Pressure-sensitive adhesives having a temperature-stable adhesive power
The invention relates to an adhesive composition that can be cross-linked by heating, said composition comprising between 20 and 85% of a polyurethane comprising 2 terminal groups of the hydrolysable alkoxysilane type of formula (I): wherein: R 1 is a hydrocarbonated radical comprising between 5 and 15 carbon atoms; R 2 is an alkylene radical comprising between 1 and 4 carbon atoms; R 3 is an alkylene radical comprising between 1 and 3 carbon atoms; R 4 and R 5 are each an alkyl radical comprising between 1 and 4 carbon atoms; n is a whole number such that the average molar mass of the polyether block of formula —[OR 2 ]n- is between 300 Da and 30 kDa; in is a whole number such that the average molar mass of the polymer of formula (I) is between 600 Da and 60 kDa; and p is a whole number equal to 0, 1 or 2. The composition also comprises between 15 and 80% of a compatible tackifying resin; and between 0.01 and 3% of a cross-linking catalyst. The invention also relates to a self-adhesive carrier coated with the cross-linked adhesive composition.
1. A heat-curable adhesive composition comprising:
from 20 to 85% of a polyurethane comprising 2 hydrolyzable alkoxysilane end groups and of formula (I):
in which:
R 1 represents a hydrocarbon-based divalent radical comprising from 5 to 15 carbon atoms which may be aromatic or aliphatic, linear, branched or cyclic;
R 2 represents a linear or branched alkylene divalent radical comprising from 1 to 4 carbon atoms;
R 3 represents a linear alkylene divalent radical comprising from 1 to 3 carbon atoms;
R 4 and R 5 , which are identical or different, each represent a linear or branched alkyl radical having 1 to 4 carbon atoms, with the possibility, when there are several R 4 or R 5 radicals, that these are identical or different;
n is an integer such that the number-average molecular weight of the polyether block of formula —[OR 2 ] n — is between 300 Da and 30 kDa;
m is an integer such that the number-average molecular weight of the polymer of formula (I) is between 600 Da and 60 kDa;
p is an integer equal to 0, 1 or 2;
from 15 to 80% of a compatible tackifying resin, having a number-average molecular weight between 200 Da and 5 kDa, that is a resin obtained:
(i) by polymerization of terpene hydrocarbons and of phenols, in the presence of Friedel-Crafts catalysts; or
(ii) by polymerization of α-methylstyrene, and optionally by reaction with phenols; and
from 0.01 to 3% of a curing catalyst.
2. The adhesive composition as claimed in claim 1 , wherein the polyurethane of formula (I) has a number-average molecular weight between 4 and 50 kDa and the polyether block of formula —[OR 2 ] n — is has a number-average molecular weight between 2 and 25 kDa.
3. The adhesive composition as claimed claim 1 , wherein in the polyurethane of formula (I):
R 1 is a divalent radical of the formula:
a) a divalent radical derived from isophorone:
e) a hexamethylene radical —(CH 2 ) 6 —;
R 2 is an ethylene and/or isopropylene divalent radical;
R 3 is a methylene and/or n-propylene divalent radical; and
R 4 and R 5 each represent methyl or ethyl.
4. The adhesive composition as claimed in claim 1 , wherein the polyurethane of formula (I):
R 1 is a divalent isophorone radical of formula:
R 2 is an isopropylene divalent radical;
R 3 is an n-propylene divalent radical; and
the —Si(R 4 ) p (OR 5 ) 3-p group is a trimethoxysilyl radical.
5. The adhesive composition as claimed in claim 1 , in which R 2 is an isopropylene radical and, the polyurethane of formula (I) has a polydispersity index between 1.3 and 1.6.
6. The adhesive composition as claimed in claim 1 , wherein the tackifying resins used are obtained by the process (i).
7. The adhesive composition as claimed in claim 1 , comprising from 40 to 65% of polyurethane of formula (I) and from 35 to 60% of tackifying resin.
8. The adhesive composition as claimed in claim 1 , comprising up to 3% of a hydrolysable alkoxysilane derivative, as a desiccant.
9. The adhesive composition according to claim 1 , wherein in formula (I), m is 1-10.
10. The adhesive composition according to claim 1 , wherein in formula (I), m is 1-4.
11. The adhesive composition according to claim 8 , wherein the desicant is a derivative of trimethoxysilane.
12. A self-adhesive label or tape comprising an adhesive according to claim 1 .
13. A self-adhesive support obtained by a process comprising:
(a) preheating the adhesive composition as defined in claim 1 at a temperature between 50 and 130° C.; then
(b) coating it onto a support layer; then
(c) curing it, by heating the thus coated support at a temperature between 50 and 150° C.
14. In a process of converting a self-adhesive support into self-adhesive labels and/or tapes, the improvement wherein said self-adhesive support is a support according to claim 13 .