NL1025641C1 - Hydrotalcite particles for stabilizing polymers have a defined particle size, soluble salt content and surface area - Google Patents

Abstract

Hydrotalcite particles for stabilizing polymers have a particle size of 0.02-0.6 mu m, a soluble salt content of less than 3 wt.% and a surface area of 40-100 m2>/g. The particles are not surface-modified with organic compounds. Independent claims are also included for: (1) producing hydrotalcite particles as above by precipitating hydrotalcite and removing soluble salts by suspending the solid material in water, stirring the suspension for at least 1 hour and separating the solid from the liquid, this procedure being carried out at least three times; (2) stabilizing polyvinyl chloride with hydrotalcite as above having a zinc/magnesium ratio of 1 or more; (3) stabilizing polymer-blended liquid and solid compounds by incorporating hydrotalcite platelets with a thickness of 0.5-1.0 mu m into the polymer; (4) producing a mixture of hydrotalcite particles with different particle sizes by subjecting part of the hydrotalcite particles to hydrothermal treatment, mixing a suspension of the treated particles with a suspension of untreated particles, and spray drying the mixture.

Description

Title: Inorganic additives for Polymers

The invention relates to the use of finely divided inorganic compounds with a layered structure in polymers. A layered structure is here understood to mean a structure in which the atoms are arranged in layers in a crystal lattice.

When the inorganic compound can react with acid-reacting compounds, such as hydrogen chloride, to neutral compounds, such substances can be used in polyvinyl chloride (PVC) or in polyolefins produced according to Ziegler-Natta. In the processing of PVC, the material is heated to a temperature of about 180 to about 200 ° C. At these temperatures, the polymer decomposes, releasing hydrogen chloride. Because of this. the PVC a very unattractive brown to black color. In the polymerization according to Ziegler-Natta, catalysts are used consisting of a chloride of titanium or vanadium, which is treated with an aluminum alkyl. With polyolefins produced according to the method of

Ziegler-Natta remains the catalyst in the polymer. Hydrolysis of the metal chlorides leads to the release of hydrogen chloride, which leads to corrosion of, for example, the processing equipment. Since discoloration of PVC and corrosion during processing or use are very undesirable, there is a great need for compounds that can be blended into the polymers that react with the hydrogen chloride to form harmless compounds.

Also polymers prepared with acid catalysts, such as polymers or synthetic resins prepared from epichlorohydrin, belong to the field of the invention, as well as polymers prepared using Friedel-Crafts catalysts. A final group of polymers is formed by polymers 1025641 prepared by suspension polymerization, such as styrene-based polymers, such as polystyrene, styrene-acrylonitrile polymers, and acrylonitrile-butadiene-styrene (ABS) polymers. In this case alkaline catalysts are sometimes used, such as calcium phosphate, magnesium hydroxide or calcium carbonate. These catalysts are removed from the polymer by treatment with sulfuric acid or hydrochloric acid. A small amount of acid generally remains in the polymer.

The invention therefore relates in particular to basic reacting solids with a layered structure that can react with chlorine hydrogen or other acidic substances released in polymers to form harmless compounds.

The invention furthermore relates to the mixing of solids with a plate-shaped crystal lattice in polymers in order to prevent the transport of other substances mixed in polymers. Certain (organic) compounds (stabilizers and plasticizers) are almost always incorporated into polymers to stabilize the polymers and to adjust the properties of polymers. In many cases, these compounds are incompatible with the polymer, whereupon the compounds migrate to the surface of the polymers and are secreted there. It is clear that such a migration is very undesirable. Migration of the pigment from the polymer also occurs when mixing pigments in polymers. The segregation of added substances during the shaping of polymers is known as "plate-out". In that case, the mixed compounds deposit on the surface of the processing equipment, which is very undesirable. With segregation during the. use of molded polymers materials is called "bleed-out", which is also undesirable. The presence in the polymer of plate-shaped solids that are not permeable to the blended compounds greatly hinders the migration of these compounds. It is important here that the inorganic layered material does not strongly change the appearance of the polymer. Due to the transparency of layered inorganic material, this task can be met.

Another application of layered inorganic materials in polymers involves the production of moldings from polymers with a wear-resistant surface. Because the surface of most plastics is not wear-resistant and therefore quickly becomes dull due to scratches and other surface imperfections, the appearance of molded parts of polymers often becomes very unattractive within a short time. Incorporation of mechanically strong plate-shaped solids into the surface of polymers results in a surface that will show scratches and other imperfections much less quickly.

A final application of inorganic materials with a layered structure is the production of so-called nanocomposites. Hereby the inorganic material is processed into particles in which a limited number of plates of the crystal lattice are stacked. Such stacks of single atomic layers or possibly even monomolecular layers are then arranged in parallel to each other in a polymer. Reducing the stacking of the atomic layers is known as exfoliation. When the surface of the inorganic material shows a sufficient interaction with the polymer, the application of a slightly stacked, layered inorganic material can lead to a molding showing the tensile strength of the inorganic material. In general, the mechanical strength of the inorganic material is much higher than that of the polymer, so that such an installation leads to mechanically strong moldings. This is technically very attractive. Therefore, much attention is currently being paid to such nanocomposites.

According to the state of the art, discoloration of PVC during shaping is prevented by adding lead compounds to the polymer. An insurmountable drawback of lead compounds, however, is that at 1025641 the final destruction of the polymer lead is emitted into the environment, which is very undesirable. It is also feared that contact with lead compounds that segregate from the polymer may occur during use. Due to the problems with lead compounds, considerable effort has been made to prevent the discolouration of PVC during the processing by mixing in uracil. However, the initial color of PVC with uracil is poor, so that perchlorate must be added as a bleaching agent, which is not attractive. According to the state of the art, therefore, it is desired to switch to mixing a mixture of calcium and zinc stearate 10 to prevent discoloration of PVC during processing. Although these compounds are inexpensive and can be blended into the polymer reasonably well, the relatively large amount of organic material from the stearates also quickly leads to an undesired initial color.

In addition to compounds for neutralizing the hydrogen chloride released, a series of other compounds are added to PVC as softeners and oxidation stabilizers. Known stabilizers against oxidation are, for example, α, β-diketones, hypophosphites or polyols. Di-octylphthalate is the best known plasticizer. The said organic compounds segregate fairly easily from the PVC, so that a solid which not only neutralizes the hydrogen chloride released, but also counteracts segregation, is very attractive. A layered material that can also neutralize hydrogen chloride would be the most obvious for this.

It has now long been proposed to incorporate basic solids into suitable polymers. For example, Japanese Patent Application No. 6 No. 3541/1958 for an alkaline reacting solid compound, such as an alkaline earth metal oxide or hydroxide, to blend into polymers. U.S. Pat. 4,379,882 mentions mixed hydroxides of magnesium and aluminum to stabilize polyolefins. • i? F 6 4 '1 5 patent application no. 3947/1947, it is proposed to introduce aluminum oxide or aluminum hydroxide into polymers as the basic compound. In Japanese Patent No. 80447/1980 it is proposed to add hydrotalcites to PVC as stabilizers, while U.S. Patent No. 5,444,816 combines a hydrotalcite with a β-diketone and metal enolate salts or organotin solvate salts for the stabilization of polymers containing halogens.

US Pat. No. 4,547,620 describes the use of a large range of hydrotalcites with different metal ions for removing Friedel-Crafts and Ziegler-Natta catalysts from organic compounds produced with such catalysts. By hydrotalcites is meant a class of compounds with a layered structure in which divalent and trivalent metal ions are incorporated side by side in a layer with hydroxyl ions on either side. Because the larger electrostatic charge of the trivalent ions does not pass through the.

• hydroxyl ions are compensated, anions are included together with water molecules in the layers between the plates with hydroxyl and metal ions. A large number of different divalent and trivalent ions can react to hydrotalcites or be incorporated into hydrotalcites. The general formula for hydrotalcites is M (H) 1-x M (IID * (0H) 2 + xCO 3 .NH 2 O

The preparation of hydrotalcites belongs to the current state of the art. U.S. Pat. No. 3,539,306 and British Pat. No. GB-A 1 348 702 discuss the preparation of hydrotalcites. The latter publication describes the preparation of a whole series of hydrotalcites with different metal ions. The German patent DE-C 2 061 114 mentions the preparation of hydrotalcites with two different metal ions.

Japanese Patent No. 37487/1977 proposes to improve the (surface) properties of polymers by dispersing hydrotalcites or metal hydroxides in the polymer. Further details about the compounds to be dispersed are not formulated. Japanese Patent Application Laid-Open No. No. 49258/1977 is referred to as stabilization of polyolefins prepared via a Ziegler-Natta polymerization by dispersion of at least 0.01% by weight, and preferably 0.1 to 1.0% by weight of an inorganic solid having the general element composition

MxAly (0H) 2x + 3y 2 * Az.nH 2 O, wherein M is Mg, Ca or Zn, A is CO 3 or HPO 4, and x, y, z, and n are positive numbers. Also in this patent no specific requirements are formulated which the hydrotalcite to be dispersed must meet.

European patent EP-B 0 189 899 proposes to use hydrotalcites for neutralizing acid components in polymers with two different divalent metal ions. At least one of the metal ions is selected from Mg, Ca, Sr, and Ba and at least one from the group Zn, Cd, Pb, and Sn. At present, due to health risks and the risk of environmental pollution, the incorporation into polymers, particularly of Cd and Pb compounds, is highly undesirable. It is most obvious to use hydrotalcite containing only magnesium and aluminum ions in polymers, since these ions can be emitted into the environment without objection.

However, the price of hydrotalcite is currently considered a little too high for stabilization of PVC, so that the lead compounds are to be replaced by calcium zinc stearates. This has led to the fact that magnesium-aluminum hydrotalcite is used on a large scale for neutralizing hydrogen chloride in polyolefins, for which only little hydrotalcite is required, but that the calcium-zinc stearate is used for stabilizing PVC. It is important in this connection that there is a noticeable tendency in which the presence of zinc in the environment is considered to be less undesirable. Nevertheless, hydrotalcite 10 2 b o 4 1 7 has great advantages for the neutralization of hydrogen chloride released during the processing of PVC. However, the hydrotalcite to be used must then meet fairly stringent conditions.

First of all, one must of course be able to produce the required hydrotalcite cheaply. Production from very inexpensive raw materials without problems with waste water is now possible if hydrotalcite is prepared from aqueous solutions of the chlorides of the metals that must be present in the hydrotalcite. Furthermore, it must be possible to discharge the wastewater containing only sodium chloride 10 into the sea or into streams in contact with the sea. For example, aqueous solutions of magnesium chloride and aluminum chloride are commercially available very cheaply.

Hydrotalcite for stabilizing PVC must meet another condition. This is because the amount of hydrotalcite required for stabilization must be as small as possible. A small amount of hydrotalcite required for stabilization of PVC requires a homogeneous distribution of the hydrotalcite in the polymer. This can be achieved by starting from very small hydrotalcite particles; one approaches the molecular distribution the most. When a fixed percentage by weight of hydrotalcite is mixed in, the mutual distance of the hydrotalcite particles with a homogeneous distribution of smaller particles is smaller. This means that only a slight concentration difference of hydrogen chloride in the polymer is sufficient to realize a sufficiently fast transport from the polymer to a hydrotalcite particle. In this way it is avoided that locally higher concentrations of hydrogen chloride occur in the polymer, which give rise to discoloration. It will be clear that more hydrotalcite is needed if the same small distances between the particles with larger particles are to be achieved.

Although hydrotalcites with elemental particles of, for example, 0.05 µm can be prepared according to the current state of the art, 1025641 of the same small particles cannot be technically used for mixing in PVC. In the first place, working with such small particles leads to a major dust problem; dusting of the extremely finely divided material is very difficult to prevent. In the second place, hydrotalcite particles cannot simply be mixed into polymers. Since the surface of hydrotalcites is hydrophilic, the material in the pores absorbs water. Small particle stacks enclose narrow pores where capillary water condensation occurs very quickly. A high water content of the hydrotalcite leads to insurmountable problems in the processing of PVC. Evaporation of the water at the processing temperature causes blisters to form in the mold, which is unacceptable.

In order to prevent condensation of water in the pores of the hydrotalcites and to make the inorganic material compatible with polymers, the surface of the hydrotalcite particles according to the prior art is covered with anions of carboxylic acids with a long CEfe chain. Stearates or palmitates are generally used for this. European patent EP 0 308 646 mentions a mixture of the anions of palmitic acid and stearic acid. Another possibility is to make the surface of the hydrotalcite hydrophobic by reaction with a silane with a long CH 2 chain. An example is the triethoxy-n-octylsilane. Research has shown that this silane oligomerizes in the aqueous solution and that the oligomer adsorbs on the surface of the hydrotalcite. Naturally, the application of compounds to the surface of the hydrotalcite leads to higher production costs due to the consumption of otherwise relatively inexpensive chemicals and the equipment required for this.

A drawback of the use of extremely small hydrotalcite particles is therefore that much of the compound is needed to make the much larger surface area of small particles hydrophobic. This leads to an increase in the cost price of the modified hydrotalcite. Moreover, a large amount of anions of palmitic or stearic acid leads to yellowing on processing. However, a much greater drawback is that extremely small hydrotalcite particles cannot be dispersed well. The preparation of hydrotalcite according to the state of the art generally consists of viral chlorides of the metals to be incorporated in the hydrotalcite, while raising the pH of the solution of the chlorides to a mixture of sodium hydroxide and sodium carbonate. When the pH is raised, the hydrotalcite precipitates. As mentioned, sodium chloride is formed during precipitation. It has now been found that it is virtually impossible to remove the sodium chloride from the hydrotalcite by washing on the filter according to the prior art the usual procedure. Even when washing out so long that the electrical conductivity of the washing water no longer differs from that of the fresh washing water, it appears that there is still a lot of salt in the hydrotalcite 15. stayed behind. This is particularly clear when the hydrotalcite is dried and the weight of the reaction product is determined. This appears to be much higher than one might expect on the basis of the hydrotalcite formed. The remaining sodium chloride has a very unfavorable effect on the dispersion properties of the hydrotalcite. The sodium chloride binds the hydrotalcite platelets together to form large conglomeres of even a few mms or more, which are very difficult to reduce by mechanical processing.

As a result, extremely small hydrotalcite particles cannot simply be dispersed in polymers in the desired manner. In Japanese Patent No. 80447/1980 is therefore proposed to work with larger hydrotalcite particles. By hydrothermal treatment, larger elemental hydrotalcite particles are obtained. A measure of the size of the elementary particles in powdered materials, such as the hydrotalcites mentioned, is the accessible surface. With smaller particles, the accessible surface area is larger. If one starts from spherical or cubic elementary particles and neglects the contact surface between the particles, the accessible surface, S, is given by S = (ό / ρφ.ΙΟ -4 m2 per gram)

Where d is the diameter of the spherically-assumed particle or the length of the cube of the cubically-assumed particle in cm and p is the (X-ray) density of the material in grams / cm 3.

In the aforementioned Japanese patent, the accessible surface area is now taken according to the procedure of Brunauer, Emmett and Teller (BET) calculated from the extent of the nitrogen adsorption at 77 K as a measure of the average particle size. A minimum particle size according to the said Japanese patent specification corresponds to a BET surface area of no more than 30 m2 per gram. In the hydrotaite described in Japanese Patent No. 80447/1980, the elemental hydrotaite particles occur in conglomerates. Assuming, for the density of hydrotaite, 2.06 grams per cm 3, an area of 30 m2 per gram corresponds to an average size of the elementary particles of 1 µm. Now the said Japanese patent states that the conglomerates of elementary particles in the hydrotaicite powder may not be greater than 5 µm, while the dimension of the elementary particles in the <003> direction may not be less than 60 nm. It according to Japanese Patent No. 80447/1980 hydrothermal treated material is much easier to purify from soluble salts. The soluble salt is bound much less strongly between the larger hydrotalcite particles than between the extremely small particles which, after precipitation, result at temperatures below about 100 ° C. The dispersibility in polymers is therefore much better than that of the non-hydrothermal treated material. In addition, a limited amount of anions of palmitic or stearic acid is sufficient to make the hydrotaicite hydrophobic.

1025641 "11

The aforementioned European patent EP-B 0 189 899 mentions aluminum as the metal ion that is preferably incorporated into the hydrotalcite. This patent also mentions requirements for the dimensions of the elementary particles, as they can be deduced from the BET surface, and for those of the conglomerates of elementary particles. The BET surface area may also not be more than 30 m 2 per gram and the dimensions of the conglomerates of elemental hydrotalcite particles are no more than 5 µm, preferably no more than 2 µm and even more preferably no more than 1 µm. The patent specification mentions a large number of additives which lead to a higher stability against discoloration and which, combined with the said hydrotalcite, increase the stability at higher temperatures. Among other things, β-diketones are mentioned as a stabilizing agent.

The European patent EP-B 0 256 872 discusses PVC to which a hydrotalcite, magnesium oxide and a B-diketone or a zinc salt of an organic acid have been mixed in for stabilization. Of the hydrotalcite, the BET surface area is less than about 50 m2 per gram and in particular less than 20 m2 per gram. The dimensions of the conglomerates of elemental hydrotalcite particles are less than 5 µm and preferably less than 1 µm. Magnesium oxide is added to bind the water and carbon dioxide released upon reaction of acidic compounds, such as hydrogen chloride, with the hydrotalcite. The formation of gas bubbles in the polymer is prevented by removing water and carbon dioxide.

EP-B 0 301 509 mentions the dispersion of hydrotalcites in polymer films to prevent the films from sticking. In this case, the hydrotalcite must be present as porous conglomerates of elementary particles that approximate the spherical shape as closely as possible. The size of these conglomerates is 1 to 8 µm; preferably 2 to 6 µm and more preferably 3 to 6 µm.

f 0? 5 £ A - 1 12

U.S. Pat. No. 5,106,898 proposes to stabilize halogen-containing polymers by dispersing a melt in the polymer of a lubricant, such as hydrogenated castor oil, in which a hydrotalcite is suspended.

The above discussion of the prior art already indicates that it has hitherto not been possible to homogeneously disperse small hydrotalcite particles in polymers such that the desired stabilization with a relatively low content of hydrotalcite is obtained. As a result, hydrotalcites are now only used with polyolefins where a relatively small content is already sufficient, even if the hydrotalcite is not homogeneously distributed in the polymer as small particles. At present, polyvinyl chloride is mainly stabilized with lead compounds, while in the future it is desired to switch to calcium-zinc stearates.

The object of the invention is therefore to provide hydrotalcite particles with dimensions of less than about 0.6 µm and preferably less than 0.2 µm that can be homogeneously dispersed in polymers which have a high reactivity with acid-reacting compounds.

According to the invention this is achieved by using hydrotalcite particles of 0.02 to about 0.6 µm with a soluble salt content of less than 3% by weight and preferably less than 1% by weight, which contain no organic compounds to modify the surface, have an accessible surface of about 40 to 100 m2 per gram, the elementary particles of which have dimensions of 0.02 to about 0.6 µm, preferably to 0.4 µm and even more preferably to 0 , 2 pm.

According to the invention, such hydrotalcite particles are obtained by precipitating hydrotalcite according to the prior art, after which the soluble salt is almost completely removed by dispersing the precipitate at least three times in water, agitating the suspension for at least about 1 hour and the solid substance then separate it from the wash water. It is very surprising that several times 1025641 suspending in water removes the soluble salt so much more efficiently than washing out on the filter, which is usual according to the prior art. The need for a method that makes it possible to purify small hydrotalcite particles from soluble salts was apparent from the above discussion of the current state of the art. According to this state of the art, hydrothermal treatment is required to wash out the soluble salts. A hydrothermal treatment requires special equipment and thereby makes the hydrotalcite more expensive, while the material is less finely dispersable in polymers due to the necessarily larger dimensions of the elementary particles. It is extremely surprising that the above simple procedure according to the invention leads to an almost complete removal of soluble salts. A hydrotalcite is hereby obtained, wherein the elementary particles exhibit very little interaction with each other.

According to the invention, the hydrotalcites are preferably prepared by starting from a solution of the chlorides of the metals to be incorporated in the hydrotalcite and using a solution of caustic soda and soda for raising the pH of the solution of the metal chlorides. The resulting sodium chloride can be discharged into the sea or into water in contact with the sea without any environmental problems.

As the above prior art discussion taught, the prior art should cover the surface of the hydrotalcite particles with anions of fatty acids with a sufficiently long CH 2 chain, or with other suitable compounds such as silanes.

First of all, this is necessary to prevent capillary condensation of water vapor in narrow pores between small hydrotalcite particles and, secondly, the polymer in this way moistens covered hydrotalcite particles such that a good dispersion is possible.

Surprisingly, it has now been found that spray drying of a suspension of hydrotalcite particles purified according to the invention leads to a powdered hydrotalcite which can be processed well without much dust formation and which can be excellently dispersed in polymers without further chemical processing. Without limiting the scope of the invention, we believe that this surprising effect of spray drying results from the fact that conglomerates of elemental hydrotalcite particles with relatively wide pores are formed during spray drying, while the cohesion of the elementary particles is indeed sufficient to make the powder properly processable. but so weak that a low mechanical force as used in dispersing into polymers is sufficient to lead to a very homogeneous dispersion of extremely small particles. Spray drying of hydrotalcite suspensions has now been described previously. US patent application US 2003078445 laid open for inspection is referred to as spray drying as a technique for separating and drying the hydrotalcite from the liquid. However, this relates to an entirely different hydrotalcite, which is prepared for a different purpose, namely the preparation of catalysts and in a different way. The hydrotalcite described in US 2003078445 has in the intermediate layer a carboxylate anion with at least one heteroatom, such as N, P, S. or a halogen.

For neutralizing the hydrogen chloride released in the polymer, tiny hydrtalcite particles are the most attractive. On the other hand, it is clear that such hydrtalcite particles with dimensions of less than 0.4 µm are not ideally suited to reduce migration of liquid stabilizers, plasticizers and pigments in the polymer. According to the invention, therefore, in polymers in which large amounts of hydrogen chloride do not have to be neutralized, such as polyolefins, hydrotalcite particles with a different morphology are used. In this case, hydrtalcite particles with lateral dimensions of the elemental plates are from 0.5 to 1.5 µm in which about 20 to 30 elemental plates are stacked. It has been found that such plate-shaped hydrotalcite particles can very effectively prevent the migration of liquid compounds into polymers.

According to the invention, such hydrotalcite particles are prepared by homogeneously raising the pH of a solution of preferably the chlorides of the divalent and trivalent metals to be incorporated into the hydrotalcite to a value which depends on the temperature of the solution of 7 (room temperature) ) to about 5 (90 ° C or higher temperatures), while at the same time carbonate ions are made homogeneous in the solution. According to a special variant of the process according to the invention which is very easy to carry out, hydroxyl ions and carbonate ions are homogeneously generated in the solution by the hydrolysis of urea at a temperature above 60 ° C. By carrying out this process under elevated pressure, the time required for the preparation can be greatly reduced. If, on the other hand, the precipitation is to be carried out at a lower temperature, cyanate is added to the solution in accordance with another variant of the method according to the invention, preferably ammonium or sodium cyanate.

A relatively large amount of hydrogen chloride is released during the design of PVC.

When the extremely small hydrotalcite particles or hydrotalcite particles are formed in the form of thin plates with larger lateral dimensions in PVC

The hydrotalcite particles are expected to react to a large extent with the hydrogen chloride released, unless a lot of hydrotalcite is mixed, making the use of hydrotalcite costly. It is therefore not to be expected that not too large amounts of hydrotalcite mixed in PVC will effectively prevent the migration of liquid stabilizers, plasticizers and pigments in the polymer.

Experiments have shown that small hydrotalcite particles are totally consumed in the reaction with hydrogen chloride released during the shaping of PVC. On the one hand this has been demonstrated by dissolving the PVC after processing and studying the remaining solid particles in the scanning 1025641 16 electron microscope. It turned out that the structure of the extremely small hydrotalcite particles is indeed lost and that mainly magnesium chloride and aluminum chloride remain.

Another indication that the hydrotalcite particles react almost completely has been obtained by intercalating a dye, quinizarin, between the plates of the hydrotalcite. As a negative ion, the quinizarin is intensively colored purple, while the molecule takes on a red color in an acid environment. When hydrotalcite is mixed with intercalated quinizarin anions in PVC powder and the PVC is processed on a two-roll, for example, to a strip, PVC with a bright red color results. Although it is possible in principle that the hydrogen chloride released only reacts with the intercalated anions of the colorant, this is unlikely. It is much more obvious that the hydrotalcite is completely consumed, whereby the quinizarin anion is exhibited on the protons of the hydrogen chloride and thereby takes on a red color.

According to the invention, the migration of liquid additives mixed into polymers that release a lot of hydrogen chloride during processing can be prevented by mixing thicker hydrotalcite plates together with extremely small hydrotalcite particles in the polymer. Said thicker hydrotalcite plates can be prepared by hydrothermal treatment of hydrotalcites. According to the invention, an intimate mixture of hydrotalcite particles of different sizes is prepared by hydrothermally treating part of the hydrotalcite particles, mixing the suspension of the treated hydrotalcite particles with a suspension of untreated hydrotalcite particles and spray-drying the liquid by spraying the liquid. separate and dry.

According to a preferred form of the method according to the invention, a mixture of extremely small hydrotalcite particles and cationic clay plates is mixed into the polymer. According to the invention, the

1025D4J

17 cationic clay plates the structure of the mineral stevensite. According to the patent application WO * A 9607613, the stevensite is prepared by suspending small silica particles (dimensions less than about 0.2 µm) in a solution of a bivalent metal salt, such as zinc or magnesium and urea. Heating this suspension to a temperature above about 60 ° C leads to precipitation of the starfishite. Starting from a magnesium salt leads to plates with very small lateral dimensions (less than 0.1 µm), while a zinc salt results in plates with dimensions up to 1.0 µm. A mixture of magnesium and zinc salts leads to plates with intermediate dimensions. It is of great importance that the stacking of the elementary cationic clay platelets in the synthesis described in WO-A 9607613 is small.

The patent application WO 9935184 describes the use of cationic clay minerals prepared according to WO-A 9607613 in polymers to reduce the permeability of molecules, such as water, and to increase the mechanical strength of the polymer composition. According to the present invention, the starch staple is also incorporated into polymers to suppress the migration of stabilizers, plasticizers and pigments. EP-A 0 747 322 and WO-A 97/31057 describe such cationic clay minerals wherein the stacking of the elemental sites is reduced by placing quaternary ammonium ions with long hydrocarbon groups or inorganic colloidal particles between the plates. It has now been found that quaternary ammonium ions with long hydrocarbon chains give rise to discolouration when forming at elevated temperature, whereby unattractive colors are formed. According to the present invention, therefore, the stacking of the elementary plates is reduced and the mutual distance between these plates is increased by intercalating a multiple alcohol, preferably glycerol or glycol, between the plates.

1025641 18

According to a preferred form of the method according to the invention! | the hydrotalcite and stevensite are combined. The starting material is a suspension of silica particles in a solution of urea and the desired divalent metals and of the trivalent metal or trivalent metals to be incorporated into the hydrotalcite. Surprisingly, this leads to a suspension of hydrotalcite and starfish platelets that are intimately mixed. The solid material of the suspension is then separated from the liquid and suspended at least three times in water and separated from the liquid, finally the solid material is separated from the liquid by spray drying and dried.

The following examples are partially illustrated with reference to a number of figures, in which

Figure 1 shows a shot in the transmission electron microscope (Philips EM 15 420 120 kV) of a filtered magnesium aluminum hydrotalcite prepared and thoroughly washed on the filter, prepared by precipitation at room temperature,

Figure 2 shows a shot in the transmission electron microscope (Philips EM 420 120 kV) of a hydrotalcite prepared three times after separation of the liquid according to the invention and filtered off by precipitation at room temperature,

Figure 3 shows a shot in the scanning electron microscope (FEI XL 30 SFEG) of a filtered magnesium aluminum hydrotalcite prepared and thoroughly washed on the filter, prepared by precipitation at room temperature,

Above: Image with secondary electrons

Below: Same image with analyzed places

Figure 4 shows places analyzed and results of the analyzes,

Figure 5 shows a recording in the scanning electron microscope (FEI XL 30 30 SFEG) of a hydrotalcite prepared and washed out according to the present invention 4025641,

Figure 6 shows analyzed sites and result of the hydrotalcite analyzes according to the present invention,

Figure 7 shows the contribution of the reaction of hydrogen chloride with carbonate ions present in the intermediate layer of the hydrotalcite, reaction A and with the hydroxyl groups of the plates of the hydrotalcite, reaction B, and Figure 8 shows a recording in the scanning electron microscope at a very high high magnification of spray-dried hydrotalcite. With mechanical loading, the spherical particles of Fig. 7 quickly disintegrate into the elemental conglomerates of hydrotalcite particles that are visible in this shot.

Figure 9 In this figure the change of the a * value is plotted vertically.

1 - blank without added sorbitol 2 - after mixing in 1.5 phr sorbitol 3 - after mixing in 1.0 phr hydrotalcite 4 - after mixing in 1.5 phr sorbitol and 1.0 phr hydrotalcite

Figure 10 Hydrothermal treated hydrotalcite at a magnification of 26,500 x in the transmission electron microscope Tecnai 12, 120 kV Figure 11 Hydrothermal treated hydrotalcite at a magnification of 59,000 x in the transmission electron microscope. Tecnai 12 120 kV Figure 12 Inclusion in the scanning electron microscope of hydrothermal treated hydrotalcite. (FEI XL 30 SFEG) 25 n 9 c; T; ¢.

'j v' <· '../ v. · »e I

20

Example 1

Preparation of magnesium and aluminum-containing hydrotalcite with a magnesium / aluminum ratio of 2.0

A solution of 0.2 mol of MgCk and 0.1 mol of AICl 3 in 1000 ml of deionized water was used as the starting point. The pH of the solution was about 3. This solution was placed in a reaction vessel equipped with an agitator and in which four baffles were mounted. The reaction vessel 10 had a double wall; water could be recirculated through this double wall, which was kept at a temperature to be set by a thermostat. In this way the solution was brought to a temperature of 60 ° C. A solution of 0.9 mole of sodium hydroxide and 0.3 mole of anhydrous sodium carbonate in 400 ml of deionized water was then added over a period of 2 hours with intensive stirring of the liquid. During the addition of this solution, the pH of the liquid increased to a value of 12 to 13. After the solution of sodium hydroxide and sodium carbonate was added, stirring was continued for 22 hours while the suspension was at a temperature of 60 ° C was held. After cooling the suspension to room temperature, the solid was separated from the liquid by filtration through a cloth filter. The filter cake was then resuspended in 1800 ml of water in the above reaction vessel and filtered off in the same manner after approximately 2 hours of intensive stirring. This operation was repeated twice so that the precipitate was suspended three times in total in 1800 ml of water and separated from the liquid. The material washed in this way was dried in an oven at 110 ° C for 16 hours.

The content of magnesium and aluminum in the dried material was determined with ICP-AES using a Thermo Jarrell 30 Ash Atom Scan 16 device (ICP inductive-couples plasma; AES Atomic f} £% r. '] -1 ί 21

Emission Spectroscopy). The soluble salt content, in this case sodium chloride, was derived from the chloride content determined by titration with Volhard rhodanide. To this end, the dried material was dissolved in nitric acid. Subsequently, after dilution of the solution, excess silver nitrate was added, after which the excess silver with ammonium rhodanide with iron (III) ammonium sulfate as an indicator was titrated in the presence of some nitrobenzene. After the above procedure according to the invention, the chloride content was less than 1% by weight.

In order to determine the homogeneity of the hydrotalcites thus prepared and the dimensions of the agglomerates of the elementary particles, the dried material with conductive carbon-containing adhesive tape was mounted on an aluminum table and subsequently made electrically conductive by evaporating in vacuo with carbon. The scanning electron microscope was equipped with a field-emission electron gun. The local element composition could be determined by measuring the emitted X-ray photons. This was done with an EDAX detector. The results were processed with equipment from the same company. The result of the analysis is included under HT-2 in Table I.

During the precipitation and washing of the hydrotalcite, about 30% of the starting material with the filtrate and the washing water is lost in the procedure followed. The magnesium / aluminum ratio appears to correspond with that of the starting solution within the measurement error. Analysis in the scanning electron microscope of areas with dimensions of approximately 0.5 µm indicate the same composition within the measurement error. This indicates that the material has a uniform chemical composition. As indicated in Table I, the X-ray diffraction pattern of the material corresponds to a crystallographic α-axis with a length of 0.3047 nm and a c-axis with a length of 2.3062 nm. In the literature one gives for these axis lengths respectively at 0.306 nm and 1025641 22 2.307 nra. This indicates that pure hydrotalcite is obtained in this way.

The X-ray diffraction pattern was recorded with an Enraf Nonius PDS 120 powder diffraction system, equipped with a position-sensitive detector with Co Ka radiation with a wavelength of 0.178897 nm.

The accessible surface of the material was determined by adsorption of nitrogen at 77 K in equipment from Micromeretics, namely ASAP 2400. Previously, the material was degassed in vacuum at 150 ° C for 24 hours. The accessible area was calculated according to Brunauer, Emmett and Teller (BET) from the adsorption of nitrogen as a function of nitrogen pressure at 77 K. The area is approximately 50 m2 per gram. Together with the density of hydrotalcite, which is 2.06 grams per cm 3, this results in a particle size of 0.58 µm.

Example 2

Preparation of hydrotalcites with a varying magnesium / aluminum ratio In the same reaction vessel and in the same manner, hydrotalcites were prepared starting from dissolution of the corresponding chlorides with a magnesium / aluminum ratio in the starting solution of 1.0 to 5.0.

• The accessible surface area of these materials was in all cases approximately 50 m2 per gram.

The results of the characterization of the hydrotalcites prepared according to the invention are shown in Table I. From the data of this table it appears that it is not possible to synthesize a hydrotalcite with a magnesium / aluminum ratio of 1.0. A hydrotalcite precipitates with a ratio of 2.0. Since the material 30 was found to be homogeneous in composition upon examination in the scanning 1025641 23 electron microscope, the aluminum that is not included in the hydrotalcite does not precipitate at a pH value of 12 to 13. This excess aluminum remains in the solution and is mixed with the filtrate and the wash water drained. The material obtained when starting from a solution in which the magnesium / aluminum ratio was 5.0 contained less magnesium, as shown in Table I. The fact that in the scanning electron microscope areas are found with a magnesium / aluminum ratio of 5.4 in addition to areas with a ratio of 4.4 indicates that magnesium hydroxide is locally precipitated.

The chloride content of all hydrotalcites after dissolution in nitric acid was determined by the method of Volhard titrimetrically. In all cases, after the washing procedure according to the invention, the chloride content was less than 1% by weight.

15

Table I.

HT-1 HT-2 HT-3 HT-4 HT-S

Yield% __ 52.0__70.2__87.2__85.4__82.7

Mg / Al calculated__h0__2j0__3J3__4j0__5.0

Mg / Al exp (ICP-AES) __ 2J) __ 2J ______ 4.6

Mg / Al local (SEM / EDX) 2.0 ± 0.1 2.0 ± 0.1 3.0 ± 0.1 4.0 ± 0.1 4.4-5.4 d | io nm__0.1521 0.1523 0.1529 0.1535 0.1535, a nm0.3042 0.047 0.3058 0.3071 0.3070 do03 nm_0.7657 0.7698 0.7873 0.8009 0.8023 c nm 2.2972 2.3062 2.3618 2.4028 2.4068 20 ^λ ^ -Μ 24

Example 3

Investigation of differently purified hydrotalcite in the transmission and scanning electron microscope 5

Starting from the chlorides of the metals to be incorporated in the hydrotalcite and the precipitation with sodium hydroxide and soda, the soluble salt which cannot be removed by washing on the filter according to the known state of the art is sodium chloride. In order to determine the influence of the presence of sodium chloride on the cohesion between the hydrotalcite particles, samples of a poorly washed out and a well washed out magnesium-aluminum hydrotalcite in the transmission electron microscope were investigated. The hydrotalcite was prepared in the manner of Example 1 with the difference that the precipitation and aging of the precipitate were carried out at room temperature. This leads to somewhat smaller hydrotalcite particles, which can be seen from the BET surface, which in this case is 80 to 90 m2 per gram. For this purpose, the hydrotalcites dried at 120 ° C are ultrasonically dispersed in ethanol and then a small amount is covered on a copper gauze pad with a thin carbon film, as is customary in the transmission electron microscopy.

Figure 1 shows an image of the hydrotalcite only washed out on the filter. In this case, water was also washed until the electrical conductivity of the wash water was equal to that of the fresh water used. The black areas in the image of Figure 1 are large sodium chloride crystals. In addition, stacks of elemental plates of hydrotalcite can be seen in the upper part of the shot. It is clear that despite the ultrasonic vibration, the plates are not dispersed apart, but are still strongly associated with the intervening sodium chloride.

Figure 2 shows a recording in the transmission electron microscope at a slightly higher magnification of a three times in U Li 1 'according to the invention. Water redispersed and filtered hydrotalcite. The difference with the inclusion of Figure 1 is clear. Crystallites of sodium chloride are no longer present and the cohesion between the hydrotalcite particles is very much less, as evidenced by the open space between the hydrotalcite particles. In the hydrotalcite that has been purified according to the present invention, the stacked elementary plates sometimes lie on the carbon web of the specimen carrier, while in other cases the stacked plates are oriented perpendicular to the face of the film. The distance of the elemental plates is approximately 0.75 nm according to the X-ray diffraction pattern of hydrotalcite. The number of stacked plates can be deduced from the thickness of the plates perpendicular to the carbon film. The thickness of the stacked plates varies from 5 to 20 nm, which corresponds to 7 to 27 elemental plates. Assuming an average lateral size of the platelets of 70 nm, in accordance with the dimensions of the particles in the recording of Figure 2, and an average thickness of 15 nm, then the resulting area / volume ratio and density follows of hydrotalcite (2.06 g / m3) an area of 85 m? per gram, which corresponds perfectly with the measured BET surface area. This correspondence shows that the contact surface between the hydrotalcite 20 particles is small.

Figure 3 shows a recording in the scanning electron microscope of the hydrotalcite washed out only on the filter. It is also clear from this recording that the hydrotalcite particles and the sodium chloride crystallites have formed very large highly cohesive conglomerates. The bottom shot is from the same place on the specimen and indicates the places where an elemental analysis has been performed.

Figure 4 shows the analyzed sites and in the lower part of the figure the results of the analysis. The large amounts of sodium and chlorine that are present in this hydrotalcite that has been washed for a long time on the filter are evident. Since part of the chloride ions is also present in the intermediate layer between the hydrotalcite plates, the amount of chloride in atomic percent is greater than the amount of sodium in atomic percent.

Figure 5 is a shot in the scanning electron microscope of hydrotalcite prepared and purified according to the invention. A comparison with the inclusion in Figure 3 clearly indicates that the particles in hydrotalcite according to the invention are packed much looser.

Figure 6 shows the analyzed sites in the preparation and the result of the analysis. Chloride is completely absent and a small amount of sodium is just detectable. Since the lower limit where the analysis in the electron microscope still yields significant results is approximately 1%, the measured amount of sodium is hardly relevant.

Example 4

Spray drying of hydrotalcite according to the invention

For spray drying, a Niro Mobile Minor spray dryer with a two-fluid nozzle (two-fluid nozzle) was used. The nozzle of the nozzle was mounted symmetrically with respect to the outlet opening. The hydrotalcite suspension contained 3% by weight of hydrotalcite in deionized water. The suspension was supplied to the spray head at a rate of 40 ml / min. The suspension was sprayed with air at a pressure of 1.4 bar. The sprayed suspension was dried with air at approximately 100 ° C. The finely divided product was separated with a cyclone and stored in sealed vessels.

Figure 7 shows an image of the spray-dried material in the scanning electron microscope (FEI XL 3 SFEG). The spherical conglomerates of hydrotalcite particles, with dimensions of approximately 2 to 1025641 27 10 µm, are excellent to handle and dose. With mechanical loading, the particles quickly disintegrate into extremely small particles. Figure 8 is a recording in the scanning electron microscope at very high magnification. The dimensions of the particles are also indicated herein. The elemental hydrotalcite particles occur in this spray-dried material as conglomerates of 0.1 to 0.2 mm; the original porous spheres quickly disintegrate under mechanical load into the particles of 0.1 to 0.2 µm that can be distinguished in the shot of Figure 8.

Example 5

Preparation of hydrotalcites with zinc and magnesium as divalent metal ions and aluminum as trivalent metal ion. AICI3.6H2O in the water were dissolved. A solution of 0.7 mole of NaOH per 1 and 0.2 mole of Na 2 CC> 3 per 1 was then prepared in another vessel. The last solution was added slowly to the magnesium, zinc and aluminum chloride solution until the pH reached a value of 10. Subsequently, the resulting suspension was heated on an oil bath with stirring (500 rpm) for 22 h at the boiling point. The suspension was then cooled to room temperature, after which the solid was separated from the liquid by filtration. The filter cake was suspended three times in 1800 ml of water and separated from the liquid by filtration. After the final filtration step, the material was resuspended in 1800 ml of water and spray dried.

Hydrotalcite with an atomic ratio of Zn / Mg / Al of 4/1/3 and 2/4/3 was prepared in an analogous manner.

• ij f | "P K C; f. ··; · 28

Example 6

Influence of hydrotalcite plates with a thickness of 0.3 Dm on the "plate-out" of sorbitol incorporated in PVC 5

For this "plate-out" use was made of a red pigment based on cadmium sulfoselenide (Cd (S, Se)), supplied by Akcros, Roermond, the Netherlands; the influence of sorbitol on the plate-out, whether or not in the presence of hydrotalcite according to the invention, has been investigated. PVC powder was mixed with the red pigment processed on a two-roll, W-150M for 8 minutes at 207 ° C at 19 rpm, 20% friction and a gap width of 0.8 mm. In accordance with use, the composition of the formulations used is given in “part per hundred parts of resin” with the abbreviation phr. The PVC powder consisted of S-PVC (Marylan S6806) 100 phr, calcium carbonate (Omyalite 95T) 2.0 phr, paraffin wax (drop point 106 - 112 ° C) 0.16 phr, synthetic paraffin wax (melting point 73 ° C ) 0.46 phr, and LDPE was (drop point 103 - 110 ° C) 0.10 phr (phr parts per 100 parts).

The amount of the red pigment deposited on the surface of the two-roller was determined by processing PVC powder with lubricants and calcium carbonate which absorbs the red dye on the two-roller. The color of the PVC after incorporation of the dye from the two-roll was determined with a Spectro-pen ® from Lange Instruments. This measures the brightness of the color, indicated by the L * value, the red-green value given by the a * value and the yellow-blue value given by the b * value. The red pigment used means that the change in the a * value is decisive for the degree of "plate-out".

Figure 9 shows the change in the value of a * for the PVC formulation without sorbitol, with sorbitol, with hydrotalcite according to the invention and with sorbitol and hydrotalcite according to the invention. It is clear from Figure 30 that the presence of sorbitol leads to a strong plate-out. The mixing of hydrotalcite in the PVC reduces the "plate-out" in;! HP.v ·.

29 strong degree. The plate-out is also low in the presence of sorbitol and hydrotalcite. This clearly illustrates the beneficial effect of brazing in hydrotalcite according to the invention on the plate-out.

Example 7

Stabilization of PVC by mixed hydrotalcite; comparative experiment The stabilization of PVC by spray-dried hydrotalcite has been compared to that of hydrotalcite prepared according to the current state of the art that has been rendered hydrophobic by adsorption of stearic acid. The comparison was made by measuring the evolution of hydrogen chloride as a function of the time that the polymer was kept at a temperature of 200 ° C. This procedure is known as the German DIN standard DIN 53381 Teü I Verfahren C.

In this test, 1.0 g of PVC film is cut into pieces of approximately 1 x 1 mm, placed in a tube, which is then sealed. The gas developed on heating is passed through a KCl solution which has a pH value of 6.0 before the start of the experiment. After the tube is connected to the KCl solution, the contents of the tube are brought to a temperature of 200 ° C using an oil bath. The time which elapses until the pH of the KCl solution reaches a value of 3.9 is now determined. This time is a measure of the rate at which hydrogen chloride is released from the PVC when heated at 200 ° C and therefore also a measure of the effectiveness with which the hydrogen chloride developed in the PVC is absorbed by the hydrotalcite.

4.0 phr (parts per hundred parts of resin) hydrotalcite were manually mixed with a mixture of 100 phr PVC (S PVC Kw 67/68), 8.0 phr calcium carbonate (Omyalite 95T), 0.6 phr calcium stearate, 0 , 1 phr 1025641 synthetic paraffin (drop point 106 - 112 ° C), 0.1 phr oxidized PE wax (drop point 102 ° C), 0.6 phr PE wax (drop point 103 - 110 ° C), 1, 0 phr sorbitol and 1.0 phr 1,4-dihydro-2,6-dimethyl-3,5-dicarbobenzoyloxypyridine (D 80). This mixture was processed into a rigid film with a thickness of 0.4 mm on a two-roll at 190 ° C for 3 minutes. For comparison, a film was made in the same way with 4.0 phr of a commercial hydrotalcite, namely Alcamizer-4 from Kyowa Chemical Ind (Japan). The Zn / Mg / Al ratio of Alkamizer-4 is 1/3/2 and the hydrotalcite is made hydrophobic with stearate ions. The dispersion of the different hydrotalcites was qualitatively compared with a light microscope.

The results are given in Table 2. It appears that, despite the fact that the surface is hydrophilic, the spray-dried hydrotalcite disperses as well in PVC as the hydrophobic Alcamizer 4. The stabilization of ZnMg 2 SD, the Zn / Mg ratio of which is somewhat higher than that of Alcamizer 4, namely 4/8/6 compared to 3/9/6, is comparable to that of the commercial hydrophobic product. Surprisingly, the stabilization of hydrotalcites with a higher Zn / Mg ratio appears to far surpass the stabilization of the commercial material.

Table 2

Stabilization of PVC by Zn / Mg / Al hydrotalcites__

Hydrotalcite__Zn / Mg / Al__Surface__Dispersion__Time (min) _

Alcamizer 4__1 / 3 / 2__Hydrophobob__Good__54.7__

ZnMg2 SD 2/4 / 3__Hydrofile__Good__50J_

ZnMg SD__1 / 1 / 1__Hydrophil__Good__70.4_, Zn2Mg SD | 4/2/3 1 Hydrophilic [Good_ 74.2 1025641

Dimensions of elemental hydrotalcite particles after hydrothermal treatment 5 31

Example 8

A hydrotalcite sample prepared according to Example 1 was heated in water under elevated pressure at 180 ° C for 6 hours. Figure 10 shows an image of the resulting material made with the transmission electron microscope.

Figure 11 shows an image at a higher magnification, namely 59,000 x. In comparison with the material of which a recording in the transmission electron microscope is shown in Figure 2, the lateral dimensions of the hydrotalcite particles are considerably larger. The thickness of the stacked elementary plates is also clearly greater.

Figure 12 shows a recording in the scanning electron microscope at a magnification of 100,000 x. The larger dimensions of the stacked elementary plates are clear here, especially if this recording is compared with that of figure 8, in which hydrotalcite not treated hydrothermally is depicted.

20 102 56 4;

Claims (15)

Hydrotalcite particles of 0.02 to about 0.6 μιη for stabilizing polymers with a soluble salt content of less than 3% by weight and preferably less than 1% by weight, containing no organic compounds to surface have an accessible surface area of about 40 to 100 m2 per gram, the elementary particles of which have dimensions of 0.02 to about 0.6 µm, preferably to 0.4 µm and even more preferably to 0.2 µm . 2. Preparation of hydrotalcite particles according to claim 1 by precipitating hydrotalcite according to the known state of the art, after which the soluble salt is almost completely removed by dispersing the precipitate in water at least three times, agitating the suspension for at least about 1 hour and agitating the solid. then separate the dust from the wash water. 3. Preparation of hydrotalcites according to claims 1 and 2 by starting from a solution of the chlorides of the metals to be incorporated in the hydrotalcite and using a solution of caustic soda and soda for raising the pH of the solution of the metal chlorides. 4. Preparation of hydrotalcite particles according to claim 1 by separating and drying a spray of hydrotalcite particles in water prepared according to claim 2 by spray drying. Stabilization of polyvinyl chloride with hydrotalcites according to claims 1 to 3 with a zinc / magnesium ratio of one or higher. 6. Stabilization of liquid and solid compounds mixed in polymers and in particular of pigments by hydrotalcite plates 1025641. with a thickness of about 0.5 to about 1.0 μπι in the polymer. 7. Preparation of hydrotalcite particles according to claim 4 by homogeneously raising the pH of a solution of preferably the chlorides of the divalent and trivalent metals to be incorporated into the hydrotalcite to a value depending on the temperature of the solution of 7 (room temperature) ) to about 5 (90 ° C or higher temperatures) while at the same time carbonate ions are made homogeneous in the solution. The preparation of hydrotalcite particles according to claim 7, wherein work is carried out at elevated pressure. The preparation of hydrotalcite particles according to claims 7 and 8, wherein the hydrolysis of urea is used to homogeneously raise the pH and to make carbonate ions available. The preparation of hydrotalcite particles according to claims 7 and 8 wherein the hydrolysis of cyanate, preferably ammonium or sodium canate, is used to homogeneously raise the pH and to make carbonate ions available. 11. Stabilization of liquid and solid compounds mixed in polymers that release a lot of hydrogen during processing and in particular of pigments through hydrotalcite plates with a thickness of approximately 0.5 to approximately 1.0 µm together with the extremely small hydrotalcite particles of Claim 1 to blend into the polymer. 12. Preparation of a mixture of hydrotalcite particles of different sizes according to confusion 11 by hydrothermally treating part of the hydrotalcite particles, mixing the suspension of the treated hydrotalcite particles with a suspension of untreated hydrotalcite particles and spray-drying the liquid by spraying the liquid. separate and dry. 10 2 5b 4 1 _____J 13. Stabilization of liquid and solid compounds mixed in polymers and in particular of pigments by incorporating a mixture of extremely small hydrotalcite particles and anionic clay plates preferably in the polymer with the structure of stevensite. 14. Preparation of an intimate mixture of stevensite and hydrotalcite by suspending small silica particles (dimensions less than about 0.2 µm) in a solution of a bivalent metal salt such as zinc or magnesium and urea and heating this suspension on a temperature above about 60 ° C and after precipitation of the starch and hydrotalcite to separate the formed solid material from the liquid and to purify it according to claim 2 from dissolved salts and to separate the aqueous suspension of the purified material by spray drying from the liquid and to dry. 15. »• 1 Π; 7> K p ·: '