Polyurethane Adhesives for Bonding Low Surface Energy Films

Abstract

The present invention relates to a polyurethane laminating adhesives, methods for producing a multilayer laminate by laminating at least two films with a polyurethane laminating adhesive, and multilayer laminates obtainable by these methods wherein the polyurethane laminating adhesive comprises an NCO-terminated polyurethane prepolymer obtainable by reacting a polyol mixture comprising: 0.1 to 20.0 wt % relative to the total weight of the polyol mixture of at least one polybutadiene polyol; and 5.0 to 99.9 wt % relative to the total weight of the polyol mixture of at least one polyether polyol, wherein the at least one polyether polyol comprises at least one polyether polyol with a number average molecular weight M.sub.n in the range of >1000 g/mol to 10000 g/mol; with at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the isocyanate groups are present in molar excess relative to the hydroxyl groups of the polyol mixture. Also encompassed are the use of the described adhesives for laminating two or more films, and the multilayer laminates obtainable by the described methods.

Claims

1. A polyurethane laminating adhesive comprising an NCO-terminated polyurethane prepolymer obtained by reacting: (a) a polyol mixture comprising: 0.1 to 20.0 wt. %, relative to the total weight of the polyol mixture of at least one polybutadiene polyol; and 5.0 to 99.9 wt. %, relative to the total weight of the polyol mixture of at least one polyether polyol, wherein the at least one polyether polyol comprises at least one polyether polyol with a number average molecular weight M.sub.n in the range of >1000 g/mol to 10000 g/mol; and (b) at least one polyisocyanate; wherein the at least one polyisocyanate is used in an amount such that the isocyanate groups are present in molar excess relative to the hydroxyl groups of the polyol mixture to obtain said NCO-terminated polyurethane prepolymer.

2. The polyurethane laminating adhesive according to claim 1, wherein the at least one polybutadiene polyol is a hydrogenated polybutadiene polyol.

3. The polyurethane laminating adhesive according to claim 1, wherein the at least one polybutadiene polyol (a) is a polybutadiene diol; and/or (b) comprised in an amount of 0.2 to 15 wt. %, relative to the total weight of the polyol mixture; and/or (c) has a number average molecular weight M.sub.n in the range of 1000 to 10000 g/mol.

4. The polyurethane laminating adhesive according to claim 1, wherein the at least one polyether polyol comprises 5.0 to 90 wt. %, relative to the total weight of the polyol mixture.

5. The polyurethane laminating adhesive according to claim 1, wherein said polyol mixture further comprises 0.1 to 50 wt. %, relative to the total weight of the polyol mixture of castor oil.

6. The polyurethane laminating adhesive according to claim 1, wherein the polyurethane laminating adhesive is a two-component adhesive comprising a binder component and a hardener component, the binder component comprising said NCO-terminated polyurethane prepolymer.

7. The polyurethane laminating adhesive according to claim 6, wherein the hardener comprises a hydroxyl-terminated polyester.

8. The polyurethane laminating adhesive according to claim 6, wherein the hardener comprises a polyester of adipic acid and/or isophthalic acid with one or more diol selected from the group consisting of neopentyl glycol, diethyleneglycol, 1,6-hexane diol and 1,2-propanediol.

9. A method for producing a multilayer laminate by laminating at least two films with a polyurethane laminating adhesive according to claim 1.

10. The method according to claim 9, wherein at least one of the films is a low energy surface film.

11. The method according to claim 9, wherein at least one of the films is a low energy surface film and the low energy surface film (a) is a plastic film; and/or (b) has a surface energy below 38 dyn/cm; and/or (c) is a polyethylene film, a polypropylene film or a metallized film.

12. A method for producing a multilayer laminate comprising the steps of: (a) applying the polyurethane laminating adhesive according to claim 1 to the surface of one or both films to be laminated; (b) contacting the two film surfaces to be laminated; (c) optionally repeating steps (a) and (b) to obtain a multilayer structure comprising more than two films; and (d) curing the adhesive to form the multilayer laminate.

13. A multilayer laminate obtained by the method of claim 12.

14. The multilayer laminate according to claim 13, wherein the laminate is a two-layer laminate film.

15. The multilayer laminate for food packaging applications obtained by the method of claim 12.

16. A package comprising the multilayer laminate for food packaging applications obtained by the method of claim 12 enclosing a food product.

Description

EXAMPLES

Example 1

According to the Invention

[0077] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 51.64 g of castor oil (OH value 163 mg KOH/g), 51.02 g of PPG 1000 (OH value 110 mg KOH/g), 87.69 g of PPG 2000 (OH value 56 mg KOH/g), 14.03 g of Krasol™ HLBH P2000 (hydrogenated polybutadiene polyol, OH value 50 mg KOH/g), and 31.29 g of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 200 g MDI were added, and the final composition stirred at 60 to 70° C. until an NCO content of 11.2 wt %. The resulting product showed a viscosity of 6300 mPas at 40° C. (Brookfield—RVTDV II, 40° C., spindle 27, 20 rpm).

[0078] The isocyanate component was combined with a hardener (polyester diol based on adipic acid, isophthalic acid, diethylene glycol and 1,2-propylene glycol; OH value between 129 and 141 mg KOH/g) (mixing ratio 100:64 by weight), and the final composition was used to laminate a PE- and a PET-film as well as an OPP- and an OPP-film (OPP=oriented polypropylene) at 40° C., respectively. The surface energy of PET was 44 dyn/cm, of PE 29 dyn/cm and of OPP was 29 dyn/cm.

[0079] Laminate adhesion was tested with a universal tensile strength testing machine with a synchronous recorder. The force range was between 10 and 50 N and was adjusted according to the expected adhesion level. For the test, 15 mm wide stripes were prepared using a stripe cutter. Before the stripes were clamped, they were slightly separated. The peeling was done at a rate of 100 mm/minute, a peeling angle of 90° and a peel length of 5 to 10 cm. The result is shown in Table 1 as laminate adhesion in N/15 mm after 2, 7 and 14 days.

TABLE-US-00001 TABLE 1 2 days 7 days 14 days PE-PET 0.35 0.43 0.41 OPP-OPP 0.98 1.3 1.26

Example 2

According to the Invention

[0080] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 33.57 g of castor oil (OH value 163 mg KOH/g), 33.16 g of PPG 1000 (OH value 110 mg KOH/g), 57.00 g of PPG 2000 (OH value 56 mg KOH/g), 9.12 g of Krasol™ LBH P2000 (OH value 50 mg KOH/g), and 20.27 g of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 130 g MDI were added, and the final composition stirred at 75° C. until an NCO content of 11.6 wt %. The resulting product showed a viscosity of 3050 mPas at 40° C. (Brookfield—RVTDV II, 40° C., spindle 27, 20 rpm).

[0081] The isocyanate component was combined with the same hardener as used in Example 1 (mixing ratio 100:65 by weight), and the final composition was used to laminate an OPP- and an OPP-film (OPP=oriented polypropylene) at 40° C.

[0082] Laminate adhesion was tested similar as in Example 1 and the results are shown in Table 2 as laminate adhesion in N/15 mm after 3, 7 and 14 days.

TABLE-US-00002 TABLE 2 3 days 7 days 14 days OPP-OPP 0.58 1.0 1.01

Example 3 (Comparative Example)

[0083] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 14.71 wt % of castor oil (OH value 163 mg KOH/g), 15 wt % of PPG 1000 (OH value 110 mg KOH/g) and 14.22 wt % of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 56.07 wt % MDI were added, and the final composition stirred at 75° C. until an NCO content of 12.96 wt %. The resulting product showed a viscosity between 3000 and 5000 mPas at 40° C. (Brookfield—RVTDV II, 40° C., Spindle 27, 20 rpm).

[0084] The isocyanate component was combined with same hardener as used in Example 1 (mixing ratio 100:75 by weight), and the final composition used to laminate a PE- and a PET-film as well as an OPP- and an OPP-film at 40° C.

[0085] Laminate adhesion was tested similar as in Example 1 and the results are shown in Table 3 as laminate adhesion in N/15 mm after 2, 7 and 14 days.

TABLE-US-00003 TABLE 3 2 days 7 days 14 days PE-PET 0.02 0.03 0.02 OPP-OPP 0.07 0.03 0.01

Example 4 (Comparative Example)

[0086] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 52.72 g of castor oil (OH value 163 mg KOH/g), 52.61 g of PPG 1000 (OH value 110 mg KOH/g), 90.82 g of PPG 2000 (OH value 56 mg KOH/g), and 31.95 g of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 200 g MDI were added, and the final composition stirred at 75° C. until an NCO content of 11.1 wt %. The resulting product showed a viscosity of 4058 mPas at 40° C. (Brookfield—RVTDV II, 40° C., Spindle 27, 20 rpm).

[0087] The isocyanate component was combined with same hardener as used in Example 1 (mixing ratio 100:68 by weight), and the final composition used to laminate a PE- and a PET-film as well as an OPP- and an OPP-film film at 40° C.

[0088] Laminate adhesion was tested similar as in Example 1 and the results are shown in Table 4 as laminate adhesion in N/15 mm after 2, 7 and 14 days.

TABLE-US-00004 TABLE 4 2 days 7 days 14 days PE-PET 0.13 0.22 0.25 OPP-OPP 0.17 0.25 0.22

Example 5 (Inventive Example)

[0089] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 51.64 g of castor oil (OH value 163 mg KOH/g), 51.02 g of PPG 1000 (OH value 110 mg KOH/g), 87.69 g of PPG 2000 (OH value 56 mg KOH/g), 14.03 g of Krasol™ HLBH P2000 (hydrogenated polybutadiene polyol, OH value 50 mg KOH/g), and 31.29 g of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 200 g MDI were added, and the final composition stirred at 60 to 70° C. until an NCO content of 11.2 wt %. The resulting product showed a viscosity of 6300 mPas at 40° C. (Brookfield—RVTDV II, 40° C., spindle 27, 20 rpm).

[0090] The isocyanate component was combined with a polyether polyol based hardener (PPG 2000), OH value 56 mg KOH/g (mixing ratio 100:133 by weight), and the final composition was used to laminate a PE- and a PET-film as well as an OPP- and an OPP-film at 30° C.

TABLE-US-00005 TABLE 5 3 days 7 days 14 days PE-PET 0.025 0.04 0.04 OPP-OPP 0.7 0.87 0.94

Example 6 (Comparative Example)

[0091] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 52.72 g of castor oil (OH value 163 mg KOH/g), 52.61 g of PPG 1000 (OH value 110 mg KOH/g), 90.82 g of PPG 2000 (OH value 56 mg KOH/g), and 31.95 g of PPG 400 (OH value 269 mg KOH/g) were added and mixed at 40° C. Once the mixture of polyols was homogeneous, 200 g MDI were added, and the final composition stirred at 75° C. until an NCO content of 11.1 wt %. The resulting product showed a viscosity of 4058 mPas at 40° C. (Brookfield—RVTDV II, 40° C., Spindle 27, 20 rpm).

[0092] The isocyanate component was combined with a polyether polyol based hardener (PPG 2000), OH value 56 mg KOH/g (mixing ratio 100:136 by weight), and the final composition was used to laminate a PE- and a PET-film as well as an OPP- and an OPP-film at 30° C.

TABLE-US-00006 TABLE 6 3 days 7 days 14 days PE-PET 0.014 0.013 0.01 OPP-OPP 0.21 0.23 0.19