Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-05
2002-12-03
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C428S480000
Reexamination Certificate
active
06489384
ABSTRACT:
The invention relates to a composition comprising a polyacrylate for processing from the melt and a stabilizer having a phosphite group.
UV-crosslinkable polymers and their use as adhesives, e.g., as hot-melt pressure sensitive adhesives (PSAs), are known, for example, from DE-A-2 411 169, EP-A-246 848, DE-A-4 037 079 or DE-A-3 844 444.
The polymers used for hot-melt adhesives are solid at room temperature and are applied to the desired substrates from the melt at relatively high temperatures.
Required polymers are often supplied already in the fluid state (by tanker truck) and held in said fluid state until subsequent processing.
At the temperatures required, there may be instances of heat-induced crosslinking. It is therefore desired to add effective stabilizers.
The stabilizers must not adversely affect in particular the performance properties in the context of the subsequent use as an adhesive.
A particular problem in this context is represented by UV-crosslinkable polymers which for the subsequent UV-crosslinking include a photoinitiator. The stabilizers may detract from the activity of the photoinitiator and so lead to poor crosslinking and to unfavorable performance properties, e.g., deficient cohesion in the adhesive film.
It is an object of the present invention to overcome the abovementioned problems.
We have found that this object is achieved by the composition defined at the outset, by its use as a hot-melt pressure sensitive adhesive, and by a process for applying said adhesive to appropriate substrates.
The composition of the invention comprises a polyacrylate.
This is an addition polymer obtainable by free-radical polymerization of acrylic monomers, which are understood to include methyl acrylic monomers, with or without further, copolymerizable monomers.
The polyacrylate is composed preferably of at least 40% by weight, with particular preference at least 60% by weight, with very particular preference at least 80% by weight, of C
1
-C
18
alkyl (meth)acrylates.
Mention may be made in particular of C
1
-C
8
alkyl (meth)acrylates, e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate.
The polyacrylate in question is preferably crosslinkable with UV light. For UV crosslinking, a photoinitiator may be added to the composition of the invention. Alternatively, the photoinitiator may be attached to the polyacrylate.
By exposure to high-energy light, especially UV light, the photoinitiator brings about crosslinking of the polymer, preferably by means of a chemical grafting reaction of the photoinitiator with a spatially adjacent polymer chain. Crosslinking may take place in particular by insertion of a carbonyl group from the photoinitiator into an adjacent C—H bond, to form a —C—C—O—H group.
The composition of the invention contains preferably from 0.0001 to 1 mol, with particular preference from 0.0002 to 0.1 mol, with very particular preference from 0.0003 to 0.01 mol, of the photoinitiator, or of the group which acts as a photoinitiator and is attached to the polymer, per 100 g of polyacrylate.
The photoinitiator comprises, for example, acetophenone, benzoin ethers, benzil dialkyl ketals or derivatives thereof.
Preferably, the photoinitiator is attached to the polyacrylate.
With particular preference, the photoinitiator has been incorporated into the polymer chain by means of free-radical copolymerization. For this purpose, the photoinitiator preferably includes an acrylic or methacrylic group.
Suitable copolymerizable photoinitiators are acetophenone derivatives or benzophenone derivatives containing at least one, preferably one, ethylenically unsaturated group. Said ethylenically unsaturated group is preferably an acrylic or methacrylic group.
The ethylenically unsaturated group may be attached directly to the phenyl ring of the acetophenone or benzophenone derivative. In general, there is a spacer group between the phenyl ring and the ethylenically unsaturated group.
The spacer group may contain, for example, up to 100 carbon atoms.
Appropriate acetophenone derivatives or benzophenone derivatives are described, for example, in EP-A-346 734, EP-A-377199 (claim
1
), DE-A-4 037 079 (claim
1
) and DE-A-3 844 444 (claim
1
) and are incorporated into the disclosure content of the present specification by this reference. Preferred acetophenone derivatives and benzophenone derivatives are those of the formula
where R
1
is an organic radical having up to 30 carbon atoms, R
2
is a hydrogen atom or a methyl group, and R
3
is a substituted or unsubstituted phenyl group or a C
1
-C
4
alkyl group.
With particular preference, R
1
is an alkylene group, especially a C
2
-C
8
alkylene group.
With particular preference, R
3
is a methyl group or a phenyl group.
Examples of further monomers of which the polyacrylate may be composed are vinyl esters of carboxylic acids containing up to 20 carbon atoms, vinylaromatic compounds having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols containing 1 to 10 carbon atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and 1 or 2 double bonds, or mixtures of these monomers.
Examples of 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 which may be mentioned include vinyl methyl ether and vinyl isobutyl ether. Preference is given to vinyl ethers of alcohols containing 1 to 4 carbon atoms.
Hydrocarbons having 2 to 8 carbon atoms and two olefinic double bonds which may be mentioned include butadiene, isoprene, and chloroprene.
Further suitable monomers are, in particular, monomers containing carboxylic acid, sulfonic acid or phosphonic acid groups. Carboxylic acid groups are preferred. Mention may be made, for example, of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid.
Further monomers include, for example, hydroxyl-containing monomers, especially C
1
-C
10
hydroxyalkyl (meth)acrylates, and (meth)acrylamide.
Mention may be made, furthermore, of phenyloxyethyl glycol mono(meth)acrylate, glycidyl acrylate, glycidyl methacrylate, and amino (meth)acrylates such as 2-aminoethyl (meth)acrylate.
Monomers which in addition to the double bond carry further functional groups, e.g., isocyanate, amino, hydroxy, amide or glycidyl, may improve, for example, the adhesion to substrates.
The polyacrylate preferably has a K value of from 30 to 80, with particular preference from 40 to 60, measured in tetrahydrofuran (1% strength solution, 21° C.).
The K value of Fikentscher is a measure of the molecular weight and viscosity of the polymer.
The glass transition temperature (Tg) of the polymer is preferably from −60 to +10° C., with particular preference from −55 to 0° C., with very particular preference from −55 to −10° C.
The glass transition temperature of the polyacrylate may be determined by customary methods such as differential thermoanalysis or differential scanning calorimetry (see, e.g., ASTM 3418/82, midpoint temperature).
The polyacrylates may be prepared by copolymerizing the monomeric components using the customary polymerization initiators and, if desired, regulators, polymerization being carried out at the customary temperatures in bulk; in emulsion, for example, in water or liquid hydrocarbons; or in solution. The novel copolymers are preferably prepared by polymerizing the monomers in solvents, especially in solvents with a boiling range from 50 to 150° C., preferably from 60 to 120° C., using the customary amount of polymerization initiators, which is generally from 0.01 to 10, in particular from 0.1 to 4,% by weight based on the overall weight of the monomers. Suitable solvents include especially alcohols, such as methanol, ethanol, n-
Fink Ralf
Schumacher Karl-Heinz
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sanders Kriellion A.
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