EP0028796A2 - Coated magnetic metal or alloy pigments, process for their production, and their use - Google Patents

Abstract

Magnetic metal and alloy pigments with a coating of at least one orthosilica ester and / or its hydrolyzates and / or condensates are described in an amount of 0.2 to 30% by weight.

Description

The present invention relates to non-pyrophoric magnetic metal and alloy pigments which superficially contain a material based on silicic acid esters, a process for the production of these pigments and the use thereof for the production of magnetic recording media.

The constantly growing demand for ever higher quality materials for magnetic recording has led to the development of magnetic metal and alloy pigments, primarily based on iron, cobalt and / or nickel, in recent years. Compared to conventional iron oxide and chromium dioxide pigments, these are characterized by considerably larger energy products and allow the production of magnetogram carriers with a storage density that is surpassed, while at the same time reducing the amount of magnetically active material used.

One of the reasons why these pigments have so far not been able to establish themselves on the market is their high chemical reactivity. Metal particles in pigment size have such a great affinity for oxygen that - if they are suddenly exposed to air at room temperature - they spontaneously convert to metal oxides with glowing (see Römpps Chemie-Lexikon, 7th edition, Franckh'sche Verlagshandlung, Stuttgart 1975 , Page 2852): They are pyrophoric and must therefore always be handled, transported and processed under inert conditions.

In the past there have been attempts to take this decisive disadvantage through appropriate measures. avoid, not missing. It is known, for example, that the pyrophoric character can be removed from the metal particles by superficial oxidation. As a result, however, a considerable part of the magnetically high-quality metal particle is converted into a magnetically low-value oxide, which is expressed in a decrease in the saturation magnetization and the remanence.

Attempts have also been made to protect metal particles against air oxidation by treatment with polymeric organic binders to form so-called masterbatches. Although this measure avoids the loss of metallic substance discussed above, it requires the use of large amounts of polymer if satisfactory environmental stability is to be achieved. However, the higher the polymer content in the masterbatch, the more problematic is its use for producing a magne that is highly filled with pigments table recording medium. In addition, the polymer used for stabilization can lead to incompatibilities when the masterbatch is subsequently processed with binders of a different chemical structure. A pigment protected in this way can therefore only be used to a very limited extent.

The known protective measures also include treating the metal powder with polymer-forming compounds in such a way that polymer layers are produced on the metal particles.

The use of silane coupling agents in magnetic pigments is also known, for example from US Pat. No. 4,076,890 for improving the strength of magnetizable layers and from Japanese Patent Application Laid-Open No. 51-. 104 594, which includes improving the stability and dispersibility of magnetic metal pigments in binders. Pigments treated with silane coupling agents cannot, however, be incorporated equally well in different binder systems.

The object of the present invention was to provide non-pyrophoric magnetic metal and alloy pigments for recording purposes which do not have the disadvantages mentioned.

When dealing with this problem, it was surprisingly found that magnetic metal and alloy pigments with a coating of at least an ortho-silicic acid ester and / or its hydrolyzates and / or condensates in an amount of 0.2 to 30% by weight, preferably 1 to 20% by weight, and particularly preferably 2 to 15% by weight are protected from the attack of atmospheric oxygen and moisture.

It has also been found that this surface protective layer can contain corrosion inhibitors, which further increases the resistance of the pigments.

The metal particles protected in this way can be dispersed very well, and there are no compatibility problems with commercially available binders.

The present invention further describes a process for producing these pigments.

Pyrophoric magnetic metal and alloy powders which can be protected against attacks by atmospheric oxygen and moisture according to the teaching of the present invention are described in the literature. They consist essentially of iron, cobalt and nickel or of alloys, which these three ferromagnetic metals can form together. They optionally contain 0.1 to 10% by weight of one or more foreign elements, such as cadmium, lead, calcium, zinc, magnesium, aluminum, chromium, tungsten, phosphorus or boron. The pyrophoric metal and alloy pigments can also contain smaller amounts of water , Oxides or oxide hydroxides. They can be produced by electrodeposition from the ent speaking salt solutions on a mercury cathode, by decomposing the corresponding metal carbonyls, by reducing the corresponding metal ions from their solutions with the aid of also reducing agents such as boranate, hypophosphite, etc., by reduction with gaseous reducing agents (usually hydrogen) from the corresponding oxides, oxide hydroxides, oxalates , Formates, etc. at temperatures above 250 ° C or by one of the less common methods mentioned in the literature. They can be isometric or anisometric particles, which are either largely homogeneous in structure or are more or less broken down into individual adhering metal cores. Because of their superior properties as recording media, metal powders are preferred, the needle-shaped individual particles of which do not average more than 5 pores and have an average of no more than 2 metal cores. Pyrcphore metal powders of this type are described in German patent application 29 09 480.

deren Hydrolysate einschließlich der Teilhydrolysate sowie die aus den Hydrolysaten bzw. Teilhydrolysaten gegebenenfalls unter Mitwirkung der monomeren, unverseiften Kieselsäureester gebildeten Kondensate.Silicic acid esters which perform the protective function according to the invention are in particular compounds of the general formula

their hydrolysates including the partial hydrolysates and the condensates formed from the hydrolysates or partial hydrolysates, optionally with the participation of the monomeric, unsaponified silicic acid esters.

R therein denotes an alkyl, cycloalkyl or alkenyl radical having 1 to 20 carbon atoms or an aryl or aralkyl radical which is optionally branched and / or interrupted one or more times by oxygen bridges. The alkyl or alkenyl radical can have a linear structure; however, a hydrocarbon radical which is branched at least once is preferred. Examples include isopropyl, t-butyl, 3-methylbutyl, 2-ethylhexyl, octadecyl, oleyl. Examples of cycloalkyl radicals are cyclopentyl, cyclohexyl or cycloheptyl. The aryl radical can be a phenyl radical. However, an alkyl-substituted phenyl radical (aralkyl radical) is preferred, it being particularly preferred if the alkyl radical (s) are in the o-position to the ester bond. Examples of these are the residues o-tolyl, o, o'-xylyl- or o, o'-diethylphenyl. Examples of other aralkyl residues are benzyl, 1-phenylethyl or 2-phenylethyl.

R 'represents an alkyl group with 1 to 4 carbon atoms. The alkyl radical R' can be branched; however, a linear unbranched hydrocarbon radical such as methyl or ethyl is preferred.

n is a number from 0 to 4, preferably 1 to 3.

Silica esters of the specified type can be prepared in a variety of ways according to the prior art, cf. W. Noll, Chemistry and Technology of Silicones, 2nd edition, Verlag Chemie, Weinheim 1968, page 554 ff. For the intended use according to the invention, production processes are preferred which allow the esters to be completely free of acidic impurities (especially hydrogen halides) without great effort. to preserved, as these are known to promote the corrosion of metal.

For the purposes of the present invention, the surface of the metal particles can be coated with only one ester, its hydrolyzate and / or condensate. However, the surface layer can also be formed from two or more silicic acid esters, their hydrolyzates or cohydrolysates and / or condensates or cocondensates. Accordingly, it is not absolutely necessary that the silicic acid esters to be used according to the invention are uniform compounds. Rather, it is quite possible to use reaction mixtures which may be produced directly for stabilization during their preparation. This eliminates the need for sometimes very complex and expensive cleaning.

Instead of the monomeric orthosilica esters, it is also possible from the outset to use their reaction products with amounts of water which are insufficient for the complete hydrolysis thereof to coat the metal particles.

wobei R einen gegebenenfalls verzweigten und/oder durch Sauerstoffbrücken ein- oder mehrfach unterbrochenen Alkyl-, Cycloalkyl- oder Alkenylrest mit 1 bis 20 Kohlenstoffatomen oder einen Aryl- oder Aralkylrest oder ein Wasserstoffatom bedeuten kann. R' steht für eine Alkylgruppe mit 1 bis 4 Kohlenstoffatomen oder ist gegebenenfalls gleich R.. o und p sind Zahlen von 0 bis 50, bevorzugt von 1 bis 35..The incomplete hydrolysis produces polysilicic acid esters, which can be described, for example, by the following formulas:

where R can mean an alkyl, cycloalkyl or alkenyl radical having 1 to 20 carbon atoms or an aryl or aralkyl radical or a hydrogen atom which is optionally branched and / or interrupted once or several times by oxygen bridges. R 'represents an alkyl group with 1 to 4 carbon atoms or is optionally equal to R .. o and p are numbers from 0 to 50, preferably from 1 to 35 ..

The amount of silicic acid ester which must at least be used in order to deprive the metal particles of the pyrophoric character depends on the particle size, the specific surface area (BET nitrogen adsorption method) and the porosity of the pigments. The degree of reduction of the pigments also goes down: Materials that contain smaller amounts of oxides or oxide hydroxides can - with comparable particle size, BET surface area and pore content - be stabilized with smaller amounts than completely reduced metal powders. With the help of simple test trials, a specialist can easily determine the minimum amount. However, since in most cases it is not just a matter of depriving the metal particles of their pyrophoric character, but of maintaining the magnetic characteristics sizes if storage in the air over a longer period of time is desired, the treatment with a somewhat larger amount of silicic acid ester than the minimum amount will be carried out anyway, especially since the surface protective layer has no adverse effect in later processing.

The magnetic metal and alloy pigments claimed therefore contain at least one orthosilica ester of the type mentioned, its hydrolyzate and / or condensate in an amount of 0.2 to 30% by weight, preferably 1 to 20% by weight, and particularly preferably 2 to 15% by weight. Although that in the claims. 1 and 2. The magnetic metal and alloy pigments claimed, even when they are embedded in the commercially available binder of a magnetic recording medium and have already been processed and show a remarkably high resistance to electrochemical corrosion processes, may be even more resistant for some purposes be.

It has been found that this is achieved with magnetic metal and alloy pigments which contain one or more corrosion inhibitors in addition to the silica ester coating. The metal powders treated in this way as such show increased stability against atmospheric oxidation in atmospheres of different relative atmospheric humidities.

As corrosion inhibitors according to the state active and technically accessible compounds are used, for example higher amines, aldehydes, alcohols or ketones, amidines, guanidines, heterocyclic compounds with nitrogen and / or oxygen and / or sulfur as heteroatoms (urotropin, pyrazoles, imidazoles, imidazolines, oxazoles, isoxazoles, Thiazoles, isothiazoles, triazoles, triazines, pyridines and the corresponding benzene-fused systems such as benzimidazoles, benzothiazoles, benzotriazcle, quinolines or isoquinolines, quinazolines and others) sulfur-nitrogen compounds, organic acetylene derivatives, organic nitro compounds, phosphonic acids and phosphonocarboxylic acids and their derivatives and Salts, nitrogen-containing phosphonic or phosphonocarboxylic acids and their derivatives and. Salts, organic and inorganic salts of carboxylic acids such as acetates; Benzoates, cinnamates, salicylates and other, organic and inorganic phosphates (polyphosphates), phosphites and sulfonates, etc. Of course, suitable mixtures of these agents can also be used.

Magnetic metal and alloy pigments in which the corrosion inhibitors in the silica ester layer are compounds from the series of the benzotriazoles, the benzothiazoles, the benzimidazoles, the guanidines, the amidines and / or the metal salts of the carboxylic acids and in an amount of 0 are particularly preferred , 01 to 5 wt .-%, preferably from 0.1 to 4 wt .-%, and particularly preferably from 0.5 to 3 wt .-%, based on metal.

The stabilizing protective layer can be applied to the pyrophoric magnetic metal and alloy pigments by treating them with the silicic acid esters previously converted into a finely divided state by evaporation or atomization in suitable apparatus (fluidized bed reactor, rotary tube, etc.), optionally with the participation of water vapor and / or catalytically active substances and, if necessary, at temperatures higher than room temperature.

It will. preferred, however, to carry out the stabilization in the liquid phase, in such a way that the. untreated pigments in suspensions in organic and / or aqueous medium are treated with at least one ortho-silicic acid ester and / or polysilicic acid ester and optionally at least one corrosion inhibitor, then separated from the organic and / or aqueous phase and dried at temperatures between 50 and 250 ° C. will.

Lower alcohols such as methanol, ethanol, isopropanol, lower ketones such as acetone, butanone (2) and lower ethers such as tetrahydrofuran, 1,4-dioxane are well suited as organic media. Since the ma ^g- netic metal and alloy pigments are self-igniting before the stabilization and be converted by the treatment only in a thermodynamically metastable state, it is for security reasons make even the treatment in organic / aqueous media or water. If necessary, auxiliaries can be added to the suspension Ease the pigments (dispersants) and / or promote the hydrolysis or condensation of the ester. These are, for example, condensed phosphates, cationic, anionic, amphoteric or non-ionic wetting agents or surfactants, acidic or alkaline substances or substance mixtures which can be in free or immobilized form, pH-stabilizing substances such as buffer mixtures.

The pyrophoric magnetic metal or alloy pigment is suspended in methods known per se in the organic and / or aqueous medium. Silicic acid esters and optionally corrosion inhibitors can be added at any time before, during or after the preparation of the suspension of the liquid phase, in which case the addition is advantageously carried out directly after the suspension. The pigment content of the suspension moves. generally between 5 and 50% by weight.

In many cases it has proven to be advantageous to leave the pigment in suspension for some time before it is then separated off and dried at temperatures of 50 to 250 ° C., preferably 80 to 150 ° C. During this period - preferably half to five hours - the suspension is stirred at room temperature or temperatures higher than room temperature, in particular at 20 to 90 ° C.

It is particularly preferred to separate the treated magnetic metal and alloy pigments from the organic and / or aqueous medium and to dry them to combine with one another by subjecting the suspension to spray drying. The temperature of the drying gas can be up to 500 ° C. The spray-dried, coated pigments can be subjected to an additional heat treatment at the temperatures indicated above and, if appropriate, can be transferred from an inert gas atmosphere to an oxygen-containing atmosphere.

The process according to the invention is normally carried out with the greatest possible exclusion of oxygen in an inert gas atmosphere (“inert atmosphere” is also understood here to mean vacuum), usually nitrogen, in order to oxidize the magnetic metal and. To avoid alloy pigments. Only after drying or tempering has been carried out is the coated pigment released into the air. If necessary, the inert gas atmosphere can be gradually replaced by an air atmosphere by metered addition of oxygen or air. This ensures that possibly. Remaining active sites that would oxidize in direct contact with air oxygen immediately and could act by the energy released as Initialzündquelle for the entire Pigmentmen ^g e, are recognized danger. This passivation can of course also be carried out with gas mixtures containing oxygen other than air.

It should be pointed out that it is extremely surprising even for the person skilled in the art that the described method leads to success despite the use of protic media, without the magnetic metal and Alloy pigments suffer here. The saturation magnetization drops by at most the percentage that the non-magnetic protective cover makes up by weight in the claimed pigment. The apparently stronger drop in the remanent magnetization, which was partly observed on powder samples, is due to texture and packing influences and is not reflected in the band remanence.

The non-pyrophoric magnetic metal and. Alloy pigments can be processed according to the known methods to dispersions of the pigments in binders and solvents, which can then be used to produce the actual magnetic recording media. Her excellent dispersion behavior falls both in organic and. also in aqueous systems. No intolerance was observed. Rather, it was unexpectedly found that in the preparation of the dispersions the amount of binder can be reduced without disadvantageous consequences by the proportion corresponding to the weight of the stabilizing protective layer on the pigments, an advantage that should not be underestimated, especially when high pigment fill levels are required.

In principle, the binders customary in the prior art for the production of magnetogram carriers, such as, for example, copolymers of vinyl chloride with vinyl acetate, including the variants which contain carboxyl, hydroxyl or epoxy groups, can be used in conjunction with the magnetic metal and alloy pigments according to the invention , Copolymers of vinyl chloride with acrylic acid esters or methacrylic acid esters including those obtained by partial ver versions available with soaping hydroxyl groups, copolymers of vinyl chloride with unsaturated OH-containing monomers, with acrylonitrile or vinylidene chloride, copolymers of acrylic esters with acrylonitrile, with vinylidene chloride or with styrene, and the analogous copolymers of methacrylic esters, copolymers of vinylidene chloride or butadiene with acrylonitrile, polyvinyl fluoride Polyvinyl acetals such as polyvinyl formals or polyvinyl butyrals, polyurethane elastomers, polyamide resins, polyester resins, binders based on cellulose, binders based on synthetic rubbers, unsaturated polyester resins, phenoplasts, aminoplasts, epoxy resins in conjunction with hardeners, reactively modified: modified alkyd ether groups, modified with isocyanate groups , Binder based on polyurethane prepolymers with reactive isocyanate groups. Suitable mixtures of these binders can of course also be used.

When creating the pigment dispersions, additives can be added at a suitable time, as are usually used in the production of magnetic recording media: dispersants, lubricants, plasticizers, fungicides, aging stabilizers, antistatic agents, non-magnetizable fillers or pigments.

Magnetic metal and alloy pigments according to the present invention can be used to manufacture any type of magnetic recording media such as tapes, video tapes, instrument tapes, computer tapes, flexible and rigid magnetic cards, flexible magnetic disks, rigid magnetic disks, drum storage.

Such magnetic information carriers are used for image and sound recording, for storing measurement data, as external storage for data processing systems, for archiving purposes, for word processing systems, for identification systems such as. ID cards, credit cards, tickets.

The invention is explained in detail below by means of examples, which, however, in no way limit the subject of the application. The magnetic data given in the examples were measured in a field of 3.5 KOe.

example 1

: 1102 Gg^-1cm³, 4

I_s/

: 1855 Gg^-1cm³, Br/4

I_s: 0,59) wurden mit Hilfe einer Mischsirene in 200 g destilliertem Wasser dispergiert. Während dieses Vorgangs wurden 4 g Kieselsäuretetraethylester zugegeben. Die Suspension wurde filtriert und der Filterkuchen im Stickstoffstrom 10 Stunden bei 105°C getrocknet. Nach dem Abkühlen wurde eine Probe an die Luft gebracht und pulverisiert. Die magnetischen Pulverdaten dieser Probe wurden sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % relativer Luftfeuchtigkeit (B) gemessen:

20 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H c: 772 Oe, Br /

: 1102 Gg ^-1 cm ³ , 4

I _s /

: 1855 Gg ^-1 cm ³ , Br / 4

I _s : 0.59) were dispersed in 200 g of distilled water using a mixed siren. During this process, 4 g of tetraethyl silicate were added. The suspension was filtered and the filter cake was dried in a stream of nitrogen at 105 ° C. for 10 hours. After cooling, a sample was taken to the air and pulverized. The magnetic powder data of this sample were measured immediately (A) and after ten days' storage in air in a thin layer at 25 ° C and 65% relative humidity (B):

Example 2

:1233 Gg^-1cm³, 4

I_s/

: 195o Gg^-1cm³,Br/⁴

I_s: 0,63) in dieser Lösung dispergiert. Nachdem die resultierende Suspension 75 Minuten bei 65°C gerührt worden war, wurden Lösungsmittel und Spaltprodukte der Ester-Hydrolyse bzw. -Kondensation am Rotationsverdampfer bei einem Restdruck von 30 mbar und Temperaturen bis zu 80°C verdampft. Das granulatförmige Material wurde eine Stunde lang unter Inertgas einer Wärmebehandlung bei 90°C unterworfen. Eine Probe des erkalteten Produktes wurde an der Luft aufgerieben. Die an. dieser Probe sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 2.5°C und. 65 % relativer Luftfeuchte (B) bestimmten magnetischen Pulverdaten waren:

3.7 g of the product obtained after separating off the low boilers (residual pressure 20 mbar, bottom temperature up to 95 ° C.) from the reaction of 1 mol of tetraethyl silicate with 1 mol of n-octadecanol was dissolved in a mixture of 120 g of butanone (2) and 30 g of distilled water. Using a dissolver, 15 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H c: 1126 Oe, Br /

: 1233 Gg ^-1 cm ³ , 4

I _s /

: 195o Gg ^-1 cm ³ , Br / ⁴

I _s : 0.63) dispersed in this solution. After the resulting suspension had been stirred at 65 ° C. for 75 minutes, solvents and cleavage products from the ester hydrolysis or condensation were evaporated on a rotary evaporator at a residual pressure of 30 mbar and temperatures up to 80 ° C. The granular material was subjected to a heat treatment at 90 ° C under an inert gas for one hour. A sample of the cooled product was rubbed in the air. The on. this sample immediately (A) and after ten days' storage in air in a thin layer at 2.5 ° C and. 65% relative humidity (B) determined magnetic powder data were:

Example 3 3 a

:₉₇₃ Gg^-1cm³, 4

I_s/

: ₁₈₆₄ Gg^-1cm³, Br/4

I_s: 0,52) mittels eines Dispolvers in dieser Lösung dispergiert. Die Pigmentsuspension wurde 1 Stunde bei 50°C gerührt und anschließend in einen Laborsprühtrockner (IRA-Mini-Sprühtrocknungsanlage HO) eingespeist, der mit Stickstoff betrieben wurde (Trocknungsgastemperatur zwischen 180 und 2.00°C). Das sprühgetrocknete Pigment wurde noch 1 Stunde unter Stickstoff bei 100°C getempert, bevor dann eine Probe des feinteiligen Materials an Luft gebracht wurde. Die magnetischen Pulverdaten dieser Probe wurden sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % (B) bzw. 95 % (C) relativer Luftfeuchtigkeit gemessen:.

10.4 g of 2-ethylhexyloxytriethoxysilane was dissolved in a mixture of 315 g of ethanol and 135 g of distilled water. The pH was adjusted to 4.5 by adding acetic acid and the solution was stirred at room temperature for 1 hour. Then 50 g of a pyrophoric iron pigment (I ^H c: 714 Oe, Br /

: ₉₇₃ Gg ^-1 cm ³ , 4

I _s /

: ₁₈₆₄ Gg ^-1 cm ³ , Br / 4

I _s : 0.52) dispersed in this solution by means of a dispenser. The pigment suspension was stirred for 1 hour at 50 ° C. and then fed into a laboratory spray dryer (IRA mini spray drying system HO) which was operated with nitrogen (drying gas temperature between 180 and 2.00 ° C.). The spray-dried pigment was annealed at 100 ° C. under nitrogen for a further hour, before a sample of the finely divided material was then exposed to air. The magnetic powder data of this sample were measured immediately (A) and after ten days' storage in air in a thin layer at 25 ° C and 65% (B) or 95% (C) relative humidity.

3 b

8.6 g of 2-Ethylhexyloxytriethoxysilan were in an _M-i research released from 160 g of ethanol and 65 g of distilled water. The pH was adjusted to 4.5 by adding acetic acid and the solution was stirred at room temperature for 1 hour. Meanwhile, a suspension of 50 g of the same pyrophoric iron pigment as in Example 3a was prepared in a mixture of 155 g of ethanol and 70 g of distilled water in which 1 g of 1,2-pentamethylene benzimidazole had previously been dissolved. With the aid of an intensive stirrer, this suspension was diluted with the silane solution and, as in Example 3a. proceed further. The measurement of the magnetic powder data was also carried out as described in Example 3a and gave:

3 c

8.6 g of 2-ethylhexyloxytriethoxysilane and 1 g ^@ Preventol CI 6 (ethoxylated 2-mercaptobenzimidazole, Bayer AG) were dissolved in a mixture of 315 g of ethanol and 135 g of distilled water. After the solution was stirred at room temperature for 1 hour, 50 g of the same pyrophoric iron pigment as in Example 3a was suspended therein. The further procedure was the same as in Example 3a. Measurement of the magnetic powder data of the stabilized pigment showed:

3 d

8.6 g of 2-ethylhexyloxytriethoxysilane and 1 g of 1-hydroxybenzotriazole were dissolved in a mixture of 315 g of ethanol and 135 g of distilled water. 50 g of the same pyrophoric iron pigment as in Example 3a were suspended in this solution. The further way of working was the same as in Example 3a, except that the suspension was used for spray drying immediately after preparation. Measurement of the magnetic powder data of the stabilized pigment showed:

3 e-

As example 3 c, but 1 g of cyclohexyliminocarbonic acid dimorpholide was used instead of 1 g of ® Preventol CI 6. Measurement of the magnetic powder data of the stabilized pigment showed:

3 f

As in Example 3b, but 1 g of isophoronediamine-biscaprolactamamidine was used instead of 1 g of 1,2-pentamethylenebenzimidazole. Measurement of the magnetic powder data of the stabilized pigment showed:

In order to assess the corrosion resistance in the strip, short test strips were produced with the stabilized pigments and for comparison with the untreated pyrophoric iron pigment:
1 g of metal pigment was dissolved in 2.5 cm ^{3 of} a 12 ^g % by weight solution of a polyvinyl chloride / polyvinyl acetate copolymer in equal parts of ethyl and butyl acetate, which also contained 4% by weight (based on pigment) of a dispersant a Muller dispersed at 6 kp load with 175 revolutions. The paint sample obtained was drawn onto a 30μ thick polyester film using a 90μ film puller, aligned in a magnetic field and then dried.

To enable a more precise statement, several sample tapes were made from each pigment sample and stored for 48 hours at room temperature. Then tape samples with a homogeneously smooth and closed surface were introduced into a climatic chamber in which a temperature of 55 ° C. and. a relative humidity of 95% prevailed. The state of the magnetic layer was assessed at 35x magnification in incident light. The results of the climatic tests are summarized in the following table:

Example 4 -

1₁₈2 Gg^-1cm³, 4

I_s/

: 1917 Gg^-1cm³, Br/4

I_s: 0,62) wurden in einer Emulsion von 1,9 g Dodecyloxytriethoxysilan in einer Mischung aus 50 g 1,4-Dioxan und 30 g destilliertem Wasser mittels eines Kotthoff-Rührwerks suspendiert. Die Suspension wurde 3 Stunden bei 40°C gerührt. Dann wurde abfiltriert und der Filterkuchen 8 Stunden im Stickstoffstrom bei 150°C getrocknet. Eine Probe des wieder abgekühlten Produktes wurde an die Luft gebracht und zerkleinert. Die magnetischen Pulverdaten dieser Probe wurden sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % relativer Luftfeuchtigkeit (B) gemessen:

10 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H c: 844 Oe, Br /

1 ₁₈ 2 Gg ^-1 cm ³ , 4

I _s /

: 1917 Gg ^-1 cm ³ , Br / 4

I _s: 0.62) were suspended in an emulsion of 1.9 g Dodecyloxytriethoxysilan in a mixture of 50 g of 1,4-dioxane and 30 g of distilled water by means of a Kotthoff agitator. The suspension was at 40 ° C for 3 hours touched. It was then filtered off and the filter cake was dried in a stream of nitrogen at 150 ° C. for 8 hours. A sample of the cooled product was taken to the air and crushed. The magnetic powder data of this sample were measured immediately (A) and after ten days' storage in air in a thin layer at 25 ° C and 65% relative humidity (B):

Example 5

: 1137 Gg^-1cm³, 4

I_s/

: 1935 Gg^-1cm³, _Br/4

I_s: 0,59) mit Hilfe einer Mischsirene hierin dispergiert. Die Pigmentsuspension wurde noch 1 Stunde bei 85°C gerührt. Es wurde abfiltriert und der Filterkuchen 9 Stunden im Stickstoffstrom bei 130°C getrocknet. Nach dem Abkühlen wurde eine Probe an Luft aufgerieben. Die sofort (A) und nach zehntägiger Lagerung an Luft .in dünner Schicht bei 25°C und 65 % relativer Luftfeuchtigkeit (B) an dieser Probe gemessenen magnetischen Pulverdaten waren:

4.4 g of o-methylphenoxytriethoxysilane were dissolved in a mixture of 80 g of isopropanol and 20 g of distilled water. The pH of the solution was adjusted to 9 with ammonia water. Then 15 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (IHc: 1313 Oe, Br /

: 1137 Gg ^-1 cm ³ , 4

I _s /

: 1935 Gg ^-1 cm ³ , _{Br / 4}

I _s: 0.59) by means of a mixing siren dispersed therein. The pigment suspension was stirred at 85 ° C for 1 hour. It was filtered off and the filter cake was dried in a stream of nitrogen at 130 ° C. for 9 hours. After cooling, a sample was rubbed in air. The magneti. Measured immediately (A) and after ten days' storage in air. In a thin layer at 25 ° C. and 65% relative atmospheric humidity (B) powder data were:

Example 6

wurden in einer Mischung aus 6750 g Ethanol und 2250 g destilliertem Wasser gelöst. Der pH-Wert der Lösung wurde durch Zugabe von Essigsäure auf 4,2 eingestellt. Nachdem die Lösung 90 Minuten bei Raumtemperatur gerührt worden war, wurden 1000 g eines nadelförmigen, im wesentlichen aus Eisen bestehenden pyrophoren Metallpigments (I^Hc: 1050 Oe, Br/

: 1182 Gg^-1cm³, 4

I_s/

: ₁910 Gg^-1cm³, Br/4

I_s: 0,62) mit Hilfe eines Dissolvers hierin dispergiert. Die resultierende Suspension wurde 2 Stunden bei 45°C gerührt und dann in einen Laborsprühtrockner (IRA-Mini-Sprühtrocknungsanlage HO) eingespeist, der mit Stickstoff betrieben wurde (Trocknungsgastemperatur zwischen 180 und 200°C). Das sprühgetrocknete Pigment wurde noch 2 Stunden bei 110°C unter Stickstoff getempert. Nach dem Erkalten wurde eine Probe des pulverförmigen Produkts an die Luft gebracht. An dieser Probe wurden sofort (A) und nach zehntägiger Lagerung in dünner Schicht bei 25°C und 65 % relativer Luftfeuchte (B) folgende Magnetwerte gemessen:

Herstellung von Magnetbändern:285 g of a mixture consisting of:

were dissolved in a mixture of 6750 g of ethanol and 2250 g of distilled water. The pH of the solution was adjusted to 4.2 by adding acetic acid. After the solution had been stirred at room temperature for 90 minutes, 1000 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H c: 1050 Oe, Br /

: 1182 Gg ^-1 cm ³ , 4

I _s /

: ₁ 910 Gg ^-1 cm ³ , Br / 4

I _s : 0.62) dispersed therein with the aid of a dissolver. The resulting suspension was stirred at 45 ° C. for 2 hours and then in a laboratory spray dryer (IRA mini spray drying system HO) fed, which was operated with nitrogen (drying gas temperature between 180 and 200 ° C). The spray-dried pigment was annealed at 110 ° C. under nitrogen for a further 2 hours. After cooling, a sample of the powdered product was brought into the air. The following magnetic values were measured on this sample immediately (A) and after ten days of storage in a thin layer at 25 ° C. and 65% relative atmospheric humidity (B):

Production of magnetic tapes:

a.) Physically drying binder system:

236 g of the stabilized metal pigment were dispersed in a solution of 53 g of polyvinyl chloride / polyvinyl acetate copolymer, 4.5 g of silicone oil and 6 g of dispersant in 440 g of a mixture of equal parts of ethyl and butyl acetate and 3.5 hours in a bead mill (grinding media: Glass balls with 1, 2 and 3 mm diameter) ground. It was then filtered, the paint was applied to a 12μ thick polyester film and the iron pigment dispersed in the paint was aligned in a magnetic field. The magnetic layer was then dried. The layer thickness in the dry state was approx. 6µ.

Magnetic measurements on the tape showed:

The data of the corresponding tape with unstabilized pigment are given in brackets. Both bands have similar volume fill factors with regard to the magnetically active material.

b) Crosslinking binder system:

2.75 g of the: stabilized metal pigment were in a solution of 14.4 g of polyvinyl chloride // polyvinyl acetate copolymer, 5 g of acrylonitrile / butadiene copolymer, 19.4 g of polyester urethane, 92.4 g of hydroxyl group-containing polyacrylate and 8.5 g of dispersant dispersed in a mixture of 231 g of tetrahydrofuran, 115.5 g of methyl isobutyl ketone and 51.7 g of cyclohexanone. The mixture was then milled for 3.5 hours in a bead mill (grinding media: glass balls with a diameter of 1, 2 and 3 mm). 30 minutes before the end of the milling period, 19.4 g of a polyfunctional aliphatic isocyanate were added to crosslink the binder system. It was then filtered, the paint was applied to a 12μ thick polyester film and the iron pigment dispersed in the paint was aligned in a magnetic field. The magnetic lacquer was then dried. Its thickness in the dry state was approx. 6µ.

Magnetic measurements on the tape showed:

c) Aqueous, physically drying binder system:

240 g of the stabilized metal pigment were suspended in 175 g of distilled water, which contained 8% by weight (based on pigment) of a dispersant. A mixture of 200 g of a 50% dispersion of an acrylate / styrene copolymer was added to the suspension. and 10 g of butyl diglycol acetate were added and the entire batch was ground in a bead mill for 3.5 hours (grinding media: glass balls with a diameter of 1, 2 and 3 mm). The mixture was then filtered, the paint was applied to a 12 μm thick polyester film and the iron pigment dispersed in the paint aligned in a magnetic field. The magnetic layer was then dried. The layer thickness in the dry state was approximately 6μ.

Magnetic measurements on the tape showed:

Example 7

5.8 g of the product obtained after deducting the volatile constituents (residual pressure 18 mbar, bottom temperature up to 175 ° C.). Reaction of 1 mole of tetraethyl silicate with 1 mole of 9-octadecen-1-ol was emulsified in a mixture of 270 g of isopropanol and 180 g of distilled water adjusted to pH 6.8 with ammonia.

:: 1108 Gg^-1cm³, 4

I_s/

: 1847 Gg^-1cm³, Br/4

I_s: 0,60) in. dieser Emulsion dispergiert. Die Suspension wurde 45 Minuten bei 50°C gerührt und anschließend unter Inertbedingungen bei einer Trocknungsgastemperatur von etwa 200°C sprühgetrocknet (IRA-Mini-Sprühtrocknungsanlage HO). Eine Probe des pulvrigen Produkts wurde an Luft gebracht. Die an dieser Probe sofort. (A) und. nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % relativer Luftfeuchte (B) bestimmten magnetischen Pulverdaten waren:

Using a dissolver, 50 g of a needle-shaped pyrophoric metal pigment consisting essentially of: iron (I ^H C: 852 Oe, Br /

:: 1108 Gg ^-1 cm ³ , 4

I _s /

: 1847 Gg ^-1 cm ³ , Br / 4

_Is : 0.60) dispersed in this emulsion. The suspension was stirred for 45 minutes at 50 ° C. and then spray-dried under inert conditions at a drying gas temperature of about 200 ° C. (IRA mini spray drying system HO). A sample of the powdery product was placed in air. The on this sample immediately. (A) and. After ten days of storage in air in a thin layer at 25 ° C and 65% relative air humidity (B) certain magnetic powder data were:

Example 8

: 1005 Gg^-1cm³, 4

I_s/

: 1771 Gg^-1cm³, Br/4

I_s : 0,57) in dieser Emulsion dispergiert. Die resultierende Suspension wurde eine halbe Stunde bei Raumtemperatur gerührt und sodann in einen Laborsprühtrockner (IRA-Mini-Sprühtrocknungsanlage HO) eingespeist, dessen Trocknungsgas Stickstoff eine Temperatur zwischen 200 und 220°C hatte. Eine Probe des sprühgetrockneten Pigments wurde an die Luft gebracht. Die Messung der magnetischen Pulverdaten sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % relativer Luftfeuchte (B) ergab:

13 g of 2-ethoxyethyloxytriethoxysilane were mixed in a Mi emulsified from 135 g of ethanol and 315 g of distilled water. Then 50 g of an acicular pyrophoric iron pigment (I ^H C: 999 Oe, Br /

: 1005 Gg ^-1 cm ³ , 4

I _s /

: 1771 Gg ^-1 cm ³ , Br / 4

_Is : 0.57) dispersed in this emulsion. The resulting suspension was stirred for half an hour at room temperature and then fed into a laboratory spray dryer (IRA mini spray drying system HO), the drying gas of which nitrogen had a temperature between 200 and 220 ° C. A sample of the spray dried pigment was placed in the air. The measurement of the magnetic powder data immediately (A) and after ten days' storage in air in a thin layer at 25 ° C and 65% relative humidity (B) showed:

Example 9

: 1150 Gg^-1cm³, 4

I_s/

: 1916 Gg^-1cm³ Br/4

I_s: 0,60) wurden mittels eines Dissolvers in einer Emulsion von 12,8 g Cyclohexyloxytriethoxysilan in einer Mischung aus 264 g Isopropanol und 396 g destilliertem Wasser suspendiert. Die Emulsion war zuvor durch Zugabe von Ammoniakwasser auf einen pE-Wert von 5 eingestellt worden. Die Metallpigmentsuspension wurde noch 30 Minuten bei 75°C gerührt und dann unter Stickstoff einer Sprühtrocknung unterworfen (IRA-Mini-Sprühtrocknungsanlage HO, Trocknungstemperatur ca. 200°C). Eine Probe des erkalteten Produktes wurde an Luft gebracht. Die magnetischen Pulverdaten dieser Probe wurden sofort (A) und nach zehntägiger Lagerung an Luft in dünner Schicht bei 25°C und 65 % relativer Luftfeuchtigkeit (B) gemessen:

75 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H C: 845 Oe, Br /

: 1150 Gg ^-1 cm ³ , 4

I _s /

: 1916 Gg ^-1 cm ³ Br / 4

_Is : 0.60) were suspended by means of a dissolver in an emulsion of 12.8 g of cyclohexyloxytriethoxysilane in a mixture of 264 g of isopropanol and 396 g of distilled water. The emulsion had previously been adjusted to a pE of 5 by adding ammonia water. The metal pigment suspension was stirred for a further 30 minutes at 75 ° C. and then subjected to spray drying under nitrogen (IRA mini spray drying system HO, drying temperature approx. 200 ° C.). A sample of the cooled product was placed in air. The magnetic powder data of this sample were measured immediately (A) and after ten days' storage in air in a thin layer at 25 ° C and 65% relative humidity (B):

Example 1'0

3.3.0 g of 2-ethylbutyloxytriethoxysilane were reacted at 70 ° C. in the presence of an immobilized acid as a catalyst with 18 g of distilled water, dissolved in 60 g of ethanol. The cooled reaction mixture was filtered and then freed from low-boiling constituents at a residual pressure of 30 mbar and a maximum temperature of 70 ° C.

: 973 Gg cm, 4

I_s/

: ₁₈₆₄ Gg ^-1cm³, Br/4

I_s: 0,52) suspendiert. Die Suspension wurde eine Stunde bei Raumtemperatur gerührt und dann bei einer Trocknungsgastemperatur zwischen 200 und 220°C unter Inertbedingungen sprühgetrocknet (IRA-Mini-Sprühtrocknungsanlage HO).5 g of the product thus obtained were emulsified in a mixture of 88 g of methanol and 352 g of distilled water. 50 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H C: 714 Oe, Br /

: 973 Gg cm, 4th

I _s /

: ₁₈₆₄ Gg ^-1 cm ³ , Br / 4

I _s : 0.52) suspended. The suspension was stirred for one hour at room temperature and then spray-dried at a drying gas temperature between 200 and 220 ° C. under inert conditions (IRA mini spray drying system HO).

A test of the fine-particle material in air had the following magnetic powder data immediately after production (A) or after ten days' storage in air in a thin layer at 25 ° C and 65% relative air humidity (B):

Example 11

wurden in Gegenwart einer immobilisierten Säure als Katalysator bei 70°C mit 17 g destilliertem Wasser, gelöst in 80 g Ethanol, umgesetzt. Anschließend wurde das _Reak- tionsgemisch abgekühlt, filtriert und dann bei einem Restdruck von 30 mbar und einer Temperatur von maximal 70°C ausgeheizt.397 g of a mixture consisting of:

were dissolved in the presence of an immobilized acid as a catalyst at 70 ° C. with 17 g of distilled water in 80 g of ethanol. Subsequently, the _R eak- tion mixture was cooled, filtered and then mbar at a residual pressure of 30 and a maximum temperature of 70 ° C baked.

: ₁086 Gg^-1cm³, 4

I_s/

: 1742 Gg^-1cm³, Br/4

I_s: 0,62) wurden in einer Emulsion von 6 g des so erhaltenen Produkts in 440 g-destilliertem Wasser dispergiert. Die Suspens:ion wurde am Rotationsverdampfer bei einem Restdruck von 30 mbar und Temperaturen bis zu 150°C zur Trockne eingedampft und das granulatförmige Material unter Stickstoff abgekühlt. Eine Probe des erkalteten Produkts wurde aufgerieben und an Luft gebracht. Die an. dieser Probe sofort (A) und nach. zehntägiger Lagerung an Luft in dünner Schicht: bei 25°C und 65 % relativer Luftfeuchtigkeit (B) bestimmten magnetischen Pulverdaten waren:

50 g of a needle-shaped pyrophoric metal pigment consisting essentially of iron (I ^H C: 1094 Oe, Br /

: ₁ 086 Gg ^-1 cm ³ , 4

I _s /

: 1742 Gg ^-1 cm ³ , Br / 4

I _s : 0.62) were dispersed in an emulsion of 6 g of the product thus obtained in 440 g of distilled water. The suspension: was evaporated to dryness on a rotary evaporator at a residual pressure of 30 mbar and temperatures up to 150 ° C. and the granular material was cooled under nitrogen. A sample of the cooled product was rubbed off and placed in air. The on. this sample immediately (A) and after. ten days' storage in air in a thin layer: at 25 ° C and 65% relative air humidity (B) certain magnetic powder data were:

Claims (7)

₁ ) Magnetic metal and alloy pigments with a coating of at least one orthosilica ester and / or its hydrolysates and / or condensates in an amount of 0.2 to 30% by weight, preferably 1 to 20% by weight and particularly preferably from 2 to 15% by weight. 2) Magnetic metal and alloy pigments according to claim 1, characterized in that the orthosilica ester is a compound of the general formula

where R is an alkyl, cycloalkyl or alkenyl radical with 1 to 20 C atoms or an aryl or aralkyl radical which is optionally branched and / or interrupted one or more times by oxygen bridges, R 'is an optionally branched alkyl radical with 1 to 4 C- Atoms, n = 0 to 4, preferably 1 to 3, mean. 3) Magnetic metal and alloy pigments according to one of claims 1 or 2, characterized in that the coating additionally contains one or more corrosion inhibitors. 4.) Magnetic metal and alloy pigments according to claim 3, characterized in that the corrosion inhibitors are compounds from the series of benzotriazoles, benzothiazoles, benzimidazoles, guanidines, amidines and / or the metal salts of carboxylic acids and in an amount of 0 , 01 to 5% by weight, preferably from 0.1 to 4% by weight and particularly preferably from 0.5 to 3% by weight, based on metal. 5) Magnetic metal and alloy pigments according to one of claims 1 to 4, obtainable by treating the untreated pigments in suspension in organic and / or aqueous medium with at least one ortho-silicic acid ester and / or polysilicic acid ester and optionally at least one corrosion inhibitor, separation of the organic and / or aqueous phase, drying at temperatures between 50 and 250 ° C and optionally transferring the pigments from an inert gas atmosphere into an oxygen-containing atmosphere. 6) Process for the preparation of magnetic metal and alloy pigments according to one of claims 1 to 5, characterized in that the untreated pigments in suspension in organic and / or aqueous medium treated with at least one ortho-silicic acid ester and / or polysilicic acid ester and optionally at least one corrosion inhibitor are then separated from the organic and / or aqueous phase, dried at temperatures between 50 and 250 ° C.
and optionally be transferred from an inert gas atmosphere into an oxygen-containing atmosphere. 7) Use of the magnetic metal and alloy pigments according to one of claims 1 to 5 for the production of magnetic recording media.