EP3186442B2 - Heat-sealing barrier paper - Google Patents

Description

The present invention relates to the field of wrapping papers.

Plastic films are widely used in flexible packaging because they have water vapor barrier properties necessary for the proper preservation of perishable products or products with a limited lifespan.

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

However, it is known to combine papers with other materials (plastics, aluminum, etc.) to obtain the barriers necessary for the packaging of various products and in particular perishable foods. In this case the paper substrate is subjected to processing operations which include for example the coating of cover layers made of dispersion 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 process for manufacturing wrapping paper.

Packaging made from barrier papers manufactured online are described in the application WO2011/056130 . By online manufacturing we mean manufacturing on a single production tool comprising all the elements useful for making paper.

However, the proposed barrier level is limited to slightly restrictive measurement conditions (temperate, i.e. 25°C, 75% relative humidity). The barrier level is measured by water vapor permeability, with a low barrier meaning 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 that therefore the barrier measured in temperate conditions is much lower.

By "barrier paper" is meant a non-porous paper, comprising a fibrous substrate covered with one or more layers, sufficiently impervious to water vapor to prevent its penetration into the packaging , in a quantity likely to affect the preservation of the product or the integrity of the product contained inside.

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

It is advantageous for the barrier paper to also be heat sealable, in order to allow the packaging to be formed by welding the paper onto itself.

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

The application of this covering layer is generally carried out offline during one or more transformation stages, which allows for good coating quality and 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 width in the ovens, at a speed for example of the order of 200m/min, so that the duration of exposure to these heating means is sufficient to completely dry the heat-sealing covering layer in depth.

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 possibly heat sealing, are generally manufactured according to the state of the art during transformation operations and as standard have covering layers of 10 to 30 g/m ² dry which are deposited in one or more thicknesses using different coating means (air blade, reverse etching, Meyer blade or bar or any other coating method) or by applying a thick layer to the using a curtain bed.

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

The invention relates to the development of a paper having, during its on-line manufacturing, water vapor barrier and heat sealability properties. This barrier and heat-sealing paper can be used to make packaging by welding the paper onto itself.

Regardless of the way in which the heat-sealing layer is applied, online or offline, the problem arises of facilitating the deposit 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 covering layer does not penetrate too deeply into the fibrous substrate, to reduce the applied quantity of paper when this layer is polymer-based. In addition, less penetration of the covering layer makes it easier to create a barrier film.

The use of a friction cylinder (Yankee cylinder in English) is a first solution to reduce 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 other of the previous 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 wettability problem during the application of the covering layer, when the latter is aqueous, leading to non-perfectly homogeneous coverage of the fibrous substrate precoated by the covering layer, especially in the case of an in-line process with high sheet speed. In addition, the surface energy of the precoat must be sufficiently different from that of the covering layer while respecting the well-known rules of wettability in order to reduce the risk of wetting defects.

There therefore remains a need to respond satisfactorily to the problem of the applicability of the covering layer.

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

The presence, in the prelayer according to this aspect of the invention, of a lamellar filler with a shape factor of at least 15 and of a finer particle filler, in particular non-lamellar, whose particle size is 80% in weight is less than 2 µm (measured according to the Sédigraph ISO13317-3 method), makes it possible to obtain a relatively high barrier level, regardless of the hydrophobic or non-hydrophobic nature of the binder.

It is known that lamellar fillers contribute to increasing the barrier effect thanks to the tortuosity they provide, as taught for example in the document 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 attempt at an 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 fillers of clay.

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 screw wettability. -with respect to the covering layer.

The invention makes it possible to have a reinforced barrier effect with the precoat, which allows a reduction in the quantity of covering layer to be applied or, for an equal quantity of covering layer, makes it possible to further increase the barrier level of the paper, which can be useful for papers that need to be waterproof against water vapor. Reducing the quantity of covering layer required, due to the stronger barrier power of pre-coated paper, makes it easier to dry and can make it easier to coat during online paper manufacturing.

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

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

Additives such as fining agents, wet strength agents, retention agents, or defoamers may be added.

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

The paper is preferably wrapping paper.

This description also includes a pre-coated paper. Pre-coated paper may be uncalendered.

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

The invention also relates to packaging according to claim 12.

The invention also relates to a process for manufacturing a paper according to claim 13.

Precoat

The precoat may be identical to the covering layer or be a pigment layer as defined below.

The precoat is preferably made up of a mixture of at least one latex and sometimes even fillers. 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 rate is preferably at least 15 dry parts relative to the dry fillers (100 parts), preferably at least, or even more, 25 and better still 30 parts per 100 filler parts.

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

The lamellar filler(s) 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 filler(s), whose particle size is 80% by weight less than 2 µm (measured according to the Sédigraph ISO13317-3 method).

To have a mixture of lamellar filler(s) and finer filler(s) whose particle size at 80% by weight is less than 2 µm, the particle size at 80% by weight of lamellar filler(s) can 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, to have finer fillers than the lamellar filler(s), the finer fillers can, according to a first example, have a smaller particle size than that of the lamellar fillers with equivalent weight distribution. According to a second example, they can have a greater weight distribution for the same particle size than that of lamellar fillers.

Finer fillers can be chosen from any other pigments used in stationery, which meet the required size requirements.

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 mixtures thereof.

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

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

The particles of the finer filler(s) may be chosen from calcium carbonate, barium sulfate, silica, titanium dioxide or mixtures thereof, etc. They are characterized by a particle size 80% lower by weight. at 2 microns, measured according to the Sédigraph ISO13317-3 method

The finer fillers can also be chosen from any other pigment, including kaolin, of sufficient fineness, in particular by a particle size at 95% by weight of less than 2 microns, measured according to the Sédigraph ISO13317-3 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 include a polymer of a chemical nature not present in the covering layer.

Cover layer

The polymers used to obtain the vapor barrier and heat sealability are chosen from copolymers based on PVdC (polyvinylidene chloride). The covering layer is substantially load-free and/or the covering layer is the only layer covering the pre-layer,

These polymers are applied pure or mixed with fillers. By “pure” we mean without particle charge. Other products can optionally be added to the polymer dispersion such as pH management agents, rheological agents (viscosity for example), anti-foam agents, wettability agents,

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

Manufacturing

Preferably, the covering layer is applied in-line.

The invention makes it possible to obtain good water vapor barrier levels with covering layer weights not exceeding 10g/m ² dry.

Despite the relatively high speed of advancement of the paper imposed by an industrial paper manufacturing machine, of the order for example of 400 m/min, the in-line coating of a composition intended to form the heat-sealing covering 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 online process increases productivity by eliminating handling operations associated with offline processing.

After drying the fibrous substrate, the paper sheet can pass through a friction cylinder (“Yankee cylinder” in English) to improve the surface condition of the sheet and thus the distribution of the first layer.

The sheet can then be processed using a size press or any other equipment of the same type. To avoid too much penetration of the precoat into the fibrous support, a pigment composition can be used beforehand to make a “pore filler”.

This pore filler composition can contain up to 20 dry parts 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, among others, from kaolins or calcium carbonates or mixtures thereof.

The precoat is applied to the support thus treated using any of the coating techniques that can be encountered on paper machines. This may include blade coating, rotogravure, reverse engraving or Meyer bar coating. The precoat is deposited with a dry coat weight preferably between 4 and 12g/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 covering coat. A Bekk level of 150 seconds is sufficient (measured according to ISO 5627).

The water vapor barrier and heat seal overcoat is applied by coating using any of the coating techniques that may be encountered on paper machines. This can be, for example, blade coating, rotogravure, reverse engraving or Meyer bar coating. The covering layer is applied with a dry layer weight of 10g/m ² maximum.

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

Coating on the opposite side can be done 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 wound.

The final weight of the paper can be between 45 and 200g/ ^m2 .

The water vapor barrier measured according to the ASTM F1249 standard at 38°C and 90% relative humidity is less than 150g/ ^m2 /24h, and preferably less than 100g/ ^m2 /24h.

Example 1:

A fibrous support with a weight of 55g/ ^m2 is produced on a paper machine operating at 400m/min. The paper machine is equipped with a friction roller placed before the size press.

The fibrous support is first rubbed then treated in-line on both sides by size-press with a pore-filling pigment composition, containing 100 dry parts of Amazon Premium type kaolin (Cadam), and a mixture of Merifilm 104 starch. (Tate&Lyle) and DL950 type latex (Dow) at a rate of 20 dry parts compared to dry kaolin. The treatment applied is 5g/m ² dry 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 (DL950 from Dow Chemical) and dried without contact on an infrared oven then a hot air oven. It is then wound into a coil without further processing. The dry weight of the applied precoat is 7g/ ^m2 and its formulation is given in the table below: Matter Reference/Nature Suppliers Shares % by mass Topsperse GX-N Dispersant COATEX 0.2 0.2 Capim NP Kaolin (lamellar filler) IMERYS 60.0 45.5 Amazon Prime Kaolin (finer filler) CADAM 40.0 30.4 Bacote 20 Cross-linker QUARRECHIM 1.5 1.1 DL950/Styrene-butadiene latex Tg 7°C Styrene-butadiene latex Tg 7°C DOW 30.0 22.8

The particle size at 97% by weight of Amazon Prime, measured using the Sédigraph ISO13317-3 method, is less than 2 microns.

The particle form factor of Capim NP is 28.

The water vapor barrier is measured by a Mocon brand device, type Permatran 3/61 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/ ^m2 /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 then treated in-line on both sides by size-press with a pore-filler pigment composition containing 100 dry parts of Amazon Premium type kaolin (Cadam) and a mixture of Merifilm 104 starch (Tate&Lyle). ) and DL950 type latex (Dow) at a rate of 20 dry parts compared to dry kaolin. The treatment applied is 5g/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 then a hot air oven. It is then wound into a coil without further processing. The dry weight of the applied precoat is 7g/ ^m2 and its formulation is given in the table below: Matter Reference/Nature Suppliers Shares % by mass Topsperse GX-N Dispersant COATEX 0.2 0.2 Capim NP Kaolin (lamellar filler) IMERYS 60.0 45.5 Hydrocarbon 95 Calcium carbonate (finer filler) OMYA 40.0 30.4 Bacote 20 Cross-linker QUARRECHIM 1.5 1.1 DL950/Styrene-butadiene latex Tg 7°C Styrene-butadiene latex Tg 7°C DOW 30.0 22.8

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

The water vapor barrier is measured by a Mocon brand device, type Permatran 3/61 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 online under the same conditions as in Example 1. But following the deposition of the precoat, it is coated online with a covering layer consisting of a dispersion of PVdC copolymer (Diofan A297 from Solvay), and dried without contact on 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 covering layer is 6.5g/ ^m2 .

The water vapor barrier is measured by a Mocon brand device, type Permatran 3/61 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 side covered with the layer recovery on itself at 110°C, under 3 bars and for 0.5 seconds. Then the force required to detach the papers stuck on samples with a 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,
• 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 have one or more of the following advantageous characteristics:

• the weight of the covering layer is strictly less than 10g/m ² in dry,
• the covering layer consists of a heat-sealable polymer,
• the lamellar filler(s) and the finer filler(s) are of the same nature,
• the shape factor of the particles of lamellar filler(s) is at least 40, more preferably at least 60,
• the finer filler(s) are non-lamellar(s),
• the finer filler(s) are lamellar(s),
• the finer filler(s) have a particle size of 95% by weight, less than 2 microns, measured according to the Sédigraph ISO 13317-3 method,
• the lamellar filler(s) are mineral,
• the finer filler(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 sulfate, silica, titanium dioxide and their mixtures,
• the finer filler(s) are chosen from kaolins,
• the weight of the lamellar filler(s) is greater than that of the finer fillers,
• 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 chemical latexes of styrene-butadiene, styrene-acrylic, acrylic, butyl-acrylate, butyl-arcylate-styrene-acrylonitrile, and their mixtures,
• the binder is chosen from latexes of a styrene-butadiene chemical nature,
• the binder is introduced in the form of latex,
• the precoat contains more than 25 dry parts of binder compared to the weight of dry fillers (100 parts), better 30 parts,
• the binder comprises a polymer of a chemical nature not present in the covering layer,
• the paper has a printability layer on the face of the substrate opposite to that carrying the precoat and the covering layer,
• the substrate carries two identical precoats on its opposite faces,
• the substrate carries two precoats of different natures 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 being preferably applied by size-press or film-press,
• the weight of the fibrous substrate is between 25 and 180g/m ² ,
• the paper is heat-sealable, particularly from 90°C, when the sealing is carried out on hot clamps, under 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 2µm (measured according to the Sédigraph ISO13317-3 method),
• the paper is heat-sealable, particularly on itself, at a manufacturing 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 of 330 mm per bag,
• the paper is heat sealable on itself with a sealing force greater than or equal to 2 N/15mm, measured at an angle of 90 degrees according to the Tappi T540 standard at a speed of 100mm/min, when sealing is carried out on pliers hot, under 3 bars, and for 0.5 s,
• the temperature of the fibrous substrate during application of the precoat is greater than or equal to 50°C,
• the temperature of the fibrous substrate during application of the covering layer is greater than or equal to 70°C,
• the final weight of the paper is between 45 and 200g/ ^m2 .

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

Claims (13)

1. Paper comprising:

   - a fibrous substrate,

   - a pre-layer comprising a binder and a mixture of lamellar filler(s) having a form factor of at least 15 and finer filler(s), in particular non-lamellar filler(s), the particle size of which at 80 wt.% is less than 2 um (measured according to the SediGraph method ISO 13317-3), the lamellar filler dry weight being between 3 and 58% of the total dry weight of the pre-layer, the finer filler dry weight being between 3 and 58% of the total dry weight of the pre-layer, the pre-layer comprising at least 15 parts dry binder to dry filler weight (100 parts),

   - at least one cover layer applied to the pre-layer, the cover layer comprising a heat-sealable polymer, the cover layer being substantially without filler and/or the cover layer being the only layer covering the pre-layer, the cover layer comprising a PVdC-based copolymer, the paper having a permeability to water vapour of at most 150g/m²/24h and preferably less than 100g/m²/24h, measured according to the ASTM F1249 standard in so-called tropical conditions at 38°C and 90% relative humidity,

   the quantity of pre-layer being less than or equal to 12g/m² by dry weight, the dry weight of the cover layer not exceeding 10g/m².
2. Paper according to claim 1, the weight of the cover layer being strictly less than 10 g/m², the cover layer preferably being composed of a heat-sealable polymer, the lamellar filler(s) and the finer filler(s) preferably being of the same kind.
3. Paper according to any of the preceding claims, the form factor of the lammelar filler particles being at least 40, more preferably at least 60, the finer filler(s) having a particle size at 95 wt.% of less than 2 microns, measured according to the SediGraph method ISO 13317-3, the lamellar filler(s) preferably being mineral and/or the finer filler(s) preferably being mineral.
4. Paper according to any of the preceding claims, the lamellar filler(s) being chosenne from among kaolins and talc and mixtures thereof.
5. Paper according to any of the preceding claims, the finer filler(s) being chosen from among kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof.
6. Paper according to any of the preceding claims, the lamellar filler weight being greater than that of the finer fillers, the percentage of lamellar filler(s), expressed in dry weight, with respect to the total of the fillers, expressed in dry weight, preferably being between 10 and 90%, preferably between 40 and 90% and even more preferably between 60 and 90%.
7. Paper according to any of the preceding claims, the binder having a glass transition temperature T_g of less than or equal to 25°C and preferably less than 10°C, the binder preferably being chosen from among the chemical latexes styrene-butadiene, styrene-acrylic, acrylics, butyl-acrylate, butyl-arcylate-styrene-acrylonitrile and mixtures thereof, the binder in particular being chosen from among the chemical latexes styrene-butadiene.
8. Paper according to any of the preceding claims, comprising in the pre-layer more than 25 parts dry binder to dry filler weight (100 parts), better 30 parts, the binder preferably comprising a chemical polymer not present in the cover layer.
9. Paper according to any of the preceding claims, the grammage of the fibrous substrate being between 25 and 180g/m².
10. Paper according to any of the preceding claims, the paper being heat-sealable, in particular from 90°C, when the sealing is carried out on hot pliers, at 3 bars and for 0.5s.
11. Paper according to any of the preceding claims, the final grammage of the paper being between 45 and 200g/m².
12. Packaging comprising paper of the like defined in any of claims 1 to 11, the paper preferably being heatsealed to itself, preferably containing a food product.
13. Method for manufacturing paper according to any of claims 1 to 11, wherein a composition comprising a binder in the form of latex and a dispersion of a mixture of lamellar filler(s) having a form factor of at least 15 and finer filler(s) of which the particle size at 80 wt.% is less than 2 um is applied to a fibrous substrate.