FR3001236A1 - AQUEOUS COMPOSITION FOR THE PRODUCTION OF FIBROUS SHEET CARRIERS WITH IMPROVED MECHANICAL STRENGTH PROPERTIES, PROCESS, USE, FIBROUS CARRIERS AND MANUFACTURED ARTICLES THEREOF - Google Patents

Abstract

The present invention relates to an aqueous composition for treating a fibrous sheet material comprising: at least one alkali metal silicate, and preferably a Na, K or Li silicate or a mixture of these alkali metals; at least one mineral filler, characterized in that the mass ratio between the inorganic filler and the alkali silicate in the dry extract of the composition is from 0.25 to 4, and preferably from 0.3 to 3 and preferably from 0 to 5 to 1.5; associated uses and processes, as well as fibrous supports and manufactured articles obtained.

Description

The present invention relates to the technical field of fibrous sheet materials, especially paper and cardboard, and more particularly paper used for the manufacture of corrugated cardboard. More specifically, the invention relates to aqueous compositions that can be used in an industrial process for the manufacture of fibrous materials in a continuous manner, enabling the manufacture of recyclable and repulpable sheet fibrous materials having a mechanical strength and, more particularly, a resistance to compression, improved, a method for making such fibrous sheet materials. A fibrous material is produced by wet process, by the dewatering through one or more webs of one or more diluted streams of dough. The various jets are so many folds that can be assembled in one step or in separate steps. The wet paper or cardboard sheet is dewatered between two rollers to extract a major portion of water and consolidate it before being dried in contact with cylinders internally heated with steam under pressure. An aqueous composition may be sprayed or deposited between the plies or on the surface of the sheet to impregnate the surface or all or part of the thickness. This composition is intended to bind the folds, to strengthen the mechanical strength of the material or to confer barrier or functional properties. A corrugated board consists of one, or most often, several sheets of fluted paper bonded to one, or most often, several sheets of flat paper. The paper sheets used can be made from recycled paper (testliner or recycled groove) or virgin paper (kraftliner, semi-chemical groove). The different leaves are usually glued by heat, with a glue, most often starchy. The corrugated cardboard used for the manufacture of packaging intended to be used under conditions of high hygrometry (tropical conditions, refrigerated food packaging, etc.) generally consist of kraft liner-based covering paper and grooves made from virgin fibers (semi-chemical pulps). Corrugated cartons are increasingly made with recycled paper. The main application of corrugated board is the formation of packaging that is often stored and / or used in wet conditions. This is the case, for example, for packaging for fresh products, such as fruits, vegetables, fish, or frozen products. However, the compressive strength of these packages is greatly degraded under conditions of high hygrometry. In order to improve the mechanical strength, particularly in the wet state, packaging, or more generally fibrous sheet materials, many treatments have been proposed, either directly in the pulp used for the manufacture of paper at the level of the pulper or in circuits upstream of the paper machine, either by surface treatment. Starches are commonly used for strengthening the mechanical characteristics of papers, most often by starch treatment in gluing press. The amounts of starch that can be incorporated in the paper are limited by the excessively high viscosity when the starch concentration is increased, and thus it is very difficult to obtain the desirable ultimate strength characteristics, otherwise increasing the weight of the papers used, which poses economic problems. In addition, because of the hydrophilic nature of the starch, the mechanical characteristics, and in particular the compressive strength, still fall sharply in a humid medium. Many other paper surface treatments have also been proposed using chemical additives. A number of commercially available starch insolubilizers have been used. Formaldehyde has been used in the past but is no longer used because of restrictive regulations limiting the permissible amount of formaldehyde vapor to very low levels. Glyoxal also sees its limited use for similar reasons. Metal salts have also been used as insolubilizers, the most commonly used being zirconium carbonate (AZC). Surface treatments with synthetic latices and / or waxes have also been proposed. US Patents 3,308,006, US 4,117,199, US 5,658,971, JP 311,856 and US 5,750,237 disclose the use of resins and / or waxes and paraffins for improving the wet strength of papers. US Pat. No. 6,066,379, for its part, describes a surface treatment, constituting a water barrier, consisting of a synthetic polymer, a wax, which may be a paraffin wax or a polyethylene wax, and a pigment. US Pat. No. 6,794,016 also describes a surface treatment of paper, constituting a water barrier, consisting of a layer applied on at least one side of corrugated cardboard, this layer comprising a synthetic resin in emulsion and a mixture of pigments. This pigment mixture contains 5 to 40% by weight of a pigment having an average particle size of 5 to 15 microns and 60 to 95% by weight of a pigment having an average particle size of less than 3 microns. The pigments may be inorganic, such as calcium carbonate, for example precipitated, silica or kaolin; or organic such as fine powders of acrylic resin, benzoguanamine resin or starch particles. Solutions based on paraffins or microcrystalline waxes, which are the most widespread, pose recyclability problems nowadays become prohibitive. Maleic anhydride (SMA) copolymers are also used, but are too expensive for industrial packaging applications. The other solution proposed is to manufacture paper corrugated cardboard consisting essentially of virgin fibers (kraft liner and semi-chemical groove) of high grammages, which also poses economic problems in many areas. In addition, soluble silicates have found a number of applications in the paper industry for the production of crates or other packaging materials. These applications concern the use of soluble silicates, as adhesives in the manufacture of paper mandrels or spiral cardboard barrels. Soluble silicates have also been used as impregnating material for kraft liner papers for the manufacture of corrugated cardboard packaging. These techniques are generally satisfactory in most cases except when these materials treated with soluble silicates are subjected to high humidity or come into contact with water. When this occurs silicates that are hygroscopic salts rehydrate and rapidly lose their adhesive properties and stiffness. High humidity, or the presence of water, also creates a migration of silicates into the mass of the paper, thus lowering the mechanical characteristics. On the other hand, coating processes with soluble silicates are more expensive than starches commonly used for strengthening the mechanical characteristics of papers, which has so far limited their use. As a result, in the paper industry, soluble silicates are mainly used for the de-inking of waste paper and for their adhesive properties in the manufacture of packaging materials such as mandrels and cardboard barrels. The following documents describe, however, the use of alkali silicates for the improvement of the mechanical properties of paper: The patent application WO 89/10448 describes a method applicable only to the laboratory scale to improve the resistance to wet state of substrates and papers, in particular by surface treatment with a composition comprising an alkali silicate, a silicate insolubilizer and a wax or paraffin. After drying the coated composition on the paper, the resulting silicate surface film is brittle and contains microcracks that alter the water barrier properties of the coated layer on the paper surface. The role of the waxes and paraffins used is to fill these microcracks, so as to maintain the continuity of the coated layer and to retain the water barrier properties. It is mentioned a synergistic effect between the silicate and the waxes or paraffins used. The insolubilizing agent may be an oxide or carbonate of a divalent or polyvalent metal, such as zinc, calcium, beryllium, copper, tin, boron or aluminum. In the case of zinc oxide, it is envisaged to use a quantity of zinc oxide of 0.1-10% by dry weight relative to the dry weight of silicate, by carrying out a heating to obtain a relatively fast drying. 30 to 60 minutes long. US patent application 2007/0208125 describes a surface treatment composition of the paper which remains recyclable and repulpable after coating. This composition preferably used for the coating of corrugated paper is compatible with the use of starch adhesives commonly used for the production of corrugated board. The composition described in this document comprises from 10% to 70%, and preferably from 40 to 60% by weight of sodium silicate; from 10 to 60%, and preferably from 30 to 50% by weight of emulsion synthetic resin; from 10% to 50% of paraffins emulsified in water; and from 5 to 25% by weight of water. This coating composition, preferentially coated on one side of the fluting paper, for economic reasons, does not include insolubilizing agents. The masses of deposited compositions are between 3 and 25 g / m 2. US Pat. No. 5,358,554 describes a composition for the treatment of cellulosic fiber mattresses, such as paper and paperboard, to improve their mechanical strength, hydrophobicity and recyclability, combining a paraffin wax and an alkali metal silicate solution. This composition is applied as a surface treatment on paper or cardboard and does not include any mineral filler or silicate insolubilizer. The silicate is present in the composition, at a rate of about 10 to 50% by weight, relative to the total solids content, and preferably at about 25 to 40%, and preferably 30 to 35%. GB Patent 1,423,253 describes a process for the preparation of paper, splines or cartons, in which are introduced at the level of the pulper, before the manufacture of the paper, an alkali metal silicate and a thixotropic agent and / or a synthetic resin in emulsion, as well as an acid and / or an acid salt. The process is particularly suitable for the manufacture of paper pulp comprising a mixture of hemicellulose and recycled paper fibers. The addition of silicate is reported to increase mechanical characteristics while reducing the amount of hemicellulose at a higher cost than recycled paper. In this document, there is no single composition since the various additives are added to the dough. In order to improve the compressive strength in the dry state of the recycled papers, it has, moreover, been proposed to add sodium silicate to starch solutions, as bonding agent for the recycled papers, as described in the article by Pengje Peng, Xiaofan Zhou & Jinxia MA "Water glass compound starch used as surface sizing agent to improve the strength of linerboard" -Bioresources 6 (4) 4158-4167. However, since sodium silicate treatment was more expensive than starch, this route did not seem to be economically viable.

In addition, in order to reduce the cost of manufacturing paper, it has also been envisaged to introduce, in corrugated packaging paper, mineral fillers that are less expensive than paper fibers. The introduction of mineral fillers into the paper has led to a decrease in mechanical characteristics and, in particular, to a decrease in the compressive strength. In high concentration, the mineral fillers caused problems of dusting on the paper machine and on the processing machines. It is generally accepted that the incorporation of large amounts of inorganic fillers in the paper decreases the bonding strengths between fibers and between fibers and mineral fillers, thus drastically reducing the mechanical strength of the material. In particular, the article "A new analysis of Mer effects on paper strength" L.Li, A. Collis and R. Pelton bring the following conclusions: - Mineral fillers reduce the mechanical characteristics of paper, and some loads are more damaging than others; - For a given load, the charges having the finest granulometries are the most damaging; - The distribution of charges is rarely uniform in the thickness of the paper; - The particle size distribution of the charges in the paper is not identical to the load distribution of the charge dispersion used, because of flocculation problems. In the article "Developing a new paradigm for linerboard fillers" (TAPPI JOURNAL March 2008) Yulin Zhao, Kim Dongho, David White et al. specify that increasing the amount of mineral fillers decreases the mechanical characteristics of the paper. In the article "The Structure and Strength of Fats of precipitated calcium carbonate induced by various polymers used in papermaking" (14th Fundamental Research Symposium, Oxford September 2009), Roger Gaudreault, Nicolas Di Cesare, The GM van den Ven and David A. Weitz recall and confirm that mineral fillers reduce the mechanical characteristics of paper by decreasing fiber-fiber bonding surfaces. Several approaches have been explored to increase the amounts of mineral fillers, without success. In particular, the preflocculation of the mineral fillers on the paper fibers has been experimented without giving convincing results. It has also been proposed to chemically treat the mineral fillers so as to improve the mineral-binder and mineral-fiber-filler bonds so as to avoid areas of weakness which alter the mechanical properties of the paper. Other solutions have been proposed: Kuboshima K. uses acrylic acid or vinyl acetate to improve the chemical bonds between the polymers and the mineral fillers. ("On functional fillers for papermaking" (High Performance Paper Soc., 21) 31-38 (1982); CA 2037525 discloses a method for improving fiber-mineral filler bonds using epichlorohydrin and polyamino- amide or polyamine - Patent Application WO 00/59965 discloses sulfonated polymers which improve the bonds between fibers and mineral fillers, especially when used with starch; the use of alkoxysilanes; However, all these treatments are costly and can not be considered in the manufacture of recycled paper for packaging purposes.The analysis of all these technologies and the previous solutions proposed confirms that the problem of treatment of paper or paperboard, or more generally fibrous sheet materials, with a view to improving their mechanical characteristics is not satisfactorily solved isante, under economically acceptable conditions and this especially in the case of paper made of 100% recycled fibers intended to manufacture corrugated cardboard for packaging used in a humid environment. Indeed, for these applications, the technical requirements are high in terms of compressive strength firstly in the dry state, and for some applications under high hygrometry. In addition, the treated papers must be able to be assembled with conventional starch glues, be repulpable and recyclable. The treatments with waxes and paraffins of the prior art pose, for example, unacceptable recycling problems. Moreover, the economic conditions acceptable for the markets concerned are very limited, which excludes a number of overly expensive technologies, such as off-the-paper processing, the use of synthetic copolymers, high concentration waxes and paraffins, mineral fillers previously treated on the surface. In this context, one of the objectives of the present invention is to provide a process and compositions for the treatment of fibrous materials in sheet, and in particular paper, which are economically acceptable and which satisfy the following criteria: mechanical strength, and more particularly to satisfactory compression in the dry state and, even for at least some compositions, in the wet state, - ability to bond with starch adhesives under standard industrial conditions, - repulpability, - recyclability, - and , at least for certain embodiments, ability to contact food (dry contact and non-greasy). The invention provides compositions for treating fibrous sheet material, in order to improve the mechanical strength in the dry state, and for some of them also in the wet state, preferably by press impregnation. gluing machine and the process for continuously manufacturing the associated fibrous sheet material. The compositions according to the invention are adapted to be directly applied to a sheet of fibrous material already formed in its finished form or during its formation, during a continuous manufacturing process. The present invention relates to aqueous compositions for treating a fibrous sheet material comprising: at least one alkali metal silicate, and preferably Na, K or Li silicate or a mixture of these alkali metals, at least one mineral filler, characterized in that the mass ratio between the inorganic filler and the alkali silicate in the dry extract of the composition is from 0.25 to 4, and preferably from 0.3 to 3 and preferably from 0.5 to 1.5. The present invention relates to aqueous compositions for the treatment of fibrous sheet material comprising: - at least one alkali metal silicate, and preferably a Na, K or Li silicate or a mixture of these alkali metals, at least one mineral filler capable of releasing multivalent metal ions which can be substituted for the alkali ions of the silicate and thus forming water-insoluble silicates precipitates and preferably selected from zinc oxide, zinc, barium carbonate, barium sulfate, calcium sulphate, beryllium carbonate, strontium carbonate and calcium carbonate, calcium carbonate being preferred to obtain an improvement of the wet mechanical properties .

Preferably, the inorganic filler used in the context of the invention has a mean particle size D50 in the range from 20 nm to 20 microns, preferably in the range from 100 nm to 10 microns. Advantageously, in the aqueous compositions preferred in the context of the invention, the mass of alkali silicate (s) and mineral filler (s) represents from 90 to 100% of the dry extract, preferably from 95 to 100%. The compositions according to the invention may comprise an insolubilising agent for the silicate, other than the mineral filler (s) present. This further improves the wet strength properties. The insolubilising agent of the silicate other than a mineral filler may be chosen from organic acids, mineral acids, salts of inorganic or organic acids, proton-releasing organic or inorganic products, esters, organic carbonates and the like. multivalent metal salts. In particular, in the dry extract of the compositions according to the invention, the mass ratio between the insolubilising agent of the silicate other than a mineral filler and the silicate is from 0.01 to 0.1, and preferably from 0, 03 to 0.05. In the context of the invention, the alkali metal silicate is preferably chosen from silicates of formula (M20) SiO2 where M is Na, K or Li or a mixture of these alkali metals, and x is the molar ratio between SiO 2 and M 2 O and advantageously belongs to the range from 0.5 to 4. Preferably, the molar ratio x of the alkali silicate is greater than 2.5 and is preferably greater than 3. The compositions according to The invention may further comprise a plasticizer. The plasticizer is, for example, selected from among glycerine, sucrose, polyethylene glycols, or, preferably, emulsion copolymers such as styrene butadiene, carboxylated or non-carboxylated, styrene butadiene acrylonitrile, or styrene emulsions. acrylic. In particular, in the dry extract of the compositions according to the invention, the mass ratio between the plasticizer and the silicate is from 0.01 to 0.06, and preferably from 0.02 to 0.04. Advantageously, the compositions according to the invention contain neither wax nor paraffin. In the compositions according to the invention, the dry extract may represent from 10 to 75% of the total mass of the composition, and preferably from 20 to 50%. The invention also relates to the use of a composition according to the invention in the manufacture of a fibrous sheet material (in particular a paper or cardboard), by deep impregnation in the thickness of said fibrous sheet material with said composition, for reinforcing the mechanical strength properties in the dry state and possibly in the wet state of the fibrous material obtained. The invention also relates to a process for treating a fibrous sheet material continuously made on at least one of the faces of the fibrous sheet material with an aqueous composition according to the invention. In particular, the treatment is performed on each of the faces of the fibrous sheet material and in its mass. The treatment is preferably incorporated into a continuous process for producing a fibrous sheet material and is applied thereto in a finished state, or in a state of design. The treatment is preferably carried out by impregnation, preferably in a sizing press. Advantageously, the fibrous material is formed from, or even consists exclusively of, recycled fibers. The invention also relates to sheet fibrous materials treated with one of the aqueous compositions according to the invention, and in particular treated to obtain a dry mass of deposited composition belonging to the range from 3 g / m 2 to 35 g / m 2, and in particular ranging from 8 g / m2 to 25 g / m2, as well as fibrous sheet materials obtained according to a method defined in the context of the invention. Such fibrous materials may be in particular in the form of a sheet of paper or cardboard, possibly in the form of a manufactured article.

Finally, the subject of the invention is corrugated cartons consisting, at least in part, of a paper as defined in the context of the invention. In the context of the invention, the mineral filler present in high concentration makes it possible on the one hand to reduce the cost of the fibrous materials obtained with such a composition, in comparison with prior treatments with starch compositions. and, on the other hand, when the mineral filler is reactive with respect to the silicate, to reinforce the cohesion of the silicates, and to insolubilize them in aqueous solution. Indeed, the silicates are very sensitive to water, and preferably require the use of insolubilizing agents which in the context of the invention are at least partially constituted by the mineral filler incorporated in the composition. Each of the constituents that may be present in the composition according to the invention will now be described in detail. Alkali metal silicates The alkali silicates act as binder for the constituent fibers of the paper and condition the achievement of good properties in terms of mechanical strength. The water-soluble alkali metal silicates, especially of formula (M20) 5iO2 where M is Na, K, Li or a mixture of these alkali metals, can be produced by melting mixtures in varying proportions of sodium carbonate, of potassium or lithium and pure sand. This fusion is conventionally carried out in an oven at a temperature of about 1400 ° C. After cooling the casting, a glassy silicate is obtained in the form of clear glass. Liquid silicates are obtained by dissolving the glassy silicates in water in an autoclave. Such silicates are commercially available, especially in the form of aqueous solution. Depending on the molar ratio x, the alkali metal silicates of formula (M 2 O) x SiO 2 where M is Na, Li or a mixture of these alkali metals have different properties. An alkali silicate having a molar ratio generally ranging from 0.5 to 4 is preferably used. The alkaline silicates are most often available in the form of an aqueous solution having a solids content of 25 to 65% by weight. Alkali silicates with the lowest molar ratios generally have higher wetting power, but are more difficult to dry and slow production speeds, those with a higher molar ratio have higher binding power and are easier to dry. to dry. In the context of the invention, it has been found advantageous to use alkali metal silicates having a molar ratio greater than 2.5 and preferably greater than 3. It is in fact this type of silicate which allows to have the best binding power that allows the best cohesion of the fibrous mat, and is the easiest to dry, thus allowing productivity gains and, for wet applications, the best resistance in the wet state. All the alkali metal silicates can be used in the composition of the invention, but sodium silicate being the most common and the most economical, it is the one that is preferred. Mineral fillers A mineral filler is characterized by a quasi-insolubility or a very low solubility in water, especially less than 0.1 g / l in water at 20 ° C.

The use of mineral fillers is intended to lower costs. The mineral fillers commonly used in the paper industry are, in particular: alumina trihydrate - Kaolin - CaCO 3 - Mica - Talc - Montmorillonite - Bentonite - Attapulgite - .... 3 0 0 12 3 6 14 There are among these inorganic fillers or pigments, those which react with silicates, by releasing in aqueous medium a multivalent metal ion which will be exchanged with the alkali metal ion of the silicate to form a water-insoluble precipitate, called "reactive" mineral fillers With regard to silicates (such as sodium silicate), or called insolubilizing agents silicates which are, in particular: ZnO-ZnCO3-BaCO3 10 -BaSO4-CaSO4-BeCO3-SrCO3-CaCO3, especially finely CaCO3 milled (GCC) or precipitated CaCO3 (PCC). These mineral fillers are almost insoluble or very slightly soluble in water. They will therefore react very slowly with the sodium silicates, potassium or lithium present in the composition which are initially insoluble in water, to form a precipitate insoluble in water. Since the reaction is very slow because it is controlled by the release of the multivalent metal ions, there is no cloudiness up to gelling or setting of the composition for at least 24 hours without stirring at 20 ° C. Most often gelling or setting the mass of the composition occurs between 24 and 72 hours when the composition is left without stirring at 20 ° C. In the case of the use of an inorganic filler of the zinc or carbonate type of Zn, Ca, ..., the sodium, lithium or potassium of the silicate is substituted by the polyvalent metal ion released by the mineral filler, forming thus a complex of silicate then insoluble. In any case, because of the very low solubility of the inorganic filler in an aqueous medium, the kinetics of reaction is very slow, which makes the use of the composition compatible in a process for the industrial treatment of a fibrous material. in sheet.

These mineral fillers are therefore described as reactive with alkali metal silicates, especially in water and at 20 ° C, with reaction rates that are dependent on the conditions of temperature, pH, concentration and particle size.

The composition according to the invention comprises at least one such inorganic filler, and in particular a so-called reactive mineral filler, in relative quantity with respect to the silicates greater than 25% by mass, and preferably greater than or equal to 50 ° h. The presence of such a quantity of mineral filler makes it possible, on the one hand, to reduce the cost of the composition, the amount of silicate being less. On the other hand, the presence of these mineral fillers does not affect the mechanical properties in the dry state conferred by the presence of silicates and, moreover, the use of so-called reactive mineral fillers makes it possible to improve the mechanical resistance to wet compression, by insolubilizing silicates. This is particularly the case when ZnO, zinc carbonate or, preferably, calcium carbonate is used. The mineral filler (s) present in the composition, such as CaCO3, has a double role of reinforcing the cohesion and insolubilizing of the silicates present. Advantageously, in the context of the invention, the mineral fillers present, such as ZnO, ZnCO3, CaCO3, have not undergone any prior coating, for example with alkoxysilanes, as was the case in certain techniques of the art. prior. Quite unexpectedly, it has been discovered that the introduction of such amounts of mineral fillers, such as small-particle crushed calcium carbonate, or precipitated calcium carbonate, in combination with alkali silicates, does not alter the mechanical characteristics of the papers and allowed to preserve the beneficial effect provided by the alkali metal silicate, with regard to the mechanical properties of the paper obtained. Such an effect was by no means predictable, especially given the work of Yuhin Zho, Dongho Kim et al. TAPPI Journal March 2008 supra) found that the addition of untreated mineral fillers to corrugated paperboard roofing paper to reduce cost price resulted in a significant loss of mechanical characteristics. Reactive mineral fillers dispersed in water, such as ZnO, ZnCO3, or CaCO3 are very insoluble in water and react slowly with silicates. The compositions according to the invention are, as a result, very stable with a viscosity which is not very evolutionary in time, the gelling reaction being very slow in solution. Of these reactive mineral fillers, CaCO3 is preferred because of its safety, high availability and low cost and optimum room temperature insolubilization capabilities.

It has also been found that by selecting a reactive mineral filler of fine and regular particle size, it was still possible to improve the mechanical characteristics of the papers treated with a composition according to the invention even under high hygrometry. Indeed, even with a small particle size, the mineral fillers used are very sparingly soluble and gradually release cations with time, which makes it possible to avoid the gelation of the composition for a long time and leads to homogeneity of the insolubilization of silicates and therefore more homogeneous papers and, therefore, more satisfactory properties. Also, advantageously, the mineral filler (s), such as in particular ZnO, or calcium carbonate present in the composition according to the invention, has (a) a controlled particle size in the range of from 20 nm to 20 microns. In particular, it has been found advantageous to use finely ground calcium carbonate (GCC) with a mean particle size D50 in the range of 0.4 to 10 microns or precipitated calcium carbonate (PCC) of particle size in the range ranging from 20 to 500 nm. The average particle size D50 can be measured by laser diffraction according to the ISO 13320: 2009 standard, in particular with a Beckman Coulter LS 13320 apparatus. The average particle size D50 is the value in microns or nm for which 50% by number of the distribution of the diameters of the particles is below this value and 50% by number of the distribution is above this value.

The well-known defloculation effect of silicates makes it possible in the context of the invention to obtain a very good dispersion of the mineral fillers in the mass of the treated paper. The composition according to the invention may also contain inorganic fillers or pigments, said to be inert with respect to silicates, such as: - alumina trihydrate - Kaolin - Mica - Talc - Montmorillonite - Bentonite - Attapulgite - quartz, - TiO2 , and / or - Fe2O3. Advantageously, the silicate (and in particular sodium silicate) / calcium carbonate or the silicate (and in particular sodium silicate) / kaolin pairs will be used in the compositions according to the invention.

The insolubilizing agents other than a mineral filler The composition according to the invention may comprise one or more insolubilizing agents for silicates, other than the mineral fillers known as reactive towards silicates. These insolubilizing agents react, in particular in aqueous solution, with the silicates to form a precipitate that is insoluble in water and lead to a precipitation of the silicate according to a reaction kinetics faster than the mineral fillers: the kinetics of reaction is such that a turbidity the solution would be observed from the first minutes or hours after the mixing of the ingredients if they were introduced in quantities as important as the mineral fillers. In a known manner, the alkali silicates can be rendered insoluble in water by two types. reaction: a) by a gelling-polymerization reaction by lowering the pH of the silicate solution below pH 10.7.

The simplest way to lower the pH is to use one or more organic or mineral acids, but the reactions are very fast. A large number of other products can also be considered, in order to better control the gel time. These include proton-releasing organic or inorganic products, such as salts of organic or inorganic acids, esters (reacted by hydrolysis to form the corresponding carboxylic acid), certain organic carbonates, etc. example of insolubilizing agents other than a mineral filler (also named in the following description insolubilizing agent additional silicate) may be used in the context of the invention include: - HCl - H2SO4 - HNO3 - triacetin - diacetin - monoacetin - sodium bicarbonate - citric acid - formic acid - acetic acid - propionic acid - NaFi2PO4 - NF-14-12PO4 - CO2 - Ethylene carbonate - Propylene carbonate When the silicate solutions are acidified, orthosilicic acid Si (OH) 4 is released, which eventually polymerizes to form a precipitate. b) by precipitation with multivalent metal salts in aqueous solution. Soluble silicates react almost instantaneously with multivalent metal cations to form the corresponding insoluble metal silicate. Metal ions that react with silicates include Ca ", Mg", Zn ", Cu", Fe3 +, Al t ...

The following multivalent metal salts may be mentioned as non-limiting examples: - CaCl 2 - MgSO 4 - Al 2 (504) 3 - CaSO 4 - The reactions between the alkali metal silicates and the multivalent metal salts are generally very fast. Also, the problem with using them in paper machine processing compositions is to control the gelling time of the compositions when the insolubilizing agents are introduced. The kinetics of gelation depend on many parameters:> The nature of the insolubilizers - The molar ratio of the alkali silicate (in particular SiO 2 / Na 2 O in the case of sodium silicate), since when the molar ratio increases the degree of polymerization increases> The concentration of the different constituents - The shear rates of the coating process> The temperature ...> The pH The insolubilizers, such as CaCl2 or salts of mineral acids in general, cause an immediate reaction with the alkali metal silicates. Such insolubilizing agents, if used alone, could be applied to the paper only in a two-step process with the introduction of insolubilizers before or after the application of the silicates. With such a two-step process, when the silicates are applied using a sizing press, the process would lead to inhomogeneous papers in the mass because of the heterogeneity of the insolubilization, which is inappropriate.

This is why, in the context of the invention, the insolubilising agent of the additional silicate chosen from inorganic or organic acids, the salts of mineral or organic acids, the proton-releasing organic or inorganic substances, the esters and the carbonates. organic and multivalent metal salts is optional and optionally acts in addition to the mineral fillers.

This additional insolubilizing agent is advantageously present in a small amount. Preferably, the weight percentage of the additional insolubilizing agent relative to the silicate in the composition is in the range of 0.01 to 0.1 and preferably in the range of 0.03 to 0.05, of way to control the gel time. Indeed, the use of reactive mineral fillers such as zinc oxide, zinc carbonate, or calcium carbonate, as main insolubilizing agent silicate can significantly increase the gel time. Plasticizers Silicate-impregnated paper (s) increase in rigidity and can be brittle depending on the concentration used in silicate (s). In order to increase the flexibility of the paper obtained after treatment with the composition according to the invention, the latter will preferably contain at least one plasticizing agent.

Plasticizers such as glycerine, sucrose, polyethylene glycols can be used. Nevertheless, since these products are very soluble in water, it has been found advantageous to use emulsion copolymers such as: carboxylated or non-carboxylated styrenes, styrene-butadiene acrylonitrile, acrylic styrenes. Preferably, in the compositions according to the invention, between the plasticizer and the silicate in the solids content of the composition is from 0.01 to 0.06, and preferably from 0.02 to 0.04.

Waxes and paraffins migrate into silicates and are difficult to use as plasticisers, because this would cause problems of gluing on corrugator during the manufacture of corrugated cardboard. Also, preferably, the composition according to the invention will contain neither wax nor paraffin. Without this being limiting, it may be advantageous to add to an aqueous composition according to the invention: one or more water-repellent agents for the paper and / or one or more dispersants such as sodium polyacrylate and / or several biocidal agents and / or - One or more defoamers and / or - One or more dyes or pigments and / or e One or more antistatic agents and / or - these various additives are conventionally used in the paper industry. The composition according to the invention is prepared by incorporating the various constituents into the water. Preferably, the silicate is introduced into the composition before the mineral charge (s). Advantageously, the composition is subjected to agitation by any device, particularly mechanical, appropriate, so as to obtain a homogeneous mixture. In the context of the invention, it has been found that contrary to what is observed with starch compositions where the solids content of the compositions is limited to about 10%, the viscosity of the compositions made with Alkaline silicates and mineral fillers remain low even with much higher dry solids. In particular, the compositions according to the invention may have a solids content of 10 to 60% and / or a Brookfield viscosity of 10 to 100 mPa.s, especially measured at 50 ° C. and with stirring at 100 rpm. The Brookfield viscosity can, for example, be determined according to the ISO 1652 standard. With such a viscosity and / or solids content, it is possible to substantially increase the composition masses deposited on the fibrous supports during the impregnation and dewatering treatments. gradually increase the mechanical properties, and more particularly the compressive strength. It has been demonstrated in the context of the invention that the joint use of alkali silicates and mineral fillers, and in particular of reactive mineral fillers, possibly in combination with one or more additional insolubilizing agents, as paper treatment product, replacing the starch treatments currently used, had the following advantages: - improvement of the dry compressive strength by increasing the deposited weights, - improvement of the compressive strength in the wet state, in particular in the case of the use of mineral filler (s) reactive vis-à-vis silicates, and in particular calcium carbonate, - economic advantage, - decrease in energy consumption. In addition, the compositions according to the invention are compatible for the treatment of paper intended for the manufacture of packaging cardboard for food use in particular. Indeed, even if some insolubilizing agents may present a health risk (borax, metaborates, glyoxal, ...), others such as citric acid, sodium bicarbonate, NH2PO4 ... are perfectly harmless to the concentrations of use and will be preferred, especially for food applications. The alkali silicates and mineral fillers, such as CaCO3, used in the context of the invention are substances classified as non-hazardous within the meaning of the European regulation (CLP Regulation 1272-2008), CaCO3 is exempted from REACH registration. (Article 2). Alkaline silicates and CaCO3 are substances that can be used in the manufacture of materials suitable for dry and non-greasy food contact. They are classified as GRAS (generally recognised as safe) by the FDA (Food and Drug Administration). According to another aspect, the invention relates to the use of an aqueous composition defined in the context of the invention for producing papers having improved mechanical strength.

Process for carrying out the composition The composition according to the invention can be applied to various fibrous sheet supports, of the paper or cardboard type, at different stages of their manufacturing process and according to different techniques. In wet part of a line of paper or paperboard in several folds, for example, the composition can be applied between two plies or mixed with the constituent dough of one or more jets. In drying or off paper machine, the composition may be applied to the surface on one or both sides of paper and cardboard. The composition, which is mainly, but not exclusively, for paper processing can be applied directly to the paper machine, after the wet part of the machine by any method known in the paper industry such as press application. gluing, spray coating, rolls engraved or not, by Champion bars, Mayer bars, air knife or other systems known to those skilled in the art. The press-gluing treatment is preferred because it allows a better distribution of the charges in the mass of the paper. The compositions according to the invention, and in particular those comprising silicates and carbonates, also have liquid life times of several days, and a low viscosity at high concentration, which makes their use very easy in a process. treatment, and allows the application of these compositions using a conventional gluing press (size-press according to the English terminology). The composition according to the invention may be applied during a step of a process for manufacturing a fibrous sheet material, which may in particular be a sheet of paper, either on the finished material, or directly during its manufacture. . The fibrous sheet material is then scrolled and the application of the composition is performed and is followed by a drying step, which may or may not correspond to the last drying step. Most often, another prior drying step is present before the application of the composition. In particular, the composition will be applied to a paper sheet having a moisture content of 5 to 14%, preferably 8 to 10%. An application by the faces, in particular in gluing press, allows a homogeneous impregnation of the compositions described throughout the thickness of the fibrous sheet material, and in particular of the paper sheet.

When the composition is applied, the following parameters, alone or in combination, will preferably be used: film running speed of 100 to 1500 m / min, temperature of the applied composition of 40 to 70 ° C, - temperature of the sheet at the time of application of 80 to 105 ° C, - after application of the composition, drying at a temperature of less than or equal to 140 ° C for a period of less than one minute, and preferably in the range of 100 to 120 ° C. The fibrous support may be formed of virgin fibers, fibers exclusively from recycled paper and / or cardboard or a mixture of such fibers. The fibrous support may also contain fibers derived from annual plants, hemicelluloses, galactomannans, CMC, etc. Although this is not the preferred application within the scope of the invention, the sheet may comprise a part low, or not at all, recycled fiber. The papers treated with the compositions according to the invention show good repulping and recycling properties. The following composition examples are given by way of example, and do not limit the scope of the invention described in the claims. Example 1: The following concentrated composition was prepared by cold mixing the following substances or preparations with a mixer rotating at 1500 rpm. Water 464 liters Sodium silicate 340-3840 (Silmaco St) Dry extract = 38% 456 Kg Density = 1.38 Molar ratio x = 3.4 pH (1%) = 11 Self-crosslinkable carboxylated styrene butadiene latex VL 10703 Synthomer) 10 liters Dry extract = 50% Tg = 58 ° C pH = 8.5 ISO 976 standard Viscosity: (Brookfield LVF 60 rpm) ISO standard 1652 200 mPa.s Insoluble agent: CaCO3 The CaCO3 used is the HYDROCARB 90 (OMYA COMPANY) Average diameter D50 0.7 microns, dry extract 75% and density = 1.89 70 Kgs Either: 30% by dry weight relative to the weight of dry silicate Total 1.000kgs Dry extract of the composition = 23 % pH = 11 Standard ISO 976 Viscosity of the composition: 30 mPa.s ISO 1652 standard This composition is very stable, no gelling of the bath is observed for more than 24 hours, and there is no variation of viscosity during this period. This composition was applied directly to the paper machine by means of a conventional sizing press on a cover paper of 136 g / m 2 based on 100% recycled fibers. Deposited mass = 14g / m2 dry final paper weight 150g / m2 final paper moisture: 8% The paper machine speed was 500m / min, the composition drying time about 20 seconds and the temperature paper at the dryer outlet was 105 ° C. Alkaline silicates, which are less water-retaining than the starches traditionally used, have resulted in an energy saving of about 10%. The mechanical characteristics of the paper were measured, and in particular the compressive strength SCT, according to ISO 9895. These measurements were carried out after conditioning of the specimens at 23 ° C. and 50% relative humidity, and after steaming at 25 ° C. ° C and 85% relative humidity for 24 hours. The quality of the treatment is evaluated according to the initial measurements of compressive strength and the ratio of the measurements made at 50% relative humidity and 85% relative humidity. This ratio is expressed as a percentage of the resilience ratio. These measurements were compared with a paper support of identical quality treated in glue press with native corn starch. There is a loss of mechanical characteristics under the high humidity conditions, less in the case of the composition containing calcium carbonate. Example 1 which comprises a silicate reactive mineral filler which behaves as an insolubilizing agent for silicates, has good dry and wet characteristics (62% resilience). .

Figs. 1 and 2 are microphotographs corresponding to transmission electron microscope (SEM) overviews in cross-sectional composition of the paper, with magnifications of x200 and x1000, respectively. These micrographs show that loads of very small sizes are found throughout the thickness of the paper and in all areas.

EXAMPLE 3 Influence of the nature of the insolubilizer Identical compositions were prepared by replacing the calcium carbonate of Example 1 with finely ground zinc oxide ZnO in Example 2 according to US Pat. invention, with citric acid in Comparative Example 1, and with kaolin with a particle size less than 2 microns in Example 3 according to the invention, with the same proportions of insolubilizing agents as in Example 1 (30% by dry weight relative to the dry weight of the silicate), except Comparative Example 1 which comprises only 5% citric acid in weight ratio relative to the silicate. The compositions with zinc oxide (Example 2) and kaolin (Example 3) are also very stable and silicate gelation is not observed for 24 hours. The mechanical characteristics in the dry state are good in all cases. On the other hand, the rates of resilience (ratio of the compressive strength in the two atmospheres 85% RH and 50% RH) are better with calcium carbonate and zinc oxide (62 and 60% respectively) than with kaolin. But in all cases, the mechanical characteristics in the wet state are higher than those obtained with starch, but are not optimal in the case of kaolin in particular. The papers treated with the citric acid composition of Comparative Example 1 retain their wet properties (60% resilience), but the composition used begins to gel after 30 minutes, with viscosity which increases rapidly, which makes the process very difficult to manage on a paper machine. The use of insolubilizers sodium silicates such as weak acids or acid-releasing organic esters, such as diacetin or triacetin for example, leads to compositions that gell quickly, with gelling times that vary between 10 minutes and one hour depending on the concentrations used. In order to be able to use these insolubilizing agents on a paper machine under good industrial operating conditions, it is necessary to use these products only in low concentrations to maintain a stable viscosity. Unfortunately, in these conditions their insolubilization capacity of silicates is limited and not sufficient. These compositions were applied to a paper machine on a paper machine under the same conditions as in Example 1, on a paper of the same basis weight. The treatment with these compositions was compared in terms of compressive strength with a paper of the same weight conventionally treated with native corn starch. All the results are presented 1., L. These different tests show that the alkali silicates are more hygroscopic than the starches commonly used, and preferably require the use of an insolubilizing agent. The most effective insolubilizing agents are generally the fastest and a short gelation time would involve a two-step process because, in the case of rapid gelation, the viscosity of the composition used in the size press is rapidly changing and the process becomes uncontrollable and incompatible with an industrial exploitation. A two-stage treatment with the introduction of the insolubilizing agents before or after the application of the silicates leads to a heterogeneous insolubilization with loss of the characteristics in the wet state. The strength gain in the dry state is independent of the nature of the aging insolubilizer because the latter has no function that to make the silicate structure insensitive to water. Examples Composition Paper weight g / m2 Mass deposited g / m2 SCT 20 ° C 50% RH KN / m SCT 23 ° C 85% RH KN / m Resilience rate (SCT 85% RH / SCT 50% RH) 1 silicate of 150 14 4.2 2.8 62% Na + CaCO3 2 silicate 150 12 3.8 2.3 60% Na + ZnO Comparative silicate 150 11 3.5 2.1 60% 1 Na + citric acid silicate 150 11 3.5 1.9 55% Na + kaolin Comparative Starch 150 6 3.1 1.7 55% 2 3 0 0 1 2 3 6 Only CaCO 3, ZnO and citric acid have an insolubilization effect on the silicate. With a weight ratio of only 5% insolubilizer to silicate, citric acid has an insolubilising effect, but with a gel time of about 30 minutes, the process is difficult to manage on a paper machine. . Example 4 Influence of the Particle Size of the Mineral Loads; Paper treatment compositions according to the invention have been prepared with finely ground reactive mineral fillers of very small particle size. These inorganic fillers also act as an insolubilising agent for silicates. Various forms of CaCO3 in aqueous dispersion (slurry) were studied, and more particularly the ground CaCO3 (GCC) Hydrocarb 90 of the company Omya of median particle size of 0.7 micron, the ground CaCO3 (GCC) Setacarb 85 OG of the company Omya of average particle size D50 0.4 micron, and the precipitated CaCO3 of the company Solvay SOCAL 31 of average particle size D50 of between 50 and 100 nm. A dry CaCO3 / sodium silicate ratio of 1/1 was used. It was found that the reactivity depended on the particle size: the finer the particle size, the more reactive the mineral filler is. However Hydrocarb 90, smaller particle size than other CaCO3, remains the cheapest, so it is 20 that has been studied in the following. Example 5 to 8 - Influence of the CaC 1 silicate ratio The compositions were prepared under the same conditions as in Example 1. TABLE 2 shows the various compositions studied. Comparative Example 3 Comparative Example 4 Exe 5 Water 368 liters 399 liters 446,523 liters 601 Na340-3840 silicate (Silmaco) molar ratio x = 3.4 Dry extract = 36.5% milled CaCO3 Hydrocarb 90 average diameter 0 , 7 micron d = 1.89 Dry extract = 75% Latex styrene butadiene VL 10703 (Synthomer) Tg = 58 Dry extract = 50% 78 10 liters 10 15F., 234 kgs 7 Comparative Example 3 Comparative Example 4 Example 5 Example Example 7 Total 1.000kgs 1,000 kgs 1,000kgs 1,000kgs 1,000kgs Dry extract of the composition 24,1% 23,25 ° h 24,0% 24,2% 24,1% These examples correspond to the following weight ratios (dry silicate on dry calcium carbonate). Comparative example 3 100% silicate Comparative example 4 90% silicate -10% CaCO 3 (CaCO 3 / silicate mass ratio of 0.11) -Example 5 75% silicate-25% CaCO 3 (CaCO 3 / silicate mass ratio of 0.33) Example 6 50 silicate - 50 ° C. CaCO 3 (CaCO 3 / silicate mass ratio of 1) - Example 7 25% silicate - 75% CaCO 3 (CaCO 3 / silicate mass ratio of 3). These compositions were applied on a paper machine using a sizing machine on a paper made of 100% recycled fiber having a final basis weight of 120 g / m 2, and the papers thus made were compared with a 100% recycled paper of the same weight and same composition treated with starch. All the results are shown in TABLE 3: TABLE 1 SSC 7: 5KHR / SCT Sample Composition Weight r g kW. Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Comparative Example Comparative Example 6 Example 8 100% silicate 90 7, and 10% CaCO3 silh 120 75 '-': :) CaCC2 Am: Jon;: 22 Corn starch corn 50% silicate 120 50% CaCO3 75% 7, ilicate 25 1 50 50 1CO3 120 120 120 120 120 150 13 13 13 2.7 2.7 2.6 1.6 54 62 58 13 13 6 In Comparative Example 5, a 1 g starch coated paper of 6 g / m 2, and is industrially a superior deposited 30012 due to the excessive viscosity of starch solutions at concentrations greater than 12% solids. A starchy solution having a viscosity greater than 60 mPa.s is indeed very difficult to use in sizing press because of the induced instability of the coating process leading to impregnation irregularities and production incidents. The silicate and carbonate compositions remain fluid even at high concentrations (Brookfield viscosity ISO 1652 of 30 mPa.s at 25% solids, in Examples 5 to 7 for example). The mechanical characteristics, and in particular the compressive strength, are proportional to the amount of binder (starch or silicate) impregnated in the paper by the gluing press. With dry extracts of silicates twice as great in the case of Examples 5 and 6 as the dry extracts of the starchy compositions of Comparative Example 5, it is possible to obtain deposited weights of silicates of 13 g / m 2 after drying. while in the case of starch, under the same conditions, it is difficult to obtain deposited weights greater than 6 g / m 2 with a paper of 120 g / m 2. The compressive strength SCT then increases from 2.1 kN / m 2 (Comparative example 5 starch) to 2.7 kN / m 2 (Example 6 Silicate-CaCO 3 50% -50%), ie a gain in compressive strength of 25% in the dry state.

In Comparative Example 6, the starch makes it possible to obtain a dry compressive strength (50% RH) of 2.7 kN / m, with a paper of 150 g / m 2. The starch substituted in an almost equivalent amount with an alkali silicate gives a paper having the same compressive strength in the dry state. Furthermore, the resilience level of a paper coated with starch is at the level of 57%, whereas in Comparative Example 3, the silicate alone makes it possible to reach a degree of resilience of 54%. The energy gain observed for the drying of papers treated exclusively with silicates does not compensate for the extra cost due to the use of silicates, and the wet strength is not improved in this configuration. In the context of the invention, it has been found that the addition of mineral filler which makes it possible to reduce the cost of the composition does not entail, quite unexpectedly, the loss of compressive strength of the papers. treated with compositions containing alkali metal silicates, even at high concentrations of mineral fillers. Moreover, the use of mineral fillers in increasing quantities has made it possible to note the following facts:> By progressively increasing the rate of reactive mineral fillers from 20 to 50% by dry weight, with reduction of the dry weight of silicate, it is noticeable that no loss of compressive strength properties (Comparative Example 4 and Examples 5 and 6). It is only from a loading rate of 75% (Example 7) in dry weight relative to the dry matter Silicate + Calcium carbonate that a reduction in the compressive strength is observed. The compressive strength is proportional to the weight of binder deposited in the paper (starch or silicate), the mineral fillers having strictly no binding power. In fact, in Comparative Example 4, by treating a 100% recycled paper of 120 g / m 2 treated with a dry deposited weight of 13 g / m 2 and and a filler content of 10% with respect to the dry matter silicate + carbonate of calcium, the deposited weight of binder is 11.7 g / m 2 of binder, while in example 6 for the same weight deposited, and a degree of load of 50% compared to the dry matter silicate + calcium carbonate the deposited weight of binder is only 6.5 g / m2. Now, quite unexpectedly, the compressive strength SCT (2.7 kN / m) remained unchanged, despite a drop of almost 50% binder in the paper. The silicate / CaCO 3 composition thus constitutes a high performance mineral composite material which makes it possible to very significantly improve the compressive strength under advantageous economic conditions, because of the low cost of CaCO 3 relative to the silicate. Resilience increases gradually to stabilize from a 25% dry weight loading rate, corresponding to a CaCO 3 / silicate dry weight ratio of 0.33 (Example 5). This demonstrates the insolubilization effect of the silicate by the reactive mineral fillers, despite the very low solubility of these mineral fillers. With a 50% dry weight mineral filler content at 50% by dry weight of silicate, the cost price of these compositions is lower than the starch compositions traditionally used. However, the use of these compositions provides an energy gain of about 10% during drying of the paper, and a better compressive strength in a humid environment. The following conclusions can be made: For a dry weight deposited with a composition comprising in dry weight of 50% of silicate and 50% of calcium carbonate, compared with the same deposit of a composition based on starch, found comparable compressive strength values in the dry state (Comparative Example 5 and Example 8 with 6 g / m 2 of weight deposited on a paper of 120 g / m 2). The wet strength of the papers treated with compositions comprising 50% reactive mineral fillers by dry weight relative to the dry weight of silicate is, however, much greater than the papers treated with starch (Example 8: 62% resilience). Comparative Example 5: Resilience 58%).

For a dry weight deposited with a composition comprising 50% of silicate and 50% of calcium carbonate by dry weight of about twice the dry weight deposited with a starch-based composition, resistance values are observed. compression much higher. In Example 6 a paper of 120 g / m 2 was treated with a deposit of 13 g / m 2 of a composition comprising 50% of CaCO 3 and 50% of silicate by dry weight; the measured SCT compressive strength is 2.7 kN / m and the resilience is 62%. These values were compared with those obtained for a 150g / m 2 paper treated with a 6g / m 2 deposition of a starch composition (Comparative Example 6) which gives a compressive strength of 2.7 SCT kN / met and a resilience of 57%. It is thus possible to advantageously replace a traditional paper of 150 g / m 2 treated with starch, with a paper of 120 g / m 2 treated with a composition comprising 50% silicate and 50% CaCO 3; both papers having comparable compressive strength in the dry state. The paper treated with the silicate composition, however, has a better wet compressive strength (62% resilience for Example 6 and 57% resilience for Comparative Example 6). On the other hand, these tests demonstrate that the use of mineral fillers makes it possible to reinforce the cohesion of the alkali silicates. Indeed, it appears that there is no loss of mechanical characteristics, despite very high mineral load rates up to more than 50% of charges. Without wishing to be bound to any scientific theory, it appears in the above examples that the CaCO3 used has a dual role of reinforcing the cohesion of silicates, but also of insolubilizing alkali silicates as demonstrated by the increase in resilience from 54% to 62% through the addition of CaCO3. The known effect of deflocculating the pigments of the silicates has, moreover, made it possible to obtain a very good dispersion of the mineral charges in the mass of the paper, observed by scanning electron microscopy of the cross-section of the paper. I - A composition was prepared by adding to the composition of Example 6 3% of triacetin by dry weight relative to the dry weight of sodium silicate used, and this composition was compared with a paper made of virgin fibers (paste 25 mi-chemical) without starch or silicate (Comparative Example 7). The gel time was approximately one hour. The results obtained are shown in Table 4: These results show that the additional use of appropriate insolubilizers, either in acid form which lowers the pH below 10.7, or in the form of multivalent salts or organic esters, still makes it possible to improve the resistance to compression in the wet state. As demonstrated in Example 9 which describes a composition identical to the composition of Example 6 to which was added 3% triacetin in dry weight relative to the dry weight of silicate: the addition of triacetin allows to pass from a resilience of 62% at 64 ° h. This demonstrates that despite the very large amounts of reactive mineral fillers used, the insolubilization of the silicates is only partial and can be further improved by the addition of a second acidic insolubilizer or acid liberator such as diacetin or triacetin . The papers thus treated with the compositions according to the invention were corrugated on corrugated cardboard under normal conditions, with traditional starchy glues without loss of adhesion between the various supports. Examples Example 9 Composition 50% silicate 50% CaCO3 3% triacetin Paper weight g / m2 150 Weight deposited g / m2 14 SCT 20 ° C 50% RH kN / m 4.2 SCT 23 ° C 85% RH kN / m 2, 65 Resilience 64% Comparative Example 7 Scandinavian 150 chemical paper 4.2 2.8 67%

Claims (8)

CLAIMS1- Aqueous compositions for treating a fibrous sheet material comprising: at least one alkali metal silicate, and preferably a Na, K or Li silicate or a mixture of these alkali metals, at least one mineral filler, characterized in that the mass ratio between the inorganic filler and the alkali silicate in the solids content of the composition is from 0.25 to 4, and preferably from 0.3 to 3 and preferably from 0.5 to 1.5. 2. Aqueous compositions for the treatment of a fibrous sheet material according to claim 1 characterized in that the inorganic filler is capable of releasing multivalent metal ions which will replace the alkali ions of the silicate to form insoluble silicate precipitates in water, and is preferably selected from zinc oxide, zinc carbonate, barium carbonate, barium sulfate, calcium sulfate, beryllium carbonate, strontium carbonate and carbonate calcium, with calcium carbonate being preferred. 3. Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims, characterized in that the inorganic filler has a mean particle size D50 in the range from 20 nm to 20 microns, preferably comprised in range from 100 nm to 10 microns. 4- Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims, characterized in that the mass of alkali silicate (s) and mineral filler (s) represents from 90 to 100%, and preferably from 95 to 100% of the dry extract of the composition. 5. Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims characterized in that they comprise an insolubilizing agent silicate, other than a mineral filler. 6 - Aqueous compositions for the treatment of a fibrous sheet material according to claim 5, characterized in that the insolubilizing agent of the silicate other than a mineral filler is chosen from organic or inorganic acids, salts of mineral acids or organic, proton-releasing organic or inorganic substances, esters, organic carbonates and multivalent metal salts. 7 - Aqueous compositions for the treatment of a fibrous sheet material according to claim 5 or 6, characterized in that the mass ratio between the insolubilizing agent silicate other than a mineral filler and the silicate in the dry extract of the composition is from 0.01 to 0.1, and preferably from 0.03 to 0.05. 8 - Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims, characterized in that the alkali metal silicate is chosen from silicates of formula (M20) SiO2 where M is Na, K or Li or a mixture of these alkali metals, and x is the molar ratio between SiO 2 and M 2 O and advantageously belongs to the range from 0.5 to 4. - Aqueous compositions for the treatment of fibrous sheet material according to claim 8 characterized in the molar ratio x of the alkali silicate is greater than 2.5 and is preferably greater than 3. 10 - Aqueous compositions for the treatment of fibrous sheet material according to one of the preceding claims, characterized in that they further comprise a plasticizer. 11 - Aqueous compositions for the treatment of a fibrous sheet material according to claim 10, characterized in that the plasticizing agent is chosen from glycerine, sucrose, polyethylene glycols, or, preferably, emulsion copolymers such as carboxylated or non styrene butadiene emulsions, styrene butadiene acrylonitrile, or acrylic styrene. 12 - Aqueous compositions for the treatment of a fibrous sheet material according to claim 10 or 11, characterized in that the mass ratio between the plasticizer and the silicate in the solids content of the composition is 0, 01 to 0.06, and preferably from 0.02 to 0.04.13 - Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims, characterized in that they contain neither wax nor paraffin. 14 - Aqueous compositions for the treatment of a fibrous sheet material according to one of the preceding claims characterized in that the solids content represents from 10 to 75%, and preferably from 20 to 50% by weight of the mass total composition. 15 - Use of a composition as defined in one of the preceding claims in the manufacture of a fibrous sheet material, by deep impregnation in the thickness of said fibrous sheet material with said composition, to enhance the properties of mechanical strength in the dry state and possibly in the wet state of the fibrous material obtained. 16 - Use according to claim 15 characterized in that the fibrous sheet material is a paper or cardboard. 17 - Process for treating a fibrous sheet material, characterized in that the treatment is carried out continuously on at least one of the faces of the fibrous sheet material with an aqueous composition according to one of claims 1 to 14. 18 - Process according to claim 17, characterized in that the treatment is performed on each of the faces of the paper and in its mass. 19 - Process according to claim 17 or 18, characterized in that the treatment is integrated in a continuous manufacturing process of a fibrous sheet material and is applied to the latter in scrolling, in a finished state or during manufacture . 20 - Process according to claim 18 or 19, characterized in that the treatment is carried out by impregnation, preferably in a gluing press. 21 - Method according to one of claims 17 to 20, characterized in that the fibrous material is formed or is exclusively composed of recycled fibers. 22 - Fibrous sheet material treated with one of the aqueous compositions according to one of claims 1 to 14. Fibrous sheet material according to claim 22, characterized in that it is treated with the composition according to one of the claims 1 to 14 to obtain a dry mass deposited in the range of 3 g / m2 to 35 g / m2, and in particular to the range of 8 g / m2 to 25 g / m2. 24 - fibrous sheet material according to claim 22 or 23 obtained according to the method of one of claims 18 to 21. 25 - Fibrous sheet material according to claim 22, 23 or 24 characterized in that it corresponds to a sheet paper or cardboard, possibly in the form of a manufactured article. 16 - Corrugated cardboard consisting, at least in part, of a paper as defined in claim 25.