A METHOD OF REDUCING BLEED AND AN INK COMPOSITION

AND SYSTEM OF PRINTING RELATED THERETO

BACKGROUND

Prior solutions to bleed problems have included the use of slower throughput, reduced drop weight, increased number of swaths to print an area, or specific changes in the ink compositions. These included reducing the wetting of the ink compositions, or carefully managing surface tension mismatches between adjacent inks, both of which can reduce the range of media that produces quality images in the printing system. Other prior solutions have been inks formulated to react with each other to produce rapid precipitation of the colorant (such as anionic with cationic, high and low pH, salt destabilization, etc.). These approaches typically have increased reliability issues (inks reacting on the print head, nozzle clogging due to the effect of exposure to air on ink in the printhead, etc.) or materials compatibility challenges. All of the above reactive ink approaches generally lead to poor gloss due to rapid precipitation of the colorants. Finally, using specific media coatings that rapidly immobilize the drop can control bleed. However, using media to solve the bleed problem may result in more expense and may limit the number of different types of media that can be used with the ink.

BRIEF DESCRIPTION OF THE DRAWINGS Features and advantages of embodiments of the present disclosure will become apparent by reference to the following detailed description and drawings, in which:

Figure 1 is a three-dimensional bar graph according to an embodiment of the present disclosure, the graph comparing bleed, dot size difference and viscosity buildup difference;

Figure 2 is a bar graph according to an embodiment of the present disclosure, the graph comparing various inks according to their weight average diameter difference at three different week intervals;

Figure 3 is a bar graph according to an embodiment of the present disclosure, the graph showing viscosity buildup increase in centipoise per weight percent of water removed; Figure 4 is a bar graph according to an embodiment of the present disclosure, the graph comparing the extent of bleed between magenta and cyan inks;

Figure 5 is a bar graph according to an embodiment of the present disclosure, the graph comparing the extent of bleed between magenta and black inks;

Figure 6 is a graph according to an embodiment of the present disclosure, the graph plotting line widening (x axis) vs. viscosity buildup (y axis);

Figure 7 is a graph according to an embodiment of the present disclosure, the graph plotting line widening (x axis) vs. dot size difference (y axis); and Figure 8 is a bar graph according to an embodiment of the present disclosure, the graph plotting viscosity buildup increase (y axis) vs. line widening (x axis) between three magenta ink samples printed against yellow ink.

DETAILED DESCRIPTION Bleed on a non-porous media is a significant problem since there is little to no absorption of the ink vehicle into the media. Bleed reduces the image quality, reduces sharpness of image elements, makes the image more grainy and makes it difficult to control color reproduction in the final printing system.

The present disclosure discloses a method to reduce bleeding and edge roughness, while maintaining gloss, media independence, throughput and

printhead reliability. This method is achieved by changing the aggregation behavior of the ink during drying primarily between inks printed next to each other. Aggregation behavior can be changed by changing one or more formulation variables, such as pigment type, dispersion type, and to a lesser extent vehicle composition. The resulting aggregation behavior changes in the ink lead to different rates of viscosity buildup. For example, if viscosity buildup is increased to at least about 0.10 centipoise (Cps) per % loss in water and, in another embodiment, from 0.2 to 0.3 Cps per % loss in water, this reduces bleed between the two inks. One way of measuring such an increase in viscosity buildup is by measuring the viscosity of inks at different solids content (water-depleted ink vs. normal ink).

Another method to achieve a viscosity buildup is by adding phosphate-ester based dispersant to the ink composition in an amount such that the viscosity buildup of the ink increases in a range from about 0.2 to about 1.8 centipoise. Such a viscosity buildup increase can be achieved by adding a phosphate ester dispersant in a range from about 0.4 weight percent to about 0.8 weight percent. Non-limiting examples of such dispersant include materials such as polyoxyethylene (3) oleyl alcohol phosphate, hereinafter "oleth-3-phosphate", available from Croda, Inc. under the trade name CRODAFOS N3® acid. Other phosphate ester-containing dispersants that might be used include CRODAFOS N 10® acid (polyoxyethylene (10) oleyl alcohol phosphate), hereinafter "oleth-10" phosphate; and CRODAFOS CAP®, PPG-10, hereinafter "cetyl ether phosphate". Besides giving improvement in overall image quality, primarily in bleed and edge roughness, the presently disclosed method also results in the maintaining and/or improvement of gloss, media independence, throughput, and print head reliability. The method also reduces the complexity of the overall ink formulation by avoiding the addition of added salt and other reactive components. The process of ink manufacturing is also simplified when the use of reactive components is avoided.

Pigmented magenta inks with different dispersants were prepared so that the surfactants' effects on stability, bleed, and viscosity buildup could be studied. The results of these studies showed that inks containing polyglycol ether non-ionic surfactants (Tergitol® 15s-9 and 15s-7) stabilize the inks and prevent viscosity buildup, which in turn causes an ink drop of a respective ink to bleed more into its respective neighboring ink drop.

It was also found that the polyglycol ether non-ionic surfactants (Tergitol® 15s-9 and 15s-7) negatively impacted bleed between pigmented magenta ink and pigmented black ink as well as between pigmented magenta ink and pigmented black ink. One of the reasons bleed is negatively impacted by the surfactant is because the ink spread is changed. Viscosity buildup is also changed as water is lost due to drying.

In general, the driving forces controlling bleed between two given inks A and B are dynamic surface tension differences, media wetting differences (Dot Spread), and viscosity buildup differences due to drying (Viscosity buildup per % water loss) or by the presence of viscosity buildup enhancing agents such as dispersants. Bleed was tested and measured by the extent of line widening or wicking between adjacent colors. Viscosity difference at any time t was measured by the following equation : (Vise) _A ,t -(Vise) _B ,t ={( Vise) _A ,t=o + d(Visc)/ dW X ( δ W)}

- {(Visc) _B ,t=o +d(Visc)/dW X (δ W)} (1 )

Where : Vise : Viscosity of ink; W : Water ( or solvent) d(Visc)/dW : Ink Viscosity buildup per percent of water( Solvent) loss. δ W : Water ( or solvent) loss between time t=0 and t=t.

It has thus been found that, in general, surfactants can hurt bleed. This may especially be true of polyglycol ether non-ionic surfactants (e.g., Tergitol®). The positive side of the addition of such surfactants is that they improve the colloidal stability of the ink by preventing particle size increase and viscosity growth. At the level of surfactant loading in the present disclosure, surfactants generally do not

have much of an impact on jetting performance and puddling. Based on the results of the data in this disclosure, if surfactants are needed for magenta stability, adjacent colors can be generally reformulated accordingly to compensate, for instance, with regard to their surfactant load to compensate for bleed. In one embodiment, the present disclosure discloses a method of reducing bleed in adjacent ink drops by changing the viscosity build up of the bleeding ink from at least 0.1 cps/ % water loss while maintaining the viscosity buildup of the other ink constant and/or by adding phosphate ester surfactant in at least one of the two adjacent inks to achieve viscosity buildup in a range from about 0.2 to about 1.8 centipoise. In this case all the bleeding inks at initial time have same viscosity and the drop weights were the same. All the inks have water and high boiling cosolvent as the vehicle. Water is typically 60-70% of the ink, cosolvent is 5 to 30% and the rest are ink solids. During drying, first water is removed and then the cosolvents (with sufficient heat). Therefore viscosification happens primarily in inks due to water removal.

Therefore Equation 1 ( viscosity difference between bleeding ink and the other ink) becomes :

(Vise) A,t - (Visc)B,t = {-BflseW-o (Visc)^} ^Constant + {{d(Visc)/dw} _A - {d (Visc)/d w} _B } ^Constant X AW (Constant due to same drop size and drying condition) or

Bleed ~ ( Visc) _A ,t -(Visc) _B ,t ~ {d(Visc)/dw} _A (2) d(Visc)/dw is estimated using two data points, water-depleted ink and non- depleted ink and d(Visc)/dW estimated as the following: d(Visc)/dW ~ {(Vise) water-depieted ink -(Vise) ink}/ Water Removed which is proportional to :

{(Vise) water- depleted ink -(Vise) ink}/ Solids change in the ink. d(Visc)/ dW would typically be a non-linear function, but in the case of dilute systems this can be assumed to be linear. Table 3 below will show that in the

region where analysis is done, the solids are sufficiently low that linearity can be assumed.

According to an embodiment, an effective way to reduce bleed in adjacent inkjet ink drops is by creating viscosity buildup in inks printed next to each other. In particular, this is achieved by either making one or both of the inks printed next to each other have a viscosity per percent water loss from at least about 0.1 centipoise per percent water loss and/or by adding phosphate ester surfactant in at least one of the two adjacent inks to achieve viscosity buildup in a range from about 0.2 to about 1.8 centipoise. A related embodiment discloses an inkjet ink composition including water, a colorant (the term colorant being defined to encompass pigments and/or dyes), and a dispersant and/or a surfactant; but does not include polyglycol ether non-ionic surfactants. When this ink composition is printed next to another ink, a viscosity buildup is achieved by making one or both of the inks printed next to each other have a viscosity per percent water loss from at least about 0.1 centipoise per percent water loss and/or viscosity buildup in a range from about 0.2 to about 1.8 centipoise in at least one of the inks by at least one of the inks further comprising phosphate ester surfactant .

In yet another embodiment, there is disclosed an inkjet printing system for providing bleed on a medium, including a first drop-on-demand fluid ejector fluidically coupled to a first reservoir, the first reservoir containing an inkjet ink composition including water, a colorant, and a dispersant and/or a surfactant. The ink in the first reservoir does not include polyglycol ether non-ionic surfactants. When the ink composition is printed next to another ink, a viscosity buildup is achieved by making one or both of the inks printed next to each other have a viscosity buildup per percent water loss from at least about 0.1 centipoise per percent water loss and/or viscosity buildup in a range from about 0.2 to about 1.8 centipoise in at least one of the inks by the at least one of the inks further comprising phosphate ester surfactant.

In still another embodiment, the present disclosure teaches an inkjet ink set including at least one ink selected from the group consisting of black, cyan, magenta and yellow inks. The ink includes water, a colorant, and a dispersant and/or a surfactant. The ink does not include polyglycol ether non-ionic surfactants. When the ink is printed next to another ink, a viscosity buildup is achieved by making one or both of the inks printed next to each other have a viscosity buildup per percent water loss from at least about 0.1 centipoise per percent water loss and/or viscosity buildup in a range from about 0.2 to about 1.8 centipoise by at least one of the inks further comprising phosphate ester surfactant. In another embodiment of the presently described method, ink composition, ink set and system, the viscosity buildup per percent water loss of one or both of the inks is in the range of from about 0.2 to about 0.3 centipoise per % loss in water.

In yet another embodiment of the presently described method, ink composition, ink set and system, the dot size difference between the inks printed next to each other is less than 500 microns.

In still another embodiment of the presently described method, ink composition, ink set and system, the dot size difference is reduced between the inks printed next to each other to be less than 100 microns. To further illustrate the embodiment(s) of the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the disclosed embodiment(s).

EXAMPLES

Example 1

When data obtained from various tests of ink physical properties (such as surface tension, viscosity buildup in the print zone, ink conductivity and dot size) in sample inks were compared with the bleed properties of those inks, it was found that viscosity buildup and dot size were significant factors. Figure 1 shows a three

dimensional bar graph based on samples of black/cyan (K/C), black/magenta (K/M), black/yellow (K/Y), cyan/magenta (C/M), cyan/yellow (C/Y) and magenta/yellow (IWY) which were measured for bleed, dot size difference and viscosity buildup difference between adjacent drops. In the graph the ink combinations are set out in the x axis. The quantities measured for each of the three categories: bleed, dot size difference and viscosity buildup difference are set out in the y axis. The three categories themselves: bleed, dot size difference and viscosity buildup difference are set out in the z axis. Overall, Figure 1 shows that certain ink combinations are more subject to the influence of viscosity and dot size. It also shows that, in general, viscosity buildup has a bigger influence on bleed than dot size.

Example 2

Nine pigmented magenta ink formulations (RM-1 , RM-6, RM-7, RM-8, RM9, RM-10, RM-11 , RM-12, RM-13) were prepared using different surfactants and the same pigment and other additives. The components for each ink are listed in Table 1.

Table 1

Example 3

Viscosity and viscosity increase over time was measured for each ink listed in Table 2.

Table 2

Viscosity was measured using a Brookfield cone and a Plate viscometer at 15 rpm and 60 rpm. As shown in Table 2, viscosity was measured at 15 and 60 rpm's for each of the inks at Week 0, Week 1 and Week 2. The results show that the control R2M1 viscosity increases after a week and then stabilizes or reduces even slightly. The inks, R2M6, R2M7, R2M8 and R2M9, all of which contained the polyglycol ether non-ionic surfactants (Tergitol® 15s-9 and 15s-7), showed either no viscosity increase or a very slight viscosity increase. The inks, R2M10, R2M11 , R2M12, and R2M13, all of which contained the non-Tergitol® surfactants had a pronounced viscosity increase over the course of 2 weeks. Figure 2 below shows a bar graph with bars representing ten of the inks: R2M1 and R2M6-R2M14, each series of three bars showing the weight average diameter (particle size in microns)

of the respective ink particles before and after temperature cycling at week 0, week 1 and week 2 respectively.

Example 4

Water-depleted ink samples of each ink type in Examples 1 and 2 were inks made with water held back from each batch of ink. The viscosity and the % solids of the normal ink and water-depleted ink were both measured. Results are shown in Table 3.

Table 3

Figure 3 is a bar graph with the nine various inks shown as bars on the x axis (R2M1 and R2M6-R2M13) and centipoise / % water removed on the y axis.

Example 5

Particle size was measured by a particle sizing device (Nanotrac, manufactured by Microtrac) for Inks R2M1 and R2M4-R2M13 as well as the Latex ink. Particle size was measured for Week 0, Week 1 and Week 2 before and after

temperature (T) cycling. The data shows that particle size increased in the inks that did not have the Tergitol®-type surfactant. The data is shown in Table 4.

Table 4

Example 6

Bleed was tested by measuring the extent of line widening or wicking between adjacent colors. Figures 4 and 5 show bar graphs comparing the extent of bleed, in terms of line widening, of magenta ink samples R2M1 and R2M6- R2M13 into different cyan and black inks respectively. Samples were printed with 2-pass unidirectional printing. Line widening was measured in microns.

Example 7

A comparison of bleed between inks and the dot size difference between inks was tested by printing samples of magenta ink (R2M1 and R2M6-R2M13) next to a cyan ink sample. Printing frequency was 6 Khz. The dot size of each of R2M1 and R2M6-R2M13 along with the surfactants present are given in Table 5.

In Figures 6 and 7, two graphs are shown comparing the effect of viscosity buildup vs. line widening (Figure 6) as well as dot size differences vs line widening (Figure 7). The results of magenta ink bleed into cyan ink as well as magenta ink bleed into black ink is considered in Figure 6. The results of magenta ink bleed into cyan ink are shown in Figure 7. In summary, increasing dot size difference between a magenta ink and another cyan increased line widening and worsened the bleed (Figure 7) and increasing the viscosity buildup of the magenta ink reduced line widening and reduced bleed (Figure 6).

Table 5

Ink Dot Size at 6k

R2M1 Control 1.792

R2M4 0.25% Tamol 731 1.9735

R2M5 0.5% Tamol 731 1.8924

R2M6 0.25% Tergitol 15s-9 2.0521

R2M7 0.5% Tergitol 15s-9 2.189

R2M8 0.25% Tergitol 15s-7 1.961

R2M9 0.5% Tergitol 15s-7 2.1934

R2M10 0.25% Surfynol 440 1.8601

R2M11 0.5% Surfynol 440 2.05384

R2M12 0.25% Surfynol CT151 1.8377

R2M13 0.5% Surfynol CT 151 1.92182

Example 8

Various black inks made with pigments of different aggregate structure were printed adjacent to other inks on glossy vinyl media. The viscosity buildup of the different black inks as well as the dot size was measured on glossy vinyl. Bleed of the black inks against other inks was qualitatively evaluated. Bleed was worse for

black inks with low viscosity buildup. Also increased dot size (-spreading) increased bleed. These results are shown in Table 6.

Table 6

Example 9

Magenta inks with and without the dispersant Crodafos N10® (polyoxyethylene (10) oleyl alcohol phosphate, also referred to as oleth-10 phosphate ), exhibited different viscosity buildup when these inks were printed against yellow ink. The magenta inks with the emulsifying agent not only had higher viscosity buildup but also bled less into the neighboring yellow ink. This again follows the equation that:

Bleed ~ ( Visc) _A ,t -(Visc) _B ,t ~ {d(Visc)/dw} _A (2)

Figure 8 shows a graph plotting the viscosity increase (y axis) vs. line width (x axis) for three different samples of magenta ink printed next to yellow ink. Of the three samples, the sample with the highest viscosity buildup/lowest line width increase included CrodafosN 10® at a concentration of 0.75 weight percent. The bottom sample with the lowest viscosity buildup/highest line width increase included the lowest amount of emulsifying agent such as Crodafos®. The middle sample with less CrodafosN 10® (0.45 weight percent) than the first sample had less viscosity buildup and greater line widening than the first sample but greater

viscosity buildup and significantly less line widening than the bottom sample which had 0.30 weight percent CrodafosNIO®.

Clause 1. A method of reducing bleed in inkjet ink, comprising: creating viscosity buildup in at least one of two inks to be printed next to each other or which are to come in contact with each other by performing at least one of the following: removing water from the at least one of two inks to achieve viscosity buildup per weight percent water loss from at least about 0.1 centipoise per weight percent water loss; and adding phosphate-ester based dispersant to the at least one of two inks in an amount to achieve viscosity buildup in a range from about 0.2 to about 1.8 centipoise.

Clause 2. The method of clause 1 wherein the viscosity buildup per weight percent water loss of the at least one of two inks is in a range from about 0.2 to about 0.3 centipoise per % loss in water.

Clause 3. The method of any of the preceding clauses wherein the phosphate ester based dispersant is selected from the group consisting of oleth-3 phosphate, oleth-10 phosphate, cetyl ether phosphate and combinations thereof and wherein the phosphate ester based dispersant is present in the at least one of the two inks in a range from about 0.4 to about 0.8 weight percent.

Clause 4. The method of any of the preceding clauses, further comprising reducing dot size difference between the two inks inkjet printed next to each other to be less than 500 microns. Clause 5. The method of any of the preceding clauses wherein the dot size difference is reduced between the two inks printed next to each other to be less than 100 microns.

Clause 6. An inkjet ink composition, comprising: water; a pigment colorant;

a dispersant; and a surfactant; wherein the ink does not include polyglycol ether non-ionic surfactants; and wherein the ink composition has at least one of: a viscosity buildup per weight percent water loss of at least about 0.1 centipoise per weight percent water loss achieved by removal of water from the ink composition; and viscosity buildup in a range from about 0.2 to about 1.8 centipoise achieved by the ink composition further including phosphate-ester based dispersant.

Clause 7. The inkjet ink composition of any of the preceding clauses wherein the viscosity buildup per weight percent water loss of the ink composition is in a range from about 0.2 to about 0.3 centipoise per weight % loss in water.

Clause 8. The inkjet ink composition of any of the preceding clauses wherein the phosphate ester-based dispersant is selected from the group consisting of oleth-3 phosphate, oleth-10 phosphate, cetyl ether phosphate and combinations thereof and wherein the phosphate ester-based dispersant is present in the ink composition in a range from about 0.4 to about 0.8 weight percent.

Clause 9. An inkjet printing system for reducing bleed on a medium, comprising: a first drop-on-demand fluid ejector fluidically coupled to a first reservoir, the first reservoir containing an inkjet ink composition including: water; a pigment colorant; a dispersant; and a surfactant; wherein the ink does not include polyglycol ether non-ionic surfactants; and wherein the ink composition has at least one of: a viscosity buildup per weight percent water loss from at least about 0.1 centipoise per weight percent water loss achieved by removal of water from the ink composition; and viscosity buildup in a range from about 0.2 to about 1.8 centipoise achieved by the ink composition further including phosphate-ester based dispersant.

Clause 10. The printing system of clause 9 wherein the viscosity buildup per weight percent water loss of one or both of the inks is in the range of from about 0.2 centipoise to about 0.3 centipoise per weight percent water loss.

Clause 11. The printing system of any of clauses 9 through 10 wherein the phosphate-ester-based dispersant is selected from the group consisting of oleth-3 phosphate, oleth-10 phosphate, cetyl ether phosphate and combinations thereof and wherein the phosphate ester-based dispersant is present in the ink composition from about 0.4 weight percent to about 0.8 weight percent.

Clause 12. An inkjet ink set comprising at least one ink selected from the group consisting of black, cyan, magenta and yellow inks, wherein the at least one ink comprises: water, a pigment colorant, a dispersant, and a surfactant; wherein the at least one ink does not include polyglycol ether non-ionic surfactants; and wherein the at least one ink has at least one of: a viscosity buildup per weight percent water loss from at least about 0.1 centipoise per weight percent water loss achieved by removal of water from the at least one ink; and a viscosity buildup in a range from about 0.2 to about 1.8 centipoise achieved by the at least one ink further comprising phosphate-ester based dispersant.

Clause 13. The inkjet ink set of clause 12 wherein the viscosity buildup per weight percent water loss of one or both of the inks is in the range of from about 0.3 to about 0.5 centipoise per % loss in water. Clause 14. The inkjet ink set of any of clauses 12 through 13 wherein the phosphate-ester-based dispersant is selected from the group consisting of oleth-3 phosphate, oleth-10 phosphate, cetyl ether phosphate and combinations thereof; and wherein the phosphate ester-based dispersant is present in the ink composition in a range from about 0.4 to about 0.8 weight percent.

While several embodiments have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.