Carrier for copying systems and manufacturing process thereof.

The developers of two-component systems for developing electrophotographic or electrostatically generated latent images usually consist of carrier particles - called carrier particles - and toner particles. In electrophotography, an invisible, latent image is generated by selective exposure of a photoconductor loaded with charge carriers. In order to make this charge pattern visible, it has to be developed. This is done by adding toner powder, which essentially consists of a coloring component and a binder and has particle sizes between 5 and 30 μm. The toner powder is transported to the photoconductor via the so-called "magnetic brush" - on a sector magnet along the field lines of aligning chains of carriers. The surface of the photoconductor must not be damaged over many copying cycles by the "brush" sliding over it. The carrier particles (carriers) are loaded with toner and are evenly brought up to the photoconductor. This transport causes a controlled, electrostatic charging of the toner powder, which is now transferred to the photoconductor. The magnetic brush made of carrier particles wipes off excess toner from the photoconductive layer and transports it back into the storage container. The developed toner image is then transferred to paper and fixed. The functioning of the development process in two-component systems is well known and is described in detail, for example, in DE-OS 24 02 982. The carrier particles (carriers) typically consist of a core, the material of which is magnetizable. The material can for example consist of iron, nickel, magnetite, Fe₂O₃ or certain ferrites (Ni-Zn ferrites, Mn-Zn ferrites and barium ferrites). The carriers can have an irregular shape; Mostly, however, spherical particles with particle sizes between 30 and 700 microns are used. To set the required electrical and mechanical properties, the carriers usually have a surface coating. Such covers mostly consist of plastic, to which an auxiliary such as metal oxides and organometallic compounds are often added in order to increase the life of the coating.

The carriers have to meet various requirements:<ul id="ul0001" list-style="none"><li>i) They should have a relatively low conductivity so that the charge applied via triboelectric forces does not flow away and the conductivity remains constant over as many cycles as possible;</li><li>ii) there must be no electrical short circuit between the photoconductor and the sector magnet;</li><li>iii) in addition, the carriers should be magnetizable, ie they should be arranged in a brush-like manner under the influence of a sector magnet;</li><li>iv) the carriers must be flowable and of such a shape that the photoconductor is not damaged.</li></ul>

These requirements for a carrier are generally met only in magnetic terms by the magnetic core materials, while the electrical properties are essentially set via the coating. The following carrier types are known from the prior art:<ul id="ul0002" list-style="none"><li>1) Carriers are widely used which consist of a ferromagnetic iron or beam core and which have a coating of fluorocarbon polymers, which mostly contains inorganic pigment particles. (US-PS 37 98 167, EP-A-142 731, US Defensive Specification T 102 004H and JP-OS 7 342/1979, 7 343/1979, 35 735/1979, 35 736/1979, 155 363/1980 , 78 553/1982, 93 355/1982, 112 758/1982, 208 754/1983, 13 243/1984, 15 259/1984 and 219 757/1984). Carriers of this type are produced in such a way that fluidized carrier cores in a fluidized bed are sprayed at elevated temperature with a dispersion containing fluorocarbon polymers and then annealed. However, it is difficult to ensure the consistency of production, as it is known that spray processes only lead to little homogeneous layer thicknesses. Investigations of such carriers show that the particles have coatings of very different thicknesses and that even the surface film is partially incomplete, so that the uncoated surface becomes apparent. Like all plastic-coated carriers, the products manufactured according to this principle have the disadvantage that they suffer from the so-called exhaustion phenomenon. So far, no polymers have become known that do not show this phenomenon. Furthermore, it is not possible to vary the electrical conductivity without auxiliary substances in the plastic coating. Another disadvantage is the material-specific position of polymers based on fluorocarbons in the triboelectric voltage series, which practically only allows one-sided, namely positive charging of the toner particles without further additives. Apart from the chargeability, the electrical conductivity of polymers can hardly be set specifically without additives.</li><li>2) A further group of carriers comprises products which have a metal-containing, ferromagnetic core and have a passivation layer produced by surface oxidation with a lower conductivity. (DE-OS 28 29 317, US-PS 3 923 503, US-PS 4 554 234, RD 221 014, JP-OS 087 601/1981, CA-PS 1 103 079, GB-PS 1 571 850, DE- OS 23 28 314 and DE-OS 22 62 745). These products are manufactured by annealing processes under certain conditions. The goal here is to cover the metallic surface of the carrier in a controlled manner with an oxidation layer that forms out of the substrate. The disadvantages of these carriers are that burning the raw carrier with limited air supply barely succeeds in producing defined layer thicknesses. In addition, unlike chromium and aluminum, iron does not form coherent oxide layers, but rather begins to rust on dislocations or impurities. The production of thick layers is particularly difficult with this process, since increased oxidation easily leads to uncontrolled oxide efflorescence. An indirect disadvantage of the method is that even slight fluctuations in the composition of the carrier core have an undesirable influence on the conductivity and can thus impair the constancy of the carriers obtained by this method.</li><li>3) Ferrite carriers based on the concept of combining the magnetic and electrical properties required for carriers with a lower specific weight in a single material have recently become known. Such carriers are, for example, Ni-Zn-Fe spinels, Zn-Mn-Cu-Fe spinels or doped barium ferrites. As a rule, it is not possible to adjust the electrical properties of ferrite carriers with the necessary precision without subsequent surface coating or treatment. Such surface coatings or treatments can consist, for example, of a plastic coating or a special surface oxidation of the ferrite particles. (JP-OS 18 955/1984; 48 774/1984, 111 157/1984, 111 158/1984, 111 159/1984, 111 160/1984, 111 161/1984, 111 162/1984, 111 163/1984, 111 926/1984, 111 927/1984, 111 929/1984, 127 057/1984, 127 058/1984, 131 942/1984, 170 863/1985, 179 749/1985, 263 955/1985 and 6 661/1986, EP -A-142 731 and 117 572).</li></ul>

Disadvantages of this carrier development are that the post-treatment does not eliminate the difficulties already listed under 1) and 2). A specific disadvantage of ferrite carriers is their material-related abrasiveness, which can lead to damage to the photoconductor, particularly in the case of an irregular external shape.

The object of the present invention was to develop coated carriers which have the disadvantages mentioned above. The particular aim of the present invention was to find a coating technique which allows homogeneous coatings to be reliably applied to iron or ferrite carriers. The coatings should be free of binders, ie free of plastic binders.

The task is solved by covering the surface of metallic or ferritic carrier cores with metal oxide films.

Accordingly, the invention relates to a carrier for a two-component dry developer which has a metal oxide layer on a ferritic or ferrous metal-containing core, which is characterized in that the metal oxide layer consists of reaction products separated from the gas phase.

The carriers according to the invention have abrasion-resistant metal oxide layers which allow electrostatic charging in both directions. The thickness of the metal oxide layer can be adjusted so that the electrical conductivity can be adjusted within certain limits regardless of the composition of the core particles.

The invention also relates to a method for producing the carriers according to the invention. The essence of the method according to the invention is that the particles are always moved against one another during the coating, as a result of which the particles are coated homogeneously. The process is characterized in that volatile metal compounds are reacted with oxygen and / or water in the presence of moving core particles at elevated temperature.

According to the method, iron oxide or titanium dioxide layers, for example, can be applied homogeneously to core particles made of iron and of ferritic material. The oxide layers are formed by the oxidation or hydrolysis of volatile metal compounds on the moving core particles at elevated temperatures.

When coating core particles of iron or ferrites (iron and ferrite carrier cores) with iron oxide films, for example, the procedure can be such that the carrier cores, for example in a moving fixed bed ("moving bed") from carrier cores, are brought to an elevated temperature and then this bed is removed from is flowed through a gas containing iron pentacarbonyl, wherein oxygen or an oxygen-containing gas is added to the gas. The iron carbonyl reacts to form an oxide layer on the carrier cores. For a uniform coating it is necessary that the temperature of the carrier cores is above 100 ° C. The carrier cores are advantageously heated to temperatures between 200 and 400 ° C., for example via wall heating. The concentration of the iron pentacarbonyl vapor added is decisive for an even film formation. Experiments have shown that the concentration of vaporous iron pentacarbonyl in the carrier gas and the oxygen concentration in the gas introduced for the oxidation must each be below 5% by volume. At higher concentrations, especially of iron carbonyl, slightly speckled, ie inhomogeneous, films form or the iron pentacarbonyl burns to form soot-like iron oxide particles without film-like deposition on the substrate. After film formation, the product is cooled and discharged and can be used without further treatment.

The film thickness can be adjusted easily and reliably over the duration of the coating. Control of the film thicknesses is easily possible, at least in the case of thin layer thicknesses in the case of iron metal carrier cores, by the formation of interference colors. The fact that interference colors develop proves, among other things, the extremely homogeneous coating on the carriers according to the invention.

The iron oxide films allow both negative and positive electrostatic charging of toners. The conductivity of the films on the carriers according to the invention is significantly lower than that of the metal and ferrite carriers and can be varied within a certain range using the coating thickness. The coating can also be modified in the direction of higher conductivities if one sets the oxygen concentrations in the oxidation of the iron carbonyl so that no complete oxidation of the iron carbonyl to Fe₂O₃ can take place.

Of course, when it comes to the gas phase assignment of the carrier cores, you are not bound to the equipment of the "moving bed". Experiments have shown that the temperature-controlled carrier cores can also be coated in other apparatus, for example in a heated rotary tube or in a fluidized bed, which is expediently provided with a "Wurster" insert. (HS Hall, RE Pondell in Controlled Release Technol .: Methods, Theory, Application, Vol. 2, S. 133-154; Coating Place Inc., Verona, Wi, USA. KW Olsen, Recent Advances in Fluid Bed Agglomerating and Coating Technology; Plant Operation Progr. V4n3 July 1985, pp. 135-138).

Long-term tests of the carriers according to the invention showed that the adhesive strength of the iron oxide films produced by gas phase reaction is extremely high. This is also evident from the measurements of the electrical, specific conductivity as a function of pressure, in which only small changes in the conductivity as a function of pressure were found. The electrical conductivity can be adjusted from 10 to 10oxidS · cm⁻¹ by coating with iron oxide. As can be seen from the exemplary embodiments, however, more conductive coatings can be set, the layer thickness playing a particularly important role.

Similar to the layers of iron oxide, titanium dioxide layers can also be produced via a gas phase reaction. When covering metal or ferrite carrier cores, the procedure in this case is that a volatile titanium compound, preferably vaporous titanium tetrachloride, is hydrolyzed in the presence of moving carrier cores brought to a higher temperature. This is expediently carried out in a "moving bed" in which the carrier cores, for example can be tempered via wall heating. Similar to the oxidation of iron carbonyl, care must be taken that the concentration of titanium tetrachloride vapor does not exceed 5% by volume, based on the total of the other gases introduced into the moving fixed bed. The other gases consist of the carrier gas for the titanium tetrachloride vapor, usually nitrogen and for the water vapor which is necessary for the hydrolysis and the carrier gas for the water vapor. The carrier gases can be air or other gases which are inert under the conditions, for example nitrogen. The coating with titanium dioxide, like that with iron oxide, can also be carried out in other apparatus, for example in a heatable rotary tube or in a fluidized bed.

The adhesive strength of the titanium dioxide films obtained is extremely high, so that the specific electrical resistance hardly changes as a function of pressure during the conductivity measurement. The specific electrical conductivity can be adjusted from 10 to 10⁻¹⁰S · cm⁻¹ for the carriers produced by the process. By varying the layer thickness of the titanium dioxide, more conductive coatings can also be set. Another advantage of the method according to the invention is that the titanium dioxide layers can be applied quickly.

Of course, iron oxide and titanium dioxide layers can also be applied alternately by the method of the present invention. Details of the nature of the films and the coating process can be found in the examples.

A. The carriers obtained according to the exemplary embodiments were examined by the following methods.

AI. Specific electrical conductivity.

This was determined as follows: In a highly insulated tablet press, a sample of the coated iron balls (carrier) is pressed together at a pressure of 500 bar. The thickness d and the cross section q of the compact were determined using a micrometer screw. A test voltage U of 100 V is applied via gold contacts and the current I is measured. The specific electrical conductivity is calculated from the measured data<maths id="math0001" num=""><img file="EP0303918A2_D0001.tif" /></maths>

AII. Electrostatic chargeability (q / m value)

Electrostatic chargeability was determined using a commercially available toner for a commercial IBM 3800 laser printer. The carrier particles are mixed with the toner in a weight ratio of 99: 1 and shaken in a glass vessel for 1 minute. A weighed quantity of this mixture is then filled into a hard blow-off cell which is coupled to an electrometer (q / m meter from PES Laboratory, Dr. R. Epping, Neufahrn). The mesh size of the sieves used in the hard-blow-off cell is 50 μm and is selected so that no carrier is discharged, but the toner powder can be blown out completely. After the toner has been blown out and suctioned off, the charge can be determined and the toner weight can be related by weighing the toner back.

AIII. Colorimetric values

To measure these values, lacquer rubbings were made with samples of the coated iron balls. Iron balls content: 10% by weight. The colorimetric evaluation of the dyeings obtained was carried out using the CIELAB measuring method (DIN 6174) on a HunterLab measuring device.

AIV. Carrier life

To determine the service life of the carrier, 500 g of the coated balls are mixed with 5 g of a commercially available toner (IBM 3800) and filled into the development unit of a service life tester (LD meter from Dr. R. Epping, Neufahrn). In a storage container next to the developer unit, a further 30 kg of the toner are provided, which can be fed to the developer room via a screw conveyor depending on the toner concentration. The toner concentration is determined via the potential measurements and kept constant by regulating the subsequent dosing. By applying a potential of -500V between the photoconductor and the developer unit, toner is constantly consumed and suctioned off on the other side of the photoconductor. The photoconductor drum has a diameter of 240 mm and is rotated at a speed of 400 mm / sec, ie one revolution of the photoconductor drum corresponds to approximately 2 A4 copies (approx. 60 Copies / min). The developer brush is moved simultaneously at about 3 revolutions per second. The service life of the carriers is determined using electrostatic chargeability measurements of samples taken at regular intervals from the LD meter. The q / m values ​​measured during the life test can be plotted against the number of copies.

In the present application, mean values ​​were formed from the q / m values ​​measured at the beginning and after every 3000 copies up to 1 × 10⁵ copies.

B. embodiments

example 1

A quartz flask with a diameter of 10 cm is filled with 2,000 g of iron powder with particle sizes between 63 and 180 µm and a surface area of ​​2.3 · 10⁻³m² · g⁻¹ (Toniolo type TC 100) and attached to a rotary evaporator. Two water-cooled inlet pipes and a thermocouple are passed gas-tight into the center of the quartz piston through the motor shaft, so that the openings of the pipes are completely covered by iron balls. Under a nitrogen flow of 60 l / h, the iron particles are heated to 240 ° C. at a piston speed of 50 rpm. Air is then introduced through the one inlet pipe instead of nitrogen at 50 l / h. An evaporator vessel (volume: 250 ml), heated and calibrated to 25 ° C., is placed in front of the second inlet pipe, through which 10 l / h of nitrogen are passed. 2 ml of iron pentacarbonyl are injected into this vessel through a rubber seal. The nitrogen is loaded with iron pentacarbonyl vapor and is introduced into the moving fixed bed. Both inlet pipes are cooled to 25 ° C. This ensures that the decomposition and the oxidation take place only in the reaction space.

After the iron pentacarbonyl has completely evaporated, the coated iron balls are allowed to cool to room temperature under a nitrogen stream of 60 l / h. The balls are colored golden brown and shine metallic. The specific electrical conductivity, the electrostatic chargeability, the colorimetric values ​​and the service life according to A) are determined on the carrier obtained.

The measurement results are summarized in Table 1 together with the results of the carriers obtained according to Examples 2 to 8.

Examples 2 to 8

2000 g of the iron powder mentioned in Example 1 are introduced into the apparatus described in Example 1 and coated with iron oxide using iron pentacarbonyl in accordance with the instructions in Example 1. The amount of iron pentacarbonyl used for coating and the properties of the carriers obtained are given in Table 1. The properties of the process products were determined according to A.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="9" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="17.50mm" /><colspec colnum="2" colname="col2" colwidth="17.50mm" /><colspec colnum="3" colname="col3" colwidth="17.50mm" /><colspec colnum="4" colname="col4" colwidth="17.50mm" /><colspec colnum="5" colname="col5" colwidth="17.50mm" /><colspec colnum="6" colname="col6" colwidth="17.50mm" /><colspec colnum="7" colname="col7" colwidth="17.50mm" /><colspec colnum="8" colname="col8" colwidth="17.50mm" /><colspec colnum="9" colname="col9" colwidth="17.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">example</entry><entry namest="col2" nameend="col2" align="center">Fe (CO) ₅ ml</entry><entry namest="col3" nameend="col3" align="center">conductivity ¹⁾ [S · cm⁻¹]</entry><entry namest="col4" nameend="col4" align="center">q / m ²⁾ [µC · g⁻¹]</entry><entry namest="col5" nameend="col5" align="center">Life span q / m ³⁾ [µC · g⁻¹]</entry><entry namest="col6" nameend="col6" align="center">Coloring visual</entry><entry namest="col7" nameend="col9" align="center">CIELAB</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /><entry namest="col7" nameend="col7" align="center">L</entry><entry namest="col8" nameend="col8" align="center">C.</entry><entry namest="col9" nameend="col9" align="center">H*</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1</entry><entry namest="col2" nameend="col2" align="right">2</entry><entry namest="col3" nameend="col3" align="char" char=",">8,3</entry><entry namest="col4" nameend="col4" align="char" char=",">10,5</entry><entry namest="col5" nameend="col5" align="char" char=",">10,4</entry><entry namest="col6" nameend="col6" align="left">brown</entry><entry namest="col7" nameend="col7" align="char" char=",">30,6</entry><entry namest="col8" nameend="col8" align="char" char=",">8,8</entry><entry namest="col9" nameend="col9" align="char" char=",">76,4</entry></row><row><entry namest="col1" nameend="col1" align="right">2</entry><entry namest="col2" nameend="col2" align="right">4</entry><entry namest="col3" nameend="col3" align="char" char=",">4,8</entry><entry namest="col4" nameend="col4" align="char" char=",">10,9</entry><entry namest="col5" nameend="col5" align="char" char=",">11,2</entry><entry namest="col6" nameend="col6" align="left">Red Blue</entry><entry namest="col7" nameend="col7" align="char" char=",">20,9</entry><entry namest="col8" nameend="col8" align="char" char=",">5,5</entry><entry namest="col9" nameend="col9" align="char" char=",">331,6</entry></row><row><entry namest="col1" nameend="col1" align="right">3</entry><entry namest="col2" nameend="col2" align="right">6</entry><entry namest="col3" nameend="col3" align="char" char=",">1,2</entry><entry namest="col4" nameend="col4" align="char" char=",">15,5</entry><entry namest="col5" nameend="col5" align="char" char=",">15,8</entry><entry namest="col6" nameend="col6" align="left">blue</entry><entry namest="col7" nameend="col7" align="char" char=",">26,9</entry><entry namest="col8" nameend="col8" align="char" char=",">10,3</entry><entry namest="col9" nameend="col9" align="char" char=",">259,7</entry></row><row><entry namest="col1" nameend="col1" align="right">4</entry><entry namest="col2" nameend="col2" align="right">8</entry><entry namest="col3" nameend="col3" align="char" char=",">6,8·10⁻²</entry><entry namest="col4" nameend="col4" align="char" char=",">17,1</entry><entry namest="col5" nameend="col5" align="char" char=",">17,6</entry><entry namest="col6" nameend="col6" align="left">blue green</entry><entry namest="col7" nameend="col7" align="char" char=",">36,4</entry><entry namest="col8" nameend="col8" align="char" char=",">5,5</entry><entry namest="col9" nameend="col9" align="char" char=",">222,4</entry></row><row><entry namest="col1" nameend="col1" align="right">5</entry><entry namest="col2" nameend="col2" align="right">10</entry><entry namest="col3" nameend="col3" align="char" char=",">3,5·10⁻⁴</entry><entry namest="col4" nameend="col4" align="char" char=",">19,0</entry><entry namest="col5" nameend="col5" align="char" char=",">19,5</entry><entry namest="col6" nameend="col6" align="left">brown</entry><entry namest="col7" nameend="col7" align="char" char=",">40,9</entry><entry namest="col8" nameend="col8" align="char" char=",">8,7</entry><entry namest="col9" nameend="col9" align="char" char=",">61,1</entry></row><row><entry namest="col1" nameend="col1" align="right">6</entry><entry namest="col2" nameend="col2" align="right">12</entry><entry namest="col3" nameend="col3" align="char" char=",">3,6·10⁻⁵</entry><entry namest="col4" nameend="col4" align="char" char=",">18,9</entry><entry namest="col5" nameend="col5" align="char" char=",">19,9</entry><entry namest="col6" nameend="col6" align="left">Red Blue</entry><entry namest="col7" nameend="col7" align="char" char=",">34,4</entry><entry namest="col8" nameend="col8" align="char" char=",">5,8</entry><entry namest="col9" nameend="col9" align="char" char=",">326,0</entry></row><row><entry namest="col1" nameend="col1" align="right">7</entry><entry namest="col2" nameend="col2" align="right">14</entry><entry namest="col3" nameend="col3" align="char" char=",">8,2·10⁻⁶</entry><entry namest="col4" nameend="col4" align="char" char=",">20,7</entry><entry namest="col5" nameend="col5" align="char" char=",">20,0</entry><entry namest="col6" nameend="col6" align="left">blue</entry><entry namest="col7" nameend="col7" align="char" char=",">34,1</entry><entry namest="col8" nameend="col8" align="char" char=",">4,2</entry><entry namest="col9" nameend="col9" align="char" char=",">250,2</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">8</entry><entry namest="col2" nameend="col2" align="right">16</entry><entry namest="col3" nameend="col3" align="char" char=",">7,6·10⁻⁶</entry><entry namest="col4" nameend="col4" align="char" char=",">20,4</entry><entry namest="col5" nameend="col5" align="char" char=",">20,3</entry><entry namest="col6" nameend="col6" align="left">blue green</entry><entry namest="col7" nameend="col7" align="char" char=",">34,2</entry><entry namest="col8" nameend="col8" align="char" char=",">4,1</entry><entry namest="col9" nameend="col9" align="char" char=",">231,5</entry></row></tbody></tgroup><tgroup cols="9" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="17.50mm" /><colspec colnum="2" colname="col2" colwidth="17.50mm" /><colspec colnum="3" colname="col3" colwidth="17.50mm" /><colspec colnum="4" colname="col4" colwidth="17.50mm" /><colspec colnum="5" colname="col5" colwidth="17.50mm" /><colspec colnum="6" colname="col6" colwidth="17.50mm" /><colspec colnum="7" colname="col7" colwidth="17.50mm" /><colspec colnum="8" colname="col8" colwidth="17.50mm" /><colspec colnum="9" colname="col9" colwidth="17.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col9" align="justify">¹⁾ specific electrical conductivity determined according to AI.)</entry></row><row><entry namest="col1" nameend="col9" align="justify">²⁾ electrostatic loadability determined according to AII.) with toner IBM 3800</entry></row><row><entry namest="col1" nameend="col9" align="justify">³⁾ Carrier lifespan determined according to AIV.) With toner IBM 3800 average</entry></row></tbody></tgroup></table></tables>

Example 9

In the apparatus described in Example 1, 2500 g of an iron powder with particle sizes between 125 and 425 microns and an average surface area of ​​1.4 · 10⁻³m² · g⁻¹ (Toniolo type 40753) and poured in with nitrogen at 250 ° C. warmed up. The gases are introduced as in Example 1 via two inlet pipes heated to 25 ° C. with water. Then 20 l / h of nitrogen are passed into the reactor through the first inlet tube. The nitrogen stream is previously passed through an evaporator vessel with 10 ml of titanium tetrachloride, whereby it becomes saturated with titanium tetrachloride. A nitrogen flow of 30 l / h saturated with water is passed through the second inlet pipe into the reactor space. In this way, the 20 ml of titanium tetrachloride are evaporated over the course of 6 hours. The product is then cooled to room temperature under nitrogen. The electrical conductivity, the electrostatic chargeability and the service life of the carrier obtained were determined in accordance with AI), AII) and AIV).

Specific electrical conductivity 8.3 · 10⁻¹⁰S · cm⁻¹, electrostatic loadability (g / m values): 4.9 µC · g⁻¹ (compared to IBM 3800 toner). Carrier life: 4.8 µC · g⁻¹.

Example 10

750 g of a ferrite carrier (Hitachi, KBN 100, type E) with particle sizes between 100 and 200 μm and an average surface area of ​​7.8 × 10 einer²m² · g⁻¹ are introduced into the apparatus described in Example 1 and nitrogen is passed in heated to 250 ° C. The gas was introduced as in Example 1 through water-cooled inlet pipes. Then, as in Example 1, the system is switched to carrier gas and air and 15 ml of iron pentacarbonyl are injected into the evaporator vessel. After the iron pentacarbonyl evaporated, the carrier was cooled under an inert gas.

The specific electrical conductivity, the electrostatic chargeability, the saturation magnetization and the coercive field strength of the starting material and the carrier are summarized in Table 3.

Example 11

2500 g of the ferrite carrier mentioned in Example 10 are introduced into the apparatus described in Example 1 and heated to 250 ° C. while introducing nitrogen. The gas was changed to carrier gas as in Example 1, but is<u style="single">no</u> Blown oxygen into the apparatus. 15 ml of iron pentacarbonyl are injected into the evaporation vessel. After the evaporation has ended, the balls are cooled under inert gas. The balls are covered with an iron film. The specific electrical conductivity, the electrostatic chargeability, the saturation magnetization and the coexitive field strength of the starting material and the coated material are summarized in Table 3.

Example 12

4.5 kg of iron powder (Toniolo type 40753) are poured into a vertical, heatable tube which has a diameter of 40 mm and a length of 600 mm and is heated to 220 ° C. The iron balls are circulated with the help of a discharge screw and a nitrogen stream at about 9 kg per hour. 20 ml of titanium tetrachloride are introduced into the hot, moving hard board at a height of 500 mm through a nozzle with a nitrogen stream of 50 l / h in 5 hours. A second nozzle at the same height supplies water vapor with a nitrogen flow of 10 l / h for hydrolysis. At the same time, 10 ml of iron pentacarbonyl are fed at a height of 200 mm within the 5-hour reaction time with a nitrogen stream of 50 l / h and 10 l / h of air through a further nozzle at the same height. The balls are coated alternately with TiO₂ and Fe₂O₃ in this way. The electrostatic chargeability and the other measurement results are summarized in Table 2. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center">example</entry><entry namest="col2" nameend="col2" align="center">spec. electr. Conductivity [S · cm⁻¹]</entry><entry namest="col3" nameend="col3" align="center">q / m [µC / g]</entry><entry namest="col4" nameend="col4" align="center">Saturation magnetization [nTm³ · g⁻¹]</entry><entry namest="col5" nameend="col5" align="center">Coexcitive field strength [kAm⁻¹]</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">10</entry><entry namest="col2" nameend="col2" align="char" char=",">5,2·10⁻⁸</entry><entry namest="col3" nameend="col3" align="char" char=",">15,8</entry><entry namest="col4" nameend="col4" align="right">59</entry><entry namest="col5" nameend="col5" align="char" char=",">&lt; 0,4</entry></row><row><entry namest="col1" nameend="col1" align="right">11</entry><entry namest="col2" nameend="col2" align="char" char=",">6,9·10⁻¹</entry><entry namest="col3" nameend="col3" align="char" char=",">12,45</entry><entry namest="col4" nameend="col4" align="right">59</entry><entry namest="col5" nameend="col5" align="char" char=",">&lt; 0,4</entry></row><row><entry namest="col1" nameend="col1" align="right">12</entry><entry namest="col2" nameend="col2" align="char" char=",">2,3·10⁻⁹</entry><entry namest="col3" nameend="col3" align="char" char=",">5,3</entry><entry namest="col4" nameend="col4" align="right">59</entry><entry namest="col5" nameend="col5" align="char" char=",">&lt; 0,4</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Starting material (cf.</entry><entry namest="col2" nameend="col2" align="char" char=",">1,2·10⁻⁷</entry><entry namest="col3" nameend="col3" align="char" char=",">8,1</entry><entry namest="col4" nameend="col4" align="right">59</entry><entry namest="col5" nameend="col5" align="char" char=",">&lt; 0,4</entry></row></tbody></tgroup></table></tables>