Abstract:
Surface-modified, pyrogenically produced titanium dioxide which has the following physico-chemical properties: 
     
       ______________________________________ 
     
     Surface        (m 2  /g)                      5 to 120Stamping density          (g/l)       50 to 250Drying loss    (%)         &lt;5Annealing loss (%)         3.5 to 15Carbon content (%)         0.5 to 12pH                         4 to 10.______________________________________

Description:
The present invention relates to a surface-modified, pyrogenically produced titanium dioxide. 
     BACKGROUND OF THE INVENTION 
     It is known to use powdery toners containing surface-modified pyrogenically produced 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). 
     It also is known that a titanium dioxide which has been surface-modified with halogen silanes can be added to electrographic developing powders (See published German patent application DE-A 12 09 427). 
     Furthermore, Published German Patent Application DE-A 34 26 685 (Canon) teaches the addition of a titanium dioxide to positively chargeable toners in which the titanium dioxide had been treated with simultaneously with the adhesion promoters γ-aminopropyltriethoxysilane and trimethylethoxysilane. 
     A similarly treated titanium dioxide 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 titanium dioxide. 
     The present invention provides a surface-modified, pyrogenically produced titanium dioxide which is surface modified with a silane mixture consisting of silane A (trimethoxyoctylsilane) and silane B (3-aminopropyl-triethoxysilane) having the following chemical formulas: ##STR2## 
     The surface-modified, pyrogenically produced titanium dioxide has the following physico-chemical characteristics: 
     
         ______________________________________Surface        (m.sup.2 /g)                      5 to 120Stamping density          (g/l)       50 to 250Drying loss    (%)         &lt;5Annealing loss (%)         3.5 to 15Carbon content (%)         0.5 to 12pH                         4 to 10.______________________________________ 
    
     The present invention also provides a method of producing the surface-modified, pyrogenically produced titanium dioxide in which the pyrogenically produced titanium dioxide is placed in a mixer and sprayed, with the mixer running, with a mixture of silanes A and B. The silanes and the pyrogenically produced titanium dioxide 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 titanium dioxide to silane mixture can be 0.5 to 40 parts by weight silane mixture per 100 parts by weight titanium dioxide. 
     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 titanium dioxide is P 25 which has been produced pyrogenically from TiCl 4  by flame hydrolysis, in an oxyhydrogen flame, and which has the following physico-chemical characteristics: 
     
         ______________________________________               Titanium dioxide               P 25______________________________________Behavior vis-a-vis water  hydrophilicAppearance                loose white powderSurface according to BET.sup.1)              m.sup.2 /g                     50 ± 15Average size of the              nm     21primary particlesStamping density.sup.2)              g/l    ca. 100Specific weight.sup.10)              g/ml   ca. 3.7Drying loss.sup.3) %      &lt;1.5(2 hours at 105° C.)Annealing loss.sup.4)7)              %      &lt;2(2 hours at 1000° C.)pH.sup.5) (in 4% aqueous dispersion)                     3-4SiO.sub.2.sup.8)   %      &lt;0.2Al.sub.2 O.sub.3.sup.8)              %      &lt;0.3Fe.sub.2 O.sub.3.sup.8)              %      &lt;0.01TiO.sub.2.sup.8)   %      &gt;99.5ZrO.sub.2.sup.9)   %      --HfO.sub.2.sup.8)   %      --HCl.sup.8)9)       %      &lt;0.3Sieve residue.sup.6)              %      &lt;0.05(according toMocker, 45 μm)______________________________________ .sup.1) according to DIN 66 131 .sup.2) according to DIN ISO 787/XI, JIS K 5101/18 (nonsieved) .sup.3) according to DIN ISO 787/II, ASTM D 280, JIS K 5101/21 .sup.4) according to DIN 55 921, ASTM D 1208, JIS K 5101/23 .sup. 5) according to DIN ISO 787 IX, ASTM D 1208, JIS K 5101/24 .sup.6) according to DIN ISO 787/XVIII, JIS K 5101/20 .sup.7) relative to the substance dried 2 hours at 105° C. .sup.8) relative to the substance annealed 2 hours at 1000° C. .sup.9) HCl content is a component of the annealing loss 
    
     The waterproofed titanium dioxide of the invention has the advantage that it has no solvent components. 
     It can be used in toners for copiers. 
    
    
     BRIEF DESCRIPTION OF FIGURE OF DRAWING 
     In the drawing: 
     FIGURE 1 is a graph which plots the q/m values of samples of toner. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following examples illustrate the invention: 
     EXAMPLE 1 
     2 kg P 25 TiO 2  produced pyrogenically from TiCl 4  in an oxyhydrogen flame and exhibiting the data indicated 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 an additional 15 minutes. The silanized oxide is tempered for 2 hours at 120° C. 
     The physico-chemical properties of the surface-modified titanium dioxide are as follows: 
     
         ______________________________________Carrier                   TiO.sub.2Surface           (m.sup.2 /g)                     38Stamping density  (g/l)   134Drying loss       (%)     0.2Annealing loss    (%)     3.5C content         (%)     3.0pH                        8.2______________________________________ 
    
     EXAMPLE 2 
     The titanium dioxide 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 system and a high charge stability in comparison to the raw toner was found (see FIGURE 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, .sup.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 
    
     
         __________________________________________________________________________The pigment black Printex 35 is characterized as follows:RCF (regular color furnace)Density: (g/cm.sup.3) 1.8-1.9Product 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     Ashing    Stamping Density                             Particle                                  BET Surface     Residue   Powder                    Beads    Size (nm)                                  (m.sup.2 /g)__________________________________________________________________________Furnace Blacks     0.3       420  550      31   65Printex 35__________________________________________________________________________ 
    
     The q/m measurement takes place under the following conditions: 
     98% carrier (spherical ferrite (80-100 m)) 
     2% titanium dioxide according to example 1 
     Activation: Rolling fixture, 360 rpms in 40 ml glass bottle, weighed portion 40 g, developer