Ultralow Monomer Polyurethanes

Abstract

The present invention relates to ultralow monomer PU prepolymers containing free NCO groups obtainable from polyols, diisocyanates and NCO-reactive compounds, obtainable by reacting at least one polyol with at least one polyisocyanate, wherein the at least one polyisocyanate is used in molar excess relative to the hydroxyl groups of the at least one polyol to obtain a polyurethane prepolymer containing free isocyanate groups; and adding at least one compound having at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups in an amount such that the molar ratio of the free isocyanate groups to H-acidic functional groups (NCO:XH ratio) is 2 to 15, preferably 2.5 to 10, more preferably 3 to 8. Also encompassed are methods for its production, laminating adhesives containing said prepolymer, methods of bonding substrates and the use of the described adhesives for laminating two or more films.

Claims

1. A prepolymer composition comprising at least one polyurethane prepolymer containing free isocyanate groups, said polyurethane prepolymer being the reaction product of a mixture, comprising: (a) an intermediate polyurethane prepolymer that is the reaction product of a mixture comprising at least one polyol and at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol to obtain the intermediate polyurethane prepolymer containing free isocyanate groups; and (b) at least one compound having at least one H-acidic functional group wherein the at least one compound is used in an amount such that the molar ratio of the free isocyanate groups to H-acidic functional groups (NCO:XH ratio) is 2 to 15.

2. The prepolymer composition according to claim 1, wherein the at least one compound having at least one H-acidic functional group is used in an amount such that the molar ratio of the free isocyanate groups to H-acidic functional groups (NCO:XH ratio) is 3 to 8.

3. The prepolymer composition according to claim 1, wherein the at least one compound having at least one H-acidic functional group: (a) comprises at least one primary amino, secondary amino, mercapto, carboxyl, hydroxyl or acidic C—H group as the at least one H-acidic functional group; and/or (b) has only one H-acidic functional group.

4. The prepolymer composition according to claim 1, wherein the at least one compound having at least one H-acidic functional group comprises at least one silane group.

5. The prepolymer composition according to claim 4, wherein the at least one compound having at least one H-acidic functional group is a silane of formula I
((R.sup.2).sub.m(R.sup.1O).sub.3-mSi-alkyl).sub.oNu  (I) wherein Nu is NH, NH.sub.2, SH, COOH or OH; R.sup.1 is selected from H and C.sub.1-20 alkyl; R.sup.2 is selected from C.sub.1-4 alkyl, m is 0, 1 or 2; alkyl is a linear or branched C.sub.1-6 alkylenyl or C.sub.3-6 cycloalkylenyl, and wherein if Nu is NH.sub.2, SH or OH o is 1 and if Nu is NH o is 2.

6. The prepolymer composition according to claim 5, wherein the at least one compound having at least one H-acidic functional group is an aminosilane selected from the group consisting of 3-aminopropyltrimethoxysilane (AMMO), 3-aminopropyltriethoxysilane (AMEO), 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (DAMO), N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-amino-propylmethyldiethoxysilane, N,N-di(2-aminoethyl)-3-aminopropyltrimethoxysilane, N,N-di(2-aminoethyl)-3-aminopropyltriethoxysilane, N,N-di(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-di(2-aminoethyl)-3-amino-propylmethyldiethoxysilane, N-(2-aminoethyl)-N′-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-N′-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-N′-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-N′-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane), bis(triethoxysilylpropyl)amine, bis(trimethoxysilylpropyl)amine, N-(2-aminobutyl)-3-aminopropyltriethoxysilane, N-(2-aminobutyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxysilane, and mixtures thereof.

7. The prepolymer composition according to claim 1, wherein the at least one polyisocyanate comprises a first diisocyanate and a second diisocyanate, wherein the first diisocyanate has first NCO groups and the second diisocyanate has second NCO groups, wherein at least one of the first NCO groups is less reactive towards the hydroxyl groups of the at least one polyol than at least one of the second NCO groups.

8. The prepolymer composition according to claim 7, wherein (a) the molar ratio of the NCO groups of the first diisocyanate to the NCO groups of the second diisocyanate is at least 6:1; and/or (b) the first diisocyanate is an asymmetric diisocyanate; and/or (c) the second diisocyanate is a symmetric diisocyanate.

9. A method for producing the prepolymer composition according to claim 1, comprising (a) reacting the at least one polyol with the at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol to obtain a polyurethane prepolymer containing free isocyanate groups; and (b) adding at least the at least one compound having at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups of step (a) in an amount such that the molar ratio of the free isocyanate groups to H-acidic functional groups (NCO:XH ratio) is 2 to 15.

10. An adhesive composition comprising the prepolymer composition according to claim 1, optionally further comprising at least one of tackifier, catalyst, stabilizer, crosslinking agent, viscosity modifier, filler, pigment, plasticizer, water scavenger and/or antioxidant.

11. The adhesive composition according to claim 10, wherein said composition further comprises at least one polymer having anhydride functional groups.

12. A method of bonding two or more substrates selected from the group consisting of plastic surface articles, metals, textiles, paper and cardboard comprising: (a) applying the adhesive composition of claim 10, alone or in a mixture with a hardener, to the surface of at least one of the substrates to be bonded; and (b) contacting the surfaces of the substrates to be bonded together with the adhesive composition therebetween under conditions suitable to form an adhesive bond between the substrates; (c) optionally repeating steps (a) and (b); wherein the hardener is selected from a compound comprising H-acidic functional groups selected from hydroxyl, primary or secondary amino, mercapto or carboxyl groups; a polyol component; or a polyol that comprise two or more hydroxyl groups per molecule.

13. The method according to claim 12, wherein two or more of the substrates are film-shaped substrates.

14. A multilayer laminate comprising the adhesive composition of claim 10.

15. The multilayer laminate according to claim 14, wherein the laminate is (a) a two-layer laminate; and/or (b) a laminate for food packaging applications.

16. A multilayer laminate comprising cured reaction products of the prepolymer composition according to claim 1.

17. An adhesive for laminating food packaging comprising the prepolymer composition according to claim 1.

18. An adhesive for laminating food packaging comprising the prepolymer composition according to claim 1 and having a primary aromatic amine migration limit of <10 ppb by weight.

Description

EXAMPLES

Example 1 (According to the Invention)

[0115] In a three-necked flask equipped with a stirrer, thermometer and a condenser, 1067.4 g of PES 218 (OH value 133 mg KOH/g), 673.58 g of PES 231 (OH value 108 mg KOH/g), 350.3 g of polypropylene glycol (OH value 113 mg KOH/g), 350.0 g of polypropylene glycol (OH value 236 mg KOH/g), and 873.7 g of ethyl acetate were mixed with 735.2 g of toluene-2,4-diisocyanate, and the resulting mixture was heated at 50° C. Due to the exothermic reaction the temperature rose and was kept at 80° C. until the NCO content as measured by titration was only 3.85% by weight. After addition of 4,4′-diphenylmethane diisocyanate (4,4′-MDI), the reaction mixture was stirred for 3 hours at 80° C., after which an NCO content of 3.05% was measured. 249.2 g of PES 231 (OH value 108 mg KOH/g) and 18 g trimethylolpropane (OH value 1254 mg KOH/g) were added and the solution stirred at the same temperature until an NCO content of 2.08% by weight. 716 g ethyl acetate and 243.2 g Desmodur® L75 (polyisocyanate based on 2,4-TDI or triisocyanate based on TDI, NCO value 13,3% by weight) were added until an NCO content of 2,2% by weight was measured.

[0116] The prepolymer was then reacted at 40° C. with Dynasylan® 1122 (bis(3-(triethoxysilyl)propyl)amine) at an NCO/NH equivalent ratio of equal to 7.3:1. The resulting product had an NCO content of 1.94% by weight, a viscosity of 1510 mPa.Math.s (measured three days after production, Brookfield/spindle 3/30 rpm), final 70% solids, and an isocyanate monomer concentration of 0.05% by weight 2,4-TDI and <0.01% by weight 4,4′-MDI. Other isocyanate monomers were not detectable (<0.01% by weight).

[0117] The modified prepolymer was utilized as a 1- or 2-K adhesive in combination with Liofol® hardener LA6152 (Henkel AG & Co. KGaA; OH component; solid content: 100% by weight) at a mixing ratio of 25:1 (NCO/OH equivalent ratio of 1.65:1) to laminate different film structures at a dry coating weight of 3.5 g/m.sup.2.

[0118] Laminate adhesion was tested using a universal tensile testing machine with a synchronous recorder. The force range was between 10 and 50 N and was adjusted according to the expected adhesion level. 15 mm wide stripes were prepared using a stripe cutter. Before the stripes were clamped, they were slightly separated. The peeling rate was 100 mm/min, the peeling angle 90° and the peel length 5 to 10 cm according to the range of variation. The results are expressed as laminate adhesion (bond strength—BS) in N/15 mm and the separation pattern is visually evaluated (% of ink transfer).

TABLE-US-00001 TABLE 1 Performance on printed OPP/OPP Ink binders: NC-PU (gravure printed) Color BS—1 day BS—14 days BS—28 days Blue 2.95/5% ink 2.2/100% ink 1.59/co-ex tear transfer transfer blue-white 2.22/0% ink 3.82/co-ex tear 2.45/co-ex tear transfer White 2.19/0% ink 1.78/100% ink 2.63/co-ex tear transfer transfer

TABLE-US-00002 TABLE 2 Performance on printed OPP/OPP Ink binders: NC-PU (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 3.25/co-ex tear 4.97/co-ex tear 4.41/co-ex tear blue-white 1.99/0% ink 4.35/co-ex tear 3.57/90% ink transfer transfer White 1.87/co-ex tear 5.99/co-ex tear 2.09/co-ex tear

TABLE-US-00003 TABLE 3 Performance on printed PET/PE Ink binders: PUR (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 2.35/0% ink 3.07/PET tear 3.26/PET tear transfer blue-white 2.23/0% ink 3.94/PET tear 4.42/PET tear transfer White 2.52/0% ink 1.33/100% ink 1.59/100% ink transfer transfer transfer

[0119] A freshly laminated OPA/PE structure coated with 3.8 g/m.sup.2 of the prepolymer as a 1K adhesive was instantly evaluated for migration of primary aromatic amines (PAAs). The migration test was performed by placing the laminates in migration cells and covering 1 dm.sup.2 (from the PE side) with 100 ml of 3% by weight acetic acid at 70° C. for 1 hour. The migration solutions were then analyzed via HPLC with a PDA detector after enrichment to detect 2,4-TDA, 2,6-TDA, 2,2′-MDA, 2,4′-MDA and 4,4′-MDA. The test result was <10 ppb by weight PAA (compliant with EC/10/2011 on plastic materials and articles intended to come into contact with food) even if the PU prepolymer was used without additional hardener.

[0120] Related to the migrated surface, the following amounts were determined for the 0 hours migration solution at 70° C. (in μg/dm.sup.2)

TABLE-US-00004 2,6-TDA 2,4-TDA 4,4′-MDA 2,4′-MDA 2,2′-MDA 0.32 <0.15 <0.15 <0.15 <0.18

Example 2 (Comparative Example)

[0121] 44 parts of polyester PE 230 were dissolved in 9.25 parts ethyl acetate and then reacted with 5 parts 2,4-TDI at 80° C. 29.75 parts of ethyl acetate and 4.5 parts of a mixture of dibutylamine and bis(3-(triethoxysilyl)propyl)amine were then added until no further isocyanate groups were present.

[0122] To this prepolymer, 7.5 parts of a styrene copolymer containing app. 50% by weight maleic anhydride building blocks was added and the mixture homogenized. The resulting final product had a viscosity of 1060 mPa.Math.s (Brookfield/spindle 3) at 20° C. and a solids content of 56% by weight.

[0123] The prepolymer was then used to laminate different film structures at a dry coating weight of 2.7 g/m.sup.2. The performance was tested as described in Example 1.

TABLE-US-00005 TABLE 4 Performance on printed OPP/OPP Ink binders: NC-PU (gravure printed) Color BS—1 day BS—14 days BS—28 days Blue 0.58/60% ink 0.47/80% ink 0.42/80% ink transfer transfer transfer blue-white 0.98/90% ink 0.49/95% ink 0.22/90% ink transfer transfer transfer White 1.9/50% ink 0.86/95% ink 0.39/100% ink transfer transfer transfer

TABLE-US-00006 TABLE 5 Performance on printed OPP/OPP Ink binders: NC-PU (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 1.09/90% ink 1.25/5% ink 0.74/0% ink transfer transfer transfer blue-white 1.15/100% ink 0.96/100% ink 1.18/80% ink transfer transfer transfer White 1.9/0% ink transfer 2.39/co-ex tear 1.19/100% ink transfer

TABLE-US-00007 TABLE 6 Performance on printed PET/PE Ink binders: PUR (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 1.3/90% ink 0.96/100% ink 0.66/100% ink transfer transfer transfer blue-white 4.21/PET tear 2.39/PET tear 1.6/90% ink transfer White 3.11/0% ink 0.95/100% ink 1.38/100% ink transfer transfer transfer

[0124] As the adhesive does not contain any remaining isocyanate groups, it is instantly compliant with EC/10/2011. However, it shows a lowered adhesive performance.

Example 3 (Comparative Example)

[0125] LOCTITE® Liofol® LA 3966-21 (Henkel AG & Co. KGaA; NCO component; solid content: 80% by weight; solvent:ethylacetate) with hardener LOCTITE® Liofol® LA 6152 at a mix ratio of 20:1 (NCO/OH index 2.13) was utilized as a laminating adhesive at 3.5 g/m.sup.2. Bis(3-(triethoxysilyl)propyl)amine was not employed.

[0126] None of the laminates showed <10 ppb by weight PAA instantly after lamination and it required more than 24 hours cure at room temperature to reach compliance with EC/10/2011.

[0127] The performance was tested as described in Example 1.

TABLE-US-00008 TABLE 7 Performance on printed OPP/OPP Ink binders: NC-PU (gravure printed) Color BS—1 day BS—14 days BS—28 days Blue 2.04/70% ink 2.1/100% ink 1.52/co-ex tear transfer transfer blue-white 4.24/0% ink 1.76/100% ink 1.33/100% ink transfer transfer transfer White 4.35/0% ink 1.26/100% ink 1.27/co-ex tear transfer transfer

TABLE-US-00009 TABLE 8 Performance on printed OPP/OPP Ink binders: NC-PU (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 2.43/co-ex tear 3.04/co-ex tear 2.45/co-ex tear blue-white 1.81/0% ink 2.53/co-ex tear 2.4/co-ex tear transfer White 1.73/0% ink 2.71/co-ex tear 1.03/100% ink transfer transfer

TABLE-US-00010 TABLE 9 Performance on printed PET/PE Ink binders: PUR (flexo printed) Color BS—1 day BS—14 days BS—28 days Blue 2.05/0% ink 4.19/PET tear 3.75/PET tear transfer blue-white 2.06/0% ink 2.88/PET tear 1.43/100% ink transfer transfer White 2.22/0% ink 1.29/100% ink 1.22/100% ink transfer transfer transfer

[0128] In sum, the examples show that only the prepolymer composition according to Example 1 showed a good adhesive performance and also led to a laminate which is instantly reaches compliance with EC/10/2011. I.e. a residual PAA content of below 10 ppb by weight is achieved directly after lamination, such that a direct use of the laminate for food packaging after lamination is possible. The prepolymers according to Example 2, even though being instantly food compliant, lacked in adhesive performance. In contrast, the NCO component according to Example 3 provided a good adhesive performance but led to higher residual PAA contents that did not allow a direct use of the laminates for food packaging after lamination.