One-component aqueous coating compositions containing polyurethane and phyllosilicates for oxygen barrier coatings

Abstract

Described is an aqueous one-component coating composition comprising dispersed polyurethane and phyllosilicate. The polyurethane carries acid groups which are at least partially neutralized with a hydrophilic base selected from inorganic bases and organic mono-amines. The hydrophilic base has a water solubility at 20° C. of at least 150 g/l, preferably of at least 200 g/l. The composition can be used for providing oxygen barrier properties to a polymer film.

Claims

1. A one-component aqueous coating composition, comprising: (a) at least one dispersed polyurethane in a range of 10 to 90 wt. % with respect to a solids content of the one-component aqueous coating composition; and (b) at least one phyllosilicate in a range of 5 to 75 wt. % with respect to the solids content; wherein the at least one dispersed polyurethane comprises at least one acid functional group; the at least one acid functional group is at least partially neutralized with at least one hydrophilic base selected from the group consisting of an inorganic base and an organic mono-amine; the at least one hydrophilic base has a water solubility at 20° C. of at least 150 g/L; and the coating composition comprises no crosslinker for the at least one dispersed polyurethane.

2. The one-component aqueous coating composition of claim 1, wherein the at least one dispersed polyurethane comprises, in reacted form: (a) at least one organic diisocyanate of formula X(NCO).sub.2; where X is a noncyclic aliphatic hydrocarbon radical having 4 to 15 carbon atoms, a cycloaliphatic hydrocarbon radical having 6 to 15 carbon atoms, an aromatic hydrocarbon radical having 6 to 15 carbon atoms, or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms; (b) at least one dihydroxy compound selected from the group consisting of a polyester diol, a polyether diol, and a polycarbonate diol; (c) at least one compound comprising: at least one functional group reactive toward an isocyanate functional group; and at least one acid functional group; and (d) optionally, at least one compound different from the compounds comprised by (a) to (c).

3. The one-component aqueous coating composition of claim 1, wherein the at least one hydrophilic base is selected from the group consisting of an inorganic metal salt and ammonia.

4. The one-component aqueous coating composition of claim 1, wherein a degree of neutralization of a total molar amount of the at least one acid functional group is in a range of 30 to 100 mol %.

5. The one-component aqueous coating composition of claim 1, wherein a weight ratio of the at least one dispersed polyurethane to the at least one phyllosilicate is in a range of 95:5 to 50:50.

6. The one-component aqueous coating composition of claim 1, wherein the at least one phyllosilicate is an exfoliated organically modified smectite.

7. The one-component aqueous coating composition of claim 1, wherein the at least one phyllosilicate is a natural or synthetic phyllosilicate with an aspect ratio greater than 400.

8. The one-component aqueous coating composition of claim 1, wherein the at least one phyllosilicate is a synthetic smectite of formula [M.sub.n/valency].sup.inter[M.sup.I.sub.m M.sup.II.sub.o].sup.oct[Si.sub.4].sup.tetO.sub.10Y.sub.2, wherein M is: a metal cation with an oxidation state in a range of 1 to 3; or H.sup.+; M.sup.I is a metal cation with an oxidation state of 2 or 3; M.sup.II is a metal cation with an oxidation state of 1 or 2; O is oxygen; Y is a mono-anion; m is: ≤2.0 for each M.sup.I metal cation with an oxidation state of 3; and ≤3.0 for each M.sup.I metal cation with an oxidation state of 2; o is ≤1.0, and n, the layer charge, is in a range of greater than or equal to 0.01 to lower than or equal to 2.0.

9. The one-component aqueous coating composition of claim 1, wherein a surface of the at least one phyllosilicate comprises at least one organic compound having at least one functional group selected from the group consisting of an amino functional group and an ammonium functional group.

10. The one-component aqueous coating composition of claim 1, wherein the at least one phyllosilicate is: (a) produced hydrothermally; or (b) produced by high-temperature melt synthesis and, subsequently, at least one selected from the group consisting of exfoliation and delamination.

11. The one-component aqueous coating composition of claim 1, wherein the at least one dispersed polyurethane is semi-crystalline.

12. A polymer film, coated with the one-component aqueous coating composition of claim 1.

13. The polymer film of claim 12, wherein an oxygen transmission rate of the polymer film after coating is less than 40% of an oxygen transmission rate of the polymer film before coating, both rates being measured at 25° C. and 75% relative humidity.

14. The polymer film of claim 12, wherein the polymer film comprises at least one material selected from the group consisting of a polyethylene terephthalate, an oriented polypropylene, a polyethylene, a casted polypropylene, a biodegradable aliphatic-aromatic copolyester, a metalized polyethylene terephthalate, a metalized oriented polypropylene, and a polyamide; wherein a thickness of a coating layer is in a range of 0.2 to 50 μm after drying.

15. A package, comprising the polymer film of claim 12.

16. A method of coating a polymeric film with the one-component aqueous coating composition of claim 1, the method comprising: (a) contacting at least one side of the polymeric film with the one-component aqueous coating composition; and (b) drying the one-component aqueous coating composition of (a) to form a barrier coating on the polymeric film.

17. A method of providing oxygen barrier properties to an article, the method comprising contacting a surface of the article with the aqueous coating composition of claim 1.

Description

EXAMPLES

(1) Measurement of Oxygen-Barrier Action:

(2) Oxygen transmission rate (OTR) is determined on coatings on polymer films at a relative humidity (RH) level of 75% and at a temperature of 25° C.

(3) Measurements are done with synthetic air (21% oxygen; results are extrapolated for 100% oxygen.

(4) Carrier material: polymer film of PET (polyethylene terephthalate) from Bleher Folientechnik with a thickness of 36 μm, one side corona treated.

(5) OTR of the uncoated film: 33 cm.sup.3 m.sup.−2 day.sup.−1 bar.sup.−1.

(6) The determination method is based on ASTM D3985-05, using a coulometric sensor. Each sample is measured twice and the mean result is calculated.

(7) OTR are obtained on a Mocon OX-TRAN 2/21 XL instrument with a lower detection limit of 0.0005 cm.sup.3 m.sup.−2 day.sup.−1 bar.sup.−1.

(8) Water vapour transmission rates (WVTR) were measured on a Mocon PERMATRAN-W model 333 at 25° C. and a relative humidity of 75% RH. The lower detection limit of the device was 0.05 g m.sup.−2 day.sup.−1.

(9) Polyurethane dispersion (PUD) samples: PUD-A: Astacin® Finish PUM; amorphous PUD stabilized by acid groups neutralized with NaOH, emulsifier free; 37% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-B: Emuldur® 360 A; amorphous PUD stabilized by acid groups neutralized with NaOH, emulsifier free; 40% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-C: Luphen® 585; semi-crystalline PUD stabilized by acid groups neutralized with NaOH, emulsifier free; 40% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-D: Luphen® D 207 E; semi-crystalline PUD stabilized by acid groups neutralized with NaOH, emulsifier free; 45% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-E: Luphen® DDS 3577; amorphous PUD stabilized by acid groups, neutralized with NH.sub.3, emulsifier free; 40% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-F: Epotal® FLX 3621; amorphous PUD stabilized by acid groups neutralized with NaOH, emulsifier free; 53% solids content, commercially available from BASF SE (Ludwigshafen, Germany) PUD-G: Astacin® Grund UH; amorphous PUD stabilized by acid groups (comparative) neutralized with triethylamine (TEA; NEt.sub.3), emulsifier free; 20% solids content, commercially available from BASF SE (Ludwigshafen, Germany)

(10) Phyllosilicates: Na-hect synthetic sodium fluorohectorite L-hect hectorite modified with L-lysine

(11) Modification Agents: L-lysine: (S)-2,6-Diaminohexanoic acid monohydrochloride C.sub.6H.sub.14N.sub.2O.sub.2.HCl, reagent grade ≥98%, Sigma-Aldrich GmbH, Germany.

(12) ##STR00002##

(13) The type of phyllosilicate used in the examples is exfoliated smectite type with layer charge of 0.5 per formula unit (p.f.u.). The synthesis procedure of the used phyllosilicate is described in M. Stoter, D. A. Kunz, M. Schmidt, D. Hirsemann, H. Kalo, B. Putz, J. Senker, J. Breu, Langmuir 2013, 29, 1280-1285. The phyllosilicate is a synthetic sodium fluorohectorite (Na-hect) and has a cation exchange capacity of 127 meq/100 g. The chemical formula is:
[Na.sub.0.5.xH.sub.2O].sup.int[Mg.sub.2.5Li.sub.0.5].sup.oct[Si.sub.4].sup.tetO.sub.10F.sub.2

(14) Modification of the Sodium Fluorohectorite:

(15) Cationic modification was used to replace sodium cations from the surface of the delaminated layered silicate. Modification provides stabilization of the delaminated layered silicates and compatibilization of the layered silicate with the polymer matrix within the suspension and in the drying step of film-formation.

Example 1: Modification of Delaminated Na-Hect (L-Hect)

(16) In a 50 ml centrifuge tube 0.25 g of Na-hect was suspended in 30 ml of distillate water. For the surface modification of the Na-hect a 125% of CEC (cation exchange capacity) of the modification agent L-Lysin (dissolved in 5 ml distillate water) was added and placed into an overhead shaker for 12 h. Afterward the modified Na-hect was centrifuged at 10000 rpm, the separated supernatant was discarded and the modified Na-hect was re-suspended in distillate water and again a 125% of CEC of the modification agent L-Lysin (dissolved in 5 ml distillate water) was added and placed into an overhead shaker for 12 h to ensure complete surface modification of Na-hect. Again the modified Na-hect was centrifuged at 10000 rpm and the separated supernatant was discarded and the resulting, completely modified clay (=L-hect) was washed with distilled water washed until the conductivity of the separated supernatant was below 25 μs.

Example 2: Manufacture of Coating Formulation by Suspension of L-Hect in Polyurethane Emulsion PUD-A and Preparation of Barrier Films

(17) Under stirring, the lysine-modified clay (L-hect) synthesized in Example 1 was added to the required amount of polyurethane PUD-A to produce a suspension with 20 wt. % (based on inorganic material, i.e. without modification agent) of phyllosilicate in the final solid material (the amount of modification agent was calculated on the side of polymer). The final solids content was adjusted to 2.5 wt. % by addition of respective amounts of distilled water yielding a ready-to-use formulation which was applied on the corona-treated side of a pre-heated PET substrate (70° C.) via doctor-blading (18 mm/s, 60 μm slit width). The resulting coating film was dried first at ambient conditions, then at 80° C. for 48 h and had a dry-film thickness of approx. 1.6 μm. Subsequently, the coating was analyzed for its barrier properties, i.e. OTR and WVTR; results are listed in Table 1.

Examples 3, 4a, 5a, 6-7: Manufacture of Coating Formulations by Suspension of L-Hect in Polyurethane Emulsions PUD-B to -F and Preparation of Barrier Films

(18) The general procedure outlined in Example 2 was followed employing polyurethane emulsions PUD-B to -F.

Example 4b: Manufacture of Coating Formulation by Suspension of Unmodified Phyllosilicate Na-hect in Polyurethane Emulsion PUD-C and Preparation of Barrier Films

(19) Employing polyurethane emulsion PUD-C, the general procedure outlined in Example 2 was followed with the exemption that instead of the lysine-modified clay (=L-hect) its unmodified precursor Na-hect was used as barrier filler.

Example 5b: Manufacture of Coating Formulation by Suspension of Higher Amounts of Modified Phyllosilicate Na-Hect in Polyurethane Emulsion PUD-D and Preparation of Barrier Films

(20) Employing polyurethane emulsion D, the general procedure outlined in Example 2 was followed with the exemption that the amount of lysine-modified clay (=L-hect) synthesized in Example 1 was increased to produce a suspension with 50 wt. % (based on inorganic material, i.e. without modification agent)) of phyllosilicate in the final solid material.

Comparative Example C8a: Manufacture of Coating Formulation by Suspension of L-Hect in Polyurethane Emulsion PUD-G, Neutralization with Triethylamine

(21) Following the general procedure outlined in Example 2, preparation of a stable coatings formulation based on PUD-G was not possible leading to gelation/flocculation. In further experiments it could be confirmed that the triethylamine used for neutralization of polyurethane PUD-G interferes malevolently with the lysine-modified clay making it too hydrophobic for being compatible with a water-borne system.

Comparative Examples C2-C8: Barrier Films Based on Clay-Free Polyurethane Emulsions

(22) The as-received polyurethane emulsions PUD-A to G were diluted with distilled water to such an extent that respective drawdowns via doctor-blading (18 mm/s, 60 μm slit width) yielded a dry-film thickness comparable to Examples 2-8 (approx 1.6 μm).

(23) TABLE-US-00001 TABLE 1 Barrier properties of polyurethane-based coatings OTR O.sub.2 permeation WVTR Example description [cm.sup.3 m.sup.−2 day.sup.−1 bar.sup.−1] [μm cm.sup.3 m.sup.−2 day.sup.−1 bar.sup.−1] [g m.sup.−2 day.sup.−1] — neat PET foil 33 — C2 pure PUD-A 32.1 51.4 2 PUD-A + 20% L-hect 02.7 04.6 0.9 C3 pure PUD-B 32.6 52.1 3 PUD-B + 20% L-hect 04.6 08.5 1.1 C4 pure PUD-C 31.8 50.8 4a PUD-C + 20% L-hect 00.7 01.1 0.4 4b PUD-C + 20% Na-hect 01.9 02.9 C5 pure PUD-D 31.4 50.2 5a PUD-D + 20% L-hect 00.8 01.3 0.5 5b PUD-D + 50% L-hect 00.3 00.5 C6 pure PUD-E 35.6 57.0 6 PUD-E + 20% L-hect 01.6 02.7 1.6 C7 pure PUD-F 36.5 58.4 7 PUD-F + 20% L-hect 04.2 07.7 0.9 C8 pure PUD-G 30.2 48.4 C8a PUD-G + 20% L-hect not determinable, formulation unstable

(24) The best barrier properties are achieved with semi-crystalline polyurethane dispersions PUD-C and PUD-D.