Flexible coated substrate with barrier and heat-sealing properties

Abstract

Title: Flexible Coated Support with Barrier and Heat-Sealing Properties The invention relates to a flexible coated support (4), intended for the manufacture of a finished product, in particular packaging, the flexible coated support having a flat shape when freely laid flat, this flexible coated support comprising a flexible support containing, by weight, at least 90%, or at least 95%, of a first natural material, this flexible support being coated with a coated layer containing, by weight, at least 50%, or at least 80%, or at least 90%, or at least 95%, of a second natural material formed by at least one heat-sealing polymer, this or these heat-sealing polymers (10) having in particular at least one of the following properties: oxygen barrier, oil / grease barrier, water barrier. Figure for the abstract: Figure 1

Description

Title of the invention: Flexible coated support with barrier and heat-sealing properties

[0001] The present invention relates to a method for manufacturing a flexible support, in particular a paper, having one face (front or back) or two faces (front and back) with a coated layer composed of one or more film-forming barrier and heat-sealing polymers.

[0002] The invention also relates to a coated flexible support. The invention also relates to packaging comprising the coated flexible support according to the invention.

[0003] The use of film-forming polymers is widespread in the field of surface coatings, particularly in the field of coating, lamination or bonding to a substrate, in particular paper or cardboard.

[0004] Indeed, these film-forming polymers make it possible to waterproof a surface in order to make it a barrier to elements such as grease.

[0005] For example, patent application FR 3107529 A describes these film-forming polymers comprising a thermoplastic material based on casein and / or caseinate, intended to coat a layer of paper or cardboard.

[0006] These polymers, for example initially in the form of a solution or a liquid, may or may not require additional treatment allowing for stabilization of functionalities.

[0007] When the surface to be waterproofed is on one side of a flexible support, in particular on a paper of low grammage, for example less than 200 g / m2, whose rigidity of the flexible support is not sufficient to counter the shrinkage induced by these film-forming polymers, the edges of the flexible support tend, after a certain time, to curl up on themselves.

[0008] This tendency of the edges of a flexible support coated with the film-forming polymer(s), initially flat, to rise up and then curl up on each side is defined as a "curl effect" or a "curl" (English terminology).

[0009] The "curl" is all the more important as the retraction induced by the film-forming polymers is significant.

[0010] Generally, the coated flexible substrate obtained using a conventional process is characterized by a very pronounced curl, meaning that the edges curl several times. Excessive curling prevents the final coated flexible substrate from being used under industrial conditions.

[0011] In addition, this type of conventional coated flexible support often requires a multitude of separate layers in order to obtain sufficient barrier properties.

[0012] The invention aims in particular to develop a new coated flexible support.

[0013] The invention thus relates to a flexible coated material, intended for the manufacture of a finished product, in particular packaging, the flexible coated material having a flat shape when freely laid flat, this flexible coated material comprising a flexible material containing, by weight, at least 90%, or at least 95%, of a first natural material, this flexible material being coated with a coated layer containing, by weight, at least 50%, or at least 80%, or at least 90%, or at least 95%, of a second natural material formed by at least one heat-sealing polymer, this or these heat-sealing polymers having in particular at least one of the following properties: oxygen barrier, oil / grease barrier, water barrier.

[0014] Thanks to the invention, it is possible to obtain a flexible, naturally coated substrate having grease and / or water and / or vapor and / or gas barrier properties and / or being heat-sealing. This is particularly advantageous in terms of environmental compliance.

[0015] According to the invention, the finished coated flexible support can contain, by weight, at least 80% or at least 90%, or even at least 95%, of natural materials, when taking into account both the first natural material of the flexible support and the second natural material formed by the heat-sealing polymer.

[0016] According to one aspect of the invention, the heat-sealing polymer(s) forming the coated layer comprise at least one natural wax such as carnauba wax, soy wax, beeswax, pine wax or rice wax.

[0017] According to another aspect of the invention, the heat-sealing polymer(s) forming the coated layer are based on polysaccharides such as alginate or starch, or chitosan or a cellulosic derivative.

[0018] According to one aspect of the invention, the heat-sealing polymer is biodegradable such as a polyhydroxyalkanoate acid (PHA), a polyhydroxybutyrate acid (PHB), a polylactic acid (PLA) or a lignin.

[0019] According to another aspect of the invention, the heat-sealing polymer(s) forming the coated layer comprise: - at least one caseinate and / or at least one casein.

[0020] According to one aspect of the invention, the heat-sealing polymer(s), in particular wax, are present in the coated layer with a percentage by weight of between 1% and 30%, in particular between 5% and 20%, in particular between 10% and 15%, in particular between 5% and 15%.

[0021] According to one aspect of the invention, the weight of the coated flexible support is between 20 and 300 g / m2, preferably between 40 and 100 g / m2.

[0022] The invention further relates to packaging comprising two zones belonging to the same coated flexible substrate as described above, or belonging respectively to two flexible coated supports as described above, these areas being applied against each other by their respective coated faces.

[0023] Thus, the sealing is preferentially carried out from one coated face to another coated face, this sealing also being called flesh-to-flesh sealing. Alternatively, the sealing can be of the flesh-to-skin type.

[0024] According to one aspect of the invention, the heat-sealing polymer is chosen to obtain a sealing force between the areas sealed together which is greater than or equal to 2.5 N / 15mm and preferably greater than or equal to 3.5 N / 15mm.

[0025] The invention also relates to a method for manufacturing packaging comprising the following steps: - provide two areas of flexible coated support as described above, - Seal these two areas together by pressing them against each other the other by applying heat, notably by means of heated jaws, in order to obtain the packaging.

[0026] Sealing can be carried out using flow-pack machines to produce different types of packaging; this is known as heat sealing. Under the effect of heat, the heat-sealing polymer seals the two coated flexible support areas together to create a package. Other technologies can also be used, such as ultrasonic sealing, which allows the heat-sealing polymer to be refined until a hermetic seal is achieved. The sealing can be either vertical or horizontal.

[0027] The manufacturing process may include the step of coating the flexible support on one front side and / or one back side, with one or more water-based sauces containing one or more barrier and heat-sealing film-forming polymers.

[0028] The manufacturing process may then include a drying step of the coated flexible support.

[0029] A distinction is made between "flexible substrate" and "coated flexible substrate." The flexible substrate is raw, not yet coated. The coated flexible substrate corresponds to the flexible substrate that has received the coating layer.

[0030] This is also applicable to any type of flexible support, namely “paper” and “coated paper”.

[0031] Thanks to the process according to the invention, the tendency (“curl”) of the edges of the coated flexible support to curl up on themselves after the manufacture of said coated flexible support is prevented.

[0032] Thus, the process according to the invention allows the industrial manufacture of said coated flexible support in an automated production line, whereas such a coated flexible support with barrier and heat-sealing properties could not be obtained until now due to both the winding effect of the coated flexible support and the application made and the results obtained. The invention makes it possible to obtain a complementarity between barrier and heat-sealing functions, from the level of barrier functions and the natural composition to at least 90% of the coated flexible support.

[0033] This is made possible by the different stages of the process according to the invention, as explained below.

[0034] The drying step(s) of the invention make it possible to dry the coated flexible support to the maximum so that said coated flexible support contains the appropriate residual moisture to obtain a flat support, without surface cracks or other defects which would limit its use in printing or degrade its barrier or heat-sealing functionalities.

[0035] Drying can take place immediately after the deposition of the barrier and heat-sealing layer so that this layer does not yet have time to dry naturally, in order to maximize the stresses to which the elements contained in the layer are subjected.

[0036] Thus, when these effects have compensated each other, the coated flexible support, placed on a flat surface, exhibits satisfactory flatness.

[0037] The heat-sealing barrier film-forming polymer deposited on the coated flexible substrate is sufficient on its own to achieve heat sealing of the coated flexible substrate. In other words, said heat-sealing film-forming polymer does not require an additional adhesive layer or additional polymer layer to achieve heat sealing of the coated flexible substrate.

[0038] Thus, the number of layers required for the coated flexible support is reduced in order to simplify the structure of said coated flexible support, while optimizing the optimal mechanical and chemical properties.

[0039] This is particularly advantageous in that the process according to the invention is more environmentally friendly and more economical than the conventional process involving several layers, because fewer steps, less material, less energy and less time are required to obtain a flexible coated support with optimal properties.

[0040] According to one aspect of the invention, the weight of the flexible support is between 20 and 300 g / m2, is between 20 and 100 g / m2, preferably is between 40 and 100 g / m2.

[0041] According to one aspect of the invention, the surface density of the thermo-sealing film-forming polymer deposit, measured by weight difference between the dry coated flexible support and the dry flexible support, is between 6 and 18 g / m2.

[0042] Within these surface density ranges, the barrier properties can be optimally obtained. The flexible substrate and the coated flexible substrate were dried before weighing to remove any traces of residual water.

[0043] According to one aspect of the invention, it is possible to apply the heat-sealing film-forming polymer at least twice on the front and / or back face of the flexible support so as to obtain a layer of the heat-sealing film-forming polymer.

[0044] For example, in the case of a 10 g / m² heat-sealing film-forming polymer deposition layer, this deposition can be achieved by two successive coatings of the same 5 g / m² polymer. Thus, the heat-sealing film-forming polymer layer has a uniform surface and good sealing.

[0045] According to one aspect of the invention, the drying temperature during is greater than or equal to 100°C.

[0046] According to one aspect of the invention, wherein the deposition method is chosen between coating or printing.

[0047] According to one aspect of the invention, the flexible substrate is selected from paper, cardboard, or any other flexible material composed of a natural polymer existing in nature. This polymer, or these polymers, are thus free from any specific chemical transformation altering their nature. Preferably, the paper has at least one smooth face obtained by at least one of the following methods: friction pressing, calendering, or coating. Advantageously, the flexible substrate contains the first natural material formed by natural fibers. This flexible substrate is, for example, paper made of natural fibers.

[0048] According to one aspect of the invention, the paper is chosen from offset paper, recycled paper, tracing paper, parchment paper, and Kraft paper.

[0049] For example, Kraft paper, whose characteristics are known in themselves, exhibits optimal mechanical resistance in view of the paper weight.

[0050] According to one aspect of the invention, the paper has a white or brown appearance.

[0051] The barrier and heat-sealing polymer is coated homogeneously and has a uniform thickness on the front face of the flexible substrate. Thus, the coating of the barrier and heat-sealing polymer obtained is perfectly even and without marks, scratches, or flaws through which a fluid (gas, liquid) could enter the coated flexible substrate and cause softening or leakage of said coated flexible substrate.

[0052] Among the different coating techniques, the air blade coating machine or the curtain coating machine equipped with a coating nozzle allows precise control of the coating deposition with high quality and ensures a uniform and regular coating on the flexible substrate.

[0053] According to one aspect of the invention, the heat-sealing film-forming polymer has one or a combination of the following properties: oxygen barrier, oil / grease barrier, water barrier, water vapor barrier, and / or antifungal barrier.

[0054] According to one aspect of the invention, the heat-sealing film-forming polymer has one or a combination of the following properties: oxygen barrier, oil / grease barrier.

[0055] According to one aspect of the invention, the heat-sealing film-forming polymer is food-safe.

[0056] According to one aspect of the invention, the heat-sealing film-forming polymer comprises a thermoplastic polymer.

[0057] According to one aspect of the invention, the heat-sealing film-forming polymer has at least one of the following properties: bio-based, biodegradable, compostable. In any event, the coated flexible substrate is advantageously at least 90% natural.

[0058] According to one aspect of the invention, the coated flexible support has at least one of the following properties: bio-based, biodegradable, compostable and / or repulpable.

[0059] According to one aspect of the invention, the coated flexible support has the following properties: bio-based, biodegradable, compostable and repulpable.

[0060] According to one aspect of the invention, the heat-sealing film-forming polymer comprising at least a caseinate and / or a casein having oil / grease and oxygen barrier properties.

[0061] The amount of water in the coating solution (also called coating sauce) depends on the desired viscosity and may depend on the nature of the flexible support.

[0062] According to one aspect of the invention, the viscosity of the coating sauce is less than 250 mPa.s, or less than 200 or 120 mPa.s.

[0063] According to one aspect of the invention, the heat-sealing film-forming polymer further comprises: - water; and - at least one plasticizer other than water.

[0064] According to one aspect of the invention, the heat-sealing film-forming polymer comprises: - at least one water-soluble polymer, namely a polymer soluble in water, preferably soluble in water at room temperature when the mass concentration of the water-soluble polymer is greater than or equal to 2.5%.

[0065] Thus, the heat-sealing film-forming polymer has improved mechanical and chemical properties.

[0066] According to one aspect of the invention, the heat-sealing film-forming polymer is associated with: - at least one water-soluble polymer, namely a polymer soluble in water, preferably soluble at room temperature.

[0067] Thus, the heat-sealing film-forming polymer has improved mechanical and chemical properties.

[0068] Preferably, water-soluble polymers comprise hydrophilic units. For example, water-soluble polymers may comprise heteroatoms such as O or N in their main chain. Water-soluble polymers may also comprise hydrophilic groups such as -OH, -NH2, -NH-, -CO2-, or -SO3-.

[0069] According to one aspect of the invention, the water-soluble polymer is selected from non-ionic water-soluble polymers, amphoteric water-soluble polymers, cationic water-soluble polymers, anionic water-soluble polymers, and mixtures thereof.

[0070] According to one aspect of the invention, the water-soluble polymer is selected from polyvinyl alcohols, polyoxyalkylenes, polyvinylpyrrolidones, poly(meth)acrylic acids, cationic polymers, and mixtures thereof.

[0071] Among water-soluble polymers, we can also mention polyacrylamides.

[0072] According to one aspect of the invention, the components of the coating sauce are selected from polyols, glycerol acetates, glycerol propionates, and mixtures thereof. Examples of polyols include glycerol, hexane triol, mannitol, sorbitol, glycols, including ethylene glycol and their derivatives. Preferably, the components of the coating sauce are selected from glycerol, sorbitol, and mixtures thereof. In one embodiment, the plasticizer is glycerol.

[0073] Thus, the elements of the coating sauce make it possible to increase the mechanical properties of the heat-sealing film-forming polymer in the face of moisture.

[0074] According to one aspect of the invention, the surfactant is selected from lecithin, diacetyl phosphonates, polysorbates. Preferably, the surfactant is lecithin.

[0075] According to one aspect of the invention, the hydrophobic agent can be chosen from:

[0076] - polycarboxylic acid esters;

[0077] - C3-C33 carboxylic acids, preferably C4-C28 fatty acids, and, even more preferentially unsaturated fatty acids in the C6-C28 range; and

[0078] - their mixtures.

[0079] Polycarboxylic acid esters can be derived from at least one polycarboxylic acid and at least one alcohol, preferably a C1-C18 alcohol.

[0080] Among the polycarboxylic acids preferably retained within the framework of the invention, citric acid, hydroxycitric acid, and tartaric acid may be mentioned. malic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid.

[0081] Among the preferred alcohols according to the invention, we can mention C2-C6 alcohols, such as for example ethanol, n-propanol, iso-propanol, n-butanol and tert-butanol.

[0082] According to one aspect of the invention, the hydrophobic agent is selected from triethyl citrate, tributyl O-acetyl citrate, tributyl citrate and mixtures thereof.

[0083] According to one aspect of the invention, the hydrophobic agent is a C3-C33 carboxylic acid, preferably a C4-C28 fatty acid, and even more preferably a C6-C28 unsaturated fatty acid.

[0084] Among the C4-C28 fatty acids retained within the framework of the invention, we can mention caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and mixtures thereof.

[0085] Among the particularly interesting C6-C28 unsaturated fatty acids, we can mention palmitoleic acid, oleic acid, linoleic acid, and their mixtures.

[0086] According to one aspect of the invention, the coated flexible support can be printable and / or printed.

[0087] According to one aspect of the invention, the oil and / or grease barrier property of the heat-sealing film-forming polymer has a Cobb 1800 index of less than 10 g / m², preferably less than 6 g / m², more particularly less than 3 g / m². The Cobb 1800 index is ideally between 1 and 2.5 g / m².

[0088] The Kit level for obtaining the oil and / or grease barrier property of the heat-sealing film-forming polymer is greater than or equal to 7, preferably greater than or equal to 10.

[0089] According to one aspect of the invention, the oxygen barrier property of the heat-sealing film-forming polymer has a permeability level less than or equal to 1000 cm3 / (m2.24h), preferably less than or equal to 100 cm3 / (m2.24h), more particularly less than or equal to 100 cm3 / (m2.24h).

[0090] According to one aspect of the invention, the water barrier property of the heat-sealing film-forming polymer has a Cobb 1800 index less than or equal to 15 g / m2, preferably less than or equal to 5 g / m2, more particularly between 1 and 2.5 g / m2.

[0091] According to one aspect of the invention, the water vapor barrier property of the heat-sealing film-forming polymer has a water vapor transmission coefficient (WVTR) less than or equal to 10 g / (m².24h) and ideally less than or equal to 5 g / (m².24h) under standard conditions (23°C / 50% RH). Under tropical conditions (38°C / 90% RH), the WVTR is less than or equal to 100 g / (m².24h) and ideally less than or equal to 50 g / (m².24h).

[0092] The manufacturing process may include the following steps: a. apply a first coating sauce, in particular water-based, containing one or more barrier and heat-sealing polymers, in particular on the front face; b) apply a second coating sauce, in particular water-based, in particular containing one or more barrier and heat-sealing polymers, in particular on the reverse side; a. dry said coated flexible support.

[0093] The sauces, after drying, form the coated layers of the coated flexible support.

[0094] Thus, the first and second coating sauces, after drying, allow the "curls" to compensate each other so that the coated flexible support has good flatness and good surface homogeneity.

[0095] According to one aspect of the invention, at least one of the first and second coating sauces contains at least one caseinate and / or one casein.

[0096] The first and second water-based coating sauces may exhibit some or all of the characteristics described above in connection with the barrier and heat-sealing film-forming polymer(s).

[0097] According to one aspect of the invention, the first and second coating sauces both comprise at least one caseinate and / or one casein.

[0098] According to another embodiment of the invention, the deposition method is chosen from extrusion-coating and lamination, complexing.

[0099] The heat-sealing film-forming polymer can be deposited as a film with low moisture content, namely less than 8%, onto the front face of the flexible substrate to form a coated flexible substrate. The heat emitted by the deposition machine removes this residual moisture.

[0100] The invention also relates to a coated flexible support obtained by the process according to the invention.

[0101] The invention further relates to packaging comprising the coated flexible support obtained by the process according to the invention.

[0102] According to one aspect of the invention, the packaging comprises a stack of several flexible supports obtained by the process according to the invention.

[0103] According to one aspect of the invention, the packaging is obtained from a coated flexible support by heat-sealing certain areas of the coated flexible support together.

[0104] According to one aspect of the invention, the flexible support has an appearance selected from: white appearance, brown appearance, matte appearance, silk-effect appearance, or glossy appearance.

[0105] According to one aspect of the invention, the packaging is manufactured by processes of lamination, coating, laminating, co-extrusion or extrusion-coating.

[0106] The invention further relates to a packaged product comprising:

[0107] - a content, for example a foodstuff, solid or liquid; and

[0108] - the packaging according to the invention enveloping the contents.

[0109] According to one aspect of the invention, the content is chosen from pharmaceutical, food, chemical and cosmetic products.

[0110] According to one aspect of the invention, the foodstuff of the contents of the packaged product is chosen, for example, from meat, fish, vegetables, fruit, pastries, viennoiseries, food additives, ingredients, dry foods, dry preparations, food powders, tea and herbal tea bags, dried tea leaves, animal feed.

[0111] According to one aspect of the invention, the content is chosen from newspapers, magazines and advertisements.

[0112] Definitions

[0113] By "coating" is meant, for example, a surface treatment consisting of applying a coating, generally liquid, to a substrate. The coating may have a composition such as a film-forming polymer.

[0114] By “complexing”, we mean, for example, a mechanical action enabling the inseparable joining of two or more materials with different mechanical and physico-chemical properties.

[0115] By "lamination" is meant, for example, a mechanical action enabling the application of a film onto a substrate

[0116] By “extrusion-coating”, we mean, for example, the technique of coating a support by depositing a layer of molten polymer onto it by extrusion.

[0117] By "printing" we mean, for example, the application of a coating via a flexographic or gravure printing system.

[0118] By "moisture" is meant the water or water vapor content in a substance. It can be expressed as a mass percentage, namely a ratio of the mass of water to the total mass of the substance.

[0119] The "basis weight" is a quantity characterizing a flexible, uncoated substrate, such as paper, corresponding to its surface mass, that is to say, its mass per unit area. The basis weight includes residual moisture which varies in particular between 4 and 8% of the total weight of the flexible substrate, in particular paper.

[0120] The basis weight of a flexible support such as paper is between 20 and 300 g / m2, preferably between 40 and 100 g / m2.

[0121] A "thin" paper has a basis weight between 10 and 60 g / m2, advantageously between 30 and 50 g / m2.

[0122] By "heat sealing" is meant, for example, a process in which the The edges of the support are welded using heat, with or without direct contact with the support.

[0123] By "heat-sealing" is meant, for example, the quality that a material has of being The seal is achieved through heat sealing without the need for an additional adhesive layer, polymer layer, or additive. In other words, the heat-sealing material itself is sufficient for the heat seal.

[0124] The term "barrier" refers, for example, to properties that protect the contents of a package formed by the support against external aggressions and substances, or that protect the exterior of the package contents. The most common barriers are those against oxygen, oil, grease, water, water vapor, and fungi and microorganisms.

[0125] By "oxygen barrier" is meant, for example, a barrier with a low oxygen permeability level, i.e., less than 100 cm³ / (m².24h) and preferably less than 10 cm³ / (m².24h). This property may be required, for example, for food products that need to be protected from oxidation, such as chocolate, cheese, or dried foods.

[0126] By "oil or grease barrier" is meant, for example, a barrier with a Kit level between 6 and 12. This property may be required, for example, for food products such as pastries or fast food.

[0127] By "water barrier" is meant, for example, a barrier having a Cobb index advantageously less than or equal to 15 g / m², preferably less than or equal to 5 g / m², and for a Cobb duration of 1800 seconds. This property may be required, for example, for food products such as fruits and vegetables and disposable tableware.

[0128] By "water vapor barrier" is meant, for example, a barrier whose water vapor transmission coefficient (WVTR) is less than 10 g / (m².24h) and ideally less than 5 g / (m².24h) under standard conditions (23°C / 50% RH). The WVTR is less than 100 g / (m².24h) and ideally less than 50 g / (m².24h) under tropical conditions (38°C / 90% RH).

[0129] By "antifungal barrier" is meant, for example, a resistant barrier against the proliferation of fungi and microorganisms. This property may be required, for example, for food products such as soft fruits, like strawberries or raspberries.

[0130] The "Cobb" test consists of measuring the amount of water that a flexible substrate, in particular paper, can absorb over a defined period of time. For example, the index Cobbl800 means that the Cobb test was performed for 1800 seconds, or 30 minutes.

[0131] This Cobb 1800 index is expressed in grams per square meter (g / m²). The lower the Cobb 1800 index value, the better the water barrier. Values ​​below 15 g / m² correspond to very good water barriers for Cobb 800.

[0132] This Cobb test is performed by pouring 100 ml of distilled or demineralized water onto a treated paper sample with a surface area of ​​100 cm² for 30 minutes (ISO 535:2014 standard). The difference in weight before and after the test corresponds to the amount of water absorbed and therefore to the Cobb index.

[0133] Measurements of vapor permeation or of the water vapor transmission rate (WVTR) according to English terminology,

[0134] These measurements assess the amount of water vapor that passes through the substrate in 24 hours under predefined temperature and humidity conditions. Generally, these tests are carried out either under "standard" conditions at 23°C / 50% relative humidity (RH), or under "tropical" conditions at 38°C / 90% RH.

[0135] The test is carried out according to ISO 2528. A cup of anhydrous CaC12 is sealed by the support to be tested. The setup is placed in a climate-controlled chamber. Water vapor passing through the support is trapped by the CaC12. The difference in weight of the CaC12 measured between the initial time and that measured after 24 h corresponds to the WVTR value expressed in g / m² / 24 h.

[0136] The lower the WVTR value, the better the water vapor barrier.

[0137] The "Test Kit" makes it possible to determine the resistance of a paper to the penetration of fatty products such as fats or oil.

[0138] This test kit includes, for example, at least 12 reagent mixtures containing varying amounts of castor oil, toluene, and heptane. The test consists of determining the highest mixture number for which there is no penetration or soiling of the surface. The barrier level increases from 1 to 12.

[0139] A drop of the mixture is placed on a sheet, then it is wiped off after 15 seconds, and the appearance of the paper is observed (ISO 16532-2 standard).

[0140] For certain specific applications, more drastic tests can be carried out by increasing the surface area to be tested, and by carrying out tests at high temperature, namely above ambient temperature, or by increasing the proportion of the most aggressive reagent in the mixtures, namely heptane.

[0141] The Cobb oil test is based on the same principle as the aforementioned Cobb water test but this time using castor oil (SCAN-P 37 standard).

[0142] A palm oil impermeability test (ISO 16532-1 standard) can also be carried out; if the results are sufficiently good, the turpentine test can be carried out (ISO 16532-3 standard).

[0143] The term "film-forming" refers, for example, to a material that can be applied in a thin layer, primarily in liquid form, onto a substrate, and which subsequently becomes a solid film, a film, or a sheet. This film-forming material can also be applied in another form, for example, by extrusion coating as a softened or molten material. Generally speaking, "film-forming" refers in particular to the tendency of a material to form a film.

[0144] The term “polymer” means, for example, long-chain molecules with a high molecular weight. A polymer may, in particular, be a substance made up of molecules characterized by the sequence of one or more types of monomer units. A “natural” polymer may include, for example, proteins.

[0145] By "thermoplastic" we mean, for example, a material which becomes malleable and foldable above a given temperature, the glass transition temperature Tg, but which below this Tg becomes hard again, these transformations being reversible.

[0146] By "plasticizer" is meant, for example, a substance that lowers the glass transition temperature Tg of the material.

[0147] By “surfactant”, we mean, for example, an amphiphilic molecule, that is to say, a molecule possessing both hydrophilic and hydrophobic properties.

[0148] By "hydrophobic" is meant, for example, a compound having little affinity for water and tending not to dissolve in it. Typically, it is a predominantly nonpolar compound.

[0149] By "hydrophilic" is meant, for example, a compound having an affinity for water and tending to dissolve in it. Typically, this is a compound having polar groups capable of forming hydrogen bonds.

[0150] By "water-soluble," we mean, for example, that which dissolves in water, preferably at room temperature. The water solubility of a polymer can be measured as follows: a polymer is added to water at a mass concentration of 2.5%. After stirring for 48 hours, the solution is filtered to check for any remaining particles. When no particles are found in the filter, the polymer is considered water-soluble.

[0151] The term “bio-based” means, for example, a material containing all or part of elements of natural or renewable origin. A bio-based material is, for example, paper containing cellulose extracted from trees or plants for various applications.

[0152] By "natural material" is meant material which exists naturally in the environment and which has not undergone chemical modification, in particular material whose chemical structure remains unchanged, even if it has been subjected to a chemical process or treatment or to a physical process of mineralogical transformation, for example to remove impurities.

[0153] By "biodegradable" is meant a material that can be broken down by microorganisms (bacteria, fungi, algae, etc.). The result of this decomposition is the formation of water, CO2 and / or methane and possibly by-products (residues, new biomass) that are not toxic to the environment. For example, this refers to a material that is biodegradable according to the European standard EN NF 13432.

[0154] By "compostable" we mean, for example, a biodegradable product which completes the product cycle according to standard EN 13432.

[0155] According to this EN13432 standard, a material can be classified as "compostable" if it possesses the following characteristics:

[0156] - be able to achieve 90% biodegradation in less than 6 months if it is subjected to an environment rich in carbon dioxide; these values ​​are tested with the standard method EN14046 (also known as ISO 14855);

[0157] - when placed in contact with organic waste for 3 months, the mass the material must consist of at least 90% residues less than 2 mm in diameter; these values ​​are tested with the standard method EN14045;

[0158] - the material must not have negative effects on the composting process;

[0159] - a low concentration of heavy metals;

[0160] - pH values ​​within established limits;

[0161] - a mineral salt content within the established limits;

[0162] - a concentration of volatile solid elements within the established limits;

[0163] - a concentration of nitrogen, phosphorus, magnesium and potassium within the limits established.

[0164] It is noted that a “bio-based” material can be compostable.

[0165] The term "repulpable" means, for example, a fibrous material, in particular paper, in which the fibers can be dispersed in an aqueous medium to produce a pulp. The repulpable material can thus be reintegrated into the papermaking process. This "repulpable" characteristic does not apply to certain polymers such as polyolefins, for example polyethylene, or polypropylene. These polymers are not soluble in water and interfere with the process of dispersing the fibers in an aqueous medium, thus preventing a flexible substrate coated with such polyolefins or polypropylene from being made "repulpable." This "repulpable" characteristic also does not apply to waxes, by For example, polyethylene- or alkane-based waxes, or ester waxes, such as beeswax. These waxes are not water-soluble, thus making it possible to "repulp" a coated flexible substrate containing such waxes.

[0166] By "caseinate" is meant, for example, a casein salt whose counter cation is chosen from the group comprising calcium, potassium, ammonium, sodium and magnesium.

[0167] “Casein” is a milk protein that is mainly obtained by precipitation by adding an acid (acid casein) or rennet (rennet casein) to milk, or by filtration (micellar casein). There are several types of casein in milk, namely alpha, beta, gamma, and kappa caseins.

[0168] Caseinate and casein form a biodegradable, compostable, and food-grade heat-sealing film-forming polymer. Casein and caseinate are also compatible with a bio-based, biodegradable, compostable, and / or repulpable coated flexible substrate.

[0169] Unless otherwise stated, percentages are expressed by mass relative to the total mass of the material. Brief description of the figures

[0170] Other features, details and advantages of the invention will become clearer upon reading the detailed description given below, and several exemplary embodiments given by way of illustration and not limitation with reference to the accompanying schematic drawings, on the other hand, in which:

[0171] [Fig. 1] is a schematic view of the automated manufacturing line for the coated flexible support according to the invention,

[0172] [Fig.2] is a schematic cross-sectional view of coated paper obtained by the process according to the invention,

[0173] [Fig.3] is a schematic cross-sectional view of coated paper obtained by a variant of the process according to the invention,

[0174] [Fig.4] is a schematic cross-sectional view of an assembly of two heat-sealed coated papers.

[0175] Detailed description of the figures

[0176] Figure 1 shows an automated manufacturing line 2 for implementing the process according to the invention to manufacture samples of coated papers 4 having a front side 6 coated 8 with a barrier and heat-sealing film-forming polymer 10 comprising a caseinate and a casein. Reference numeral 10 also designates the coated layer obtained at the end of the process.

[0177] The heat-sealing polymer(s) of the coated layer 10 comprise at least one natural wax such as carnauba wax, soy wax, beeswax, pine wax or rice wax.

[0178] The paper 12 used for coated paper 4 has a weight of 50 g / m2.

[0179] The method according to the invention comprises the following steps:

[0180] a) deposit a coating sauce in order to form the coated layer 10 on the front face 6 of each paper 12;

[0181] b) dry the coated paper 4 so that the moisture content of the coated paper 4 is greater than 5%;

[0182] c) apply water to one reverse side 16 of the coated paper 4 so as to create a difference in humidity between the front side 6 and the reverse side 16 of each coated paper 4; and

[0183] d) dry the coated paper 4.

[0184] Step a) of the process according to the invention is carried out by means of a coating technique which is an air-blade coating machine 18 which includes rollers 22, an air blade 24 and a heat-sealing film-forming polymer tray 26.

[0185] The coating sauce contained in a tray 26 is abundantly deposited on the front face 6 of the paper 12 by one of the rollers 22 which is directly in contact with said heat-sealing film-forming polymer 10.

[0186] The excess of the heat-sealing film-forming polymer 10 is removed by means of an air jet from the air blade 24. This excess is collected in the collection bin 28 arranged to recycle said excess into the bin of the heat-sealing film-forming polymer 10.

[0187] This air blade coating machine 18 allows for high-quality coating deposition and ensures a uniform and regular coating on the paper 12.

[0188] The coating deposit having a surface density of 8 to 12 g / m2, made with this air-blade coating machine 18 makes it possible to give the coated paper 4 the grease and oxygen barrier properties. The oxygen barrier properties are improved compared to the case where the paper 12 is not coated.

[0189] Thus, coated paper 4 has a Cobb index 1800 of the order of 1 to 4 g / m2 and a Kit level of the order of 7 to 12.

[0190] Step b) of the process according to the invention is carried out using a dryer 30.

[0191] This step b) allows the coated paper 4 to dry as much as possible so that said coated paper 4 contains as little residual moisture as possible.

[0192] Following this high-intensity drying process, the coated heat-sealing barrier sauce exerts strong stresses on the paper 12, specifically on some of its fibers, which would cause the coated paper 4, laid flat after manufacturing, to curl. This curling effect is to be avoided.

[0193] Thus, the drying step b) takes place immediately after the application of the coated heat-sealing barrier sauce so that this sauce does not yet have time to dry naturally, in order to maximize the stresses to which the coated layer 10 from the sauce is subjected.

[0194] Step c) of the process according to the invention is carried out with water applied to the reverse side 16 of the coated paper 4 using a rotating roller 22 in contact with water contained in a water tank 32.

[0195] Step d) of the process according to the invention is carried out with a dryer 30.

[0196] During the drying step d), the humidity of the front side 6 being very low, of The water evaporates predominantly from the reverse side 16, causing stress on the fibers forming the paper 12, a stress which will induce a curling effect on the reverse side 16. This curling effect on the reverse side 16 is opposite to the curling effect on the front side 6 so that a compensation of the curling effects on the front side 6 and the reverse side 16 can be obtained. This compensation may require some time for the coated paper 4 to stabilize.

[0197] Thus, when these effects have compensated each other, the paper 12, placed on a flat surface, exhibits satisfactory flatness.

[0198] Figure [Fig.2] schematically represents, in cross-section, a coated paper 4 obtained by the process according to the invention.

[0199] The coated paper 4 having front face 6 and back face 16, has on its front face 6 a coated layer 10 while the back face 16 of said coated paper 4 does not have a heat-sealing film-forming polymer 10.

[0200] Figure 3 schematically represents, in cross-section, a coated paper 400 obtained by a variant of the process according to the invention.

[0201] The coated paper 400 thus obtained has a front face 6 on which a coated layer 50 is deposited and a back face 16 on which a second layer 60 is deposited, the first and second coated layers 50, 60 comprising natural polymers with the compositions presented above.

[0202] Figure 4 schematically represents, in cross-section, an assembly 70 by heat sealing of two coated papers 4 obtained by the process according to the invention.

[0203] Two coated papers 4 having a front face 6 and back face 16, each coated paper 4 having on its front face 6 a coated layer 10, are assembled without the need to insert an additional adhesive layer (not shown) between each layer of the heat-sealing film-forming polymer 10.

[0204] It is noteworthy that the process according to the invention makes it possible to obtain a coated paper 4 intended for packaging, said coated paper 4 being bio-based, biodegradable, compostable and repulpable with mechanical and chemical properties equivalents of a paper coated with a non-biodegradable film-forming polymer (not shown), namely a plastic film-forming polymer commonly used in commerce.

[0205] In particular, said coated paper 4 obtained with the process according to the invention exhibits barrier properties to oil and grease (a Cobb index 1800 of the order of 1 to 4 g / m2 and a Kit level of the order of 7 to 12) and to oxygen (level of oxygen permeability less than 10 cm3 / (m2.24h)) in combination with thermo-sealing properties.

[0206] Furthermore, the process according to the invention allows the industrial manufacture of said coated paper 4 in an automated paper manufacturing line, whereas such coated paper 4 could not be obtained via this manufacturing line until now because of the winding effect of the coated paper 4.

[0207] Furthermore, the process according to the invention makes it possible to reduce the number of layers required for coated paper 4 while making it more ecological, economical and compatible with various applications such as packaging applications, in particular food packaging applications.

[0208] In one embodiment of the invention, the coated layer is based on a natural wax such as carnauba wax, soy wax, beeswax, pine wax or rice wax.

[0209] Preferably, the heat-sealing polymer(s), in particular wax, are present in the coated layer with a percentage by weight of between 1% and 30%, in particular between 5% and 20%, in particular between 10% and 15%, in particular between 5% and 15%.

Claims

Demands

1. A coated flexible substrate (4) intended for the manufacture of a finished product, in particular packaging, the coated flexible substrate having a flat shape when freely laid flat, this coated flexible substrate comprising a flexible substrate containing, by weight, at least 90% or at least 95% of a first natural material, this flexible substrate being coated with a coated layer containing, by weight, at least 50%, or at least 80%, or at least 90%, or at least 95% of a second natural material formed by at least one heat-sealing polymer, this or these heat-sealing polymers (10) having, in particular, at least one of the following properties: oxygen barrier, oil / grease barrier, water barrier, this or these heat-sealing polymers (10) comprising at least one natural wax such as camauba wax, soy wax, beeswax, pine wax or rice wax, this or these heat-sealing polymers, particularly wax,being present in the coated layer with a percentage by weight between 1% and 30%, in particular between 5% and 20%, in particular between 10% and 15%, in particular between 5% and 15%, the basis weight of the coated flexible support (4) being between 20 and 300 g / m2, preferably being between 40 and 100 g / m2.

2. Flexible coated support according to claim 1, wherein the heat-sealing polymer(s) forming the coated layer are based on polysaccharides such as alginate or starch, chitosan or a cellulosic derivative.

3. Packaging comprising two zones belonging to the same flexible substrate coated according to one of the preceding claims or belonging respectively to two flexible substrates coated according to one of the preceding claims, these zones being applied to each other by their respective coated faces.

4. Packaging according to the preceding claim, wherein the heat-sealing polymer is chosen to obtain a sealing force between areas sealed together which is greater than or equal to 2.5 N / 15mm and preferably greater than or equal to 3.5 N / 15mm.

5. A method for manufacturing a package, comprising the following steps: - providing two areas of flexible coated support according to one of claims 1 and 2, - sealing these two areas together by pressing these two areas against each other while applying heat, in particular by means of heated jaws, so as to obtain the package.

6. A method according to the preceding claim, comprising the step of coating the flexible support on one front face and / or one back face, with one or more water-based sauces containing one or more barrier and heat-sealing film-forming polymers, the viscosity of the coating sauce being in particular less than 250 rnPa.s, or less than 200 or 120 rnPa.s.

7. A method according to any one of claims 5 and 6, comprising a drying step of the coated flexible support.

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