Abstract:
Silanized, structurally modified, pyrogenically produced silicas, characterised by groups fixed to the surface, wherein the groups are dimethylsilyl and/or monomethylsilyl, are produced in that pyrogenically produced silica is treated by a known method with dimethyldichlorosilane and/or monomethyltrichlorosilane, the groups dimethylsilyl and/or monomethylsilyl being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground. They are used to improve scratch resistance in lacquers.

Description:
INTRODUCTION AND BACKGROUND 
     The invention relates to a silanised, structurally modified, pyrogenically produced silica, a process for the production thereof and its use. 
     It is known to use nanoscale particles in transparent coating compositions. 
     Thus, according to U.S. Pat. No. 6,020,419, pyrogenically produced silicon dioxides, deagglomerated in situ, which have been made hydrophobic with dimethyldichlorosilane (Aerosil® R 972), are used in polyurethane lacquers to improve the scratch resistance of the coatings. 
     The known silica has the disadvantage that it cannot be produced in powder form without a lacquer binder. 
     The object therefore existed of developing a silica that does not have these disadvantages. 
     SUMMARY OF THE INVENTION 
     The present invention provides silanised, structurally modified, pyrogenically produced silicas, which are characterised by groups fixed on the surface, the groups being dimethylsilyl and/or monomethylsilyl, preferably dimethylsilyl. 
     In a preferred embodiment of the invention the silicas can have the following physico-chemical characteristics: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 BET surface area m 2 /g: 
                 25-400 
               
               
                   
                 Average size of the primary particles nm: 
                 5-50 
               
               
                   
                 pH value: 
                 3-10 
               
               
                   
                 Carbon content %: 
                 0.1-10   
               
               
                   
                 DBP value %: 
                 &lt;200 
               
               
                   
                   
               
             
          
         
       
     
     The silica according to the invention can have a tamped density of 100 to 280, preferably 100 to 240 g/l. 
     A tamped density of more than 280 g/l leads to poorer results in the technical lacquer tests. 
     Pyrogenic silicas are known from Winnacker-Küchler Chemische Technologie, volume 3 (1983) 4th edition, page 77 and Ullmanns Enzyklopädie der technischen Chemie, 4th edition (1982), volume 21, page 462. 
     In particular, pyrogenic silicas are produced by flame hydrolysis of vaporisable silicon compounds, such as e.g. SiCl 4 , or organic silicon compounds, such as trichloromethylsilane. 
     The invention also provides a process for the production of the silanised, structurally modified, pyrogenically produced silicas according to the invention, which is characterised in that pyrogenically produced silica is treated with dimethyldichlorosilane and/or monomethyltrichlorosilane by a known method, the dimethylsilyl and/or monomethylsilyl groups being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground. 
     In one embodiment of the invention a tempering can take place after the structural modification and/or post-grinding. 
     The silicas according to the invention can be produced e.g. as follows: 
     The silicas, which can be produced as described in DE 1 163 784, are then structurally modified by mechanical action and possibly post-ground in a mill. A tempering can possibly take place after the structural modification and/or post-grinding. 
     The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The post-grinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen. 
     The silicas according to the invention can be incorporated into lacquers, as a result of which these lacquers have increased scratch resistance. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Examples 
     Production and Physico-chemical Properties of the Silicas 
     Production of the Comparative Silicas: 
     The production of the comparative silicas 1, 2 and 3 takes place as described in DE 1 163 784. 
     Production of the silicas according to the invention: 
     The silicas, which are produced as described in DE 1 163 784, are then structurally modified by mechanical action and possibly post-ground in a mill. A tempering can possibly take place after the structural modification and/or post-grinding. 
     The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The post-grinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Overview of the production of the comparative silicas 
               
               
                 and the silicas according to the invention (Examples) 
               
             
          
           
               
                   
                   
                   
                 Post-grinding 
                   
               
               
                   
                 Surface-fixed 
                 Structural 
                 after structural 
                 Tempering after 
               
               
                 Designation 
                 group 
                 modification 
                 modification 
                 post-grinding 
               
               
                   
               
               
                 Comparative silica 1 
                 Dimethylsilyl 
                 No 
                 — 
                 — 
               
               
                 Comparative silica 2 
                 Dimethylsilyl 
                 No 
                 — 
                 — 
               
               
                 Comparative silica 3 
                 Dimethylsilyl 
                 No 
                 — 
                 — 
               
               
                 Silica 1 
                 Dimethylsilyl 
                 Yes 
                 No 
                 No 
               
               
                 Silica 2 
                 Dimethylsilyl 
                 Yes 
                 No 
                 No 
               
               
                 Silica 3 
                 Dimethylsilyl 
                 Yes 
                 No 
                 No 
               
               
                 Silica 4 
                 Dimethylsilyl 
                 Yes 
                 No 
                 No 
               
               
                 Silica 5 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 No 
               
               
                 Silica 6 
                 Dimethylsilyl 
                 Yes 
                 No 
                 No 
               
               
                 Silica 7 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 No 
               
               
                 Silica 8 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 Yes 
               
               
                 Silica 9 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 Yes 
               
               
                 Silica 10 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 No 
               
               
                 Silica 11 
                 Dimethylsilyl 
                 Yes 
                 Yes 
                 No 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Physico-chemical data of the silicas according to the invention 
               
               
                 (Examples) and the comparative silicas 
               
             
          
           
               
                   
                 Temped 
                 Loss on 
                 Loss on 
                   
                 C 
                 DHP 
                 HRT specific 
               
               
                   
                 density 
                 dying 
                 ignition 
                 pH 
                 content 
                 adsorption 
                 surface area 
               
               
                 Designation 
                 [g/l] 
                 [%] 
                 [%] 
                 value 
                 [%] 
                 [%] 
                 [m 3 /g] 
               
               
                   
               
             
          
           
               
                 Comparative 
                 64 
                 0.1 
                 0.5 
                 4.0 
                 0.8 
                 243 
                 113 
               
               
                 silica 1 
               
               
                 Comparative 
                 67 
                 0.5 
                 0.6 
                 4.8 
                 1.0 
                 256 
                 165 
               
               
                 silica 2 
               
               
                 Comparative 
                 72 
                 0.7 
                 1.0 
                 4.0 
                 1.6 
                 255 
                 256 
               
               
                 silica 3 
               
               
                 Silica 1 
                 236 
                 0.1 
                 0.6 
                 4.0 
                 0.8 
                 127 
                 115 
               
               
                 Silica 2 
                 204 
                 0.1 
                 0.6 
                 3.9 
                 0.8 
                 137 
                 116 
               
               
                 Silica 3 
                 223 
                 0.3 
                 0.7 
                 4.2 
                 1.0 
                 160 
                 169 
               
               
                 Silica 4 
                 186 
                 0.3 
                 0.7 
                 4.2 
                 1.1 
                 152 
                 171 
               
               
                 Silica 5 
                 109 
                 0.2 
                 0.7 
                 4.4 
                 1.1 
                 159 
                 167 
               
               
                 Silica 6 
                 193 
                 1.2 
                 0.7 
                 5.2 
                 1.7 
                 157 
                 258 
               
               
                 Silica 7 
                 125 
                 0.2 
                 0.7 
                 4.1 
                 0.8 
                 130 
                 110 
               
               
                 Silica 8 
                 108 
                 0.7 
                 1.3 
                 5.0 
                 1.7 
                 156 
                 257 
               
               
                 Silica 9 
                 123 
                 0.3 
                 0.5 
                 4.3 
                 1.1 
                 157 
                 165 
               
               
                 Silica 10 
                 102 
                 0.7 
                 1.2 
                 6.2 
                 1.7 
                 164 
                 256 
               
               
                 Silica 11 
                 160 
                 0.2 
                 0.7 
                 4.0 
                 0.8 
                 132 
                 115 
               
               
                   
               
             
          
         
       
     
     Example 1  
     For the investigation of the improvement in scratch resistance, a conventional 2-component polyurethane lacquer was used. The formulation of the lacquer and its production, including application, are summarised below: 
     Formulation 
     
       
         
               
               
               
             
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Parts 
               
               
                   
                   
                 by wt. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Millbase 
               
             
          
           
               
                   
                 Acrylic copolymer, mod. with synthetic fatty 
                 43.4 
               
               
                   
                 acids, 60% solution 
               
               
                   
                 Butyl acetate 98% 
                 17.8 
               
               
                   
                 Xylene 
                 3.9 
               
               
                   
                 AEROSIL 
                 5.0 
               
               
                   
                 Σ 
                 70.7 
               
               
                   
                 Lacquer make-up 
               
               
                   
                 Xylene 
                 11.3 
               
               
                   
                 Ethoxypropyl acetate 
                 3.4 
               
               
                   
                 Butyl glycol acetate 
                 1.6 
               
               
                   
                 Aliphatic polyisocyanate, approx. 75% in 1- 
                 18.6 
               
               
                   
                 methoxypropyl-2-acetate/xylene 1:1 
                   
               
               
                   
                 Σ 
                 105.0 
               
               
                   
                   
               
             
          
         
       
         
         Binder concentration: 40% 
         AEROSIL calculated on the basis of millbase (solids): 19.2% 
         AEROSIL calculated on the basis of lacquer (total): 5.0% 
         AEROSIL calculated on the basis of lacquer (solids): 12.5%
 
Production and Application of the Lacquers
 
       
    
     The binder is mixed with the solvents. Then, for the purpose of predispersion, the AEROSIL is incorporated into this mixture with the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Øapprox. 1 mm). The millbase is tested with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm. 
     The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way. 
     After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C. 
     Scratch Tests: 
     The metal sheets are abraded with a quartz/water slurry (100 g water +1 g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog&#39;s bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle). 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Summary of the properties of the liquid lacquers relevant in terms 
               
               
                 of lacquer technology, and of the applied and dried films. 
               
             
          
           
               
                   
                 Comparative 
                 Silica 
                 Silica 
                   
                 Comparative 
                 Silica 
                 Silica 
                   
               
               
                   
                 silica 1 
                 1 
                 2 
                 Reference 
                 silica 2 
                 3 
                 4 
                 Reference 
               
               
                   
                   
               
             
          
           
               
                 Grindometer value [μm] 
                 &lt;10 
                 &lt;10 
                 &lt;10 
                 / 
                 &lt;10 
                 &lt;10 
                 &lt;10 
                 / 
               
               
                 Viscosity (millbase) 
               
               
                 [mPas] 
               
             
          
           
               
                  6 rpm 
                 4710 
                 421 
                 772 
                 571 
                 4990 
                 802 
                 772 
                 55 
               
               
                 60 rpm 
                 1120 
                 210 
                 264 
                 225 
                 1200 
                 279 
                 264 
                 52 
               
               
                 Viscosity 
               
               
                 (lacquer + hardener) 
               
               
                 [mPas] 
               
               
                  6 rpm 
                 882 
                 105 
                 210 
                 135 
                 857 
                 235 
                 105 
                 70 
               
               
                 60 rpm 
                 239 
                 75 
                 92 
                 79 
                 242 
                 100 
                 26 
                 37 
               
               
                 Flow 
                 Orange-peel 
                 OK 
                 OK 
                 OK 
                 Orange-peel 
                 OK 
                 OK 
                 OK 
               
               
                 Scratch resistance 
               
               
                 20° reflectometer value 
                 39.0 
                 83.4 
                 83.5 
                 88.8 
                 67.2 
                 84.2 
                 82.6 
                 89.3 
               
               
                 before scratching 
               
               
                 Haze before scratching 
                 430 
                 30 
                 40 
                 3 
                 235 
                 18 
                 10 
                 2 
               
               
                 40 strokes with Sikron F 500 
                 / 
                 83.7 
                 82.3 
                 56.0 
                 / 
                 74.7 
                 80.4 
                 47.2 
               
               
                 residual gloss [%] 
               
               
                   
               
             
          
         
       
     
     The silicas 1+2 and 3+4 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silicas 1 and 2. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface. 
     Example 2  
     In this example the influence of the structural modification was investigated on the basis of a high solids 2-component PU clear lacquer. The formulation of the lacquer and its production, including application and testing, are summarised below: 
     Formulation 
     
       
         
               
               
               
             
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Parts 
               
               
                   
                   
                 by wt. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Millbase 
               
             
          
           
               
                   
                 Acrylic copolymer, mod. with synthetic 
                 61.0 
               
               
                   
                 fatty acids, 
               
               
                   
                 70% in n-butyl acetate 
               
               
                   
                 Butyl acetate 98% 
                 7.3 
               
               
                   
                 Methoxypropyl acetate 
                 1.7 
               
               
                   
                 Solvesso 100 
                 2.0 
               
               
                   
                 Xylene 
                 2.0 
               
               
                   
                 Baysilon OL 17, 10% in xylene 
                 0.7 
               
               
                   
                 (silicone oil) 
               
               
                   
                 AEROSIL 
                 5.0 
               
               
                   
                 Σ 
                 79.7 
               
               
                   
                 Lacquer make-up (hardener) 
               
               
                   
                 Aliphatic polyisocyanate, 90% in n- 
                 22.3 
               
               
                   
                 butyl acetate 
               
               
                   
                 Butyl acetate 98% 
                 2.0 
               
               
                   
                 Solvesso 100 
                 1.0 
               
               
                   
                 Σ 
                 105.0 
               
               
                   
                   
               
             
          
         
       
         
         Binder concentration: 62.8% 
         Aerosil calculated on the basis of millbase (solids):11.7% 
         Aerosil calculated on the basis of lacquer (total): 5.0% 
         Aerosil calculated on the basis of lacquer (solids): 8.0%
 
Production and Application of the Lacquers
 
       
    
     The binder is mixed with the solvents. Then, for the purpose of predispersion, the AEROSIL is incorporated into this mixture with the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). The millbase is tested with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm. 
     The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way. 
     After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C. 
     Scratch Tests: 
     The metal sheets are abraded with a quartz/water slurry (100 g water +1 g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog&#39;s bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20 ° irradiation angle). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Summary of the properties of the liquid lacquers 
               
               
                 relevant in terms of lacquer technology, and of the 
               
               
                 applied and dried films. 
               
             
          
           
               
                   
                 Comparative 
                   
                   
                   
               
               
                   
                 silica 2 
                 Silica 3 
                 Silica 4 
                 Reference 
               
               
                   
               
             
          
           
               
                 Grindometer value [μm] 
                 &lt;10 
                 &lt;10 
                 &lt;10 
                 / 
               
               
                 Viscosity (millbase) [mPas] 
               
               
                  6 rpm 
                 6200 
                 1500 
                 541 
                 140 
               
               
                 60 rpm 
                 2100 
                 900 
                 559 
                 195 
               
               
                 Viscosity (lacquer + 
               
               
                 hardener) [mPas] 
               
               
                  6 rpm 
                 3821 
                 1041 
                 497 
                 167 
               
               
                 60 rpm 
                 1320 
                 666 
                 446 
                 195 
               
               
                 Flow 
                 marked 
                 OK 
                 OK 
                 OK 
               
               
                   
                 orange-peel 
               
               
                 20° reflectometer value 
                 81.0 
                 83.5 
                 82.8 
                 88.0 
               
               
                 before scratching 
               
               
                 Haze 
                 25 
                 5 
                 6 
                 2 
               
               
                 40 strokes with Sikron 
                   
                 94.3 
                 93.4 
                 82.0 
               
               
                 F 500 residual gloss [%] 
               
               
                   
               
             
          
         
       
     
     The silicas 3+4 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silica 2. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface. 
     Example 3  
     Direct comparison of the silicas according to the invention with a scratch-resistant lacquer according to DE 198 11 790 A1, in which AEROSIL R 972 is used to improve the scratch resistance. 
                                                                           Silicas 2)               Prior   according to               art 1)   the invention                                        Millbase                   Desmophen A 2009/1       190.2           Methoxypropyl acetate:       36.8           Solvesso 100 1:1           AEROSIL       23.0           Σ       250.0           Lacquer make-up           Desmophen A YEP4-55A,   96.0   —           contains           AEROSIL R 972           Millbase   —   48.9           Desmophen 2009/1   —   24.9           OL 17, 10% in MPA   —   —           Modaflow 1% in MPA   —   —           MPA: Solvesso 100 1:1   11.6   33.8           Butyl glycol acetate   10.5   10.5           Byketol OK   7.5   7.5           Byk 141   0.8   0.8           Hardener addition           Desmodur N 3390   23.6   23.6           Σ   150.0   150.0                        
Production and Application of the Lacquers
     1) Comparative silica 1 is incorporated into the binder in accordance with DE 198 11 790 Al using a jet disperser.   2) The binder is mixed with the solvents. Then, for the purpose of predispersion, the AEROSIL is incorporated into this mixture with the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Øapprox. 1 mm). The millbase is tested with a grindometer, 25 μm, according to DIN ISO 1524. It must be smaller than 10 μm.   
     The conversion to lacquer of the millbases corresponding to 1) or 2) takes place in accordance with the formulation, the components being mixed at 2000 rpm with a vane agitator. The hardener is incorporated in the same way. 
     After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C. 
     Scratch Tests: 
     The metal sheets are abraded with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Sikron F 500) using an abrasion and washing resistance tester (Erichsen, 5 brush with hog&#39;s bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20 ° irradiation angle). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Summary of the properties of the liquid lacquers 
               
               
                 relevant in terms of lacquer technology, and of 
               
               
                 the applied and dried films. 
               
             
          
           
               
                   
                 Prior art 
                 Silica 1 
                 Silica 4 
                 Reference 
               
               
                   
                   
               
             
          
           
               
                 Grindometer value [μm] 
                 &lt;10 
                 &lt;10 
                 &lt;10 
                 / 
               
               
                 Viscosity (millbase) 
               
               
                 [mPas] 
               
               
                  6 rpm 
                 58 
                 30 
                 26 
                 30 
               
               
                 60 rpm 
                 48 
                 43 
                 33 
                 40 
               
               
                 Wave scan 
               
               
                 long wave 
                 4.8 
                 1.2 
                 1.1 
                 1.4 
               
               
                 short wave 
                 6.5 
                 3.0 
                 3.1 
                 4.7 
               
               
                 20° reflectometer value 
                 89.0 
                 90.2 
                 89.6 
                 90.8 
               
               
                 before scratching 
               
               
                 Haze before scratching 
                 4 
                 4 
                 3 
                 4 
               
               
                 40 strokes with Sikron F 500 
                 78.3 
                 85.9 
                 86.2 
                 55.3 
               
               
                 Residual gloss [%] 
               
               
                   
               
             
          
         
       
     
     It is shown that a substantially better improvement in the residual gloss is achieved after a scratch stressing of the lacquer surface by using the silicas according to the invention than with the prior art. In addition, owing to their low rheological efficiency, the silicas according to the invention do not cause an orange-peel effect.