Ink additives for improved ink-jet performance

Abstract

Oxo anions (both singly and multiply charged), such as phosphates, polyphosphates, and phosphate esters, serve as additives, and in the case of cationic dyes, may serve as replacement counter-ions, for use in thermal ink-jet inks to reduce kogation significantly. The addition of such additive essentially eliminates kogation for the life of ink pens. Further, such additives will prevent kogation for inks containing dyes with negatively-charged water-solubilizing groups, such as sulfonate and carboxylate.

1. An ink for thermal ink-jet printing comprising a vehicle and an anionic dye, characterized by the presence of at least one oxo anion therein, said at least one oxo anion selected from the group consisting of phosphates, polyphosphates, phosphate esters, arsenate, molybdate, sulfate, sulfite, and oxalate and present in an amount ranging from about 9 mg/L to 14 wt%,
   wherein said ink further comprises ammonium  ( NH   4   + )  cations, and    
   wherein said at least one oxo anion is selected from monobasic phosphate  ( H   2 PO 4   − ) , dibasic phosphate  ( HPO   4   2− ) , or diphosphate  ( P   2 O 7   4− )  anions or combinations thereof .  
 
     
     
       2. The ink of  claim 1  wherein said vehicle comprises at least one glycol and the balance water. 
     
     
       3. The ink of  claim 2  wherein said vehicle comprises up to about 10 wt% diethylene glycol and the balance water. 
     
     
       4. The ink of  claim 1  wherein said vehicle comprises at least one pyrrolidone and the balance water. 
     
     
       5. The ink of  claim 4  wherein said vehicle comprises up to about 10 wt% 2-pyrrolidone and the balance water. 
     
     
       6. The ink of  claim 1  comprising about 1 to 12 wt% of said dye. 
     
     
       7. The ink of  claim 1  wherein said phosphate is in the form of dibasic, monobasic, or diphosphate anions. 
     
     
       8. The ink of  claim 1  wherein said phosphate ester is selected from the group consisting of mono-organo and di-organo phosphate esters. 
     
     
       9. The ink of  claim 1  wherein said at least one oxo anion is present in an amount ranging from about 0.01 to 1 wt%. 
     
     
       10. An ink for thermal ink-jet printing comprising a vehicle and an anionic dye, characterized by the presence of anions selected from the group consisting of phosphates, polyphosphates, and phosphate esters, said anions present in an amount ranging from about 9 mg/L to 14 wt%,
   wherein said ink further comprises ammonium  ( NH   4   + )  cations,    
   wherein said anions are selected from monobasic phosphate  ( H   2 PO 4   − ) , dibasic phosphate  ( HPO   4   2− ) , or diphosphate  ( P   2 O 7   4− )  anions or combinations thereof, and    
   wherein the ink provides substantially constant drop volume through  5  million resistor firings .  
 
     
     
       11. The ink of  claim 10  wherein said vehicle comprises at least one glycol and the balance water. 
     
     
       12. The ink of  claim 11  wherein said vehicle comprises up to about 10 wt% diethylene glycol and the balance water. 
     
     
       13. The ink of  claim 10  wherein said vehicle comprises at least one pyrrolidone and the balance water. 
     
     
       14. The ink of  claim 13  wherein said vehicle comprises up to about 10 wt% 2-pyrrolidone and the balance water. 
     
     
       15. The ink of  claim 10  comprising about 1 to 12 wt% of said dye. 
     
     
       16. The ink of  claim 18  wherein said phosphate anion is in the form of dibasic, monobasic, or diphosphate anions. 
     
     
       17. The ink of  claim 10  wherein said phosphate ester is selected from the group consisting of mono-organo and di-organo phosphate esters. 
     
     
       18. The ink of  claim 12  wherein said phosphate anion is present in an amount ranging from about 0.01 to 1 wt%. 
     
     
       19. A method of reducing kogation in an ink used in thermal ink-jet printers, said ink comprising a vehicle and an anionic dye, characterized in that at least one salt containing at least one oxo anion is added thereto, said at least one oxo anion selected from the group consisting of phosphates, polyphosphates, phosphate esters, arsenate, molybdate, sulfate, sulfite, and oxalate and present in an amount ranging from about 9 mg/L to 14 wt%,
   wherein said ink further comprises ammonium  ( NH   4   + )  cations, and    
   wherein said at least one oxo anion is selected from monobasic phosphate  ( H   2 PO 4   − ) , dibasic phosphate  ( HPO   4   2− ) , or diphosphate  ( P   2 O 7   4− )  anions or combinations thereof .  
 
     
     
       20. The method of  claim 19  wherein said at least one oxo anion is added in an amount of 0.01 to 1 wt%. 
     
     
       21. The method of  claim 19  wherein said phosphate is in the form of dibasic, monobasic, or diphosphate anions. 
     
     
       22. The method of  claim 19  wherein said phosphate ester is selected from the group consisting of mono-organic and di-organic phosphate esters. 
     
     
       23. A method of reducing kogation in an ink used in thermal ink-jet printers, said ink comprising a vehicle and an anionic dye, characterized in that from about 9 mg/L to 14 wt% of a salt containing an anion selected from the group consisting of phosphate, polyphosphates, and phosphate esters is added thereto,
   wherein said ink further comprises ammonium  ( NH   4   + )  cations, and    
   wherein said anion is selected from monobasic phosphate  ( H   2 PO 4   − ) , dibasic phosphate  ( HPO   4   2− ) , or diphosphate  ( P   2 O 7   4− )  anions or combinations thereof, and    
   wherein the ink provides substantially constant drop volume through  5  million resistor firings .  
 
     
     
       24. The method of  claim 23  wherein said phosphate is in the form of dibasic, monobasic, or diphosphate anions. 
     
     
       25. The method of  claim 23  wherein said phosphate is in the form of dibasic, monobasic, or diphosphate anions. 
     
     
       26. The method of  claim 23  wherein said phosphate ester is selected from the group consisting of mono-organic and di-organic diphosphate esters. 
     
     
       27. An ink for thermal ink-jet printing comprising a vehicle and an anionic dye, characterized by the presence of at least one oxo anion therein, said at least one oxo anion selected from the group consisting of phosphates, polyphosphates, phosphate esters, arsenate, molybdate, sulfate, sulfite, and oxalate and present in an amount ranging from about  9  mg/L to  14  wt% , wherein said ink further comprises ammonium  ( NH   4   + )  cations.