Colorless salts of heteropolyacids as charge control substances in toners
The invention relates to heteropolyacid salts of the formula ##STR5## R 1  and R 2  independently of one another stand for hydrogen, chlorine, bromine, hydroxyl, C 1  - to C 4  -alkoxy, nitro or carboxyl, 
     A stands for C 1  - to C 5  -alkylene or --C 6  H 4  --CH 2  -- (m- or p-), 
     m stands for 0 or 1, 
     n stands for 1 or 2, 
     K.sup.⊕ stands for ##STR6## R 3  stands for C 1  - to C 24  -alkyl, carbamoyl-C 1  - to C 2  -alkyl, C 1  - to C 4  -alkoxycarbonyl-C 1  - to C 2  -alkyl, benzyl, cyclohexyl or allyl, 
     R 4  stands for C 1  - to C 4  -alkyl or a single bond linked to D, 
     R 5  stands for C 1  - to C 4  -alkyl, 
     D stands for --CH 2  --, --CH 2  --CO--, --CH 2  --CO--NH-- or --CH 2  --CO--NH--CH 2  --, 
     W stands for ##STR7##  CO or a single bond, Z stands for --CH 2  --, ##STR8##  --O--, --S--, --SO 2  -- or a single bond and X⊖ stands for an anion of a heteropolyacid based on tungsten and/or molybdenum containing phosphorus, silicon, vanadium, cobalt, nickel, manganese, chromium and/or aluminium. Preferably, R 1  and R 2  denote hydrogen. 
     C 1  - to C 5  -alkylene radicals A can be straightchain or branched. Of these, C 2  -C 5  -alkylene radicals and, in particular, the n-propylene radical are preferred. 
     Preferred alkyl radicals R 3  are C 1  - to C 16  -alkyl radicals. 
     Preferably, X.sup.⊖ stands for the anion of a heteropolyacid based on tungsten and/or molybdenum containing phosphorus or silicon. 
     The salts of the formula I are almost colourless and virtually insoluble in water. Their solubility in water at room temperature is preferably less than 0.1% by weight. 
     The invention further relates to toners for developing latent electrostatic images in electrostatic recording and printing processes containing as charge control substance a compound of the formula I. 
     Preferred compounds of the formula I correspond to the formula ##STR9## A 1  stands for C 2  -C 5  -alkylene, K.sup.⊕1 stands for ##STR10## R 6  stands for C 1  -C 16  -alkyl, carbamoylmethyl or benzyl, R 7  stands for methyl or ethyl or a single bond linked to D, 
     R 8  stands for methyl or ethyl, 
     W 1  stands for ##STR11## Z 1  stands for --CH 2  --, ##STR12##  --O-- or --SO 2  -- and X.sup.⊖ stands for the anion of a heteropolyacid based on tungsten and/or molybdenum containing phosphorus or silicon and D, m and n have the same meaning as in formula I. 
     Of particular industrial importance are those compounds of the formula I in which 
     X.sup.⊖ stands for the phosphotungstomolybdate anion. 
     The compounds of the formula I can be prepared by precipitation from aqueous solutions of the colourless cationic substances described in German Offenlegungsschrift No. 3,604,827, European Patent No. 233,544 and U.S. Pat. No. 4,493,883 with a heteropolyacid of the formula 
     
         H.sup.⊕ X.sup.⊖ 
    
     in which 
     X.sup.⊖ has the abovementioned meaning, in the pH range from 2-4 and by isolation of the precipition product of the formula I. 
     Charge-reinforcing, colourless additives for electro-photographic toners--also colourless charge control substances--are already known. They are described in the abovementioned published specifications and patents. 
     Latent electrostatic recorded images are developed by depositing the toner inductively on the electrostatic image. The charge control substances reinforce the cationic charge of the toner. As a result, the image is reinforced and has sharper contours. 
     The resins contained in the toners are known. They are thermoplastic and have a softening temperature between 50° and 130° C., preferably between 65° and 115° C. Examples of such resins include polystyrene, copolymers of styrene with an acrylate or methacrylate, copolymers of styrene with butadiene and/or acrylonitrile, polyacrylates and polymethacrylates, copolymers of an acrylate or methacrylate with vinyl chloride or vinyl acetate, polyvinyl chloride, copolymers of vinyl chloride with vinylidene chloride, copolymers of vinyl chloride with vinyl acetate, polyester resins (U.S. Pat. No. 3,590,000), epoxy resins, polyamides and polyurethanes. 
     In addition to the compounds I and the thermoplastic resins, the toners according to the invention contain known amounts of dye materials and magnetically attractable material. The dye material can consist of an organic dyestuff such as nigrosine, aniline blue, 2,9-dimethylquinacridone, C.I. Disperse Red 15 (=C.I. 60,710), C.I. Solvent Red 19 (=C.I. 26,050), C.I. Pigment Blue 15 (=C.I. 74,160), C.I. Pigment Blue 22 (=C.I. 69,810) and C.I. Solvent Yellow 16 (=C.I. 12,700), or of an inorganic pigment such as soot, red lead, yellow lead oxide or chromium yellow. In general, the amount of the dye material present in the toners does not exceed about 15% by weight. 
     The magnetically attractable material can consist, for example, of iron, nickel, chromium oxide, iron oxide or a ferrite of the general formula MFe 2  O 4  in which M represents a divalent metal such as iron, cobalt, zinc, nickel or manganese. 
     The preparation of the toners containing the compounds I is carried out by conventional processes, for example by mixing the components in a kneader, followed by pulverizing or by melting the thermoplastic resin or a mixture of the thermoplastic resins followed by finely dividing one or more charge control substances of the formula I and the other additives, if they are used, in the melted resin using known mixing and kneading machines for this purpose, followed by cooling the melt to give a solid mass and finally grinding this solid mass to give particles of the desired particle size. It is also possible to suspend the thermoplastic resin and the compound I in a common solvent and to incorporate the other additives in the suspension. In this form, the suspension can be used as liquid toner. However, it is also possible to spray dry the liquid in a manner known per se or to evaporate the solvent(s) and to grind the solid residue to give particles of the desired particle size. 
     According to a modification of this preparation process, the charge control substance of the formula I is not dissolved but finely dispersed in the solution of the thermoplastic resin. 
     The toner formulation thus obtained can be used in a xerographic recorded image process analogously to U.S. Pat. No. 4,265,990. 
     The charge control substances used must meet a variety of requirements. 
     1. Capability to develop the latent electrostatic image to give a strong visible image. 
     2. Easy distribution in the toner formulation and uniform distribution on the image surface to produce a uniform image free of defects and having sharp contours. 
     3. Insensitivity to moisture. 
     4. High thermal stability. 
     5. Resistance to the hot mixture consisting of lead oxide and a vinylidene fluoride/hexafluoropropylene copolymer resin (for example VITON®E-430 from Dupont) which makes it possible to fix the image by means of a hot roll. The coating material must not turn black due to decomposition products. 
     6. Non-toxic. 
     The charge control substances known from the above-mentioned published patents and specifications do not meet all of these requirements. 
     Surprisingly, it has now been found that the substances of the formula I in comparison with the hitherto known cationic compounds mentioned have, in addition to an increase in the depth of shade of the developed image and an improvement in the image sharpness, in particular a lower sensitivity to high humidity and a higher service life of the toner (more than 50,000 copies). 
     Particularly valuable are the phosphotungstomolybdates of the formula I. 
    
    
     EXAMPLE 1 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N,N-trimethylammonium phosphotungstomolybdate 
     (a) Preparation of the phosphotungstomolybdate solution: 
     1290 g of water are initially introduced into a 2 stirring apparatus equipped with reflux condenser and thermometer and 8.5 g of sodium hydroxide (0.2 mol) are added. The solution is heated to 90° C. 461.4 g of ammonium tungstate solution (50% of WO 3 ,=230.7 g, 100% strength, =1 mol), 28.5 g of molybdenum(VI) oxide (about 0.2 mol), 35.7 g of disodium hydrogenphosphate dihydrate, 27.9 g of crude hydrochloric acid (32% strength, =0.24 mol) and 53.6 g of sodium bisulphite solution 40% strength (0.2 mol) are then added in the sequence given and the solution is heated to boiling for 30 minutes (about 102° C.), cooled to 30° C. and the pH is adjusted to 4 with about 6.2 ml of hydrochloric acid (about 32% strength). 
     (b) Preparation of the solution to be precipitated: 
     3500 g of water are initially introduced into a 6 l stirring apparatus equipped with thermometer, dropping funnel and reflux condenser, 234 g of N-(3-naphthalimido-N&#39;-propyl)-N,N,N-trimethylammonium toluenesulphonate (0.5 mol, prepared according to German Offenlegungsschrift No. 3,604,827, Example 22) are added with stirring and the mixture is heated to 50° C. to give a clear solution. The pH is then adjusted to 2 by dropwise addition of about 9 ml of hydrochloric acid. 
     (c) Precipitation: 
     1600 ml of the solution prepared in (a) are run into the solution prepared in (b) at 50°-55° C. over a period of 30-60 minutes with stirring. The reaction product crystallizes and the pH rises to &gt;4. By dropwise addition of about 5.7 ml of hydrochloric acid, the pH is adjusted to 3.3 and stirring of the suspension is continued for 30 minutes at 50°-55° C. The crystalline precipitate is filtered off with suction at 50°-55° C., washed with a total of 5000 ml of water in 5 portions and dried in vacuo at 80° C. Yield: 388 g of the phosphotungstomolybdate mentioned in the title. 
     (d) Preparation of the toner: 
     100 g of styrene/n-butyl methacrylate copolymer (molecular weight: 50,000) and 5 g of the abovementioned phosphotungstomolybdate are evenly mixed in a kneader. After cooling, the resin is powdered in a jet mill to a mean grain fineness of 12μ. 5 g of this toner powder are charged by rotation with 95 g of a carrier material consisting of iron coated with a polymer and the charge is determined by the blow-off method. It amounts to 11.2 μC/g and is still as high as ever after 50,000 copies. 
     EXAMPLE 2 
     N-(3-Phthalimido-N&#39;-propyl)-N,N,N-trimethylammonium phosphotungstomolybdate 
     Example 1 is repeated except that instead of the naphthalimido compound an equivalent amount of N-(3-phthalimido-N&#39;-propyl)-N,N,N-trimethylammonium methosulphate (prepared according to U.S. Pat. No. 4,493,883, Example 1) is used. 
     This gives 319 g of the abovementioned phosphotungstomolybdate. After incorporation in the toner mixture mentioned in Example 1 (instead of the charge control substance used there), a positive charging of 13.0 μC/g is obtained. 
     EXAMPLE 3 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N,N-trimethylammonium silicomolybdate 
     (a) Preparation of the complex solution as the precipitant 
     82.5 g of sodium molybdate×2 H 2  O and 9.9 g of sodium metasilicate×5H 2  O are added to 900 ml of water at 30° C. and the mixture is stirred for 30 minutes at 30° C. 0.9 g of sodium dichromate is then added to the solution and 60 ml of concentrated hydrochloric acid is added dropwise bringing the pH to 2.5-2.6. The solution is stirred for 15 minutes at 30° C. and the pH mentioned, brought to a volume of 1575 ml by adding water, heated to 50° C. and stirring is continued at this temperature for 10 minutes. 
     (b) Preparation of the ROSIN solution 
     2 l of water at 50° C. are initially introduced. 123.7 mg of NALCO-71-D5, 343 mg of AVITEX ML, 16.1 ml of glacial acetic acid and 46.8 g of N-(3-naphthalimido-N&#39;-propyl)-N,N,N-trimethylammonium tosylate (0.1 mol) are added. The mixture is stirred for 5 minutes at 50° C. giving a cloudy solution. 40.3 g of ROSIN amine D acetate are added to the mixture at 50° C., which is stirred for a short time and brought to a volume of 2.6 ml with water. 
     (c) Precipitation 
     2600 ml of ROSIN amine solution, the preparation of which has been described in (b), are heated to 50° C., and 1525 ml of complex solution at 50° C., the preparation of which has been described in (a), are added dropwise. Excess complex solution in the suspension is detected using 0.1% strength quinine×HCl×2H 2  O solution. To this effect, about 5 ml of the suspension are filtered and about 4 ml of quinine solution are added to the filtrate, excess complex solution being indicated by cloudiness in the form of flocs. 
     After the equivalence point is reached, the suspension is filtered off at 50° C., the precipitate is washed with 1 l of warm water at 50° C. and dried in vacuo at 60° C. Yield: 96.5 g of the silicomolybdate mentioned in the title. 
     Incorporation in the toner mixture mentioned in Example 1 (instead of the charge control substance used there) gives a positive charging of 7.8 μC/g. 
     The examples which follow can be prepared analogously, and--incorporated in a toner mixture according to Example 1(d)--have the following triboelectric chargings: 
     EXAMPLE 4 
     N-(3-Phthalimido-N&#39;-propyl)-N,N,N-trimethylammonium silicomolybdate, positive charging: 3.6 μC/g. 
     EXAMPLE 5 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N-dimethyl-N-hexadecylammonium silicomolybdate, positive charging: 3.7 μC/g. 
     EXAMPLE 6 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N-dimethyl-N-octadecylammonium silicomolybdate 
     EXAMPLE 7 
     N-(3-Phthalimido-N&#39;-propyl)-N,N-dimethyl-N-octadecylammonium silicomolybdate 
     EXAMPLE 8 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N-dimethyl-N-hexadecylammonium phosphotungstomolybdate 
     A solution of 274 g (0.47 mol) of N-(3-naphthalimido-N&#39;-propyl)-N,N-dimethyl-N-hexadecylammonium bromide (EP No. 233,544) in 1 l of isopropanol is run into a phosphotungstomolybdate solution prepared according to Example 1(a) with vigorous stirring at 50°-55° C., which leads to the precipitation of the corresponding phosphotungstomolybdate. The suspension is heated to 70°-75° C. for 15 minutes and then cooled. The crystalline precipitate is filtered off with suction, washed with water and dried in vacuo at 80° C. This gives 430 g of the phosphotungstomolybdate mentioned in the title. 
     Positive charging: 17.1 μC/g. 
     After 4 days in 65% humidity (20° C.), the positive charging is still 13.8 μC/g. 
     The examples which follow are prepared analogously to Example 8: 
     EXAMPLE 9 
     N-(3-Phthalimido-N&#39;-propyl)-N,N-dimethyl-N-hexadecylammonium phosphotungstomolybdate 
     EXAMPLE 10 
     N-(3-Naphthalimido-N&#39;-propyl)-N,N-dimethyl-N-octadecylammonium phosphotungstomolybdate 
     EXAMPLE 11 
     N-(3-Phthalimido-N&#39;-propyl)-N,N-dimethyl-N-octadecylammonium phosphotungstomolybdate. 
     
         ______________________________________                                    
Formula                                                                   
 ##STR13##                                                                
Ex-                                                                       
am-                                                                       
ple  Y         R            X.sup.⊖                               
______________________________________                                    
      ##STR14##                                                           
               CH.sub.3     Phosphotungstomolybdate                       
2                                                                         
      ##STR15##                                                           
               &#34;            &#34;                                             
3                                                                         
      ##STR16##                                                           
               &#34;            Silicomolybdate                               
4                                                                         
      ##STR17##                                                           
               &#34;            &#34;                                             
5                                                                         
      ##STR18##                                                           
               CH.sub.3(CH.sub.2).sub.15                                  
                            &#34;                                             
6                                                                         
      ##STR19##                                                           
               CH.sub.3(CH.sub.2).sub.17                                  
                            Silicomolybdate                               
7                                                                         
      ##STR20##                                                           
               &#34;            &#34;                                             
8                                                                         
      ##STR21##                                                           
               CH.sub. 3(CH.sub.2).sub.15                                 
                            Phosphotungstomolybdate                       
9                                                                         
      ##STR22##                                                           
               &#34;            &#34;                                             
10                                                                        
      ##STR23##                                                           
               CH.sub.3(CH.sub.2).sub.17                                  
                            &#34;                                             
11                                                                        
      ##STR24##                                                           
               &#34;            &#34;                                             
______________________________________                                    
 
    
     EXAMPLE 12 
     Methylenebis[(phenylene-4-amidomethyl)-(3-naphthalimido-N&#39;-propyl)-dimethylammonium]chloride phosphotungstomolybdate 
     The preparation of the phosphotungstomolybdate solution is carried out as described in Example 1(d). This solution is slowly run into a solution of 458 g (0.5 mol) of methylenebis[(phenylene-4-amidomethyl)-(3-naphthalimido-N&#39;-propyl)-dimethylammonium]dichloride (prepared according to German Offenlegungsschrift No. 3,604,827, Example (1) in 4.2 l of water and 3.3 ml of concentrated hydrochloric acid at 80°-90° C. The pH is kept constant at 3-4 by the dropwise addition of a further 25 ml of concentrated hydrochloric acid. Stirring of the suspension is then continued for another 30 minutes at 80° C., followed by cooling of the suspension. The crystalline precipitate is filtered off with suction, washed with 4 l of water and dried in vacuo at 80° C. This gives 697 g of the phosphotungstomolybdate mentioned in the title. Under the conditions described in Example 1(d), it shows a positive charging of 15.5 μC/g. ##STR25## 
     Compounds 13 to 21 which follow are prepared analogously to Example 12, Examples 22 to 23 which then follow are prepared analogously to Example 3: 
     
           ##STR26##
  Example Y A .sup.⊕K D W X.sup.⊖
         13
  ##STR27##
  ##STR28##
  ##STR29##
  CH.sub.2CONH
  ##STR30##
  Phosphotungstomolybdate
  14
 ##STR31##
  ##STR32##
  &#34; &#34;
  ##STR33##
  &#34;
  15 &#34; CH.sub.2CH.sub.2
 ##STR34##
  &#34;
  ##STR35##
  &#34;
  16
 ##STR36##
  CH.sub.2CH.sub.2CH.sub.2
  ##STR37##
  &#34;
  ##STR38##
  &#34;
  17
 ##STR39##
  ##STR40##
  ##STR41##
  CH.sub.2CONHCH.sub.2
  ##STR42##
  Phosphotungstomolybdate
  18 &#34; CH.sub.2CH.sub.2
 ##STR43##
  CH.sub.2 CO &#34;
  19 &#34;
 ##STR44##
  ##STR45##
  &#34;
  ##STR46##
  &#34;
  20 &#34; CH.sub.2CH.sub.2
 ##STR47##
  CH.sub.2CO
  ##STR48##
  &#34;
  21
 ##STR49##
  ##STR50##
  ##STR51##
  CH.sub.2CONH
  ##STR52##
  &#34;
  22
 ##STR53##
  CH.sub.2CH.sub.2CH.sub.2
  ##STR54##
  CH.sub.2CONH
  ##STR55##
  Silicomolybdate
  23
 ##STR56##
  &#34; &#34; &#34; &#34; &#34;
 
    
     The compounds which follow are also prepared analogously to Example 12: 
     
         __________________________________________________________________________
 ##STR57##                                                                
X.sup.⊖  = phosphotungstomolybdate                                
Example     S.sup.1                                                       
                   S.sup.2                                                
__________________________________________________________________________
24          Cl     H                                                      
25          Cl     Cl                                                     
26          CH.sub.3O                                                     
                   H                                                      
27          C.sub.2 H.sub.5O                                              
                   H                                                      
28          CH.sub.3O                                                     
                   CH.sub.3O                                              
29          C.sub.2 H.sub.5O                                              
                   C.sub.2 H.sub.5O                                       
30          Br     H                                                      
31          Br     Br                                                     
32          COOH   H                                                      
33          COOH   COOH                                                   
__________________________________________________________________________
 
    
     The compounds which follow are prepared analogously to Example 8: 
     
         __________________________________________________________________________
 ##STR58##                                                                
X.sup.⊖  = phosphotungstomolybdate                                
Example                                                                   
     Y          A          .sup.⊕K.sup.1                              
__________________________________________________________________________
34                                                                        
      ##STR59##                                                           
                 ##STR60##                                                
                            ##STR61##                                     
35                                                                        
      ##STR62## CH.sub.2CH.sub.2                                          
                            ##STR63##                                     
36                                                                        
      ##STR64##                                                           
                 ##STR65##                                                
                            ##STR66##                                     
37                                                                        
      ##STR67##                                                           
                 ##STR68##                                                
                            ##STR69##                                     
38                                                                        
      ##STR70## (CH.sub.2).sub.2                                          
                            ##STR71##                                     
39                                                                        
      ##STR72## (CH.sub.2).sub.3                                          
                            ##STR73##                                     
40                                                                        
      ##STR74## (CH.sub.2).sub.2                                          
                            ##STR75##                                     
41                                                                        
      ##STR76## (CH.sub.2).sub.3                                          
                            ##STR77##                                     
42                                                                        
      ##STR78##                                                           
                 ##STR79##                                                
                            ##STR80##                                     
43                                                                        
      ##STR81## (CH.sub.2).sub.3                                          
                            ##STR82##                                     
__________________________________________________________________________