Two-layer composition and its use for waterproofing

Abstract

The invention relates to a sealed porous support comprising at least one surface, said surface being covered with a first layer comprising natural latex and a second layer comprising a natural or artificial wax, the first layer being in contact with said at least one surface of said porous support, and said second layer being in contact with said natural or artificial wax. The invention also relates to a method for obtaining such a support. Figure for abstract: no figure

Description

Title of the invention: Two-layer composition and its use for waterproofing

[0001] The invention relates to a two-layer composition and its use for sealing surfaces, in particular porous surfaces.

[0002] Fibrous substrates, such as paper, cardboard, preformed paper containers, fabric and other fiber-based materials, are widely used in packaging operations.

[0003] However, fibrous substrates are porous and therefore do not prevent the penetration of water, steam, solvents, etc. into them. To improve their resistance and impregnation, fibrous substrates have long been coated with a wide variety of compositions, particularly when the substrates are used for food packaging.

[0004] Many coatings of this type are known, for example those described in patent US3632424 which describes the use of a wax or waxes incorporated in a latex and applied to a fibrous substrate as a coating. The latex used is 21 / 76 / 3 ethylene / vinyl chloride / acrylamide latex terpolymer. It therefore requires the transformation of the latex.

[0005] Reference may also be made to application WO2007140009, which again describes a hydrophobic coating capable of covering fibrous materials such as paper or cardboard, these coated materials being impermeable to steam, the materials however being recyclable after covering. The coating is composed of latex derivatives and crystalline lamellar structures, and above all are free of waxes.

[0006] Indeed, beyond the question of waterproofing, the question of the recyclability of materials now takes an important place in the field in question. Also, it is important to consider both the waterproofing of packaging supports, but also to be able to recycle and reuse them.

[0007] The invention therefore aims to resolve these problems identified in the prior art.

[0008] One of the objects of the invention is a porous support made waterproof and which remains recyclable.

[0009] Another object of the invention is to provide a simple and effective method for making porous supports watertight.

[0010] Yet another aim of the invention is to provide a kit making it possible to implement the above-described method, and in particular in the context of packaging in the agri-food sector.

[0011] Also, the subject of the invention is a sealed porous support comprising at least one surface, said surface being covered with a first layer comprising or essentially consisting of natural latex and a second layer comprising or essentially consisting of a natural or artificial wax, the first layer being in contact, in particular by direct contact, with said at least one surface of said porous support, and said second layer being in contact with the first layer, in particular said second layer being exclusively in contact with said first layer.

[0012] The invention is based on the surprising observation made by the inventors that the successive stacking of a layer of natural latex, then a layer of mineral or vegetable wax makes it possible to seal a support, so that this support becomes impermeable to fluids, in particular aqueous liquids with a pH of 1 to 14, or organic solvents.

[0013] In addition, the superposition of the layers allows, by voluntary mechanical action, to easily remove the wax layer from the support to enhance its recyclability. This is particularly appropriate in the context of porous type supports, in particular in the context of fibrous type supports such as paper or cardboard.

[0014] The wax coating of a paper or cardboard support is well known in the state of the art, and widely used in the food industry. However, even if such a coating is very useful, it poses a problem in terms of recyclability of the papers and cardboards thus coated. Indeed, the direct application of waxes on fibrous supports leads to penetration of the waxes between the fibers, which thus makes the recycling of said fibers difficult due to the presence of wax.

[0015] The invention provides a simple solution to this problem by proposing to insert a layer of natural latex between the support and the wax, which will serve as a “barrier” to prevent the wax from penetrating the fibers.

[0016] In the invention, the composition therefore comprises a natural latex. In the context of the invention, we will speak of “natural latex” to designate any latex composition derived from the rubber tree, and which has not undergone treatment aimed at modifying the properties of the polyterpenoid polymers which it contains, as is the case for the manufacture of rubber.

[0017] Natural latex consists mainly of 1,4 cis polyisoprene, proteins and water, the proteins allowing the stabilization of the polymer dispersion in water. It is a macroscopically homogeneous but thermodynamically unstable binary system. Natural evolution over time leads to the irreversible separation of the two phases. This rupture of the pseudo-equilibrium, called coacervation, is necessary for the production of rubber articles but proves very restrictive during the transport or storage of the latex. The dispersed phase is essentially consisting of spherical particles (diameter less than 0.5 qm) surrounded by a peripheral layer of proteins adsorbed at the water-polymer interface. It is this protein film that plays a major role in the stability of the latex.

[0018] However, when talking about natural latex, the addition of ammonia will be accepted, in order on the one hand to protect it from acid coagulation, and on the other hand to avoid its contamination by bacteria. The addition of ammonia to the latex serum has the effect of reducing the detectable protein content. These hydrolysis reactions lead to the formation of ionized long-chain fatty acids which adsorb to the surface of the particles and lead to an increase in the colloidal stability of the latex.

[0019] Among natural latexes, the most widely used grade is latex with a low ammonia concentration, known as “low ammonia”, which comprises approximately 0.2% by mass of ammonia relative to the total mass of latex.

[0020] Another grade of latex is used, so-called “high ammonia” latex, which comprises from about 0.3% to about 0.6% by mass of ammonia relative to the total mass of latex.

[0021] One of the advantages of natural latex in the context of the manufacture of a coating, particularly for paper, is that this material does not disrupt the recyclability of the support, in particular a cellulosic or fibrous support. Indeed, the committee for the evaluation of the recyclability of paper-cardboard packaging issued a favorable opinion in 2015 on the recyclability of packaging containing 65% paper and 15% natural latex. This is notably due to its biodegradable nature and the latter is an asset in the current context of pollution caused by packaging waste.

[0022] In the context of the invention, it is particularly advantageous for the natural or artificial wax to be in a molten form and not dispersed in water.

[0023] Advantageously, or said natural latex is a latex comprising up to 70% by mass of latex particles relative to the total mass of said natural latex.

[0024] It is specified that the above-described support is in direct contact with the first layer of natural latex. This means that the natural latex is in direct contact with the support so that no other layer of material can exist between said support and said first layer.

[0025] The support, once covered with latex, is then covered with a second layer of natural or artificial wax. Here again, the first layer is in direct contact with the second layer, so that no other material is found between said first and said second layer.

[0026] The wax containing or forming said second layer may be of natural or synthetic origin, that is to say resulting from an artificial synthesis.

[0027] For a material to be considered a wax, it must meet the following criteria as defined in Wolfmeier et al. 2012, Waxes - Encyclopedia of Industrial Chemistry, vol. 39, ed. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim:

[0028] - A dropping (melting) point above 40°C.

[0029] - The melt viscosity must not exceed 10000 mPa.s at 10°C above the drop point.

[0030] - The material must be polishable under low pressure and have a consistency and a solubility that strongly depends on temperature.

[0031] - At 20°C, the material must be breakable, hard or crumbly, transparent or opaque. It does not must not be glassy, ​​very viscous or liquid.

[0032] - Above 40°C, the material must melt without decomposing.

[0033] - Above the melting point, the viscosity of the material must decrease at the same time as the temperature increases.

[0034] - Melt generally between 50°C and 90°C (exceptional case observed above 200°C).

[0035] - Generally burn with a flame that produces soot.

[0036] - Be a thermal and electrical insulator.

[0037] In the invention we will distinguish

[0038] - natural waxes which include fossil waxes (coal or petroleum waxes) and non-fossil waxes (animal or vegetable waxes), and

[0039] - synthetic waxes which include partially synthetic waxes (amide waxes) fatty acids) and completely synthetic (polyolefin waxes, such as polyethylene or polypropylene or Fisher-Tropsch or polar synthetic waxes).

[0040] The natural waxes advantageous for the composition according to the invention are the following:

[0041] - Camauba wax (natural vegetable wax): this wax is made up of a mixture aliphatic esters (40%), 4-hydroxycinnamic acid diester (21%), hydroxycarboxylic acid esters (13%), fatty alcohol (12%), 4-methoxycinnamic acid diesters (7%), aliphatic and aromatic acids (5%), terpenes and other compounds 4.4%, etc. It also contains about 1% hydrocarbons. It is one of the natural waxes with high hardness and a high dropping point, generally around 83°C. Advantageously, the camauba wax used has a dropping point of 85°C. It is a dispersion of camauba wax in water with a particle size mainly between 100 and 200nm. The mass percentage of solids is 30%. The surfactant is anionic and the pH is between 5 and 7;

[0042] - Sugarcane wax (natural vegetable wax): Sugarcane produces a wax representing approximately 0.1 to 0.25% of its mass. The sugarcane wax, the refining of which is necessary, is composed of aliphatic esters and sterol esters (78 to 82%), free fatty acids (14%), fatty alcohol (6-7%) and hydrocarbons (3 to 5%). The melting temperature is generally between 68°C and 81°C. The sugarcane wax to be used in the context of the invention is advantageously a wax dispersed in water with an anionic surfactant. The mass percentage of the dispersion is 35%;

[0043] - Hydrogenated vegetable oil: The hydrogenation of vegetable oils makes it possible to obtain almost totally saturated oils whose melting point is higher than that of the non-hydrogenated oil from which they are derived. The hydrogenation reaction is most often carried out between 150 and 200°C, with a pressure between 0.1 and 0.5 MPa and in the presence of a catalyst, often nickel-based. The advantageous hydrogenated vegetable oil is an oil with a dropping point of 75°C. It has been used in dispersed form. The surfactant used is anionic and the mass percentage of hydrogenated vegetable oil is 40%.

[0044] - Beeswax (natural vegetable wax): the wax is a particular natural wax secreted by honey bees (Apis melifera) which is obtained in a conventional way in beekeeping and is composed among other things of hydrocarbons (10 to 20%) having between 23 and 35 carbons. It is often treated with carbon or aluminum or magnesium silicates to eliminate part of its color and its odor

[0045] - Petroleum waxes: Two types of petroleum wax can be distinguished: macrocrystalline waxes, commonly called mineral paraffins, and microcrystalline waxes. Mineral paraffin is mainly composed of linear alkanes and a small proportion of weakly branched isoalkanes and monocyclic alkanes, called naphthenic compounds. According to the European Federation of Wax Producers, the number of carbons constituting the linear alkanes of paraffin is between 18 and 45, and the amount of weakly branched isoalkanes and monocyclic alkanes is between 0 and 40%. Microcrystalline waxes are distinguished from macrocrystalline waxes by a majority proportion of isoalkanes and naphthenic compounds.

[0046] The synthetic waxes advantageous for the composition according to the invention are the following:

[0047] - Polyethylene wax (completely synthetic wax): Polyethylene waxes can be considered as very low molar mass polyethylene. The weight average molar mass does not exceed 37000g.mol1 and is generally around 6000g.mol-l. The kinematic viscosity must not exceed 20000mm2.s 1 to 120°C. Generally the melting point is between 105°C and 115°C. They are manufactured in the same way as PE by radical polymerization of ethylene and the operating conditions (type of reactor, pressure and temperature of the reactor, type and quantity of radical initiator and regulating agent, type of catalyst) determine the structure and molar mass of synthesized PE waxes. It is possible to manufacture polar PE waxes by oxidation of apolar PE wax, or by radical polymerization of ethylene in the presence of polar co-monomers. These polar PE waxes can then be dispersed in water in the presence of surfactants.

[0048] - Fischer Tropsch Wax: Fischer-Tropsch waxes are manufactured by the process of the same name which consists of the synthesis of hydrocarbons from synthesis gas or syngas. The latter being a mixture of carbon monoxide (CO) and dihydrogen (H2). The reaction takes place between 220-240°C at 2 MPa in the presence of a generally iron-based catalyst. Alkanes and alkenes are formed, of which approximately 40% are compounds that will form the wax. They are separated by distillation and condensation then purified and the wax obtained at the end is practically only composed of linear alkanes between 20 and 50 carbons. The viscosity is generally lower than macrocrystalline paraffin but their melting point is higher.

[0049] Advantageously, the second layer, or second layer, comprises or is essentially composed of a wax comprising less than 1% by mass of unsaturated carbon chains.

[0050] Even more advantageously, the second layer, or second layer, is a paraffin layer.

[0051] Also, the invention advantageously relates to a sealed porous support comprising at least one surface, said surface being covered with a first layer comprising or essentially consisting of natural latex and a second layer comprising or essentially consisting of paraffin, the first layer being in contact, in particular by direct contact, with said at least one surface of said porous support, and said second layer being in contact with the first layer, in particular said second layer being exclusively in contact with said first layer.

[0052] In an advantageous aspect, the first layer consists only of natural latex and the second layer consists only of paraffin.

[0053] Even more advantageously, the invention relates to the support described above, where said at least one surface of said support is covered with a first layer of 10 to 80 g.m2 of natural latex, and said first layer is covered with a second layer of 10 to 120 g.m2 of natural or synthetic wax or a mixture of waxes.

[0054] When covering at least one support to be waterproofed, the first layer of natural latex will be deposited at a rate of 10 to 80 g.m2. This means that 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, can be deposited. 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79 or 80 g.m2 of natural latex. The person skilled in the art will be able to determine which is the appropriate quantity for a given medium.

[0055] Once the first layer has been applied to the support, the second layer is applied at a rate of 10 to 120 g.m2. This means that 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, can be deposited. 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 100, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119 or 120 gm 2 of natural or artificial wax.

[0056] A method for making the above-mentioned support is described below.

[0057] In another aspect, the invention relates to a kit or case comprising

[0058] - a composition comprising or consisting essentially of natural latex, and

[0059] - a composition comprising or consisting essentially of a natural wax or artificial.

[0060] The aforementioned kit or case is suitable for carrying out the covering of a porous support, in particular a support permeable to liquids, in particular aqueous liquids having a pH of 1 to 14 or to liquid organic solvents, in order to make the support impermeable.

[0061] Advantageously, the aforementioned kit comprises:

[0062] - a composition comprising or consisting essentially of natural latex, and

[0063] - a composition comprising or consisting essentially of a paraffin wax, or paraffin.

[0064] In another aspect, the invention relates to the use of the aforementioned kit or set, i.e. a kit or set comprising

[0065] - a composition comprising or consisting essentially of natural latex, and

[0066] - a composition comprising or consisting essentially of a natural wax or artificial, especially paraffin wax, or paraffin,

[0067] for sealing a support, in particular a porous support, or a support permeable to liquid aqueous solutions having a pH of 1 to 14 and to certain organic solvents.

[0068] In the invention described above and below, we will speak uniformly of waterproofing and sealing.

[0069] It will be particularly suitable to use the aforementioned kit or set for waterproofing or sealing fibrous type supports, such as paper, cardboard, or one of their derivatives, and textile fibers.

[0070] The invention also relates to a method for waterproofing, or sealing, a surface of a support, said method comprising the following steps:

[0071] - bringing into contact a first composition comprising or essentially made of natural latex with the surface of the support, to obtain a support surface covered with latex,

[0072] - drying the latex-coated support surface at a higher temperature at 40°C in order to eliminate both the water contained in the natural latex composition and in the support, to obtain a dried surface,

[0073] - a step of bringing the dried surface into contact with a wax composition natural or artificial, to obtain a double-covered surface, and

[0074] - a step of cooling the double-covered surface to a lower temperature at the melting point of said natural or artificial wax, to obtain a waterproofed support surface.

[0075] The first step of this process is therefore to apply, or to bring into contact a first natural latex composition on at least one of the surfaces, or all the surfaces simultaneously, of a support.

[0076] Advantageously, when the support to be sealed or waterproofed is thin and flat, such as for example sheets of paper or fibrous fabrics, the contacting of the support with the first composition can be carried out by the following techniques:

[0077] - immersion coating: the support to be waterproofed is immersed vertically in a container filled with the first composition and then always came out vertically, in particular using the so-called elevator technique;

[0078] - curtain coating: the support to be covered is placed on a mobile device under in which there is a reservoir containing the first composition. The reservoir allows, by means of an opening, the first composition to flow at a constant rate under the action of gravity (coating curtain), so that the entire support will be covered with said first composition due to its movement;

[0079] - coating by a sizing press: the support to be coated is passed between two rollers, one of the rollers being immersed in the first composition. During rotation of the roller being immersed in the first composition, said first composition is driven and is applied to a surface of the support to be coated;

[0080] - coating by coating bar: the first composition is applied from non-uniform manner on the support to be covered, and a bar comes to flatten and distribute the first composition over the entire surface of the support to be coated.

[0081] Obviously, other coating techniques well known in the art are applicable by those skilled in the art.

[0082] Once the support is covered, on at least one of its surfaces with the first composition, the support thus covered is dried at a temperature above 40°C, more particularly above 60°C, in particular above 80°C or even 90°C or more. However, it is preferable that this drying is not carried out at a temperature which induces swelling of the film due to drying that is too rapid. Indeed, if the drying is too rapid, the surface of the film will dry first and the water contained in the substrate and in the film that is not completely dried will no longer be able to evaporate; which will cause the film to swell. The maximum drying temperature depends on the quantity of mixture deposited and the ventilation of the oven. For example, a temperature of 160°C in a ventilated oven causes swelling to appear if the mass concentration of the mixture is 40%.Drying conditions must be determined by trial and error in order to know the optimal drying time and temperature depending on the tool used. Advantageously, this drying is carried out in an oven, in particular with ventilation. The purpose of using ventilation is to better distribute the heat and therefore to be able to lower the temperature.

[0083] The objective of this heating step is to remove the water contained in both the first composition and possibly in the support, both of which form the coated support. By removing the water, the first composition will form a film on the surface of the support. The formation of a polymer film on paper from a latex is a complex and multi-step phenomenon. Three main steps are generally distinguished:

[0084] - the reduction in the distance between particles following the evaporation of the solvent,

[0085] - the coalescence of polymer particles, and

[0086] -interdiffusion of polymer chains between adjacent particles. The drying therefore makes it possible to fix the film of composition according to the invention. As demonstrated in the examples below, the drying temperature plays an important role in the film-forming and sealing properties of the composition according to the invention.

[0087] Once dried, the surface of the support covered with the first composition is brought into contact with the second composition comprising or essentially consisting of a natural or synthetic wax. As a result, the surface covered with the first composition will be covered with a second layer, i.e. will be covered with the second composition.

[0088] This second covering can also be carried out by the methods described above which apply mutatis mutandis.

[0089] It is particularly advantageous that the above-described method implements two contacting steps which are soaking steps.

[0090] It will be noted that it is possible to combine the methods so that the first covering (the application of the first layer) is carried out by a first method, and the second covering (the covering by the second composition) is carried out by a second method different from the first method.

[0091] It will be advantageous for the second composition to be liquid or semi-liquid in order to allow it to be brought into contact with the first layer which has been dried on the surface of the support. In the example of paraffin, it will be heated above its melting point, in order to make it liquid and to be able to deposit it uniformly on the first layer.

[0092] Also, after applying the second composition, the whole will be cooled, either by leaving the whole at room temperature (from 17 to 35°C), or by applying a current of cold air (for example at less than 16°C) or by placing the double-covered support in a refrigerated enclosure (at less than 4°C).

[0093] At the end of the above-mentioned process, a support will therefore be obtained which is in particular, before treatment, permeable to fluids, which will have one of its surfaces covered with a first layer of a first composition comprising or consisting essentially of natural latex, this layer itself being covered with a second composition comprising or consisting essentially of a natural or artificial wax, in particular paraffin.

[0094] The invention further relates to a food container, in particular recyclable, in particular made of a fibrous and / or porous material, comprising an internal part capable of receiving a food product and an external part, said container being such that at least the internal part is covered with a first layer of a latex composition, and said first layer is covered with a second layer of natural or artificial wax.

[0095] In other words, the invention relates to a food container, in particular made of a fibrous and / or porous material, consisting of a wall or several walls defining an internal part capable of receiving a food product and an external part, the wall having an internal face exposed to the internal part and an external face exposed to the external face,

[0096] said container being such that the internal face is covered with a first layer of a latex composition, and said first layer is covered with a second layer of natural or artificial wax.

[0097] The above-mentioned method is particularly suitable for covering at least the inner face of a food container intended to receive products edible by humans, such as for example liquids or solids, such as dairy products.

[0098] Also, the food container covers, without being limiting, yogurt or dairy product pots, frozen product containers but also beverage cups intended to be used for hot or cold drinks.

[0099] By way of example, referring to Figure No. 1, a pot 1 is described for receiving a dairy product 2 such as yogurt or cottage cheese. The pot 1 is formed by at least one wall 10, or a wall 10 by making a cylinder or a truncated cone using a sheet of cellulosic material such as paper or cardboard, and a base.

[0100] The wall 10 therefore delimits an interior space 101 in which the food 2 will be placed, and an exterior space. In order to protect the wall 10 from the humidity of the food 2, the internal face 11 of the wall 1 is covered with a first layer 3 of natural latex then this layer of latex is itself covered with a second layer 4 of wax, here paraffin.

[0101] Obviously, it is also possible to cover the external face 12 of the wall 10 with the same arrangement of first and second layers 3 and 4 respectively. This is also the case when the pot 1 is coated with the first and then the second layer 3 and 4 respectively, by an immersion process.

[0102] All configurations making it possible to obtain a food container where at least the covering of the wall 10 in its internal face are covered by the invention.

[0103] More particularly, it is possible to use a sheet of paper or cardboard, and to coat it with the two aforementioned layers, in the order as defined in the invention, and to shape the desired food container using this sheet, so that the part of the covered sheet is exposed to the food when the container is finalized.

[0104] In another aspect, the invention relates to a waterproof textile fibrous material, said textile fibrous material comprising on at least one of its surfaces a layer of natural latex, the natural latex layer itself being covered with natural or artificial wax, in particular paraffin, said layer of wax not being in direct contact with said surface of said textile fibrous material.

[0105] The textile fibrous materials according to the invention are in particular cotton, linen, hemp or wool fabrics, but also synthetic textiles or fabrics obtained by weaving polyamide, polyester, acrylic fibers, etc.

[0106] This list is obviously not exhaustive.

[0107] It is therefore covered by the invention of waterproof textiles, such as for example raincoats, jackets, trench coats, hats, umbrellas, hats or caps, wetsuits, particularly for aquatic activities, bibs, towels, tablecloths, mattress protectors, furniture textiles such as seat, armchair or sofa coverings, or any other textile likely to come into contact with water or an aqueous liquid.

[0108] In another aspect, the invention relates to a waterproof fibrous material, said textile fibrous material comprising on at least one of its surfaces a layer of natural latex, the natural latex layer itself being covered with natural or artificial wax, in particular paraffin, said layer of wax not being in direct contact with said surface of said fibrous material.

[0109] These materials may be papers used for certifications or protection, and include cigar bands, guarantee seals or official seals, paper intended for use in issuing banknotes, etc.

[0110] The invention will be better understood by reading the figures and examples which follow: Brief description of the figures [YES] [Fig.l] Figure No. 1 is a schematic representation of a food container according to the invention. The circle represents the enlargement area allowing the composition layers to be viewed.

[0112] [Fig.2] Figure No. 2 represents a curve showing the water absorption in g.m2 over time (in h) after soaking in water of paper covered with paraffin alone (A) or covered with natural latex, then paraffin (B).

[0113] [Fig.3] Figure No. 3 represents a graph showing the maximum compressive force (in N) to be applied to deform pots covered with paraffin (A) or paraffin and latex (C). The same tests are carried out after adding water to the pots for 30 days. B: Pot covered with paraffin with water for 30 days; D: Pot covered with latex and paraffin with water for 30 days. Examples

[0114] Example 1: Production of a water barrier coating by double impregnation: latex then paraffin

[0115] 1) Products used:

[0116] In order to waterproof paper according to the above-described process, a macrocrystalline paraffin whose specifications are provided in the table below was used. The dropping point corresponds to the temperature at which the paraffin is sufficiently liquid for a drop to fall under its own weight. The cooling curve corresponds to the solid-liquid phase transition temperature. The setting temperature corresponds to the liquid-solid transition temperature. For this paraffin, noted PMI in the rest of the manuscript, these temperatures are around 60°C. The different molecules constituting this paraffin contain a carbon number between 20 and 46. The kinematic viscosity is 6.9 mm2.s 1 and the density is 779.4 kg.m-3. The kinematic viscosity is equal to the ratio of the dynamic viscosity to the density. The oil content is 0.12%, this indicates that it is a refined macrocrystalline paraffin. Test Value Specification PMI Standards Dropping Point (°C) 62 - ASTM D 127 Cooling Curve (JC) 58.7 ASTM D 87 Freezing Temperature 61.5 58 - 62 ASTM D 938 Oil Content (%) 0.12% - ASTM D 721 Kinematic Viscosity 100°C 6.9 6-7 ASTM D 7042 imirTs1) Density 70,;,C (kg.m'3) 779.4 770 - 790 ASTM D 4052 Distribution in C C20 - C46 EWF Method

[0117] The natural latex used is a latex comprising 25% by mass of solid particles. It was obtained by simple dilution with distilled water of a latex concentrated at 60% by mass and classified as “high ammonia”.

[0118] 2) Double dipping process

[0119] In order to achieve the paper covering, the following process was used:

[0120] - The paper pot to be coated was dipped for a few seconds into the 25% latex in order to to deposit 0.5 g of latex, corresponding to a latex weight of approximately 50 g.m2.

[0121] - the latex-covered paper pot is then left to dry, taking 6 min at a temperature of 160°C.

[0122] - Once dried, the latex-coated paper pot is dipped in paraffin melted for a few seconds, then drain at room temperature to deposit 3 g of paraffin, corresponding to a paraffin weight of approximately 90 gm 2

[0123] The paper pot thus obtained has now become watertight.

[0124] Example 2: Waterproofing measurement: water absorption measurement

[0125] In order to measure the effect of the latex and paraffin coating on the waterproofing, paper coated with paraffin alone, or latex and paraffin as in Example 1 was immersed in water and the amount of water accumulated was measured over time.

[0126] The results are presented in figure 2.

[0127] As shown in Figure 2, very quickly after immersion in water, a paper covered only with paraffin accumulates water (approximately 15g.m2 at the end 24 hours). Conversely, even after more than 600 hours immersed in water, paper coated with latex and paraffin does not accumulate more than 5g.m2 of water.

[0128] This therefore shows that the double covering according to the invention effectively makes it possible to seal the paper.

[0129] Example 3: Compressive strength of pots coated with latex and paraffin according to the method of the invention

[0130] In order to test the performance of the waterproof covering according to the invention, the inventors tested the water resistance of yogurt pots coated according to the method described in example 1.

[0131] The pots manufactured (0.5 g latex, 3 g paraffin) must have a certain mechanical resistance to withstand the various constraints to which they are subjected (stacking, conveying, pressure difference, gripping, etc.).

[0132] A compression test between two plates was developed by the inventors in order to determine the maximum force necessary to deform the pot between 0 mm and 10 mm. The lower plate is fixed and the upper plate is movable. The speed of the pretest is 1 cm.min 1 up to 0.1N then the test is carried out at a descent speed of 50 mm.min-1. The value of the maximum force is recorded between 0 and 10 mm. This test makes it possible to evaluate the influence of the coating on the mechanical strength of the paper pot. It also makes it possible to evaluate the loss of compressive strength after the pot has been exposed to liquid water for a given period.

[0133] The results obtained on pots covered with paraffin or covered with latex and paraffin (according to the invention) are shown in figure no. 3.

[0134] It is found that the initial resistance of the pots is almost identical after covering them with paraffin alone or with latex and paraffin.

[0135] However, after adding water to the pots for 30 days, it is found that the pots covered only with paraffin are much less resistant to compression than the pots covered with latex and paraffin. This is in agreement with the data of Example 2 and the water absorption according to the covering achieved.

[0136] Example 4: Recyclability.

[0137] The recyclability of paper pots coated with the latex / paraffin two-layer coating described in the previous examples was evaluated at the paper technical center (CTP) in Grenoble. The packaging studied is a pot composed of 6.0 g of paper, 2.1 g of paraffin and 0.5 g of latex, which corresponds respectively to the following mass percentages: 69.8%, 24.4% and 5.8%. The percentage of non-cellulosic material is therefore 30.2%.

[0138] The resuspension of the pots in the pulper took place without difficulty. Visual observation of the suspension shows good individualization of the fibers. In this recyclability test, there are two classification steps. The rejection rate after the classification step is 27.2% on a 15 / 100 mm sieve and the second rejection rate is 0.21% on a 10 / 100 mm sieve. If the classification had been carried out directly with the 10 / 100 mm sieve, the rejection rate would have been 27.4%. This theoretical rejection rate is close to the 30.2% of non-cellulosic material. The rejections are composed of some fibers, latex film and paraffin. The forms produced after classification have a very good surface condition. This means that at the end of classification, all pieces of latex and paraffin have been eliminated. Paper pots coated with latex and paraffin with the quantities described can therefore be recycled according to the EN 13430 standard.

[0139] A recyclability certificate was therefore issued without reversals within the meaning of standard EN 13430 “requirements relating to packaging recoverable by material recycling” for these pots coated with the two-layer coating according to the invention.

Claims

Claims

1. A sealed porous support comprising at least one surface, said surface being covered with a first layer consisting essentially of natural latex and a second layer consisting essentially of a paraffin wax, the first layer being in direct contact with said at least one surface of said porous support, and said second layer being exclusively in contact with the first layer.

2. A carrier according to claim 1, wherein said natural latex is a latex comprising up to 70% by mass of latex particle relative to the total mass of said natural latex.

3. A support according to any one of claims 1 to 2, wherein said at least one surface of said support is covered with a first layer of 10 to 80 gm-2 of natural latex, and said first layer is covered with a second layer of 10 to 120 gm-2 of paraffin.

4. A method of waterproofing a surface of a support, said method comprising the following steps: - bringing a first composition essentially consisting of natural latex into contact with the surface of the support, to obtain a latex-covered support surface, - drying the latex-covered support surface at a temperature above 40°C in order to remove both the water contained in the natural latex composition and the support, to obtain a dried surface, - a step of bringing the dried surface into contact with a paraffin wax composition, to obtain a double-covered surface, and - a step of cooling the double-covered surface to a temperature below the melting point of said paraffin wax, to obtain a waterproofed support surface.

5. A method according to claim 4, wherein the contacting steps are soaking steps.

6. Food container (1), in particular made of a fibrous and / or porous material, consisting of one or more walls (10) defining an internal part (101) capable of receiving a food product (2), and an external part (102), the wall (10) having an exposed internal face (11) to the internal part (101) and an external face (12) exposed to the outside of said container, said container being such that the internal face (11) is covered with a first layer (3) of a composition consisting essentially of natural latex, and said first layer is covered with a second layer (4) of paraffin wax.

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