FLEXIBLE FOOD PACKAGING LAMINATES

Abstract

Described herein are adhesive compositions, and in particular to solventless adhesive compositions, which can be used to construct laminates, such as flexible laminate materials used to construct flexible packaging (among other things). In another aspect, the solventless adhesive materials are essentially monomer and/or catalyst free, making them well suited for use in making laminates for packaged foods, beverages, and other sensitive materials, e.g., materials which should not be contaminated or not contaminated to unacceptable levels. Also described are laminates made with the adhesive compositions. Laminates made with the adhesive compositions exhibit sufficient bond strength to be slit after 4-8 hours after formation and even 4-5 hours after formation.

Claims

1. An adhesive composition comprising: a) amine-free polyol; b) polyol including one or more tertiary amine groups; and c) polyurethane prepolymer.

2. The adhesive composition of claim 1, wherein the adhesive composition free or is essentially free of solvent.

3. The adhesive composition of claim 1, wherein the adhesive composition is free or essentially free of isocyanate monomers; wherein free or essentially free of isocyanate monomer is an amount of monomer extractable from the adhesive composition that is 0 wt % to 0.5 wt %.

4. (canceled)

5. (canceled)

6. The adhesive composition of claim 3, wherein the monomer comprises a diisocyanate monomer.

7. (canceled)

8. The adhesive composition of claim 3, wherein the monomer is toluene diisocyanate.

9. The adhesive composition of claim 1, wherein amine-free polyol is present in an amount of 10 wt % to 40 wt %; the polyol including one or more tertiary amine groups is present in an amount of 0.5 wt % to 10 wt %; and the polyurethane prepolymer is present in an amount of 40 wt % to 90 wt %.

10. (canceled)

11. (canceled)

12. The adhesive composition of claim 1, further comprising one or more of: a plurality of amine-free polyols; a plurality of polyols including one or more tertiary amine groups; or a plurality of polyurethane prepolymers.

13. (canceled)

14. (canceled)

15. The adhesive composition of claim 1, wherein the adhesive composition is free of catalyst.

16. The adhesive composition of claim 1, further comprising catalyst.

17. The adhesive composition of claim 16, wherein the catalyst is present in an amount of 0.05 wt % to 0.5 wt %.

18. A laminate comprising: first and second substrate layers, adhered together with the adhesive composition of claim 1.

19. The laminate of claim 18, wherein the substrate layers are flexible polymeric materials.

20. A roll of laminate sheet, comprising the laminate of claim 18.

21. Flexible packaging comprised of the laminate of claim 18.

22. (canceled)

23. A method of forming laminate material suitable for slitting in relatively short time after laminate formation comprising the steps of: forming a laminate comprising first and second substrate layers adhered together with the adhesive composition of claim 1; curing the laminate for 4 to 8 hours, in which 4 to 8 hours bond strength sufficient to slit the laminate develops.

24. The method of claim 23, further comprising the step of slitting the laminate into slit laminate material 4 to 8 hours after forming the laminate.

25. (canceled)

26. (canceled)

27. The method of forming a slit laminate material of claim 23, wherein the laminate comprises a long continuous formed laminate sheet.

28. The method of forming a slit laminate material of claim 23, further comprising the step of rolling the long continuous formed laminate sheet onto a roll.

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

38. (canceled)

39. (canceled)

40. (canceled)

41. (canceled)

42. (canceled)

43. (canceled)

44. (canceled)

45. The adhesive composition of claim 1, wherein the polyol including one or more tertiary amine groups is present in an amount of 0.5 wt % to 5.0 wt %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0057] The present application presents laminate adhesives and laminate structures that overcome the problems mentioned herein. For example, flexible laminates constructed of two polymeric films bonded together with the adhesives described herein can be used in making food packaging. The laminate adhesives are free or essentially free of migratable monomers and can be free or essentially free of solvent. Further, laminates formed with these adhesives possesses sufficient bond strength for slitting about 4 to 5 hours after formation.

[0058] Described herein are adhesive compositions that include:

[0059] a) amine-free polyol;

[0060] b) polyol including one or more tertiary amine groups; and

[0061] c) polyurethane prepolymer.

[0062] In one aspect, the adhesive composition is free or is essentially free of solvent.

[0063] In one aspect, the amine-free polyol is present in an amount of 10 wt % to 40 wt %, preferably 15 wt % to 35 wt %. This is the total amount of amine-free polyol that is present (e.g., the total whether one amine-free polyol is present or more than one amine-free polyol is present). The amount is also based on the total weight of the adhesive composition.

[0064] In one aspect, the polyol including one or more tertiary amine groups, e.g., tertiary amine groups on the polyol backbone, is present in an amount of 0.5 wt % to 10 wt %; preferably 0.5 wt % to 5.0 wt %. This is the total amount of polyol including one or more tertiary amine groups that is present (e.g., the total whether one polyol including one or more tertiary amine groups or more than one polyol including one or more tertiary amine groups is present). The amount is also based on the total weight of the adhesive composition.

[0065] In one aspect, the polyurethane prepolymer is present in an amount of 40 wt % to 90 wt %, preferably 50 wt % to 90 wt %. This is the total amount of polyurethane prepolymer that is present (e.g., the total whether one polyurethane prepolymer or more than one polyurethane prepolymer is present). The amount is also based on the total weight of the adhesive composition.

[0066] In one aspect, the polyurethane prepolymer is isocyanate monomer-free and solvent-free.

[0067] The present application is also drawn to a method for making laminates using the combination of materials shown above, as well the laminates made from such a method.

[0068] The present disclosure provides for preparing fast curing laminates with no migratable components by combining polyols commonly used in lamination adhesives for flexible packaging (i.e. polyols not having amine in their backbone) with polyols including one or more tertiary amine groups, e.g., tertiary amine groups on the polyol backbone, and reacting such combinations with polyurethane pre-polymers that preferably are monomer-free and solvent-free. A catalyst does not have to be employed, though it is possible to use one, such as when the resulting flexible packaging is not being used for food and migratable component contamination is not an important issue.

[0069] Commercially available polyols including one or more tertiary amine groups, e.g., tertiary amine groups on the polyol backbone, which are suitable for use in the present laminate adhesives include, for example Desmophen 4051B (amine-based tetrafunctional polyether polyol) and Desmophen 4050E (amine-based tetrafunctional polyether polyol), available from Covestro; Voranol RA 640, Voranol 800, and Voranol RA500, available from Dow Chemical; EDP 300 and EDP 450, available from Adeka; Poly-Q® 40-480, Poly-Q® 43-455, Poly-Q® 40-770 from Monument Chemical (these Poly-Q® products are described as polyether polyol that is an ethylene diamine-initiated, four-functional polyether polyol), Carpol® (SPA-357 (sucrose diethanolamine and propylene oxide based polyether polyol (5.5 functional)) and Carpol® SPA-530 (sucrose/amine-initiated polyether polyol), Carpol® TEAP-265 (triethanolamine-initiated polyether polyol), Carpol® EDAP-770 (ethylene diamine-initiated polyether polyol), and Carpol® EDAP-800770 (ethylene diamine-initiated polyether polyol), available from Carpenter Chemical; and Huntsman (Jeffol® A-630 (amine-based polyether polyol), Jeffol® A-800 (amine containing polyether polyol), Jeffol® AD-310 (aromatic amine/diethylene glycol (DEG)-initiated polyol (MW 580)), Jeffol® AD-500 (aromatic amine/diethylene glycol (DEG)-initiated polyol (MW 360)), Jeffol® R-350, Jeffol® R350X (aromatic amino polyol), Jeffol® R425X (aromatic amine polyol), Jeffol® R470X (amine polyol (nonyl-phenol initiated)), available from Huntsman Chemical.

[0070] It is believed that the polyol including one or more tertiary amine groups, e.g., tertiary amine groups on the polyol backbone, accelerate the reaction of the alcohol groups of the standard polyol, while also reacting and integrating into the polymer network, since they have a plurality of reactive alcohol groups that will react with the isocyanate groups of the prepolymer. Thus, they cannot migrate out of the composition. As accelerants of the reaction (e.g., as amine-initiating polyols), they are comparable to the role of catalysts, but again they are made part of the polymer network. Based on the same principle, other amino polyols could be considered, for example triethanolamine.

[0071] Suitable (a) materials, the amine-free polyol, include castor oil (for example, Albodry Castor Oil PU Quality from Alberdingk Boley). Other suitable standard polyols include Sunlam HA520B, a polyester polyol based on adipic acid (1,4-butane dicarboxylic acid), diethylene glycol and glycerin, and Sunlam HA105B, a 70/30 mixture of a polypropylene glycol and a polyester polyol based on diethylene glycol and phthalic anhydride.

[0072] The polyurethane pre-polymer material (material (c)), may be Polurflex 7910, available from SACIPI. Polurflex 7910 is described as being solvent-less and monomer-free. Other suitable urethane pre-polymers include Trixene SC 7721 (isocyanate-terminated prepolymer), Trixene SC 7722 (toluene diisocyanate-based prepolymer (TDI-based)) and Trixene SC 7725 9 (TDI-based prepolymer), available from Baxenden Chemicals, Ltd.; Polurgreen PRP450 01 (ultra-low monomer-free linear urethane prepolymer) and Polurgreen PRP 750 01 (ultra-low monomer-free linear urethane prepolymer, available from SACIPI.

[0073] Monomer-free prepolymers are advantageous because diisocyanate monomer species are particularly prone to migrating and causing contamination. 2,4-toluene diisocyanate (2,4-TDI), 2,6-TDI, 2,2′-methylene diphenyl diisocyanate (2,2′-MDI), 2,4′-MDI, and 4,4′-MDI are known as monomers that are prone to migrating. The adhesive compositions described herein do not include these monomers, or include them in the very small amounts described herein.

[0074] Since there are virtually no monomers present in the above components and thus in the laminating adhesive systems (e.g., they are free or essentially free thereof), there is no monomer to migrate from the adhesive, which makes the adhesive compositions well suited for making laminates used in food packaging.

[0075] Applicants have found that the amount of polyol including one or more tertiary amine group plays an interesting role in the success of the described compositions. If the amount is small, e.g., less than 0.5 wt %, then sufficient bond strength will not develop in order to slit the laminate within a relatively short time (e.g., 4 to 8) hours. If the amount is large, e.g., greater than 10 wt %, then the pot life of the adhesive composition is too short for forming laminates. Applicants have found that the amounts stated herein, e.g., 0.5 wt % to 10 wt %, preferably 0.5 wt % to 5.0 wt %, provides the combination of desired properties and a sufficiently long pot life.

[0076] Suitable substrate films used to make the laminates include OPP and PE. OPP may be employed as the primary web, and PE may be used as the sealant web. Other films that can be used include OPA, PET, CPP, PETg, Met-PET, Met-OPP, Met-CPP, Alox or SiOx coated film, PE, EVOH PE, and aluminum foil, among others.

[0077] The amine-free polyol, the polyol including one or more tertiary amine groups, and the urethane prepolymer can be mixed at temperatures of about 45° C. to 55° C. to form the adhesive compositions described herein.

[0078] In some instances, a catalyst may be included in the present compositions, such as when the laminate compositions will be used in situations where including migratable components is a lesser issue or is not an issue at all. Suitable catalysts include tin catalysts, bismuth catalysts, zinc catalysts, zirconium catalysts, aluminum catalysts and tertiary amines. The catalysts may be present in the composition in amounts of 0.05 wt % to 0.5 wt %, preferably 0.1 wt % to 0.5 wt % and more preferably 0.2 wt % to 0.5 wt %.

[0079] Examples of suitable catalysts include tertiary amines such as 1,4-diazabicyclo [2.2.2] octane (DABCO), metallic compounds such as dibutyl tin dilaurate, stannous octoate and bismuth neodecanoate, triphenyl bismuth (King Industries K-KAT XC-B221, K-KAT 348, K-KAT XK-651, K-KAT XK-614), zirconium tetrakis (2,4-pentanedionato) (King Industries K-KAT 4205, K-KAT 6212). Suitable catalysts are the known polyurethane catalysts such as, for example, compounds of divalent and tetravalent tin, more particularly the dicarboxylates of divalent tin and the dialkyl tin dicarboxylates and dialkoxylates. Examples of such catalysts are dibutyl tin dilaurate, dibutyl tin diacetate, dioctyl tin diacetate, dibutyl tin maleate, tin(II) octoate, tin(II) phenolate or even the acetyl acetonates of divalent and tetravalent tin. Tertiary amines or amidines may also be used as catalysts, optionally in combination with the tin compounds mentioned above. Suitable amines are both acyclic and, in particular, cyclic compounds. Examples include tetramethyl butane diamine, bis-(dimethylaminoethyl)-ether, 1,4-diazabicyclooctane (DABCO), 1,8-diazabicyclo-(5.4.0)-undecane, 2,2′-dimorpholinodiethyl ether or dimethyl piperazine or even mixtures of the amines mentioned above.

[0080] Applicants have found that initial viscosity should be about 900 mPa.Math.s to 1600 mPa.Math.s (millipascal-second) at the application temperature, more preferably 1000-1500. After 30 minutes, the viscosity should be 2000 mPa.Math.s to 8000 mPa.Math.s after 30 minutes, more preferably from about 2000 mPa.Math.s to 5000 mPa.Math.s.

EXAMPLES

[0081] The following examples are intended to exemplify particular embodiments of the compositions described herein and are not intended to limit the scope thereof in any respect and should not be so construed.

[0082] Exemplary adhesive compositions as described herein and comparison exemplary adhesive compositions were prepared and are described below. The adhesive components were mixed at 50° C. Adhesive compositions were maintained at this temperature for 30 minutes. Tables 1, 2 and 3 report the viscosities of the adhesive compositions at 1, 10, 20 and 30 minutes, in order to evaluate reaction times and pot life. Component parts by weight (PBW) are given in the left column of Tables 1-3.

[0083] The amount of component (b), polyol including one or more tertiary amine groups, e.g., tertiary amine groups on the polyol backbone, was varied (the comparative examples do not contain component (b)).

TABLE-US-00001 TABLE 1 Adhesive Compositions including Castor Oil as Component (a) Time (minutes) PBW: Polurflex 7910 (c)/castor 0 10 20 30 oil (a)/Desmophen 4051B (b) Viscosity mPa .Math. s at 50° C. Example 1 (comparative) 100/25/0 980 1050 1230 1460 Example 2 (inventive) 100/24/1 1075 1340 1610 1930 Example 3 (inventive) 100/23/2 1200 1650 2060 2520 Example 4 (inventive) 100/22/3 1375 2170 2720 3340 Example 5 (inventive) 100/21/4 1400 2375 3295 4220 Example 6 (comparative) 100/50/0 615 675 800 935 Example 7 (inventive) 100/46/4 900 1395 1905 2540

[0084] Table 1 shows that the adhesive compositions of Comparative Examples 1 and 6, which do not contain polyol including one or more tertiary amine groups, undergo very slow reactions, as evidenced by viscosity increasing to only 935 mPa.Math.s (CE6) and 1460 mPa.Math.s (CE1). The inventive adhesive compositions, which contain polyol including one or more tertiary amine groups (Examples 2, 3, 4, 5, 7), exhibit much faster reaction times (viscosity increases to 1930 mPa.Math.s to 4220 mPa.Math.s).

[0085] For further testing, Examples 1, 4, 6 and 7 were chosen for the preparation of the laminates (results for these combinations are presented in Table 4).

TABLE-US-00002 TABLE 2 Adhesive Compositions including Sunlam HA520B as Component (a) Time (minutes) PBW: Polurflex 7910 (c)/HA520B 0 10 20 30 (a)/Desmophen 4051B (b) Viscosity mPa .Math. s at 50° C. Example 8 (comparative) 100/50/0 1150 1125 1170 1270 Example 9 (inventive) 100/49/1 1330 1520 1700 2045 Example 10 (inventive) 100/48/2 1375 1876 2320 2800 Example 11 (inventive) 100/46/4 1700 2630 3860 5235

[0086] SunlamHA520B is a polyester polyol based on adipic acid (1,4-butane dicarboxylic acid), diethylene glycol and glycerin.

[0087] Table 2 shows that the adhesive composition of Comparative Example 8, which does not contain polyol including one or more tertiary amine groups, undergoes a very slow reaction, as evidenced by a viscosity increase from 1150 mPa.Math.s to only 1270 mPa.Math.s in 30 minutes. The inventive adhesive compositions that contain polyol including one or more tertiary amine groups (Examples 9, 10, 11), exhibit much faster reaction times (viscosity increases to 2045 mPa.Math.s, 2800 mPa.Math.s, and 5235 mPa.Math.s respectively).

[0088] For further testing, Examples 8 and 10 were chosen for the preparation of the laminates (results for these combinations are presented in Table 5).

TABLE-US-00003 TABLE 3 Adhesive Compositions including Sunlam HA105B as Component (a) Time (minutes) PBW: Polurflex 7910 (c)/HA105B 0 10 20 30 (a)/Desmophen 4051B (b) Viscosity mPa .Math. s at 50° C. Example 12 (comparative) 100/30/0 990 1085 1270 1475 Example 13 (inventive) 100/29/1 965 1140 1350 1590 Example 14 (inventive) 100/28/2 1110 1700 2150 2630

[0089] Sunlam HA105B is a 70/30 mixture of a polypropylene glycol and a polyester polyol based on diethylene glycol and phthalic anhydride, as described above.

[0090] Table 3 shows that the adhesive composition of Comparative Example 12, which does not contain polyol including one or more tertiary amine groups, undergoes a very slow reaction (viscosity only increases from 990 mPa.Math.s to 1475 mPa.Math.s over 30 minutes). The inventive adhesive compositions that contain polyol including one or more tertiary amine groups (Examples 13, 14) exhibit faster reaction times, particularly example 14 with a viscosity increases from 1110 mPa.Math.s to 2630 mPa.Math.s.

[0091] For further testing, Examples 12 and 14 were chosen for the preparation of the laminates (results for these combinations are presented in Table 6).

Laminate Examples

[0092] The laminates were produced on a Labo Combi 400 laminator made by Nordmeccanica Group using the following conditions:

[0093] Primary Web: RLC30, 30 μm OPP Film from Innovia.

[0094] Secondary Web: 50 μm PE from Ticinoplast.

[0095] Coating weight: 2.1 gsm/dry.

[0096] Adhesive Roller Speed: 80%.

[0097] Adhesive Roller Temp: 45° C.

[0098] Application Roller Temp: 50° C.

[0099] Tension Unwinder A (OPP): 23 N.

[0100] Tension Unwinder B (PE): 9 N.

[0101] Tension Rewinder (Laminate): 28 N.

[0102] Coating head pressure: 3 bars.

[0103] Nip pressure: 3 bars.

[0104] Nip temperature 50° C.

[0105] Laminates cured at 30° C., 50% RH.

TABLE-US-00004 TABLE 4 T-peel bond strength (N/15 mm) at Laminate 100 mm/min after x hours of curing Example Adhesive 1 Hour 3 Hours 5 Hours 24 Hours Example 15 Example 1 0.07 0.14 0.13 3.9 (comparative) Example 16 Example 6 0.07 0.11 0.13 4.3 (comparative) Example 17 Example 4 0.1 0.2 0.5 3.2 (inventive) Example 18 Example 7 0.1 0.5 1.6 3.4 (inventive)

[0106] Mode of failure: all encountered adhesive split between 1-5 hours. Film-break OPP for all after 24 hours. Adhesive split: when the laminate is opened, adhesive is on both laminate sides; the split happening in the adhesive. Film break: the cohesion of the laminate in the peeling tests is stronger than the film.

[0107] Table 4 shows that within 4 to 5 hours, the bond strengths of the laminates made with the adhesives described herein increase to 0.5N/15 mm and 1.6N/15 mm (Examples 17 and 18 respectively) after 5 hours, which are bond strengths that allow for good slitting of the laminates. In contrast, the Comparative Examples 15 and 16, which are laminates made using adhesives of comparative Examples 1 and 6, only display 0.13N/15 mm of bond strength after 5 hours, which is insufficient for laminate slitting. After 24 hours all of the laminated material had reacted sufficiently for slitting.

TABLE-US-00005 TABLE 5 T-peel bond strength (N/15 mm) at Laminate 100 mm/min after x hours of curing Example # Adhesive 1 Hours 3 Hours 5 Hours 24 Hours Example 19 Example 8 0.15 0.26 0.27 3.2 (comparative) Example 20 Example 10 0.17 0.40 1.27 3.4 (Inventive)

[0108] Mode of failure: all encountered adhesive-split between 1 to 5 hours. Film-break OPP for all after 24 hours.

[0109] Table 5 shows that within 5 hours, the bond strength of Example 20, a laminate made with the adhesive of Example 10 has increased to 1.27N/15 mm, which is a bond strength that allows for good slitting of the laminate. In contrast, the laminate of Comparative Example 19, made with the adhesive of Comparative Example 8, only has bond strength of 0.27N/15 mm after 5 hours, which is insufficient for slitting. After 24 hours, all of the laminates possess sufficient bond strength for slitting.

TABLE-US-00006 TABLE 6 T-peel bond strength (N/15 mm) at Laminate 100 mm/min after x hours of curing Example # Adhesive 1 Hour 3 Hours 5 Hours 24 Hours Example 21 Example 12 0.22 0.36 0.36 3.4 (comparative) Example 22 Example 14 0.22 0.41 0.76 3.4 (Inventive)

[0110] Mode of failure: all encountered adhesive-split between 1 to 5 hours. Film-break OPP for all after 24 hours.

[0111] Table 6 shows that within 5 hours, the bond strength of Example 22, a laminate made with the adhesive of Example 14, has increased to 0.76N/15 mm, which is bond strength that allows for good slitting of the laminate. In contrast, the laminate of Comparative Example 21, made with the adhesive of Comparative Example 12, only has bond strength of 0.36N/15 mm after 5 hours, which is insufficient for slitting. After 24 hours, all of the laminates possess sufficient bond strength for slitting.

[0112] As there are none and/or virtually no isocyanate monomers present in the described laminating adhesives, there can be no monomer migration into food packaged in laminates made with the described adhesives.

[0113] Primary aromatic amine extractions were carried out after 24 hours with 3% acetic acid stimulant at 70° C. for 2 hours. The extracts were analyzed in a liquid chromatography with mass spectrum detector (LCMS) for purposes of detecting the following primary aromatic amine analytes: 2,4-diaminotoluene (2,4-TDA, CAS #95-80-7), 2,6-diaminotoluene (2,6-TDA, CAS #823-40-5). None of the target analytes were detected (thus containing <1 ppb), as these diisocyanate monomers are used to prepare the Polurflex 7910 polyurethane prepolymer used in the adhesive composition examples described above.

Test Methods:

[0114] Bond Strength Test—These tests were carried out to ASTM D903 test procedure, except that the test sample size used in every case was 1.5×20 cm.

[0115] Migration Test—The samples were supplied in brown amber jars with sealed tape each containing volumes of approximately 55 mL extracted from print areas of 275 cm.sup.2. Direct aliquot samples were transferred into brown GC vials for LCMS analysis for the following primary aromatic amine analytes: 2,4-TDA and 2,6-TDA. An extra sample was made using 30 ml of 3% acetic acid and spiked with target analytes to enable analyte recoveries to be checked. The spiking intermediate solution was a 0.60 μg/mL aryl amine mixture.

[0116] The following conditions were used for the migration testing:

[0117] Instrument: Shimadzu LCMS 8040 QQQ with Nexera UPLC

[0118] Column Details: Kinetix 100 mm×2.3 mm×1.7u C18 with Guard column (P/N: 00-4678-w9)

[0119] Mobile Phase: [A] LCMS Water (0.1% Formic Acid)

[0120] [B] LCMS Methanol (0.1% Formic Acid)

[0121] Gradient: 1% B (4 min)-85% B (10 min)-1% B (10 min)-1% B (15 min)

[0122] Flow rate: 0.3 ml/min

[0123] Column temp ° C.: 40

[0124] Rinse solvent: Acetonitrile

[0125] Injection Volume: 10 μL

[0126] Pot Life/Reactivity—The increases of viscosities, used to determine pot life of the mixed adhesives, were measured on a TA Instruments rheometer model AR 1500 ex, at 50° C. and 30 s.sup.−1 using a 2-degree 60 mm cone.

[0127] The present invention has been described in detail, including the preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and/or improvements on this invention that fall within the scope and spirit of the invention.