CS229797B1 - A filler based on natural or synthetic carbonates - Google Patents

Abstract

The invention relates to fillers based on natural or synthetic carbonates. A perfectly homogenized mixture of 50 to 99.9 parts by weight of carbonates and 0.1 to 50 parts by weight of silicates with a particle size of 0.05 to 10 µg is impregnated with silane or titanate binders, which perfectly hydrophobicize the filler, so that the composite materials have higher strength than composites with carbonate fillers and a surface hydrophobicized with fatty acids.

Description

The invention relates to fillers and pigments for plastics, coatings and extenders for rubber compounds based on natural or artificial carbonates.

Carbonate raw materials, especially natural finely ground calcium carbonate, have found application as fillers, pigments or extenders, mainly in the paint, rubber or plastics industries, due to their properties and affordability.

From these areas of greatest applicability of carbonate fillers, it is clear that the primary environment in which inorganic fillers are found is organic, most often polymer matrices, which brings with it two main problems: - the need to suppress undesirable chemical interactions of the inorganic filler surface with the organic matrix}

- the necessity of modifying the inorganic surface in such a way that it becomes organophilic and thus enables easier dispersibility in the organic matrix, mutual compatibility and thus good connection of both phases.

The first group of problems consists of influences caused by the physical nature of the filler surface and its chemical composition, i.e. original and further induced disorders of the crystal lattice, morphology and isomorphic replacement of the supporting carbonate cation, which, together with the manifestation of anisominerally present accompanying impurities, especially in the conditions of preparation of composite mixtures and polymer matrices, when these materials are exposed to increased temperatures and mechanical stress, always have an unfavourable effect. The prerequisite for successful resolution of these issues is selective mining, knowledge of the chemical and mineralogical composition of the mined raw material and finally optimization of grinding and sorting procedures.

The issues of the second group associated with surface treatment are crucial for the behavior of fillers in the matrix and also influence the level of desired properties of the final composite.

The basic property of fillers, generally valid and required for all inorganic fillers, is the mutual compatibility of the filler with the matrix.

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The better the inorganic surface is, the more organophilic it is. This can be achieved by providing the inorganic surface with an organic coating, preferably one that is chemically bonded to the filler surface and at the same time has the possibility of interacting with the surrounding organic environment. Substances that meet these requirements are called coupling agents and their representatives are compounds that have at best two types of functional groups. One that ensures connection with the inorganic surface and the other with the surrounding organic, most often polymeric, environment. Typical such coupling agents are, for example, multifunctional compounds based on organosilanes or organotitanates.

However, the use of these coupling agents is significantly disadvantaged in carbonate fillers. The reason is the composition of the crystal lattice of carbonates, which lacks structurally built-in and interactionally suitable functional groups, such as -OH groups. Therefore, the application of multifunctional coupling agents is very ineffective in carbonates, because the forces by which these agents are surface-bound are of the nature of only weak dispersion forces. And if some molecules of coupling agents, especially multifunctional ones, are chemically bound, then only to water molecules, which are in turn only physically bound on the surface of the particles. Therefore, only monofunctional coupling agents based on higher fatty acids are used in carbonate fillers.

This limits the applicability of carbonate fillers, especially where not only an increase but also long-term maintenance of the strength characteristics of composites is required.

Systematic studies of the properties of carbonate fillers have now shown that even such disadvantaged fillers can be modified to be usable in areas of application that require surface treatment performed with more than one monofunctional binder to form chemical bonds.

The subject of the invention is a filler based on natural or synthetic carbonates and silicates with a hydrophobic surface, which is composed of 50 to 99.9 parts by weight of carbonates and 0.1 to 50 parts by weight of silicates with a particle size of 0.05 to 10 μm, perfectly homogenized and, after homogenization, impregnated with silane or titanate binders.

The most typical representative of carbonate fillers is natural calcium carbonate, the mineralogical representative of which is kaloite.

The basic crystal cell of calcite is formed by a lattice, in the corners and in the centers of the faces of which Ca ²⁺ cations are located, and the planar CO^ ² “ anions are located in the middle of the edges. This essentially determines the concentration of ions.

229 797 at individual crystal sites, thus the unsaturation of binding forces and therefore the intensity of force fields, which in addition to these factors are modified by natural anomalies and defects of the crystal lattice, the representation of the calcium cation by isomorphic cations of calcite, i.e. magnesium, manganese, iron, zinc, cadmium, cobalt, strontium or lead, further by anisomineral impurities present both in isolation and in intergrowths and finally by morphological disorders caused by crushing and grinding, including inhomogeneities caused by sorted density-uneven ma-Frial·

Both the physical and chemical nature of the surface thus formed is the result of all the above-mentioned factors, which are necessarily applied when applying fasteners.

If we require the coupling agent to form relatively strong, preferably chemical bonds between its molecules and the filler surface, then the surface of carbonate fillers itself provides only a negligible possibility for such an interaction, since, for example, the limestone crystal lattice contains practically none of the required functional groups suitable for such an interaction. And if any functional groups are present on the surface, for example -OH groups, then only as an ionized part of physically or very sporadically chemisorptionally bound water molecules.

Therefore, in carbonate fillers, the use of coupling agents requiring, for example, reactive, structural -OH groups for interaction is debatable and practically inconclusive, and the use of modifiers used in practice and documented in the literature is limited mainly to monofunctional agents, for example higher fatty acids and their derivatives or lubricants based on polyethylene or polypropylene oxides, in all these cases these are only agents increasing organophilicity, with the binding of these modifiers to the filler surfaces being carried out only with the help of weak dispersion forces.

However, carbonate fillers, pigments or extenders can be successfully modified to be able to create mutual and strong filler-matrix bonds, by admixture of secondary fillers, which are miscible with carbonate fillers and contain structurally bound and surface-localized reactive groups, which, when interacting with the binders, form a chemical bond. By appropriate type, amount and particle size distribution of the secondary filler, choice and concentration of the binder together with selection of the environment and conditions for formation and fixation of the binder layer, a

229 797 mixed filler, a continuous network of the binder, anchored by chemical and rtτ spA-r^n forces both on the secondary filler particles and on the carbonate particles, which enables the desired interaction with the organic matrix.

One of the prerequisites for the successful use of a secondary filler is its miscibility and compatibility with the carbonate filler, which θ

is dependent on the structural and ohmic composition of both fillers

On the surface of carbonate fillers, the most important places from the point of view of the desired interactions with the secondary filler are the crystal corners, i.e. the positions of cations that exhibit the maximum of unsaturated bonding forces. Therefore, the selection of secondary fillers will be preferentially focused on those that not only contain structurally bound and surface-localized reactive -OH groups, but also such centers that are capable of both cation exchange and catalysis of interaction processes.

These requirements are clearly best met by all aluminosilicates and other structurally suitable compounds, for example silicates themselves, such as activated silicas or aluminas with a minimum Si0 ₂ content.

Typical representatives of such materials are natural or synthetic silicates or their weathered forms - hydrous silicates, clays and their components, calcareous clays or claystones.

The most suitable of them are those that are industrially processed and therefore available in the required range and properties. These include, for example, kaolins, bentonites, micas, talc, silicas and the like, which, in addition to structurally satisfactory properties, are also characterized by suitable hardness, comparable to the hardness of carbonates.

If a portion of the carbonate filler in an amount of 0.1 to 50% by weight is replaced by a silicate filler containing structurally bound and surface-localized reactive functional groups, preferably hydroxyl, capable of mutual reaction with coupling agents, it contains structurally bound reactive centers, preferably of the Brondsted type, capable not only of exchange with cations of the crystal lattices of carbonate fillers, pigments and extenders, but also of catalysis of the relevant interaction reactions and, with its polydispersity, chemical composition, density and hardness, it forms a mixture compatible with the primary carbonate filler, pigment or extender and capable of further applications, thereby enabling the particles of the mixed filler, pigment or extender to form a firmly anchored, usually polymeric network-like layer of coupling agents, especially multifunctional agents, on their surface, capable of further, subsequent interaction with organic or polymeric matrices. ⁷⁹⁷

This ensures that carbonate fillers, pigments and extenders obtain such a significant improvement in their surface properties that they can be advantageously used even in areas previously unused.

The procedure for preparing such a mixed filler may be as follows: A mixture of limestone, filler, ground and sorted to a grain size of medium size of loam and fine kaolin fraction with an average particle size of 1-2 µm is mixed in a fluid high-speed mixer for 30 minutes, after which it is impregnated with a multifunctional silane or titanate coupling agent by a known procedure, for example from a solution or preferably according to AO 188553, i.e. also in a high-speed mixer.

The same effect is achieved by a process in which coarsely crushed limestone raw material is ground in the presence of aluminosilicate, for example in a pneumatic mill for 30 minutes, and then sorted into the desired fraction, treated with a binding agent according to the above-mentioned process.

The invention will be further illustrated by the following examples, in which the parts or percentages given are by weight, unless otherwise indicated.

Example 1

Limestone from the Čertovy schody site, containing according to analysis 2.9% insoluble fraction (15% HC1), in the soluble phase 98 ppm Pe, ppm Mn and 12 ppm Cu, was ground and sorted to the following grain size:

2% below 2 µm, 4.8% below 10 µm, 77% below 15 µm and 91% below 20 µm; the median particle size at 50% was 10 µm.

100 g of this filler was impregnated with silane A 1100 (gamma-aminopropyltriethoxysilane) in an amount of 0.5% per filler as follows: in a 400 ml beaker, 100 g of limestone was mixed in 100 ml of ethanol/water mixture 9:1. While stirring, 50 ml of ethanol/water mixture 9:1 containing 0.5 g of silane A 1100 was added to the suspension and stirred at laboratory temperature for another 2 hours. The suspension was then poured into a flat crystallization dish and dried in a laboratory hot-air oven at 130 C for 8 hours. After drying, the product was brought to a powder state by grinding in a laboratory porcelain ball mill filled with agate balls for 1 hour at laboratory temperature and a frequency of 2 revolutions/min.

After one week of storage in a polyethylene bag under laboratory conditions, the amino silane coating was analyzed on the thus treated sample using the procedure described in AO 195896 of 15.6.1982, which, in addition to the total amount of silane coating, determines ^

229 797 and its chemisorbed, i.e. chemically bound portion on the filler surface.

In this case, it was found that of the originally used amount of silanes, only 12% - 2.5% of the silanes were chemisorbed.

Example 2 g of limestone from the Čertovy schody site characterized in Example 1 and 20 £ of kaolin grade DS-ex, Chlumčany, sorted into a mixture with a maximum particle size of 5^um and a main particle fraction of 1-3/un, were mixed and shaken for 3 h<Ux on a laboratory shaker at room temperature. Then the mixture was impregnated with aminosilane A 1100 in an amount of 0.5% per mixture, using the procedure as in Example 1. The silane deposition was analyzed in the same way and it was found that the mixture thus treated contained 71% - 3% chemisorbed fraction. Example 3

Limestone from the Bohdaneč site, containing according to analysis 14.3% insoluble fraction (15% HCl), in the soluble phase 1050 ppm Pe, 480 ppm Mn and 28 ppm Cu, was ground and sorted into the following grain size: 7% below 2/om, 46% below 10 /im, 70% below 15 /im and 86% below 20 >umj the average size at 50% was 11.5 ,A>m.

200g of this filler was mixed in 100ml of distilled water and 100ml of a 2% ethanol solution of silanes A 1160 (urea-modified aminosilane) was added to the resulting suspension while stirring. The resulting suspension was mixed, dried and ground as in example 1 and analyzed in the same way as described there. It was found that 12.8 - 3% of the silanes from the original amount used were chemisorbed.

Example 4 g of limestone from Example 3 and 15 g of talc with a particle distribution of up to 10 µm were mixed and shaken for 2 h. 100 g of the mixture thus obtained were impregnated with aminosilane A 1100, as in Example 1, and analyzed in the same way for the content of tightly bound silanes.

63 - 5% chemisorbed silanes were found.

Example 5 g of limestone from Example 1 and 1 g of precipitated silica with a particle distribution of up to 0.2 µm and a surface area of 158 m2/g were, after mixing and shaking for 2 h at a temperature of 110 - 115 °C, impregnated with aminosilane A 1100 and analyzed as in Example 1. The mixture prepared in this way showed a chemisorbed fraction of 73.0 ± 5%.

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Example 6

100 g of synthetic, precipitated CaCO^ with a maximum particle size of up to 2µm was mixed with 0.5 g of silica from example 5 and shaken for 2 h at a temperature of 110-115°C. The mixture was then impregnated with silanate A 1160 and analyzed in the same way as the sample in example 3. The value of the chemisorbed fraction found was 65.5-3%.

Example 7

100 g of limestone from example 1 was suspended in 100 ml of ethanol/water 9:1 mixture with stirring and after adding 100 ml of 1% ethanol solution of vinyltriethoxysilane A 151 the suspension was stirred at laboratory temperature for another 2 hours. It was then dried by heating in a hot air dryer at 130°C for 16 hours and the obtained product was homogenized by grinding for one hour in a laboratory porcelain ball mill filled with corundum balls.

parts of the filler thus obtained and 60 parts of linear polyethylene DGH 5220 were homogenized by kneading in a Brabender laboratory kneader at a temperature of 200°C for 25 min. Test specimens were pressed from the obtained composite at a temperature of 220°C, which gave the following data when determining the notch toughness by the CHARPY method:

Composite sample Ratio polyethylene/ Notch toughness____ , filler___tost^CHARPY^^k

Polyethylene/limestone from e.g. 1

DGH 5220 unsealed 60/40 14.6

Polyethylene/limestone from example 1 "DGH 5220 modified according to this example

60/40

15.9

Example 8 100g of dolomitic limestone, ground and sorted for distribution with a maximum particle content of up to 25 µm and with a main fraction of particle size of 7-8 µm, was impregnated with aminosilane A 1100 in an amount of 0.5% by the same procedure as in Example 1.

100 g of dolomitic limestone of the above-mentioned grain size was mixed with 20% of finely ground, calcined and sorted mica (muscovite, iron content 0.08%, maximum fraction with a mean particle size of 5 µm) and after shaking for one hour the mixture was impregnated with silane A 1100, in the same way and in the same amount as for dolomitic limestone. The following values of the elastic modulus were found for test specimens of polyethylene composites prepared with these fillers in the same way as in Example 7:

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Sample PE/filler ratio

Modulus of elasticity ________

Polyethylene DGH 5220 PE/Dolomite Composite DGH 5220 limestone with treatment A 1100 60/40 PX composite/dolomite mixture. DGH 5220 limestone + muscovite with A 1100 modification 60/40 PE composite/80% dolomite blend. DGH 5220 limestone without silane treatment + 2 0% rauskovite with A 1100 modification 60/40

0.91

1.60

2.25

1.83

Example 9

100 g of precipitated CaCO^, specified in Example 6, was stirred in 100 ml of a 9:1 ethanol/water mixture and 100 ml of ethanol containing 0.75 g of triisostearoyl-isopropyl titanate was added with stirring. After 2 h^aC· stirring at room temperature, the suspension was dried in a hot-air oven at 125°C for 16 h. Then it was milled as in Example 7·

100 g of the mixture, obtained by mixing and shaking for 1 h with 95 g of precipitated CaCO3 from Example 6 and 5 g of silica from the same example, was impregnated with titanate, dried and ground in the same way as the limestone filler itself in this example. From both fillers, test specimens of composites with polyethylene DGH 5220 were prepared according to Example 7, which gave the following tensile impact strengths:

Composite polyethylene DGH 5220/filler Impact strength in the ratio 60/40 ________________________ Á, .foC-l..CaCO^ alone treated with titanate 95

CaCO^/silica mixture, titanate treated 162

Example 10 parts of limestone crushed stone with an average particle size of 5 mm, characterized by the same chemical composition as in Example 1, and 2 parts of DS-ex kaolin from Example 2 were ground together in a laboratory pneumatic mill of the MAJAC type, HETZSCH system for 30 minutes.

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The mixture thus obtained was impregnated with aminosilane á 1100 in an amount of 0.5% per mixture, using the procedure as in Example 1, and the silane deposit was analyzed in the same manner. The amount of chemisorbed portion in this case was 73 - 2%.

Claims (1)

Fillers based on natural or synthetic carbonates and silicates with a hydrophobized surface, characterized in that it consists of 50 to 99.9 parts by weight of carbonates and 0.1 to 50 parts by weight of silicates with a particle size of 0.05 to 10 perfectly homogenized and impregnated with silanoate after homogenization or titanate binding agents.