Low-outgassing acrylic pressure-sensitive adhesive compositions
View Patent ↗A pressure-sensitive adhesive composition comprising polymers and/or copolymers based at least predominantly on (meth)acrylic acid and/or derivatives thereof, wherein said composition possesses an outgassing level of not more than 50 μg/g in total, preferably less than 10 μg/g, when said composition is measured by the tesa method.
1. A UV crosslinked pressure-sensitive adhesive composition comprising polymers, copolymers, or both, based at least predominantly on (meth)acrylic acid, derivatives thereof, or both, wherein said crosslinked pressure-sensitive adhesive composition comprises a residual volatile component fraction of in total less than 50 μg/g, as measured by the tesa method.
2. The UV crosslinked pressure-sensitive adhesive composition as claimed in claim 1 , wherein the polymers, copolymers or both are prepared using at least the following monomers:
(a) from 65 to 100% by weight of acrylic acid derivatives, methacrylic acid derivatives, or both, of the general formula
where R 1 =H or CH 3 and R 2 =an alkyl chain of 2 to 20 carbon atoms,
(b) from 0 to 35% by weight of vinyl compounds containing functional groups.
3. A process for preparing a UV crosslinked pressure-sensitive adhesive composition as claimed in claim 1 , using a polyacrylate solution obtainable by free-radical addition polymerization, which comprises
a concentration step in which
after polymerization, an entrainer is added to the polyacrylate solution,
the entrainer-admixed polyacrylate solution is passed into an extruder in which said solution is subjected to a carrier distillation,
in at least one further step following concentration, a postpurification step is conducted by adding the same entrainer again, or a further entrainer, to the concentrated polyacrylate composition and carrying out a further carrier distillation in the extruder,
the concentration thus produces a polyacrylate composition which is processed further from the melt, and
the polyacrylate composition is crosslinked by exposure to UV-A radiation.
4. The processes claimed in claim 3 , wherein at least the extruder in the concentration step is a corotating or counterrotating twin-screw extruder.
5. The process as claimed in claim 3 , wherein steam is used as entrainer.
6. The process as claimed in claim 3 , wherein
the concentrated polyacrylate composition is applied to a backing material
and the polyacrylate composition on the backing material is subjected to a crosslinking reaction.
7. The process as claimed in claim 6 , wherein crosslinking is carried out using UV light in a wavelength range from 250 to 400 nm, with the proviso that the output of light in the wavelength range from 300 to 400 nm makes up at least 70% of the total irradiated light output.
8. An adhesive tape comprising a backing material having a UV crosslinked pressure-sensitive adhesive composition as claimed in claim 1 or 2 applied to one or both sides.
9. The adhesive tape as claimed in claim 8 , comprising a backing material having en outgassing tendency of less than 5 μg/g.
10. The UV crosslinked pressure-sensitive adhesive composition of claim 1 , wherein said volatile component fraction is less than 10 μg/g.
11. The process of claim 3 , wherein said further carrier distillation is conducted at higher temperatures and lower vacuums than the preceding distillation.
12. The process of claim 7 , wherein the light in the wavelength range of 300 to 400 nm makes up at least 90% of the total irradiated light output.