Patent Abstract:
Surface-modified, pyrogenically produced aluminum oxide which has the following physico-chemical properties: 
     
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     Surface          (m 2  /g)                        50 to 150Stamping density (g/l)       50 to 90Drying loss      (%)         &lt;5Annealing loss   (%)         5.0 to 15C content        (%)         0.5 to 12pH                           4 to 8.______________________________________

Full Description:
The present invention relates to a surface-modified, pyrogenically produced aluminum oxide. 
     BACKGROUND OF THE INVENTION 
     It is known to use powdery toners containing pyrogenically produced surface-modified silicon dioxide in electrostatic developing processes. Various silanes, especially dimethyldichlorosilane are used for surface modification (See U.S. Pat. No. 3,720,617). 
     It is also known that pyrogenically produced silicon dioxide waterproofed with compounds of the general formula ##STR1## can be added to positively chargeable resin powders in order to increase their flowability (See published European Patent Application EP-A 0,293,009). 
     Published German Patent Application DE-A 12 09 427 discloses aluminum oxide whose surface has been modified with halogen silanes can be added to electrographic developing powders. 
     Published German Patent Application DE-A 34 26 685 (Canon) teaches the addition of aluminum oxide to positively chargeable toners in which the aluminum oxide has been treated simultaneously with the adhesion promoter γ-aminopropyltriethoxy-silane and trimethylethoxysilane. 
     A similarly treated aluminum oxide is described in Published Japanese Patent Application JP-OS 31442 (Nippon Aerosil Corporation). 
     The known method has the disadvantage that it must use an organic solvent system. Alcohols, hydrocarbons and halogenated hydrocarbons are used as solvents which cannot be completely removed from the reaction product. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to avoid these problems and produce a solvent-free, waterproofed aluminum oxide. 
     The present invention provides a surface-modified, pyrogenically produced aluminum oxide which is surface modified with a silane mixture consisting of silane A (trimethoxyoctylsilane) and silane B (3-aminopropyltriethoxysilane) having the chemical formulas: ##STR2## The surface-modified, pyrogenically produced aluminum oxide has the following physico-chemical properties: 
     
         ______________________________________Surface (m.sup.2 /g)   50 to 150Stamping density (g/l) 50 to 90Drying loss (%)        &lt;5Annealing loss (%)     0.5 to 15C content (%)          0.5 to 12pH                     4 to 8.______________________________________ 
    
     The present invention also provides a method of producing the surface-modified, pyrogenically produced aluminum oxide in which the pyrogenically produced aluminum oxide is placed in a mixer and sprayed, with the mixer running, with the mixture of silane A and silane B. The silane and aluminum oxide are mixed after the addition of the silane mixture and the resulting mixture is tempered at 100° to 150° C., preferably at 115° to 125° C. 
     The ratio of aluminum oxide to silane mixture can be 0.5 to 40 parts by weight silane mixture per 100 parts by weight aluminum oxide. 
     The silane mixture can consist of 1 to 99 parts by weight silane A and 99 to 1 parts by weight silane B. 
     A mixture can be used with preference consisting of 50±20 parts by weight silane A and 50±20 parts by weight silane B. 
     A particularly suitable aluminum oxide is Aluminum Oxide C which is produced pyrogenically from aluminum trichloride by flame hydrolysis in an oxyhydrogen flame and which has the following physico-chemical characteristics: 
     
         ______________________________________                    Al.sub.2 O.sub.3                    C______________________________________AppearanceSurface according to BET m.sup.2 /g                      100 ± 15Average size of the        20primary particles nanometerStamping density.sup.1) g/l                      --Drying loss.sup.2)         &lt;5(2 hours at 105° C.) %Annealing loss.sup.2)6)    &lt;3(2 hours at 1000° C.) %pH.sup.3) (in 4% aqueous dispersion)                      4-5SiO.sub.2 .sup.5) %        &lt;0.1Al.sub.2 O.sub.3 .sup.5) % &gt;99.6Fe.sub.2 O.sub.3 .sup.5) % &lt;0.02TiO.sub.2 .sup.5) %        &lt;0.1HCl.sup.5)7) %             &lt;0.5Sieve residue.sup.4)       &lt;0.05according toMocker (45 m)packing drum size (net)normal goods kg            5compressed goods(additive &#34;V) kg______________________________________ Technical data of the AEROSIL standard types .sup.1) according to DIN 53 194 .sup.2) according to DIN 55 921 .sup.3) according to DIN 53 200 .sup.4) according to DIN 53 580 .sup.5) relative to the substance annealed 2 hours at 1000° C. .sup.6) relative to the substance dried 2 hours at 105° C. .sup.7) HCl content is a component of the annealing loss 
    
     The waterproofed aluminum oxide of the invention has the advantage that it has no solvent components. It can be used in toners for copiers, 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following examples illustrate the invention. 
     Example 1 
     2 kg Al 2  O 3  C produced pyrogenically from aluminum trichloride in an oxyhydrogen flame and having the properties given above are placed in a 135 liter Lodige mixer and sprayed with 100 g of a silane mixture consisting of 50 g trimethoxyoctylsilane and 50 g 3-aminopropyltriethoxysilane with the mixer running. The mixture is mixed for 15 minutes more. The silanized oxide is tempered 2 hours at 120° C. 
     Physico-chemical properties of the surface-modified aluminum oxide 
     
         ______________________________________Carrier           Al.sub.2 O.sub.3 CSurface (m.sup.2 /g)             92Stamping density (g/l)             70Drying loss (%)   0.9Annealing loss (%)             5.3C content (%)     2.9pH                5.7______________________________________ 
    
     Example 2 
     The aluminum oxide waterproofed according to Example 1 is tested in a positive toner system. The toner system consists of the following components: 
     
         ______________________________________Pigment black Printex 35                7%Copy-Blau PR (Hoechst AG)                3%Toner resin          90%______________________________________ 
    
     The repeated activation was tested with this toner and a high charge stability in comparison to the raw toner was determined (see FIG. 1). 
     Copy-Blau PR is a charge regulating agent for positive toners. It is characterized as follows: 
     Area of Application 
     1. Charge regulating agents for positive toners (1- or 2-component toners for copiers or laser printers) 
     2. Clearing agents for black toners 
     Chemical characterization: triphenylmethane derivative 
     Thermal resistance: &gt;200° C. 
     Solubility: insoluble in water slightly soluble in organic solvents 
     The toner resin used is characterized as follows: 
     
         ______________________________________         Unit      Theoretical value______________________________________Melt flow Index.sup.1)           g/10 min    5-10(150° C./2, 16 kp)Viscosity number.sup.2)           cm.sup.3 /g 37-43Weight loss.sup.3)           % by weight &lt;1Residual monomers.sup.4)           % by weight &lt;0.35Styrene                     &lt;0.25n-BMA                       &lt;0.10Other product properties:Monomer composition           70% by weight styrene           30% by weight           n-butylmethacrylateGlass transition           60-65° C.temperature Tg.sup.5)Average grain diameter.sup.6)           0.200-0.314 mm(d 50% RS)______________________________________ .sup.1) DIN 53 735, 2/88 edition Specimen pretreatment: Drying at 50° C. oil pump vacuum, 1 hour or 4 hours drying oven, 50° C. .sup.2) DIN 7745, 1/80 edition .sup.3) IR drier until weight constancy .sup.4) Gas chromatography .sup.5) DSC method, ASTM D 3418/75 .sup.6) DIN 53 734, 1/73 edition, evaluation according to DIN 66 141, 2/7 edition 
    
     
         __________________________________________________________________________RCF (regular color furnace)density: (g/cm.sup.3) 1.8-1.9__________________________________________________________________________   Product specifications                   DBP Adsorption    Extract      Depth of            Color  (mg/100 g)                            Volatile contents                                          Sieve      Color Strength                   powder beads                            Components                                     toluene                                          ResiduePrintex 35 RCF   Class      M.sub.γ -value            IRB 3 = 100                   Powder                        Beads                            (%)    pH                                     (%)  (%)__________________________________________________________________________Furnace Blacks   RCF      236   100    42   42  0.9    9.5                                     &lt;0.1 0.05Printex 35__________________________________________________________________________                       Further technical data                                          BET                       Ashing                            Stamping Density                                     Particle                                          Surface               Printex 35 RCF                       Residue                            Powder                                 Beads                                     Size (nm)                                          (m.sup.2 /g)__________________________________________________________________________               Furnace Blacks                       0.3  420  550 31   65               Printex 35__________________________________________________________________________ 
    
     The q/m measurement takes place under the following conditions: 
     98% carrier (spherical ferrite (80-100 m)) 
     2% aluminum oxide according to Example 1 
     Activation: Rolling fixture, 360 rpms in 40 ml glass bottle, weighed portion 40 g, developer 
     BRIEF DESCRIPTION OF FIGURES OF DRAWING 
     In the drawing, the FIGURE is a graph of q/m versus activation time.

Technology Classification (CPC): 8