EP3186442B1 - Heat-sealing barrier paper - Google Patents

Description

The present invention relates to the field of packaging papers.

Plastic films are widely used in flexible packaging because they have water vapor barrier properties necessary for the good preservation of perishable products or having a limited shelf life.

Papers are materials made from fibers, generally cellulosic, therefore of plant origin. They are naturally porous and gas permeable and cannot, as such, be used for this application.

However, it is known to associate papers with other materials (plastics, aluminum, etc.) to obtain the barriers necessary for the packaging of various products and in particular perishable foodstuffs In this case the paper substrate is subjected to processing operations which include, for example, coating of cover layers made of dispersed polymers, extrusion coating of molten polymers or lamination with plastic films or aluminum. The cost of this paper-based composite with barrier properties has become expensive.

The document US 2,653,870 A describes a method of making wrapping paper.

Packaging made from barrier papers produced online are described in the application. WO2011 / 056130 . By on-line production is meant the production on a single production tool comprising all the elements useful for producing the paper.

However, the proposed barrier level is limited to light measurement conditions (temperate, i.e. 25 ° C, 75% relative humidity). The barrier level is measured by water vapor permeability, a low barrier signifying high water vapor permeability. It is known in the literature that “tropical” conditions (i.e. 38 ° C, 90% relative humidity) are much more severe than temperate conditions, and therefore the barrier measured in temperate conditions is much lower.

The term “barrier paper” should be understood to mean a non-porous paper, comprising a fibrous substrate covered with one or more layers, sufficiently impervious to water vapor to oppose the penetration of the latter into the packaging. , in an amount likely to affect the shelf life of the product or the integrity of the product contained therein.

The invention relates in particular but not exclusively to water vapor barrier papers having a water vapor permeability of at most 150 g / m ² / 24h and, preferably, less than 100 g / m. ² / 24h, measured according to standard ASTM F1249 under so-called tropical conditions of 38 ° C and 90% relative humidity.

It is advantageous that the barrier paper is also heat-sealable, in order to allow the formation of the packaging by sealing the paper on itself.

The manufacture of heat-sealable papers involves, for example, the deposition of a cover layer of a heat-sealing polymer on a cellulosic substrate. Such a covering layer has a fairly strong tack when not dry, and must be able to be dried completely before the paper is rolled up on itself, otherwise the various turns of the reel will stick together.

The application of this cover layer is generally carried out offline during one or more processing steps, which makes it possible to have a good coating quality, to benefit from a paper at room temperature at the time of coating. which allows the covering layer not to penetrate too much into the fibrous support, and to be able to adapt the passage time of the web in the ovens, at a speed for example of the order of 200 m / min, so that the duration exposure to these heating means is sufficient to completely dry the heat-sealing cover layer.

The documents US 2004/121079 A1 , WO 2010/052571 A2 , US 2014/113080 A1 and WO 2009/112255 A1 disclose papers that are processed offline.

Papers offering a barrier to water vapor and optionally heat-sealing, are generally manufactured in the state of the art during converting operations and have, as standard, cover layers of 10 to 30 g / m ² sec which are deposited in one or more thicknesses using different coating means (air knife, reverse engraving, Meyer blade or bar or any other coating method) or by applying a thick layer to the using a sleeping curtain.

The off-line transformation of a paper to give it water vapor barrier and heat-sealability properties is therefore an additional step in the manufacture of paper which increases its cost significantly and which limits the development of the paper in the process. flexible packaging in favor of packaging by plastic films. There is therefore an economic need to improve the productivity of the manufacture of water vapor barrier and heat-sealing papers.

The invention relates to the development of a paper having, when produced in-line, water vapor barrier and heat-sealability properties. This barrier and heat-sealing paper can be used to make packaging by welding the paper to itself.

Regardless of the way in which the heat-sealing layer is applied, on-line or off-line, the problem arises of facilitating the removal of the heat-sealing layer and more generally of any covering layer, heat-sealing or not, applied to a fibrous substrate.

It is generally desirable that the cover layer does not penetrate too deeply into the fibrous substrate, to reduce the amount of paper applied when this layer is polymer based. In addition, less penetration of the cover layer makes it easier to create a barrier film.

The use of a Yankee cylinder is a first solution for reducing the surface porosity.

A second possibility is the use of a calender before any treatment of the paper.

Another possibility is to provide for the presence of a precoat to reduce the porosity of the paper.

Another possibility is to combine one or the other of the preceding ones.

Certain hydrophobic and very film-forming latexes can be used in the formulation of the precoat.

However, the hydrophobic nature of the precoat can then pose a problem of wettability during the application of the cover layer, when the latter is aqueous, leading to a non-perfectly homogeneous coverage of the fibrous substrate precoated by the cover layer, especially in the case of an in-line process with a high sheet speed. In addition, the surface energy of the precoat must be sufficiently different from that of the cover layer while respecting the well-known rules of wettability in order to reduce the risk of wetting defects.

There therefore remains a need to satisfactorily address the problem of the applicability of the cover layer.

The invention meets this need, according to one of its aspects, by means of a paper according to claim 1.

The presence, in the precoat according to this aspect of the invention, of a lamellar filler with a form factor of at least 15 and of a finer particulate filler, in particular non-lamellar, the particle size of which is 80% by weight. weight is less than 2 µm (measured according to the ISO13317-3 Sedigraph method), makes it possible to obtain a relatively high barrier level, regardless of the hydrophobic nature or not of the binder.

It is known that the lamellar fillers contribute to increasing the barrier effect thanks to the tortuosity which they bring, as the document teaches for example. Imerys Technical Guide, Pigments for Paper, May 2008 . The presence according to this aspect of the invention of at least one finer particulate filler, in particular non-lamellar, increases this effect. An attempted explanation is that this charge, by interfering between the lamellar particles, further hinders the movement of water molecules, in particular around the lamellar particles. The document WO 2009/117040 A1 discloses lamellar clay fillers.

Due to the barrier effect linked to the particular choice of fillers present in the precoat, greater freedom exists as to the nature of the binder used.

It is thus possible to use in particular any paper binder without any particular barrier property, which makes it possible to obtain the double advantage of low water vapor permeability for the precoat and good wettability. -to the cover layer.

The invention makes it possible to have a reinforced barrier effect with the precoat, which allows a reduction in the amount of cover layer to be applied or, for an equal amount of cover layer, makes it possible to further increase the barrier level of the paper, which may prove useful for papers which must be impermeable to water vapor. The reduction in the amount of cover layer required, due to the stronger barrier power of the pre-coated paper, facilitates its drying and can make it easier to coat it during in-line papermaking.

The paper of the invention is preferably produced on a paper machine from a fibrous substrate consisting of cellulose fibers and optionally of synthetic fibers.

Cellulose fibers are generally a mixture of short fibers and long fibers.

Additives such as sizing agents, wet strength agents, retention agents, or defoamers can be added.

The paper can also contain paper fillers such as titanium dioxide, kaolin, calcium carbonate, talc, among others.

The paper is preferably wrapping paper.

A further subject of the invention is a precoated paper according to claim 13. The precoated paper may be uncalendered.

The present description also comprises a precoating composition for the manufacture of a paper according to the invention, comprising a binder in the form of a latex and a dispersion of a mixture of lamellar filler (s) of form factor. at least 15 and finer filler (s) whose particle size at 80% by weight is less than 2 µm.

A further subject of the invention is a packaging according to claim 14.

A further subject of the invention is a method for manufacturing a paper according to claim 15.

Precoat

The precoat can be identical to the cover layer or be a pigmentary layer as defined below.

The precoat preferably consists of a mixture of at least one latex and fillers also sometimes called “pigments”.

The document US 4,018,647 A describes examples of latex.

The latex according to the invention preferably has a Tg (glass transition temperature) measured according to the ASTM E1356 standard of less than 25 ° C and more preferably less than 10 ° C. The latex can be chosen from latexes of the following chemical natures: styrene-butadiene, styrene-acrylic, acrylics, butyl-acrylate, butyl-acrylate-styrene-acrylonitrile, etc. and more particularly from styrene-butadiene emulsions.

The latex content is preferably at least 15 parts dry relative to the dry loads (100 parts), preferably at least, or even more, 25 and better still 30 parts per 100 parts load.

The fillers are preferably constituted by a mixture of lamellar filler (s) and finer fillers, in particular non-lamellar.

The lamellar fillers are particles in the form of lamellae having a form factor (ratio between greatest length and thickness) greater than or equal to 15, more preferably at least 40 and even more preferably at least 60 .

The precoat comprises a binder and a mixture of lamellar filler (s) with a form factor of at least 15 and finer filler (s), in particular non-lamellar (s), whose particle size is 80% by weight less than 2 μm (measured according to the ISO13317-3 Sedigraph method).

To have a mixture of lamellar filler (s) and finer filler (s) whose 80% by weight particle size is less than 2 µm, the 80% by weight particle size of lamellar filler (s) may for example be greater than or equal to 2 μm. According to another example, less than 80% by weight of lamellar particles may be less than 2 μm.

In other words, in order to have fillers finer than the lamellar filler (s), the finer fillers may according to a first example have a particle size smaller than that of the lamellar fillers with an equivalent weight distribution. According to a second example, they can have a greater weight distribution for the same particle size than that of the lamellar fillers.

The finer fillers can be chosen from all the other pigments used in stationery, which meet the required size conditions.

The percentage of lamellar fillers relative to the total fillers can vary from 10 to 90%, preferably from 40 to 90% and even more preferably from 60 to 90%.

The lamellar fillers can be chosen, for example, from kaolin and talc, and their mixtures.

Between 30% and 80% by weight of lamellar particles can be of a size less than or equal to 2 μm (measured according to the ISO13317-3 Sedigraph method).

The particles of the lamellar charge (s) are in particular oriented substantially parallel to the surface of the substrate.

The particles of the finer charge (s) can be chosen from among calcium carbonate, barium sulphate, silica, titanium dioxide or their mixtures ... They are characterized by a particle size at 80% by weight less at 2 microns, measured according to the ISO13317-3 Sedigraph method

The finer fillers can also be chosen from any other pigment, including kaolin, of sufficient fineness, in particular with a particle size at 95% by weight of less than 2 microns, measured according to the ISO13317-3 Sedigraph method.

The binder is preferably chosen from the aforementioned latexes but other binders or co-binders such as PVOH, starch, CMC, etc. can be used. The binder may comprise a polymer of a chemical nature not present in the cover layer.

Cover layer

The polymers used to obtain the vapor barrier and the heat-sealability are preferably chosen from polymers or copolymers based on PVdC (polyvinylidene chloride) or acrylic.

These polymers are applied pure or mixed with fillers. By “pure” is meant without particulate filler. It is optionally possible to add other products to the dispersion of polymers, such as agents for managing the pH, rheological agents (viscosity for example), anti-foaming agents, wetting agents,

The use of fillers within the covering layer can in particular help reduce the risk of the turns of the coil sticking together.

Manufacturing

Preferably the topcoat is applied in-line.

The invention makes it possible to obtain good levels of water vapor barrier with cover layer weights not exceeding 10 g / m ² in sec.

Despite the relatively high speed of advance of the paper imposed by an industrial papermaking machine, for example of the order of 400 m / min, in-line coating of a composition intended to form the heat-sealing cover layer is possible. , provided that sufficient drying capacity is used to dry the layer before the winding operation. In particular, a relatively low cover layer weight can facilitate in-line drying, while providing sufficient barrier properties.

The on-line process increases productivity by eliminating the handling operations associated with off-line processing.

After drying the fibrous substrate, the paper sheet can pass over a Yankee cylinder to improve the surface condition of the sheet and thus the distribution of the first layer.

The sheet can then be treated in a size press or any other equipment of the same type. To prevent the precoat from penetrating too much into the fibrous support, a pigment composition can be used beforehand in order to make “filler”.

This filler composition can contain up to 20 parts dry relative to the dry fillers of binder such as latex, of a styrene-butadiene chemical nature for example, and up to 20 dry parts relative to the dry pigments of co-binders such as starch for example.

This composition preferably contains fillers which are generally less than 2 microns in size. These fillers can be chosen, inter alia, from kaolins or calcium carbonates or their mixtures.

The precoat is applied to the substrate thus treated using any of the coating techniques which may be encountered on paper machines. This may in particular be blade coating, rotogravure, reverse engraving or Meyer bar coating. The precoat is deposited with a dry layer weight preferably between 4 and 12 g / m ² .

This precoat is then dried without contact by one or more infrared ovens and / or one or more hot air ovens.

It is not necessary to have a very high level of satin before applying the top coat. A level of 150 seconds Bekk is sufficient (measured according to ISO 5627).

The water vapor barrier and heat sealing cover layer is applied by coating using any of the coating techniques which may be encountered on paper machines. This may for example be a blade coating, rotogravure, reverse engraving or a Meyer bar coating. The cover layer is deposited with a dry layer weight of 10 g / m ² at most.

This covering layer is then sufficiently dried, to prevent the turns from sticking to the winding reel, using one or more infrared ovens and / or one or more hot air ovens. .

A coating on the opposite face can be carried out to reinforce the barrier and / or to provide other functionalities such as printability, curl correction, etc.

The paper thus produced can optionally be calendered in-line to reduce surface roughness before being taken up.

The final paper weight can be between 45 and 200g / m ² .

The barrier to water vapor measured according to ASTM F1249 at 38 ° C and 90% relative humidity is less than 150g / m ² / 24h, and preferably to 100g / m ² / 24h.

Example 1 :

A fibrous support of 55 g / m ^{2 basis} weight is produced on a paper machine operating at 400 m / min. The paper machine is equipped with a Yankee roller placed before the size-press.

The fibrous support is first rubbed and then treated in-line on both sides by size-press with a pigmentary filler composition, containing 100 dry parts of Amazon Premium type kaolin (Cadam), and a mixture of Merifilm 104 starch. (Tate & Lyle) and LD950 type latex (Dow) in an amount of 20 parts dry relative to the dry kaolin The treatment applied is 5 g / m ² sec in total.

It is then coated using a Meyer bar coater with a precoat formulation containing a mixture of lamellar fillers and finer particulate fillers and a styrene-butadiene chemical latex of Tg = 7 ° C (LD950 from Dow Chemical) and dried without contact on an infrared oven and then a hot air oven. It is then wound into a coil without further processing. The dry weight of the applied precoat is 7g / m ² and its formulation is given in the table below: Material Reference / Nature Suppliers Parts % mass Topsperse GX-N Dispersing COATEX 0.2 0.2 Capim NP Kaolin (lamellar filler) IMERYS 60.0 45.5 Amazon Premium Kaolin (finer charge) CADAM 40.0 30.4 Bacote 20 Crosslinking QUARRECHIM 1.5 1.1 LD950 / Styrene-butadiene latex Tg 7 ° C Styrene-butadiene latex Tg 7 ° C DOW 30.0 22.8

Amazon Premium's 97% by weight particle size, measured using the ISO13317-3 Sedigraph method, is less than 2 microns.

Capim NP particle shape factor is 28.

The water vapor barrier is measured by a device of the Mocon brand, of the Permatran 3/61 type according to the ASTM F1249 standard at 38 ° C. and 90% relative humidity to determine the barrier contribution of this precoat. It is measured at 334 +/- 13g / m ² / 24h. After coating the covering layer, a barrier of less than 150 g / m ² / 24h is obtained.

Example 2

The fibrous support is first rubbed and then treated in-line on both sides by size-press with a pigmentary filler composition containing 100 dry parts of Amazon Premium type kaolin (Cadam) and a mixture of Merifilm 104 starch (Tate & Lyle ) and LD950 (Dow) type latex in an amount of 20 parts dry relative to the dry kaolin. The treatment applied is 5 g / m ² sec in total.

It is then coated using a Meyer bar coater with a formulation containing a mixture of lamellar fillers and finer particulate fillers and a styrene-butadiene chemical latex of Tg = 7 ° C (DL950 from Dow Chemical) and dried without contact on an infrared oven and then a hot air oven. It is then wound into a coil without further processing. The dry weight of the applied precoat is 7g / m ² and its formulation is given in the table below: Material Reference / Nature Suppliers Parts % mass Topsperse GX-N Dispersing COATEX 0.2 0.2 Capim NP Kaolin (lamellar filler) IMERYS 60.0 45.5 Hydrocarb 95 Calcium carbonate (finer filler) OMYA 40.0 30.4 Bacote 20 Crosslinking QUARRECHIM 1.5 1.1 LD950 / Styrene-butadiene latex Tg 7 ° C Styrene-butadiene latex Tg 7 ° C DOW 30.0 22.8

The particle size at 95% by weight of Hydrocarb 95, measured according to the ISO13317-3 Sedigraph method, is less than 2 microns.

The water vapor barrier is measured by a device of the Mocon brand, of the Permatran 3/61 type according to the ASTM F1249 standard at 38 ° C. and 90% relative humidity to determine the barrier contribution of this precoat. It is measured at 315 +/- 9g / m ² / 24h. After coating the covering layer, a barrier of less than 150 g / m ² / 24h is obtained.

Example 3 :

A paper is produced in line under the same conditions as in Example 1. But following the removal of the precoat, it is coated in line with a cover layer consisting of a dispersion of PVdC copolymer (Diofan A297 from Solvay), and dried without contact in an infrared oven then a hot air oven. It is then wound into a coil without further treatment and no sticking between turns is observed. The dry weight of the cover layer is 6.5g / m ² .

The water vapor barrier is measured by a Mocon brand device, of the Permatran 3/61 type according to the ASTM F1249 standard at 38 ° C and 90% relative humidity. It is measured at 21.0 +/- 2.4g / m2 / 24h.

The sealing is then simulated on a laboratory heat sealer by gluing the face covered with the covering layer on itself at 110 ° C, under 3 bars and for 0.5 seconds. Then the force necessary to detach the papers glued on samples of width of 15mm is then measured at an angle of 90 degrees according to the Tappi T540 standard at a speed of 100mm / min.

A sealing force of 3.5N / 15mm is obtained.

The invention is not limited to the examples described.

• le poids de la couche de recouvrement est strictement inférieur à 10g/m² en sec,
• la couche de recouvrement est constituée par un polymère thermoscellable,
• la ou les charge(s) lamellaire(s) et la ou les charge(s) plus fine(s) sont de même nature,
• le facteur de forme des particules de charge(s) lamellaire(s) est d'au moins 40, plus préférentiellement d'au moins 60,
• la ou les charge(s) plus fine(s) sont non lamellaire(s),
• la ou les charge(s) plus fine(s) sont lamellaire(s),
• la ou les charge(s) plus fine(s) ont une taille de particule à 95% en poids, inférieure à 2 microns, mesurée selon la méthode Sédigraph ISO 13317-3,
• la ou les charges lamellaires sont minérales,
• la ou les charge(s) plus fine(s) sont minérale(s),
• la ou les charge(s) lamellaire(s) sont choisie(s) parmi les kaolins et le talc et leurs mélanges,
• la ou les charge(s) plus fine(s) sont choisie(s) parmi les kaolins, carbonate de calcium, le sulfate de baryum, la silice, le dioxyde de titane et leurs mélanges,
• la ou les charge(s) plus fine(s) sont choisie(s) parmi les kaolins,
• le poids de charge(s) lamellaire(s) est supérieur à celui des charges plus fines,
• le pourcentage de charge(s) lamellaire(s), exprimé en poids sec, par rapport au total des charges, exprimé en poids sec, est compris entre 10 et 90%, préférablement entre 40 et 90% et encore plus préférablement entre 60 et 90%,
• le liant présente une température de transition vitreuse T_g inférieure ou égale à 25°C et de manière plus préférée inférieure à 10°C,
• le liant est choisi parmi les latex de nature chimique styrène-butadiène, styrène-acrylique, acryliques, butyl-acrylate, butyl-arcylate-styrène-acrylonitrile, et leurs mélanges,
• le liant est choisi parmi les latex de nature chimique styrène-butadiène,
• le liant est introduit sous forme de latex,
• la précouche comporte plus de 25 parts en sec de liant par rapport au poids en charges à sec (100 parts), mieux 30 parts,
• le liant comporte un polymère de nature chimique non présente dans la couche de recouvrement,
• la couche de recouvrement est sensiblement sans charge,
• la couche de recouvrement est l'unique couche recouvrant la précouche,
• la couche de recouvrement comporte un ou plusieurs polymères choisis parmi les copolymères à base de PVdC ou de styrène-acrylique et leurs mélanges,
• le papier comporte une couche d'imprimabilité sur la face du substrat opposée à celle portant la précouche et la couche de recouvrement,
• le substrat porte deux précouches identiques sur ses faces opposées,
• le substrat porte deux précouches de natures différentes sur ses faces opposées,
• une composition bouche-pores est appliquée sur le substrat, et la précouche est appliquée sur la composition bouche-pores, la composition bouche-pores étant appliquée de préférence par size-press ou film-press,
• le grammage du substrat fibreux est compris entre 25 et 180g/m²,
• le papier est thermoscellable, notamment à partir de 90°C, lorsque le scellage est effectué sur des pinces chaudes, sous 3 bars et durant 0.5s,
• la perméabilité à la vapeur d'eau du papier barrière est inférieure à 100 g/m²/24h.
• entre 30% et 80% en poids de particules lamellaires sont de taille inférieure ou égale à 2µm (mesurée selon la méthode Sédigraph ISO13317-3),
• le papier est thermoscellable, notamment sur lui-même, à une cadence de fabrication supérieure ou égale à 40 sacs par minute, sur des machine d'emballage verticales de type VFFS (Vertical Form, Fill and Seal), le long de lignes de scellage longitudinales de 330 mm par sac,
• le papier est thermoscellable sur lui-même avec une force de scellage supérieure ou égale à 2 N/15mm, mesurée sous un angle de 90 degrés selon la norme Tappi T540 à une vitesse de 100mm/min, lorsque le scellage est effectué sur des pinces chaudes, sous 3 bars, et durant 0,5 s,
• la température du substrat fibreux lors de l'application de la précouche est supérieure ou égale à 50°C,
• la température du substrat fibreux lors de l'application de la couche de recouvrement est supérieure ou égale à 70°C,
• le grammage final du papier est compris entre 45 et 200g/m².

In summary, the invention may exhibit one or more of the following advantageous characteristics:

• the weight of the covering layer is strictly less than 10g / m ² in sec,
• the covering layer consists of a heat-sealable polymer,
• the lamellar charge (s) and the finer charge (s) are of the same nature,
• the form factor of the particles of lamellar filler (s) is at least 40, more preferably at least 60,
• the finer charge (s) are non-lamellar (s),
• the finer charge (s) are lamellar (s),
• the finer filler (s) have a particle size of 95% by weight, less than 2 microns, measured according to the ISO 13317-3 Sedigraph method,
• the lamellar fillers are mineral,
• the finer charge (s) are mineral (s),
• the lamellar filler (s) are chosen from kaolins and talc and their mixtures,
• the finer filler (s) are chosen from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and their mixtures,
• the finer filler (s) are chosen from kaolins,
• the weight of the lamellar charge (s) is greater than that of the finer charges,
• the percentage of lamellar filler (s), expressed in dry weight, relative to the total fillers, expressed in dry weight, is between 10 and 90%, preferably between 40 and 90% and even more preferably between 60 and 90%,
• the binder has a glass transition temperature T _g less than or equal to 25 ° C and more preferably less than 10 ° C,
• the binder is chosen from styrene-butadiene, styrene-acrylic, acrylic, butyl-acrylate, butyl-arcylate-styrene-acrylonitrile chemical latexes, and mixtures thereof,
• the binder is chosen from latex of styrene-butadiene chemical nature,
• the binder is introduced in the form of latex,
• the precoat comprises more than 25 parts in dry binder compared to the weight in dry loads (100 parts), better 30 parts,
• the binder comprises a polymer of chemical nature not present in the cover layer,
• the cover layer is substantially load-free,
• the cover layer is the only layer covering the precoat,
• the covering layer comprises one or more polymers chosen from copolymers based on PVdC or on styrene-acrylic and their mixtures,
• the paper has a printability layer on the face of the substrate opposite to that carrying the precoat and the cover layer,
• the substrate has two identical pre-layers on its opposite faces,
• the substrate has two pre-layers of different types on its opposite faces,
• a pore-filler composition is applied to the substrate, and the precoat is applied to the pore-filler composition, the pore-filler composition preferably being applied by size-press or film-press,
• the basis weight of the fibrous substrate is between 25 and 180 g / m ² ,
• the paper is heat-sealable, in particular from 90 ° C, when the sealing is carried out on hot tongs, at 3 bars and for 0.5s,
• the water vapor permeability of the barrier paper is less than 100 g / m ² / 24h.
• between 30% and 80% by weight of lamellar particles are of a size less than or equal to 2 μm (measured according to the ISO13317-3 Sédigraph method),
• the paper is heat-sealable, in particular on itself, at a production rate greater than or equal to 40 bags per minute, on vertical packaging machines of the VFFS (Vertical Form, Fill and Seal) type, along sealing lines longitudinal 330 mm per bag,
• the paper is heat-sealable on itself with a sealing force equal to or greater than 2 N / 15mm, measured at an angle of 90 degrees according to the Tappi T540 standard at a speed of 100mm / min, when the sealing is carried out on clamps hot, under 3 bars, and for 0.5 s,
• the temperature of the fibrous substrate during the application of the precoat is greater than or equal to 50 ° C,
• the temperature of the fibrous substrate during the application of the covering layer is greater than or equal to 70 ° C,
• the final paper weight is between 45 and 200g / m ² .

The expression “comprising a” should be understood as being synonymous with “comprising at least one”.

Claims (15)

1. Paper comprising:

   - a fibrous substrate,

   - a precoat layer comprising a binder and a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), notably non-platy filler(s), the size of the particles of which is, for 80% by weight, less than 2 µm (measured according to the ISO 13317-3 SediGraph method), the dry weight of platy filler(s) being between 3% and 58% of the total dry weight of the precoat layer, the dry weight of finer filler(s) being between 3% and 58% of the total dry weight of the precoat layer, the precoat comprising at least 15 parts when dry of binder relative to the weight of fillers when dry (100 parts),

   - at least one covering layer applied to the precoat layer, the covering layer comprising a heat-sealable polymer,

   the paper having a water vapour permeability of at most 150 g/m²/24 h and preferably of less than 100 g/m²/24 h, measured according to the ASTM F1249 standard under so-called tropical conditions of 38°C and 90% relative humidity,
   the amount of precoat layer being less than or equal to 12 g/m² by dry weight, the weight of the covering layer not exceeding 10 g/m² when dry.
2. Paper according to Claim 1, the weight of the covering layer being strictly less than 10 g/m², the covering layer being preferably constituted by a heat-sealable polymer, the platy filler(s) and the finer filler(s) being preferably of the same nature.
3. Paper according to one of the preceding claims, the shape factor of the platy filler particles being at least 40, more preferably at least 60, the finer filler(s) having a particle size, for 95% by weight, of less than 2 microns, measured according to the ISO 13317-3 SediGraph method, the platy filler(s) being preferably mineral filler(s) and/or the finer filler(s) being preferably mineral filler(s).
4. Paper according to any one of the preceding claims, the platy filler(s) being selected from kaolins and talc and mixtures thereof.
5. Paper according to any one of the preceding claims, the finer filler(s) being selected from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof.
6. Paper according to any one of the preceding claims, the weight of platy filler(s) being greater than that of the finer fillers, the percentage of platy filler(s), expressed by dry weight, relative to the sum of the fillers, expressed by dry weight, being preferably between 10% and 90%, preferably between 40% and 90% and more preferably still between 60% and 90%.
7. Paper according to any one of the preceding claims, the binder having a glass transition temperature T_g below or equal to 25°C and preferably below 10°C, the binder being preferably selected from latices of styrene-butadiene, styrene-acrylic, acrylic, butyl acrylate, butyl acrylate-styrene-acrylonitrile chemical nature, and mixtures thereof, the binder being notably selected from latices of styrene-butadiene chemical nature.
8. Paper according to any one of the preceding claims, comprising in the precoat layer more than 25 parts when dry of binder relative to the weight of fillers when dry (100 parts), better still 30 parts, the binder comprising preferably a polymer of chemical nature not present in the covering layer.
9. Paper according to any one of the preceding claims, the covering layer being substantially free of filler and/or the covering layer being the only layer that covers the precoat layer, the covering layer comprising preferably one or more polymers selected from copolymers based on PVdC or on styrene-acrylic and mixtures thereof.
10. Paper according to any one of the preceding claims, the basis weight of the fibrous substrate being between 25 and 180 g/m².
11. Paper according to any one of the preceding claims, the paper being heat-sealable, in particular starting from 90°C, when the sealing is carried out by hot clamps, under 3 bar and for 0.5 s.
12. Paper according to any one of the preceding claims, the final basis weight of the paper being between 45 and 200 g/m².
13. Precoated paper suitable for the manufacture of a paper as defined in any one of Claims 1 to 12, the precoated paper comprising:

    - a fibrous substrate,

    - a precoat layer comprising a binder and a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), notably non-platy filler(s), the size of the particles of which is, for 80% by weight, less than 2 µm (measured according to the ISO 13317-3 SediGraph method), the dry weight of platy filler(s) being between 3% and 58% of the total dry weight of the precoat layer, the dry weight of finer filler(s) being between 3% and 58% of the total dry weight of the precoat layer, the precoat comprising at least 15 parts when dry of binder relative to the weight of fillers when dry (100 parts), the amount of precoat layer being less than or equal to 12 g/m² by dry weight.
14. Packaging comprising a paper as defined in one of Claims 1 to 12, the paper being preferably heat-sealed to itself, containing preferably a food product.
15. Process for manufacturing a paper according to any one of Claims 1 to 12, in which a composition is applied to a fibrous substrate, the composition comprising a binder in latex form and a dispersion of a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), the size of the particles of which is, for 80% by weight, less than 2 µm.