DIRECTLY ATTACHING, HALOGEN-FREE, FAST-DRYING, HEAT-SEALING BINDER FOR SEALING POLYESTER FILMS TO POLYSTYRENE, POLYESTER OR PVC

Abstract

The present invention comprises a single-component binder for heat-sealing applications which can be used for the sealing of polyester foils, in particular of polyethylene terephthalate foils (PET foils) with respect to containers made of polystyrene, of PVC, and of polyester. These polyesters can in particular be polyethylene terephthalate (PET) or polylactic acid (PLA). The binders here feature not only good seal seam strengths but also in particular good transparency and excellent application properties. A substantive aspect of the invention is that the sealing can be achieved without addition of adhesion promoters, in particular without addition of adhesion promoters based on polyvinyl chloride (PVC) or on polyester, and that barrier properties and sealing properties achieved in respect of containers made of PS and of PET are nevertheless at least comparable with, and sometimes better than, those achieved with heat-sealing systems already marketed.

Claims

1: A heat-sealable coating system suitable for the sealing of a substrate, the coating system comprising a film-forming dispersion, wherein the dispersion comprises from 10% to 60% by weight of a polyester or a polyester mixture as a polymer type A, from 10% to 60% by weight of a poly(meth)acrylate as a polymer type B, from 1% to 20% by weight of a graft copolymer comprising the polymer type A and the polymer type B as a polymer type AB, from 1% to 30% by weight of a polyolefin as a polymer type C, and from 1 to 35% by weight of a graft copolymer as a polymer type CD, comprising the polymer type C and a poly(meth)acrylate as a polymer type D, based on the total mass of the polymer types A, B, C, AB, and CD, wherein the total amount of the polymer type C, inclusive of the amount of the polymer type C comprising the polymer type CD, based on the total mass of the polymer types A, B, C, AB, and CD, is from 5 to 40% by weight, wherein from 10% to 40% of the carbon atoms of the main chain of the polymer type C are tertiary carbon atoms, and wherein the solids content of the dispersion is from 25 to 70% by weight.

2: The coating system according to claim 1, wherein the polymer type A is a mixture comprising a polyester A1 with a number-average molar mass M.sub.n from 700 to 5000 g/mol, obtained by a copolycondensation of itaconic acid, and a polyester A2 with a number-average molar mass M.sub.n from 5000 to 50000 g/mol which has no double bonds, and wherein the polymer type AB comprises only the polyester A1 as the polymer type A.

3: The coating system according to claim 2, wherein the number-average molar mass M.sub.n of the polyester A1 is from 2000 to 4000 g/mol and the number-average molar mass M.sub.n of the polyester A2 is from 10000 to 35000 g/mol, and wherein the coating system comprises, based on the total mass of the polymer types A, B, C, AB, and CD, inclusive of the proportions amount of the polyester A1 comprising the polymer type AB, from 1% by weight to 15% by weight of the polyester A1 and from 10% by weight to 50% by weight of the polyester A2.

4: The coating system according to claim 1, wherein the polymer type A is fully or partially a polyester obtained by a copolycondensation of itaconic acid.

5: The coating system according to claim 2, wherein the polymer type A, the polyester A1, or both are a polyester obtained by a copolycondensation reaction of itaconic acid and at least one additional polycarboxylic acid wherein a proportion of itaconic acid in reacted form, based on the total quantity of polycarboxylic acids reacted, is from 0.1 mol % to 20 mol %.

6: The coating system according to claim 2, wherein the polymer type A, the polyester A1, or both are a polyester obtained by a copolycondensation reaction of itaconic acid and at least one additional polycarboxylic acid wherein a proportion of itaconic acid in reacted form, based on the total quantity of polycarboxylic acids reacted, is from 2 mol % to 8 mol %.

7: The coating system according to claim 1, wherein the polymer type AB is a graft copolymer comprising a polyester main chain and poly(meth)acrylate side chains.

8: The coating system according to claim 1, wherein the polymer type C is at least one selected from the group consisting of an ethylene-propylene copolymer, a hydrogenated polybutadiene, and a copolymer of ethylene and an α-olefin having from 4 to 12 carbon atoms.

9: The coating system according to claim 8, wherein the polymer type C comprises from 20 to 70% by weight of repeating ethylene units and has a weight-average molecular weight M.sub.w of from 10000 to 250000.

10: The coating system according to claim 1, wherein the graft copolymers AB and CD are obtained by a grafting of the polymer type B onto the polymer type A and a grafting of the polymer type D onto the polymer type C wherein both of the graftings are carried out simultaneously, and wherein the polymer type B and polymer type D have the same statistical composition.

11: A process for sealing a polyester foil or a polyethylene terephthalate coated foil with a material comprising at least one selected from the group consisting of polystyrene, polyester, and polyvinyl chloride, the process comprising: coating the polyester or polyethylene terephthalate coated foil with the coating system according to claim 1 to form a side of the foil comprising a coating, drying the coating, and placing the side of the foil comprising a coating onto the material to be sealed comprising at least one selected from the group consisting of polystyrene, polyester, and polyvinyl chloride, and sealing at a temperature of from 160 to 220° C. and with a pressure of from 2 to 6 mPas over a period of time from 0.1 to 1 s to form a sealed object.

12: A sealed object obtained by the process according to claim 11.

13: The process according to claim 11, wherein the sealed object exhibits a uniform peel or a smooth peel behavior during opening.

14: The process according to claim 11, wherein the sealed object has an opacity measured as a haze percentage as determined in accordance with ASTM D1003 of 10-30%.

15: The process according to claim 11, wherein the sealed object has a reduced opacity measured as a haze percentage as determined in accordance with ASTM D1003 relative to a substantially similar sealed object obtained by a substantially similar process employing a coating system that does not comprise the polymer type C wherein from 10% to 40% of the carbon atoms of the main chain of the polymer type C are tertiary carbon atoms.

16: The process according to claim 11, wherein the sealed object has an increased heat-seal-seam strength relative to a substantially similar scaled object obtained by a substantially similar process employing a coating system that does not comprise the polymer type C wherein from 10% to 40% of the carbon atoms of the main chain of the polymer type C are tertiary carbon atoms.

17: The process according to claim 11, wherein the foil is a polyester foil, the material comprises polystyrene and the sealed object has a heat-seal-seam strength of greater than 8.1 N/15 mm.

18: The process according to claim 11, wherein the foil is a polyethylene terephthalate coated foil, the material comprises polystyrene and the sealed object has a heat-seal-seam strength of greater than 5.0 N/15 mm.

19: The process according to claim 11, wherein the foil is a single-side-aluminum-coated polyethylene terephthalate foil, the material comprises polystyrene and the sealed object has a heat-seal-seam strength of greater than 7.7 N/15 mm.

20: The process according to claim 11, wherein the material comprises polyester in the form of amorphous polyethylene terephthalate and the sealed object has a heat-seal-seam strength of greater than 5.0 N/15 mm.

Description

INVENTIVE EXAMPLE 1

[0089] 65.0 g of Dutral CO 043, 26.0 g of polyester of the type A1, and 104.0 g of polyester of the type A2, and also 120.0 g of a suitable emulsifier, were used as initial charge in 335 g of propyl acetate and 60.0 g of cyclohexane (CH) in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer, and stirred at 95° C. until the material had dissolved. A mixture of 64.9 g of methyl methacrylate and 64.9 g of butyl methacrylate, with 2.60 g of admixed tert-butylperoxy 2-ethylhexanoate, is metered into the system by means of a metering pump over a period of 1.5 h at 95° C. Once addition has ended, a further 0.26 g of tert-butylperoxy 2-ethylhexanoate is added twice, with one hour between each addition, and the mixture is stirred for a further 2 h.

INVENTIVE EXAMPLE 2

[0090] 86.0 g of Engage 7447, 32.3 g of polyester of the type A1, and 97.8 g of polyester of the type A2, and also 80.0 g of a suitable emulsifier, were used as initial charge in 336 g of propyl acetate and 18.7 g of cyclohexane (CH) in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer, and stirred at 95° C. until the material had dissolved. A mixture of 64.5 g of methyl methacrylate and 64.5 g of butyl methacrylate, with 2.58 g of admixed tert-butylperoxy 2-ethylhexanoate, is then metered into the system by means of a metering pump over a period of 1.5 h at 95° C. Once addition has ended, the reaction mixture is stirred for a further 5 h at 95° C., and finally diluted with 8.7 g of CH and 18.7 g of methyl ethyl ketone (MEK) for viscosity adjustment.

INVENTIVE EXAMPLE 3

[0091] The procedure for the production of inventive example 3 is exactly the same as in inventive example 2. 86.0 g of Engage 8407 are used instead of Engage 7447.

INVENTIVE EXAMPLE 4

[0092] 68.8 g of Dutral CO 043, 34.4 g of polyester of the type A1, and 103.2 g of polyester of the type A2, and also 80.0 g of a suitable emulsifier, were used as initial charge in 335 g of propyl acetate and 37.3 g of cyclohexane (CH) in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer, and stirred at 95° C. until the material had dissolved. A mixture of 64.9 g of methyl methacrylate and 64.9 g of butyl methacrylate, with 2.60 g of admixed tert-butylperoxy 2-ethylhexanoate, and 0.28 g of the chain-transfer agent DYNASILAN MTMO (Evonik Industries AG) is then metered into the system by means of a metering pump over a period of 1.5 h at 95° C. Once addition has ended, a further 0.26 g of tert-butylperoxy 2-ethylhexanoate is added twice, with one hour between each addition, and the mixture is stirred for a further 2 h.

INVENTIVE EXAMPLE 5

[0093] 86.0 g of Dutral CO 043, 32.3 g of polyester of the type A1, and 96.8 g of polyester of the type A2, and also 80.0 g of a suitable emulsifier, were used as initial charge in 313 g of propyl acetate and 60.0 g of cyclohexane (CH) in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer, and stirred at 95° C. until the material had dissolved. A mixture of 64.5 g of methyl methacrylate and 64.5 g of butyl methacrylate, with 2.60 g of admixed tert-butylperoxy 2-ethylhexanoate, is then metered into the system by means of a metering pump over a period of 1.5 h at 95° C. Once addition has ended, a further 0.26 g of tert-butylperoxy 2-ethylhexanoate is added twice, with one hour between each addition, and the mixture is stirred for a further 2 h.

COMPARATIVE EXAMPLE 1 (CE1)

[0094] 42.9 g of an EPDM and 20.0 g of an itaconic acid-containing polyester of the type 1 are dispersed in a mixture of 50.0 g of propyl acetate, 20.0 g of ethyl acetate and 10.0 g of isooctane at 90° C. in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer. The following are added to this mixture: firstly 2.0 g of tert-butylperbenzoate, and then a mixture of 18.5 g of n-butyl methacrylate and 18.5 g of methyl methacrylate, over a period of 90 min. Polymerization is then carried out at 90° C. over a period of 120 min. Finally, a further 0.5 g tert-butylperoxy 2-ethylhexanoate is added for post-initiation, and the mixture is stirred at 90° C. for a further 90 min.

COMPARATIVE EXAMPLE 2 (CE2)

[0095] 35.2 g of propyl acetate and 30 g of polyester of the type A1 are used as initial charge in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer. The polyester is completely dissolved at 95° C. with stirring, and 0.06 g of tert-butyl 2-ethylperhexanoate is then admixed. In order to obtain an ideal yield of free radicals along the polyester chains, this solution is stirred at 90° C. for a period of 30 min before a mixture of 9.50 g of methyl methacrylate, 9.50 g of butyl methacrylate, 1.00 g of butyl acrylate, and 0.15 g of tert-butyl 2-ethylperhexanoate is metered into the system by using a metering pump within 2 h. In order to reduce residual monomer content, the mixture is then stirred with 0.15 g of tert-butyl 2-ethylperhexanoate at 90° C. for a further 4 h. The mixture is diluted with 31.3 g of propyl acetate for solution viscosity adjustment. After 150 min of total reaction time, the polymer solution is cooled, and diluted with 13.5 g of propyl acetate to reduce solution viscosity.

COMPARATIVE EXAMPLE 3 (CE3)

[0096] 66.9 g of propyl acetate and 30 g of polyester of the type A1 are used as initial charge in a jacketed vessel with attached thermostat, reflux condenser, blade stirrer, and internal thermometer. The polyester is completely dissolved at 95° C. with stirring, and 0.06 g of tert-butyl 2-ethylperhexanoate is then admixed. In order to obtain an ideal yield of free radicals along the polyester chains, this solution is stirred at 90° C. for a period of 30 min before a mixture of 17.50 g of methyl methacrylate, 17.50 g of butyl methacrylate, 1.00 g of butyl acrylate, and 0.15 g of tert-butyl 2-ethylperhexanoate is metered into the system by using a metering pump within 2 h. In order to reduce residual monomer content, the mixture is then stirred with 0.15 g of tert-butyl 2-ethylperhexanoate at 90° C. for a further 4 h.

Experimental Results

[0097]

TABLE-US-00003 TABLE 3 Properties of the binder Dyn. visc. SC Example [mPas] (%) Appearance 1 2 900 47.5 white, disperse 2 2 000 47.3 white, disperse 3 2 000 47.1 white, disperse 4 3 300 47.0 white, disperse 5 3 100 47.8 white, disperse CE1 2 800 47.2 white, disperse CE2 3 900 54.1 white, disperse CE3 2 000 44.9 white, disperse

[0098] All of the inventive examples and comparative examples exhibit solids-viscosity ratios that firstly ensure processability for users and secondly meet the requirement to achieve the highest possible solids contents.

Heat-Sealing Properties

[0099]

TABLE-US-00004 TABLE 4 Heat-seal-seam strength values of the inventive examples, sealed with respect to PS pot material Example 5 48 h Foil 1 2 3 4 5 storage in water Mixpap HSS [N/15 mm] 5.9 8.6 7.7 4.4 6.6 6.6 Appearance of seal r.u. nonuniform nonuniform u. u. u. AluPET HSS [N/15 mm] — 8.2 8.2 4.6 7.2 7.5 Appearance of seal r.u. r.u. r.u. u. r.u. PET36 HSS [N/15 mm] — 4.1 5.4 3.0 5.3 5.5 Appearance of seal nonuniform nonuniform r.u. u. r.u. Aluminum HSS [N/15 mm] 6.0 10.6 10.6 7.5 7.1 7.7 Appearance of seal r.u. nonuniform u. u. u. r.u. HSS: heat-seal strength; r.u.: relatively uniform peel; u.: uniform peel (smooth peel)

TABLE-US-00005 TABLE 5 Heat-seal-seam strength values of the comparative examples, sealed with respect to PS pot material Foil Example CE1 CE2 CE3 Mixpap HSS [N/15 mm] 8.0 <1 1.1 Appearance of seal nonuniform — nonuniform AluPET HSS [N/15 mm] 7.6 n.d. n.d Appearance of seal nonuniform — — PET36 HSS [N/15 mm] 4.8 n.d. n.d. Appearance of seal nonuniform — — Aluminum HSS [N/15 mm] 9.6 n.d. n.d. Appearance of seal nonuniform — — n.d.: not determined, because HSS is inadequate on Mixpap foil

TABLE-US-00006 TABLE 6 Heat-seal seam strength values of inventive example 5, sealed with respect to APET pot material Foil Mixpap AluPET PET36 Aluminum HSS [N/15 mm] 7.0 8.1 5.1 7.8

TABLE-US-00007 TABLE 7 Comparison of opacity of the coated foils Layer thickness Haze Example [μm] [%] PET36-foil 36 3.9 1 4-5 17 2 4-5 25 3 4-5 18 4 n.d. n.d. 5 4-5 23 CE 1  4 60