A CIRCULATION SYSTEM AND METHOD FOR MIXING AN INK JET INK

Abstract: A circulation system (10) for mixing ink jet ink includes a container (20), a pump (40), a first (50) and second (60) tubes. The container (20) has a bottom surface (22) and a top portion (26) opposing the bottom surface (22). The pump (40) has an inlet port (42) and an outlet port (44). The first tube (50) has first (52) and second (54) ends. The first end (52) of the first tub (50) is connected to the inlet port (42) of the pump (40), and the second end (54) of the first tube (50) includes a plurality of openings (56) in close proximity to the bottom surface (22) of the container (20). The second tube (60) has first (62) and second (64) ends. The first end (62) of the second tube (60) is connected to the outlet port (44) of the pump (40), and the second end (64) of the second tube (60) has an opening (66) disposed in the top portion (26). A method for mixing ink jet ink includes circulating pigment particles from a bottom surface (22) of a container (20) to a top portion (26) of the container (20). The circulation provides sufficient agitation to maintain the pigment particles suspended in the ink and to prevent agglomeration of pigment particles.

Description: A CIRCULATION SYSTEM AND METHOD FOR MIXING AN INK JET INK The present invention in general relates to a circulation system for mixing ink jet ink and in particular to a circulation system for mixing pigmented ink jet ink. Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is well - suited for application of characters onto a variety of surfaces including porous and non-porous surfaces. Reviews of various aspects of ink jet printing can be found in these publications: Kuhn et al., Scientific American, April, 1979, 162-178; and Keeling, Phys. Technol, 12(5), 196-303 (1981). Various ink jet apparatuses are described in the following U.S. Patents: 3,060,429, 3,298,030, 3,373,437, 3,416,153, and 3,673,601. Pigmented ink, which includes insoluble pigment particles, is frequently used in ink jet printing. Although it has a number of desirable characteristics, pigmented ink also has a significant drawback. The pigment particles tend to agglomerate and settle at the bottom surface of the ink supply container, causing nozzle clogging and disruption in printing, as well as a decrease in print contrast. The nozzles typically have a diameter around about 2.5 to 3.0 thousandths of an inch. Attempts have been made to maintain pigment particles uniformly suspended in the ink jet ink. However, many of these attempts have not been successful or provide techniques having drawbacks. For example, one technique involves the use of a magnetic stirrer disposed in the ink container. The rod-shaped magnetic stirrer, usually disposed at the bottom of the container, is driven by a varying magnetic field generated by rotating magnets outside of the container. Use of this technique in ink jet printing, however, is costly and complex. The system occupies a large volume of printer space. In addition, the system has a relatively short service life, because it involves moving mechanical parts causing significant mechanical wear. Further, it is time-consuming to extract the magnetic rod from a depleted ink container and deposit the magnetic rod in a full container every time a depleted ink container is replaced by a new ink container. The foregoing indicates that there exists a need for a system that reduces or eliminates pigment settling. There further exists a need for an ink jet printing system that prints without nozzle clogging for extended periods of time. The present invention utilizes the technique of circulation to maintain the pigment particles suspended in the ink and prevent agglomeration of pigment particles. In accordance with one aspect of the invention, a circulation system for mixing ink jet ink includes a container, a pump, and first and second tubes. The container has a bottom surface. The pump has an inlet port and an outlet port. The first tube has first and second ends. The first end of the first tube is connected to the inlet port of the pump, and the second end of the first tube includes a plurality of openings in close proximity to the bottom surface of the container. The second tube has first and second ends. The first end of the second tube is connected to the outlet port of the pump, and the second end of the second tube has an opening disposed in the container. In accordance with another aspect of the invention, a method for mixing ink jet ink includes drawing ink from a bottom surface of a container through a first tube having a plurality of openings in close proximity to the bottom surface of the container; and returning the ink drawn from the container to the container through a second tube having an opening disposed in the container. In accordance with a further aspect of the invention, a method for ink jet printing onto a substrate includes drawing ink from a bottom surface of a container through a first tube having a plurality of openings in close proximity to the bottom surface of the container, returning the ink, which is drawn from the container through the first tube, to the container through a second tube, drawing ink from the container through a third tube, directing a stream of ink droplets, formed from the ink from the third tube, to the substrate, and controlling the direction of the droplets to form a desired image. The circulation system in accordance with embodiments of the present invention has a number of advantages over known devices. For example, a printer device incorporating the circulation system of the present invention is relatively simple to operate and inexpensive. Embodiments of printer devices can be of small size. In addition, the device involves a minimum number of moving mechanical parts, reducing mechanical wear and increasing its service life. Further, because the tube connected to the inlet port of the pump includes a number of openings disposed in close proximity to the bottom surface of the container, the device is effective in collecting pigment particles from substantially all portions of the bottom surface and returning the particles to other portions of the container, thus resulting in pigment particles uniformly suspended in the container. The invention will now be described, by way of example, with reference to the accompanying Figure 1 drawing which is a partial cross sectional side view of a circulation system for mixing ink jet ink according to the present invention. Figure 1 illustrates a circulation system 10 for mixing ink jet ink according to the present invention. The circulation system 10 includes a container 20, a pump 40, and first and second tubes 50, 60 extending into the container 20. The first and second tubes 50, 60 are connected respectively to the inlet and outlet ports 42, 44 of the pump 40. The pump 40 is adapted to draw ink in the container 20 through the first tube 50 and return the ink to the container 20 through the second tube 60. The container may have any suitable regular or irregular configuration. Although the container 20 shown in Figure 1 has a generally cylindrical configuration, it may have, for example, a parallelepipedal, conical or spherical configuration. The container includes a bottom surface, which is defined by the interior surface of the container, on which pigment particles tend to accumulate if sufficient mixing is not provided. The bottom surface is usually the interior surface of the lowest portion of the container. For example, if the container 20 shown in Figure 1 is installed upright, the bottom surface is the interior end wall 22 of the container 20. Alternatively, if the container 20 is installed sideways, a portion of the interior side wall 24 of the container 20 is the bottom surface. The container also includes a top portion which is defined as the interior space of the container, which is opposite of the bottom surface. The term "top portion of the container" as used herein is the space above the ink surface and the space immediate below the ink surface. The term "immediate below" as used herein can be defined in many different ways, depending on, for example, the dimension of the container and/or the depth of ink in the container. Alternatively, the term "top portion of the container" can be defined as the interior container space other than the space in close proximity to the bottom surface of the container. The term "in close proximity" is defined below. The container 20 includes an opening 28 and a cover 30 (or a plurality of openings and covers), through which ink can be withdrawn from or deposited into the container 20 through, for example, one or more tubes 50, 60 extending through the cover 30. The opening can be located anywhere on the container. The pump can be any suitable device that can be used to circulate ink in the container. Examples of the pump include a piston-type pump, a vane pump and a gear pump. In general, the pump can be any device that generates a pressure difference between its inlet and outlet ports. The pump can be powered electrically, hydraulically, pneumatically or mechanically. The pump may be placed inside or outside the container 20 as shown in Figure 1. In some embodiments, the pump may be wholly or partially submerged in the ink. Each of the inlet and outlet ports 42, 44 of the pump 40 includes fittings so that it can be sealingly connected to a tube. The first tube 50 can be any flexible or rigid fluid conduit. The first tube 50 includes a first end 52 connected to the inlet port 42 of the pump 40 and a second end 54 submerged in the ink. If the pump 40 is disposed outside of the container 20, the first tube 50 may extend through an opening 28 of the container 20 (and a cover 30, if a cover 30 is placed over the opening 28). The second end 54 of the first tube 50 includes a plurality of openings 56, some or all of which are in close proximity to the bottom surface 22 of the container 20. In some embodiments, some or all of the openings are in contact with the bottom surface of the container. In some preferred embodiments, the openings of the second end are generally evenly distributed throughout the bottom surface of the container to ensure that the pigment particles at all portions of the bottom surface are drawn into the first tube. Each of the openings 56 of the first tube 50 may be oriented in any suitable direction. Preferably, each opening 56 is oriented in a direction such that the opening 56 is not closed by the bottom surface 22 of the container 20, for example. The term "close proximity" can be defined in many different ways and can be affected by a number of factors. The amount of the pigment particles drawn into the openings 56 of the first tube 50 depends not only on the distance between the openings 56 and the bottom surface 22 of the container 20, but also on, for example, the velocity at which the ink is drawn into the openings 56. The velocity is a function of, for example, the pump pressure and the inner diameters of the first tube. In one embodiment, for example, the term "close proximity" can be defined as a distance less than about 30 mm, preferably less than about 10 mm, more preferably less than about 5 mm, and even more preferably less than about 2 mm. In some embodiments, the distance is less than about 0.5 mm. The second end 54 of the first tube 50 may also include a plurality of branches 58, each of which includes at least one of the openings 56 of the second end 54 of the first tube 50. In the embodiment shown in Figure 1, the second end 54 of the first tube 50 includes a plurality of laterally extending branches 58, each of which includes an opening 56 at its end. The second tube 60 can also be any flexible or rigid fluid conduit. The second tube 60 includes a first end 62 connected to the outlet port 44 of the pump 40 and a second end 64 preferably at or near the top portion 26 of the container 20. Generally, the second end 64 of the second tube 60 can be disposed at any location in the container 20. In a preferred embodiment, the second end 64 may not be disposed above the surface of the ink to prevent or reduce foaming of the ink. If the pump 40 is disposed outside the container 20, the second tube 60 may extend through an opening 28 of the container 20 (and a cover 30, if a cover 30 is placed over the opening 28). The first and second tubes may extend through the same opening or different openings of the container. The second end 64 of the second tube 60 includes one opening 66, as shown in Figure 1. In a preferred embodiment, the second end 64 of the second tube 60 is positioned away from the bottom surface 22 of the ink container 20, as the uniformity of mixing through the entire container can be significantly reduced, e.g., at low ink circulation velocities, if the openings 56 and the second end 64 are in close proximity to the bottom surface. In certain embodiments, the second end 64 of the second tube 60 may include a plurality of openings and/or branches disposed in the top portion 26 of the container 20. In addition to the first and second tubes 50, 60, one or more additional tubes may be provided. As shown in Figure 1, for example, third and fourth tubes 70, 80 are used to monitor the ink level in the container 20 and to supply ink jet ink to the printer, respectively. The third tube 70 is used to pump air into the ink, and the ink level in the container 20 is determined from the air pressure in the third tube 70. The third tube 70 has an opening 72 disposed in the container 20, for example, near the bottom surface 22 of the container 20, and the air exists the third tube 70 through the opening 72. The air pressure in the third tube 70 is equal to the ink pressure at the opening 72 of the tube 70, and the ink pressure at the opening 72 is proportional to the ink level in the container. Thus, as the ink level in the container decreases, the air pressure in the third tube 70 also decreases. When the ink level falls below the opening 72 of the tube 70, the air pressure in the tube 70 becomes equal to the atmospheric pressure. Thus, the ink level in the container 70 can be monitored by a pressure transducer 74, which can be mounted on the third tube 70 to sense the air pressure in the third tube 70. When the air pressure in the third tube 70 falls below a predetermined level, thereby indicating the ink in the container is depleted, the pump 40 of the circulation system 10 may be shut down, and the depleted container may be replaced by a new full container. The operation of the circulation system 10 can be described while referring to Figure 1. When a new container of ink jet ink is installed in the ink jet printer, the second ends 54, 64 of the first and second tubes 50, 60 are placed in the container 20. The first ends 52, 62 of the first and second tubes 50, 60 are connected respectively to the inlet and outlet ports 42, 44 of the pump 40. At least some of the openings 56 of the second end 54 of the first tube 50 are placed in close proximity to the bottom surface 22 of the container 20, and the opening 66 (or openings) of the second end 64 of the second tube 60 is placed in the top portion 26 of the container 20. When the ink jet printer is in operation, the pump 40 may be powered on to draw ink jet ink from the bottom surface 22 of the container 20 through the first tube 50 into the inlet port 42 of the pump 40, and to return ink drawn from the container 20 to the container 20 through a second tube 60. The circulation system 10 may be operated continuously or periodically, and the system 10 may be automatically operated or may be manually powered on when the printing quality begins to deteriorate. The present invention further provides an ink jet printer that includes the circulation system described above. The printer can be of any type, such as a continuous ink jet printer or a drop-on-demand ink j et printer. In accordance with the present invention, the circulation system can be used to keep inks containing any suitable pigment. Examples of pigments include titanium dioxide and carbon black. Additional examples of pigments can be found in U.S. Patent 5,286,288. The efficacy or the advantages of the circulation system of the present invention can be determined by methods known to those skilled in the art. For example, the uniformity of pigment dispersion in the ink container can be determined by taking samples of the inks at periodic height or time intervals and measuring the pigment concentration in the samples. Pigment concentration can be determined by methods known to those skilled in the art, for example, by light scattering. Alternatively, or in addition, the quality of the print can be monitored, for example, by measuring the reflectance of the printed images. The circulation system of the prevent invention is superior to certain systems known in the art, e.g., those providing a suction tube which is not in close proximity to the bottom surface of the ink container or which contains a single opening as disclosed in U.S. Patent 5,798,781. The following example further illustrates the present invention. EXAMPLE This Example illustrates an advantage of an embodiment of the present invention. The ink circulation system of the present invention was effective in maintaining the pigment suspended in the ink. A white ink having a sedimentation rate of 10-20 mg/hour was employed to print images on black paper. The ink contained TiO 2 as the pigment and a mixture of MEK and methanol as the solvent. Prints were produced with and without the use of the ink circulation system of the present invention. A new full ink supply container containing 950 ml of white ink was installed in an ink jet printer. The container was shaken well prior to installing on the printer to achieve even distribution of pigment particles in the container. The contrast of the images was measured on a Kidder Optical Character Tester Model No. 082. Without the ink circulation system installed, the image obtained when the ink level was at 950 ml showed a reflectance value of 28%. As the volume of the ink in the container dropped to 450 ml, the image obtained had a reflectance value of 11%, and at 150 ml volume, the image obtained had a reflectance value of 5%. However, with the ink circulation system of the present invention installed in the ink jet printer, the images obtained had a reflectance of from 28% to 26% at all measured volume levels. The substantially uniform and high reflectance values of the images confirmed that the pigment particles were kept in suspension and that the pigment concentration in the ink was uniform.

Claims: CLAIMS: 1. A circulation system (10) for mixing an ink jet ink, the system (10) comprising: a container (20) having a bottom surface (22); a pump (40) having an inlet port (42) and an outlet port (44); a first tube (50) having first (52) and second (54) ends, the first end (52) of the first tube (50) being connected to the inlet port (42) of the pump (40), the second end (54) of the first tube (50) including a plurality of openings (56) in close proximity to the bottom surface (22) of the container (20); and a second tube (60) having first (62) and second (64) ends, the first end (62) of the second tube (60) being connected to the outlet port (44) of the pump (40), the second end (64) of the second tube (60) having an opening (66) disposed in the container (20). 2. A circulation system according to claim 1, wherein the second end (54) of the first tube (50) includes a plurality of branches (58), and each branch (58) includes at least one of the openings (56) of the second end (54) of the first tube (50). 3. A circulation system according to claim 2, wherein at least one opening (56) of each branch (58) contacts the bottom surface (22) of the container (20). 4. A circulation system according to claim 1, wherein the distance between the bottom surface (22) of the container (20) and any one of the openings (56) of the second end (54) of the first tube (50) is less than 30 mm. 5. A circulation system according to claim 4, wherein the distance is less than 5 mm. 6. A circulation system according to claim 5, wherein the distance is less than 0.5 mm. 7. A circulation system according to claim 1, wherein the openings (56) of the first tube (50) are in contact with the bottom surface (22) of the container (20). 8. A circulation system according to any one of the preceding claims including a third tube (70) having an opening (72) disposed in the container (20), whereby air can be pumped into the ink in the container (20) through the third tube (70) and the opening (72) of the third tube (70). 9. A circulation system according to claim 8 including a pressure transducer (74) connected to an inner space of the third tube (70) to monitor the pressure in the third tube (70). 10. A circulation system according to any one of the preceding claims wherein said container (20) has a top portion (26) opposing said bottom surface (22) of the container (20), and said opening (66) of said second end (64) of said second tube (60) is disposed in said top portion (26). 11. A method for mixing ink jet ink, the method comprising: drawing ink from a bottom surface (22) of a container (20) through a first tube (50) having a plurality of openings (56) in close proximity to the bottom surface (22) of the container (20); and returning the ink drawn from the container (20) to the container (20) through a second tube (60) having an opening (66) disposed in the container (20). 12. A method for ink jet printing onto a substrate, the method comprising: providing a circulation system (10) according to claim 1; directing a stream of ink droplets to the substrate; and controlling the direction of the droplets to form a desired image. 13. A method according to claim 11 or claim 12, wherein the first tube (50) has an end (54) having a plurality of branches (58), each of which includes at least one of the openings (56) of the first tube (50). 14. A method according to claim 11 or claim 12 or claim 13 wherein a pump (40) is used to draw the ink from the container (20) and return the ink to the container (20). 15. A method according to claim 14, wherein the pump (40) is powered on periodically. 16. A method according to any one of claims 11 to 15, wherein said ink is a pigmented ink. 17. A method according to any one of claims 11 to 16 wherein said container (20) has a top portion (26), and said opening (66) of said second tube (60) is disposed in said top portion (26). 18. A method for ink jet printing onto a substrate, the method comprising: drawing ink from a bottom surface (22) of a container (20) through a first tube (50) having a plurality of openings (56) in close proximity to the bottom surface (22) of the container (20); returning the ink, which is drawn from the container (20) through the first tube (50), to the container (20) through a second tube (60); drawing ink from the container (20) through a third tube (80); directing a stream of ink droplets to the substrate; and controlling the direction of the droplets to form a desired image. 19. An ink jet printer including a circulation system (10) according to any one of claims 1 to 10.

Inventors: MURAD GEORGE, MURAD, GEORGE
Applicants: MARCONI CORP PLC, MARCONI CORPORATION PLC
Application year: 2000
Main classification: B41J2
IPC codes: B41J2