Abstract:
The invention relates to dissolving an anionic dye/cationic polymer complex comprising the step of applying to the complex a water-soluble solvent having a dielectric constant from 20 to 43 at standard temperature and pressure.

Description:
FIELD OF THE INVENTION  
       [0001]     In inkjet printing, anionic dye and cationic polymer fixer are often used. Together they form a complex that sometimes must be dissolved and removed from places where it has formed, such as the printhead.  
       BACKGROUND OF THE INVENTION  
       [0002]     Dye-based inkjet inks have become a dominant technology in the inkjet ink arena. However, as many dyes are water-soluble, images printed using many of such dye-based inkjet inks are not as waterfast as may be desirable. The waterfastness and durability of anionic dye-based inkjet ink printed on media has been shown to be enhanced by overprinting or underprinting the printed image with a fixer, preferably from a separate pen. Fixers work to crash the colorants, e.g. anionic dyes, anionic pigments or carboxylated dyes, by changing the pH of the printed inkjet image or by adding salts such as Ca 2+  and Mg 2+  to the printed inkjet image. These fixers had the disadvantages of lacking durability, of causing pen wear and tear and corrosion due to the high salt content and the low pH.  
         [0003]     More recently, cationic polymers have been used in the fixer. Thus, when the cationic polymer and the anionic dye contact one another on a substrate, a reaction between the dye and the polymer creates an image with improved durability and waterfastness. Inkjet images with improved waterfastness and durability can therefore be obtained by underprinting or overprinting a printed inkjet image with a cationic polymeric fixer.  
         [0004]     Thus, anionic inks can be rendered more durable by printing with a fluid containing a cationic polymer. Sometimes during printing, the ink and the polymer fluids come into contact on the surface of one of the printheads, creating a durable complex which is difficult to remove with such servicing fluids as 1,2 hexanediol, glycerol and water.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to a method of dissolving an anionic dye/cationic polymer complex comprising the step of applying to the complex a water-soluble solvent having a dielectric constant from 20 to 43 at standard temperature and pressure.  
         [0006]     The present invention additionally relates to an inkjet printhead cleaning system, wherein an anionic dye/cationic polymer complex on the printhead is removed by applying to the complex on the printhead a water-soluble solvent having a dielectric constant from 20 to 43 at standard temperature and pressure.  
         [0007]     Also, the present invention relates to a method of removing an anionic dye/cationic polymer complex from an inkjet printhead, comprising the step of applying to the complex on the printhead a water-soluble solvent having a dielectric constant from 20 to 43 at standard temperature and pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     For a detailed description of embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0009]      FIGS. 1A and 1B  plot the Fixer/Dye ratio against the % Colorant Soluble for complexes of anionic dyes with cationic fixers in deionized (DI) water.  
         [0010]      FIGS. 2A and 2B  plot the Fixer/Dye ratio against the % Colorant Soluble for complexes of anionic dyes with cationic fixers in 8% 2P.  
         [0011]      FIGS. 3A and 3B  plot the Fixer/Dye ratio against the % Colorant Soluble for complexes of anionic dyes with cationic fixers in 40% 2P.  
         [0012]      FIGS. 4A and 4B  plot the %2P against the % Colorant Soluble with the Fixer/Dye Weight Ratio equal to 1/1.  
     
    
     DETAILED DESCRIPTION  
       [0013]     In order to obtain images that are durable to highlighter smear or water drip and smudge, inks containing anionic dyes are underprinted and/or overprinted with fluids containing cationic polymers. The dye/polymer complex forms a durable mixture. When the ink and the polymer fluid end up on a printhead surface, the mixture is not easily removed by typical water-soluble servicing solvents such as 1,2-hexane diol, glycerol and water.  
       Effective and Ineffective Water Soluble Solvents  
       [0014]     To study which water-soluble servicing solvents are best for removing the ink/polymer complex, the solubility of the precipitate formed between dye and fixers was evaluated in a variety of solvents. Specifically inks and fixers were pipetted onto cellulose TLC plates, dried and developed in a variety of solvents as described in Examples 1 and 2.  
         [0015]     As shown in the Examples below, it was found that the dye/fixer complex precipitate is immobile in water, dipropylene glycol, 1,2 hexanediol, and 1,6-hexanediol indicating a lack of solubility in these solvents. In 2-amino-2-methyl propanol and 1,2 propanediol, it was found that some, but not all, of the complex precipitates are mobile, indicating that at least some of the complex precipitates are soluble in these solvents.  
         [0016]     Also in the Examples, it is seen that all of the complex precipitates are mobile and therefore solubilized in 2-pyrrolidone, diethylene glycol, 1,2-propanediol, tetraethylene glycol, 1-methyl-2-pyrrolidone and n,n-dimethyl propionamide.  
         [0017]     It has been found that 2-pyrrolidone is very effective at dissolving the dye-polymer complex. Furthermore, mixtures of 2-pyrrolidone and water are capable of dissolving the complex and are compatible with the printhead materials. The weight percentage ratio of 2-pyrrolidone to water can be from 100:0 to 20:80. In a preferred embodiment, the weight percentage ratio is 40:60.  
         [0018]     It has also been found that 2-pyrrolidone inhibits precipitation of the anionic dye/cationic polymeric fixer complex as manifested by a greater equilibrium solubility and a slower precipitation rate. No precipitation was observed in systems containing less than 45 weight % 2-pyrrolidone.  
         [0019]     Dielectric constants at standard temperature and pressure for most of the water-soluble servicing solvents tested have been obtained at standard temperature and pressure. Generally, it has been found that solvents that are “effective” at solubilizing anionic dye/cationic fixer complexes have dielectric constants that fall within the range of from approximately 20 to approximately 43 at standard temperature and pressure. In contrast, it has been found that solvents that are “ineffective” at solubilizing anionic dye/cationic fixer complexes have dielectric constants that fall outside the above range of 20-43 at standard temperature and pressure. Comparative tables are shown below:  
                                                             Dielectric Constants at STP                                        “Effective” Solvents               2-pyrrolidone   28.18           Diethylene glycol   31.82           1,2-propanediol   32           Tetraethylene glycol   20.44           1-methyl-2-pyrrolidone   32.2           N,n-dimethylpropionamide   34.6           Triethylene glycol   23.7           1,5-pentanediol   26.2           1,4-pentanediol   31.9           “Ineffective” Solvents           Water   78           Cyclohexanone   16.1           Butoxyethanol   9.43           Diacetone alcohol   18.2           1-pentanol   16.9           1,2-pentanediol   17.3           Glycerol   46.5                      
 
       Anionic Dyes Forming a Complex with Fixer  
       [0020]     Non-limiting examples of anionic dyes that are effective with this invention are: direct black dyes, such as Direct Black 168 (DB168), Direct Black 19 (DB19) or variants of Fast Black 2; phthalocyanine cyan dyes, such as ProJet Cyan 485; acid cyan dyes, such as Acid Blue 9 (AB9); mixtures of acid cyan and phthalocyanine cyan, such as AB9 and ProJet Cyan 485 (PJ485); gamma acid magenta dyes, such as Magenta 377 (M377); H-acid magenta dyes, such as ProJet Magenta 364 (M364); Xanthene magenta dyes, such as Acid Red 289 (AR289); mixtures of H-acid magenta and Xanthene magenta dyes, such as mixtures of ProJet Magenta 364 and AR289; direct yellow dyes, such as Direct Yellow 132 (DY132); acid yellow dyes such as Acid Yellow 23 (AY23); and mixtures of direct yellow dyes and acid yellow dyes, such as mixtures of DY132 and AY23.  
       Cationic Polymeric Fixers Forming a Complex with Anionic Dyes  
       [0021]     In a preferred embodiment of the fixer, polyguanidines and polyethyleneimines, have been found to be effective cationic polymers for this purpose.  
         [0022]     In a more preferred embodiment, the cationic polymers are polymonoguanidines, preferably poly (C 3-18 -hydrocarbyl monoguanidines).  
         [0023]     In a most preferred embodiment, the poly(C 3-18 -hydrocarbyl monoguanidines) comprise groups selected from the group consisting of Formula (1) and Formula (2) or salts thereof:  
                         
 
 wherein: 
 
         [0024]     each m is independently 0 or 1;  
         [0025]     each Y is independently a C 2-18 -hydrocarbyl group;  
         [0026]     A and B are hydrocarbyl groups which together comprise a total of 3 to 18 carbon atoms; and  
         [0000]     each R is independently hydrogen, alkyl, alkoxy, substituted alkyl or substituted alkoxy.  
         [0027]     In another most preferred embodiment, the poly(C 3-18 -hydrocarbyl monoguanidines) comprise at least one group of Formula (3) or salts thereof:  
                         
 
 wherein: 
 
         [0028]     n is from 2 to 50.  
       EXAMPLES  
     Example 1  
       [0029]     For each of Runs 1, 2 and 3, 1 microliter anionic dye-based ink and cationic polymeric fixer is pipetted in the order Fixer/Color/Fixer for each of colors black, cyan, magenta and yellow onto cellulose thin layer chromatography (TLC) plates. The three TLC plates were dried for 30 minutes at ambient temperature. The TLC plates were developed in solvent at 55° C.  
         [0030]     The table below summarizes the mobility of Run 1, Run 2, and Run 3 dye/fixer complex/precipitates in various water-based servicing solvents.  
                                               TABLE 1                       Run/           Dipropylene   1,2       Tetraethylene   Diethylene           Ink   Dye   Fixer   glycol   Hexanediol   Water   glycol   glycol   2-pyrrolidone                   Run   Direct Black   Poly-alkyl   Immobile   Immobile   Immobile   Slight   Slight   Moderate       1/K       amine       Run   Phthalocyanine   Poly-alkyl   Immobile   Immobile   Immobile   Immobile   Immobile   Slight       1/C   cyan   amine       Run   Gamma acid   Poly-alkyl   Immobile   Immobile   Immobile   Immobile   Immobile   Completely       1/M   magenta   amine       Run   Direct yellow   Poly-alkyl   Immobile   Immobile   Immobile   Slight   Moderate   Completely       1/Y       amine       Run   Direct Black   Poly-guanidine   Immobile   Immobile   Immobile   Slight   Slight   Moderate       2/K   (different from           1/K)       Run   Phthalocyanine   Poly-guanidine   Immobile   Immobile   Immobile   Immobile   Immobile   Slight       2/C   cyan       Run   H-acid   Poly-guanidine   Immobile   Immobile   Very   Slight   Moderate   Moderate       2/M   magenta               slight       Run   Direct yellow   Poly-guanidine   Immobile   Immobile   Immobile   Slight   Moderate   Completely       2/Y       Run   Direct Black   Poly-guanidine   Immobile   Immobile   Immobile   Slight   Slight   Moderate       3/K   (different from           1/K)       Run   Mixture of acid   Poly-guanidine   Immobile   Immobile   Immobile   Slight   Slight   Moderate       3/C   cyan and           phthalocyanine           cyan       Run   Mixture of H-   Poly-guanidine   Very slight   Very slight   Very   Slight   Moderate   Moderate       3/M   acid magenta               slight           and xanthene           magenta       Run   Mixture of   Poly-guanidine   Immobile   Immobile   Very   Slight   Moderate   Completely       3/Y   direct yellow               slight           and acid           yellow                  
 
       Example 2  
       [0031]     For each of Runs 4, 5 and 6, 1 microliter anionic dye-based ink and cationic polymeric fixer is pipetted in the order Fixer/Color/Fixer for each of colors black, cyan, magenta and yellow onto cellulose TLC plates. The three TLC plates were dried for 30 minutes at ambient temperature. The TLC plates were developed in various water-based servicing solvent at 55° C.  
         [0032]     The table below summarizes the mobility of Run 3, Run 4, and Run 5 dye/fixer complex/precipitates in the various solvents.  
                                           TABLE 2                                               2-amino-2-                                   methyl       Fixer/               Butoxy-   Diacetone   propanol   1,2-       Ink   Dye   Fixer   Cyclohexanone   ethanol   alcohol   (AMP)   propanediol                   Run   Direct   Polyalkyl   Immobile   Immobile   Immobile   Moderate   Slight       4/K   Black   amine       Run   Phthalocyanine   Polyalkyl   Immobile   Immobile   Immobile   Completely   Immobile       4/C   cyan   amine       Run   Gamma   Polyalkyl   Immobile   Immobile   Immobile   Moderate   Very       4/M   acid   amine                   slight           magenta       Run   Direct   Polyalkyl   Immobile   Immobile   Immobile   Completely   Slight       4/Y   yellow   amine       Run   Direct   Poly-   Immobile   Immobile   Immobile   Immobile   Slight       5/K   Black   guanidine           (different           from 1/K)       Run   Phthalocyanine   Poly-   Immobile   Immobile   Immobile   Immobile   Very       5/C   cyan   guanidine                   slight       Run   H-acid   Poly-   Immobile   Immobile   Immobile   Immobile   Moderate       5/M   magenta   guanidine       Run   Direct   Poly-   Immobile   Immobile   Immobile   Slight   Moderate       5/Y   yellow   guanidine       Run   Direct   Poly-   Immobile   Immobile   Immobile   Slight   Slight       6/K   Black   guanidine           (different           from 1/K)       Run   Mixture   Poly-   Immobile   Immobile   Immobile   Slight   Moderate       6/C   of acid   guanidine           cyan and           phthalocyanine           cyan       Run   Mixture   Poly-   Very   Very   Very slight   Slight   Moderate       6/M   of H-acid   guanidine   slight   slight           magenta           and           xanthene           magenta       Run   Mixture   Poly-   Immobile   Immobile   Immobile   Slight   Moderate       6/Y   of direct   guanidine           yellow           and acid           yellow                  
 
       Example 3  
       [0033]     A stock solution of ink containing anionic dye, Acid Blue 9(AB9), and fixer containing cationic polymer, Polyguanidine, are diluted with ratios of water and 2-P. For steady state solubility, equal volumes of the ink solutions and the fixer solutions are mixed. Solubility is determined by examining the mixture for precipitate after 1-day at ambient conditions  
         [0034]     Stock solutions are listed in Table 3A below:  
                                                       TABLE 3A                           Ink A   FIXER B            Components   % active   Components   % active                    Dye AB-9   6   Polyguanidine   4       Bis(2-   0.90   1,2-Hexanediol   7.5       ethylhexyl)sulfosuccinate       Fluorocarbon surfactant   0.30   2,3,4,5-   7.5               Tetrahydrothiophene-               1,1-dioxide       4-Octylphenol   0.4   Fluorocarbon   0.3       Polyethoxylate       surfactant       Na 2 EDTA   0.2   POE (4) lauryl ether   0.4       MOPS   0.4   B-Alanine   0.2               Na 2 EDTA   0.05                  
 
         [0035]     Table 3B below summarizes the solubility of Ink A and the Polyguanidine Fixer at various water/2P ratios. The concentration of 2-pyrrolidone has a strong effect on the interaction of the dye and fixer. Increasing the concentration of 2-P increases the solubility of the dye/fixer complex.  
                                                                                 Weight %   Weight %       ppt with   ppt with       Sample   (Dye)   water   Weight % 2P   Sample X   Sample Y               1   0.60   90   0   Yes   Yes       2   0.60   80   20   Yes   Yes       3   0.60   60   40   Yes   None       4   0.60   40   60   Yes   None       5   0.60   20   80   Yes   None       6   0.60   0   90   None   None                            Weight %   Weight %               Sample   (Fixer)   water   Weight % 2P                       X   2   98    0           Y   2   48   50                      
 
 In &gt;45% 2-P, Ink A/Polyguanidine Fixer complex does not precipitate. 
 
       Example 4  
       [0036]     The solubility of the DB168 Dye/Polyguanidine Fixer complex was tested in various solvents. Dye and fixer were added to aqueous cosolvent solutions to attain a concentration of 9.4 g/L DB168 Dye and 9.4 g/L Polyguanidine Fixer—the resulting mixture partitions into a liquid supernatant phase and a solid precipitate phase. Entries in Table 4 below represent the % of the total colorant that goes into the supernatant phase (100% would represent complete dye/fixer solubility in a solvent). The data shows that DB 168 Dye/Polyguanidine Fixer is the most soluble in 88% 2P—and that the reproducibility of this measurement is good (comparing ‘2P’ and replicate ‘2P-2’). It also shows that the relative ability of solvents to dissolve the dye/fixer complex changes as water is taken out of the system. For example, at 44% aq TMS is a better solvent for DB 168 Dye/Polyguanidine Fixer than 44% aqueous TEG, but 88% aqueous TEG is a better solvent than 88% aqueous TMS.  
                                                                     44% solvent   88% solvent                                        2-pyrrolidone   0.28   34.27           2-pyrrolidone (rep 2)   0.27   34.87           1,2-hexanediol   0.11   0.18           Tetramethylene sulfone   0.38   7.63           1-methyl-2-pyrrolidone   0.45   30.54           1,2-propanediol   0.00   0.67           Diethylene glycol   0.00   3.47           Tetraethylene glycol   0.00   8.86           Glycerol   0.00   0.00           Ethylene glycol   0.00   0.40           Tetrahydrofuran   1.32   15.45           n,n-dimethylpropionamide   0.76   20.30                      
 
       Example 5  
       [0037]     Fixer-dye mixtures containing 0, 8, and 40% 2P were made by mixing 3% of dye in water or in 40% 2P with 3% of FA11/5 (polymonoguanidine) or FA2 (polybiguanadine) in water, pH adjusted to 4. Higher 2P-containing solutions (40% 2P in mixture) were prepared by mixing 3% dye in water with 6% FA11/5 or FA2 (in water, pH adjusted to 4) As dyes, PJ485, AB9, M364, AR289, DY132, AY23-TMA, DB19 and DB168 were used in this study. The samples were centrifuged.  
         [0038]     The “Colorant Soluble” was plotted in  FIGS. 1, 2 ,  3  in DI water, 8% 2P and 40% 2P, respectively, where “% Colorant Soluble” is defined as absorbance at λ max  (w/o fixer). For DB168 and DB19, the minimum of “% Colorant Soluble” was reached at ˜0.5 fixer/dye ratio. There was virtually no difference observed in “% Colorant Soluble” of the fixer-black dye complexes using FA2 or FA11/5.  
         [0039]     Regardless of fixer type or % 2P present in the solution, fixer-DB168 complex is the least soluble. Fixer-DB19 complex was more soluble than fixer-DB168 complex but still less soluble than most of the fixer-color dye complexes.  
         [0040]     As shown in  FIG. 4 , “% Colorant Soluble” increased with increasing % 2P. The amount of colorant soluble increased by roughly one order of magnitude from 0 to 40% 2P for most dyes including DB19. “% Colorant Soluble” of fixer-DB168 appeared to be insensitive to 2P content in this region.  
       Example 6  
       [0041]     As in Example 1, 1 microliter anionic dye-based ink and cationic polymeric fixer is pipetted in the order Fixer/Color/Fixer for each of colors black, cyan, magenta and yellow onto cellulose thin layer chromatography (TLC) plates. The TLC plates were dried for 30 minutes at ambient temperature. The TLC plate was developed in solvent at 55° C.  
         [0042]     The table below summarizes the mobility of Run 2 dye/fixer complex/precipitates in various additional water-based servicing solvents. The dielectric constants at standard temperature and pressure are given for each of the solvents. Both “ineffective” and “effective” solvents are included on the list. The more “effective” solvents tend to occur within the range of 20-41 dielectric constant at standard temperature and pressure.  
                                                                             TABLE 6                       Run/               1,2-   Triethylene   1,5-   1,4-   Ethylene       Ink   Dye   Fixer   1-pentanol   pentanediol   glycol   pentanediol   butanediol   glycol                   Run   Direct   Poly-   Immobile   Slight   Slight   Immobile   Very slight   Slight       2/K   Black   guanidine       Run   Phthalocyanine   Poly-   Immobile   Very slight   Slight   Slight   Slight   Moderate       2/C   cyan   guanidine       Run   H-acid   Poly-   Immobile   Very slight   Slight   Slight   Slight   Moderate       2/M   magenta   guanidine       Run   Direct   Poly-   Immobile   Immobile   Slight   Very slight   Slight   Moderate       2/Y   yellow   guanidine            Dielectric Constants at STP   16.9   17.3   23.7   26.2   31.9   41.4                  
 
         [0043]     Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.