WO1999052816A1 - Method for preparing an aqueous dispersion of at least one platelet inorganic compound with improved rheological properties - Google Patents

Method for preparing an aqueous dispersion of at least one platelet inorganic compound with improved rheological properties Download PDF

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Publication number
WO1999052816A1
WO1999052816A1 PCT/FR1999/000591 FR9900591W WO9952816A1 WO 1999052816 A1 WO1999052816 A1 WO 1999052816A1 FR 9900591 W FR9900591 W FR 9900591W WO 9952816 A1 WO9952816 A1 WO 9952816A1
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Prior art keywords
shearing
aqueous dispersion
dispersion
shear
controlled
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PCT/FR1999/000591
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French (fr)
Inventor
Jérôme Bibette
Roland Bernon
Philippe Gorria
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Centre National De La Recherche Scientifique (Cnrs)
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Priority to AU27358/99A priority Critical patent/AU2735899A/en
Publication of WO1999052816A1 publication Critical patent/WO1999052816A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/50—Mixing liquids with solids
    • B01F23/53—Mixing liquids with solids using driven stirrers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
    • B01F27/27—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices
    • B01F27/272—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices with means for moving the materials to be mixed axially between the surfaces of the rotor and the stator, e.g. the stator rotor system formed by conical or cylindrical surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
    • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
    • B01F27/94—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis with rotary cylinders or cones

Definitions

  • the present invention relates to a method useful for improving and controlling the rheological properties of concentrated aqueous dispersions of at least one inorganic platelet material.
  • inorganic platelet material is intended to denote inorganic, natural or synthetic compounds in the form of a powder in which the grains have a flat shape of small dimensions and small thickness.
  • This type of inorganic compound is used in the composition of a wide variety of materials such as papers, rubbers and polymers, soaps and cosmetic products in which it is generally incorporated as a filler.
  • these materials are introduced therein in the form of an aqueous dispersion.
  • talc it is conventionally used in the form of an aqueous platelet dispersion (variable shape, size and thickness) stabilized by surfactants.
  • aqueous talc dispersions are conventionally obtained according to a two-step process: a first step called micronization and a second step called disintegration.
  • the first step makes it possible to fix the average particle size of the powder and leads to a platelet powder whose average size can be roughly adjusted (from 5 to 50 microns) according to the micronization process.
  • the second step is empirically recognized as necessary to achieve good flow property at the same time as suspension.
  • the entire dispersion is stirred with a pale device for a sufficient time (approximately one hour) until the material heats up considerably (80 ° C ).
  • This operation is carried out in the presence of surfactants or amphiphilic polymers.
  • aqueous dispersions of inorganic platelet materials of the talc type must be satisfactory in terms of flow, sedimentation and redispersibility after drying.
  • conventional methods such as that mentioned above do not make it possible to satisfactorily meet all of these requirements.
  • the object of the present invention is precisely to propose a new process making it possible to confer on concentrated aqueous dispersions in at least one inorganic platelet material, properties improved and predictable rheology.
  • the method according to the invention also has the advantage of leading to formulations of said materials which can be dried in order to obtain redispersible powders without energy.
  • the invention derives from the observation by the inventors that an aqueous dispersion of talc at 64%, subjected to shearing, is, at low shear rate, shear-thinning and becomes, above a certain threshold , rheo-thickening.
  • Figure 1 illustrates this phenomenon in particular. Beyond this threshold known as “critical shear threshold”, the dispersion develops an area which no longer flows. It is probably the appearance of this phase transition under flow which is at the origin of the rheodilating tendency of the dispersions observed.
  • the critical shear threshold is constant up to 30% in volume and decreases towards zero in the vicinity of the volume fraction 40% by volume (which corresponds to the 64% by mass formulation adopted at the industrial level).
  • the inventors have demonstrated that by subjecting a concentrated aqueous dispersion of at least one inorganic platelet compound to a shearing operation under specific conditions, it was possible to increase this critical shearing threshold and therefore d significantly optimize the rheological properties of the resulting dispersion and considerably improve the redispersibility of the inorganic material thus treated.
  • the subject of the present invention is a process for preparing a concentrated aqueous dispersion of at least one inorganic platelet compound and endowed with improved and controlled rheological properties implementing the shearing of a concentrated primary aqueous dispersion of minus an inorganic platelet compound characterized in that: said primary aqueous dispersion has a concentration of inorganic compound sufficient to allow during its shearing, the application of a mechanical stress sufficient to delaminate the platelets of said organic compound, - the shearing applied to said dispersion is a controlled shearing that is ie in such a way that the entire dispersion is subjected to the same minimum shear and in that said shearing is carried out with sufficient intensity to lead to a concentrated aqueous dispersion of at least one inorganic platelet compound whose threshold Shear critical is significantly increased compared to that of the primary aqueous dispersion.
  • controlled shearing is understood to mean shearing which has the effect of applying the same minimum mechanical stresses to all parts of the dispersion thus treated.
  • the conventional methods for preparing aqueous talc dispersions use a pale type device to impart good fluidity to the aqueous talc dispersion thus sheared. It is clear that the shear rates undergone at different points of the dispersion thus treated are different insofar as these points are not located in an equivalent manner relative to the stirring axis of the blade and that the recirculation does not is not controlled.
  • the controlled shear required according to the present invention can be obtained according to several variants.
  • the shear rate can be distinct, at a given time, for two points of the dispersion.
  • the geometry of the device used to generate the shear forces it is possible to modulate the shear rate applied to said dispersion in time and / or in space.
  • the dispersion is in flow when subjected to shearing, each part thereof can thus be subjected to a shearing rate which varies over time.
  • the shear is said to be controlled when, whatever the variation in time of the shear rate, it passes through a minimum value which is the same for all the parts of the dispersion, at a given instant which can differ from one place to the other of the dispersion.
  • the primary dispersion is introduced into an appropriate device.
  • This device can have various configurations. The exact configuration is not essential according to the invention since, on leaving this device, the entire dispersion has been subjected to the same minimum shear.
  • the controlled shearing is carried out by bringing said dispersion into contact with a solid moving surface.
  • the dispersion is animated by a circulation movement when it is subjected to controlled shearing.
  • a duvet cell is shown schematically in Figure 4. It consists of two concentric cylinders, in constant rotation with respect to each other. According to a particular embodiment, the external cylinder is stationary and the internal cylinder animated by a uniform rotational movement by in relation to a drive axis. These concentric cylinders define an annular enclosure.
  • the Duvet cell is supplied with primary aqueous dispersion at the level of the enclosure. The primary dispersion circulates in the enclosure while being subjected to shear forces generated by the uniform rotation of the internal cylinder on itself.
  • the primary dispersion is subjected to a constant shear rate, the shear rate being defined here as the ratio of the linear speed at the point of contact with the surface of the external cylinder to the difference (R3-R2) where R 2 and R 3 are the radii of the inner and outer cylinders, respectively.
  • the shear rate being defined here as the ratio of the linear speed at the point of contact with the surface of the external cylinder to the difference (R3-R2) where R 2 and R 3 are the radii of the inner and outer cylinders, respectively.
  • the second device In the case of the second device, it consists of two concentric discs delimiting an enclosure in which the primary dispersion circulates. One of the discs is stationary and the other animated by a uniform movement of rotation around its axis.
  • Such a device comprises a primary dispersion supply line which passes through the upper disc to open into the central part of the enclosure. The other end of the pipe is connected to a tank containing said primary dispersion.
  • Such a device is more particularly suitable for the continuous production of the aqueous dispersion according to the invention.
  • the plane / cone type cell As for the third type of device, the plane / cone type cell, it comprises a cone, the point of which is directed towards a plane and the axis of which is perpendicular to this plane, which rotates at a constant angular speed at distance from the plane.
  • These cells are commonly used in commercial devices, in particular rheometers for measuring the viscoelastic properties of liquids.
  • moving surfaces can be smooth, rough, wavy or have more or less large cavities.
  • preference will be given to rough surfaces.
  • the minimum value of the shear rate to which the primary dispersion is subject depends on the frequency of rotation, the frequency of oscillation and / or the amplitude of oscillation of the movement of the plates, cylinders and discs of the devices described above. -above.
  • the person skilled in the art can play on several parameters, namely the frequency of rotation, the frequency of oscillation of the movement of the plates, cylinders and discs of the devices described above, as well as on the dimension of the respective enclosures of these various devices in the direction perpendicular to the direction of the flow imposed by the movement of the surface.
  • the minimum shear rate varies linearly with the amplitude of oscillation and / or the frequency of the movement and inversely proportional with the dimension of the enclosure in a direction perpendicular to the flow.
  • the controlled shear is a shear of the confined transverse type.
  • this flow must be homogeneous, in contrast to a heterogeneous flow with the formation of fractures.
  • a homogeneous flow is characterized by a constant velocity gradient in a direction perpendicular to the solid surface in motion.
  • One way to control the flow is to play on the size of the speakers in the direction perpendicular to the direction of flow imposed by the movement of the surface.
  • this dimension is defined by the difference (R3-R2).
  • this dimension is defined by the distance separating the two discs in the direction of the axis of rotation of the lower disc.
  • a heterogeneous flow can be made homogeneous by reducing the size of the enclosure and more particularly by reducing its size in the direction perpendicular to the direction of the flow.
  • the minimum shear rate is between 1,000 and 10,000 s "1 .
  • the minimum shear rate is in the range 5,000-8,000 s ' 1 .
  • controlled shearing operation it is applied in accordance with the claimed process with an intensity such that it leads to an aqueous dispersion having a critical shear significantly increased compared to that of the primary aqueous dispersion.
  • this critical shear threshold corresponds to the minimum viscosity value above which a phase transition is observed under gelled flow.
  • this shearing step is a delamination step of the platelets and that the presence and proportion of thin and therefore more flexible platelets has a considerable and unexpected impact on the rheology of the material.
  • This observation is in fact contrary to commonly accepted ideas in colloid physics.
  • delamination comparable to a process of dividing dispersed objects, improves the flow. This effect must have its origin in the flexibility of the pads which increases although the total surface of the dispersed objects increases.
  • the inorganic platelets are more or less delaminated, that is to say cleaved into finer platelets and that this delamination rate fixes at the same time the viscosity of the dispersion, its maximum incorporation rate. in aqueous solution to remain pumpable and its sedimentation rate.
  • the aqueous suspension of delaminated inorganic material recovered at the end of said process is in turn subjected to a shearing operation in accordance with the invention.
  • the suspension is thickened beforehand. This thickening is carried out either by partially removing the water from said suspension, for example by evaporation, or by readjusting the concentration of inorganic platelet material by additional addition of non-delaminated material. 10
  • the concentration of the primary aqueous dispersion in inorganic platelet material is also a determining factor for optimizing the application of effective shearing.
  • the sheared dispersion has a concentration of inorganic material sufficient to allow the application of a sufficient stress to delaminate the platelets of the inorganic compound.
  • the concentration of the primary aqueous dispersion is adjusted so as to maximize the effect of the stress applied to the dispersion.
  • this concentration must also make it possible to retain a flow property for the corresponding aqueous dispersions so that they can be conveyed through the shear zone.
  • the primary aqueous dispersion has a concentration of inorganic platelet compound of at least 50% by mass and preferably greater than 65%.
  • the method according to the invention advantageously leads to predictable materials insofar as all the material sees the same constraint.
  • the talc type materials obtained in accordance with the present invention hardly decant. They are therefore particularly advantageous in terms of use because they make it possible to overcome the usual problems encountered during transport, pumping and spreading of the corresponding dispersions.
  • the claimed process is particularly advantageous insofar as it makes it possible to prepare dispersions of materials with improved rheological properties which, after drying, lead to materials which are easily redispersible and at concentrations which have hitherto not been 11
  • a talc obtained at the end of the claimed process can be redispersed at a concentration greater than 64% by mass and for example of the order of 70% by mass.
  • particulate inorganic materials are obtained which are more efficient and less costly in terms of manufacture and transport. They can also be packaged in powder and therefore make it possible to avoid the transport of the water which was conventionally associated with them.
  • the claimed process is particularly advantageous for preparing talc dispersions.
  • a specific embodiment of the invention consists in applying a controlled shear according to a transverse flow.
  • aqueous dispersion of primary talc having a mass content of approximately 64% or even of the order of 70% it is possible according to the invention to effectively apply a shear of the order of 4000 s * 1 .
  • the talc obtained at the end of the shearing step can be isolated in the form of a powder by drying which is easily redispersible at a mass rate of 64% or more.
  • the present invention also relates to the powders of inorganic platelet materials obtained by drying the aqueous dispersions prepared according to the claimed process.
  • Figure 1 Variation in viscosity as a function of the shear rate applied for a sample at 64% by mass obtained according to a conventional process.
  • Figure 2 Evolution of the critical shear rate ⁇ c as a function of the talc volume fraction of a sample prepared according to a conventional process.
  • FIG. 4 Schematic diagram of a Duvet cell assembly. 1 stator
  • Figure 5 Variation in the rheological behavior of four talcs redispersed at 64% by mass and having undergone a different imposed shear during the manufacturing process.
  • Figure 6 Evolution of the critical shear of talcs redispersed at 64% by mass as a function of the shear imposed during the manufacturing process.
  • Figure 7 Evolution of the critical viscosity of talcs redispersed at
  • Figure 8 Evolution of the viscosity as a function of shear for a material obtained according to the invention, with a controlled shear of 7500 s ⁇ 1 in a Couette cell and redispersed at a mass rate of 64%.
  • Figure 9 Evolution of the viscosity as a function of shear for a material obtained according to a conventional process with a pale mill and redispersed at a mass rate of 64%.
  • the wetting solution (1% of lumiten PE® marketed by BASF and 1% of Polysel® (solution of a salt of polyacrylic acid marketed by BASF) in water) is brought into contact by fraction with a crude powder until to enrich it to 64% At this concentration the mixture is pasty in the sense that it can no longer flow
  • the material is then forced to pass between the wall of a glass cylinder and the surface of a 2 cm Teflon cylinder radius, rotated at 300 rpm.
  • the space between the glass surface and the Teflon can vary between 0 and 300 microns. Once sheared, the material is dried and then redispersed effortlessly at a mass fraction of 64%.
  • FIG. 3 shows its rheogram and presents the viscosity as a function of the shear Compared with a talc obtained according to a conventional process with the same composition (64% having undergone one hour of kneading at high speed in a pale mill) the viscosity is already about the same (70cP) and the critical shear is 2 times greater (40 s "1 instead of 20 s " 1 ). This experience suggests that the delamination operation is clearly reached.

Abstract

The invention concerns a method for preparing a concentrated aqueous dispersion of at least one platelet inorganic compound with controlled and improved rheological properties consisting in shearing a primary aqueous dispersion with at least a platelet compound concentration, characterised in that: said primary aqueous dispersion has a sufficient inorganic compound concentration to enable a sufficient mechanical load being applied for delaminating said inorganic compound while it is being sheared; the shearing applied to said dispersion is a controlled shearing, that is such that the whole dispersion is subjected to a minimal common shearing; and said shearing is performed with sufficient intensity to result in an aqueous dispersion with at least a platelet powder inorganic compound concentration whereof the critical shearing threshold is significantly increased compared to that of the primary aqueous dispersion.

Description

- 1 - "Procédé de préparation d ' une dispersion aqueuse d ' au moins un composé inorganique plaquettaire à propriétés rhéologiques améliorées" - 1 - "Process for the preparation of an aqueous dispersion of at least one inorganic platelet compound with improved rheological properties"
La présente invention se rapporte à un procédé utile pour améliorer et contrôler les propriétés rhéologiques de dispersions aqueuses concentrées d'au moins un matériau inorganique plaquettaire.The present invention relates to a method useful for improving and controlling the rheological properties of concentrated aqueous dispersions of at least one inorganic platelet material.
Au sens de l'invention on entend désigner par « matériau inorganique plaquettaire», des composés inorganiques, naturels ou synthétiques se présentant sous la forme d'une poudre dans laquelle les grains ont une forme plate de petites dimensions et de faible épaisseur.For the purposes of the invention, the term “inorganic platelet material” is intended to denote inorganic, natural or synthetic compounds in the form of a powder in which the grains have a flat shape of small dimensions and small thickness.
A titre illustratif de ces matériaux on peut notamment citer le talc, les kaolins et le mica.By way of illustration of these materials, mention may in particular be made of talc, kaolins and mica.
Ce type de composés inorganiques entre dans la composition d'une grande variété de matériaux comme les papiers, caoutchoucs et polymères, savons et produits cosmétiques dans lesquels il est généralement incorporé à titre de charge.This type of inorganic compound is used in the composition of a wide variety of materials such as papers, rubbers and polymers, soaps and cosmetic products in which it is generally incorporated as a filler.
Généralement, ces matériaux y sont introduits sous la forme d'une dispersion aqueuse. Dans le cas particulier du talc, celui-ci est classiquement mis en œuvre sous la forme d'une dispersion aqueuse plaquettaire (forme, taille et épaisseur variables) stabilisée par des agents de surface.Generally, these materials are introduced therein in the form of an aqueous dispersion. In the particular case of talc, it is conventionally used in the form of an aqueous platelet dispersion (variable shape, size and thickness) stabilized by surfactants.
Ces dispersions aqueuses de talc sont classiquement obtenues selon un procédé en deux étapes : une première étape dite de micronisation et une deuxième étape dite de délitage.These aqueous talc dispersions are conventionally obtained according to a two-step process: a first step called micronization and a second step called disintegration.
La première étape permet de fixer la granulométrie moyenne de la poudre et conduit à une poudre de plaquettes dont la taille moyenne peut être sommairement ajustée (de 5 à 50 microns) selon le procédé de micronisation.The first step makes it possible to fix the average particle size of the powder and leads to a platelet powder whose average size can be roughly adjusted (from 5 to 50 microns) according to the micronization process.
La seconde étape est empiriquement reconnue nécessaire pour atteindre une bonne propriété d'écoulement en même temps qu'une mise en suspension. Pour atteindre une bonne fluidité à un taux de talc le plus élevé possible, l'ensemble de la dispersion est brassé avec un dispositif type pâle pendant un temps suffisant (environ une heure) jusqu'à provoquer un échauffement important du matériau (80°C). Cette opération est effectuée en présence de tensioactifs ou polymères amphiphiles. Pour des raisons évidentes d'utilisation, les dispersions aqueuses de matériaux inorganiques plaquettaires du type talc se doivent de donner satisfaction en termes d'écoulement, sédimentation et redispersabilité après séchage. Or, les procédés classiques tel celui évoqué ci-dessus ne permettent pas de répondre de manière satisfaisante à l'ensemble de ces exigences.The second step is empirically recognized as necessary to achieve good flow property at the same time as suspension. To achieve good fluidity at the highest possible talc content, the entire dispersion is stirred with a pale device for a sufficient time (approximately one hour) until the material heats up considerably (80 ° C ). This operation is carried out in the presence of surfactants or amphiphilic polymers. For obvious reasons of use, aqueous dispersions of inorganic platelet materials of the talc type must be satisfactory in terms of flow, sedimentation and redispersibility after drying. However, conventional methods such as that mentioned above do not make it possible to satisfactorily meet all of these requirements.
On est généralement confronté à un problème de sédimentation lorsque les dispersions sont conservées immobiles pendant un délai excédant 3 jours, notamment lors de leur transport. Une pâte se forme alors au fond des cuves contenant les dispersions qui rend difficile voire impossible leur pompage.We are generally faced with a sedimentation problem when the dispersions are kept immobile for a period exceeding 3 days, in particular during their transport. A paste then forms at the bottom of the tanks containing the dispersions which makes it difficult or even impossible to pump them.
De même, une rhéologie mal adaptée des dispersions actuellement disponibles pose problème au niveau de certaines de leurs applications. C'est en particulier le cas des dispersions aqueuses de talc utilisées dans l'industrie du couchage du papier où elles sont appliquées par injection rapide. En fait, cette application particulière nécessiterait des dispersions les plus concentrées possible mais également les plus fluides possible, non accessibles avec les procédés actuellement utilisés pour préparer les dispersions de talc.Likewise, a poorly adapted rheology of the dispersions currently available poses a problem in terms of some of their applications. This is in particular the case of the aqueous talc dispersions used in the paper coating industry where they are applied by rapid injection. In fact, this particular application would require the most concentrated dispersions possible but also the most fluid possible, not accessible with the processes currently used to prepare talc dispersions.
En effet, comme évoqué précédemment, l'opération de délitage telle que réalisée actuellement, conduit à des dispersions dont la concentration en talc ne peut rarement excédée 64 % en poids et qui par ailleurs conservent toujours de très mauvaises aptitudes à s'écouler.Indeed, as mentioned above, the disintegration operation as currently carried out, leads to dispersions whose talc concentration can rarely exceed 64% by weight and which, moreover, always retain very poor flowability.
En conséquence, les procédés disponibles à ce jour ne permettent pas d'obtenir des dispersions aqueuses de matériaux inorganiques plaquettaires donnant totalement satisfaction notamment en termes de sédimentation et de propriétés rhéologiques.Consequently, the methods available to date do not make it possible to obtain aqueous dispersions of inorganic platelet materials giving total satisfaction, in particular in terms of sedimentation and rheological properties.
La présente invention a précisément pour objet de proposer un nouveau procédé permettant de conférer à des dispersions aqueuses concentrées en au moins un matériau inorganique plaquettaire, des propriétés rhéologiques améliorées et prédictibles. Qui plus est, le procédé selon l'invention a en outre pour avantage de conduire à des formulations desdits matériaux qui peuvent être séchées afin d'en obtenir des poudres redispersables sans énergie.The object of the present invention is precisely to propose a new process making it possible to confer on concentrated aqueous dispersions in at least one inorganic platelet material, properties improved and predictable rheology. What is more, the method according to the invention also has the advantage of leading to formulations of said materials which can be dried in order to obtain redispersible powders without energy.
En fait, l'invention dérive de l'observation par les inventeurs qu'une dispersion aqueuse de talc à 64 %, soumise à un cisaillement, est, à bas taux de cisaillement, rhéofluidifiante et devient, au-dessus d'un certain seuil, rhéoépaississante. La figure 1 illustre notamment ce phénomène. Au delà de ce seuil dit « seuil de cisaillement critique », la dispersion développe une zone qui ne coule plus. C'est vraisemblablement l'apparition de cette transition de phase sous écoulement qui est à l'origine de la tendance rhéodilatante des dispersions observée.In fact, the invention derives from the observation by the inventors that an aqueous dispersion of talc at 64%, subjected to shearing, is, at low shear rate, shear-thinning and becomes, above a certain threshold , rheo-thickening. Figure 1 illustrates this phenomenon in particular. Beyond this threshold known as “critical shear threshold”, the dispersion develops an area which no longer flows. It is probably the appearance of this phase transition under flow which is at the origin of the rheodilating tendency of the dispersions observed.
Ce phénomène rhéologique a par ailleurs également été vérifié pour des dispersions à concentrations variables, comme l'indique la figure 2. Le seuil de cisaillement critique est constant jusqu'à 30 % en volume et décroît vers zéro au voisinage de la fraction volumique 40 % en volume (ce qui correspond à la formulation 64 % en masse retenue au niveau industriel).This rheological phenomenon has also been verified for dispersions at variable concentrations, as shown in Figure 2. The critical shear threshold is constant up to 30% in volume and decreases towards zero in the vicinity of the volume fraction 40% by volume (which corresponds to the 64% by mass formulation adopted at the industrial level).
De manière inattendue, les inventeurs ont mis en évidence qu'en soumettant une dispersion aqueuse concentrée d'au moins un composé inorganique plaquettaire à une opération de cisaillement dans des conditions spécifiques, il était possible d'augmenter ce seuil de cisaillement critique et donc d'optimiser significativement les propriétés rhéologiques de la dispersion résultante et d'améliorer considérablement la redispersabilité du matériau inorganique ainsi traité.Unexpectedly, the inventors have demonstrated that by subjecting a concentrated aqueous dispersion of at least one inorganic platelet compound to a shearing operation under specific conditions, it was possible to increase this critical shearing threshold and therefore d significantly optimize the rheological properties of the resulting dispersion and considerably improve the redispersibility of the inorganic material thus treated.
Plus précisément, la présente invention a pour objet un procédé de préparation d'une dispersion aqueuse concentrée d'au moins un composé inorganique plaquettaire et dotée de propriétés rhéologiques améliorées et contrôlées mettant en œuvre le cisaillement d'un dispersion aqueuse primaire concentrée d'au moins un composé inorganique plaquettaire caractérisé en ce que : ladite dispersion aqueuse primaire possède une concentration en composé inorganique suffisante pour permettre lors de son cisaillement, l'application d'une contrainte mécanique suffisante pour délaminer les plaquettes dudit composé organique, - le cisaillement appliqué à ladite dispersion est un cisaillement contrôlé c'est-à-dire de telle sorte que l'ensemble de la dispersion est soumise à un même cisaillement minimal et en ce que ledit cisaillement est effectué avec une intensité suffisante pour conduire à une dispersion aqueuse concentrée d'au moins un composé inorganique plaquettaire dont le seuil critique de cisaillement est significativement augmenté comparativement à celui de la dispersion aqueuse primaire.More specifically, the subject of the present invention is a process for preparing a concentrated aqueous dispersion of at least one inorganic platelet compound and endowed with improved and controlled rheological properties implementing the shearing of a concentrated primary aqueous dispersion of minus an inorganic platelet compound characterized in that: said primary aqueous dispersion has a concentration of inorganic compound sufficient to allow during its shearing, the application of a mechanical stress sufficient to delaminate the platelets of said organic compound, - the shearing applied to said dispersion is a controlled shearing that is ie in such a way that the entire dispersion is subjected to the same minimum shear and in that said shearing is carried out with sufficient intensity to lead to a concentrated aqueous dispersion of at least one inorganic platelet compound whose threshold Shear critical is significantly increased compared to that of the primary aqueous dispersion.
Au sens de la présente invention, on entend par cisaillement contrôlé, un cisaillement qui a pour effet d'appliquer les mêmes contraintes mécaniques minimales en toute part de la dispersion ainsi traitée.For the purposes of the present invention, the term “controlled shearing” is understood to mean shearing which has the effect of applying the same minimum mechanical stresses to all parts of the dispersion thus treated.
Dans le cas des procédés classiques évoqués ci-dessus, cette homogénéisation du taux de cisaillement au niveau de l'ensemble de la dispersion traitée ne peut être obtenue. L'opération de cisaillement est en effet appliquée à l'aide de dispositifs qui ne permettent pas d'assurer à l'ensemble de la dispersion traitée, un taux de cisaillement minimal identique.In the case of the conventional methods mentioned above, this homogenization of the shear rate at the level of the whole of the treated dispersion cannot be obtained. The shearing operation is in fact applied with the aid of devices which do not make it possible to ensure that the entire dispersion treated has an identical minimum shearing rate.
C'est ainsi que les procédés classiques de préparation de dispersions aqueuses de talc utilisent un dispositif type pâle pour conférer une bonne fluidité à la dispersion aqueuse de talc ainsi cisaillée. Il est clair que les taux de cisaillement subis en différents points de la dispersion ainsi traitée sont différents dans la mesure où ces points ne sont pas situés de manière équivalente par rapport à l'axe d'agitation de la pâle et que la recirculation n'est pas contrôlée.Thus, the conventional methods for preparing aqueous talc dispersions use a pale type device to impart good fluidity to the aqueous talc dispersion thus sheared. It is clear that the shear rates undergone at different points of the dispersion thus treated are different insofar as these points are not located in an equivalent manner relative to the stirring axis of the blade and that the recirculation does not is not controlled.
Le cisaillement contrôlé requis selon la présente invention, peut être obtenu selon plusieurs variantes.The controlled shear required according to the present invention can be obtained according to several variants.
Selon une première variante, on peut envisager de soumettre l'ensemble de la dispersion primaire à un taux de cisaillement constant. Cependant, l'invention n'entend pas se limiter à ce mode de réalisation particulier.According to a first variant, it is possible to envisage subjecting the whole of the primary dispersion to a constant shear rate. However, the invention is not intended to be limited to this particular embodiment.
De fait, le taux de cisaillement peut être distinct, à un temps donné, pour deux points de la dispersion. C'est ainsi qu'en variant la géométrie du dispositif utilisé pour générer les forces de cisaillement, il est possible de moduler le taux de cisaillement appliqué à ladite dispersion dans le temps et/ou dans l'espace.In fact, the shear rate can be distinct, at a given time, for two points of the dispersion. Thus by varying the geometry of the device used to generate the shear forces, it is possible to modulate the shear rate applied to said dispersion in time and / or in space.
Pour autant que la dispersion soit en écoulement lorsque soumise au cisaillement, chaque partie de celle-ci peut être ainsi soumise à un taux de cisaillement qui varie dans le temps. Le cisaillement est dit contrôlé lorsque quelle que soit la variation dans le temps du taux de cisaillement, celui-ci passe par une valeur minimale qui est la même pour toutes les parties de la dispersion, à un instant donné qui peut différer d'un endroit à l'autre de la dispersion. De manière préférée, de façon à générer un cisaillement contrôlé, on introduit la dispersion primaire dans un dispositif approprié. Ce dispositif peut présenter des configurations variées. La configuration exacte n'est pas essentielle selon l'invention dès lors qu'en sortie de ce dispositif l'ensemble de la dispersion a été soumis au même cisaillement minimal.Provided that the dispersion is in flow when subjected to shearing, each part thereof can thus be subjected to a shearing rate which varies over time. The shear is said to be controlled when, whatever the variation in time of the shear rate, it passes through a minimum value which is the same for all the parts of the dispersion, at a given instant which can differ from one place to the other of the dispersion. Preferably, in order to generate a controlled shear, the primary dispersion is introduced into an appropriate device. This device can have various configurations. The exact configuration is not essential according to the invention since, on leaving this device, the entire dispersion has been subjected to the same minimum shear.
Selon une première variante, le cisaillement contrôlé est réalisé par mise en contact de ladite dispersion avec une surface solide en mouvement. Dans une seconde variante, la dispersion est animée d'un mouvement de circulation lorsqu'elle est soumise au cisaillement contrôlé.According to a first variant, the controlled shearing is carried out by bringing said dispersion into contact with a solid moving surface. In a second variant, the dispersion is animated by a circulation movement when it is subjected to controlled shearing.
A titre illustratif mais non limitatif des dispositifs pouvant être mis en œuvre selon l'invention, pour appliquer un cisaillement contrôlé, on peut notamment citer les dispositifs dits de Couette, de type cellule délimitée par 2 disques et de type plan/cône. Une cellule dite de Couette est schématisée en figure 4. Elle est constituée de deux cylindres concentriques, en rotation constante l'un par rapport à l'autre. Selon un mode de réalisation particulier, le cylindre externe est immobile et le cylindre interne animé d'un mouvement de rotation uniforme par rapport à un axe d'entraînement. Ces cylindres concentriques délimitent une enceinte annulaire. La cellule de Couette est alimentée en dispersion aqueuse primaire au niveau de l'enceinte. La dispersion primaire circule dans l'enceinte tout en étant soumise à des forces de cisaillement engendrées par la rotation uniforme du cylindre interne sur lui-même. Dans un tel dispositif, la dispersion primaire est soumise à un taux de cisaillement constant, le taux de cisaillement étant défini ici comme le rapport de la vitesse linéaire au point de contact avec la surface du cylindre externe à la différence (R3-R2) où R2 et R3 sont respectivement les rayons des cylindres interne et externe. Lorsque la dispersion est récupérée à la sortie du dispositif, celle-ci a les caractéristiques de la dispersion attendue.By way of illustration but not limitation of the devices which can be implemented according to the invention, for applying controlled shearing, mention may be made of the so-called Couette devices, of cell type delimited by 2 discs and of plane / cone type. A duvet cell is shown schematically in Figure 4. It consists of two concentric cylinders, in constant rotation with respect to each other. According to a particular embodiment, the external cylinder is stationary and the internal cylinder animated by a uniform rotational movement by in relation to a drive axis. These concentric cylinders define an annular enclosure. The Duvet cell is supplied with primary aqueous dispersion at the level of the enclosure. The primary dispersion circulates in the enclosure while being subjected to shear forces generated by the uniform rotation of the internal cylinder on itself. In such a device, the primary dispersion is subjected to a constant shear rate, the shear rate being defined here as the ratio of the linear speed at the point of contact with the surface of the external cylinder to the difference (R3-R2) where R 2 and R 3 are the radii of the inner and outer cylinders, respectively. When the dispersion is recovered at the outlet of the device, it has the characteristics of the expected dispersion.
Dans le cas du second dispositif, il est constitué de deux disques concentriques délimitant une enceinte dans laquelle circule la dispersion primaire. L'un des disques est immobile et l'autre animé d'un mouvement uniforme de rotation autour de son axe. Un tel dispositif comprend une conduite d'alimentation en dispersion primaire laquelle traverse le disque supérieur pour déboucher dans la partie centrale de l'enceinte. L'autre extrémité de la conduite est reliée à un réservoir contenant ladite dispersion primaire. Un tel dispositif est plus particulièrement approprié pour la production en continu de la dispersion aqueuse selon l'invention.In the case of the second device, it consists of two concentric discs delimiting an enclosure in which the primary dispersion circulates. One of the discs is stationary and the other animated by a uniform movement of rotation around its axis. Such a device comprises a primary dispersion supply line which passes through the upper disc to open into the central part of the enclosure. The other end of the pipe is connected to a tank containing said primary dispersion. Such a device is more particularly suitable for the continuous production of the aqueous dispersion according to the invention.
Pour ce qui est du troisième type de dispositif, la cellule de type plan/cône, il comprend un cône, dont la pointe est dirigée vers un plan et dont l'axe est perpendiculaire à ce plan, qui tourne à une vitesse angulaire constante à distance du plan. Ces cellules sont couramment utilisées dans des appareils commerciaux, en particulier des rhéomètres permettant de mesurer les propriétés viscoélastiques de liquides.As for the third type of device, the plane / cone type cell, it comprises a cone, the point of which is directed towards a plane and the axis of which is perpendicular to this plane, which rotates at a constant angular speed at distance from the plane. These cells are commonly used in commercial devices, in particular rheometers for measuring the viscoelastic properties of liquids.
Dans chacun de ces dispositifs la nature du matériau constituant les cylindres, disques et plaques en mouvement, directement en contact avec le matériau à traiter n'est pas essentielle selon l'invention.In each of these devices the nature of the material constituting the cylinders, discs and plates in movement, directly in contact with the material to be treated is not essential according to the invention.
Dans les dispositifs utilisés pour générer les forces de cisaillement, les surfaces en mouvement peuvent être lisses, rugueuses, ondulées ou présenter des cavités plus ou moins importantes. Toutefois dans le cadre de la présente invention, on privilégiera des surfaces rugueuses.In devices used to generate shear forces, moving surfaces can be smooth, rough, wavy or have more or less large cavities. However, in the context of the present invention, preference will be given to rough surfaces.
Les contraintes de cisaillement générées par les dispositifs décrits ci-dessus n'entraînent généralement pas d'importantes fluctuations de la température. Par prudence, il peut être utile cependant de thermostater les dispositifs à cisaillement mécanique utilisés.The shear stresses generated by the devices described above generally do not cause significant temperature fluctuations. As a precaution, it may however be useful to thermostate the mechanical shearing devices used.
Généralement, la valeur minimale du taux de cisaillement auquel est soumise la dispersion primaire dépend de la fréquence de rotation, de la fréquence d'oscillation et/ou de l'amplitude d'oscillation du mouvement des plaques, cylindres et disques des dispositifs décrits ci-dessus.Generally, the minimum value of the shear rate to which the primary dispersion is subject depends on the frequency of rotation, the frequency of oscillation and / or the amplitude of oscillation of the movement of the plates, cylinders and discs of the devices described above. -above.
De façon à augmenter la valeur du taux de cisaillement minimal, l'homme du métier peut jouer sur plusieurs paramètres, à savoir la fréquence de rotation, la fréquence d'oscillation du mouvement des plaques, cylindres et disques des dispositifs décrits ci-dessus, ainsi que sur la dimension des enceintes respectives de ces différents dispositifs dans la direction perpendiculaire au sens de l'écoulement imposé par le mouvement de la surface.In order to increase the value of the minimum shear rate, the person skilled in the art can play on several parameters, namely the frequency of rotation, the frequency of oscillation of the movement of the plates, cylinders and discs of the devices described above, as well as on the dimension of the respective enclosures of these various devices in the direction perpendicular to the direction of the flow imposed by the movement of the surface.
On notera que le taux minimal de cisaillement varie de façon linéaire avec l'amplitude d'oscillation et/ou la fréquence du mouvement et de façon inversement proportionnelle avec la dimension de l'enceinte dans une direction perpendiculaire à l'écoulement.It will be noted that the minimum shear rate varies linearly with the amplitude of oscillation and / or the frequency of the movement and inversely proportional with the dimension of the enclosure in a direction perpendicular to the flow.
Selon un mode de réalisation préféré, le cisaillement contrôlé est un cisaillement de type transverse confiné. C'est ainsi que, lorsque la dispersion, soumise au cisaillement contrôlé est en écoulement, cet écoulement doit être homogène, par opposition à un écoulement hétérogène avec formation de fractures.According to a preferred embodiment, the controlled shear is a shear of the confined transverse type. Thus, when the dispersion, subjected to controlled shear is in flow, this flow must be homogeneous, in contrast to a heterogeneous flow with the formation of fractures.
Plus précisément, lorsque le cisaillement contrôlé est réalisé par mise en contact de ladite dispersion avec une surface solide en mouvement, un écoulement homogène est caractérisé par un gradient de vitesse constant dans une direction perpendiculaire à la surface solide en mouvement. Un moyen de contrôler l'écoulement consiste à jouer sur la dimension des enceintes dans la direction perpendiculaire au sens de l'écoulement imposé par le mouvement de la surface.More precisely, when the controlled shearing is achieved by bringing said dispersion into contact with a solid surface in motion, a homogeneous flow is characterized by a constant velocity gradient in a direction perpendicular to the solid surface in motion. One way to control the flow is to play on the size of the speakers in the direction perpendicular to the direction of flow imposed by the movement of the surface.
On notera que, dans le cas du dispositif de type couette, cette dimension est définie par la différence (R3-R2). Dans le cas du second dispositif, cette dimension est définie par la distance séparant les deux disques dans la direction de l'axe de rotation du disque inférieur.It will be noted that, in the case of the comforter type device, this dimension is defined by the difference (R3-R2). In the case of the second device, this dimension is defined by the distance separating the two discs in the direction of the axis of rotation of the lower disc.
De façon générale, un écoulement hétérogène peut être rendu homogène par réduction de la taille de l'enceinte et plus particulièrement par réduction de sa dimension dans la direction perpendiculaire au sens de l'écoulement.In general, a heterogeneous flow can be made homogeneous by reducing the size of the enclosure and more particularly by reducing its size in the direction perpendicular to the direction of the flow.
De façon générale, le taux minimal de cisaillement est compris entre 1 000 et 10 000 s"1.Generally, the minimum shear rate is between 1,000 and 10,000 s "1 .
De manière préférée cependant le taux minimal de cisaillement est situé dans l'intervalle 5 000- 8 000 s'1.Preferably, however, the minimum shear rate is in the range 5,000-8,000 s ' 1 .
En ce qui concerne plus particulièrement l'opération de cisaillement contrôlé, elle est appliquée conformément au procédé revendiqué avec une intensité telle qu'elle conduit à une dispersion aqueuse possédant un cisaillement critique significativement augmenté comparativement à celui de la dispersion aqueuse primaire.As regards more particularly the controlled shearing operation, it is applied in accordance with the claimed process with an intensity such that it leads to an aqueous dispersion having a critical shear significantly increased compared to that of the primary aqueous dispersion.
Comme défini précédemment, ce seuil de cisaillement critique correspond à la valeur minimale de viscosité au-delà de laquelle on observe une transition de phase sous écoulement gélifié.As defined above, this critical shear threshold corresponds to the minimum viscosity value above which a phase transition is observed under gelled flow.
Les inventeurs ont ainsi mis en évidence qu'il était possible d'augmenter significativement le cisaillement critique d'une dispersion aqueuse primaire en lui appliquant un cisaillement conforme à l'invention.The inventors have thus demonstrated that it was possible to significantly increase the critical shear of a primary aqueous dispersion by applying a shear in accordance with the invention.
C'est ainsi que si l'on met en contact avec une solution mouillante une poudre brut de talc jusqu'à en obtenir une dispersion aqueuse possédant un taux massique de 64% et ayant donc l'aspect d'une pâte onctueuse, que l'on soumet cette dispersion à un cisaillement contrôlé conforme à la présente invention et que l'on sèche le produit final, il s'avère possible de redisperser ce talc sec sans aucune difficulté à une fraction massique de 64%. La figure 3 en annexe, qui rend compte de l'évolution de la viscosité de la dispersion aqueuse ainsi obtenue en fonction du cisaillement, montre que le taux de cisaillement critique correspondant est d'environ 30 s"1. Pour une dispersion de même concentration, obtenue selon un procédé classique et dont l'évolution de viscosité est représentée en figure 1 , ce taux de cisaillement critique n'est que de l'ordre de 17 s"1.Thus, if a crude talcum powder is brought into contact with a wetting solution until an aqueous dispersion is obtained having a mass content of 64% and therefore having the appearance of a creamy paste, that the this dispersion is subjected to a controlled shear in accordance with the present invention and that the final product is dried, it proves possible to redisperse this dry talc without any difficulty at a mass fraction of 64%. Figure 3 in the appendix, which gives an account of the evolution of the viscosity of the aqueous dispersion thus obtained as a function of the shear, shows that the corresponding critical shear rate is around 30 s "1. For a dispersion of the same concentration , obtained according to a conventional process and the change in viscosity of which is shown in FIG. 1, this critical shear rate is only of the order of 17 s "1 .
Ces résultats suggèrent que cette étape de cisaillement est une étape de délaminage des plaquettes et que la présence et la proportion de plaquettes fines et donc plus souples a un impact considérable et inattendu sur la rhéologie du matériau. Cette observation est en fait contraire aux idées communément admises en physiques des colloïdes. De manière générale, en divisant les matériaux on attend une propriété d'écoulement de plus en plus mauvaise. Avantageusement, pour les matériaux de type talc, le délaminage assimilable à un processus de division des objets dispersés, améliore l'écoulement. Cet effet doit trouver son origine dans la flexibilité des plaquettes qui augmente bien que la surface totale des objets dispersés augmente.These results suggest that this shearing step is a delamination step of the platelets and that the presence and proportion of thin and therefore more flexible platelets has a considerable and unexpected impact on the rheology of the material. This observation is in fact contrary to commonly accepted ideas in colloid physics. In general, when dividing the materials, an increasingly poor flow property is expected. Advantageously, for talc type materials, delamination comparable to a process of dividing dispersed objects, improves the flow. This effect must have its origin in the flexibility of the pads which increases although the total surface of the dispersed objects increases.
Il semblerait que selon l'intensité du cisaillement, les plaquettes inorganiques sont plus ou moins délaminés c'est à dire clivées en plaquettes plus fines et que ce taux de délaminage fixe à la fois la viscosité de la dispersion, son taux d'incorporation maximal en solution aqueuse pour demeurer pompable et sa vitesse de sédimentation.It would seem that according to the intensity of the shearing, the inorganic platelets are more or less delaminated, that is to say cleaved into finer platelets and that this delamination rate fixes at the same time the viscosity of the dispersion, its maximum incorporation rate. in aqueous solution to remain pumpable and its sedimentation rate.
Selon une variante de l'invention, la suspension aqueuse en matériau inorganique délaminé récupérée à l'issue dudit procédé est à son tour soumise à une opération de cisaillement conforme à l'invention.According to a variant of the invention, the aqueous suspension of delaminated inorganic material recovered at the end of said process is in turn subjected to a shearing operation in accordance with the invention.
Pour se faire, on procède au préalable à un épaississement de ladite suspension. Cet épaississement est effectué soit en éliminant en partie l'eau de ladite suspension, par exemple par évaporation, soit en réajustant la concentration en matériau inorganique plaquettaire par ajout complémentaire en matériau non délaminé. 10To do this, the suspension is thickened beforehand. This thickening is carried out either by partially removing the water from said suspension, for example by evaporation, or by readjusting the concentration of inorganic platelet material by additional addition of non-delaminated material. 10
La concentration de la dispersion aqueuse primaire en matériau inorganique plaquettaire est également un élément déterminant pour optimiser au mieux l'application d'un cisaillement efficace.The concentration of the primary aqueous dispersion in inorganic platelet material is also a determining factor for optimizing the application of effective shearing.
Il est en effet avantageux que la dispersion cisaillée possède une concentration en matériau inorganique suffisante pour permettre l'application d'une contrainte suffisante pour délaminer les plaquettes du composé inorganique.It is in fact advantageous that the sheared dispersion has a concentration of inorganic material sufficient to allow the application of a sufficient stress to delaminate the platelets of the inorganic compound.
En conséquence, selon un mode de réalisation privilégié de l'invention, la concentration de la dispersion aqueuse primaire est ajustée de manière à amplifier au maximum l'effet de la contrainte appliquée à la dispersion.Consequently, according to a preferred embodiment of the invention, the concentration of the primary aqueous dispersion is adjusted so as to maximize the effect of the stress applied to the dispersion.
Bien entendu cette concentration doit par ailleurs permettre de conserver une propriété d'écoulement aux dispersions aqueuses correspondantes pour qu'elles puissent être véhiculées à travers la zone de cisaillement.Of course, this concentration must also make it possible to retain a flow property for the corresponding aqueous dispersions so that they can be conveyed through the shear zone.
Selon un mode de réalisation particulier de l'invention, la dispersion aqueuse primaire possède une concentration en composé inorganique plaquettaire d'au moins 50 % en masse et de préférence supérieure à 65 %.According to a particular embodiment of the invention, the primary aqueous dispersion has a concentration of inorganic platelet compound of at least 50% by mass and preferably greater than 65%.
Le procédé selon l'invention conduit avantageusement à des matériaux prédictibles dans la mesure où tout le matériau voit la même contrainte. Qui plus est, les matériaux de type talc, obtenus conformément à la présente invention ne décantent quasiment pas. Ils sont donc particulièrement avantageux en terme d'utilisation car ils permettent de s'affranchir des problèmes usuels rencontrés lors du transport, pompage et étalement des dispersions correspondantes.The method according to the invention advantageously leads to predictable materials insofar as all the material sees the same constraint. What is more, the talc type materials obtained in accordance with the present invention hardly decant. They are therefore particularly advantageous in terms of use because they make it possible to overcome the usual problems encountered during transport, pumping and spreading of the corresponding dispersions.
En conséquence, le procédé revendiqué est particulièrement avantageux dans la mesure où il permet de préparer des dispersions de matériaux à propriétés rhéologiques améliorées qui après séchage conduisent à des matériaux facilement redispersables et à des concentrations jusqu'ici non 11Consequently, the claimed process is particularly advantageous insofar as it makes it possible to prepare dispersions of materials with improved rheological properties which, after drying, lead to materials which are easily redispersible and at concentrations which have hitherto not been 11
accessibles. C'est ainsi qu'un talc obtenu à l'issue du procédé revendiqué peut être redispersé à une concentration supérieure à 64 % en masse et par exemple de l'ordre de 70%, en masse.accessible. Thus, a talc obtained at the end of the claimed process can be redispersed at a concentration greater than 64% by mass and for example of the order of 70% by mass.
On obtient donc selon l'invention des matériaux inorganiques particulaires plus performants et moins coûteux en terme de fabrication et de transport. Ils peuvent en outre être conditionnés en poudre et donc permettent d'éviter le transport de l'eau qui leur était classiquement associée.According to the invention, therefore, particulate inorganic materials are obtained which are more efficient and less costly in terms of manufacture and transport. They can also be packaged in powder and therefore make it possible to avoid the transport of the water which was conventionally associated with them.
Le procédé revendiqué est particulièrement avantageux pour préparer des dispersions de talc.The claimed process is particularly advantageous for preparing talc dispersions.
Dans ce cas particulier, un mode de réalisation spécifique de l'invention consiste à appliquer un cisaillement contrôlé selon un écoulement transverse. Pour une dispersion aqueuse de talc primaire possédant un taux massique d'environ 64% voire de l'ordre de 70%, on peut conformément à l'invention appliquer efficacement un cisaillement de l'ordre de 4000 s*1.In this particular case, a specific embodiment of the invention consists in applying a controlled shear according to a transverse flow. For an aqueous dispersion of primary talc having a mass content of approximately 64% or even of the order of 70%, it is possible according to the invention to effectively apply a shear of the order of 4000 s * 1 .
Comme le confirme l'exemple 2, plus le cisaillement contrôlé imposé lors de la fabrication du talc est élevé, plus le talc redispersé à 64% coule bien, possède une viscosité plus faible et un seuil de cisaillement critique plus élevé. La valeur de son seuil critique de cisaillement est environ doublée. Les graphes présentés en figures 6 et 7 illustrent clairement ces phénomènes.As confirmed in Example 2, the higher the controlled shear imposed during the manufacture of the talc, the more the talc redispersed at 64% flows well, has a lower viscosity and a higher critical shear threshold. The value of its critical shear threshold is approximately doubled. The graphs presented in Figures 6 and 7 clearly illustrate these phenomena.
Avantageusement, le talc obtenu à l'issue de l'étape de cisaillement peut être isolé sous forme d'une poudre par séchage qui est facilement redispersable à un taux massique de 64% ou plus.Advantageously, the talc obtained at the end of the shearing step can be isolated in the form of a powder by drying which is easily redispersible at a mass rate of 64% or more.
La présente invention a également pour objet les poudres de matériaux inorganiques plaquettaires obtenues par séchage des dispersions aqueuses préparées selon le procédé revendiqué.The present invention also relates to the powders of inorganic platelet materials obtained by drying the aqueous dispersions prepared according to the claimed process.
Les exemples et figures figurant ci-après sont présentés à titre illustratif et non limitatif de la présente invention.The examples and figures appearing below are presented by way of illustration and without limitation of the present invention.
FIGURES 12FIGURES 12
Figure 1 : Variation de la viscosité en fonction du taux de cisaillement appliqué pour un échantillon à 64 % massique obtenu selon un procédé conventionnel.Figure 1: Variation in viscosity as a function of the shear rate applied for a sample at 64% by mass obtained according to a conventional process.
Figure 2 : Evolution du taux de cisaillement critique γc en fonction de la fraction volumique en talc d'un échantillon préparé selon un procédé conventionnel.Figure 2: Evolution of the critical shear rate γ c as a function of the talc volume fraction of a sample prepared according to a conventional process.
Figure 3 : Comportement rhéologique d'une dispersion de talc àFigure 3: Rheological behavior of a talc dispersion at
64% massique obtenu selon le procédé revendiqué.64% by mass obtained according to the claimed process.
Figure 4 : Schéma de principe d'un montage de cellule de Couette. 1 StatorFigure 4: Schematic diagram of a Duvet cell assembly. 1 stator
2 Rotor2 Rotor
3 Entrefer de largeur variable (100, 200 ou 300 μm)3 Variable width air gap (100, 200 or 300 μm)
4 Milieu réactionnel4 Reaction medium
A Injection du mélange B Régulation de la vitesse de rotation du rotorA Injection of the mixture B Regulation of the rotational speed of the rotor
C Extrusion du matériauC Extrusion of the material
Figure 5 : Variation du comportement rhéologique de quatre talcs redispersés à 64% massique et ayant subi un cisaillement imposé différent lors du procédé de fabrication.Figure 5: Variation in the rheological behavior of four talcs redispersed at 64% by mass and having undergone a different imposed shear during the manufacturing process.
Figure 6 : Evolution du cisaillement critique de talcs redispersés à 64% massique en fonction du cisaillement imposé lors du procédé de fabrication. Figure 7 : Evolution de la viscosité critique de talcs redispersés àFigure 6: Evolution of the critical shear of talcs redispersed at 64% by mass as a function of the shear imposed during the manufacturing process. Figure 7: Evolution of the critical viscosity of talcs redispersed at
64% massique en fonction du cisaillement imposé lors du procédé de fabrication. 1364% by mass depending on the shear imposed during the manufacturing process. 13
Figure 8 : Evolution de la viscosité en fonction du cisaillement pour un matériau obtenu selon l'invention, avec un cisaillement contrôlé de 7500 s"1 dans une cellule de Couette et redispersé à un taux massique de 64%.Figure 8: Evolution of the viscosity as a function of shear for a material obtained according to the invention, with a controlled shear of 7500 s −1 in a Couette cell and redispersed at a mass rate of 64%.
Figure 9 : Evolution de la viscosité en fonction du cisaillement pour un matériau obtenu selon un procédé classique avec un broyeur à pâle et redispersé à un taux massique de 64%.Figure 9: Evolution of the viscosity as a function of shear for a material obtained according to a conventional process with a pale mill and redispersed at a mass rate of 64%.
EXEMPLE 1EXAMPLE 1
La solution mouillante (1 % de lumiten PE® commercialisé par BASF et 1 % de Polysel® (solution d'un sel d'acide polyacrylique commercialisé par BASF) dans l'eau) est mise en contact par fraction avec une poudre brute jusqu'à l'enrichir à 64 % A cette concentration le mélange est pâteux au sens ou il ne peut plus couler Le matériau est ensuite forcé à passer entre la paroi d'un cylindre de verre et la surface d'un cylindre en téflon de 2 cm de rayon, mis en rotation à 300 trs par minutes. L'espace entre la surface de verre et le téflon peut varier entre 0 et 300 microns. Une fois cisaillé, le matériau est séché puis redispersé sans effort à une fraction massique de 64 %.The wetting solution (1% of lumiten PE® marketed by BASF and 1% of Polysel® (solution of a salt of polyacrylic acid marketed by BASF) in water) is brought into contact by fraction with a crude powder until to enrich it to 64% At this concentration the mixture is pasty in the sense that it can no longer flow The material is then forced to pass between the wall of a glass cylinder and the surface of a 2 cm Teflon cylinder radius, rotated at 300 rpm. The space between the glass surface and the Teflon can vary between 0 and 300 microns. Once sheared, the material is dried and then redispersed effortlessly at a mass fraction of 64%.
La figure 3 montre son rhéogramme et présente la viscosité en fonction du cisaillement Par rapport à un talc obtenu selon un procédé classique à la même composition (64 % ayant subi une heure de malaxage à grande vitesse dans un broyeur à pâle) la viscosité est déjà à peu près identique (70cP) et le cisaillement critique est 2 fois plus grand (40 s"1 au lieu de 20 s"1). Cette expérience suggère que l'opération de délaminage est clairement atteinte.FIG. 3 shows its rheogram and presents the viscosity as a function of the shear Compared with a talc obtained according to a conventional process with the same composition (64% having undergone one hour of kneading at high speed in a pale mill) the viscosity is already about the same (70cP) and the critical shear is 2 times greater (40 s "1 instead of 20 s " 1 ). This experience suggests that the delamination operation is clearly reached.
Pour déterminer l'origine exacte de cette transformation, un appareil capable de vérifier quantitativement l'hypothèse du cisaillement transverse dans une géométrie de Couette a été mis au point. Cet appareil permet d'appliquer un cisaillement homogène sur une épaisseur de 200 μm. Il est schématisé sur la figure 4. 14To determine the exact origin of this transformation, an apparatus capable of quantitatively verifying the hypothesis of transverse shear in a Couette geometry was developed. This device makes it possible to apply a homogeneous shear on a thickness of 200 μm. It is shown schematically in Figure 4. 14
EXEMPLE 2EXAMPLE 2
La poudre est ajoutée progressivement à la solution mouillante sous agitation à un taux de 70 %. A ce stade on a une pâte certes humide mais qui ne coule pas. Cette pâte est ensuite forcée à circuler dans l'entrefer du Couette sur un parcours de 3 cm. A la sortie du Couette on récupère un matériau qui coule, séchable et redispersable (sans énergie) au taux désiré. Nous reportons sur la figure 5 les caractéristiques rhéologiquesThe powder is gradually added to the wetting solution with stirring at a rate of 70%. At this stage we have a dough which is certainly moist but which does not run. This paste is then forced to circulate in the air gap of the Duvet on a path of 3 cm. At the exit of the Duvet, a flowing, recoverable and redispersible material (without energy) is recovered at the desired rate. We show in Figure 5 the rheological characteristics
(viscosité et contrainte en fonction du taux de cisaillement) pour des talcs redispersés à 64 % mais obtenus à des cisaillements contrôlés variables. Le cisaillement lors de la mise en forme est modulé en changeant la vitesse de rotation du cylindre intérieur (de 1 000 à 4 000 s'1). Cette expérience démontre qu'un cisaillement transverse homogène change la rhéologie du talc ainsi mis en forme et donc change le taux de délaminage. En effet, on constate que plus le cisaillement à la fabrication est élevé, plus le talc redispersé à 64 % coule bien : viscosité plus faible et seuil de cisaillement critique plus élevé comme en témoigne les figures 4 et 5.(viscosity and stress as a function of the shear rate) for talcs redispersed at 64% but obtained at variable controlled shears. The shear during shaping is modulated by changing the speed of rotation of the inner cylinder (from 1000 to 4000 s ' 1 ). This experiment shows that a homogeneous transverse shear changes the rheology of the talc thus formed and therefore changes the delamination rate. In fact, it is found that the higher the shear during manufacture, the more the talc redispersed at 64% flows well: lower viscosity and higher critical shear threshold as shown in FIGS. 4 and 5.
Cette expérience démontre qu'avec un cisaillement homogène aussi petit que 5000 s'1 on obtient déjà par ce procédé un talc équivalent à celui issu d'un procédé classique mettant en œuvre un broyeur à pâle (voir ligne horizontale pointillée sur les graphes de figures 6 et 7). Sur les figures 8 et 9, on reporte les courbes η(γ), pour le matériau de l'invention à 64 % obtenu au plus fort cisaillement exploré (7500 s"1), et pour la référence témoin obtenue selon le protocole précédemment décrit. On remarque que l'allure des courbes est très différente, en ce sens que la remontée rhéoépaississante devient très atténuée, voire quasi inexistante, ce qui peut autoriser ces matériaux à couler à haut cisaillement. En effet la transition de gel, observée avec les procédés classiques, tend à disparaître lorsque le délaminage est opéré ; ceci est une première différence par rapport 15 aux matériaux témoins obtenus par le procédé classique. Enfin, les talcs obtenus par le procédé de l'invention ne décantent pas ou peu. This experience shows that with a homogeneous shear as small as 5000 s ' 1, a talc equivalent to that already obtained by a conventional process using a pale mill is already obtained by this process (see horizontal dotted line on the graphs of figures 6 and 7). In FIGS. 8 and 9, the curves η (γ) are reported, for the material of the invention at 64% obtained at the highest shear explored (7500 s "1 ), and for the reference reference obtained according to the protocol previously described We note that the shape of the curves is very different, in the sense that the rheo-thickening rise becomes very attenuated, even almost non-existent, which can allow these materials to flow at high shear. conventional processes, tends to disappear when delamination is carried out; this is a first difference compared to 15 to the control materials obtained by the conventional method. Finally, the talcs obtained by the process of the invention do not decant or little.

Claims

16REVENDICATIONS 16 CLAIMS
1. Procédé de préparation d'une dispersion aqueuse concentrée d'au moins un composé inorganique plaquettaire et dotée de propriétés rhéologiques améliorées et contrôlées mettant en œuvre le cisaillement d'une dispersion aqueuse primaire d'au moins un composé plaquettaire caractérisé en ce que : ladite dispersion aqueuse primaire possède une concentration en composé inorganique suffisante pour permettre lors de son cisaillement, l'application d'une contrainte mécanique suffisante pour délaminer les plaquettes dudit composé inorganique, le cisaillement appliqué à ladite dispersion est un cisaillement contrôlé c'est-à-dire de telle sorte que l'ensemble de la dispersion est soumise à un même cisaillement minimal et en ce que ledit cisaillement est effectué avec une intensité suffisante pour conduire à une dispersion aqueuse concentrée d'au moins un composé inorganique plaquettaire dont le seuil critique de cisaillement est significativement augmenté comparativement à celui de la dispersion aqueuse primaire.1. Process for the preparation of a concentrated aqueous dispersion of at least one inorganic platelet compound and endowed with improved and controlled rheological properties using the shearing of a primary aqueous dispersion of at least one platelet compound characterized in that: said primary aqueous dispersion has a concentration of inorganic compound sufficient to allow during its shearing, the application of sufficient mechanical stress to delaminate the platelets of said inorganic compound, the shearing applied to said dispersion is controlled shearing, that is to say -to say so that the entire dispersion is subjected to the same minimum shearing and in that said shearing is carried out with sufficient intensity to lead to a concentrated aqueous dispersion of at least one inorganic platelet compound whose critical threshold shear is significantly increased compa ratively to that of the primary aqueous dispersion.
2. Procédé selon la revendication 1 , caractérisé en ce que la concentration est ajustée de manière à conserver une propriété d'écoulement à la dispersion aqueuse.2. Method according to claim 1, characterized in that the concentration is adjusted so as to maintain a flow property for the aqueous dispersion.
3. Procédé selon la revendication 1 ou 2 caractérisé en ce que la concentration est ajustée de manière à amplifier au maximum l'effet de la contrainte appliquée à ladite dispersion. 3. Method according to claim 1 or 2 characterized in that the concentration is adjusted so as to maximize the effect of the stress applied to said dispersion.
4. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que la dispersion aqueuse primaire possède une concentration d'au moins 50 % en masse.4. Method according to one of claims 1 to 3, characterized in that the primary aqueous dispersion has a concentration of at least 50% by mass.
5. Procédé selon l'une des revendications 1 à 4, caractérisé en ce que le cisaillement est effectué à l'aide d'un dispositif propice à la génération d'un cisaillement contrôlé.5. Method according to one of claims 1 to 4, characterized in that the shearing is carried out using a device conducive to the generation of a controlled shearing.
6. Procédé selon la revendication 5, caractérisé en ce que le dispositif est tel qu'en sortie de celui-ci l'ensemble de la dispersion a été soumise à un même cisaillement minimal. 176. Method according to claim 5, characterized in that the device is such that at the output thereof the entire dispersion was subjected to the same minimum shear. 17
7. Procédé selon l'une des revendications 1 à 6, caractérisé en ce que le cisaillement contrôlé est réalisé par mise en contact de ladite dispersion avec une surface solide en mouvement.7. Method according to one of claims 1 to 6, characterized in that the controlled shearing is achieved by bringing said dispersion into contact with a moving solid surface.
8. Procédé selon l'une des revendications 1 à 6, caractérisé en ce que la dispersion est animée d'un mouvement de circulation lorsqu'elle est soumise à un cisaillement contrôlé.8. Method according to one of claims 1 to 6, characterized in that the dispersion is animated by a movement of circulation when it is subjected to a controlled shear.
9. Procédé selon l'une des revendications précédentes, caractérisé en ce que le cisaillement est appliqué dans un dispositif couette.9. Method according to one of the preceding claims, characterized in that the shear is applied in a quilt device.
10. Procédé selon l'une des revendications 1 à 8, caractérisé en ce que le dispositif est une cellule de type plan/cône.10. Method according to one of claims 1 to 8, characterized in that the device is a plane / cone type cell.
1 1. Procédé selon l'une des revendications 1 à 8, caractérisé en ce que le dispositif est une cellule de type enceinte délimité par deux disques.1 1. Method according to one of claims 1 to 8, characterized in that the device is a cell of enclosure type delimited by two discs.
12. Procédé selon l'une des revendications 1 à 1 1 , caractérisé en ce que le cisaillement contrôlé est un cisaillement de type transverse confiné.12. Method according to one of claims 1 to 1 1, characterized in that the controlled shear is a shear of confined transverse type.
13. Procédé selon l'une des revendications 1 à 12, caractérisé en ce que le taux minimal de cisaillement est compris entre 1 000 et 10 000 s"1.13. Method according to one of claims 1 to 12, characterized in that the minimum shear rate is between 1,000 and 10,000 s "1 .
14. Procédé selon la revendication 13 caractérisé en ce qu'il est compris entre 5 000 et 8 000 s"1.14. The method of claim 13 characterized in that it is between 5,000 and 8,000 s "1 .
15. Procédé selon l'une des revendications précédentes caractérisé en ce que le composé inorganique particulaire est un talc.15. Method according to one of the preceding claims characterized in that the particulate inorganic compound is a talc.
16. Procédé selon la revendication 15 caractérisé en ce que la dispersion aqueuse primaire comprend un taux massique en talc d'environ 64 % et est soumise à un cisaillement de l'ordre de 4000 s'1.16. The method of claim 15 characterized in that the primary aqueous dispersion comprises a talc mass content of approximately 64% and is subjected to a shear of the order of 4000 s ' 1 .
17. Procédé selon la revendication 15 ou 16 caractérisé en ce que la valeur du seuil de cisaillement critique de la dispersion aqueuse obtenue à l'issue de l'étape de cisaillement contrôlé est environ doublée comparativement à celui de la dispersion aqueuse primaire. 18. Procédé selon l'une des revendications 15 à 17 caractérisé en ce que le talc obtenu à l'issue de l'étape de cisaillement peut être isolé sous forme d'une poudre par séchage et être facilement redispersé à un taux massique de 64% ou plus. 17. The method of claim 15 or 16 characterized in that the value of the critical shearing threshold of the aqueous dispersion obtained at the end of the controlled shearing step is approximately doubled compared to that of the primary aqueous dispersion. 18. Method according to one of claims 15 to 17 characterized in that the talc obtained at the end of the shearing step can be isolated in the form of a powder by drying and be easily redispersed at a mass rate of 64 % or more.
1818
19. Poudre d'un matériau inorganique plaquettaire obtenue par séchage d'une dispersion aqueuse préparée selon l'une des revendications 1 à 18. 19. Powder of an inorganic platelet material obtained by drying an aqueous dispersion prepared according to one of claims 1 to 18.
PCT/FR1999/000591 1998-04-10 1999-03-16 Method for preparing an aqueous dispersion of at least one platelet inorganic compound with improved rheological properties WO1999052816A1 (en)

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FR98/04583 1998-04-10
FR9804583A FR2777206B1 (en) 1998-04-10 1998-04-10 PROCESS FOR THE PREPARATION OF AN AQUEOUS DISPERSION OF AT LEAST ONE PLATELET INORGANIC COMPOUND WITH IMPROVED RHEOLOGICAL PROPERTIES

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0212930A2 (en) * 1985-08-12 1987-03-04 W.R. Grace & Co.-Conn. Vermiculite dispersions and method of preparing same
EP0366417A2 (en) * 1988-10-24 1990-05-02 W.R. Grace & Co.-Conn. Vermiculite dispersions and method of preparing same

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0212930A2 (en) * 1985-08-12 1987-03-04 W.R. Grace & Co.-Conn. Vermiculite dispersions and method of preparing same
EP0366417A2 (en) * 1988-10-24 1990-05-02 W.R. Grace & Co.-Conn. Vermiculite dispersions and method of preparing same

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