Method for cross-linking polyacrylates
View Patent ↗Method for producing a polyacrylate adhesive compound by a hot-melt method in which a polyfunctional α-cleaving initiator, which is present as an oligomer, is added to the polymer to be crosslinked prior to the hot-melt method and ultraviolet crosslinking is carried out after treatment in the hot-melt method.
1. A process for preparing crosslinked polyacrylates, in which a monomer mixture comprising (meth)acrylates is copolymerized to produce a polymer and, after the polymerization, the polymer is subjected to a hotmelt process after which crosslinking of the polymer is brought about by ultraviolet radiation, wherein 0.5 to 10% by weight of the monomer mixture of copolymerizable monomers containing one or more epoxy groups are incorporated into the polymers during the copolymerization by glycidyl methacrylate, and, prior to crosslinking, at least one photocation generator and also one or more di- or polyfunctional epoxides and/or alcohols are added.
2. The process of claim 1 , wherein the monomer mixture is one which will result in polymers which are pressure sensitively adhesive.
3. The process of claim 1 , wherein the composition of the monomer mixture is as follows:
a) 60 to 99.5% by weight of (meth)acrylic acid and/or (meth)acrylate esters of the following formula
where R 1 =H or CH 3 and R 2 is an alkyl chain having 1 to 20 carbon atoms,
b) 0.5 to 10% by weight of copolymerizable monomers which contain one or more epoxy groups and/or one or more hydroxyl groups,
c) optionally up to a maximum of 39.5% by weight of copalymerizable olefinically unsaturated monomers containing functional groups which activate the double bond for the polymerization reaction,
the components of the monomer mixture adding up to 100%,
and/or wherein, prior to crosslinking,
d) 0.01 to 25% by weight of a photocation generator and
e) 0.1 to 5% by weight of glycidyl methacrylate is added to the polymers, so that the polymers and components d) and e) add up to 100% by weight.
4. The process of claim 1 , wherein a triarylsulfonium hexafluoro salt from group 15 of the periodic system is used as photocation generator.
5. The process of claim 1 , wherein, in the course of crosslinking, structuring of the crosslinked polyacrylates is achieved by covering the polyacrylates to be crosslinked with a mask having regions of different ultraviolet transparency, the structuring of the polyacrylates being the presence within the polyacrylates of regions of high crosslinking alongside regions of low crosslinking and/or noncrosslinked regions.
6. A method of crosslinking by ultraviolet radiation in the presence of a photocation generator, of polyacrylates functionalized by epoxy groups, which comprises carrying out said crosslinking with di- or polyfunctional epoxides or alcohols as crosslinking reagents.
7. The process of claim 3 , wherein R 2 is an alkyl chain having from 4 to 14 carbon atoms.
8. The process of claim 3 , wherein R 2 is an alkyl chain having from 4 to 9 carbon atoms.
9. The process of claim 4 , wherein said triarylsulfonium hexafluoro salt is selected from the group consisting of triarylsulfonium hexafluorophosphate, triarylsulfonium hexafluoroantimonate and mixtures thereof.