Permanently tacky adhesives with improved environmental compatibility
The invention provides resin- and mineral oil-free pressure-sensitive adhesive compositions, comprising 55%-100% by weight of a copolymer of propylene and one or more further monomers selected from the group composed of ethylene and 1-olefins having 4 to 20 carbon atoms, wherein the copolymer has been prepared with the aid of metallocene catalysts and is characterized by a. a melt viscosity at 170° C. of 20 to 8000 mPas (DIN 53019); b. a density of 0.84 to 0.90 g/cm 3 (23° C., ISO 1183); c. a glass transition temperature of less than −30° C. (DIN EN ISO 11357-2:2014); and d. a flow point, measured according to ASTM D97, of less than 50° C., which due to their permanently tacky properties are suitable as pressure-activated pressure-sensitive adhesives.
1. A resin- and mineral oil-free pressure-sensitive adhesive composition, comprising 55%-99% by weight of a copolymer of propylene and one or more further monomers selected from ethylene and 1-olefins having 4 to 20 carbon atoms,
wherein the copolymer has been prepared with the aid of metallocene catalysts and has
a melt viscosity at 170° C. of 20 to 8000 mPas (DIN 53019),
a density of 0.84 to 0.90 g/cm 3 (23° C., ISO 1183),
a glass transition temperature of less than −30° C. (DIN EN ISO 11357-2:2014),
a flow point, measured according to ASTM D97, of less than 50° C., and
wherein a further polymer may optionally be present in the pressure-sensitive adhesive composition.
2. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer has an enthalpy of fusion, measured according to ISO 11357-2, of 0-50 J/g.
3. The pressure-sensitive adhesive composition as claimed in claim 2 , wherein the enthalpy of fusion, measured according to ISO 11357-2, is 0-30 J/g.
4. The pressure-sensitive adhesive composition as claimed in claim 3 , wherein the enthalpy of fusion, measured according to ISO 11357-2, is 0-20 J/g.
5. The pressure-sensitive adhesive composition as claimed in claim 1 , comprising 55%-99% by weight of the copolymer and 1%-45% by weight of at least one further polymer selected from polyolefins, waxes, natural or synthetic rubbers, polyacrylates, polyesters, polychloroprenes, polyvinyl ethers and polyurethanes.
6. The pressure-sensitive adhesive composition as claimed in claim 5 , wherein the at least one further polymer is at least one polyolefin.
7. The pressure-sensitive adhesive composition as claimed in claim 6 , wherein the at least one polyolefin has
a glass transition temperature of less than −15° C. (DIN EN ISO 11357-2:2014),
a melt viscosity at 170° C. of less than 50 000 mPas (DIN 53019) and
a flow point of greater than 50° C. (ASTM D97).
8. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the pressure-sensitive adhesive composition has a Dahlquist criterion of G′≤105 Pa at 25° C. and 1 Hz.
9. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer is derived from 70%-95% by weight of propylene and from 5%-30% by weight of ethylene.
10. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer has a melt viscosity at 170° C. (DIN 53019) of 30 to 5000 mPas.
11. The pressure-sensitive adhesive composition as claimed in claim 10 , wherein the melt viscosity at 170° C. (DIN 53019) is 50 to 3000 mPas.
12. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer has a glass transition temperature, measured according to DIN EN ISO 11357-2:2014, of less than −35° C.
13. The pressure-sensitive adhesive composition as claimed in claim 12 , wherein the glass transition temperature, measured according to DIN EN ISO 11357-2:2014, is less than −40° C.
14. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer has a flow point, measured according to ASTM D97, of less than 40° C.
15. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the pressure-sensitive adhesive composition further comprises at least one of organic or inorganic pigments, fillers, flame retardants, stabilizers, antistats, antioxidants and light stabilizers.
16. The pressure-sensitive adhesive composition as claimed in claim 1 , wherein the copolymer has undergone polar modification.
17. A method of joining substrates comprising wetting and adhesively bonding the substrates with the pressure-sensitive adhesive composition as claimed in claim 1 .
18. The method as claimed in claim 17 wherein the substrates comprise a substrate with a surface energy of less than 35 mN/m and one or more substrates with any surface energy.
19. The method as claimed in claim 18 wherein the substrate with a surface energy of less than 35 mN/m is a substrate made from Teflon or a substrate having a siliconized surface.