FR3141949A1 - Process for manufacturing a flexible support coated with a heat-sealing film-forming polymer - Google Patents

Abstract

Method for manufacturing a flexible support coated with a heat-sealing film-forming polymer The invention relates to a method for manufacturing a flexible coated support (4), in particular a coated paper (4), having a front side (6) coated (8) with a heat-sealing film-forming polymer (10). Said method comprises the following steps: a) depositing said heat-sealing film-forming polymer (10) on the front face (6) of the flexible support (12); b) drying said coated flexible support (4) so that the humidity of said coated flexible support (4) is less than 4.5%, preferably less than or equal to 3%, more particularly less than or equal to 2.5%; c) applying a damp material, in particular water, to a reverse side (16) of the coated flexible support (4) so as to create a difference in humidity between the front side (6) and the reverse side (16) coated flexible support (4); and d) drying said coated flexible support (4). Figure for abstract: Figure 1

Description

Process for manufacturing a flexible support coated with a heat-sealing film-forming polymer

The present invention relates to a process for manufacturing a flexible support, in particular a paper, having a front side coated with a heat-sealing film-forming polymer.

The invention also relates to a coated flexible support. The invention also relates to packaging comprising the coated flexible support obtained by such a process.

The use of film-forming polymers is widespread in the field of surface coatings, particularly in the field of coating, lamination or lamination on a support, in particular paper or cardboard.

In fact, these film-forming polymers make it possible to waterproof a surface in order to make it a barrier to elements such as grease.

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.

These polymers, for example initially in the form of a solution or a liquid, require a stabilization period so that they are stabilized with a view to forming a dry film on the support.

This stabilization period varies depending on the chemical nature of the film-forming polymers and the conditions to which these film-forming polymers have been subjected. During this stabilization period, the film formed by the film-forming polymers can shrink.

When the surface to be waterproofed is on one of the faces of a flexible support, in particular on a light weight paper, for example less than 200 g/m ² , where the rigidity of the flexible support is not sufficient to counter shrinkage induced by these film-forming polymers, the edges of the flexible support tend, after a certain time, to roll up on themselves.

This tendency for the edges of a flexible support coated with the film-forming polymer, initially flat, to rise up, then to roll up, on each side is defined as a “winding effect” or a “curl”. (English terminology).

The “curl” is all the more important as the retraction induced by the film-forming polymers is significant.

Generally speaking, the flexible coated support obtained using a conventional process is characterized by a very significant “curl”, i.e. the edges roll up several turns.

Too much curl prevents the final coated flexible support from being used in industrial conditions.

Furthermore, the classic coated flexible support requires an additional adhesive layer in order to achieve heat sealing with this coated flexible support.

In addition, this type of classic coated flexible support often requires a multitude of distinct layers in order to obtain sufficient barrier properties.

The invention aims in particular to overcome these drawbacks.

The subject of the present invention is thus a process for manufacturing a coated flexible support, in particular a coated paper, having a front side coated with a heat-sealing film-forming polymer, said process being characterized in that it comprises the following steps :

a) deposit said heat-sealing film-forming polymer on the front face of the flexible support;

b) drying said coated flexible support so that the humidity of said coated flexible support is less than 4.5%, preferably less than or equal to 3%, more particularly less than or equal to 2.5%;

c) applying a damp material, in particular water, to a reverse side of the coated flexible support so as to create a difference in humidity between the front side and the reverse side of the coated flexible support; And

d) drying said coated flexible support.

We distinguish between “flexible support” and “coated flexible support”. The flexible support is raw, not yet coated. The coated flexible support corresponds to the flexible support having received the heat-sealing film-forming polymer.

This is also applicable for any type of flexible support, namely “paper” and “coated paper”.

Thanks to the method according to the invention, the tendency ("curl") that the edges of the coated flexible support have to roll up on themselves after the manufacture of said coated flexible support is prevented.

Thus, the method according to the invention allows the industrial manufacture of said coated flexible support in an automated flexible support manufacturing line whereas such a coated flexible support could not be obtained via this production line until now because of the winding effect of the flexible coated support.

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

The second step b) allows the coated flexible support to dry as much as possible so that said coated flexible support contains as little residual moisture as possible. Following this high-intensity drying, the heat-sealing film-forming polymer causes strong stresses on the flexible support, for example, where appropriate, on fibers of this flexible support, stresses which would have the effect of rolling up the flexible coated support placed at dish after manufacturing. We want to avoid this winding effect.

Thus, the drying step b) occurs immediately after the deposition of the heat-sealing film-forming polymer so that this heat-sealing film-forming polymer does not yet have time to dry naturally, in order to maximize the constraints to which the heat-sealing film-forming polymer is subjected. .

The aim of step c) following drying step b) is to create a marked difference in humidity between the front and back sides. The front side has a humidity of less than 4.5%, preferably less than or equal to 3%, more particularly less than or equal to 2.5% while the reverse side is wet. This humidity after drying step b) can advantageously be between:

2.5 and 3.5%;

3.5 and 4.5%; Or

2.5 and 4.5%.

During the drying step d), the humidity of the front side being very low, the wet material, in particular water, evaporates largely from the back side, causing stress on the material forming the flexible support, this material being for example fibers, a constraint which will induce a winding effect on the reverse side. This winding effect on the back side is opposed to the winding effect on the front side so that we can obtain compensation for the winding effects on the front and back sides. This compensation may require a certain period of time for the flexible coated support to stabilize. During this period, the coated flexible support stabilizes, for example by remaining on a roll.

For example, when the flexible support is paper, the coated paper, namely the paper coated with the heat-sealing film-forming polymer, obtained at the machine outlet has a certain winding effect. After a certain period of time, for example five to seven days following production, the heat-sealing film-forming polymer film present on the surface will stabilize, causing it to shrink. By retracting, the rolling effect generated during production will fade, until a solid surface is obtained when the heat-sealing film-forming polymer is completely stabilized.

Thus, when these effects have compensated for each other, the flexible coated support, placed on a flat surface, has satisfactory flatness.

The drying step d) is carried out by conventional drying means known per se, the drying temperature of which is less than or equal to 120 ° C, on the one hand, to prevent the difference in humidity between the two recto faces and back of the coated flexible support is canceled, and on the other hand, to prevent the coated flexible support at the outlet of the drying means chain from being too dry, which can cause defects such as folds or cords due to the absorption of humidity from the flexible coated support.

In addition, the drying temperature during step d) is preferably greater than or equal to 45°C to prevent the flexible support from remaining too wet. Thus, it is possible, for example, to dry the flexible support during step d) at a temperature range of between 50 and 90°C, more particularly between 60 and 80°C, ideally between 60 and 70°C to compensate these aforementioned disadvantages.

After this step d), the humidity of the flexible support is less than 10%, preferably between 2 to 10%, more particularly between 4 and 8% or 6 and 10%. The humidity of the flexible support after step d) can advantageously be between:

7 and 9%; Or

8 and 9%.

The humidity of the flexible support after step d) can also be around 4%.

In addition to the fact that the invention makes it possible to prevent the tendency ("curl") that the edges of the coated flexible support have to roll up on themselves after the manufacture of said coated flexible support, the heat-sealing film-forming polymer deposited on the coated flexible support is sufficient in itself to heat seal the coated flexible support. In other words, said heat-sealing film-forming polymer does not require an additional adhesive layer or an additional polymer layer in order to heat-seal the coated flexible support.

Thus, a number of layers necessary 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.

This is more 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 is necessary to obtain a flexible coated support whose properties are optimal.

According to one of the aspects of the invention, the coated flexible support is dried during step b) and during step d) so that the humidity of the flexible support obtained after step d) is greater than 'after step b).

According to one of the aspects of the invention, the weight of the flexible support is between 20 and 300 g/m ² , is between 20 and 100 g/m ² , preferably is between 30 and 60 g/m ² . The weight is more particularly between 50 and 60 g/m ² .

According to one of the aspects of the invention, the surface density of the deposit of the heat-sealing film-forming polymer, measured by difference in weight between the dry coated flexible support and the dry flexible support, is between 6 and 14 g/m ² , more particularly between 8 and 12 g/m ² or between 7.5 and 8.4 g/m ² .

In these surface density ranges, the barrier properties can be obtained optimally. The flexible support and the coated flexible support were dried before weighing to remove any residual water.

According to one of the aspects of the invention, step a) consists of applying the heat-sealing film-forming polymer at least twice to the front face of the flexible support so as to obtain a layer of the heat-sealing film-forming polymer.

For example, in the case of a deposition layer of the heat-sealing film-forming polymer of 10 g/m ² , this deposition can be carried out by two successive coating stations of the same polymer of 5 g/m ² . Thus, the layer of heat-sealing film-forming polymer has a uniform surface and good sealing.

According to one of the aspects of the invention, the difference in humidity between the front face and the rear face at the end of step b) is greater than 95.5%, preferably greater than 97%.

According to one of the aspects of the invention, in which the drying is done with:

- an airborne dryer comprising a plurality of hot air dryers; and or

- an infrared dryer.

The hot air dryer is defined as a non-contact air flow drying device. This hot air dryer allows a gradual rise in temperature. In addition, said dryer makes it possible to evaporate significant quantities of water.

The infrared dryer is a non-contact, radiation drying device that provides high thermal transmission. It is possible to modulate the wavelength depending on the flexible support used. This type of infrared drying is particularly useful for very quickly raising the temperature of the flexible support and/or the heat-sealing film-forming polymer.

Conversely, a hot air dryer is gentler in its temperature rise but allows large quantities of water to evaporate more easily.

The infrared dryer can be used alone, or coupled with an airborne dryer, for example during step b) and/or during step d) of the process according to the invention.

According to one of the aspects of the invention, in which the drying temperature during step b) is greater than or equal to 100°C. It is preferably between 140 and 150°C.

This drying temperature is dependent on drying adjustment parameters known per se for a given drying device.

For example, the following two parameters such as the speed at which the flexible support or the coated flexible support advances in a manufacturing line, called the “machine speed” and the length of the drying device can be taken into account, the temperature of drying will be all the higher as the “machine speed” is high and the length of the drying device is less.

In an alternative embodiment, when the drying during step b) is carried out with an infrared dryer, the drying temperature can be greater than 130°C, preferably is between 130 and 170°C, more particularly is included between 150 and 170°C.

According to one of the aspects of the invention, the wet material is water in liquid form, in the form of a vapor or a mixture of the two.

According to one aspect of the invention, the wet material is applied to the reverse side of the flexible support using a rotating roller.

According to one of the aspects of the invention, in which the deposition method according to step a) is chosen between coating or printing.

According to one of the aspects of the invention, the flexible support is chosen from paper, plastic films based on polyethylene (PE), polypropylene (PP), and polylactic acid (PLA). Preferably, the paper has at least one smooth side obtained by at least one of the following methods: rubbing, calendering or coating.

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

For example, Kraft paper, whose characteristics are known in itself, has optimal mechanical resistance in view of the weight of the paper.

According to one of the aspects of the invention, the paper has a white appearance or a brown appearance.

According to one of the aspects of the invention, step a) and/or step c) is carried out using at least one of the following means: a doctor blade passing over the flexible support, a Meyer bar, a curtain coater fitted with a coating nozzle, or an air knife coater.

In this way, during step a), the heat-sealing film-forming polymer is coated homogeneously and has a uniform thickness on the front side of the flexible support. Thus, the coating of the heat-sealing film-forming polymer thus obtained is very regular and without marks, scratches or flaws through which a fluid (gas, liquid) could enter the coated flexible support and generate softening or leaks of said coated flexible support. . In addition, the regular coating obtained makes it possible to achieve high quality heat sealing.

Among the different coating techniques, the air knife coater or the curtain coater equipped with a coating nozzle, makes it possible to precisely control the coating deposit with high quality and to ensure a uniform and regular coating on the flexible support. During step c), the wet material, in particular water, can be applied uniformly to the reverse side of the flexible support coated with these different coating techniques.

• Un bac de récupération du polymère filmogène thermoscellant ou de la matière humide, agencé pour recycler l’excès dudit polymère filmogène thermoscellant ou de ladite matière humide.

According to one of the aspects of the invention, the air blade coater comprises:

• A recovery tank for the heat-sealing film-forming polymer or the wet material, arranged to recycle the excess of said heat-sealing film-forming polymer or of said wet material.

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 barrier antifungal.

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

According to one of the aspects of the invention, the heat-sealing film-forming polymer is food compatible.

According to one of the aspects of the invention, the heat-sealing film-forming polymer comprises a thermoplastic polymer.

According to one of the aspects of the invention, the heat-sealing film-forming polymer comprises:

- at least one caseinate and/or at least one casein.

Thus, caseinate and/or casein correspond to products accessible in large quantities and presenting optimal mechanical and chemical properties at a lower cost, compared to other polymers of natural origin presenting similar properties.

According to one of the aspects of the invention, the heat-sealing film-forming polymer has at least one of the following properties: biosourced, biodegradable, compostable.

According to one of the aspects of the invention, the heat-sealing film-forming polymer is water-soluble.

This water-soluble nature makes it possible to make the film-forming polymer compatible with the coated flexible support having the following properties: biosourced, biodegradable, compostable and/or repulpable, in particular repulpable.

According to one of the aspects of the invention, the coated flexible support has at least one of the following properties: biosourced, biodegradable, compostable and/or repulpable.

According to one of the aspects of the invention, the coated flexible support has the following properties: biosourced, biodegradable, compostable and repulpable.

For example, a coated paper manufactured following the process according to the invention with the heat-sealing film-forming polymer comprising at least one caseinate and/or one casein has all of these properties.

According to one of the aspects of the invention, the heat-sealing film-forming polymer comprising at least one caseinate and/or one casein having barrier properties to oil/fat and to the oxygen barrier.

According to one of the aspects of the invention, the heat-sealing film-forming polymer is initially in the form of granules, preferably thermoplastic granules.

The heat-sealing film-forming polymer, initially in the form of thermoplastic granules, is dissolved in water to form a solution. This solution is intended to form a dry film on the paper to form a coated paper. The quantity of water depends on the desired final viscosity and may depend on the nature of the flexible support.

According to one of the aspects of the invention, said caseinate and/or said casein has a weight which represents 50 to 80% relative to the weight of the granule, preferably 55 to 75%, more particularly 60 to 70%. Said caseinate and/or casein represents 60 to 65% of the weight of the granule.

According to one of the aspects of the invention, the heat-sealing film-forming polymer further comprises:

- some water ; And

– at least one plasticizer different from water.

According to one of the aspects of the invention, water represents 10 to 15% of the weight of the granule, preferably 10 to 12% of the weight of the granule.

• Un plastifiant dont le poids représente de 10 à 30 % du poids du granulé, préférentiellement de 15 à 25 % ; et
• Un tensioactif dont le poids représente de 1 à 5 % du poids du granulé, préférentiellement de 1 à 3 %.

According to one of the aspects of the invention, the heat-sealing film-forming polymer further comprises:

• A plasticizer whose weight represents 10 to 30% of the weight of the granule, preferably 15 to 25%; And
• A surfactant whose weight represents 1 to 5% of the weight of the granule, preferably 1 to 3%.

According to one of the aspects of the invention, the heat-sealing film-forming polymer comprises:

at least one water-soluble polymer, namely a water-soluble polymer, preferably soluble in water at room temperature when the mass concentration of the water-soluble polymer is greater than or equal to 2.5%.

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

• au moins un polymère hydrosoluble, à savoir un polymère soluble dans l’eau, de préférence soluble à température ambiante.

According to one of the aspects of the invention, the heat-sealing film-forming polymer is associated with:

• at least one water-soluble polymer, namely a water-soluble polymer, preferably soluble at room temperature.

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

According to one of the aspects of the invention, the water-soluble polymer represents 1 to 7% of the weight of the granule, preferably 2 to 6% of the weight of the granule, more particularly 3 to 5% of the weight of the granule.

Preferably, the water-soluble polymers comprise hydrophilic units. For example, water-soluble polymers can include heteroatoms such as O or N in their main chain. The water-soluble polymers can also include hydrophilic groups such as -OH, -NH2, -NH-, -CO2-, or -SO3-.

According to one of the aspects of the invention, the water-soluble polymer is chosen from non-ionic water-soluble polymers, amphoteric water-soluble polymers, cationic water-soluble polymers, anionic water-soluble polymers, and mixtures thereof.

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

Among the water-soluble polymers, we can also cite polyacrylamides.

According to one of the aspects of the invention, the plasticizer is chosen from polyols, glycerol acetates, glycerol propionates and their mixtures. As examples of polyols, we can cite glycerol, hexane triol, mannitol, sorbitol, glycols, including ethylene glycol and their derivatives. Preferably, the plasticizer is chosen from glycerol, sorbitol, and mixtures thereof. According to one embodiment, the plasticizer is glycerol.

Thus, said plasticizer makes it possible to increase the mechanical properties of the heat-sealing film-forming polymer in the face of humidity.

According to one of the aspects of the invention, the surfactant is chosen from lecithin, diacetyl phosphonates and polysorbates. Preferably, the surfactant is lecithin.

According to one of the aspects of the invention, the hydrophobic agent can be chosen from:

- polycarboxylic acid esters;

- C3-C33 carboxylic acids, preferably C4-C28 fatty acids, and even more preferably C6-C28 unsaturated fatty acids; And

- their mixtures.

The polycarboxylic acid esters can be derived from at least one polycarboxylic acid and at least one alcohol, preferably a C1-C18 alcohol.

Among the polycarboxylic acids preferentially retained in the context of the invention, mention may be made of citric acid, hydroxycitric acid, tartaric acid, malic acid, oxalic acid, malonic acid, acid succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid.

Among the preferred alcohols in accordance with the invention, mention may be made of C2-C6 alcohols, such as for example ethanol, n-propanol, iso-propanol, n-butanol and tert-butanol.

According to one of the aspects of the invention, the hydrophobic agent is chosen from triethyl citrate, tributyl O-acetyl citrate, tributyl citrate and their mixtures.

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 an unsaturated C6-C28 fatty acid.

Among the C4-C28 fatty acids retained in the context of the invention, mention may be made of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and their mixtures.

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

According to one of the aspects of the invention, the heat-sealing film-forming polymer can be printable and/or printed.

According to one of the aspects of the invention, the oil and/or fat barrier property of the heat-sealing film-forming polymer has, for a Cobb 1800 index less than 10 g/m ² , preferably less than 6 g/m ² , more particularly less than 3 g/m ² . The Cobb 1800 index is ideally between 1 to 2.5 g/m ² .

The Kit level to obtain the oil and/or fat barrier property of the heat-sealing film-forming polymer is greater than or equal to 7, preferably greater than or equal to 10.

According to one of the aspects of the invention, the oxygen barrier property of the heat-sealing film-forming polymer has a permeability level less than or equal to 1000 cm ³ /(m ² .24h), preferably less than or equal to 100 cm ³ /(m ² .24h), more particularly less than or equal to 100 cm ³ /(m ² .24h).

According to one of the aspects 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/m ² , preferably less than or equal to 5 g/m ² , more particularly between 1 to 2.5 g/m ² .

According to one of the aspects 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) in standard conditions (23°C/50%RH). In 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).

1. déposer un premier polymère filmogène sur la face recto ;
2. déposer un deuxième polymère filmogène sur la face verso,

l’un des premier et deuxième polymères filmogènes étant thermoscellant ; et

1. sécher ledit support souple enduit.

The present invention also relates to a process for manufacturing a coated flexible support, in particular a coated paper, having a front side and a back side, characterized in that said process comprises the following steps:

1. deposit a first film-forming polymer on the front side;
2. deposit a second film-forming polymer on the reverse side,

one of the first and second film-forming polymers being heat-sealing; And

1. dry said coated flexible support.

Thus, the first and second film-forming polymers, one of which is heat-sealing, after drying c), present “curls” which will compensate for each other so that the coated flexible support has good flatness.

According to one of the aspects of the invention, one of the first and second film-forming polymers contains at least one caseinate and/or one casein.

These film-forming polymers may have some or all of the characteristics described above in connection with the heat-sealing film-forming polymer comprising caseinate and/or casein.

According to one of the aspects of the invention, the first and second film-forming polymers both comprise at least one caseinate and/or one casein.

According to another embodiment of the invention, the deposition method according to step a) is chosen from extrusion-coating and lamination and complexing.

At the end of this step a), the deposition of the heat-sealing film-forming polymer in the form of a film with low humidity, namely less than 8%, can be done on the front side of the flexible support in order to form a support flexible coating. The heat emitted by the machine used to make the deposit removes this residual humidity.

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

The invention also relates to packaging comprising the coated flexible support obtained by the process according to the invention.

According to one of the aspects of the invention, the packaging comprises a stack of several flexible supports obtained by the method according to the invention.

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

According to one of the aspects of the invention, the flexible support has an appearance chosen from: the white appearance, the brown appearance, the matte appearance, the silk effect appearance, or the shiny appearance.

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

The invention also relates to a packaged product comprising:

- content, for example a foodstuff; And

- the packaging according to the invention enveloping the contents.

According to one of the aspects of the invention, the product is in solid or liquid form.

According to one of the aspects of the invention, the content is chosen from pharmaceutical, food, chemical and cosmetic products.

According to one of the aspects of the invention, the foodstuff of the contents of the packaged product is chosen for example, meat, fish, vegetables, fruits, pastries, pastries, food additives, ingredients, dry foods, dry preparations, food powders, tea and herbal tea bags, dried tea leaves, animal food.

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

Definitions

By “coating”, we mean, for example, a surface treatment consisting of applying a generally liquid coating to a support. The coating may have a composition such as a film-forming polymer.

By “complexing”, we mean, for example, a mechanical action making it possible to assemble in an inseparable manner two or more materials with different mechanical and physico-chemical properties.

By “lamination”, we mean, for example, a mechanical action allowing a film to be applied to a support

By “extrusion-coating” we mean, for example, the technique consisting of coating a support by depositing a layer of molten polymer on it by extrusion.

By “printing”, we mean, for example, an application of a coating via a flexography or engraving type printing system.

By “humidity” we mean the water or water vapor content in a substance. It can be expressed as a mass percentage, i.e. a ratio between the mass of water and the total mass of the substance.

The “grammage” is a quantity characterizing a flexible support, not yet coated, such as paper, corresponding to its surface mass, that is to say its mass per unit area. The weight includes residual humidity which varies in particular between 4 and 8% of the total weight of the flexible support, in particular paper.

The weight of a flexible support such as paper is between 10 to 300 g/m ² , preferably between 20 to 100 g/m ² , more preferably between 30 to 60 g/m ² .

A “thin” paper has a weight of between 10 and 60 g/m ² , advantageously between 30 and 50 g/m ² .

By “heat sealing”, we mean, for example, a process during which the edges of the support are welded using heat, with or without direct contact with the support.

By “heat sealant”, we mean, for example, the quality of a material to be welded by heat sealing without adding an additional adhesive layer, an additional polymer layer or an adjuvant. In other words, the heat sealing material is sufficient in itself to achieve heat sealing.

By “barrier”, we mean, for example, the properties which protect the contents of packaging formed by the support against external attacks and substances, or which protect the exterior of the contents of the packaging. The most common barriers are those against oxygen, oil, grease, water, water vapor, and fungi and microorganisms.

By “oxygen barrier”, we mean, for example, a barrier with a low level of permeability to oxygen, that is to say less than 100 cm ³ /(m ² .24h) and preferably lower at 10 cm ³ /(m ² .24h). This property may be required, for example, for food products requiring protection from oxidation such as chocolate, cheese or dry foods.

By “oil or fat barrier”, we mean, for example, a barrier whose Kit level is between 6 and 12. This property may be required, for example, for food products such as pastries or fast food.

By “water barrier” is meant, for example, a barrier whose Cobb index is advantageously less than or equal to 15 g/m², preferably less than or equal to 5 g/m ² and for the Cobb duration of 1800 seconds. This property may be required, for example, for food products such as fruits and vegetables and disposable tableware.

By “water vapor barrier”, we mean, 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) in standard conditions (23°C/50%RH). The WVTR coefficient is less than 100 g/(m².24h) and ideally less than 50 g/(m².24h) in tropical conditions (38°C/90%RH).

By “antifungal barrier”, we mean, 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, such as strawberries or raspberries.

The “Cobb” test consists of measuring the quantity of water that the flexible support, particularly paper, can absorb for a defined time. For example, the Cobb1800 index means that the Cobb test was performed for 1,800 seconds, or 30 minutes.

This Cobb 1800 index is expressed in grams per square meter (g/m²). The lower the value of the Cobb1800 index, the better the water barrier. Values below 15 g/m² correspond to very good water barriers for Cobb1800.

This Cobb test is carried out by pouring 100 ml of distilled or demineralized water onto a sample of treated paper 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 quantity of water absorbed and therefore to the Cobb index.

Measurements of vapor permeation or water vapor transmission rate (Water Vapor Transmission Rate (WVTR) according to English terminology),

These measurements evaluate the quantity of water vapor which passes through the support in 24 hours at predefined temperature and humidity conditions. Generally speaking, these tests are either carried out in “standard” conditions at 23°C/50% relative humidity (RH), or in “tropical” conditions at 38°C/90% RH.

The test is carried out according to the ISO 2528 standard, a cup of anhydrous CaCl ₂ is sealed by the support to be tested. The assembly is placed in a regulated climatic chamber. The water vapor which passes through the support is trapped by the CaCl ₂ . The difference in weight of CaCl ₂ measured between the initial instant and that measured after 24 h corresponds to the value of the WVTR expressed in g/m ² / 24 h.

The lower the WVTR value, the better the water vapor barrier.

The “Test Kit” allows you to determine the resistance of a paper to the penetration of fatty products such as grease or oil.

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

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).

For certain particular applications, more drastic tests can be carried out by increasing the surface to be tested, and by testing at high temperature, i.e. above ambient temperature, or by increasing the proportion of the most aggressive reagent in the mixtures. , namely heptane.

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

A palm oil waterproofing test can also be carried out (ISO 16532-1 standard), if the results are good enough, the turpentine test can be carried out (ISO 16532-3 standard).

By “film-forming” we mean, for example, a material that can be applied in a thin layer, mainly in liquid form, on a support, and which then becomes a solid film, a film, or a sheet. This film-forming material can also be applied in another form, for example in extrusion-coating in the form of a softened or molten material. In general, the term “film-forming” means, in particular, the tendency of a material to form a film.

By “polymer” we mean, for example, molecules with long chains of high molecular mass. A polymer can 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.

By “thermoplastic”, we mean, for example, a material which becomes malleable and pliable above a given temperature, the glass transition temperature Tg, but which below this Tg becomes hard again, these transformations being reversible.

By “plasticizer” we mean, for example, a substance making it possible to lower the glass transition temperature Tg of the material.

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

By “hydrophobic”, we mean, for example, a compound having little affinity with water and tending not to dissolve in it. Typically, it is a predominantly nonpolar compound.

By “hydrophilic” we mean, for example, a compound having an affinity with water and having a tendency to dissolve in it. Typically, it is a compound having polar groups capable of forming hydrogen bonds.

By “water soluble” we mean, for example, 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 if any particles remain. When there are no particles in the filter, the polymer is considered water soluble. This water-soluble nature does not concern certain polymers such as waxes, for example waxes based on polyethylene or alkane, or ester waxes, for example beeswax. Indeed, these waxes are not soluble in water.

By “biosourced”, we mean, for example, a material containing all or part of elements of natural or renewable origin. The biosourced material is, for example, paper comprising cellulose which is extracted from trees or plants for different applications.

By “biodegradable” we mean a material that can be decomposed under the action of microorganisms (bacteria, fungi, algae, etc.). The result of this decomposition is the formation of water, CO ₂ and/or methane and possibly by-products (residues, new biomass) which are non-toxic for the environment. It is, for example, a biodegradable material according to the European standard EN NF 13432.

By “compostable”, we mean, for example, a biodegradable product ending the product cycle according to standard EN 13432.

According to this EN13432 standard, a material can be qualified as “compostable” if it has the following characteristics:

- be able to achieve 90% biodegradation in less than 6 months if subjected to an environment rich in carbon dioxide; these values are tested with the standard method EN14046 (also called ISO14855);

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

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

- a low concentration of heavy metals;

- pH values within established limits;

- mineral salt content within established limits;

- a concentration of volatile solid elements within established limits;

- a concentration of nitrogen, phosphorus, magnesium and potassium within established limits.

We note that a “biosourced” material can be compostable.

By “repulpable” we mean, for example, a fibrous material, in particular paper, for which it is possible to disperse the fibers in an aqueous medium in order to produce a paste called pulp. Thus, the repulpable material can be integrated back into the paper processing chain. This “repulpable” character does not concern certain polymers such as polyolefins, for example polyethylene, or polypropylene. These polymers are not soluble in water and interfere with the fiber dispersion process in an aqueous medium, thus preventing a flexible support coated with such polyolefins or polypropylene from being “repulpable”. This “repulpable” character does not concern waxes either, for example waxes based on polyethylene or alkane, or ester waxes, for example beeswax. In fact, these waxes are not hydrosoluble in water, thus making it possible to make a flexible coated support comprising such waxes “repulpable”.

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

“Casein” is a protein from milk which 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 casein.

Caseinate and casein form a biodegradable, compostable and food-compatible heat-sealing film-forming polymer. Casein and caseinate are also compatible with a biosourced, biodegradable, compostable and/or repulpable flexible coated support.

Unless otherwise stated, percentages are expressed as mass relative to the total mass of the material.

Brief description of the figures

Other characteristics, details and advantages of the invention will emerge more clearly on reading the detailed description given below, and several examples of embodiment given for informational and non-limiting purposes with reference to the schematic drawings annexed on the other hand. , on which ones :

is a schematic view of the automated manufacturing line of the coated flexible support according to the invention,

is a schematic view of a coated paper, in cross section, obtained by the process according to the invention,

is a schematic view of a coated paper, in cross section, obtained by a variant of the process according to the invention,

is a schematic view, in cross section, of an assembly of two papers coated by heat sealing,

represents schematic views of the three samples of flexible supports obtained under various experimental conditions seven days after drying in ambient air,

Detailed description of the figures

We represented on the , an automated manufacturing line 2 making it possible to implement the method according to the invention to manufacture samples of coated papers 4 having a front side 6 coated 8 with a heat-sealing film-forming polymer 10 comprising a caseinate and a casein.

• le caséinate, dont le poids représente de 63 % du poids du granulé ;
• de l’eau, dont le poids représente 10 % du poids du granulé ;
• Un glycérol comme un plastifiant dont le poids représente de 23,5 % du poids du granulé ;
• De la lécithine comme un tensioactif dont le poids représente de 2,3 % du poids du granulé ;
• l’acide oléïque comme acide gras dont le poids représente 1,2 % du poids du granulé.

The heat-sealing film-forming polymer 10 used for the three coated paper samples 4, namely comparative example 100, example 1 (200) and example 2 (300), is initially in the form of thermoplastic granules and comprises:

• caseinate, the weight of which represents 63% of the weight of the granule;
• water, the weight of which represents 10% of the weight of the granule;
• A glycerol as a plasticizer whose weight represents 23.5% of the weight of the granule;
• Lecithin as a surfactant whose weight represents 2.3% of the weight of the granule;
• oleic acid as a fatty acid whose weight represents 1.2% of the weight of the granule.

The paper 12 used for the coated paper 4 has a weight of 50 g/m ² .

The heat-sealing film-forming polymer 10, initially in the form of thermoplastic granules, are dissolved in water to form a solution. This solution is intended to form a dry film on the paper 12 in order to form a coated paper 4. The quantity of water is dependent on the desired final viscosity and may depend on the nature of the paper 12.

Experimental tests have shown that the quantity of water added to dissolve the thermoplastic granules does not significantly influence the winding effect of the coated paper 4.

The method according to the invention comprises the following steps:

a) deposit the heat-sealing film-forming polymer 10 on the front face 6 of each paper 12;

b) drying the coated papers 4 so that the humidity of the coated paper 4 is greater than 5% (comparative example 100), of the order of 5% (example 1 (200)) and of the order of 3% (example 2 (300));

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

d) dry each coated paper 4.

Step a) of the method according to the invention is implemented by means of a coating technique which is an air blade coater 18 which comprises rollers 22, an air blade 24 and a tray of heat-sealing film-forming polymer 26.

The heat-sealing film-forming polymer 10, contained in a tank of heat-sealing film-forming polymer 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.

The excess of the heat-sealing film-forming polymer 10 is removed by means of a jet of air emitted by the air blade 24. This excess is recovered in the recovery tank 28 arranged to recycle said excess in the tank of the heat-sealing film-forming polymer 10.

This air blade coater 18 makes it possible to control the coating deposition with high quality and to ensure a uniform and regular coating on the paper 12.

The coating deposition having a surface density of 8 to 12 g/m ² , produced with this air blade coater 18 makes it possible to confer barrier properties to grease and oxygen to the coated paper 4. The barrier properties to oxygen are improved compared to the case where the paper 12 is not coated.

Thus, the coated paper 4 has a Cobb 1800 index of around 1 to 4 g/m ² and a Kit level of around 7 to 12.

Step b) of the method according to the invention is implemented by means of an airborne dryer 30 comprising a plurality of hot air dryers (not shown), each dryer being maintained at a temperature of around 145 ° C, counting taking into account drying adjustment parameters such as the speed at which the paper 12 or the coated paper 4 advances in a manufacturing line 2, called the “machine speed” and the length of the airborne dryer 30.

For example, the following two parameters such as the speed at which the paper 12 advances in a manufacturing line 2, called the “machine speed” and the length of the airborne dryer 30 can be taken into account. The drying temperature will be all the higher as the “machine speed” is high and the length of the airborne dryer 30 is less.

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.

Following this high-intensity drying, the heat-sealing film-forming polymer 10 causes strong stresses on the paper 12, on the fibers of this paper 12, stresses which would have the effect of rolling up the coated paper 4 laid flat after manufacturing. We want to avoid this winding effect.

Thus, the drying step b) occurs immediately after the deposition of the heat-sealing film-forming polymer 10 so that this heat-sealing film-forming polymer 10 does not yet have time to dry naturally, in order to maximize the constraints to which the heat-sealing film-forming polymer 10 is submitted.

The purpose of step c) following drying step b) is to create a marked difference in humidity between the front faces 6 and back 16. The front face 6 has a humidity less than or equal to 3%, while the reverse side 16 is wet.

Step c) of the method 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 tray of water 32. This step aims to create a marked difference in humidity between the front 6 and back 16 sides.

Step d) of the process according to the invention is carried out with an airborne dryer 30 comprising a plurality of hot air dryers (not shown), each dryer being maintained at a temperature around 65 ° C in order to evaporate the excess of water which was added to the reverse side 16 of the coated paper 4 so as to arrive at a humidity of approximately 6%.

During the drying step d), the humidity of the front side 6 being very low, most of the water evaporates from the back side 16, causing stress on the fibers forming the paper 12, stress which will induce a winding effect on the back side 16. This winding effect on the back side 16 is opposed to the winding effect of the front side 6 so that we can obtain compensation for the effects winding on the front 6 and back 16 faces. This compensation may require a certain duration for the coated paper 4 to stabilize.

Thus, when these effects have compensated for each other, the paper 12, placed on a flat surface, has satisfactory flatness.

The paper coated 4 with the heat-sealing film-forming polymer 10, obtained at the machine outlet, has a certain winding effect. Five to seven days following production, the heat-sealing film-forming polymer film 10 present on the surface will stabilize, generating its shrinkage. By retracting, the rolling effect generated during production will fade, until a solid color is obtained when the heat-sealing film-forming polymer 10 is completely stabilized.

We represented on the , schematically, in cross section, a coated paper 4 obtained by the process according to the invention.

The coated paper 4 comprising the front side 6 and back side 16, comprises on its front side 6 a layer of said film-forming polymer 10 comprising caseinate with the composition described above while the back side 16 of said coated paper 4 does not contain any film-forming polymer heat sealer 10.

We represented on the , schematically, in cross section, a coated paper 400 obtained by a variant of the process according to the invention.

The coated paper 400 thus obtained has a front side 6 on which a first film-forming polymer 50 is deposited and a reverse side 16 on which a second film-forming polymer 60 is deposited, the first and second polymers 50, 60 being heat-sealing and comprising caseinate with the compositions presented above. The first and second film-forming polymers 50, 60, after a drying step, exhibit “curls” which will compensate for each other so that the coated paper 400 exhibits good flatness.

We represented on the , schematically, in cross section, an assembly 70 by heat sealing of two coated papers 4 obtained by the process according to the invention.

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

We represented on the , schematically, three samples of coated papers 4, namely the sample of comparative example 100, the sample of example 1 (200) and the sample of example 2 (300), placed on a flat surface. These samples 100, 200, 300 are obtained after seven days of drying in ambient air after production. The experimental conditions, namely the nature of the heat-sealing film-forming polymer 10, the nature of the paper 12 as well as the aforementioned tools and machines for the manufacture of these three samples of coated papers 100, 200, 300 are identical, with the exception of the drying step b) allowing the coated paper samples 100, 200, 300 to be dried so as to obtain a desired humidity of the paper which is detailed below.

From left to right, we first see the sample from comparative example 100 obtained according to standard drying conditions (humidity greater than 5%).

Then, the sample corresponding to example 1 (200) obtained with the process according to the invention with a humidity of 5% obtained after the first drying (step b)).

Finally, the sample corresponding to example 2 (300) obtained with the process according to the invention with a humidity of 3% obtained after the first drying (step b)).

For the sample of comparative example 100, the winding effect is very pronounced. The coated paper 4 rolled up on itself, forming several turns. The presence of these towers does not make the sample of comparative example 100 usable in industry.

Regarding example 1 (200), each edge of the coated paper 4 forms a half turn of winding, while the middle of the coated paper 4 remains flat. The presence of the winding half-turn does not make example 1 (200) usable in industry.

With regard to example 2 (300), the coated paper 4 is completely flat, highlighting the elimination of the winding effect observed with the sample of comparative example 100 and example 1 ( 200). Thus, we obtain a coated paper 4 with very good flatness in the case of example 2 (300).

Thus, it is notable to observe that the greater the difference in humidity between the front 6 and back 16 faces during the second drying (step d), the winding effect observed after production is reduced, or even eliminated.

Furthermore, in the absence of the implementation of the process according to the invention, despite drying in ambient air for a period of seven days after production, the winding effects persist as is illustrated by sample of comparative example 100 and example 1 (200). Conversely , this same drying in ambient air makes it possible to completely compensate for the winding effects of the sample of example 2 (300) placed on a flat surface.

It is remarkable to note that the process according to the invention makes it possible to obtain a coated paper 4 intended for packaging, said coated paper 4 being biosourced, biodegradable, compostable and repulpable with equivalent mechanical and chemical properties of a plastic film or a paper coated with a non-biodegradable film-forming polymer (not shown), namely a rot-proof film-forming polymer commonly used commercially.

In particular, said coated paper 4 obtained with the process according to the invention has barrier properties to oil and grease (a Cobb 1800 index of the order of 1 to 4 g/m ² and a Kit level of the order of 7 to 12) and oxygen (oxygen permeability level less than 10 cm ³ /(m ² .24h)) in combination of heat sealing properties. Said coated paper 4 therefore does not require an additional layer.

Furthermore, the method 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 coated paper 4.

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

Claims (11)

Method of manufacturing a coated flexible support (4), in particular a coated paper (4), having a front face (6) coated (8) with a heat-sealing film-forming polymer (10), said method being characterized in that that it includes the following steps:
a) deposit said heat-sealing film-forming polymer (10) on the front face (6) of the flexible support (12);
b) drying said coated flexible support (4) so that the humidity of said coated flexible support (4) is less than 4.5%, preferably less than or equal to 3%, more particularly less than or equal to 2.5%;
c) applying a damp material, in particular water, to a reverse side (16) of the coated flexible support (4) so as to create a difference in humidity between the front side (6) and the reverse side (16) coated flexible support (4); And
d) drying said coated flexible support (4). Method according to claim 1, in which the heat-sealing film-forming polymer (10) has at least one of the following properties: biosourced, biodegradable, compostable. A method according to claim 1 or 2, wherein the heat-sealing film-forming polymer (10) is water-soluble. Method according to claim 3, in which the coated flexible support (4) has at least one of the following properties: biosourced, biodegradable, compostable, repulpable. A method according to any preceding claim, wherein the heat-sealing film-forming polymer (10) comprises a thermoplastic polymer. Method according to any one of the preceding claims, in which the heat-sealing film-forming polymer (10) comprises:
- at least one caseinate and/or at least one casein. Method according to any one of the preceding claims, in which the weight of the coated flexible support (4) is between 20 and 100 g/m ² , preferably between 30 and 60 g/m ² . Process according to any one of the preceding claims, in which the drying temperature during step b) is greater than or equal to 100°C. Method according to any one of the preceding claims, the heat-sealing film-forming polymer (10) has at least one of the following properties: oxygen barrier, oil/grease barrier. Coated flexible support (10) obtained by the method according to one of claims 1 to 9. Packaging comprising the coated flexible support (10) obtained according to claim 10.