AQUEOUS ETHYLENE-VINYL ALCOHOL COPOLYMER DISPERSION AND OXYGEN BARRIER MULTILAYER FILM COATED WITH SAID DISPERSION

Abstract

An aqueous dispersion of ethylene-vinyl alcohol copolymers suitable to be used as lacquer to realize a thin coating both for flexible or rigid substrates, characterized by excellent oxygen and carbon dioxide barrier performances especially under high humidity conditions. The dispersion comprises a first ethylene-vinyl alcohol copolymer in the form of capsules with an ethylene content comprised between 24 and 38 mol % and a second ethylene-vinyl alcohol copolymer with an ethylene content lower than 15 mol %.

Claims

1. An aqueous dispersion, comprising: a first ethylene-vinyl alcohol copolymer in the form of capsules with an ethylene content ranging between 24 and 38 mol %; and a second ethylene-vinyl alcohol copolymer with an ethylene content lower than 15 mol %, wherein a weight ratio between said first ethylene-vinyl alcohol copolymer and said second ethylene-vinyl alcohol copolymer is in a range of from 0.40 to 0.70.

2. The aqueous dispersion according to claim 1, wherein the first ethylene-vinyl alcohol copolymer in the form of capsules has an ethylene content ranging between 27 and 32 mol %.

3. The aqueous dispersion according to claim 1, further comprising: an alcohol in an amount ranging between 5 and 10% by weight.

4. The aqueous dispersion according to claim 1, wherein the first ethylene-vinyl alcohol copolymer capsules have a particle size distribution with a volume mean diameter ranging between 0.1 and 10.0 m.

5. The aqueous dispersion according to claim 4, wherein the first ethylene-vinyl alcohol copolymer capsules with a diameter larger than 1.0 m comprise an internal cavity.

6. The aqueous dispersion according to claim 1, further comprising: a filler in an amount ranging between 0.1 and 7% by weight.

7. The aqueous dispersion according to claim 6, wherein the filler is selected from the group consisting of zeolites, graphene, graphene oxide, cellulose, and zirconium phosphate.

8. The aqueous dispersion according to claim 1, further comprising: tetraethoxysilane (TEOS) in an amount ranging between 25 and 100% by weight with respect to EVOH the first and second ethylene-vinyl alcohol copolymers.

9. The aqueous dispersion according to claim 1, further comprising: chitosan in an amount ranging between 0.5 and 5% by weight with respect to the first and second ethylene-vinyl alcohol copolymers.

10. A lacquer-coated barrier laminate, comprising: at least a substrate; and at least a coating layer, wherein said coating layer comprises a first ethylene-vinyl alcohol copolymer in the form of capsules with an ethylene content ranging between 24 and 38 mol %, and a second ethylene-vinyl alcohol copolymer with an ethylene content lower than 15 mol %, wherein a weight ratio between said first ethylene-vinyl alcohol copolymer and said second ethylene-vinyl alcohol copolymer is in a range of from 0.40 to 0.70.

11. The lacquer-coated barrier laminate according to claim 10, wherein the substrate is selected from the group consisting of polyethylene terephthalate (PET), polyamide (PA), polyethylene furanoate (PEF), polyethylene (PE), polypropylene (PP), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyhydroxyalkanoates (PHA), starch blends, lignin cellulose blend, and cellophane.

12. The lacquer-coated barrier laminate according to claim 10, wherein the substrate has a thickness ranging between 8 and 150 m.

13. The lacquer-coated barrier laminate according to claim 10, wherein the coating layer has a thickness ranging between 0.1 and 10.0 m.

14. The lacquer-coated barrier laminate according to claim 10, further comprising: an adhesive layer.

15. The lacquer-coated barrier laminate according to claim 14, wherein the coating layer is in contact with the adhesive layer.

16. The lacquer-coated barrier laminate according to claim 14, wherein the adhesive layer is a polyurethane laminating adhesive.

Description

[0029] Hereinafter, the invention will be explained in more detail with reference to the following examples.

[0030] According to the present invention, in Samples A-H the high-ethylene EVOH capsules have been prepared by adding the ethylene-vinyl alcohol copolymer to an hydroalcoholic solution kept under stirring (at 100 rpm and 80 C.). Following the solubilization of the polymer, the resulting formulation has been spray-dried, and if required has been further submitted to jet-milling treatment in order to obtain monodispersed capsules with a Volume Mean Diameter of 5 m (20%) and a D90 lower than 10 m (where D90 is defined as the particle dimension at 90% of the cumulative particle size distribution). This formulation was then added to an aqueous formulation of the low-ethylene EVOH copolymer with an ethylene content lower than 15 mol %, in order to get the final aqueous dispersion with the aimed gas barrier properties. Finally, for the preparation of the lacquer-coated barrier laminate, the dispersion has been casted using a spiral bar, the solvent has been evaporated and the obtained coating submitted to a baking process at a temperature between 80 C. and 150 C.

[0031] The comparative samples 1, 2 and 3 have been prepared with the above-described method but using relative ratios between the EVOH copolymers outside the presently claimed range.

[0032] Comparative sample 4 has been prepared according to EP 1816159. Specifically, a first solution (A) has been prepared by the solubilization of acrylic acid and NaOH in H.sub.2O at 80 C. under stirring. For the second solution (B), the amount of EVOH 27 mol % has been solubilized in 2-propanol and H.sub.2O at 80 C. under stirring. Subsequently, the first solution (A) has been injected into the second one (B) and the resulting solution was cooled at 5 C. for 12 hours and then mixed with a solution based on low-ethylene EVOH (15 mol %) and subsequently casted.

TABLE-US-00001 TABLE 1 List of Samples and Comparative Samples. high- low- high- OTR high- ethylene eth- ethylene/ (cm.sup.3 day.sup.1 ethylene EVOH ylene low- m.sup.2) EVOH amount EVOH ethylene Thickness 80% RH, OTR/ Sample (wt %) (mol %) (wt %) EVOH (m) T = 23 C. m A 30 27 70 0.43 5.0 2.4 0.5 B 33 27 67 0.50 4.0 2.6 0.6 C 33 32 67 0.50 7.0 4.3 0.6 D 33 38 67 0.50 6.0 6.0 1 E 35 27 65 0.54 5.0 4.2 0.8 F 40 27 60 0.67 5.0 3.1 0.6 G 33 27 67 0.50 10.0 1.4 0.1 H 33 27 67 0.50 15.0 <1 0.07 C1 0 27 100 0 5.0 65 13 C2 25 27 75 0.33 5.0 30 6 C3 100 27 0 5.0 >100 >20 C4 4.06 27 2.64 1.54 4.0 10.5 2.6

[0033] Sample compositions A to H are in accordance with the present invention and the relative OTR values for unit of thickness (OTR/m) are much better compared with the values of Comparative samples 1, 2 and 3, characterized by a different ratio between the two EVOH components, as well as with Comparative sample 4 which was prepared according to EP 1816159.

[0034] The obtained results for all the above samples and comparative samples (summarized in table 1), point out that a weight ratio between the high- and low-ethylene content EVOH outside the range claimed by the present invention, either lower than 0.4 or higher than 0.7, leads to oxygen permeability values not suitable for a film with a reduced thickness (i.e. lower than 10.0 m) and high gas barrier requirements in high humidity conditions.

[0035] As representatives of the secondary technical effects that can be obtained by using compositions according to the present invention, tables 2 and 3 show the observed values of Transmittance, Haze and CO.sub.2 permeation rates for some samples.

TABLE-US-00002 TABLE 2 Optical properties OTR Thickness [cc day.sup.1 m.sup.2] Transmittance Haze Sample [m] 80% RH, T = 23 C. (%) (%) B 4.0 2.6 >90 49.2 G 10.0 1.4 >90 82.8 H 15.0 <1 >90 >80

[0036] The CO.sub.2 permeation rates were measured by exposing both surfaces of the sample at 50% RH (50% RH/50% RH) and then increasing the relative humidity on the lacquer-coated surface of the barrier laminate to a value of 80% RH (80% RH/50% RH).

[0037] In particular, the experimental data have shown the ability of the coating obtained according with the composition of the present invention to act also as a CO.sub.2 barrier, in different humidity conditions, with better performance if compared to the prior art (Sample B versus Comparative sample 1).

TABLE-US-00003 TABLE 3 CO.sub.2 barrier properties high-ethylene EVOH/ CO.sub.2TR CO.sub.2TR low-ethylene [cc day.sup.1 m.sup.2] [cc day.sup.1 m.sup.2] Sample EVOH 50% RH, T = 23 C. 80% RH, T = 23 C. C1 0 26 500 B 0.5 6 50