Lamination adhesive for sterilisation

1 . A solvent-based two-component polyurethane adhesive composition, comprising an —OH component and an —NCO component, such that:

the —OH component is a composition (A) comprising an amorphous prepolymer which includes two —OH end groups, the number-average molar mass M n of which ranges from 8000 to 12,000 g/mol and which is chosen from:

a copolyester (A1) obtained by a polycondensation reaction:

of at least one aliphatic diol (i); with

at least one aromatic diacid (ii) chosen from terephthalic acid, isophthalic acid, phthalic acid and one of their diester or anhydride derivatives; and

at least one aliphatic diacid (iii) or one of its diester or anhydride derivatives; and

a polyurethane (A2) obtained by a polyaddition reaction between an aliphatic diisocyanate compound (A2.P1) and an amorphous copolyester diol (A2.P2), the number-average molecular weight M n of which ranges from 4000 to 11 500 g/mol, said copolyester being obtained by the polycondensation reaction as defined above for (A1); and

the component —NCO is a composition (B) comprising a compound (B1) which includes three —NCO end groups, and which is obtained by the reaction of meta-xylylene diisocyanate (m-XDI) with a triol, said compound (B1) being:

either the only compound comprised in (B) including three-NCO end groups;

or else a mixture with another compound (B2) including three-NCO end groups, (B2) being an isocyanurate (B2-1) of an aliphatic diisocyanate and the content of (B1) in said mixture being at least 40% by weight, based on the total weight of said mixture.

2 . The adhesive composition as claimed in claim 1 , wherein the amorphous prepolymer included in the composition (A) is the amorphous copolyester diol (A1) and the diol (i) is selected from the group consisting of ethylene glycol, diethylene glycol, trimethylene glycol, hexamethylene glycol, propylene glycol, propane-1,3-diol, (1,4-, 1,3- or 1,2-) butanediol, neopentyl glycol, 2-methyl-1,3-propanediol, hexanediol and cyclohexanedimethanol.

3 . The adhesive composition as claimed in claim 2 , wherein the aliphatic diacid (iii) is selected from the group consisting of adipic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, dodecanedicarboxylic acid, 1,10-decanedicarboxylic acid and succinic acid.

4 . The adhesive composition as claimed in claim 2 , wherein the copolyester diol (A1) is obtained by polycondensation:

of two aliphatic diols (i) consisting respectively of ethylene glycol and diethylene glycol; with

two diacids (ii) consisting respectively of terephthalic acid and isophthalic acid; and

adipic acid as aliphatic diacid (iii).

5 . The adhesive composition as claimed in claim 1 , wherein the compound (B1) is the only compound comprised in the composition (B) including three-NCO end groups.

6 . The adhesive composition as claimed in claim 1 , wherein the compound (B1) is the adduct of m-XDI and of trimethylolpropane (TMP).

7 . The adhesive composition as claimed in claim 1 , wherein the compound (B1) is as a mixture with the compound (B2).

8 . The adhesive composition as claimed in claim 7 , wherein the compound (B2) is an isophorone diisocyanate (IPDI) derivative.

9 . The adhesive composition as claimed in claim 7 , wherein the composition (B) comprises a mixture of:

the adduct (B1) of m-XDI and of trimethylolpropane (TMP); and of

IPDI isocyanurate as compound (B2).

10 . The adhesive composition as claimed in claim 7 , wherein the content of (B1) in the mixture of (B1) and (B2) is within a range extending from 40% to 80% weight/weight.

11 . The adhesive composition as claimed in claim 1 , wherein the composition further comprises an adhesion promoter included in the —NCO component or in the —OH component.

12 . The adhesive composition as claimed in claim 11 , wherein the adhesion promoter is an aminosilane.

13 . The adhesive composition as claimed in claim 1 , wherein the amounts of the —NCO and —OH components are such that the —NCO/—OH molar equivalent ratio is within a range extending from 3 to 5.

14 . A multilayer film comprising two thin layers of material bonded together by a continuous layer, wherein said layer is constituted by the two-component adhesive composition as defined in claim 1 in the crosslinked state, in a proportion of an amount of less than 7 g/m 2 .

15 . A process for the continuous preparation of the multilayer film as defined in claim 14 , comprising the sequential stages of:

(i) combining the —NCO and —OH components and, if appropriate, diluting with a solvent, in order to form an adhesive mixture;

(ii) coating, with said adhesive mixture, a first thin layer of material in the form of a substantially continuous layer;

(iii) evaporating the organic solvent;

(iv) laminating a second thin layer over the first thin layer coated in accordance with stage (ii), then

(v) crosslinking the adhesive mixture.