Multilayer film of polyvinyl alcohol

Abstract

The present invention relates to a film of PVOH and a layered silicate, which is particularly suitable for the manufacture of food packaging. Therein, the film can be used to manufacture a layer of a multilayer packaging. Therein, the film can form a gas barrier as well as a water barrier, in particular can provide excellent interlayer adhesion.

Description

[0001] This invention relates to films particularly suitable for manufacturing food packaging. Specifically, this film can be used to manufacture multilayer packaging. Furthermore, the film can form gas and water barriers, and in particular provides excellent interlayer adhesion, while also being easily detachable during recycling.

[0002] Universal and important sustainability principles also apply to packaging materials. This paper presents different approaches. One is the use of biopolymers. Another approach is recycling-friendly design, where the packaging construction does not require highly complex, energy-intensive, and cumbersome processing methods during recycling, and produces clean, separated raw materials that can be directly reused after separation. This makes the entire process economical and fully sustainable—a circular process. In this paper, it is important that the material be processed as completely as possible into clean, separated secondary raw materials. For multi-layered materials, it is therefore important to separate the individual raw materials from each other as cleanly as possible without expending too much energy. It is also advantageous to achieve the desired characteristics of the packaging with as few layers or materials as possible.

[0003] Of course, even with packaging designs that facilitate recycling, efforts are still made to use biopolymers rather than fossil-based polymers to ensure that no microplastics are released into the environment, even under "improper" handling. Polymers based on renewable resources or biodegradable polymers are considered biopolymers or bio-based polymers. The most commonly used renewable raw material is cellulose, which is primarily extracted from wood, cotton, and annual plants. However, cellulose has inherent drawbacks that limit its applications: poor solubility in common solvents, making its application as a coating more difficult, and a lack of the thermoplasticity necessary for direct extrusion. Additionally, cellulose is hygroscopic and, under absorbent-desorbent equilibrium conditions, absorbs water vapor or water depending on the relative humidity of the environment, resulting in volume expansion during absorption and volume contraction during release. Therefore, it lacks both strong gas barrier properties and aroma barrier properties. Most importantly, the latter hinders the use of cellulose-based materials in packaging applications for high-moisture foods or in humid environments. To overcome these drawbacks, cellulose is combined with barrier layers. They can meet high requirements (moisture resistance, water and grease resistance, and oxygen permeability (OTR)) and further meet requirements regarding shelf life. However, these layers often pose an obstacle during recycling because they cannot be completely detached from the substrate material, meaning that once detached, they are difficult to separate or require considerable effort to separate.

[0004] Polyvinyl alcohol (PVOH) is frequently used as a barrier layer in cellulose-based multilayer food packaging systems due to its excellent barrier properties against oxygen, CO2, and other polar gaseous / volatile compounds such as flavorings, as it dissolves in the added water during recycling without leaving any residue (no microplastics form in the recycled or wash water). A drawback is its lack of water vapor barrier properties in its current applications.

[0005] Typically, water resistance is improved through cross-linking. However, depending on the cross-linking density, the barrier effect against gases and the degradation rate also decrease. To combine good water resistance with a high barrier level, metal chelating agents can be used alternatively. However, this leads to the formation of reversible networks, which is problematic for environmental reasons due to the accumulation of these metal chelating agents in the wash water, and results in high separation and treatment costs. Non-polar water vapor barrier layers can also be combined with PVOH layers. However, non-polar water vapor barrier layers are difficult to apply to polar PVOH. Good adhesion values ​​can be obtained through non-polar surface pretreatment with corona (plasma) or the application of adhesion promoters. However, this often means more input and higher costs.

[0006] The purpose of this invention is to provide improved oxygen barrier for packaging, especially food packaging, without compromising the recycling of the packaging, or even improving or simplifying recycling.

[0007] At least one of these aspects of the objective is achieved by a membrane comprising:

[0008] 2-95% polyvinyl alcohol by weight

[0009] 3-70% by weight of layered silicates, mixtures of layered silicates, or equivalent minerals

[0010] 0-30% by weight of plasticizer and / or other additives and optional water

[0011] The layered silicate or mixture of layered silicates exists in the form of microparticles and nanoparticles. The particles are preferably sheet-like. This means they are thin but extended. In other words, the length and width of the particles are greater than their thickness. This film is suitable for a variety of packaging applications, especially for food packaging.

[0012] One embodiment of the present invention relates to a film, particularly a film for manufacturing food packaging, comprising:

[0013] 30-89% polyvinyl alcohol by weight

[0014] 10-50% by weight of layered silicates or mixtures of layered silicates

[0015] Plasticizer 1-30% by weight

[0016] It is characterized in that the layered silicate or mixture of layered silicates exists in the form of microparticles and nanoparticles.

[0017] The film according to the invention can also exist in the form of a coating on a substrate material, or in the form of a layer of multilayer material, particularly in the form of a multilayer composite material or a multilayer packaging layer.

[0018] The amounts of polyvinyl alcohol (PVA) and layered silicates can vary depending on which positive properties of the membrane are prioritized. Higher amounts of PVA, especially when combined with suitable plasticizers (including water), increase viscosity and elasticity, but reduce the barrier effect of mineral additives. Essentially, layered silicates have a positive effect on adhesion to polar substrates due to their chemical composition, which contains numerous surface-present OH groups. Therefore, the membrane can contain 2-95% PVA by weight, preferably 20-80% PVA by weight, more preferably 30-70% PVA by weight, and even more preferably 40-65% PVA by weight.

[0019] In this article, polyvinyl alcohol (PVOH) is a synthetic polymer of vinyl alcohol. Vinyl alcohol does not exist as a free monomer; therefore, it is produced through the more or less complete hydrolysis of polyethylene ester. Polyvinyl alcohol is characterized by the vinyl alcohol unit [CH₂CH(OH)₂]. n Typically, polyvinyl alcohol (PVOH) is slightly branched, with a degree of polymerization of about 500 to 2500. PVOH is usually produced by exchanging acetate groups with hydroxyl groups in polyvinyl acetate, for example, through hydrolysis or alcoholysis. The percentage of acetate groups replaced by hydroxyl groups is the degree of hydrolysis of the generated PVOH, characterizing the percentage of hydroxyl groups present in the PVOH relative to the total number of possible hydroxyl groups. The present invention particularly includes films with a PVOH degree of hydrolysis of 60 to 98 mol%, preferably 70 to 95 mol%, more preferably 75 to 90 mol%, and even more preferably 80 to 90 mol%. A PVOH degree of hydrolysis of 86 to 89 mol% is particularly preferred.

[0020] The present invention also includes membranes and materials with PVOH molecular weights of 13,000 to 80,000, preferably 15,000 to 60,000, and more preferably 30,000 to 50,000. The PVOH used preferably has good solubility at low water temperatures. Preferably, an aqueous solution of at least 4% can be prepared using the PVOH of the present invention at 20°C. By adding microparticles and nanoparticles of layered silicates, the lower water barrier properties of the cold-soluble PVOH (with the aforementioned advantages) can be compensated for by its absolute impermeability to most gases. Thus, good barrier properties are combined with good solubility in cold water.

[0021] PVOH is a water-soluble plastic and, depending on its degree of hydrolysis, is biodegradable in aqueous environments. PVOH plastics are characterized by high tear strength and elasticity. These properties depend on air humidity because the plastic absorbs water. Depending on their composition, they have a controllable water dissolution temperature of 5-90°C. It is preferred if an aqueous solution of at least 4% PVOH of the present invention can be prepared at 20°C. One possible embodiment of the membrane of the present invention is soluble in water at a maximum of 40°C, preferably 20°C. In one embodiment, the PVOH portion of the membrane can be completely dissolved in water. In dissolved form, it can be processed and recycled, or alternatively, it can be completely degraded into water (H2O) and carbon dioxide (CO2) due to the action of microorganisms and bacteria. No toxic intermediate compounds are produced herein due to the chemical composition. Compared to non-degradable polymers (whether fossil-based or bio-based), water-soluble PVOH particles and products do not produce microplastics once dissolved.

[0022] Silicates composed of vertices-shared SiO4 tetrahedral layers are called layered silicates (also known as foliated silicates or leaf silicates). These layers or bilayers are not interconnected into a lattice via further Si-O bonds. Possible layered silicates for the films according to the present invention are bentonite, montmorillonite, lithium montmorillonite, pyrophyllite, and Al2[(OH)2|Si4O 10 [The following are suitable materials:] apophyllite, muscovite, phlogopite, and talc, with talc being the preferred choice due to its good usability. Montmorillonite is also suitable.

[0023] One embodiment relates to a membrane in which layered silicates in the form of microparticles and nanoparticles are present as a mixture of talc and related similar layered silicates such as montmorillonite, wherein the microparticles may consist of talc and the nanoparticles may consist of another layered silicate such as montmorillonite. Another embodiment relates to a membrane in which layered silicates in the form of microparticles and nanoparticles consist solely of talc.

[0024] Mineral talc, also known as powdered talc, has the chemical composition Mg3[(OH)2|Si4O 10 Therefore, from a chemical perspective, it is magnesium silicate hydrate.

[0025] The synthesis of talc microparticles and nanoparticles can be based on physical and chemical methods. Regarding physical methods, particles are produced by reducing the size of the starting material, for example, through milling after extraction (a top-down approach). However, talc can also be synthesized (a bottom-up approach). It has been found that it is advantageous if the nanoparticles used are chemically synthesized, as a more uniform size distribution and improved stratification can be achieved.

[0026] To influence membrane properties in a targeted manner, the amounts of components can be adjusted. Due to its hydrophilic properties, polyvinyl alcohol (PVA) is suitable as a barrier layer for oils and mineral oils. The hydrogen bonds between polymer chains, combined with the crystalline structure, give PVA excellent barrier properties against oxygen, nitrogen, carbon dioxide, and organic solvents. In general, a higher solid-matter share is possible due to the use of layered silicates in the PVOH solution. This allows for greater layer thickness, and the method of manufacturing the coating with less water is energy-efficient. Furthermore, a significantly higher oxygen barrier value can be obtained compared to using pure PVOH, while maintaining a comparable layer thickness. Additionally, the proportion of the total oil-based mixture is significantly reduced due to the addition of bio-based plasticizers and natural minerals.

[0027] The mixing of PVOH with layered silicates significantly improves adhesion to other materials, particularly similarly modified nonpolar materials. In membrane fabrication, higher processing stability (due to a significant reduction in foam formation) and fewer defects are achieved. More stable mixtures are also obtained, where, given a high proportion of (multiple) layered silicates, the solid portion exhibits no stratification or sedimentation behavior.

[0028] To maximize adhesion-promoting properties, moisture barrier properties, and gas barrier properties, it has been found advantageous for the film to contain 25-70% polyvinyl alcohol by weight, preferably 30-65% by weight, and even more preferably 35-55% by weight. The amount of (various) layered silicates (the sum of microparticles and nanoparticles) can be 3-70% by weight, preferably 10-50% by weight, more preferably 15-40% by weight, and even more preferably 18-30% by weight.

[0029] For all embodiments described herein, it is preferred if the microparticles have a diameter of 0.3-5 μm and the nanoparticles have at least one size less than 100 nanometers. One embodiment of the invention relates to a membrane in which the maximum diameter of the microparticles is 0.3-10 μm, preferably 0.3-5 μm, and more preferably 0.5-4 μm. The microparticles can be characterized more precisely by their maximum and average (median) particle sizes. Here, it is preferred that the maximum particle size (d98%) is less than 15 μm, preferably less than 12 μm, and more preferably less than 10 μm. The median particle size (d50%) can be in the range of 0.5 μm to 5 μm, preferably 1 μm to 2.5 μm. The microparticles can be regular, irregular, layered, or shaped in an extended or sheet-like manner. If, in the case of microparticles, these are irregularly shaped particles, the ranges specified above relate to an equivalent diameter, which has been determined by comparing the physical properties of the particles (such as, for example, their sinking velocity in a liquid) with those of a sphere of corresponding diameter.

[0030] In this document, the term "nanoparticle" refers to a particle having a size of at least 100 nm. The term "nanoparticle" includes materials composed of solid particles, which may exist individually or as components of aggregates or agglomerates. One embodiment of the invention relates to a membrane in which the maximum diameter of the nanoparticles is 1-100 nm, preferably 2-80 nm, and more preferably 5-50 nm. Nanoparticles can be more precisely characterized by their maximum and average (median) particle size. Here, it is preferred that the maximum particle size (d98%) is less than 100 nm. The median particle size (d50%) can be in the range of 2 to 50 nm.

[0031] Nanoparticles can have a sheet-like shape, with one or two external dimensions less than 100 nm and another external dimension ranging from 2 to 50 nm. This smaller external dimension is preferably the thickness or height of the nanoparticle, which is therefore in the range of 2 to 50 nm, preferably 8-25 nm, and more preferably 10-20 nm. Preferably, the thickness of the nanoparticle is in the range of 5 to 50 nm, and the length ratio of the longest external dimension to the thickness is in the range of 20,000 to 5, preferably 5,000 to 20, and ideally 500 to 50. This relates to single, non-aggregated nanoparticles.

[0032] In the membrane according to the invention and in a single layer of the membrane or multilayer material, the weight percentage of microparticles to nanoparticles can be from 60:40 to 95:5. Here, a range of 70:30 to 90:10 or 75:25 to 85:15 is preferred.

[0033] Substances that make films or layers, and the materials made from them, softer, more flexible, and more supple are used as plasticizers. They increase plasticity and reduce viscosity.

[0034] In the context of this invention, plasticizers may be selected from glycerol, glyceryl esters, sorbitol, propylene glycol, triethyl citrate, and 2-methyl-1,3-propanediol. Glycerol is preferred. Plasticizers whose effects are based on intermolecular interactions are superior to those that act via copolymerization. For this reason, the remaining (equilibrium) water also acts as a plasticizer.

[0035] The membrane according to the invention may contain a solvent, preferably water, and additional additives, in addition to the components already mentioned (PVOH, layered silicates, and plasticizers). Due to evaporation caused by pressure loss at the die head, the foam membrane can be manufactured specifically by adding water prior to melt processing at processing temperatures significantly above 100°C.

[0036] The solvent may comprise up to 90% by weight of the composition from which the membrane is made. The membrane according to the invention may have up to 15% by weight, preferably up to 5% by weight, and more preferably up to 2% by weight of water, that is, a water content of 1-15% by weight, and more preferably 2-10% by weight of water.

[0037] Additional additives may comprise up to 2% by weight of the membrane of the present invention. Preferably, the unmentioned additives comprise less than 1% by weight, or the additive content is 0.1-1% by weight, and more preferably 0.01-0.5% by weight. Possible additives include other polymers, stabilizers such as light stabilizers, pigments, and dyes. However, due to the optimization of the recycling process, which is also a matter of the purity of the recycled materials, it is also advantageous if no additional additives are present and the membrane consists only of PVOH, (various) layered silicates, and plasticizers.

[0038] Therefore, one embodiment relates to a film, particularly a film for manufacturing food packaging, which comprises or is composed of the following components:

[0039] 30-70% polyvinyl alcohol by weight

[0040] 15-40% by weight of layered silicates or mixtures of layered silicates

[0041] Plasticizer 5-30% by weight

[0042] 0-2% by weight of additives

[0043] It is characterized in that the layered silicate or mixture of layered silicates exists in the form of microparticles and nanoparticles.

[0044] Another embodiment relates to a film, particularly a film used in the manufacture of food packaging, which comprises or is composed of the following components:

[0045] 30-70% polyvinyl alcohol by weight

[0046] 15-30% by weight of layered silicates or mixtures of layered silicates

[0047] Plasticizer 5-30% by weight

[0048] Solvent content of 0-20% by weight, preferably water.

[0049] It is characterized in that the layered silicate or mixture of layered silicates exists in the form of microparticles and nanoparticles.

[0050] Other embodiments relate to films, particularly films used in the manufacture of food packaging, which contain or consist of the following components:

[0051] 30-80% polyvinyl alcohol by weight

[0052] 20-50% by weight of layered silicates or mixtures of layered silicates

[0053] Plasticizer 5-30% by weight

[0054] Additives at 0-1% by weight, and

[0055] Solvent, preferably water, is 0-5% by weight.

[0056] It is characterized in that the layered silicate or mixture of layered silicates exists in the form of microparticles and nanoparticles.

[0057] Other embodiments relate to films, particularly films used in the manufacture of food packaging, which contain or consist of the following components:

[0058] Polyvinyl alcohol comprises 30-70% by weight, preferably 55-65% by weight.

[0059] 15-30% by weight, preferably 18-25% by weight, of layered silicates or mixtures of layered silicates

[0060] Plasticizer, 5-30% by weight, preferably 15-25% by weight, and

[0061] Solvent, preferably water, is 0-10% by weight.

[0062] The membrane is characterized by being composed of layered silicates or mixtures of layered silicates in the form of microparticles and nanoparticles. Apart from unavoidable impurities, the membrane contains no other additives, said unavoidable impurities being less than 0.1% by weight, preferably less than 0.01% by weight.

[0063] One embodiment of the present invention includes a membrane comprising:

[0064] 4-40% polyvinyl alcohol by weight, preferably 2% PVOH by weight.

[0065] The product comprises 20-80% by weight layered silicate, preferably 8% by weight, containing nanoparticles and microparticles in a 3:1 ratio, preferably talc nanoparticles and microparticles.

[0066] Plasticizer at 0-8% by weight.

[0067] The membrane can be manufactured from a composition comprising the following components:

[0068] 1-10% polyvinyl alcohol by weight, preferably 2% PVOH by weight

[0069] The product comprises 5-20% by weight layered silicate, preferably 8% by weight, containing nanoparticles and microparticles in a 3:1 ratio, preferably talc nanoparticles and microparticles.

[0070] 0-2% plasticizer by weight, and

[0071] It contains 80-90% water by weight.

[0072] These films can be made very thin and have very good oxygen barrier properties or generally very good gas barrier properties. However, they are difficult to deposit into a uniform coating and tend to become brittle after drying, especially when the content of layered silicates is very high. This can be improved with a small amount of plasticizer.

[0073] One embodiment of the present invention includes a membrane comprising:

[0074] 30-50% polyvinyl alcohol by weight,

[0075] A mixture of layered silicates or layered silicates comprising 40-50% by weight, and containing nanoparticles and microparticles in a ratio of 3:1.

[0076] 0-10% plasticizer by weight.

[0077] The membrane can be manufactured from a composition comprising the following components:

[0078] 1-40% polyvinyl alcohol by weight, preferably 15-20% PVOH by weight

[0079] The product comprises 5-40% by weight layered silicates, preferably 20-30% by weight, containing nanoparticles and microparticles in a 3:1 ratio, preferably talc nanoparticles and microparticles.

[0080] 0-10% plasticizer by weight, and

[0081] 50-90% water by weight.

[0082] Another embodiment of the present invention includes a membrane comprising:

[0083] 30-60% polyvinyl alcohol by weight,

[0084] 40-75% by weight of layered silicates or mixtures of layered silicates and microparticles.

[0085] Plasticizers at 6-18% by weight.

[0086] An alternative embodiment of the present invention includes a membrane comprising:

[0087] Polyvinyl alcohol (PVA) of 50-75% by weight, preferably 60-65% by weight.

[0088] The mixture comprises 15-25% by weight of layered silicates or mixtures of layered silicates, preferably 18-22% by weight of layered silicates or mixtures of layered silicates, wherein the mixture contains nanoparticles and microparticles in a ratio of 1:3 to 1:20.

[0089] 10-25% by weight of plasticizer, preferably glycerin, and

[0090] 0-5% water by weight.

[0091] If the ratio of solid substances in these films is PVOH / plasticizer : (multiple) microparticle layered silicates : (multiple) nanoparticle layered silicates = 4 : 3 : 1, then it is preferred.

[0092] These films have been found to be inexpensive and versatile barrier layers. Furthermore, if deposited as a solution or dispersion, they are also suitable as adhesion-promoting layers for multilayer materials. These layers can bond well to a variety of substrates, such as paper, PET film, or PE / PP film.

[0093] Another aspect of the present invention is a method for manufacturing a membrane according to the invention, comprising the following steps:

[0094] - By mixing a solution of polyvinyl alcohol and a plasticizer with a dispersion of microparticles and adding the nanoparticles, a nanoparticle dispersion of layered silicates or mixtures of layered silicates, a microparticle dispersion of layered silicates / multiple layered silicates, and a solution of polyvinyl alcohol and a plasticizer are prepared.

[0095] - Extruding a film of the composition.

[0096] The manufacture of the composition for making the membrane may include the following steps:

[0097] - Dispersions of nanoparticles providing layered silicates or mixtures of layered silicates.

[0098] - Providing a dispersion of microparticles of layered silicates or mixtures of layered silicates.

[0099] - Solutions containing polyvinyl alcohol and plasticizers

[0100] - Mix a solution of polyvinyl alcohol and plasticizer with a dispersion of microparticles.

[0101] - Dispersions with added nanoparticles.

[0102] Water is preferably used as a solvent for dispersions of nanoparticles, dispersions of microparticles, and solutions of polyvinyl alcohol and plasticizers.

[0103] It has been found that the use of a high-speed mixer is particularly useful in the manufacture of dispersions of nanoparticles and microparticles, and in the mixing of such dispersions with solutions of polyvinyl alcohol and plasticizers. Alternatively, the composition can also be manufactured by the following steps:

[0104] - Dispersions of nanoparticles providing layered silicates or mixtures of layered silicates.

[0105] - Provides microparticles of layered silicates or mixtures of layered silicates in powder form.

[0106] - Solutions containing polyvinyl alcohol and plasticizers

[0107] - Mix the solution of polyvinyl alcohol and plasticizer with the powdered particles under stirring.

[0108] - Dispersions with added nanoparticles.

[0109] Using the method described above, a sufficient amount of layered silicate can be added and the particles can be uniformly distributed, which results in an increase in the oxygen barrier value of the produced product (membrane).

[0110] The alternative manufacturing method utilizes the principle of melt mixing (=composite) by directly processing microparticles and nanoparticles into a provided PVOH melt containing plasticizer. The uniform particles produced in this way are therefore easy to meter and can be used in all common melt processing methods, such as multilayer casting or blown films, co-extrusion coatings, and injection molding.

[0111] Therefore, the membrane can be manufactured by thermoforming, injection molding, or blow molding. In the manufacture of multilayer composites, the membrane can be formed as a coating of one of the adjacent layers (e.g., paper or polymer). When using an aqueous solution to form the layer or membrane, the still-wet layer can also be used as an adhesive for another adjacent layer. The membrane according to the invention can also be manufactured by co-extrusion with another layer.

[0112] In membrane manufacturing, it can be advantageous to use no water at all, or at least substantially no water, as this eliminates the need for complex and energy-intensive drying steps. If the membrane is made from anhydrous compositions, these can be manufactured directly or deposited onto a substrate, for example, by melt processing, or directly incorporated into a multilayer membrane as a barrier interlayer by co-extrusion. They can be deposited as a coating, for example, using a slit die. Thus, for example, the precise thickness of the membrane or layer can be set in a targeted manner.

[0113] In the manufacture of multilayer composite materials, the membrane according to the invention can be deposited directly as a coating onto various provided substrate layers (e.g., paper or polymer), or deposited onto a pre-deposited (e.g., aqueously deposited) pre-barrier layer. When an aqueous solution is used to form the layer or membrane, the still-wet layer can also be used as an adhesive for one or more additional supplied mesh materials (paper, foil, aluminum foil, or composite material).

[0114] Another aspect of the invention is a multilayer material, wherein at least one layer of the multilayer material is composed of a membrane according to the invention. In this document, the membrane may form one or more layers of the material.

[0115] The membrane according to the invention, as an intermediate layer in a multilayer material, typically achieves clean separation of adjacent layers. This is made possible by the fact that the membrane dissolves in cold water after the packaging material is reduced in size (shredded). Therefore, various raw materials previously used in multilayer or composite materials, such as different polymers or papers, can first be cleanly separated from each other according to type, and after separation, processing can be carried out (e.g., by flotation according to density), i.e., granulation or dispersion according to the raw materials. Soluble PVOH, including plasticizers, and contained materials can also be purified by filtration, concentration, and recovery. Since the washing step with cold water is an integral part of most established recovery methods, such a method requires little or no modification.

[0116] In addition to the membrane according to the invention, other layers that may be included in the multilayer material of the invention may consist of paper, polymer, or polymer mixtures. Additional additives may also be included. However, it is preferred if these layers consist of at least 95% by weight, preferably 99% by weight, paper, or at least 95% by weight, preferably 99% by weight, polymer. The polymer may be a biopolymer or a bio-based polymer. The polymer may be selected from polyolefins, such as PE (polyethylene), polypropylene (PP), EEA (ethylene ethyl acrylate copolymer or ethylene acrylate copolymer), polybutylene succinate, polyhydroxyalkanoates in homopolymer and copolymer form, such as, for example, polyhydroxybutyrate, polyhydroxyvalerate, and blends thereof, blends of polylactic acid and polyhydroxyalkanoates, or blends of poly(butylene adipate-co-terephthalate) and polylactic acid.

[0117] Polybutylene succinate (PBS) belongs to the polyester family. PBS is an industrially (synthetically) manufactured biodegradable bioplastic. PBS is produced from the synthetic reaction of the starting materials succinic acid and 1,4-butanediol. These starting materials can be manufactured in two ways: based on fossils or derived from glucose. In the past, PBS was obtained only from fossil raw materials, but today, depending on the source of the raw materials, bioplastics can be produced with up to 100% bio-based content and are then also biodegradable. The biopolymer polyhydroxybutyrate (PHB) is a fermentable polyester with properties similar to petrochemically produced polypropylene. It can be manufactured based on sugar and starch, but can also be synthesized from other nutrients such as glycerol and palm oil. PBAT is a biodegradable and compostable polyester copolymer. Polylactic acid is a synthetic polymer (polyester) lactic acid molecule. Preferred polymers are mixtures of PBAT and PLA, particularly mixtures from Bayer's ecovio® (PBAT, PLA) series. Compostable and primarily bio-based polymers offer a variety of advantageous properties, such as good adhesion to a wide range of types of paper and paperboard and temperature stability up to 100°C.

[0118] Many paper products have coatings that are impermeable to fluids or air. Therefore, one aspect of the present invention also relates to multilayer composite materials comprising a paper layer or paper base layer having an impermeable coating, wherein the film according to the invention is located between the paper layer and the impermeable coating.

[0119] The impermeable coating can be composed of PE or copolymers of acrylate and ethylene (ethylene-acrylic acid copolymer; EAA), particularly copolymers of ethyl acrylate and ethylene (EEA). EAA-based barrier varnishes, in particular, exhibit excellent water vapor barrier properties, but they present significant challenges in paper recycling. Therefore, it is advantageous if the EAA varnish can be completely separated from the paper in a very early washing step, leaving no residue in the waste paper. This can be achieved by a membrane or interlayer according to the invention, applied between the paper and the EAA varnish.

[0120] The membrane according to the invention can be dissolved in the cold washing step of the recycling process, leaving two completely separated, previously adjacent layers for further processing. These layers can then be recycled as pure recyclables. In this case, pure means free from contamination due to residues from the other layers. Furthermore, the membrane according to the invention also functions as a gas barrier layer and provides good adhesion.

[0121] Multilayer materials can also consist of a paper layer having a membrane according to the invention as a barrier coating and a fluid-impermeable coating or a more general sealing layer. This can be produced by applying different polymers. Bio-based or biodegradable polymers are preferred. A preferred multilayer material consists of a first layer of paper, an intermediate layer of the membrane according to the invention, and a second layer (fluid-impermeable coating or sealing layer) of a mixture of PBAT and PLA. Alternatively, the second layer can be composed of EEA. However, the second layer can also be composed of PVOH, such as PVOH with low water solubility.

[0122] This material is suitable for producing paper- or cardboard-based packaging and disposable tableware, such as paper cups, cardboard plates, or wrapping paper. The packaging is also particularly suitable for coffee.

[0123] In addition to the possibility of composting the packaging, this material also offers the possibility of paper recycling. PVOH, and thus the intermediate layer of the membrane according to the invention, completely detaches in a cold washing step with water. In this way, the polymer layer is completely separated from the paper without any residue. PVOH can be recycled from water or completely biodegraded. Talc, insoluble in water, precipitates. However, the residue of talc does not hinder the use of paper fibers.

[0124] One embodiment relates to a multilayer material according to the invention, wherein at least one layer of the multilayer material comprises a film according to the invention, and the additional layers comprise or are composed of another polymer. In this document, in addition to the polymer, these additional layers may also comprise a mixture of microparticles and nanoparticles of layered silicates or mixtures of layered silicates, particularly the same layered silicate / multiple layered silicates as the film according to the invention. This increases interlayer adhesion. The film layer according to the invention is preferably a middle layer or intermediate layer of material located between the additional layers. The film according to the invention is particularly suitable as an intermediate layer because it exhibits excellent adhesion to other materials. However, additional adhesion-promoting layers, such as PVOH-based adhesion-promoting layers, may also be present.

[0125] If the membrane according to the invention contains glycerol, it can serve as a barrier layer in a thin-layer multilayer structure of the membrane according to the invention, which does not contain glycerol but has a relatively high proportion of layered silicates. This barrier layer can be attached to one or both sides of the glycerol-containing membrane, allowing for a 4-5 layer structure. The thin barrier layer of layered silicates / multiple layered silicates prevents glycerol from migrating to the outermost (polymer) layers.

[0126] The method for manufacturing the multilayer material according to the invention preferably comprises co-extrusion of different layers. Thus, these layers are bonded together during manufacturing. This has been found to be particularly good for adhesion, especially if all layers are filled with their respective layered silicates of different sizes. Then, it is advantageous to forcefully press the three layers together in a viscoelastic melt state to achieve good adhesion. However, other manufacturing methods can also be applied.

[0127] A further preferred multilayer material consists of a first layer of polymer or polymer mixture, an intermediate layer of the film according to the invention, and a second layer of polymer or polymer mixture. For packaging high-moisture foods, it is advantageous if the first and second layers form a water barrier layer or a water vapor barrier layer. A preferred multilayer material consists of a first layer of PE, an intermediate layer of the film according to the invention, and a second layer of PE or PP. The PE in the first and second layers can be the same. However, the layers can also include different types of PE (HDPE, MDPE, LDPE, LLD-PE).

[0128] The stiffness and temperature stability of multilayer materials can be set depending on the polymer used to form the first or second layer. The thickness of each individual layer also has an impact.

[0129] The film according to the invention can have a thickness of 0.5 μm to 2 mm. Thin layers, particularly adhesion-promoting layers, can be 0.5 to 10 μm thick, while layers forming gas barrier layers, particularly or otherwise, have a thickness of 10 μm to 1 mm, preferably 100 μm to 0.5 mm. The paper layer can be 100 μm to 5 mm thick. Additional polymer layers can be 10 μm to 2 mm thick.

[0130] The first and second layers surrounding the membrane according to the invention may be composed of PBS and / or PHB, and may be relatively thick layers. This multilayer material is temperature stable, waterproof, and has excellent gas barrier properties.

[0131] The multilayer materials or membranes according to the invention are generally, and particularly, suitable for manufacturing capsules for beverage preparation systems, wherein the capsule comprises a capsule wall comprising a multilayer material or membrane. In this context, the capsule is preferably a coffee capsule containing coffee powder. The membrane according to the invention serves to promote adhesion and forms an excellent barrier layer that also protects the aroma of the coffee, preventing oxygen from entering and damaging the aroma. Furthermore, it achieves clean separation of polymers if adjacent layers are made of different polymers.

[0132] The multilayer material of this invention is suitable for single capsules and so-called coffee bags. In particular, the material, consisting of paper, a membrane according to the invention as a barrier layer, and a polymer sealing layer, meets the high requirements for product protection and coffee brewing settings in pressure coffee machines. If the sealing layer is composed of a biodegradable polymer (EEA, ecovio®) or a PVOH-based polymer blend, it can also be composted.

[0133] It has been found that the films according to the invention exhibit excellent adhesion to aluminum layers or foils, or layers or foils with a very high aluminum content. Therefore, they are well-suited as adhesion promoters between aluminum layers and additional polymer or paper layers in multilayer composites. The added layered silicates improve the adhesion between individual layers. Furthermore, by dissolving the films according to the invention in water, the individual layers can be separated from each other very cleanly, as has been described. This is a significant advantage during recycling.

[0134] Therefore, a further preferred multilayer material comprises a first and a second layer of the film according to the invention, and an additional layer composed of aluminum, wherein the aluminum layer is located between the first and second layers of the film according to the invention. Different polymer or paper layers located on the outside may also be added to these three layers. Thus, the layer structure from the outside in is polymer or paper / film according to the invention / aluminum / film according to the invention / polymer.

[0135] Suitable polymers include polypropylene (also known as cast polypropylene-CPP, oriented polypropylene-OPP), polyethylene terephthalate (PET), and polyethylene. In this paper, the innermost layer is preferably made of PE. Possible composite materials may include the following layers (from outside to inside):

[0136] - PP / film according to the invention / aluminum / film according to the invention / PE

[0137] - PET / film according to the invention / aluminum / film according to the invention / PE

[0138] - Paper / Film according to the invention / Aluminum / Film according to the invention / PE

[0139] - Paper / Film according to the invention / Aluminum / Film according to the invention / PP

[0140] These multi-layered materials are excellent for manufacturing bags used to store roasted coffee. They provide excellent aroma protection for months. This, combined with improved recycling, allows for clean separation by type and reuse of individual components.

[0141] Basically, where applicable, what has already been stated in the context of membranes also applies to manufacturing methods, multilayer materials, and capsules or coffee bags. Example

[0142] By using polyvinyl alcohol (Selvol) TM An aqueous solution of 205 (4% ​​by weight) was mixed with an aqueous dispersion of microparticles, and an aqueous dispersion of nanoparticles was added to the resulting mixture to prepare an aqueous composition comprising 60% by weight H2O, 16% by weight PVOH, 4% by weight glycerol, 15% by weight talc (Finntalc M05SL) as microparticles, and 5% by weight talc (Nanolay) as nanoparticles. The components were gradually and uniformly mixed with a provided PVOH plasticizer solution using a high-speed mixer. This solution was deposited as a coating on various known materials and dried. Thus, the membrane consisted of 40% by weight PVOH, 10% by weight glycerol, 15% by weight talc (Finntalc M05SL) as microparticles, and 5% by weight talc (Cloisite®) as nanoparticles. The OTR (Oxygen Transmission Rate) was then measured. OTR is the stable rate at which oxygen permeates through individual membranes (potentially several layers) under certain conditions (temperature and relative humidity). The test conditions were water at 23°C and air humidity at 50%.

[0143] The following results were obtained:

[0144]

[0145] A separate membrane, consisting of 60% PVOH (hydrolysis degree mol% 87.0-89.0; viscosity (cps) 5.2-6.2, Brookfield, according to ISO 2555) by weight, 8% glycerol by weight, 24% talc as microparticles (Finntalc M05SL) by weight, and 8% talc as nanoparticles by weight, was manufactured by mixing an aqueous solution of polyvinyl alcohol (4% by weight) with an aqueous dispersion of microparticles, and then adding the aqueous dispersion of nanoparticles to the resulting mixture. The components were gradually and uniformly mixed with the provided PVOH plasticizer solution using a high-speed mixer. This solution was deposited as a coating on paper (PackPro 7, 80g Brigl & Bergmeister) and dried. The OTR (oxygen permeability) was then measured as previously described.

[0146] The following results were obtained

[0147]

[0148] A membrane comprising 78% PVOH (hydrolysis degree mol% 87.0-89.0; molecular weight 30-50000 D by weight), 2% water by weight, 5% glycerol by weight, 10% talc (Finntalc M05SL) as microparticles by weight, and 3% montmorillonite as nanoparticles by weight was manufactured by mixing an aqueous solution of polyvinyl alcohol (4% by weight) with an aqueous dispersion of microparticles, and then adding the aqueous dispersion of nanoparticles to the resulting mixture. The components were gradually and uniformly mixed with the provided PVOH plasticizer solution using a high-speed mixer. This solution was deposited as a coating onto a PE laminate (60 μm) and paper (PackPro 7, 80g Brigl & Bergmeister) and dried. OTR (oxygen permeability) was measured as previously described.

[0149] The following results were obtained:

[0150]

[0151] Another membrane, consisting of 70% PVOH (98% mol% hydrolysis by weight), 12% glycerol by weight, 14% talc (Finntalc M05SL) as microparticles by weight, and 4% talc as nanoparticles by weight, was manufactured by mixing an aqueous solution of polyvinyl alcohol (4% by weight) with an aqueous dispersion of microparticles, and then adding the aqueous dispersion of nanoparticles to the resulting mixture. The components were gradually and uniformly mixed with the provided PVOH plasticizer solution using a high-speed mixer, and the solution was heated to 80°C. In this study, it was observed that adding significantly more layered silicates was nearly impossible, or resulted in poor bonding, leading to defective coatings. The resulting solution was deposited as a coating on paper (Packpro7, 80g Brigl & Bergmeister) and dried. OTR (oxygen permeability) was measured as previously described. Compared to the membrane of the previous embodiment, this membrane showed no residue-free dissolution in cold water (room temperature) after 30 minutes.

[0152] The following results were obtained:

[0153]

Claims

1. A film, particularly a film for manufacturing food packaging, comprising: 30-89% polyvinyl alcohol by weight 10-50% by weight of layered silicates Plasticizer 1-30% by weight Its features The layered silicate exists in the form of microparticles and nanoparticles, wherein the microparticles have a diameter of 0.3-5 μm and the nanoparticles have at least one size of less than 100 nanometers.

2. The membrane according to claim 1, wherein the layered silicate is Mg3Si4O 10 Talc of (OH)2.

3. The membrane according to claim 1, wherein the degree of hydrolysis of polyvinyl alcohol is 80 to 90 mol%.

4. The membrane according to any one of the preceding claims, wherein the thickness of the membrane is from 0.5 μm to 2 mm.

5. A multilayer material, wherein at least one layer of the multilayer material comprises a film according to any one of claims 1 to 4.

6. The multilayer material according to claim 5, wherein at least one layer of the multilayer material is composed of a film according to any one of claims 1 to 4, and another layer or another multilayer is composed of paper or polymer.

7. The multilayer material according to claim 5 or 6, wherein the film is disposed as an intermediate layer between the other layers.

8. The multilayer material according to any one of claims 5-7, wherein the additional layer comprises polyethylene, polypropylene, ethylene-acrylic acid copolymer, polybutylene succinate, homopolymer and copolymer forms of polyhydroxyalkanoates such as polyhydroxybutyrate, polyhydroxyvalerate and blends thereof, blends of polylactic acid and polyhydroxyalkanoates, or blends of poly(adipic acid-co-butylene terephthalate) and polylactic acid.

9. The multilayer material according to any one of claims 5 to 8, wherein the material further comprises a polyvinyl alcohol-based adhesion promoter layer.

10. The multilayer material according to any one of claims 5 to 7, comprising a paper layer, a film according to any one of claims 1 to 4, and at least one additional polymer or polymer mixture layer, wherein the film according to any one of claims 1 to 4 is located between the paper layer and the additional polymer or polymer mixture layer.

11. The multilayer material according to claim 10, wherein the additional layer is composed of a blend of poly(butylene adipate-co-terephthalate) and polylactic acid or an ethylene-acrylic acid copolymer.

12. The multilayer material according to any one of claims 5 to 7, wherein the first and second layers of the multilayer material are composed of a film according to any one of claims 1 to 4, and the additional layer is composed of aluminum, wherein the aluminum layer is located between the first and second layers of the film according to any one of claims 1 to 4.

13. A capsule for a beverage preparation system, wherein the capsule includes a capsule wall comprising a multilayer material according to any one of claims 5 to 11.

14. A method for manufacturing a membrane according to any one of claims 1 to 4, comprising the following steps: - By mixing a solution of polyvinyl alcohol and a plasticizer with a dispersion of microparticles, and subsequently adding the dispersion of nanoparticles, a composition is prepared comprising a dispersion of layered silicate nanoparticles, a dispersion of layered silicate microparticles, and a solution of polyvinyl alcohol and a plasticizer. - Extruding a film from the composition.

15. A method for manufacturing a multilayer material according to any one of claims 5 to 11, wherein the layers are bonded together by co-extrusion.

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