Modified polyvinyl alcohol coatings with enhanced performance in humid conditions

Abstract

The invention relates to a composition comprising a) water, b) a layered material having the composition Nax[Mg3-z Liy]Si4O10(T)2, and c) a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises repeating units of a polymerized olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups.

Description

[0001] Modified polyvinyl alcohol coatings with enhanced performance in humid conditions

[0002] The invention relates to a composition comprising water, a layered material, and a modified polyvinyl alcohol. The invention further relates to a method of improving the barrier properties of a substrate, a sheet or film coated with the composition, and to the use of the sheet or film for the packaging of food.

[0003] International patent application WO 2022 / 152793 A1 describes a synthetic layered materials which easily delaminate into single clay lamellae, and which provide good barrier properties when included in aqueous coating compositions comprising an organic polymeric binder.

[0004] European patent application EP 2263869 A1 relates to a gas barrier film including a resin composition layer, with a dispersed swellable inorganic layered silicate, having a high gas barrier property. In some embodiments, the resin composition layer comprises an ethylenevinyl alcohol-based polymer.

[0005] The coatings described in these documents generally provide adequate barrier properties. However, it has been found that the barrier properties decrease at high relative humidity. A severe decrease of barrier properties at high relative humidity is undesirable. Acceptable barrier properties should be maintained under various conditions. The invention seeks to provide a composition for barrier coatings, which show a reduced decrease of barrier properties at high humidity.

[0006] The invention provides a composition comprising a) water, b) a layered material having the composition Nax[Mg3-z Liy]Si4O10(T)2, wherein x is in the range of 0.4 to 0.8, y is in the range of 0.0 to 0.8, z is in the range of 0.2 to 0.8, T independent of each occurrence represents F or OH, and x + (3-z) + y < 4, wherein the powder X-ray diffraction pattern of the layered material has a 001 peak in the range of 8.00 to 5.88 ° 2Theta, and wherein the 001 peak has a full width at half of the peak maximum of larger than 0.10°, and wherein the layered material has a Z-average particle size of 500 nm or higher, determined by dynamic laser light scattering on an aqueous dispersion of the material containing at most 1 .5 % by weight of the material, and c) a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises repeating units of a polymerized olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups.

[0007] The composition according to the invention allows for preparation of coatings having a very good degree of barrier properties at low relative humidity, and a reduced decrease of barrier properties at high humidity. Improved barrier properties mean that the permeation of gases and liquids through a layer is reduced. Examples of gases for which the permeation is reduced include oxygen, carbon dioxide, hydrogen, water vapor, and nitrogen. Reducing the permeation of these gases is of particular importance in the field of packaging for food and beverage, pharmaceuticals and healthcare products, cosmetics and personal care products, and other non-food applications, such as gas storage or corrosion protection of metals.

[0008] The composition of the invention generally is a liquid composition at a temperature of 20°C. The composition comprises water as liquid diluent. Generally, the main or only liquid diluent used is water. In a preferred embodiment, the composition comprises water in an amount of 50 to 99 % by weight, calculated on the weight of the composition.

[0009] If so desired, the composition can optionally comprise one or more volatile organic solvents in the liquid phase. Preferred are water miscible organic solvents, for example alcohols having 1 to 3 carbon atoms, such as ethanol.

[0010] Preferably, the composition contains less 50 % or less by weight, 25 % or less by weight, 20 % or less by weight, or even less than 10 % by weight of volatile organic solvents, based on the total weight of water and organic solvent in the liquid formulation. In some embodiments, aqueous composition is free of organic solvents.

[0011] The composition further comprises a layered material as defined above.

[0012] The layered material is a clay material and can generally be categorized as a hectorite. Hectorites are magnesium based smectite clays. The layered material of the invention is generally a synthetic clay.

[0013] The layered material has the composition Nax[Mg3-z Liy]Si4O10(T)2, wherein x is in the range of 0.4 to 0.8, y is in the range of 0.0 to 0.8, z is in the range of 0.2 to 0.8,

[0014] T independent of each occurrence represents F or OH, and x + (3-z) + y < 4.

[0015] It is preferred that in at least 50 %, more preferably at least 70 %, and most preferred at least 90 % of the occurrences T represents F. In some embodiments, T represents F in 100% of the occurrences.

[0016] The ratio of Na, Mg, and Li can vary within the ranges indicated above. In preferred embodiments, the material contains lithium. In these embodiments, y is generally in the range of 0.4 to 0.8. In further preferred embodiments, x is in the range of 0.4 to 0.6, y is in the range of 0.4 to 0.6, and z is in the range of 0.4 to 0.6.

[0017] The powder X-ray diffraction pattern of the layered material has a 001 peak in the range of 8.00° to 5.88° 2Theta, and the 001 peak has a full width at half of the peak maximum of larger than 0.10°. It has been found that these features lead to a very easy delamination of the layered material into single lamellae.

[0018] The powder X-ray diffraction pattern is generally taken on a powder sample of the layered material, which has been equilibrated with atmospheric moisture at a relative humidity of 43 % at 23°C for a period of at least 12 hours. For measurement of the X-ray diffraction pattern use is made of Copper K-alpha radiation having a wavelength of 1.541 A.

[0019] The position of the 001 peak is defined as the position of peak maximum.

[0020] The full width at half of the peak maximum is defined as the width of the 001 peak, expressed in °. The width of the peak is measured at the height which corresponds to half of the value of the maximum intensity.

[0021] In preferred embodiments, the full width at half of the peak maximum is at least 0.15°, more preferably at least 0.20°. Generally, the full width at half of the peak maximum is at most 0.60°, preferably at most 0.50°. In typical embodiments, the full width at half of the peak maximum is in the range of 0.15° to 0.60°, preferably 0.20° to 0.50°.

[0022] The layered material has a Z-average particle size of 500 nm or higher, determined by dynamic laser light scattering on an aqueous dispersion of the material containing at most 1.5 % by weight of the layered material. Generally, the aqueous dispersion contains 0.2 to 1.5 % by weight of the layered material. Dynamic light scattering results are often expressed in terms of the Z-average. The Z- average arises when dynamic light scattering data is analyzed by the use of the technique of cumulants. Since the calculation of the Z-average is mathematically stable, the Z-average is insensitive to noise. The Z-average can be expressed as the intensity based harmonic mean and is shown by the equation below:

[0023] Here, Si is the scattered intensity from particle / and Di is the diameter of particle / . The result is in the form of a harmonic mean. Since this mean is calculated from the intensity weighted distribution, leading to the statement that the Z-average size is the intensity weighted harmonic mean size.

[0024] Generally, the Z-average particle size is in the range of 500 nm to 25000 nm. In preferred embodiments, the Z-average particle size is at least 1000 nm, more preferably at least 1500 nm, and most preferably at least 1800 nm. In typical embodiments, the Z-average particle size is in the range of 1500 to 25000 nm.

[0025] The layered material is suitable prepared by a process comprising the steps of i) Providing a mixture comprising Na compounds, Mg compounds, Li compounds, and Si compounds, wherein the compounds are selected from carbonates, halides, and oxides, and wherein the molar ratio of Na : Mg : Li : Si is in the range of 0.4 to 0.8 : 2.2 to 2.8 : 0.0 to 0.8 : 4.0, ii) Heating the mixture to a temperature above 1100 °C to form a homogeneous liquid, iii) Cooling the mixture to a temperature below 1000°C during a period of at least 0.5 h.

[0026] The composition of the invention further comprises a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises repeating units of a polymerized olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups.

[0027] Polyvinyl alcohol is a well-known polymer. Polyvinyl alcohol is usually prepared by polymerization of vinyl acetate, followed by hydrolysis of the ester groups to hydroxyl groups. The hydrolysis is suitably carried out by a transesterification reaction with methanol or ethanol under alkaline conditions. Commercial grades of polyvinyl alcohol are available with different degrees of hydrolysis. When less than 100 % of the ester groups are hydrolyzed, polyvinyl alcohol with residual ester groups is obtained. According to the present invention, a modified polyvinyl alcohol polymer is used. The modified polyvinyl alcohol polymer comprises repeating units of a polymerized olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups. Such modified polyvinyl alcohol is suitably prepared by copolymerization of vinyl acetate with one or more unsaturated hydrocarbon monomers having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups, followed by hydrolysis of ester groups as described above.

[0028] Examples of suitable monomers for the copolymerization include ethylene, propylene, 1- butylene, 2-butylene, olefins having 5 to 8 carbon atoms, styrene, as well as hydrocarbon monomers having 1 or 2 hydroxyl groups, such as 2-butene-1 ,4-diol and 3-butene-1,2-diol. Instead of the hydroxyl-functional monomers is also possible to use the corresponding esters, for examples acetates, as monomers in the polymerization reaction. The corresponding esters would be hydrolyzed to the hydroxyl groups during the hydrolysis reaction described above.

[0029] So far very good barrier properties have been obtained with modified polyvinyl alcohol polymers wherein the comprises repeating units of at least one of polymerized ethylene, 2- butene-1,4-diol, and 3-butene-1,2-diol.

[0030] In preferred embodiments, the modified polyvinyl alcohol polymer comprises polymerized olefinically unsaturated hydrocarbon monomers having 2 to 8 carbon atoms, optionally having one or two hydroxyl groups, in an amount of 1 to 20 mol-%, more preferably 2 to 15 mol-%, calculated on the total monomers of the modified polyvinyl alcohol polymer. With such polymers a good balance of film-forming properties, water solubility, and barrier properties has been obtained.

[0031] As mentioned above, modified polyvinyl alcohol polymers are available with different degrees of hydrolysis and different degrees of residual ester groups. For use according to the invention, it is preferred to use modified polyvinyl alcohol polymers having a high degree of hydrolysis and a low content of residual ester repeating units. Such modified polyvinyl alcohol polymers are generally water-soluble.

[0032] It particularly preferred to use modified polyvinyl alcohol polymers which contain ester containing repeating units in an amount of 0 to 20 mol-%, more preferably in an amount of 0 to 10 mol-%, calculated in the total number of repeating units in the polymer. In typical embodiments, the modified polyvinyl alcohol polymer has a weight average molecular weight in the range of 10000 to 200000 g / mol, preferably 15000 to 150000 g / mol. The weight average molecular weight may suitably be determined by size exclusion chromatography using water as eluent.

[0033] Suitable modified polyvinyl alcohol polymers for use according to the invention are commercially available. Examples of commercial materials are polymers available under the trade designation Kuraray Exceval™. These are copolymers of ethylene and vinylacetate, wherein the acetate groups have been fully or partially hydrolyzed to hydroxyl groups. Other commercially available polymers are available from Mitsubishi Chemical Corporation under the trade designation Nichigo G-Polymer™.

[0034] In typical embodiments of the composition, the weight ratio of the layered material to modified polyvinyl alcohol polymer is in the range of 0.5:99.5 to 30.0:70.0. When lower amounts than 0.5 parts by weight of layered material are used, the barrier properties may be insufficient. When higher amounts than 30.0 parts by weight are used, the film-forming properties of the composition may deteriorate.

[0035] The composition of the invention may comprise other ingredients and additives commonly used in aqueous compositions, for example organic co-solvents, crosslinkers, anti-foaming agents, dispersing aids, UV stabilizers, colorants or pigments, and rheology control agents.

[0036] The composition of the invention is very suitable as a coating composition providing barrier properties to substrates. For formation of a barrier coating, the liquid composition is suitably applied to a substrate and the water is caused or allowed to evaporate. Application of the composition to a substrate can be carried out by known coating application techniques, such as brushing, rolling, dipping, spraying, or casting. Evaporation of water may occur at ambient temperature, or at elevated temperature, for example in a drying oven. Suitable drying conditions are selected based on the desired drying speed and the heat sensitivity of the substrate.

[0037] Therefore, the invention also relates to method of improving the barrier properties of a substrate, the method comprising the step of a applying the composition according to the invention to at least a part of the surface of the substrate and allowing or causing the water to evaporate.

[0038] The substrate to be coated can be any suitable substrate to receive a coating layer.

[0039] Examples of suitable substrate materials are polymers, such as polyesters, polyacrylates, polyvinylchloride, and polyolefins, as well as paper, cardboard, and metals. In some embodiments, the substrate is a polymer film, for example a polymer film suitable for food packaging. In other embodiments, the substrate may be in the form of a tray, container or bottle suitable for packaging of food or beverages. In still further embodiments, the substrate may be a metal substrate to be protected against corrosion, such as an iron, steel, or copper or aluminum substrate. The substrate may also be present in the form of a laminate, comprising two or more layers of different materials. Furthermore, the coating layer may itself form an inner, outer or intermediate layer in a multi-layer material.

[0040] In preferred embodiments, the substrate is present in the form of a fiber-based sheet or a polymer film. Examples of fiber-based sheets include sheets based on natural fibers, in particular plant-based fibers, such as wood fibers. Such sheets may be paper sheets, impregnated paper sheets, or cardboard sheets. Sheets based on synthetic fibers may contain for example, contain polyester or polyamide fibers. The synthetic fibers may be present in woven or non-woven form. Examples of suitable polymer films are films based on polyolefin, polyvinyl chloride, polyester, or polycarbonate.

[0041] In further embodiments, the invention relates to a sheet or film obtained by applying the composition according to the invention to at least a part of the surface of a film or sheet and allowing or causing the water to evaporate and to the use of the sheet or film for the packaging of food.

[0042] Examples

[0043] Preparation of a layered material for use according to the invention

[0044] Step a)

[0045] A layered material of the formula Na0.5 [Mg2.5 Li0.5] Si4O10 F2 was prepared from a mixture of sodium carbonate (68.8 g, purity 99.9%), Lithium carbonate (47.8 g, purity 99.9 %), Magnesium oxide (159.8 g, purity 98.0 % ), Magnesium fluoride (161.4 g, purity 99.9 %), and silicon dioxide (623.0 g, purity 99.9%). The raw material mixture was heated in a platinum crucible to 1530 °C to form a homogeneous melt and kept at this temperature for 2 hours. After this time the melt was poured into a ceramic crucible. The ceramic crucible with the melt was placed in an oven and cooled to a temperature of 400 °C during a period of 6 hours. Step b)

[0046] After cooling to room temperature, 3.0 g of the layered material prepared in step a) was dispersed in 97.0 g of distilled water by stirring. The aqueous dispersion was heated to a temperature of 80 °C for a period of 45 minutes. Subsequently, about 0.3 g of nondelaminated material was removed from the dispersion by centrifugation (5000 rpm for 10 minutes). The dispersion was dried by evaporation of water and the residue was grinded to a powder.

[0047] Determination of X-ray diffraction pattern

[0048] The powder of the layered materials of the examples was exposed to a relative humidity of 43 % at 23°C for a period of 12 h before determination of the X-ray diffraction pattern. The X- ray diffraction pattern was determined on an X-ray device of Panalytical empyrean with Pixcel detector. The samples were measured using the following measurement condition and device settings;

[0049] The 001 of Miller indices were used to determine full width at half of the peak maximum (FWHM). The FWHM values were observed from powder x-ray diffraction patterns in Panalytical data viewer software. The results are summarized in Table 1 below.

[0050] Determination of Z-average particle size

[0051] The Z-average particle size of the layered materials was determined by dynamic laser light scattering on an aqueous dispersion of the material containing 1.0 % by weight of the layered material. The instrument was a Malvern Zetasizer Nano ZS.

[0052] The following measurement and device settings were used:

[0053] The following properties were determined for the material

[0054] FWHM: 023 ° Z average particle size: 10000 nm

[0055] Layer distance d001 calculated from SAXS: 433 nm

[0056] Application test results Raw materials:

[0057] Measurement of barrier properties

[0058] The powder of layered silicate material described above was dispersed in deionized water under stirring with a Dispermat LC3 (VMA Getzmann) 3 h with 1.5 m / s at a temperature of 23°C. A solution of the respective polyvinylalcohol was added slowly to the silicate dispersion with stirring for 15 min. The total non-volatile content was 5 % by weight. The weight ratio of layered silicate: binder was 0.5:99.5, 5:95, 10:90 and 30:70. The composite dispersion was coated on a 50 pm polyethylene terephthalate (PET) film with a 50pm wire bar using an automatic film applicator Printing Proofer (Erichsen GmbH) with an application speed of 20mm / s. The dry layer thickness of the coating layer was approximately 1 pm. The coating layer was dried 3 h at 23°C and afterwards over night at 80 °C in a convection oven Binder FDL 115 (Binder GmbH). The oxygen transmission rate OTR of the coated films was measured using a Mocon Ox-Tran (2 / 21) (Ametek GmbH) type at 25°C with a relative humidity of 90%. The water vapor transmission rate WVTR of the coated films was measured with a Mocon Permatran W (3 / 61) (Ametek GmbH) type at 25°C with a relative humidity of 75 % and 90% and at 40°C with a relative humidity of 90%. The samples are summarized in Table 1. The results for oxygen transmission rate measurements are summarized in Table 2. The results for water vapor transmission rate are summarized in Table 3.

[0059] Table 1 Table 2 Table 3 From Tables 2 and 3 it can be inferred that the modified polyvinyl alcohol polymers alone, in the absence of layered material, provide no improved barrier properties at high relative humidity in comparison to polyvinyl alcohol polymers. This can be concluded by comparing Samples C12 and C13 with Samples C2 and C7. From these results one would not expect to find improved effects when the modified polyvinyl alcohol polymers are combined with specific layered materials used according to the invention.

[0060] It was therefore particularly surprising to find that at 90 % relative humidity the oxygen transmission rates of Samples according to the invention E1 to E8 was much lower than the oxygen transmission rates of Comparative Samples C3 to C6 and C8 to C11. It should be noted that an improvement in oxygen barrier properties was already observed at a weight ratio of layered material to polymer of 0.5 to 99.5. From Table 3 it can be inferred that the water vapor transmission rate increases for all samples at high relative humidity. However, for the samples according to the invention E1 to E4 the increase in water vapor transmission rate at high humidity is less pronounced than for the comparative Samples. Hence, improved water vapor barrier properties can be obtained with the compositions according to the invention.

Claims

Claims1 . A composition comprising a) water, b) a layered material having the composition Nax[Mg3-z Liy]Si4O10(T)2, wherein x is in the range of 0.4 to 0.8, y is in the range of 0.0 to 0.8, z is in the range of 0.2 to 0.8,T independent of each occurrence represents F or OH, and x + (3-z) + y < 4, wherein the powder X-ray diffraction pattern of the layered material has a 001 peak in the range of 8.00 to 5.88 ° 2Theta, and wherein the 001 peak has a full width at half of the peak maximum of larger than 0.10°, and wherein the layered material has a Z-average particle size of 500 nm or higher, determined by dynamic laser light scattering on an aqueous dispersion of the material containing at most 1 .5 % by weight of the material, and c) a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises repeating units of a polymerized olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms, and optionally having one or two hydroxyl groups.

2. The composition according to claim 1 , wherein the olefinically unsaturated hydrocarbon comprises at least one of ethylene, 2-butene-1 ,4-diol, and 3-butene-1 ,2- diol.

3. The composition according to claim 1 or 2, wherein T in at least 50 % of the occurrences represents F.

4. The composition according to any one of the preceding claims, wherein y is in the range of 0.4 to 0.8.

5. The composition according to any one of the preceding claims, wherein the weight ratio of the layered material to modified polyvinyl alcohol polymer is in the range of 0.5:99.5 to 30.0:70.0.

6. The composition according to any one of the preceding claims, wherein the composition comprises water in an amount of 50 to 99 % by weight, calculated on the weight of the composition.

7. The composition according to any one of the preceding claims, wherein modified polyvinyl alcohol polymer contains ester containing repeating units in an amount of 0 to 20 mol-%, calculated in the total number of repeating units.

8. The composition according to any one of the preceding claims, wherein the modified polyvinyl alcohol polymer comprises polymerized olefi nically unsaturated hydrocarbon monomers having 2 to 8 carbon atoms, optionally having one or two hydroxyl groups, in an amount of 1 to 20 mol-%, calculated on the total monomers of the modified polyvinyl alcohol polymer.

9. The composition according to any one of the preceding claims, wherein the modified polyvinyl alcohol polymer has a weight average molecular weight in the range of 10000 to 200000 g / mol.

10. A method of improving the barrier properties of a substrate, the method comprising the step of a applying the composition according to any one of the preceding claims to at least a part of the surface of the substrate and allowing or causing the water to evaporate.11 . The method according to claim 10, wherein the substrate is present in the form of a fiber-based sheet or a polymer film.

12. A sheet or film obtained by the method of claim 10 or 11 .

13. Use of the sheet or film according to claim 12 for the packaging of food.

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