INK JET PRINTER

Abstract: An ink jet printer in which means (40, 42; 50) are provided for creating a temperature differential between the ink (12) in an ink container (10) and the ink in the ink droplet ejecting means (18) such that the temperature of the ink in the ink droplet ejecting means (18) is the lower. The temperature differential in the ink tends to reduce or substantially eliminate any air or gas bubbles which may be present in the ink at the lower temperature. The temperature differential is established either by heating the ink in the ink container (10), or by cooling the ink in the ink droplet ejecting means (18).

Description: INK JET PRINTER Technical Field This invention relates to an ink jet printer/ and, in particular, to an ink jet printer of the drop-on- demand type. Background Art In ink jet printers it is considered a basic requirement to provide some type of means for reducing or substantially eliminating any air or other type of gas bubbles that may form in the ink fluid. In a drop-on- demand ink jet printing device, the presence of such gas bubbles has been suspected to be a primary factor affect¬ ing performance and, in certain instances, even inhibit¬ ing ejection of ink droplets. It has been determined that the presence of air in or passing through the nozzle of the piezoelectric element affects ink droplet ejection and also that nozzle surface conditions, wherein various forms of contamination such as lubricants, detergents, wetting agents, smoke, paper dust or other materials, have an effect on and may even provoke the ingestion of air through the nozzle. Further, it has been observed that air can be ingested into the ink channel either by disturbing the supply conduit leading from the ink reser¬ voir to the ink jet print head, as represented by the piezoelectric element, or air can be ingested into the system by subjecting the print head to axial accelera¬ tion. It is also known that the size of the air bubble or the amount of air within the system affects the ejection of ink droplets in the manner wherein a small air bubble or amount of air may increase or de¬ crease the velocity of the ink droplets being ejected, whereas a large air bubble or amount of air may block the ink channel and thereby inhibit ejection of ink droplets. It is further noted that purging the system normally removes the larger amounts of air that tend to block the ink channel; however, smaller bubbles or amounts of air may remain in the channel and thus affect the velocity of the ink droplets. Disclosure of the Invention It is an object of the present invention to provide means for reducing or substantially eliminating gaseous bubbles in the ink fluid of an ink jet printer. In a preferred ^ embodiment of the invention, the supply of ink in the reservoir is heated so as to maintain a temperature differential between the temper¬ ature of the reservoir contents and the ambient temper¬ ature. A constant wattage heater, sized and formed to at least partially envelop or surround the ink reser¬ voir, is provided for increasing the temperature of the ink fluid in the reservoir by an amount and in the range of 10 degrees to 15 degrees C. above the ambient tem¬ perature. As the ink fluid cools, the gas solubility capability increases and effectively reduces or mini¬ mizes presence of gas bubbles in the fluid. An alternative method of reducing or sub¬ stantially eliminating air bubbles in the ink fluid is to decrease the temperature of the piezoelectric element and therefore the ink in the nozzle channel relative to the temperature of the ink in the reservoir. In such latter method, a thermoelectric cooling device is pro¬ vided to envelop or surround the piezoelectric element of the print head and reduce the temperature thereof in a range of about 10 degrees to 15 degrees C. below the ambient temperature. Brief Description of the Drawing Embodiments of the invention will now be de¬ scribed, by way of example, with reference to the accom¬ panying drawings, in which: Fig. 1 shows a diagrammatic view, partly in section, of a printing system incorporating the subject matter of the present invention; O ?I_ Fig. 2 shows a similar view of the printing system incorporating an alternate arrangement of the subject matter of the present invention; and Fig. 3 shows an enlarged view, partly in section, of a print head commonly used in printing operations. Best Mode for Carrying Out the Invention As seen in Fig. 1 of the drawing, an ink reservoir 10 contains a supply of printing ink 12 which is sufficient for printing upwards of, for example, several million characters. A length of tubing 14, made of Tygon (a polyvinyl chloride material manufactured by The Norton Chemical Company) or the like, is immersed at one end thereof into the ink fluid 12 in the reser- voir 10 and is connected at the other end thereof to a glass or like conduit 16, in turn, being a part of an ink jet print head 18 of the transducer type. The print head 18 includes a body portion 20 of cylindrical form having a glass tube or glass lined passageway 22 there- through (see also Fig. 3) for receiving the conduit 16 which terminates in a nozzle 24 for ejecting a droplet 26 of printing ink to be applied to record media 28, which media may be in the form of paper carried on a drum or platen (not shown) . A filter-type vent 30 is provided in the top of the reservoir 10 for access to the atmosphere and a grommet 32 is provided to support the tube 14 in proper position and to seal the tube with the reservoir top. As better seen in the enlarged view of Fig. 3, the print head 18 may be of a type, as disclosed in Arndt U.S. Patent No. 3,832,579, appropriate for and commonly used in printing operations and which includes a piezoelectric device or tubular type transducer 34 for causing ejection of the ink droplets 26 (Fig. 1) either in synchronous or asynchronous manner from the nozzle 24. The ink droplets 26 so produced are of essentially the same size and are normally ejected at a constant velocity. Leads 36. and 38 are appropriately connected to the print head 18 for actuating the transducer 34 to cause ejection of the ink droplets. A constant wattage heater 40, sized and formed to at least partially envelop or surround the reservoir 10 (Fig. 1), provides and establishes a temperature differential between the temperature of the ink fluid 12 in the reservoir 10 and the temperature of the ink fluid in the print head 18. Thermostatic control of the resistance-type heater 40 is not required, since advan¬ tage is taken of one consequence of Newton's law of cooling wherein the rise in the temperature of a body above ambient temperature is approximately proportional to the flow of heat to the surrounding area. Another way of stating such law is that the rate at which a body cools by radiation is proportional to the temper¬ ature difference between the body and the ambient tem¬ perature, in the case where the body is warmer than ambient. This law is shown by the following equation: where dT dt = rate of cooling and K = proportionality constant T . = Temperature of body T = Ambient Temperature It has been found that if the ink liquid 12 in the reservoir 10 is continuously heated by means of the heater 40 from a . ower supply 42, the dissolved gas capacity of the liquid is reduced, that is, gas bubbles are formed and released in the reservoir prior to entry of the liquid into the conduit 16 within the ink channel or passageway 22 of the print head 18. Also, the liquid being subjected to ambient temperatures that are cooler than the liquid 12 in the reservoir 10 is reduced in temperature and thereby displays increased dissolved gas volume capability. It is thus seen that ink 12 in the nozzle 24 can generate air bubbles around the nucleation point and air bubbles also can be dissolved out of solution. In this regard, as the ink 12 in the reservoir 10 is heated, the dissolved gases are forced out of solution, thus forming bubbles which are released into the atmosphere. The volume of the dissolved gas is less in warm liquids than in cool liquids, and the warm liquid in effect is undersaturated. Therefore, it is seen that as the warm ink cools in the passageway 22 of the print head 18 and any air bubbles present are reduced or dissolved and the possibility of generating air bubbles is minimized. Hence, the heating of the fluid 12 in the reservoir 10 results in a fluid having a lower gas solubility and further that when the fluid enters the print head 18 and is cooled, the gas solubility of the fluid increases and the tendency is to dissolve any air bubbles which may be in the print head 18 or any air bubbles which may be generated therein. The material for making the reservoir 10, which it should be noted is of a size to contain a few ounces of the ink 12, is a high temperature plastic capable of withstanding temperatures up to and perhaps above 40 degrees C. The heater 40 may be a suitable conduction- type with 110 volts applied as the power supply 42. Fig. 2 shows an alternate means for reducing or substantially eliminating gas bubbles in the printing system and wherein like reference numerals are used for the various common elements, as described for Fig. 1. The reservoir 10 contains the ink 12 which travels through tubing 14 and conduit 16 and then to the print head 18. The print head 18 has a body portion 20 with passageway 22 and a nozzle 24 along with a transducer 34 for initiating and generating the ink droplets 26. The leads 36 and 38 also are appropriately connected for actuating the transducer 34, as shown in Fig. 3. In this arrangement (Fig. 2), the temperature differential is accomplished or established by use of a thermoelectric cooling element 50 surrounding the print head 18 to cool the ink 12 from an ambient temperature in the reservoir 10 and to thereby increase the air or other type gas solubility capability of the ink 12. The cooling device 50 may be an appropriate heating and cooling or absorption type apparatus connected with a suitable power supply 52 for causing a decreasing or lowering of the temperature of the passageway 22 in an amount of 10 degrees to 15 degrees C. be^ow the temper¬ ature of the ink 12 in the reservoir 10, and thereby cooling the ink as it travels through the print head 18 to the nozzle 24. In the print head cooling arrange- ment a thermostat or like control device 54 may be used to control the cooling element 50. O PI

Claims: CLAIMS : 1. An ink jet printer including means (10) containing a supply of ink (12), and means (18) oper- ably associated with the ink containing meajs (10) for ejecting droplets of ink onto record media, character- ized by means (40, 42; 50) for creating a temperature differential between the ink in the ink containing means (10) and the ink in the ink ejecting means (18) such that the ink in the ink ejecting means (18) is at the lower temperature, whereby the lower temperature ink has the increased capability of dissolving gaseous bubbles present therein and inhibits generation of such bubbles in the ink ejecting means (18). 2. Ink jet printer according to claim 1, characterized in that the ink containing means (10) is a reservoir made of a material responsive to conduct heat to the ink (12) therein. 3. Ink jet printer according to claim 2, characterized in that the temperature differential creating means comprises heating means (40, 42) intim¬ ately associated with the reservoir for conducting heat to the ink (12) therein. 4. Ink jet printer according to claim 3, characterized in that the heating means (40, 42) com¬ prises a heating element (40) partially surrounding the reservoir (10) for transferring heat to the ink (12) therein. 5. Ink jet printer according to claim 4, characterized in that the heating means (40, 42) com¬ prises a constant wattage heater (42). 6. Ink jet printer according to claim 1, characterized in that the ink ejecting means (18) is a piezoelectric transducer (34). 7. Ink jet printer according to claim 1, characterized in that the temperature differential creating means comprises cooling means (50) intimately associated with the ink ejecting means (18) for cooling the ink therein. 8. Ink jet printer according to claim 7, characterized in that the cooling means comprises a cooling element (50) partially surrounding the ink ejecting means (18) for cooling the ink therein. 9. Ink jet printer according to claim 8, characterized in that the cooling element is a thermo¬ electric cooling element (50) controlled by a thermostat (54). 10. Ink jet printer according to claim 1, characterized in that the temperature differential between the ink in the ink containing means (10) and the ink in the ink ejecting means (18) is between 10 degrees and 15 degrees C. OMPI

Inventors: BANGS RICHARD GORDON, BANGS, RICHARD, GORDON
Applicants: NCR CO, NCR CORPORATION
Application year: 1983
Main classification: B41J3
IPC codes: B41J2