVC as support material.
2. Description of the Background
The manufacture of self-adherent labels and tapes and also printed films for exterior applications presently involves, in many cases, the use of soft PVC films coated with a self-adhesive. In this case, use is made, inter alia, of PVC films containing low-molecular plasticizers based on phthalate. One problem arising from the use of these plasticizers is that the plasticizer can migrate from the film into the self-adhesive. The application-technological adhesive properties are greatly reduced as a result. Both the cohesion of the adhesive and the adhesion of the adhesive to the surface to which the label or film is stuck can be distinctly reduced on account of the migration of the plasticizer into the adhesive.
Attempts at solving this problem hitherto described in the literature involve the use of barrier layers (EP 103,407) to prevent or reduce such migration, or the use of crosslinking agents (EP 330,272) or specific comonomers (WO 96/26221).
The solutions previous proposed call for elaborate changes to be made to the polymer system by appropriate selection of specific comonomers or demand elaborate pretreatment of the support material.
The present invention relates to adhesives which are also suitable for use on support materials of flexible PVC and which are capable of adequately preventing or reducing the migration of plasticizers or at least of alleviating the results of such migration.
Accordingly, we have found the mixtures defined above and the use thereof.
SUMMARY OF THE INVENTION
The mixture of the invention necessarily contains a polyacrylate A) and a poly(alkyl vinyl ether) B).
The polyacrylate consists to an extent of at least 40 wt %, preferably to an extent of at least 60 wt %, and more preferably to an extent of at least 80 wt %, of C
1
-C
18
alkyl (meth)acrylates.
Particular mention may be made of C
1
-C
18
alkyl (meth)acrylates, eg, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The mixture preferably contains a photoinitiator to make the polyacrylate uv-crosslinkable. To render the mixture of the invention uv-crosslinkable, a photoinitiator can be added thereto. Alternatively, the photoinitiator can be bonded to the polyacrylate.
By irradiation with high-energy light, particularly UV light, the photoinitiator causes crosslinking of the polyacrylate, preferably by a chemical grafting reaction of the photoinitiator with an adjacent polymer chain. In particular, crosslinking can take place by insertion of a carbonyl group of the photoinitiator into an adjacent carbon-hydrogen bond to produce a —C—C—O—H group.
The mixture of the invention contains preferably from 0.0001 to 1 mol, more preferably from 0.0002 to 0.1 mol, and most preferably from 0.0003 to 0.01 mol, of the photoinitiator or the group of molecules bonded to the polyacrylate and acting as photoinitiator, per 100 g of polyacrylate.
The photoinitiator comprises, for example, acetophenone, benzoin ether, benzyl dialkyl ketols or derivatives thereof.
Preferably, the photoinitiator is bonded to the polyacrylate.
More preferably, the photoinitiator is one which has been built into the polymer chain by free-radical copolymerization. Preferably, the photoinitiator additionally contains an acrylic or methacrylic group.
Suitable copolymerizable photoinitiators are acetophenone or benzophenone derivatives containing more than one, but preferably one, ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acrylic group.
The ethylenically unsaturated group can be bonded directly to the phenyl ring of the acetophenone or benzophenone derivative. Generally, a spacer group is located between the phenyl ring and the ethylenically unsaturated group.
The spacer group can contain, eg, up to 100 carbon atoms.
Suitable acetophenone or benzophenone derivatives are described in, eg, EP-A 346,734, EP-A 377,199 (claim 1), DE-A 4,037,079 (claim 1), and DE-A 3,844,444 (claim 1) and are included herein by reference. Preferred acetophenone and benzophenone derivatives are those of the formula
in which R
1
stands for an organic radical containing up to 30 carbons, R
2
stands for a hydrogen atom or a methyl group and R
3
stands for an optionally substituted phenyl group or a C
1
-C
4
alkyl group.
R
1
very preferably stands for an alkylene group, in particular a C
2
-C
8
alkylene group.
R
3
very preferably stands for a methyl group or a phenyl group.
Examples of other monomers of which the polyacrylate can be composed are vinyl esters of carboxylic acids containing up to 20 carbons, vinyl aromatic compounds containing up to 20 carbons, ethylenically unsaturated nitrites, vinyl halides, vinyl ethers of alcohols containing from 1 to 10 carbons, aliphatic hydrocarbons containing from 2 to 8 carbons and 1 or 2 double bonds, or mixtures of these monomers.
Examples of suitable vinylaromatic compounds are vinyl toluene &agr;- and &pgr;-methylstyrenes, &agr;-butylstyrene, 4-n-butylstyrene, 4-n-de-cylstyrene, and preferably styrene. Examples of nitrites are acrylonitrile and methacrylonitrile.
The vinyl halides are ethylenically unsaturated compounds that are substituted by chlorine, fluorine or bromine, preferably vinyl chloride and vinylidene chloride.
Examples of suitable vinyl ethers are vinyl methyl ether, vinyl ethyl ether or vinyl isobutyl ether. Preference is given to a vinyl ether of alcohols containing from 1 to 4 carbons.
As examples of hydrocarbons containing from 2 to 8 carbons and two olefinic double bonds there may be mentioned butadiene, isoprene and chloroprene.
Other monomers which are particularly suitable are monomers containing carboxylic, sulfonic or phosphonic acid groups. Preference is given to carboxylic acid groups. Examples thereof are acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid.
Other monomers are eg monomers containing hydroxyl groups, particularly C
1
-C
10
hydroxyalkyl (meth)acrylates, and (meth)acrylamide.
Mention may also be made of phenyloxyethyl glycol mono(meth)acrylate, glycidyl acrylate, glycidyl methacrylate, and amino (meth)acrylates such as 2-aminoethyl (meth)acrylate.
Monomers containing, in addition to the double bond, other functional groups, such as isocyanate, amino, hydroxy, amide or glycidyl groups, can improve the adhesion to substrates, for example.
The polyacrylate preferably has a K value of from 30 to 80 and more preferably from 40 to 60, measured in tetrahydrofuran (1% strength solution, 21° C.).
The Fikentscher K-value is an indication of the molecular weight and viscosity of the polymer.
The glass-transition temperature (T
g
) of the polyacrylate is preferably from −60° to +10° C., more preferably from −55° to 0° C., and most preferably from −55° to −10° C.
The glass-transition temperature of the polyacrylate can be determined by conventional methods such as differential thermal analysis or differential scanning calorimetry (cf, eg, ASTM 3418/82, “midpoint temperature”).
The polyacrylates can be produced by copolymerization of the monomeric components using the conventional polymerization initiators and, optionally, modifiers, polymerization being carried out at the usual temperatures in substance, in emulsion, eg, in water

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