JPH09302290A - Production of water-base black pigment ink having high-resistivity dry film for continuous ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ink jet ink composition which is a water-base black pigment ink and does not cause electric short circuit due to the conductivity of the dry ink film on a charge lead by adding a polymer to a pigment ink.

SOLUTION: This composition comprises a liquid vehicle, a pigment and a polymer. This is obtained by adding a polymer such as an acrylic resin or a polyester resin to an ink containing a carbon black pigment. The liquid vehicle is selected from the group consisting of wetting agents, biocides, corrosion inhibitors, deionized water and a mixture thereof. The liquid vehicle may further contain a lower aliphatic alcohol, a pH controlling agent such as an amine, sodium hydroxide or potassium hydroxide and a pH buffer for keeping the pH at a desired value.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pigment ink,
More particularly, it relates to a method of making an aqueous black pigment ink that does not cause electrical shorts in continuous ink jet printers due to the conductivity of the dry ink film on the charge leads.

[0002]

In continuous ink jet printing, ink is supplied under pressure to a manifold region which distributes the ink to a plurality of orifices, typically arranged in one or more linear arrays. Ink is ejected from the orifice into filaments, which are subdivided into droplet streams. The approach for printing with these droplet streams is to selectively charge and deflect certain droplets from their normal trajectory. The reproduction of the graphic selectively electrifies and deflects the droplets from the stream of droplets, depositing at least some of the droplets on the print receiving medium, while
This is done by applying another drop to the drop catcher device. The continuous flow inkjet printing method is, for example,
U.S. Pat. Nos. 4,255,754 and 4,698,1
23 and 4,751,517. The disclosure of each of these patents is incorporated herein by reference in its entirety.

In ink jet printing technology, water soluble dyes are desirable for their operability. However, waterfast inks are highly desirable for producing permanent images. Decreasing the solubility of the dye increases the waterfastness,
The reverse is also true. In the continuous inkjet industry, there has been a desire for some time to obtain permanent inks (100% waterfastness and 100% rubfastness). Although this has been accomplished by several continuous inkjet manufacturers (Elmjet)
EJ-101 Ink, Videojet by Videojet
VT-16-2000, Inc. and Eastman Kodak Company and Scitex Digital Pr.
Admark Fast Black Ink by Inting, Inc.), all of these inks are solvent-based inks. Ideally, the industry prefers water-based inks with durable qualities.

In current state-of-the-art aqueous inkjet inks, water-soluble dyes are used to obtain acceptable redissolvability of the dried ink at the orifice plate. This redissolvability is essential for good mechanical actuation as well as startup of continuous inkjet printers that do not have a separate printhead cleaning liquid mechanism.

Current dye-based inks use dyes that are water soluble (at least have limited solubility) and negatively impact waterfastness.
Water-based pigmented inks, on the other hand, could provide waterfastness because the pigments are dispersed rather than dissolved. So, for pigmented inks, to have good system start-up, redispersibility rather than resolubility must be achieved. The use of pigments rather than dyes raises some additional complications that do not exist with dyes. For example, dye-based inks provide dry films with high dry film electrical resistivity. On the other hand, pigment-based inks, especially carbon black inks, give dry films that are electrically conductive.

In particular, carbon black pigments are highly desirable in formulating ink jet inks because they are insoluble in water and thereby make waterfast inks. However, carbon pigments can cause electrical shorts and printer failure when they form a conductive dry film on charged conductors. This is due to the fact that carbon black pigments are electrically conductive. The conductivity of carbon black is well known and carbon black pigments are used in rubbers and plastics as conductive and antistatic fillers.

It can be seen, therefore, that there is a need for a method of making aqueous carbon black pigment inks in continuous ink jet printers that does not cause electrical shorts due to the conductivity of the dry ink film on the charging leads.

[0008]

This need is a method of making a carbon black pigment (not conventional dye-based) aqueous inkjet ink that does not cause electrical shorts due to the conductivity of the dried ink film on the charged conductors. It is achieved by the method according to the invention. The carbon black pigmented aqueous inkjet inks of the present invention achieve elevated dry ink film resistivity to acceptable levels and thus have acceptable print quality without any electrical shorts. By including the polymer or polymers in the pigment ink, the film resistivity can be increased sufficiently to prevent charging conductor-charging conductor short circuits, i.e., the conductivity of the film can be reduced.

According to one aspect of the invention, the ink jet ink composition comprises a liquid vehicle, a pigment and a polymer. The inclusion of the polymer reduces the conductivity, thereby increasing the resistivity. The dry ink film resistivity of the aqueous carbon black pigmented inks formulated with this composition is improved by raising it to a level where electrical shorts causing printer failure or printing defects are not observed during printing.

Other objects and advantages of the invention will be apparent from the description and claims that follow.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention is a continuous ink jet printer that does not cause an electrical short circuit due to the conductivity of the dry ink film on the charged conductors, the ink is not a conventional dye based carbon black pigment aqueous solution. Provided is a waterfast ink composition which is an inkjet ink.

Conventional aqueous dye-based inks are made with dyes that have at least limited solubility in aqueous media. Therefore, in the ink, there is a "true" solution of the dye in the medium. When this particular ink dries, the film formed has a very high dry film resistivity.

With some carbon black pigment inks,
When the film is formed, the dry film exhibits much lower dry film resistance, as shown in Example 1 below. This is probably due to the interparticle bonds at the bare carbon black pigment surface, since the carbon black pigment is conductive. So, this provides at least one passage through which the pigment is bound on the "bare" surface (without any adsorbate) of the carbon particles. Thus, inks containing carbon black pigments can cause the negative consequence of electrical shorts in continuous inkjet printers due to the conductive ink film deposited on the charging leads.

The inkjet ink composition according to the present invention comprises a liquid vehicle, a pigment and a polymer.
This polymer is included to suppress conductivity and thereby increase resistivity. The dry ink film resistivity of the aqueous carbon black pigmented inks formulated with this composition is improved by raising it to a level where electrical shorts causing printer failure or printing defects are not observed during printing.

The liquid vehicle comprises a wetting agent, a biocide,
It is selected from the group consisting of corrosion inhibitors, deionized water and mixtures thereof. In addition, the liquid vehicle may contain lower aliphatic alcohols; pH adjusting agents such as amines, sodium hydroxide or potassium hydroxide; and pH buffering agents to maintain the desired pH.

The present invention reduces the conductivity of the ink film, thereby increasing the resistivity and thus preventing electrical short circuits. According to the present invention, the resistivity of the ink film can be increased by adding a polymer such as an acrylic resin or a polyester resin to the ink containing the carbon black pigment. To clearly understand this, the invention is illustrated in the following examples. In the examples below, electrical resistivity was measured on the dry drop of each ink over a distance of 1 cm. This drop was made by using a # 6 drawdown bar on the coated paper.

[0017]

【Example】

Example 1 A carbon black pigment ink was evaluated for its dry film resistivity. The table below shows the results for two carbon black pigment inks, one without polymer and one with polymer.

[0018]

Formulations 1A 1B T5 93.65% 83.5% Surfactant 0.5% 0.5% Joncryl 950 0% 16.0% Electrical resistivity 10kΩ 520kΩ

In Example 1, T5 is an aqueous dispersion containing 5% by weight carbon black pigment. Formulation 1A ink contains no polymer, so 1
It has a low dry ink film electrical resistance of only 0 kΩ. When Formulation 1A was used in a Scitex 5000 inkjet printer, the printer had start-up problems due to electrical shorts. This problem is due to Jon
Minimized according to the invention by adding a polymer such as cryl 95. This is shown in Formulation 1B above. Formulation 1B gave a dry ink film resistivity of 520 kΩ.

Example 2 As will be appreciated by those skilled in the art, varying amounts of different polymers can be added to the ink to provide improved dry ink film electrical resistance. In Example 2, for example, to improve the dry ink film electrical resistance of Formulation 1A, Joncryl 50 in Formulation 2B was used.
Was added to the ink.

[0021]

Formulation 2A 2B Water 93.65% 89.65% Surfactant 0.25% 0.25% DMEA 1.80% 1.80% Carbon black pigment 2.20% 2.20% Acrylic resin 1.80% 1.80% Corrosion inhibitor 0.10% 0.10% Biocide 0.20% 0.20% Joncryl 500% 4.00% Electrical resistivity 180kΩ 700kΩ

As seen in Example 2 above, in Formulation 1A by the presence of some polymer, such as a resin, in the ink (acrylic resin 1.80% in Formulation 2A). When not containing a different polymer
The electrical resistance is improved to 180 kΩ when compared to the electrical resistance of kΩ. However, the addition of more polymer (eg, 4.0% Jon in formulation 2B).
Cryl 50), the electrical resistance is further improved to 700 kΩ. Although Formulation 2A gave better dry ink film electrical resistance than Formulation 1A, Formulation 2A still did not have enough polymer to provide the desired dry ink film electrical resistance. When Formulation 2A was used in a Sitex 5000 inkjet printer, the printed samples showed dark defects due to electrical shorts between the charged leads. According to the present invention, this problem was minimized by adding more polymer (ie, Joncryl 50), as shown in Formulation 2B, which provided a dry ink film resistance of 700 kΩ.

Example 3 Since more conductive paths are present in a dry ink film with a higher carbon black pigment content,
As shown in the table below, dry film conductivity increases or electrical resistivity decreases with the amount of carbon black pigment in the ink.

[0024]

Table 3 Aqueous dispersion 99.5% T2 99.5% T3 99.5% T5 Wetting agent 0.5% 0.5% 0.5% Electric resistance 50kΩ 20kΩ 10kΩ

In Example 3, T2, T3 and T5
Are aqueous dispersions containing respectively 2, 3 and 5% by weight of carbon black pigment. Electrical resistance was measured on the dry dropout of each ink over a distance of 1 cm. This drop was made by using a # 6 drawdown bar on the coated paper.

According to the present invention, a polymer can be added to the ink to increase its electrical resistance. The amount of increase in electrical resistance depends on the amount and type of polymer applied. In particular, the addition of Joncryl acrylic polymer to the ink is effective in increasing the electrical resistance of the dried ink film.

Example 4 SC Johnson Company
Is Joncryl 56, Joncryl 58, J
oncryl 61, Joncryl 62, Jonc
ryl 95, Joncryl 537, Joncry
Jo like l 554 and Joncryl 1 679
Manufacture ncryl acrylic polymers, all with different properties. As shown in Example 4 below,
Polymer Joncryl 95 was the most effective of the different polymers tested. Ink to ink
The addition of ryl 95 had the desirable result of providing low viscosity due to the low amount of polymer added as compared to other types of polymers.

[0028]

Table 4 Formulation T5 99.5% 91.5% 91.5% 91.5% Wetting agent 0.5% 0.5% 0.5% 0.5% Polymer 0% 8.0% 8.0 % 8.0% Joncryl Type None 56 58 61 Electric resistance 10kΩ 23kΩ 20kΩ 15kΩ T5 91.5% 91.5% 91.5% Wetting agent 0.5% 0.5% 0.5% Polymer 8.0% 8 0.0% 8.0% Joncryl type 62 95 537 Electric resistance 15 kΩ 42 kΩ 23 kΩ T5 83.5% 83.5% 83.5% 83.5% Wetting agent 0.5% 0.5% 0.5% 0.5. 5% Polymer 16.0% 16.0% 16.0% 16.0% Joncryl type 56 58 61 62 Electric resistance 117kΩ 141kΩ 43kΩ 46kΩ T5 83.5% 83.5% 83.5% 83.5% Wetting agent 0.5% 0.5% 0.5% 0 0.5% Polymer 16.0% 16.0% 16.0% 16.0% Joncryl type 95 537 554 1679 Electric resistance 520kΩ 160kΩ 110kΩ 60kΩ

In Example 4, T5 is an aqueous dispersion containing 5% by weight carbon black pigment. Electrical resistance was measured on the dry dropout of each ink over a distance of 1 cm. This drop was made by using a # 6 drawdown bar on the coated paper.

When the polymer is added to the ink, the electric resistance increases. Of course, the amount of increase in electrical resistance depends on both the amount and type of polymer applied. Joncr
Although yl95 was very effective among the different polymers tested, at 8% polymer content,
Dry ink film resistance was not yet high enough to prevent electrical shorts in printers.

As mentioned above, by increasing the polymer content in the ink for each polymer from 8% to 16%, the dry ink film electrical resistance can be increased. With a polymer content of 16%, Jo
It was found that ncryl 95 is very effective in raising electrical resistance.

Then, from Example 4 above, it can be seen that the electrical resistance of the dried ink film increases with the amount and type of polymer added to the ink.

Example 5 Focusing on Joncryl 95, which had the most dramatic effect on electrical resistance measurements in Example 4 above, other advantages are also realized by including a polymer in the ink.

[0034]

[Table 5] T2 (%) 99.5 95.5 93.5 91.5 89.5 87.5 Wetting agent (%) 0.5 0.5 0.5 0.5 0.5 0.5 Polymer Joncryl 95 (%) 0 4.0 6.0 8.0 10.0 12.0 Pigment,% by weight 1.99 1.91 1.87 1.83 1.79 1.75 Electrical resistance kΩ 50 170 460 1400 6700 76000 Optical Density 1.39 1.52 1.57 1.57 1.58 1.71 Wet Friction Resistance Poor Good Good Good Good Good Good Dry Weight Ratio Polymer / Pigment 0 0.63 0.96 1.31 1.68 2.06 T3 (%) 99.5 95.5 93.5 91.5 89.5 87.5 Wetting agent (%) 0.5 0.5 0.5 0.5 0.5 0.5 Polymer Joncryl 95 (%) 0 4.0 6.0 8.0 10.0 12.0 Pigment,% by weight 2.99 2.87 2.81 2.75 2.69 2.63 Electrical resistance kΩ 20 41 88 180 400 906 Optical density 1.72 1.79 1.84 1.87 1.97 2.04 Wet friction resistance Poor average Good Good Good Good Dry Weight Ratio Polymer / Pigment 0 0.42 0.64 0.87 1.12 1.37

At lower carbon black pigment contents, the amount of Joncryl 95 required is lower to obtain good wet rub fastness and high electrical resistance. For example, for T2 only 4% Joncryl 95 is needed to obtain good wet rub fastness, while for T3 6% Joncryl 95 is needed to obtain good wet rub fastness. Is. 460k with the addition of 6% Joncryl 95 for T2
An electrical resistance of Ω is obtained, while an equivalent 40 for T3
10% Joncryl to obtain 0 kΩ electrical resistance
95 is required.

Other advantages of including a polymer in the ink, as shown in Example 5 above, include higher optical density and improved wet rub resistance. The optical density increases with the amount of polymer in the ink, and by adding more polymer higher optical density can be obtained with less carbon black pigment.
While all these ink droppers have good waterfastness, the ink drops that do not contain any polymer do not have wet rub resistance. Wet rub resistance increases with the amount of polymer in the ink. In the above examples, for T3, the wet rub fastness of dropouts is comparable when the ink contains 4% polymer, and good wet rub fastness is at least 6% polymer in the ink. Obtained when included.

In Example 5 above, Joncryl
A dry weight ratio of 95 to carbon black pigment is given. According to the invention, this ratio is preferably greater than about 0.9 in order to obtain both good wet rub resistance and high electrical resistance.

The examples herein also have an electrical resistance preferably greater than at least 200 kΩ, and in a preferred embodiment greater than 500 kΩ. The electrical resistance increases with the addition of polymer to the ink, the amount of increase also depending on the particular polymer added. In a preferred embodiment of the invention, the amount of polymer in the ink formulation should be greater than the minimum amount of polymer in the ink formulation that provides an electrical resistance of 200 kΩ in dry drawdown. Also, the maximum amount of polymer in the ink formulation is limited by the maximum ink viscosity that the printer can tolerate.

Although the Joncryl polymer has been described herein, this should not be considered as limiting the scope of the invention. Inks having high resistivity dry ink films can be formulated according to the present invention using a number of different polymers without departing from the scope of the present invention. For example, other polymers that are effective in increasing high dry ink film electrical resistance include Jon.
cryl 50, Joncryl 52, Joncry
Joncryls manufactured by SC Johnson, such as L 74 and Joncryl 130 acrylic polymers, BF Goodrich (BF
Carboset acrylic polymers G514H, G552, G1903, G19 manufactured by Goodrich)
93, GA1086, GA1324, GA1604, G
A2136 and GA2137, Vancryl445,
Vancryl 915, Vancryl 937 and Va
Air Products such as ncryl 989 (Air P
vancryl acrylic polymer manufactured by Roducts, as well as Eastman Chem.
ical) manufactured by Eastek 1200 and 1300 polyester polymers.

Referring to the drawings, the present invention relates to a variety of continuous ink jet printing systems, such as those developed and manufactured by Cytex Digital Printing, Inc. of Dayton, Ohio, USA. In such a system, multiple jets are created with high spatial resolution by a droplet generator that stimulates the spontaneous breakdown of the jets into a uniform stream of droplets.

FIG. 1 is a front isometric view of a charging plate 10 having an inkjet disposed in front of the charging plate. The droplet generator provides an essentially coplanar and collinear stream of droplets 12 parallel to the front of the charging plate 10. Each droplet stream 12 is in linear alignment with the electrically conductive charging wire 14. Prior to collapsing, the ink stream 12 is conductive. When an electric potential is applied to one of the plurality of charging conductors 14, the last droplet still connected to the jet in front of that charging conductor receives an inductive charge. The next drop can be charged or uncharged by applying a predetermined voltage to any of the charging conductors in a timed relationship to the jet collapse process. In response to the impulse electrostatic force, the charged droplets are attracted towards the front of the catcher. The trajectory of the uncharged droplets is not deflected towards the catcher, so that the uncharged droplets move unhindered by the print medium.
Appropriate programming of the plurality of charging conductors 14 in synchronization with the breakup of the jet into the stream 12 of droplets can produce the desired pattern of droplets moving toward the support.

When the carbon pigment forms a conductive dry film 16 over the charging conductors 14, the carbon pigment can cause electrical shorts and printer failure. Ink film 1
6 may be formed when the printer is started up, shut down or activated. This film covers all or part of the charging plate, which can result in electrical shorts between the charging conductors covered by the film.

The method according to the present invention is a method for producing a carbon black pigment (not a conventional dye-based) aqueous inkjet ink which does not cause an electrical short circuit due to the conductivity of the dry ink film on the charged conductor. The carbon black pigmented aqueous inkjet inks of the present invention achieve elevated dry ink film resistivities to acceptable levels and thus to acceptable print quality without any electrical shorts. The present invention reduces the dry ink film conductivity by including a polymer.

[0044]

The present invention is useful in the field of ink jet printing and has the advantage of incorporating aqueous carbon black pigment inks having increased dry film resistivity for use in ink jet printing inks. The present invention has the further advantage of providing a method in which the intrinsic dry ink film resistivity is improved to avoid any electrical shorts.

Although the present invention has been described in detail with particular reference to certain preferred embodiments thereof, it will be understood that modifications and variations can be practiced within the spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 is a front isometric view of a charging plate having an inkjet disposed in front of the charging plate.

[Explanation of symbols]

 10 Charging Plate 12 Droplet Flow 14 Charging Lead Wire 16 Ink Film

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C09D 11/10 PTV B41J 3/04 101Y (72) Inventor John W. Hixenburg, Genia United States Ohio State 45424-2522, Huber Heights, Taylorsville Road 5212 (72) Inventor She A George Liu United States Ohio 45458, Dayton, Quailwood Trail 9652 (72) Inventor Rauff Botross Ohio United States State 45459-1655, Center Building, Hugh Drive 5647

Claims (10)

[Claims] 1. An inkjet ink composition comprising a liquid vehicle, a pigment and a polymer. 2. The inkjet ink composition according to claim 1, wherein the polymer is a resin. 3. The ink jet ink composition according to claim 1, wherein the polymer is selected from the group consisting of acrylic resins. 4. The inkjet ink composition according to claim 1, wherein the polymer is selected from the group consisting of polyester resins. 5. The inkjet ink composition of claim 1, wherein the polymer comprises Joncryl 95. 6. An ink jet printing apparatus containing the ink composition according to claim 1, wherein an image is formed by ejecting the ink onto the support as droplets, thereby generating an image on the support. Image generation method consisting of. 7. The method of claim 6, wherein the image is generated by a continuous flow inkjet printing method. 8. The inkjet composition of claim 1, wherein the liquid vehicle is selected from the group consisting of wetting agents, biocides, deionized water, corrosion inhibitors, lower aliphatic alcohols and mixtures thereof. 9. The inkjet composition of claim 8, wherein the liquid vehicle is selected from the group consisting of wetting agents, biocides, deionized water, corrosion inhibitors, lower aliphatic alcohols, pH adjusting agents and mixtures thereof. Stuff. 10. The pH adjusting agent comprises an amine.
The inkjet composition described.