Patent Publication Number: US-4094698-A

Title: Dye or color developing inorganic pigments

Description:
This invention relates to dye or color developing inorganic pigments and particularly to an improved oxidizing clay produced from bentonite. 
     The use of alumino-silicates in pressure sensitive record materials is well known. Typical of the various patents relating to this subject are, U.S. Pat. Nos. 3,455,721; 2,712,507; 2,730,456; 3,226,252; 3,293,060; and Canadian Pat. No. 780,254. 
     The pressure sensitive record materials are frequently termed &#34;carbonless carbon papers&#34; and are based upon use of oxidizing clays which react with another chemical to produce a colored product. 
     I have found that the oxidizing capacity of clays as well as their reactivity can be markedly enhanced. I have discovered first that by controlling leaching time, the oxidizing capacity of a clay can be varied. Secondly, I have found that the addition of cupric ions in the form of a cupric salt to acid leached bentonites will markedly improve their activity for pressure sensitive record materials and that the amount of cupric ion picked up will vary depending upon leaching time. For example, I have found that the most active clay, as determined by the oxidation of leuco methylene blue, was found to be the 4 hour leached sample, exchanged with cupric ion. The most reactive, non-exchanged clay was found to be the 16 hour leached material. The reactivity of pigment towards aniline (converting aniline to aniline black) was found to be highest on the bentonite which had been acid leached for four hours and exchanged with cupric ion. 
     The subject matter of this invention can, however, best be understood by reference to the following examples: 
    
    
     EXAMPLE I 
     Two hundred grams of bentonite was added to a solution of H 2  SO 4  and water (200 g. H 2  SO 4  in 800 ml. H 2  O). This mixture was then heated at 90° C. for a period of 4 hours, after which the slurry was then filtered. The filter cake was then reslurried and 12 g. of CuCl 2  was added and the slurry was allowed to stir for 15-30 minutes. The Cu(II) saturated clay was then filtered, rinsed, and dried at 105° C. 
     EXAMPLE 2 
     One gram of the material prepared in Example 1 was weighed out in a watchglass and 2.0 ml. of a 1% solution of leuco methylene blue in xylene was added and allowed to stand exposed to the air for 24 hours and the intensity of the color was compared visually among the various samples. The results appear as item 12 on Table I. 
     Other color reactive materials were incorporated into the clay and color intensity was compared using xylene and DBP as solvent. The results appear in Table I. 
     
                                           TABLE I                                 
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                   Acid Activated Bentonite                               
                                 Oxidizing Clay                           
Compound      Solvent                                                     
                   (after 72 hours in dark)                               
                                 Cu(II) Acid Activated Bentonite          
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  m-phenylenediamine                                                      
              xylene                                                      
                   light brown   pink few seconds,                        
                                 dark red 10 minutes                      
              DBP  light brown   dark brown few minutes,                  
                                 black-brown 10 minutes                   
  p-phenylenediamine                                                      
              xylene                                                      
                   green         light green ca.10 minutes                
              DBP  green fringe, light brown                              
                                 dark green ca. 10 minutes                
                   center with black specks                               
                                 dark blue after 72 hours                 
  o-phenylenediamine                                                      
              xylene                                                      
                   light pink    pink, 10 minutes                         
              DBP  light pink, brown center                               
                                 light brown, 10 minutes                  
  p-nitroaniline                                                          
              xylene                                                      
                   light yellow initially                                 
                                 light yellow few seconds                 
                   and 72 hours  and 10 minutes                           
              DBP  light yellow initially                                 
                                 light yellow-green                       
                   and 72 hours  10 minutes                               
  p-aminophenol                                                           
              xylene                                                      
                   very faint yellow                                      
                                 no color                                 
              DBP  pale violet   very pale brown                          
  bis-cyanoethyl aniline                                                  
              xylene                                                      
                   yellow        yellow, 10 minutes                       
              DBP  light blue center,                                     
                                 light green, 10 minutes                  
                   yellow fringe                                          
  m-diethylamino                                                          
              xylene                                                      
                   light brown   gray, 10 minutes                         
  phenol                                                                  
              DBP  gray          slight gray, 10 minutes                  
  aniline          pink          black with green rim                     
                                 ca. 10 minutes                           
  N,N dimethylaniline                                                     
                   no color      light green, 10 minutes                  
                                 (dark blue after 1 week)                 
10.                                                                       
  N,N diethylaniline                                                      
                   no color      dark blue, 10 minutes                    
                                 (dark green after 1 week)                
  m-choroaniline   very pale yellow                                       
                   with pink fringe                                       
                                 dark gray, 10 minutes                    
  leuco methylene blue                                                    
                   dark blue     dark blue, 10 minutes                    
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     The same results are obtained using montmorillonite for bentonite. 
     It can be seen fron the foregoing test data that the materials of this invention using cupric ion exchange produce more intense colors in shorter times than do oxidized clays alone. This is, of course, highly desirable. 
     In the foregoing specification I have illustrated and described certain preferred embodiments and practices of my invention, however, it will be understood that this invention may be otherwise embodied within the scope of the following claims.