Modified polyvinyl alcohol coating with enhanced performance under humid conditions

Abstract

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

Description

[0001] The present invention relates to a composition comprising water, a layered material and a modified polyvinyl alcohol. The present invention further relates to a method of improving barrier properties of a substrate, a sheet or film coated with said composition, and the use of said sheet or film for food packaging.

[0002] International patent application WO 2022 / 152793 A1 describes a synthetic layered material which is easily delaminated into individual clay platelets and provides good barrier properties when included in an aqueous coating composition comprising an organic polymeric binder.

[0003] European patent application EP 2263869 A1 relates to a gas barrier film having high gas barrier properties comprising a layer of a resin composition having dispersed swellable inorganic layered silicate. In some embodiments, the layer of resin composition comprises an ethylene-vinyl alcohol based polymer.

[0004] The coatings described in these documents generally provide sufficient barrier properties. However, it has been found that the barrier properties decrease at high relative humidity. A severe decrease in barrier properties at high relative humidity is undesirable. Acceptable barrier properties should be maintained under various conditions. The present invention is to provide a composition for a barrier coating which exhibits a reduced decrease in barrier properties at high humidity.

[0005] The present invention provides a composition comprising

[0006] a) water,

[0007] b) a layered material having the composition Nax[Mg3-z Liy]Si4O10(T)2, wherein

[0008] x is in the range of 0.4 to 0.8,

[0009] y is in the range of 0.0 to 0.8,

[0010] z is in the range of 0.2 to 0.8,

[0011] T independently represents F or OH at each occurrence, and

[0012] x + (3-z) + y < 4,

[0013] 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 more than 0.10°, and wherein the layered material has a Z-average particle size of 500 nm or more, determined on an aqueous dispersion of the material containing up to 1.5 wt% of the material by dynamic laser scattering, and

[0014] c) a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises polymerized repeating units of an olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms and optionally one or two hydroxyl groups.

[0015] The composition according to the present application enables the preparation of coatings having very good barrier properties at low relative humidity and a reduced decrease of the barrier properties at high humidity. Improved barrier properties mean a reduction of the permeation of gases and liquids through the layer. Examples of gases whose permeation is reduced include oxygen, carbon dioxide, hydrogen, water vapor and nitrogen. A reduction of the permeation of these gases is of particular importance in the field of packaging of food and beverages, pharmaceutical and health care products, cosmetics and personal care products, and other non-food applications such as gas storage or corrosion protection of metals.

[0016] The composition of the present application is typically a liquid composition at a temperature of 20°C. The composition comprises water as liquid diluent. Typically, the primary or only liquid diluent used is water. In a preferred embodiment, the composition comprises water in an amount of 50 to 99 wt.%, calculated on the weight of the composition.

[0017] If 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.

[0018] Preferably, the composition contains 50 wt.% or less, 25 wt.% or less, 20 wt.% or less, or even less than 10 wt.% of volatile organic solvents, based on the total weight of water and organic solvents in the liquid formulation. In some embodiments, the aqueous composition contains no organic solvents.

[0019] The composition further comprises a layered material as defined above.

[0020] The layered material is a clay material, and can typically be classified as hectorite. Hectorite is a magnesium based smectite clay. The layered material of the present invention is typically a synthetic clay.

[0021] The layered material has the composition Nax[Mg3-z Liy]Si4O10(T)2, wherein

[0022] x is in the range of 0.4 to 0.8,

[0023] y is in the range of 0.0 to 0.8,

[0024] z is in the range of 0.2 to 0.8,

[0025] T independently represents F or OH at each occurrence, and

[0026] x + (3-z) + y < 4.

[0027] It is preferred that, in at least 50%, more preferably at least 70%, most preferably at least 90% of the cases, T represents F. In some embodiments, in 100% of the cases, T represents F.

[0028] 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 typically 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.

[0029] 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 maximum of more than 0.10°. It has been found that these characteristics make the layered material very easy to delaminate into individual flakes.

[0030] The powder X-ray diffraction pattern is typically taken on a powder sample of the layered material that has been equilibrated with atmospheric moisture at 23 °C at a relative humidity of 43% for at least 12 hours. For measuring the X-ray diffraction pattern, copper K-alpha radiation with a wavelength of 1.541 A is used.

[0031] The position of the 001 peak is defined as the position of the peak maximum.

[0032] The full width at half maximum is defined as the width of the 001 peak, expressed in °. The width of the peak is measured at a height corresponding to half of the maximum intensity value.

[0033] In a preferred embodiment, the full width at half maximum is at least 0.15°, more preferably at least 0.20°. Typically, the full width at half maximum is at most 0.60°, preferably at most 0.50°. In a typical embodiment, the full width at half maximum is in the range of 0.15° to 0.60°, preferably 0.20° to 0.50°.

[0034] The layered material has a Z-average particle size of 500 nm or more, as determined on an aqueous dispersion of the material containing up to 1.5 wt% of the layered material by dynamic laser light scattering. Typically, the aqueous dispersion contains 0.2 to 1.5 wt% of the layered material.

[0035] Dynamic light scattering results are typically expressed in Z-average. The Z-average is produced when dynamic light scattering data is analyzed using the technique of cumulants. The Z-average is not sensitive to noise as the calculation of the Z-average is mathematically stable. The Z-average can be expressed as the intensity based harmonic mean and is shown in the following equation:

[0036]

[0037] Here, S i is the scattered intensity from a particle i and D i is the diameter of the particle i . The result is in the form of a harmonic mean. As this mean is calculated from an intensity weighted distribution, it follows that the Z-average particle size is the intensity weighted harmonic average particle size.

[0038] Typically, the Z-average particle size is in the range of 500 nm to 25000 nm. In a preferred embodiment, the Z-average particle size is at least 1000 nm, more preferably at least 1500 nm, most preferably at least 1800 nm. In a typical embodiment, the Z-average particle size is in the range of 1500 to 25000 nm.

[0039] The layered material is suitably prepared by a process comprising the steps of:

[0040] i) providing a mixture comprising a Na compound, a Mg compound, a Li compound and a Si compound, wherein the compounds are selected from the group consisting of 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,

[0041] ii) heating the mixture to a temperature above 1100 °C to form a homogeneous liquid,

[0042] iii) cooling the mixture to a temperature below 1000 °C over a period of at least 0.5 hours.

[0043] The composition according to the present application further comprises a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises polymerized repeating units of an olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms and optionally one or two hydroxyl groups.

[0044] Polyvinyl alcohol is a well-known polymer. Polyvinyl alcohol is typically prepared by polymerization of vinyl acetate followed by hydrolysis of the ester groups to hydroxyl groups. The hydrolysis is suitably performed by an ester exchange reaction with methanol or ethanol under basic 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 is obtained with residual ester groups. According to the present application, a modified polyvinyl alcohol polymer is used. The modified polyvinyl alcohol polymer comprises polymerized repeating units of an olefinically unsaturated hydrocarbon having 2 to 8 carbon atoms and optionally 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 one or two hydroxyl groups, followed by hydrolysis of the ester groups as described above.

[0045] Examples of suitable monomers for copolymerization include ethylene, propylene, 1-butene, 2-butene, olefins having 5 to 8 carbon atoms, styrene, and 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, also the corresponding esters, for example acetates, can be used as monomers in the polymerization reaction. The corresponding esters will be hydrolyzed to hydroxyl groups in the course of the hydrolysis reaction described above.

[0046] Very good barrier properties have been obtained with a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises polymerized repeating units of at least one of ethylene, 2-butene-1,4-diol and 3-butene-1,2-diol.

[0047] In a preferred embodiment, the modified polyvinyl alcohol polymer comprises the polymerized olefinically unsaturated hydrocarbon monomer having 2 to 8 carbon atoms, optionally one or two hydroxyl groups, in an amount of 1 to 20 mole %, more preferably 2 to 15 mole %, 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.

[0048] As described above, modified polyvinyl alcohol polymers with different degrees of hydrolysis and different levels of residual ester groups can be obtained. For the purposes of the invention, modified polyvinyl alcohol polymers with high degrees of hydrolysis and low content of residual ester repeating units are preferred. Such modified polyvinyl alcohol polymers are generally water-soluble.

[0049] It is particularly preferred to use a modified polyvinyl alcohol polymer containing ester-containing repeating units, calculated based on the total number of repeating units in the polymer, in an amount of 0 to 20 mol%, more preferably 0 to 10 mol%.

[0050] In a typical embodiment, the modified polyvinyl alcohol polymer has a weight-average molecular weight in the range of 10,000 to 200,000 g / mol, preferably 15,000 to 150,000 g / mol. The weight-average molecular weight can be suitably determined by size exclusion chromatography using water as the eluent.

[0051] Suitable modified polyvinyl alcohol polymers used according to the present invention are commercially available. Examples of commercial materials are polymers available under the trade name Kuraray Exceval™. These are copolymers of ethylene and vinyl acetate, wherein the acetate groups have been completely or partially hydrolyzed to hydroxyl groups. Other commercially available polymers are available from Mitsubishi Chemical Corporation under the trade name Nichigo G-Polymer™.

[0052] In a typical embodiment of this composition, the weight ratio of the layered material to the modified polyvinyl alcohol polymer is in the range of 0.5:99.5 to 30.0:70.0. When less than 0.5 parts by weight of the layered material is used, the barrier properties may be insufficient. When more than 30.0 parts by weight is used, the film-forming properties of the composition may deteriorate.

[0053] The compositions of the present invention may contain other ingredients and additives commonly used in aqueous compositions, such as organic cosolvents, crosslinking agents, defoamers, dispersants, UV stabilizers, colorants or pigments, and rheology control agents.

[0054] The compositions of the present invention are particularly well-suited as coating compositions that provide barrier properties to a substrate. To form a barrier coating, the liquid composition is suitably applied to the substrate, and water is allowed to evaporate. The application of the composition to the substrate can be performed using known coating application techniques, such as brushing, rolling, dipping, spraying, or casting. Water evaporation can occur at ambient temperature or at elevated temperatures, for example, in a drying oven. Suitable drying conditions are selected based on the desired drying rate and the heat sensitivity of the substrate.

[0055] Therefore, the present invention also relates to a method for improving the barrier properties of a substrate, the method comprising the steps of applying a composition according to the invention to at least a portion of the surface of the substrate and allowing or causing water to evaporate.

[0056] The substrate to be coated can be any suitable substrate that receives the coating. Examples of suitable substrate materials are polymers such as polyesters, polyacrylates, polyvinyl chloride, and polyolefins, as well as paper, paperboard, and metals. In some embodiments, the substrate is a polymer film, such as a polymer film suitable for food packaging. In other embodiments, the substrate can be in the form of a tray, container, or bottle suitable for food or beverage packaging. In a further embodiment, the substrate can be a metallic substrate to be protected against corrosion, such as an iron, steel, copper, or aluminum substrate. The substrate can also be in the form of a laminate comprising two or more layers of different materials. Furthermore, the coating itself can form an inner, outer, or intermediate layer in a multilayer material.

[0057] In a preferred embodiment, the substrate exists in the form of a fiber-based sheet or a polymer film. Examples of fiber-based sheets include sheets based on natural fibers, particularly plant-based fibers such as wood fibers. Such sheets can be paper sheets, impregnated paper sheets, or paperboard sheets. Synthetic fiber-based sheets may, for example, contain polyester or polyamide fibers. Synthetic fibers can be present in woven or non-woven forms. Examples of suitable polymer films are films based on polyolefins, polyvinyl chloride, polyester, or polycarbonate.

[0058] In a further embodiment, the present invention relates to a sheet or film obtained by applying a composition according to the invention to at least a portion of the surface of a film or sheet and allowing or causing water to evaporate, and the use of said sheet or film for food packaging.

[0059] Example

[0060] Preparation of layered materials according to the present invention

[0061] Step a)

[0062] A layered material of the formula Na0.5[Mg2.5Li0.5]Si4O10F2 was prepared from a mixture of sodium carbonate (68.8 g, 99.9% purity), lithium carbonate (47.8 g, 99.9% purity), magnesium oxide (159.8 g, 98.0% purity), magnesium fluoride (161.4 g, 99.9% purity), and silicon dioxide (623.0 g, 99.9% purity). The raw material mixture was heated to 1530 °C in a platinum crucible to form a homogeneous melt and held at this temperature for 2 hours. The melt was then poured into a ceramic crucible. The ceramic crucible containing the melt was placed in an oven and cooled to 400 °C over 6 hours.

[0063] Step b)

[0064] 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 80°C for 45 minutes. Approximately 0.3 g of unlayered material was then removed from the dispersion by centrifugation (5000 rpm, 10 minutes). The dispersion was dried by evaporating the water, and the residue was ground into powder.

[0065] Determination of X-ray diffraction patterns

[0066] Before determining the X-ray diffraction pattern, the powder of the layered material of the example was exposed to 43% relative humidity at 23°C for 12 hours. The X-ray diffraction pattern was determined on a Panalytical empyrean X-ray apparatus equipped with a Pixcel detector. The measurement sample was set up using the following measurement conditions and apparatus;

[0067]

[0068] The Miller indices (001) are used to determine the full width at half maximum (FWHM). FWHM values ​​are observed from powder X-ray diffraction patterns in Panalytical data viewing software. The results are summarized in Table 1 below.

[0069] Determination of Z-average particle size

[0070] The Z-average particle size of the layered material was determined by dynamic laser scattering on an aqueous dispersion containing 1.0 wt% of the layered material. The instrument was a Malvern Zetasizer NanoZS.

[0071] Use the following measurements and device settings:

[0072]

[0073] The following properties of the material were determined:

[0074] FWHM: 023 °

[0075] Z-average particle size: 10000 nm

[0076] The layer distance d001 calculated by SAXS is 433 nm.

[0077] Application test results

[0078] Raw materials:

[0079]

[0080] Measurement of barrier properties

[0081] The powder of the above-mentioned layered silicate material was dispersed in deionized water for 3 hours at 23°C with Dispermat LC3 (VMA Getzmann) at a stirring speed of 1.5 m / s. Solutions of various polyvinyl alcohols were slowly added to the silicate dispersion for 15 minutes with stirring. The total non-volatile content was 5% by weight. The weight ratio of layered silicate to binder was 0.5:99.5, 5:95, 10:90, and 30:70. The composite dispersion was applied onto a 50 µm polyethylene terephthalate (PET) film using an automated film applicator, Printing Proofer (Erichsen GmbH), with a 50 µm wire bar at an application speed of 20 mm / s. The dry layer thickness of the coating was approximately 1 µm. The coating was dried in a convection oven, Binder FDL 115 (Binder GmbH), at 23°C for 3 hours, and then dried overnight at 80°C. The oxygen transmission rate (OTR) of the coated film was measured at 25°C and 90% relative humidity using a Mocon Ox-Tran (2 / 21) (Ametek GmbH) model. The water vapor transmission rate (WVTR) of the coated film was measured at 25°C and 75% and 90% relative humidity, and at 40°C and 90% relative humidity using a Mocon Permatran W (3 / 61) (Ametek GmbH) model. The samples are summarized in Table 1. The results of the oxygen transmission rate measurements are summarized in Table 2. The results of the water vapor transmission rate measurements are summarized in Table 3.

[0082] Table 1

[0083]

[0084] Table 2

[0085]

[0086] Table 3

[0087]

[0088] As can be seen from Tables 2 and 3, the modified polyvinyl alcohol polymer alone, in the absence of the layered material, does not provide improved barrier properties at high relative humidity compared to the polyvinyl alcohol polymer. This conclusion can be drawn by comparing samples C12 and C13 with samples C2 and C7. These results did not anticipate the improved effect observed when the modified polyvinyl alcohol polymer is combined with the specific layered material used according to the present invention.

[0089] It was therefore particularly surprising to find that, at 90% relative humidity, the oxygen permeability of samples E1 to E8 according to the invention was significantly lower than that of comparative samples C3 to C6 and C8 to C11. It should be noted that an improvement in oxygen barrier properties was observed when the weight ratio of the layered material to the polymer was 0.5 to 99.5. As can be seen from Table 3, for all samples, water vapor permeability increased at high relative humidity. However, for samples E1 to E4 according to the invention, the increase in water vapor permeability at high humidity was less pronounced than that of the comparative samples. Therefore, improved water vapor barrier properties can be obtained using the compositions according to the invention.

Claims

1. 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 represents independently at each occurrence 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 ° 2 theta, and wherein the 001 peak has a full width at half maximum of more than 0.10°, and wherein the layered material has a Z-average particle size of 500 nm or more as determined by dynamic laser scattering on an aqueous dispersion of the material containing up to 1.5 wt.% of the material, and c) a modified polyvinyl alcohol polymer, wherein the modified polyvinyl alcohol polymer comprises polymerized repeating units of an 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 represents F in at least 50% of the cases.

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 wt.%, calculated on the weight of the composition.

7. The composition according to any one of the preceding claims, wherein the modified polyvinyl alcohol polymer contains ester-containing repeating units in an amount of 0 to 20 mol%, calculated on 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 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%, 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 10,000 to 200,000 g / mol.

10. A method of improving the barrier properties of a substrate, the method comprising the steps of applying a composition according to any one of the preceding claims to at least a portion of the surface of a 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 polymeric film.

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

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

Images