Extrudable hot-melt pressure-sensitive adhesives for resealable packaging having improved organoleptic properties

Abstract

Hot-melt pressure-sensitive adhesive composition with MFI of 0.01 to 200 g/10 minutes containing: 45 to 70% by weight of styrene block copolymers of SIS type with an SI diblock content of 30 to 90% and a content of styrene units of 10 to 40%; and 30 to 55% by weight of a tackifying resin having a softening temperature of 5 to 150° C., and obtained by a process containing: polymerizing a composition (i) essentially composed of unsaturated hydrocarbons having 9 carbon atoms, or a composition (ii) essentially composed of dicyclopentadiene and of its derivatives having 10 carbon atoms; then hydrogenating the polymer. Multilayer film containing an adhesive layer composed of the composition with a thickness of 7 to 50 μm. Process for making the film by coextrusion. Using the said film for resealable cartons.

1 . A hot-melt pressure-sensitive adhesive composition a having a melt flow index ranging from 0.01 to 200 g/10 minutes and comprising, on the basis of the total weight of the said composition a:
 from 45 to 70% by weight of a composition a1 of styrene block copolymers comprising at least one elastomer block, the said composition a1 comprising, on the basis of its total weight:
 of 30 to 90% by weight of at least one diblock copolymer of Styrene-Isoprene (SI) type, and 
 of 10 to 70% by weight of at least one Styrene-Isoprene-Styrene (SIS) linear triblock copolymer; 
   the total content of styrene units of the said composition a1 varying from 10 to 40% by weight on the basis of the total weight of a1; and   from 30 to 55% by weight of at least one tackifying resin a2 having a softening temperature of between 5 and 150° C. and obtained by a process comprising:
 a first stage of polymerization of
 a composition comprising dicyclopentadiene and its derivatives having 10 carbon atoms; then 
 
 a second stage of hydrogenation of the polymer thus obtained. 
   
     
     
         2 . The hot-melt pressure-sensitive adhesive composition according to  claim 1 , wherein the content of SI diblocks in the composition a1 varies from 50 to 80%. 
     
     
         3 . The hot-melt pressure-sensitive adhesive composition according to  claim 1 , wherein the softening temperature of the tackifying resin a2 is between 80 and 150° C. 
     
     
         4 . The hot-melt pressure-sensitive adhesive composition according to  claim 1 , which consists of the composition a1 and a tackifying resin a2 and optionally one or more components in an amount not exceeding 5%. 
     
     
         5 . The hot-melt pressure-sensitive adhesive composition according to  claim 1 , whose melt flow index ranges from 2 to 70 g/10 minutes. 
     
     
         6 . The hot-melt pressure-sensitive adhesive composition according to  claim 1 , which is in the form of granules with a size of between 1 and 10 mm. 
     
     
         7 . A multilayer film comprising two thin layers B and C of thermoplastic material bonded together by an adhesive layer A, wherein the said layer A has a thickness of between 7 and 50 μm and consists of the hot-melt pressure-sensitive adhesive composition a as defined in  claim 1 . 
     
     
         8 . The multilayer film according to  claim 7 , wherein the thickness of the adhesive layer A is between 7 and 35 μm. 
     
     
         9 . The multilayer film according to  claim 7 , comprising, in addition to the layers A, B and C, two tie layers D and E such that the adhesive layer A is:
 connected to the layer B via the layer D, and   connected to the layer C via the layer E.   
     
     
         10 . The multilayer film according to  claim 9 , wherein the tie layers D and E consist of compositions d and e, which are identical or different, which have a melting point from approximately 80 to 120° C. and comprise polymers chosen from:
 ethylene homopolymers or copolymers, 
 propylene homopolymers or copolymers, 
 copolymers of ethylene with a polar comonomer, and 
 grafted olefin homopolymers or copolymers. 
 
     
     
         11 . A three-layer film according to  claim 7 , which consists of the adhesive layer A and the two layers B and C, according to the sequence B/A/C in which the “/” sign means that the faces of the layers concerned are in direct contact. 
     
     
         12 . A film comprising five layers according to  claim 9 , which consists of the adhesive layer A, the two intermediate layers D and E and the two external layers B and C, according to the sequence B/D/A/E/C in which the “/” sign means that the faces of the layers concerned are in direct contact. 
     
     
         13 . A process for the manufacture of the multilayer film as defined in  claim 7 , which comprises a stage of coextrusion of the hot-melt pressure-sensitive adhesive composition a and of the constituent materials of the layers B and C and, if appropriate, of the layers D and E. 
     
     
         14 . The manufacturing process according to  claim 13 , wherein the constituent compositions and materials of the layers A, B, C and, optionally D and E are fed into the coextrusion device in the form of granules with a size of between 1 and 10 mm. 
     
     
         15 . The process for the manufacture of the multilayer film according to  claim 13 , wherein the coextrusion device is a bubble blowing coextrusion device. 
     
     
         16 . A resealable packaging, comprising the multilayer film as defined in  claim 7 . 
     
     
         17 . The hot-melt pressure-sensitive adhesive composition according to  claim 4 , which consists of the composition a1 and a tackifying resin a2 and one or more components in an amount not exceeding 5%, which are selected from the group consisting of stabilizers, antioxidants, plasticizers, inorganic fillers, organic fillers, pigments and dyes.