Patent Publication Number: US-2006009545-A1

Title: Laquer formulations

Description:
The invention relates to lacquer formulations.  
      Lacquer formulations are used for sealing or coating surfaces. In the case of special surfaces such as, for example, surfaces of parquet floors or other floors, or motor vehicle bodies, special scratch resistance is desired.  
      DE 198 11 790 A1 describes improving the scratch resistance of transparent lacquer binders by the use of pyrogenic hydrophilic and/or hydrophobic silicas. In that case, the silica is incorporated into the binder using a special process.  
      It is a disadvantage that, with the known silicas, despite the use of a special dispersing device, the rheology of the lacquer system is affected to a very great extent and highly flawed lacquer surfaces are obtained (orange-peel effect).  
      The invention provides lacquer formulations containing 
          from 5 to 99.5 wt. %, preferably from 20 to 80 wt. %, particularly preferably from 35 to 70 wt. %, of solids of a polymer component or of a mixture of two or more physically or chemically crosslinking polymer components (binder components and hardener components),     from 0 to 80 wt. %, preferably from 20 to 70 wt. %, particularly preferably from 30 to 55 wt. %, of a low molecular weight component acting as solvent or of a mixture of such low molecular weight components,     from 0.5 to 50 wt. %, preferably from 1 to 25 wt. %, particularly preferably from 2 to 10 wt. %, of a silanised, structurally modified pyrogenic silica to the surface of which there are attached alkylsilyl groups (SiC n H 2n+1 , where n=from 2 to 18), preferably octylsilyl and/or hexadecylsilyl groups, or dimethylsilyl and/or monomethylsilyl groups, preferably dimethylsilyl groups,     from 0 to 10 wt. % of commercially available additives which have a positive effect on the properties of a lacquer, such as, for example, the Theological behaviour of the liquid system, stabilisation and dispersibility of fillers and pigments, appearance and flow of the lacquer surface.        

      As binders there may be used the resins conventional in lacquers and coatings technology, as are described, for example, in Lackharze, Chemie, Eigenschaften und Anwendungen, Eds. D. Stoye, W. Freitag, Hanser Verlag, Munich, Vienna 1996. Examples which may be mentioned include, inter alia, polymers and copolymers of (meth)acrylic acid and their esters, optionally carrying further functional groups, with further olefinically unsaturated compounds, such as, for example, styrene; also polyether, polyester, polycarbonate, polyurethane and epoxy resins, as well as any desired mixtures of those polymers.  
      As polymeric organic compounds there are preferably used polymers carrying hydroxyl groups, for example polyacrylate, polyester, polycaprolactone, polyether, polycarbonate and polyurethane polyols and hydroxy-functional epoxy resins, as well as any desired mixtures of those polymers. As particularly preferred polymeric organic compounds there are used aqueous or solvent-containing or solvent-free polyacrylate and polyester polyols, as well as any desired mixtures thereof. Suitable polyacrylate polyols are copolymers of hydroxyl-group-containing monomers with other olefinically unsaturated monomers, such as, for example, esters of (meth)acrylic acid, styrene, α-methylstyrene, vinyltoluene, vinyl esters, maleic and fumaric acid mono- and di-alkyl esters, α-olefins and other unsaturated oligomers and polymers.  
      Particularly suitable polyacrylate polyols have an average weight-average molecular weight, which can be determined by means of gel permeation chromatography (standard polystyrene), of from 2000 to 10,000 g/mol., preferably from 2500 to 50,000 g/mol. and particularly preferably from 3100 to 40,000 g/mol., a glass transition temperature TG of from −50° C. to +100° C., preferably from −40° C. to +90° C. and particularly preferably −30° C. (to +80° C.), an acid number of &lt;30 mg KOH/g, preferably &lt;25 mg KOH/g, and a hydroxyl group content of from 0.5 to 14.0 wt. %, preferably from 0.5 to 10.0 wt. % and particularly preferably from 1.0 to 8.0 wt. %, and consist of 
          a) from 0 to 70 parts by weight, preferably from 5 to 70 parts by weight, of at least one unsaturated, aromatic monomer, such as styrene, methylstyrene or vinyltoluene,     b) from 0 to 70 parts by weight, preferably from 5 to 70 parts by weight, of at least one (cyclo)aliphatic ester of acrylic and/or methacrylic acid having from 1 to 18 carbon atoms in the (cyclo)alkyl radical,     c) from 4 to 95 parts by weight, preferably from 10 to 60 parts by weight, of at least one hydroxyalkyl ester of acrylic and/or methacrylic acid having from 2 to 4 carbon atoms in the hydroxyalkyl radical, and/or addition products of monoepoxides with acrylic and/or methacrylic acid,     d) from 0 to 10 parts by weight, preferably from 0.1 to 5 parts by weight, of at least one monoolefinically unsaturated mono- or di-carboxylic acid having from 3 to 7 carbon atoms, and/or at least one maleic acid or fumaric acid semi-ester having from 1 to 14 carbon atoms in the alcohol radical, and     e) from 0 to 30 parts by weight, preferably from 0 to 20 parts by weight, of further copolymerisable, olefinically (also polyolefinically) unsaturated monomeric and/or polymeric compounds.        

      The described hydroxyl-functional polyols can be used in both one-component and two-component lacquer systems together with the hardeners conventional in lacquers and coatings technology. There come into consideration as hardeners therefor, for example, polyisocyanates or polyisocyanates blocked with cleaving agents such as methyl ethyl ketoxime, caprolactam, malonic acid esters, triazole or 2,5-dimethylpyrazole, or (partially) etherified melamine-formaldehyde resins, as are described, for example, in Lackharze, Chemie, Eigenschaften und Anwendungen, Eds. D. Stoye, W. Freitag, Hanser Verlag, Munich, Vienna 1996.  
      Preference is given to the use of the aqueous or solvent-containing binders according to the invention in two-component systems together with polyisocyanates based on hexamethylene diisocyanate, isophorone diisocyanate, 4,4-diisocyanatodicyclohexylmethane, tetramethylene diisocyanate, 2-methylpentamethylene diisocyanate, 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate (THDI), 1,4-diisocyanato-cyclohexane, 3-isocyanatomethyl-1-methyl-1-isocyanatocyclohexane (IMCI), a,a,a′,a′-tetramethyl-m- or -p-xylylene diisocyanate (TMXDI), 1,4- and 1,3-xylylene diisocyanate (XDI), hexahydroxylylene diisocyanate (H6-XDI) and/or mixtures thereof and optionally their variants rendered hydrophilic for aqueous binders, as are described, for example, in DE-A 41 36 618.  
      Particular preference is given, however, to polyisocyanates based on hexamethylene diisocyanate, isophorone diisocyanate and 4,4-diisocyanatodicyclohexylmethane.  
      Such polyisocyanates are used as hardeners in high-quality polyurethane lacquers which have outstanding resistance to chemicals and a high degree of gloss.  
      The conventional solvents are suitable for formulating the lacquers according to the invention, such as aromatic, aliphatic, araliphatic or cycloaliphatic hydrocarbons, partially or completely halogenated aromatic, aliphatic, araliphatic or cycloaliphatic hydrocarbons, alcohols, such as, for example, methanol, ethanol, isopropanol, butanol, benzyl alcohol, diacetone alcohol, esters, such as, for example, ethyl acetate, propyl acetate, butyl acetate, ether esters, such as, for example, methoxypropyl acetate or butyl glycol acetate, ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone or cyclohexanone, strongly polar solvents, such as, for example, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxite, N-methylpyrrolidone.  
      Further suitable solvents are water, liquid acid esters, such as, for example, phosphoric acid dibutyl ester, phosphoric acid tributyl ester, sulfonic acid esters, borates or derivatives of silica, for example tetraethoxysilane, methyltrimethoxysilane, 3-aminopropyl-trimethoxysilane, 3-aminopropyltriethoxysilane, glycidyl-oxypropyltrimethoxysilane, glycidyloxypropyl-triethoxysilane.  
      If those solvents are used as dispersing media for the silicas according to the invention, further substances may be added to those materials that are used. Preference is given to those substances which are also provided for subsequent further use or which improve the deagglomeration or the properties, for example the stability, of the deagglomerated materials.  
      Particular preference is given to oligomeric or polymeric organic compounds, such as, for example, the above-mentioned resins and binders conventional in lacquers and coatings technology.  
      It is also possible to use in the dispersing medium amounts of the combination resins used in multi-component systems, such as, for example, the amine and melamine resins acting as hardeners, polyisocyanates, the adducts, referred to as blocked polyisocyanates, consisting of aromatic or aliphatic polyisocyanates and so-called cleaving agents, such as methyl ethyl ketoxime, caprolactam, malonic acid esters or triazole and 2,5-dimethylpyrazole. For procedures in which water is used as a substantial constituent of the dispersing medium, suitable additives are especially compounds which are soluble in or compatible with water, such as, for example, partially or completely saponified polyvinyl acetate, or variants of the above-mentioned classes of compounds which have been rendered hydrophilic. Further additives which are suitable and which are preferably used in aqueous media are, for example, silica sol and the sols of metallic oxides of the elements aluminium, titanium, zirconium, tantalum and tin.  
      As low molecular weight additives by means of which it is possible, for example, to achieve stabilisation of the deagglomerated silicas according to the invention against further agglomeration, there are suitable in principle all compounds which are used for stabilising nanoscale materials prepared by other means, for example by one of the methods mentioned above. Mention may be made of, for example, hydrolysable compounds carrying silane groups, such as alkoxysilanes or chlorosilanes. Particular amphiphilic compounds may also be used. The solvents and additives that are suitable for the preparation of the dispersing medium can be mixed with one another as desired.  
      The lacquer binders according to the invention can be mixed with any conventional hardeners (combinations) to produce coatings.  
      The lacquer formulations according to the invention are transparent lacquer formulations containing pyrogenic, structurally modified silicas, the silicas according to the invention having an extremely small effect on the rheology of the lacquer formulation while at the same time exhibiting increased resistance of the lacquer surface to scratching.  
      The lacquer formulations according to the invention are particularly suitable for the production of clear lacquers, because significant improvements in the properties, such as an improvement in scratch resistance, can be achieved thereby while transparency and a high degree of gloss are retained. Typical clear lacquer applications in which the lacquer formulations according to the invention lead to particularly marked advantages are, for example, the series and repair lacquering of motor vehicles, and the wear-resistant coating of parquet floors and other floors.  
      In addition, owing to the structural modification, the pyrogenic silicas have a reduced tendency to dust formation, and incorporation into the lacquer binders is simplified.  
      The following two tables contain an overview of the production and the physicochemical data of the comparison silicas and the silicas according to the invention used in the Examples.  
               TABLE 1                          Overview of the preparation of the comparison silicas and of       the silicas according to the invention (Examples)                                         Milling after           Group attached to   Structural   structural       Description   the surface   modification   modification               Comparison silica 1   Hexadecylsilyl   No   —       Comparison silica 2   Octylsilyl   No   —       Comparison silica 3   Dimethylsilyl   No   —       Comparison silica 4   Dimethylsilyl   No   —       Silica 1   Hexadecylsilyl   Yes   Yes       Silica 2   Hexadecylsilyl   Yes   No       Silica 3   Octylsilyl   Yes   Yes       Silica 4   Octylsilyl   Yes   No       Silica 5   Dimethylsilyl   Yes   No       Silica 6   Dimethylsilyl   Yes   No       Silica 7   Dimethylsilyl   Yes   No       Silica 8   Dimethylsilyl   Yes   No                  
 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                   
               
               
                 Physicochemical data of the comparison silicas and of the silicas according to the 
               
               
                 invention (Examples) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Tamped 
                 Loss on 
                   
                   
                   
                   
                 Specific 
               
               
                   
                 density 
                 drying 
                 Ignition 
                   
                 C content 
                 DBP adsorption 
                 BET surface 
               
               
                 Description 
                 [g/l] 
                 [%] 
                 loss [%] 
                 pH value 
                 [%] 
                 [%] 
                 area [m 2 /g] 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparison silica 1 
                 57 
                 0.5 
                 1.8 
                 4.6 
                 1.2 
                 302 
                 195 
               
               
                 Comparison silica 2 
                 51 
                 0.6 
                 6.8 
                 5.3 
                 5.4 
                 236 
                 175 
               
               
                 Comparison silica 3 
                 64 
                 0.1 
                 0.5 
                 4.0 
                 0.8 
                 243 
                 113 
               
               
                 Comparison silica 4 
                 67 
                 0.5 
                 0.6 
                 4.8 
                 1.0 
                 256 
                 165 
               
               
                 Silica 1 
                 123 
                 0.7 
                 2.6 
                 6.0 
                 1.4 
                 208 
                 197 
               
               
                 Silica 2 
                 146 
                 1.1 
                 2.3 
                 5.8 
                 1.4 
                 192 
                 195 
               
               
                 Silica 3 
                 240 
                 0.8 
                 6.7 
                 4.8 
                 5.3 
                  87 
                 169 
               
               
                 Silica 4 
                 322 
                 0.3 
                 6.9 
                 6.0 
                 5.3 
                 not 
                 172 
               
               
                   
                   
                   
                   
                   
                   
                 determinable 
               
               
                 Silica 5 
                 236 
                 0.1 
                 0.6 
                 4.0 
                 0.8 
                 127 
                 115 
               
               
                 Silica 6 
                 204 
                 0.1 
                 0.6 
                 3.9 
                 0.8 
                 137 
                 116 
               
               
                 Silica 7 
                 223 
                 0.3 
                 0.7 
                 4.2 
                 1.0 
                 160 
                 169 
               
               
                 Silica 8 
                 186 
                 0.3 
                 0.7 
                 4.2 
                 1.1 
                 152 
                 171 
               
               
                   
               
            
           
         
       
     
    
    
     EXAMPLE 1  
      A conventional 2-component polyurethane lacquer was used for investigating the improvement in scratch resistance. The recipe for the lacquer and the preparation, including application, thereof are summarised hereinbelow:  
                              Recipe 1:                                 Parts by               weight                                         Material to be ground               Acrylate resin, 50% in xylene/ethyl benzene 3:1   53.3           Butyl acetate 98%   6.7           Xylene   6.7           Silica   5.0           Σ   71.7           Making up into a lacquer           Acrylate resin, 50% in xylene/ethyl benzene 3:1   1.1           Xylene   12.2           Ethoxypropyl acetate   1.5           Butyl glycol acetate   1.5           Butyl acetate 98%   —           Aliphatic polyisocyanate, about 75% in 1-   17.0           methoxypropyl acetate-2/xylene 1:1               Σ   105.0           Binder concentration:     40%           Silica calculated on material   18.8%           to be ground (FK):           Silica calculated on lacquer (total):    5.0%           Silica calculated on lacquer (FK):   12.5%                      
 
 Preparation and Application of the Lacquers 
 
      The binder is mixed with the solvents. For preliminary dispersion, the silica is then incorporated into that mixture using a dissolver (plate Ø 45 mm) and pre-dispersed for 5 minutes at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 minutes at 2500 rpm and 60% pump capacity using glass beads (Ø about 1 mm). The dispersed material is checked using a grindometer, 25 μm, according to DIN ISO 1524. It must be smaller than 10 μm.  
      The ground material is made up into a lacquer according to the recipe, the components being mixed by means of a blade-type stirrer at 2000 rpm. The hardener is incorporated in the same manner.  
      After adjusting the lacquers to spraying viscosity according to DIN 53411, the lacquers are applied by means of spray application to black-lacquered metal sheets, e.g. DT 36 (Q-Panel) (layer thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 hours at room temperature and then for 2 hours in a drying oven at 70° C.  
      Scratching Tests:  
      By means of a scouring- and washing-resistance testing machine (Erichsen, pig-bristle brush), the metal sheets are scoured using a quartz/water suspension (100 g of water +1 g of Marlon A 350, 0.25%+5 g of Sikron F500) and also using a CaCO 3 /water mixture (100 g of water +1 g of Marlon A 350, 0.25%+5 g of Millicarb BG). The gloss before scouring and 10 minutes after scouring is determined using a reflectometer (angle of irradiation 20°).  
      Table 3: next page  
      Because of their substantially lower rheological activity as compared with the comparison silicas, all the silicas according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface. In addition, the silicas according to the invention exhibit a substantial improvement in the scratch resistance of the lacquer surfaces.  
               TABLE 3                       Summary of the relevant lacquer-related properties of the liquid lacquers and of       the applied and dried films                                                                        Comparison           Reference               Reference           S1   S1   S2   without S   Comparison S2   S3   S4   without S               Grindometer value [μm]   &lt;10   &lt;10   &lt;10   &lt;10   &lt;10   &lt;10   &lt;10   /       Viscosity (ground       material) [mPas]        6 rpm   409   210   220   /   5670   935   832   /       60 rpm   407   210   212   /   1260   409   407   /       Viscosity       (lacquer + hardener) [mPas]        6 rpm   120   80   80   60   446   195   175   55       60 rpm   113   82   82   61   194   146   144   64       Flow   poor   o.k.   o.k.   o.k.   orange-peel   o.k.   o.k.   o.k.           fine cracks               effect                 Scratch resistance                                                 20° reflectometer value   81   89.5   89.1   91.3   38   85.5   85.3   91.7       before scratching       Haze before scratching   101   9   12   2   423   18   19   2       40 strokes with Sikron       F 500       residual gloss [%]   83.4   88.5   90.7   51.8   /   80.4   84.3   56.1                   Comparison           Reference               Reference           S3   S5   S6   without S   Comparison S4   S7   S8   without S               Grindometer value [μm]   &lt;10   &lt;10   &lt;10   /   &lt;10   &lt;10   &lt;10   /       Viscosity (ground       material) [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   o.k.   o.k.   o.k.   orange-peel   o.k.   o.k.   o.k.           effect               effect                 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       residual gloss [%]   /   83.7   82.3   56.0   /   74.7   80.4   47.2                  
 
     EXAMPLE 2  
      In this Example, the effect of structural modification has been investigated with reference to a high solids 2K PUR clear lacquer. The recipe for the lacquer and the preparation, including application and testing, thereof are summarised hereinbelow:  
                              Recipe 2:                         Parts by           weight                                         Material to be ground               Acrylic copolymer, modified 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)           Silica   5.0           Σ   79.7           Making up into a lacquer (hardener)           Aliphatic polyisocyanate, 90% in n-butyl   22.3           acetate           Butyl acetate 98%   2.0           Solvesso 100   1.0           Σ   105.0           Binder concentration:   62.8%           Silica calculated on material   11.7%           to be ground (FK):           Silica calculated on lacquer (total):   5.0%           Silica calculated on lacquer (FK):   8.0%                      
 
 Preparation and Application of the Lacquers 
 
      The binder is mixed with the solvents. For preliminary dispersion, the silica is then incorporated into that mixture using a dissolver (plate Ø 45 mm) and pre-dispersed for 5 minutes at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 minutes at 2500 rpm and 60% pump capacity using glass beads (Ø about 1 mm). The dispersed material is checked using a grindometer, 25 μm, according to DIN ISO 1524. It must be smaller than 10 μm.  
      The ground material is made up into a lacquer according to the recipe, the components being mixed by means of a blade-type stirrer at 2000 rpm. The hardener is incorporated in the same manner.  
      After adjusting the lacquers to spraying viscosity according to DIN 53411, the lacquers are applied by means of spray application to black-lacquered metal sheets, e.g. DT 36 (Q-Panel) (layer thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 hours at room temperature and then for 2 hours in a drying oven at 70° C.  
      Scratching Tests:  
      By means of a scouring- and washing-resistance testing machine (Erichsen, pig-bristle brush), the metal sheets are scoured using a quartz/water suspension (100 g of water +1 g of Marlon A 350, 0.25%+5 g of Sikron F500)-. The gloss before scouring and 10 minutes after scouring is determined using a reflectometer (angle of irradiation 20°).  
               TABLE 4                          Summary of the relevant lacquer-related properties of the liquid       lacquers and of the applied and dried films                                                     Comparison           Reference   Comparison           Reference           S1   S1   S2   without S   S4   S7   S8   without S                                                         Grindometer value [μm]   &lt;10   &lt;10   &lt;10   /   &lt;10   &lt;10   &lt;10   /       Viscosity (ground       material) [mPas]        6 rpm   767   376   376   205   6200   1500   541   140       60 rpm   717   359   361   205   2100   900   559   195       Viscosity       (lacquer + hardener) [mPas]        6 rpm   459   279   281   120   3821   1041   497   167       60 rpm   399   272   274   120   1320   666   446   195       Flow   poor (fine   o.k.   o.k.   o.k.   pronounced   o.k.   o.k.   o.k.           “cracks”)               orange peel                 Scratch resistance                                                 20° reflectometer value   82.3   86.5   86.3   88.2   81.0   83.5   82.8   88.0       before scratching       Haze before scratching   3   4   4   2   25   5   6   2       40 strokes with Sikron       F 500       residual gloss [%]   63.2   78.2   75.4   30.2       94.3   93.4   82.0                  
 
      Because of their substantially lower rheological activity as compared with the comparison silicas 1 and 4, the silicas 1+2 and 7+8 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface. In addition, the silicas according to the invention exhibit a substantial improvement in the scratch resistance of the lacquer surface.  
     EXAMPLE 3  
      A conventional 2-component polyurethane lacquer was used for investigating the improvement in scratch resistance. The recipe for the lacquer and the preparation, including application, thereof are summarised hereinbelow:  
                              Recipe 3                         Parts by           weight                                         Material to be ground               Acrylic copolymer, modified with synthetic   43.4           fatty acids, 60% solution           Butyl acetate 98%   17.8           Xylene   3.9           Silica   5.0           Σ   70.7           Making up into a lacquer           Xylene   11.3           Ethoxypropyl acetate   3.4           Butyl glycol acetate   1.6           Aliphatic polyisocyanate, about 75% in 1-   18.6           methoxypropyl acetate-2/xylene 1:1               Σ   105.0           Binder concentration:     40%           Silica calcuated on material   19.2%           to be ground (FK):           Silica calculated on lacquer (total):    5.0%           Silica calculated on lacquer (FK):   12.5%                      
 
 Preparation and Application of the Lacquers 
 
      The binder is mixed with the solvents. For preliminary dispersion, the silica is then incorporated into that mixture using a dissolver (plate Ø 45 mm) and pre-dispersed for 5 minutes at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 minutes at 2500 rpm and 60% pump capacity using glass beads (Ø about 1 mm). The dispersed material is checked using a grindometer, 25 μm, according to DIN ISO 1524. It must be smaller than 10 μm.  
      The ground material is made up into a lacquer according to the recipe, the components being mixed by means of a blade-type stirrer at 2000 rpm. The hardener is stirred in in the same manner.  
      After adjusting the lacquers to spraying viscosity according to DIN 53411, the lacquers are applied by means of spray application to black-lacquered metal sheets, e.g. DT 36 (Q-Panel) (layer thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 hours at room temperature and then for 2 hours in a drying oven at 70° C.  
      Scratching Tests:  
      By means of a scouring- and washing-resistance testing machine (Erichsen, pig-bristle brush), the metal sheets are scoured using a quartz/water suspension (100 g of water +1 g of Marlon A 350, 0.25%+5 g of Sikron F500). The gloss before scouring and 10 minutes after scouring is determined using a reflectometer (angle of irradiation 20°).  
      Table 5: see next page  
      Because of their substantially lower Theological activity as compared with the comparison silicas 1 and 2, 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. In addition, the silicas according to the invention exhibit a substantial improvement in the scratch resistance of the lacquer surface.  
               TABLE 5                          Summary of the relevant lacquer-related properties of the liquid       lacquers and of the applied and dried films                                                                 Reference               Reference           Comparison           without   Comparison           without           silica 1   Silica 1   Silica 2   silica   silica 2   Silica 3   Silica 4   silica                                                         Grindometer value [μm]   &lt;10   &lt;10   &lt;10   /   &lt;10   &lt;10   &lt;10   /       Viscosity (ground       material) [mPas]        6 rpm   409   210   220   /   5670   935   832   /       60 rpm   407   210   212   /   1260   409   407   /       Viscosity       (lacquer + hardener) [mPas]        6 rpm   120   80   80   60   446   195   175   55       60 rpm   113   82   82   61   194   146   144   64       Flow   poor   o.k.   o.k.   o.k.   orange-peel   o.k.   o.k.   o.k.           fine cracks               effect                 Scratch resistance                                                 20° reflectometer value   81   89.5   89.1   91.3   38   85.5   85.3   91.7       before scratching       Haze before scratching   101   9   12   2   423   18   19   2       40 strokes with Sikron       F 500       residual gloss   83.4   88.5   90.7   51.8   /   80.4   84.3   56.1                  
 
     EXAMPLE 4  
      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.  
                              Recipe 4                                 Silicas according           Prior art   to the invention           1)   2)                                             Material to be ground                   Desmophen A 2009/1       190.2           Methoxypropyl acetate:       36.8           Solvesso 100 1:1           Silica       23.0           Σ       250.0           Making up into a lacquer           Desmophen A YEP4-55A,   96.0   —           contains AEROSIL R 972           Ground material   —   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           Addition of hardener           Desmodur N 3390   23.6   23.6           Σ   150.0   150.0                      
 
 Preparation and Application of the Lacquers 
 
      1) The comparison silica 1 is incorporated into the binder according to DE 198 11 790 A1 by means of a jet disperser.  
      2) The binder is mixed with the solvents. For preliminary dispersion, the silica is then incorporated into that mixture using a dissolver (plate Ø 45 mm) and pre-dispersed for 5 minutes at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 minutes at 2500 rpm and 60% pump capacity using glass beads (Ø about 1 mm). The dispersed material is checked using a grindometer, 25 μm. according to DIN ISO 1524. It must be smaller than 10 μm.  
      The ground material is made up into a lacquer corresponding to 1) or 2) according to the recipe, the components being mixed by means of a blade-type stirrer at 2000 rpm. The hardener is stirred in in the same manner.  
      After adjusting the lacquers to spraying viscosity according to DIN 53411, the lacquers are applied by means of spray application to black-lacquered metal sheets, e.g. DT 36 (Q-Panel) (layer thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 hours at room temperature and then for 2 hours in a drying oven at 70° C.  
      Scratching Tests:  
      By means of a scouring- and washing-resistance testing machine (Erichsen, pig-bristle brush), the metal sheets are scoured using a CaCO 3 /water suspension (100 g of water +1 g of Marlon A 350, 0.25%+5 g of CaCO 3  Millicarb). The gloss before scouring and 10 minutes after scouring is determined using a reflectometer (angle of irradiation 20°).  
               TABLE 6                          Summary of the relevant lacquer-related properties       of the liquid lacquers and of the applied and dried films                                         Prior               Reference           art   Silica 1   Silica 5   Silica 8   without S                                             Grindometer value   &lt;10   &lt;10   &lt;10   &lt;10   /       [μm]       Viscosity (ground       material)        6 rpm   58   30   30   26   30       60 rpm   48   43   43   33   40       Surface   orange   o.k.   o.k.   o.k.   o.k.           peel       20° reflectometer   88.0   86.5   90.2   89.6   98.5       value before       scratching       100 strokes with       Millicarb       residual gloss   88.3   96.3   95.4   97.1   59.6                  
 
      It is found that, by the use of the silicas according to the invention, a substantially greater improvement in the residual gloss after scratching of the lacquer surface is achieved than in the case of the prior art. In addition, owing to their low rheological activity, the silicas according to the invention do not cause an orange-peel effect.