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 m.

Process for making the film by coextrusion.

Using the said film for resealable cartons.

Claims

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 m 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 m.

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.

Description

EXAMPLE A (REFERENCE)

[0115] 1. Preparation of a hot-melt pressure-sensitive adhesive composition a:

[0116] The adhesive composition shown in the following Table is prepared in the form of granules with a size of approximately 4 mm by mixing its ingredients at 160 C. using a twin-screw extruder, extruding through a die, then cutting up the extruded product and cooling to ambient temperature.

[0117] The MFI measured is 57 g/10 minutes.

[0118] 2. Preparation of a three-layer B/A/C film comprising a layer A of the composition of Example A:

[0119] This three-layer film is manufactured using a bubble blowing coextrusion pilot-scale device operated continuously, in which three extruders are fed: [0120] for one, with the composition a of Example A, and [0121] for the other two, with LDPE;
the three compositions being in the form of granules with a size of approximately 4 mm.

[0122] The parameters of the process are adjusted so as to manufacture a three-layer film composed: [0123] as layer A, of a layer with a thickness of 15 m consisting of the composition of Example A, [0124] as laminatable thin layer B, of a layer with a thickness of 30 m consisting of LDPE; [0125] as sealable and cleavable thin layer C, of a layer with a thickness of 15 m also consisting of LDPE.

[0126] Mention may be made, among the parameters normally fixed, of a degree of radial expansion of the bubble equal to 3, a drawing rate of 7 m/minute and an overall throughput of 11 kg/hour.

[0127] The three-layer film thus obtained has a total thickness of 60 m and a length of 50 m and is packaged in the form of a reel with a machine width of 250 mm.

[0128] Measurement of the Force of First Opening by T-Peeling at 23 C.:

[0129] A sample in the form of a rectangular sheet with A4 format (2129.7 cm) is cut out from the three-layer film thus obtained.

[0130] The external face of the laminatable layer B of this sample is: [0131] in a first step, subjected to a corona surface treatment (using a plasma), then [0132] in a second step, laminated to a PET film with a thickness of 23 m using a polyurethane-based solvent-based adhesive and using a coating device of the Mayer bar type.

[0133] The rectangular sheet is then placed under a press for 24 h.

[0134] The said rectangular sheet is then folded along a line located in its middle and parallel to the small side of the rectangle, resulting in the sealable and cleavable layer C being brought into contact with itself.

[0135] Partial sealing is then carried out using two heating clamping jaws at 130 C. applied under a pressure of 6 bar for 1 second, so as to obtain sealed regions of rectangular shape (8 cm in length and 1 cm in width) positioned perpendicularly to the folding line. Each sealed region is cut out in order to obtain a tensile test specimen in which the sealed region with a length of 8 cm is extended (at that of its ends which is opposite the folding line) by two strips of approximately 2 cm in length left free and unsealed.

[0136] These two free strips are attached to two holding devices (known as jaws) respectively connected to a stationary part and a movable part of a tensile testing device which are located on a vertical axis. This tensile testing device is a dynamometer.

[0137] While a drive mechanism imparts a uniform rate of 300 mm/minute to the movable part, resulting in the peeling of the two sealed layers, the ends gradually move along a vertical axis with the formation of an angle of 180. A force sensor connected to the said movable part measures the force withstood by the test specimen thus held. The measurement is carried out in a climate-controlled chamber maintained at a temperature of 23 C.

[0138] The force obtained is shown in the Table.

[0139] Measurement of the Force of Second Opening by T-Peeling at 23 C.:

[0140] The two parts of the preceding test specimen are, after peeling, repositioned facing one another and brought into contact manually. They are then subjected to a pressure exerted by means of a roller with a weight of 2 kg, with which a to-and-fro movement is carried out along a direction parallel to the length of the test specimen.

[0141] A tensile test specimen is thus obtained which is identical in shape to that prepared for the preceding peel test, which is then repeated.

[0142] The force obtained is shown in the Table.

[0143] Test for evaluating the detrimental change in the taste of butter brought into contact with the adhesive composition:

[0144] This test is carried out on a 125 g block of butter having dimensions of 1106517 mm.

[0145] This block is centred horizontally on a rectangle having dimensions of 11065 mm cut out from the sheet of three-layer film with the A4 format mentioned above, the block being in contact with the sealable and cleavable layer C of the said film.

[0146] The upper face of the block of butter is subsequently covered with a second rectangle of three-layer film identical to the first, and is also in contact with the sealable and cleavable layer C.

[0147] The structure thus obtained is overwrapped in tinfoil and then placed for 10 days in a refrigerator maintained at 10 C.

[0148] As control, a block of butter identical to the preceding one, which is simply wrapped in tinfoil, is also stored in the same refrigerator for the same time.

[0149] After 10 days, the two blocks of butter are recovered, are each cut up into 20 pieces weighing approximately 6 g and are passed on to a panel of ten people for evaluation of the taste. Each member of the panel assigns, after tasting, a grade of 0 to 4 to the pieces resulting from the block brought into contact with the three-layer film comprising the adhesive layer A, in comparison with the pieces resulting from the control block, according to the following scale: [0150] 0=no perceptible difference [0151] 1=barely perceptible difference [0152] 2=slight difference [0153] 3=marked difference [0154] 4=strong difference.

[0155] The mean grade obtained is shown in the Table.

EXAMPLES 1 AND 2 (ACCORDING TO THE INVENTION)

[0156] Example A is repeated with the compositions a shown in the Table.

[0157] The MFI obtained for each composition a and the forces measured for the 1st and 2nd opening are shown in the Table, along with the results of the tests for evaluating the detrimental change in the taste of the butter.

[0158] It is observed that the force of 1st opening remains substantially stable with respect to that measured for the reference Example A. On the other hand, the force of 2nd opening is lowered but is assessed as corresponding to a quality of resealing (following the first opening of the packaging) which is still acceptable.

[0159] Furthermore, the detrimental change in the taste of the butter resulting from the composition a is very significantly reduced in comparison with Example A.

TABLE-US-00001 TABLE Content as % weight/weight Example A Ingredient (ref.) Example 1 Example 2 Composition a Kraton D1113BT 59.7 39.8 39.8 Quintac 3520 19.9 19.9 Escorez 1310LC 24.9 Regalite R1125 39.8 Escorez 5340 39.8 Dercolyte S115 14.9 Irganox 1010 0.5 0.5 0.5 Composition a1 Content of styrene units 16 16 16 (as % weight/weight) Content of diblocks (as % 56 63 63 weight/weight) Composition a MFI (in g/10 min) 57 56 56 Three-layer film Force of 1st opening 3 2.8 3.1 (in N/cm) Force of 2nd opening 0.84 0.5 0.6 (in N/cm) Detrimental change in the 0.4 0.2 0.1 taste of the butter

[0160] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0161] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.