EP2526057A1

EP2526057A1 - Method for producing phyllosilicate discs having a high aspect ratio

Info

Publication number: EP2526057A1
Application number: EP11700424A
Authority: EP
Inventors: Josef Breu; Michael Möller; Hussein Kalo; Arno Nennemann
Original assignee: Bayer Intellectual Property GmbH
Current assignee: Bayer Intellectual Property GmbH
Priority date: 2010-01-20
Filing date: 2011-01-17
Publication date: 2012-11-28
Also published as: JP2013517215A; WO2011089089A1; US20130035432A1

Abstract

The invention relates to a method for producing phyllosilicate discs having a high aspect ratio, to a phyllosilicate disc that can be obtained by means of the method according to the invention, to the use of phyllosilicate discs according to the invention for producing a composite material, to a flame protection barrier, or a diffusion barrier, and a composite material comprising or obtainable using phyllosilicate discs according to the invention.

Description

Process for the preparation of high aspect ratio phyllosilicate platelets

The present invention relates to a process for producing high aspect ratio phyllosilicate platelets, a phyllosilicate platelet obtainable by the process according to the invention, the use of phyllosilicate platelets according to the invention for producing a composite material, a flame retardant barrier or a diffusion barrier and a composite material comprising or obtainable using layered silicate platelets according to the invention.

It is known in the art to add layered silicates to paints or composites. This can improve the mechanical properties of the resulting systems. In particular, it is possible in this way to increase the barrier effect of a paint or composite material layer.

It has been found that the degree of improvement of the properties is significantly dependent on the aspect ratio of the platelet silicate forming platelets. In principle, it is therefore desirable to produce sheet silicate platelets with a high aspect ratio, since these can be used to obtain coating or composite material layers which are distinguished by particularly good mechanical properties and a high barrier effect.

The aspect ratio is the quotient of the platelet length and the height of the platelet. Thus, both increasing the platelet length and decreasing the platelet height causes an increase in the aspect ratio. The theoretical lower limit of platelet height of layered silicates is a single silicate lamella, which is about one nanometer for 2: 1 layered silicates.

As a rule, phyllosilicates have stacks of silicate lamellae, so-called tactoids with heights of several nanometers up to a few millimeters. Depending on their composition and formation, the platelet diameters of phyllosilicates range from a few nanometers (hydrothermally produced smectites) to a few centimeters (mica). natural

Phyllosilicates therefore have aspect ratios of from 20 to about 400.

By chemical and / or physical treatment, the aspect ratio can be subsequently increased in certain areas by the platelets are split (exfoliated) along their stack axis. However, increasing the platelet lengths is only possible by varying the synthesis conditions. The increase in the aspect ratio associated with exfoliation is considered, for example, as an essential condition for the preparation of polymer-phyllosilicate nanocomposites with improved properties (HA Stretz, DR Paul, R. Li, H. Keskkula, PE Cassidy, Polymer 2005, 46, 2621 -2637 and LA Utracki, M. Sepehr, E. Boccaleri, Polymers for Advanced Technologies 2007, 18, 1-37). Explanation Exfoliation or delamination is referred to G. Lagaly, JEFC Gardolinsky, Clay Miner. 2005, 547-556. Intercalatable and exfoliable phyllosilicates are, for example, montmorillonites or hedetites from the class of smectites.

Disadvantage in the processing of previously known phyllosilicates are their partly conflicting properties. For example, it is known that hydrothermally produced smectites (e.g., Optigel SH) exhibit extremely good swelling behavior, thereby achieving spontaneous exfoliation into individual silicate lamellae (delamination). However, such smectites have small platelet diameters of about 50 nanometers, whereby the aspect ratios do not exceed a value of 50. Although natural layer silicates of the montmorillonite or vermiculite type have platelet diameters of several hundred nanometers down to a few micrometers, spontaneous delamination does not occur. However, elaborate exfoliation steps can increase the aspect ratio.

Mica-type layered silicates have platelet lengths of several centimeters, but exfoliation is not possible due to the strong interlamellar forces, which can not effectively reduce the enormous platelet height.

The synthetic preparation of layered silicates is described, for example, in J.T. Kloprogge, S. Komarneni, J.E. Amonette, Clays Clay Miner. 1999, 47 529-554. Synthetic phyllosilicates have hitherto been used analogously to the naturally occurring phyllosilicates, i. they are chemically modified in order then to arrive at intercalated or as far as possible exfoliated sheet silicate platelets (L.T. J. Korley, S.M. Liff, N. Kumar, G.H. McKinley, P.T. Hammond, Macromolecules 2006, 39 7030-7036).

US Pat. No. 4,045,241 discloses the synthesis of a swellable tainiolite-type phyllosilicate. This material is produced by a multi-hour, energy-consuming process. As a general disadvantage, a massive loss of volatile binary riden. This mass loss must be compensated for by a drastically increased addition of fluorides during weighing

In the not yet published P C T application with the application number PCT EP2009 / 006560 a process for the preparation of non-swellable layer silicate tactoids medium layer charge is described. In this case, in a first step, synthetic smectites are obtained with a layer charge in the range of 0.2 to 0.8.

The object of the present invention was to provide a process for producing high aspect ratio phyllosilicate platelets.

This object is achieved by a method in which

A) a s nthetic smectite of the formula

in the

M metal cations of oxidation state 1 to 3, M ¹ metal cations of oxidation state 2 or 3, M ¹¹ metal cations of oxidation state 1 or 2

M ¹¹¹ atoms of the oxidation state 4 X Di-anions and Y are mono-anions, m for metal atoms M ^{1 of} the oxidation state 3 <2.0 and for metal atoms M ^{1 of} the oxidation state 2 <3.0, o <1.0 and the layer charge n> 0.8 and <1.0, produced via a high-temperature pain synthesis and

B) the synthetic smectite of step A) is exfoliated and / or delaminated into high aspect ratio phyllosilicate platelets.

With the aid of the process according to the invention, phyllosilicate platelets with an average aspect ratio greater than 400 can be obtained.

Another advantage of the layered silicate platelets obtainable by the process according to the invention is that, in contrast to natural montmorillonites and vermiculites, which are more or less yellowish-brown in color, they are colorless. This makes it possible to produce colorless composite materials from them. Preferably, M has the oxidation state 1 or 2. Particularly preferred is M Li ⁺ , Na ⁺ , Mg ²⁺ , or a mixture of two or more of these ions. Most preferably, M is Li ⁺ .

M ¹ is preferably Mg ²⁺ , Al ³⁺ , Fe ²⁺ , Fe ³⁺ or a mixture of two or more of these ions.

M ¹¹ is preferably Li ⁺ , Mg ²⁺ or a mixture of these cations.

M ¹¹¹ is preferably a tetravalent silicon cation. X is preferably O ^{2 "} .

Y is preferably OH ^" or F ^" , particularly preferably F ^" .

The layer charge n is preferably> 0.85 and <0.95.

According to a particularly preferred embodiment of the invention, M = Li ⁺ , Na ⁺ , Mg ²⁺ , or a mixture of two or more of these ions, M ¹ = Mg ²⁺ , Al ³⁺ , Fe ²⁺ , Fe ³⁺ or a mixture two or more of these ions, M ¹¹ = Li ⁺ , Mg ²⁺ or a mixture of these ions, M ^{111 is} a tetravalent silicon cation, X = O ^{2 "} and Y = OH ^" or F ^" .

The synthetic smectites of the formula [M ¹ _m M ⁿ ₀ ] ^oct [M ⁿⁱ ₄ ] ^tet Xi ₀ Y ₂ can be prepared by reacting compounds of the desired metals (salts, oxides, glasses) in heated in a chiometric ratio in an open or closed crucible system for homogeneous melt and then cooled again.

In the synthesis in a closed crucible system can be used as starting compounds alkali metal salts / alkaline earth metal salts, alkaline earth oxides and silicon oxides, preferably binary Alkalifluori- de / alkaline earth fluorides, alkaline earth oxides and silicon oxides particularly preferably LiF, NaF, MgF ₂ , MgO, quartz.

The quantitative ratios of the starting compounds are then, for example, 0.4-0.6 mol of F ^" in the form of the alkali metal / alkaline earth fluorides per mole of silicon dioxide and 0.4-0.6 moles of alkaline earth oxide per mole of silica, preferably 0.45-0.55 mol F ^" in the form of the alkali / alkaline earth fluorides per mole of silicon dioxide and 0.45-0.55 moles of alkaline earth oxide per mole of silica, more preferably 0.5 moles F ^" in the form of alkali / alkaline earth fluorides per mole of silica and 0.5 mole of alkaline earth oxide per mole of silica.

The feeding of the crucible is preferably carried out so that first the more volatile substances, then the alkaline earth oxide and finally the silicon oxide are weighed. Typically, a refractory crucible of chemically inert or inert metal, preferably molybdenum or platinum, is used.

Preferably, the sealed, still open crucible is baked before being sealed in vacuo at temperatures between 200 ° C and 1100 ° C, preferably between 400 and 900 ° C to remove residual water and volatile impurities. Experimentally, it is preferred to proceed in such a way that the upper crucible edge glows red while the lower crucible region has lower temperatures.

Optionally, a pre-synthesis in the pressure-tight sealed crucible for 5-20 min at 1700 to 1900 ° C, more preferably carried out at 1750 to 1850 ° C to homogenize the reaction mixture. The annealing and pre-synthesis is typically carried out in a high frequency induction furnace. The crucible is thereby protected from oxidation by a protective atmosphere (eg argon), reduced pressure or a combination of both measures. The main synthesis is carried out with a temperature program adapted to the material. This synthesis step is preferably carried out in a rotary graphite furnace with horizontal orientation of the axis of rotation. In a first heating step, the temperature is increased at a heating rate of 1 to 50 ° C / min, preferably from 10 to 20 ° C / min, from room temperature to 1600 to 1900 ° C, preferably to 1700 to 1800 ° C. In a second step is at

1600 to 1900 ° C, preferably heated at 1700 to 1800 ° C. The heating phase of the second step preferably lasts 10 to 240 minutes, more preferably 30 to 120 minutes. In a third step, the temperature is lowered at a cooling rate of 10-100 ° C / min, preferably from 30 to 80 ° C min to a value of 1100 to 1500 ° C, preferably from 1200 to 1400 ° C. In a fourth step, the temperature is lowered at a cooling rate of 0.5 to 30 ° C / min, preferably from 1 to 20 ° C / min to a value of 1200 to 900 ° C, preferably from 1100 to 1000 ° C. , The reduction of the heating rate after the fourth step to room temperature, for example, at a rate of 0, l-100 ° C / min, preferably uncontrolled by switching off the furnace.

Typically, working under inert gas such as Ar or N ₂ . The layered silicate is obtained as a crystalline, hygroscopic solid after breaking the crucible.

In the synthesis in the open crucible system, preference is given to using a glass stage of the general composition wSiO ₂ -xM ^a yM ^b -zM ^c , where 5 <w <7; 0 <x <4; 0 <y <2; 0 <z <1.5 and M ^a , M ^b , M ^{c are} metal oxides and M ^{a is} equal to M ^b other than M ^c . M ^a , M ^b , M ^c can independently of one another be metal oxides, preferably Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, MgO, particularly preferably Li ₂ O, Na ₂ O, MgO. M ^a does not equal M ^b other than M ^c .

The glass stage is prepared in the desired stoichiometry from the desired salts, preferably the carbonates, more preferably Li ₂ C0 ₃ , Na ₂ C _{3 3} and a silicon source such as silicon oxides, preferably silica. The powdered ingredients are converted to a glassy state by heating and rapid cooling. Preferably, the conversion is carried out at 900 to 1500 ° C, more preferably at 1000 to 1300 ° C. The heating phase in the production of the glass stage lasts 10 to 360 minutes, preferably 30 to 120 minutes, particularly preferably 40 to 90 minutes. This process is typically carried out in a glassy carbon crucible under a protected atmosphere and / or reduced pressure performed by high frequency induction heating. The temperature is reduced to room temperature by switching off the oven. The resulting glass step is then finely ground, which can be done for example by means of a powder mill.

The glass stage is added to further reactants in a weight ratio of 10: 1 to 1:10 in order to achieve the stoichiometry in A). Preferred are 5: 1 to 1: 5. If necessary, an excess of the volatile additives of up to 10% may be added. These are, for example, alkali or alkaline earth compounds and / or silicon compounds. Preference is given to using light alkali metal and / or alkaline earth fluorides and their carbonates or oxides, and also silicon oxides. Particular preference is given to using NaF, MgF ₂ , LiF and / or an annealed mixture of MgC0 ₃ Mg (OH) ₂ and silica.

Subsequently, the mixture is heated above the melting temperature of the eutectic of the compounds used, preferably at 900 to 1500 ° C., more preferably at 1100 to 1400 ° C. The heating phase preferably lasts 1 to 240 minutes, more preferably 5 to 30 minutes. The heating is carried out at a heating rate of 50-500 ° C / min, preferably at the maximum possible heating rate of the furnace. The cooling after the heating phase to room temperature takes place at a rate of 1-500 ° C / min, preferably uncontrolled by switching off the furnace. The product is obtained as a crystalline, hygroscopic solid.

The synthesis is typically carried out in a glassy carbon crucible under an inert atmosphere. The heating is typically done by high frequency induction. Due to the energy-efficient heating via high-frequency induction, the use of low-cost starting compounds (no high degree of purity required, no predrying of the starting materials required, wider Eduktpalette such as cheap carbonates) and a much shorter synthesis time compared to the synthesis in the closed crucible system and a possible multiple use of the crucible is presented Process much more economical. Therefore, high temperature melt synthesis in an open crucible system is particularly preferred.

The synthetic layered silicate can preferably be freed from soluble synthesis products after the synthesis. This can be diluted by washing with polar solvents, preferably with aqueous or water-soluble solvents, more preferably with water Acids or alkalis, methanol or mixtures thereof. The washing process is preferably carried out by means of dialysis, centrifugation or filtration.

Preferably, in step B) the synthetic smectite may be incorporated into a polar solvent to exfoliate and / or delaminate it.

It is particularly preferred if, in step B), the polar solvent used is water, water-miscible solvents, dilute aqueous acids or bases and / or mixtures thereof.

The synthetic smectite shows swelling after introduction into polar solvents. The swelling takes place without further chemical treatment of the smectite. Swelling causes exfoliation or delamination.

In this way, it is also easy to prepare dispersions of the layered silicate platelets in polar solvents. Such dispersions are also an object of the invention.

Although chemical or physical treatment for exfoliation is not necessary, such treatment may aid, accelerate or further promote exfoliation. The physical dispersion with high shear forces, more preferably by means of rotor-stator disperser, multi-roll mill, ball mill, ultrasound or high-pressure jet dispersion, is preferred.

Another object of the invention is a layer silicate platelets obtainable by the process according to the invention.

Likewise provided by the invention is the use of layered silicate platelets according to the invention for producing a composite material, a flame retardant barrier or a diffusion barrier.

For example, a dispersion of the layered silicate platelets in a polar solvent, such as water, can be used to apply a flame retardant or diffusion barrier to a substrate. For this purpose, the dispersion can be applied to the substrate and then the solvent can be removed, for example by drying.

A composite material comprising or obtainable using sheet silicate platelets according to the invention is a further subject of the invention.

Particularly preferred here is when the composite material contains a polymer. The phyllosilicate platelets can be incorporated, in particular for the preparation of polymer composites, into all customary polymers which have been prepared by polycondensation, polyaddition, free-radical polymerization, ionic polymerization and copolymerization. Examples of such polymers are polyurethanes, polycarbonate, polyamide, PMMA, polyesters, polyolefins, rubber, polysiloxanes, EVOH, polylactides, polystyrene, PEO, PPO, PAN, polyepoxides.

The introduction into polymers can be carried out by means of customary techniques such as, for example, extrusion, kneading method, rotor-stator method (Dispermat, Ultra-Turrax, etc.), milling method (ball mill etc.) or jet dispersion and depends on the viscosity of the polymers.

Examples

The invention will be explained in more detail below with reference to examples.

methods:

Oxygen barrier: The determination of the oxygen barrier was carried out according to DIN 53380, part 3, with a measuring instrument of the company Modern Controls, Inc. at a temperature of 23 ° C with pure oxygen (99.95%). The rel. Moisture of measuring and carrier gas was 50%.

X-ray diffraction: The d (001) values were determined by measurements of the layer silicate samples on a Panalytical XPERT-Pro powder diffractometer (Cu anode, nickel filter, Cu-Ka:

1.54187 Ä) in Bragg-Brentano geometry.

Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES): Quantitative elemental analysis via ICP-AES was performed on a JY 24 spectrometer (Jobin Yvon).

Atomic Absorption Spectroscopy (AAS): Quantitative elemental analysis of the chemically digested silica samples (using a standard procedure) via AAS was performed on a Varian AA100.

Atomic Force Microscopy (AFM): Imaging of particles under AFM was performed on an MFP3D ™ AFM (Asylum Research) with silicon cantilever (k _^ : 46 Nm ¹ ).

Scanning Electron Microscopy (SEM): Scanning electron micrographs were performed on a LEO 1530 FESEM with field emission cathode.

Laser diffraction: The particle size distribution of the aqueous dispersions was measured by laser diffraction on a particle analyzer Horiba LA 950 (Retsch GmbH). Conductivity: The electrical conductivity of the aqueous washings was measured at RT using a mobile conductometer HI 99300 (Hanna Instruments).

Materials:

Self-adhesive polypropylene film, No. 7005, thickness about 63μιη. HERMA GmbH, Fabrikstrasse 16, 70794 Filderstadt, Germany

Cloisite Na +; Sodium montmorillonite, Southern Clay Products Inc., 1212 Church Street, Gonzales, Texas 78629, USA.

Optigel SH; Hectorite from hydrothermal synthesis, formerly: Süd Chemie AG, Ostenrieder Str. 15, 85368 Moosburg; now: Rockwood Clay Additives GmbH, Stadtwaldstr. 44, 85368 Moosburg, Germany. 2CO ₃ ; >99%; Merck Eurolab GmbH, John-Deere-Str. 5, 76646 Bruchsal.

Silica (SiQ ₇ ^χ ηΗ, Ο:> 99.5%: Sigma-Aldrich Chemie GmbH, Eschenstr. 5, 82024 Taufkirchen.

MgCChMgfOHk extra pure; Fischer Scientific GmbH, Im Heiligen Feld 17; 58239 sword.

LiF; > 99%; Merck Eurolab GmbH, John-Deere-Str. 5, 76646 Bruchsal.

MgF ₉ ; >99.5%; Alfa Aesar GmbH & Co. KG, Zeppelinstrasse 7, 76185 Karlsruhe. Example 1: Preparation of A (Li _0, 9-hectorite)

The synthesis of Li-hectorite with a planned composition [Li ₀ , 9] ^mter [Mg _2; iLi ₀ , 9] ^oct [Si4] ^tet OioF ₂ takes place via an amorphous alkali glass (called precursor a) of the composition Li ₂ O ₂ SiO ₂ . This glass is produced by the salts L1CO ₃ (13.83 g) and silica (Si0 ₂ ^x nH ₂ 0; 24.61 g) and finely mixed inductively heated lh at 1150 ° C under argon in a glassy carbon crucible.

In parallel, a second precursor (called: precursor ß) is prepared by finely mixing MgC0 ₃ Mg (OH) ₂ (7.52 g) and silica (Si0 ₂ x nH ₂ 0, 10.47 g) and lh at 900 ° C heated in an aluminum oxide crucible in the chamber furnace.

After cooling, 28.09 g of the precursor α and the entire amount of the precursor ß are pulverized and finely mixed with 12.50 g of MgF ₂ . The mixture is heated in an open glassy carbon under argon within 5 min by inductive heating to 1300 ° C and left for 8 min at this temperature. After this step, turning off the oven lowers the temperature to RT.

The highly hygroscopic phyllosilicate is obtained as a colorless or grayish solid with low hardness, which already crumbles in air after a short service life. In water, a very slowly sedimenting dispersion forms, which contains a large proportion of a colloidal phase, which shows little sedimentation.

Identification: d (001) = 12.2 Ä (at 40% relative humidity). In measurements of aqueous pastes (3 parts by weight of water: 1 part by weight of solid), a reflex occurs at about. 70 A, which indicates high-grade osmotic swelling.

The composition (from ICP-AES and AAS measurements) is [Li ₀ , ₈ 5] ^mter [Mg _2; i ₅ Li ₀ , 85] ° ^ct [Si ₄ ] ^tet O ₁₀ F ₂ .

In scanning electron micrographs (SEM) of aqueous Li-hectorite dispersions, which were dried slowly in air, hardly any sheet silicate tactoids can be detected. For this purpose, there is a homogeneously appearing film that flexibly clings to the substrate surface.

Under the Atomic Force Microscope (AFM), the layer silicate platelets can be well imaged due to the higher z-resolution (resolution of the sample height). One recognizes this flexible Slats, with lateral dimensions up to 20μιη and a lamella height of 1 nm (aspect ratio: 20,000). Partly there are also stacks of several lamellae (less than 5).

By laser diffraction, a median particle size of 29.3 μιη was determined.

Example 2: Barrier Properties of a Li-Hectorite Film

The Li-hectorite from Example 1 is added after the synthesis in deionized water (about 20 g / 1) and the soluble impurities of the synthesis are removed by dialysis against demineralized water (dialysis membrane with pore diameter 25-30 Ä). The wash water of dialysis is renewed several times until the conductivity no longer rises above a value of 30 μ8. The washed hectorite is freeze-dried. From the dry Li-hectorite, a dispersion of the concentration of 3.4 g / 1 is set by adding demineralized water. 145 ml of this diluted dispersion are stored in a shallow glass vat (19.4 x 19.4 cm) in a quiet place at RT until the dispersion is completely dried. Although the resulting film having a solids content of 100% by weight can be easily peeled off in one piece, a self-adhesive polypropylene film (Herma) is adhesively bonded to the surface as a carrier material in order to prevent mechanical damage. Dissolve this 2-layer composite from the glass trough and test the oxygen barrier of this material. As a reference, the pure polypropylene film is measured.

The measurement of the oxygen transmission of the PP film gave a value of 2097.9 cm ² / m ² -d-bar (mathematical standardization to 100 μm film thickness: 1335.64 cm ² / m ² -d-bar).

The measurement of the oxygen transmission of the 2-layer composite Li-hectorite / PP film gave a value of 7.3-9.8 cm ² / m ² -d-bar at a film thickness of Li-hectorite of 6.5-15, 1 μιη. (mathematical standardization to 100 μm film thickness: 0.98 cm ² / m ² -d-bar)

Comparative Example 1: Barrier properties of a film of Na montmorillonite

500 mg of sodium montmorillonite (cloisite Na +) are added to 150 ml of demineralized water and stirred for 1 d. Thereafter, the montmorillonite dispersion is poured into a flat glass vat (19.4 x 19.4 cm) and stored in a quiet location at RT until the dispersion is completely dried. The resulting film with a solids content of 100% by weight is less easily removed from the glass surface than the Li hectorite in Example 2. If a self-adhesive PP film is used as the carrier material, suitable samples for the 0 ₂ barrier measurement are prepared.

Measurement of the oxygen transmission of the 2-layer composite Na-montmorillonite / PP film gave a value of 145.7-169.1 cm ² / m ² -d-bar at a film thickness of the montmorillonite film of 6.7-7, 8 μιη. (mathematical standardization to 100 μm film thickness: 48.5 cm ² / m ² -d-bar)

Comparative Example 2: Barrier properties of a film of hydrothermally synthesized hectorite (Optigel SH)

The hectorite type Optigel SH used is a commercial product produced by hydrothermal synthesis, limiting the platelet diameter to an average of 50 nanometers. Optigel SH spontaneously delaminates in water. 500 mg of Optigel dry hectorite are added to 150 ml of deionized water and stirred. Thereafter, the colloidal solution is poured into a flat glass vat (19.4 ^x 19.4 cm) and stored in a quiet place at RT until the dispersion is completely dried. The resulting transparent film can not be detached from the trough and thus not examined with regard to its barrier properties.

Although an alternative preparation method, where the same aqueous dispersion of Optigel SH was directly dried on the polypropylene substrate, resulted in a homogeneous film, the brittleness of this film and the resulting mechanical damage caused by cracking also prevented the measurement of 0 ₂ Barrier occur.

Discussion of the properties:

The layered silicate of the Li-hectorite type according to the invention in Example 1 has very large platelet diameters far above those of natural and hydrothermally produced smectites and approximately in the vermiculite range. The swelling properties are more pronounced compared to natural layered silicates such as vermiculites and montmorillonites. This manifests itself in the spontaneous exfoliation of the Li hectorite from Example 1 in suitable solvents, such as water. The result is inventive, flexible sheet silicate plates or lamellae which have extremely high aspect ratios »400. Materials with such high aspect ratios have not yet been produced economically and poorly in crystalline impurities. The outstanding natural Shafts of this material are particularly evident in gas barrier measurements. Here, the drastic reduction in O ₂ permeability of 2097.9 cm ² / m ² -d-bar to an average of 8.6 cm ² / m ² -d-bar was demonstrated by using a thin Li-hectorite film (average thickness 10 , 8 μιη) was placed on a PP substrate.

It should be noted that no chemical or physical pretreatment is needed to achieve these results.

Comparison with conventional layered silicates, e.g. Natural montmorillonite or commercial, hydrothermally synthesized hectorite clearly shows the superiority of the layered silicate according to the invention.

The described synthesis additionally introduces a scalable process by means of which the phyllosilicates according to the invention can be prepared in high purity from simple basic chemicals in a short time. This represents a significant increase in efficiency over lengthy hydrothermal methods.

Claims

Claims:

A process for producing high aspect ratio phyllosilicate platelets, in which

A) a s nthetic smectite of the formula

in the

M atoms of the oxidation state 4

X Di-anions and Y are mono-anions, m for metal atoms M ^{1 of} the oxidation state 3 <2.0 and for metal atoms M ^{1 of} the oxidation state 2 <3.0, o <1.0 and the layer charge n> 0.8 and <1.0, prepared via a high temperature melt synthesis and

2. The method according to claim 1, characterized in that M = Li, Na, Mg, or a mixture of two or more of these ions, M ¹ = Mg ²⁺ , Al ³⁺ , Fe ²⁺ , Fe ³⁺ or a mixture of two or more of these ions, M ¹¹ = Li ⁺ , Mg ²⁺ or a mixture of these ions, M ^{111 is} a tetravalent silicon cation, X = O ^{2 "} and Y = OH ^" or F ^" .

3. The method according to any one of claims 1 or 2, characterized in that M = Li ⁺ .

4. The method according to any one of claims 1 to 3, characterized in that the layer charge n> 0.85 and <0.95.

5. The method according to any one of claims 1 to 4, characterized in that the high-temperature melt synthesis is carried out in an open crucible system.

6. The method according to claim 5, characterized in that for the preparation of the synthetic smectite, a glass stage of the general composition wSi0 ₂ -xM ^a -yM ^b -zM ^{c is} used, wherein 5 <w <7; 0 <x <4; 0 <y <2; 0 <z <1.5 and M ^a , M ^b , M ^{c are} metal oxides and M ^{a is} equal to M ^b other than M ^c .

7. The method according to any one of claims 1 to 6, characterized in that in step B) the synthetic smectite is introduced into a polar solvent in order to exfoliate and / or to delaminate.

8. The method according to claim 7, characterized in that are used in step B) as the polar solvent water, water-miscible solvents, dilute aqueous acids or bases and / or mixtures thereof.

9. layered silicate platelets obtainable by a process according to one of claims 1 to 8.

10. Use of layered silicate platelets according to claim 9 for the production of a composite material, a flame retardant barrier or a diffusion barrier.

A composite material comprising or obtainable using sheet silicate platelets according to claim 9.

12. Composite material according to claim 1 1, characterized in that it contains a polymer.