Use of macromonomers to prepare acrylic PSAs
View Patent ↗The use of macromonomers which have a glass transition temperature of at least 20° C., have at least one oligomeric and/or polymeric structural unit which is incompatible with polyacrylates, and have at least one polymerizable double bond in the form of a vinyl, acrylate and/or methacrylate unit as comonomers in the preparation of oriented polyacrylate pressure sensitive adhesives.
1. A method for the preparation of oriented polyacrylate pressure sensitive adhesives comprising the polymerization of a monomer mixture, wherein said monomer mixture comprises macromonomers which have
a glass transition temperature of at least 20° C.,
at least one oligomeric and/or polymeric structural unit which is incompatible with polyacrylates, and
at least one polymerizable double bond in the form of a vinyl, acrylate and/or methacrylate unit
and said polymerized monomer mixture is applied as a coating to a carrier and oriented during or after said application.
2. The method as claimed in claim 1 , wherein the oligomeric or polymeric structural unit is inert to a radical polymerization.
3. The method as claimed in claim 1 , wherein the oligomeric or polymeric structural unit is inert to an anionic polymerization.
4. The method as claimed in claim 1 , wherein the oriented polyacrylate pressure sensitive adhesives have a preferential direction such that the refractive index measured in the preferential direction, n MD , is greater than the refractive index measured in a direction perpendicular to the preferential direction, n CD , with the difference Δn=n MD −n CD being at least 1·10 −6 .
5. The method of claim 1 , wherein the oriented pressure sensitive adhesives immediately after their preparation exhibit a shrinkback of at least 3% in the free film, determined in accordance with test D.
6. The method of claim 1 , wherein, 3 months after their preparation, with storage at 23° C. and 50% relative humidity during that time, the oriented pressure sensitive adhesives exhibit a shrinkback of at least 3% in the free film, determined in accordance with Test D.
7. The method of claim 1 , wherein the fraction of the macromonomers in the polymerization mixture is up to 40% by weight.
8. The method of claim 7 , wherein said fraction is up to 30% by weight.
9. The method of claim 1 , wherein, said macromonomers are acrylate- and/or methacrylate-functionalized polystyrenes and/or poly-α-methylstyrenes of the formula:
in which, independently of one another,
R 1 =a radical which is a residue of a polymerization initiator,
R 2 =H or CH 3
R 3 =H or CH 3
n=20to 350.
10. The method of claim 9 , wherein said radical is an optionally branched alkyl radical.
11. The method of claim 10 , wherein said radical is CH 3 CH 2 C(CH 3 )H.
12. The method of claim 9 , wherein n=45 to 250.