Ink tank

Abstract: An ink tank (11) is provided in which the tank is filled with compressed fibre materials in intimate contact with each other for transmission of ink therethrough by capillary action. The bulk density of the fibre material (13) in the region adjacent the ink feed passage of the ink tank is greater than the bulk density of the fibre material (12) in the region remote from the ink feed passage (10). This ensures that ink is drawn towards the ink feed passage (10). The invention also provides an ink feed cartridge.

Description: The present invention relates to an ink tank, in particular to an ink tank used in an ink jet printer. Ink jet printers have had the disadvantage that, because they use a liquid ink, the performance and quality of printing changes remarkably according to the printing posture. Accordingly, a method has been devised which comprises modifying the flow of ink in an ink tank due to capillary action and surface tension by putting fibres into the ink tank and correcting the deterioration of the printing characteristics due to the printing posture. Figure 6 of the accompanying drawings is a transverse section through a first conventional ink tank. Ink 5 is fed from an ink tank 3 to an ink jet printer 1 via an ink feed passage 2. Fibres 4 are put into the ink tank 3 and air is introduced from an air intake 6 into the space 7 created by ink being sucked into the fibres. In this case, if the suction power of the ink jet printer 1 is strong, the ink 5 in the ink tank 3 is sucked towards the ink feed passage 2. However, if there is too little suction power, it is impossible to feed ink sufficiently due to surface tension 20. In addition, if the level of the ink 5 in the ink tank is lower that the nozzle of the ink jet printer 1, the ink does not run out of the nozzle. Hence, the ink jet printer disclosed in Japanese Patent Publication No. 11152/1988 uses ink usefully by collecting ink in the ink tank towards the ink feed passage and, at the same time, prevents ink from spouting by transferring cells in the ink tank to the side of the space in the ink tank. The ink jet printer disclosed in Japanese Patent Publication No. 11152/1988 is shown in transverse cross-section in Fig. 7 of the accompanying drawings. An ink jet head 1 is connected with an ink tank 3 via an ink feed passage 2. The internal diameter of the ink tank 3 decreases as it approaches the ink feed passage 2. The ink tank 3 is filled with a single kind of fibre 4, the density of the fibre increasing continuously as it approaches the side of the ink feed passage 2 since there is neither cutting-off of, nor joints in, the fibre, and hence ink is collected to one side. Air is introduced into the space 7 from which ink is sucked out from an air intake 6 which is covered with a cover 8 when not used. According to this conventional construction however, it is hard to design a place for the ink tank to fit in a carriage, not only because the shape is thin but also because the fibre is compressed gradually, so that ink cannot be introduced into the ink tank and a sufficient amount of ink cannot be kept in the ink tank. Consequently, there is a problem in that the ink tank must be large. Moreover, when only ink is introduced into a vessel, it leaks due to changes in atmospheric temperature and pressure and hence, in a cartridge-type ink tank to be used in various forms of ink jet printers, various constructions and methods are employed for preventing leakage of ink and bestowing a certain back pressure upon a printing head. For this, a method is proposed in which an ink support material (urethane foam) in the vessel is impregnated with ink to maintain ink according to the capillary tube power of the support material and that the back pressure in the vessel is adjusted to an appropriate negative pressure (e.g. Japanese Patent Publication No. 87242/1988). However, according to this construction, the storage volume of ink reduces by the volume of the ink support material and also ink cannot be used up usefully due to the capillary tube power of the ink support material. Figure 8 of the accompanying drawings is a transverse cross-section of a first conventional ink cartridge. As shown in Fig. 8, a longitudinally arranged construction is proposed, in which an ink vessel 33 is divided into two chambers, namely, a main tank storage part 35 for storing ink alone and a secondary ink storage part 34 adjusting overflowed ink (Japanese Patent Publication No. 522/1990). In this construction, an ink flow path 38 is set between the main ink storage part 35 and the secondary ink storage part 34 and a porous material is installed between the printing head support part 36 for supporting a printing head 39, the ink flow path 38 and the secondary ink storeroom 34. According to this construction, however, since the secondary ink storage part adjusting overflowed ink is not open to the atmosphere, ink is kept in the secondary ink storage part without printing taking place when a temperature change occurs. At this time, the diameter of droplets changes according to the occurrence of the difference in liquid heights between the printing head and the secondary ink storage part and hence due to the change of the back pressure upon the printing head, there is a risk of ink leakage from the nozzle and it is difficult to adjust the back pressure. A transverse cross-section through a second conventional ink cartridge in which the ink chamber is divided into two chambers is shown in Fig. 9 of the accompanying drawings (Japanese Patent Publication No. 99631/1975). In this example, a liquid well 40 as one ink chamber is filled with foamed plastic 41 impregnated with ink and has a feed pocket 46 for feeding ink into a printing head at the lowest part. An air hole 43 is installed in the upper part of a liquid fill device 42 as another ink chamber and the inside of the liquid fill device 42 is filled with ink 44. A wick 45 is dipped therein, the tip 47 of the wick passing through the outer wall of the liquid fill device 42 and an opening 48 on the outer wall of the liquid well 40 and coming into contact with the foamed plastic 41 to feed ink. According to the above construction, however, there is a problem with ink storage since the liquid fill device has an air hole. Besides, since the liquid well is filled with the foamed plastic impregnated with ink, ink cannot be used up usefully owing to the capillary tube power and back pressure increases with the decrease of ink and thus it is difficult to adjust back pressure. An object of the present invention is to provide an ink cartridge for an ink jet printer which makes it possible to increase the amount of ink to be used and bestow a certain back pressure upon a printing head. According to the present invention, there is provided an ink cartridge for an ink-jet printer, comprising: a reservoir compartment for ink; and an adjustment compartment having a feed outlet, for feeding ink to a printing head, located at a lower region thereof, said adjustment compartment being occupied by material which, in use, is impregnated with ink and a part of which extends from said adjustment compartment to the bottom of said reservoir compartment, characterised in that said adjustment compartment has an air hole open to the atmosphere located in an upper region thereof and is occupied by fibre material, said reservoir compartment being air-tight and the respective compartments being divided by a bulkhead which has a connection opening for communication therebetween, said part of said material extending from said adjustment compartment to the bottom of said reservoir compartment via said connection opening. In one embodiment in accordance with the present invention, the inside of an ink cartridge is divided into two chambers, namely, a storage chamber and an adjusting chamber, by a bulkhead installed in a longitudinal direction. The storage chamber is filled to the full with ink and the adjusting chamber is filled with a fibre-like material impregnated with ink, part of the fibre-like material reaching the lower part of the storage chamber through a connection opening installed in the bulkhead. Moreover, an air hole open to the atmosphere is installed at the upper part of the adjusting chamber and a feed pocket opening to the printing head is installed at the lower part, the storage chamber being connected with the adjusting chamber through the connection opening installed at the lower part of the bulkhead, the remaining part being airtight. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:- Fig. 1 is a transverse cross-section of an ink tank cartridge in accordance with the present invention; Fig. 2 is a transverse cross-section in the direction perpendicular to that of Fig. 1; Fig. 3 is a view similar to Fig. 1 showing the ink cartridge in an initial state; Fig. 4 is a view similar to Fig. 3 showing the ink cartridge partially used; Fig. 5 is a view similar to Fig. 3 showing the ink cartridge almost fully used; Fig. 6 is an explanatory view showing a first conventional ink tank; Fig. 7 is an explanatory view showing a second conventional ink tank; Fig. 8 is an explanatory view showing a first conventional ink cartridge; and Fig. 9 is an explanatory view showing a second conventional ink cartridge. Fig. 1 and Fig. 2 are transverse cross-sections in two opposite directions, showing the internal structure of a cartridge-type ink tank in accordance with the present invention. The inside of an ink cartridge 21 is divided into two compartments, namely, an adjustment compartment 22 and a store compartment 23, by a bulkhead 30 installed longitudinally. An air hole 27 opening to the atmosphere is located at the upper part of the adjustment compartment 22 and a feed pocket 32 feeding ink into a printing head is located at the lowest part. The store compartment 23 opens into the adjustment compartment 22 through a connection opening 28 installed in the lower part of the bulkhead 30 and the remaining part of the store compartment 23 is airtight. The store compartment 23 is filled full of ink 31 and the adjustment compartment 22 is filled with fibre material impregnated with ink. A part of the fibre material reaches the bottom of the store compartment 23 through the connection opening 28. The fibre material filled in the adjustment compartment 22 comprise a plurality of felt blocks 24, 25 and 26 having different bulk densities. The felt blocks with higher bulk densities are arranged nearer to the feed pocket 23 opening to the printing head 29. Moreover a part of the wall surface of the store compartment 23 is made of a transparent material; it is therefore possible to detect optically the ink remaining therein. The operation of the device in accordance with the present invention will be described according to Figs. 3-5. Fig. 3 shows the device in an initial state. Figs. 4 and 5 are transverse cross sections of the cartridge showing the consumption of ink. The store compartment is filled with ink 31. Felt 24, 25 and 26 in the adjustment compartment 22 are thus impregnated with ink. When the level of ink contained in the felt in the adjustment compartment 22 is above the connection opening 28, the storage compartment 23 is in an airtight state as the connection opening 28 is covered with ink and hence ink does not flow into the adjustment compartment 22. When printing is conducted by means of the printing head 29, ink in the ink cartridge 21 is consumed from ink contained in the felt 24 of the adjustment compartment 22. Because the fibre density of felt 24, 25 and 26 increases in this order, ink is induced in the direction of the feed pocket according to the difference of the capillary tube power of the respective felts 24, 25, 26. Moreover, when the level of ink contained in the felt of the adjustment compartment falls below the upper rim of the connection opening 28, as shown in Fig. 4, air is introduced into the storage compartment from the upper rim of the connection opening 28. At the same time, the ink 31 in the storage compartment 23 passes through the felt according to the amount of air introduced into the store compartment and is fed into the adjustment compartment 22. This operation is repeated as long as the ink 31 of the storage compartment 23 is above the connection opening 28 and the ink level in the felt 25 and the felt 26 of the adjustment compartment 22 does not change. Thus, the back pressure in the ink cartridge 32 can be kept specific during the above operation. In addition, when air inflation occurs due to the change of circumstances during the feeding of ink from the storage compartment 23, the ink 31 of the storage compartment 23 flows into the adjustment compartment 22 and is absorbed in the felt 24. When the internal pressure becomes normal again, the ink of the felt 24 returns to the storage compartment 23, but all of the ink does not return to the storage compartment 23 because of the ink retention capacity of the felt 24 and ink is fed from the adjustment compartment 22 in the same way as in Fig. 3. After the further performance of the printing operation, the level of the ink 31 in the storage compartment falls below the connection opening 28 as shown in Fig. 5. The ink 31 is then sucked up by the felt 25 inserted into the storage compartment 23 from the adjustment compartment 22 and is fed into the adjustment compartment 22 until all of the ink 31 in the storage compartment 23 is sucked up. Afterwards, ink is consumed from the felt 25 and then the felt 26. If the connection opening 28 is located in the lowest part of the bulkhead 30, the ink 31 flows to the bottom of the adjustment compartment 22 and back pressure increases when air inflation occurs according to the change of circumstances when there is little ink 31 remaining in the store compartment 23. Besides, when the remainder of the ink is detected, the liquid surface changes and hence it is difficult to recognise it exactly. Hence, it is desirable to position the connection opening 28 above the lower part of the bulkhead 30. By positioning the connection opening in this way, the air in the storage compartment 23 passes through the connection opening 28 and the felt 24 of the adjustment compartment and is discharged out from the air hole 27, even if air inflation occurs due to the change of circumstances insofar as the liquid surface is below the connection opening 28. Thus, neither the liquid surface of the ink 31 nor the back pressure changes. Moreover, since the liquid surface is stable, the amount of ink remaining in the storage compartment 23 can be detected exactly and optically if a part of the wall surface of the storage compartment 23 is composed of a transparent material. Further, according to the above arrangement, even if the storage compartment 23 becomes empty, there is no fear of the ink running-out immediately after a warning thereof since there still remains ink in the felt 25 and the felt 26 of the adjustment compartment 22. After all of the ink in the ink cartridge 21 is used up, the ink cartridge 21 is removed from the printing head 29 and replaced with a new one to perform printing again. As described above, in the ink cartridge of the present invention, it is possible to keep a sufficient holding volume of ink in a storage compartment which is filled to the full only with ink and an adjustment compartment which is filled with fibre materials impregnated with ink. At the same time, it is possible to avoid the waste of ink and maintain back pressure properly according to the cooperating operation of the adjustment compartment and the storage compartment. In addition, the inducement of ink flow is enhanced by employing plural felt blocks with different fibre densities and fibre materials. Moreover, it is easy to detect reliably the remaining amount of ink optically.

Claims: An ink cartridge (21) for an ink-jet printer, comprising: a reservoir compartment (23) for ink; and an adjustment compartment (22) having a feed outlet (32), for feeding ink to a printing head (29), located at a lower region thereof, said adjustment compartment (22) being occupied by material which, in use, is impregnated with ink and a part of which extends from said adjustment compartment (22) to the bottom of said reservoir compartment (23), characterised in that said adjustment compartment (22) has an air hole (27) open to the atmosphere located in an upper region thereof and is occupied by fibre material (24,25,26), said reservoir compartment (23) being air-tight and the respective compartments (22,23) being divided by a bulkhead (30) which has a connection opening (28) for communication therebetween, said part of said material extending from said adjustment compartment (22) to the bottom of said reservoir compartment (23) via said connection opening (28). An ink cartridge (21) as claimed in claim 1, wherein said fibre material comprises a plurality of felt blocks (24,25,26) having different bulk densities, the felt blocks with higher or highest bulk density being arranged adjacent the feed outlet.

Inventors: KOMIYAMA TAKEO, WASEDA TAKAYUKI, KOMIYAMA, TAKEO, WASEDA, TAKAYUKI
Applicants: CITIZEN WATCH CO LTD, CITIZEN WATCH CO. LTD.
Application year: 1993
Main classification: B41J2
IPC codes: B41J2