JP2005103759A - Inkjet printer and its buffer tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variations in liquid level of ink as much as possible by making air rapidly flow out into an ink cartridge when the liquid level in the buffer tank decreases. <P>SOLUTION: In the buffer tank 4 of an ink jet printer 1, an air outlet passage 35 for allowing the air in the buffer tank 4 to flow out into the ink cartridge 3 is equipped with an air outlet pipe 38 which is provided in a top plate part 31 of the buffer tank 4 and which is elongated in a vertical direction, and a tube member 39 which has a larger diameter than the air outlet pipe 38, which communicates with the air outlet pipe 38 and which is elongated from the top plate part 31 to a position below a lower end of the air outlet pipe 38 and above a lower end of an ink inlet passage 34. Thus, when the liquid level of the ink I decreases, a meniscus, which is formed in the tube member 39, is easily broken, so that the air in the buffer tank 4 can rapidly flow out into the ink cartridge 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet printer capable of adjusting the back pressure of ink acting on a nozzle to be substantially constant and a buffer tank for adjusting the back pressure.

  In an ink jet printer that prints by ejecting ink from a nozzle toward a recording sheet, if the back pressure of the ink acting on the nozzle fluctuates due to the remaining amount of ink in the ink cartridge or the like, the fluctuation in the back pressure Affects the discharge accuracy. For this reason, ink jet printers are often provided with a mechanism for suppressing the back pressure fluctuation of the ink.

  As an example of such an ink jet printer, there is one provided with a buffer tank that suppresses fluctuations in back pressure acting on the nozzle by keeping the liquid level of the ink stored in the inside substantially constant (for example, Patent Documents). 1). As shown in FIGS. 7 and 8, in such a buffer tank 100, an ink inflow pipe 102 for allowing ink I to flow into the buffer tank 100 from the ink cartridge 101 and an atmosphere for causing the ink cartridge 101 to flow out of the atmosphere. An air outflow pipe 103 is provided on the top plate portion 104 of the buffer tank 100. In the buffer tank 100, the ink inflow tube 102 extends below the atmospheric outflow tube 103. Here, when the ink cartridge 101 is attached to the buffer tank 100, the ink inflow pipe 102 and the atmospheric outflow pipe 103 pass through the two plug members 106 provided in the ink cartridge 101, respectively. The inflow pipe 102 and the atmospheric outflow pipe 103 are each formed into a thin hollow needle shape.

  As shown in FIG. 7, in a state where the ink I is not ejected from the nozzle, the ink I does not flow out from the buffer tank 100 to the nozzle, and the liquid level of the ink I is at a position near the lower end of the atmospheric outflow pipe 103. The ink is stopped and the ink has entered the inside of the lower end of the air outflow pipe 103. That is, in this state, the atmosphere does not enter the atmosphere outflow pipe 103 and the atmosphere does not flow out to the ink cartridge 101, so that the ink I does not flow into the buffer tank 100 from the ink cartridge 101. In this state, when the ink I is ejected from the nozzle, the ink I flows out from the ink supply port 105 formed at the bottom of the buffer tank 100 to the nozzle, and the liquid level of the ink I in the buffer tank 100 is lowered.

Then, the liquid level of the ink I is separated from the lower end of the atmospheric outflow pipe 103, and a meniscus is formed inside the lower end portion of the atmospheric outflow pipe 103 due to the surface tension of the ink I. Further, when the liquid level of the ink I falls and the water head difference becomes equal to or greater than a predetermined h ₀ as shown in FIG. 8, the meniscus formed in the atmospheric outflow pipe 103 is broken, and the atmospheric outflow pipe 103 enters the buffer tank 100. Enters the ink cartridge 101. Then, the ink I flows from the ink cartridge 101 into the buffer tank 100 via the ink inflow tube 102 so as to be replaced with the atmosphere. When the liquid level of the ink I in the buffer tank 100 rises and reaches the vicinity of the lower end of the atmospheric outflow pipe 103, the air does not flow out from the atmospheric outflow pipe 103 to the ink cartridge 101 again. Inflow of ink I stops.

Japanese Patent Laying-Open No. 2002-307711 (FIG. 3)

However, in the buffer tank as shown in FIGS. 7 and 8, the meniscus is formed in the atmospheric outflow pipe when the ink level is lowered. The meniscus is finally broken when the liquid level drops until the water head difference from the air outflow pipe to the ink liquid level reaches h _0, and the ink flows into the buffer tank. That is, the ink level in the buffer tank fluctuates by the water head difference h ₀ . However, as described above, since the atmospheric outflow pipe is formed in the shape of a thin hollow needle, the water head difference h ₀ from the atmospheric outflow pipe to the ink level necessary for breaking the meniscus is inevitably large. It will be a thing. Therefore, since the liquid level fluctuation of the ink in the buffer tank becomes large, it is difficult to keep the back pressure of the ink acting on the nozzle almost constant. Furthermore, depending on the magnitude of the water head difference h ₀ required for the meniscus break, there may be a case where the meniscus in the air outflow pipe is not broken even if the ink level drops to near the bottom of the buffer tank. There is a risk that bubbles may be mixed into the ink supplied to the nozzles.

  An object of the present invention is to suppress the fluctuation of the ink liquid level as much as possible by configuring the air to flow out to the ink cartridge promptly when the liquid level in the buffer tank is lowered.

Means for Solving the Problems and Effects of the Invention

  According to a first aspect of the present invention, there is provided an ink jet printer comprising: a nozzle that ejects ink; and a buffer tank that holds ink flowing from an ink cartridge mounted above the ink tank and causes the ink to flow toward the nozzle. Is for causing the ink in the ink cartridge to flow into the buffer tank, and at least the ink inflow path including a portion extending downward from the top plate portion of the tank body in the buffer tank and the atmosphere from the outside. An atmosphere introduction port for introducing, and an atmosphere outflow path for allowing the atmosphere in the buffer tank to flow out to the ink cartridge, the atmosphere outflow path being provided in the top plate portion and extending vertically. At least at the lower end, the hollow portion has a larger cross-sectional area than the atmospheric outflow pipe and communicates with the atmospheric outflow pipe. A cylindrical member, comprising: a first cylindrical member extending from the top plate portion to a position below the lower end of the air outflow pipe and above the lower end of the ink inflow passage. To do.

  In this ink jet printer, when the ink cartridge is mounted on the buffer tank, the atmosphere is introduced into the buffer tank through the atmosphere introduction port, and the atmosphere flows out from the atmosphere outflow path to the ink cartridge. Ink in the ink cartridge flows into the buffer tank from the ink inflow path so as to be replaced. Then, ink flows out from the buffer tank to the nozzle, and ink is ejected from the nozzle. Here, the air outflow path includes an air outflow pipe extending vertically and a first cylindrical member communicating with the air outflow pipe. The first cylindrical member has a hollow cross-sectional area larger than that of the air outflow pipe at least at the lower end, and extends to a position below the lower end of the air outflow pipe and above the lower end of the ink inflow passage. doing.

  When the ink is not discharged from the nozzle, the ink does not flow out from the buffer tank to the nozzle, and the liquid level of the ink in the buffer tank extends below the lower end of the air outflow pipe. The ink stops in the vicinity of the lower end of the ink and the ink has entered the inside of the lower end of the first cylindrical member, so that the atmosphere does not flow out from the atmosphere outflow path to the ink cartridge. In this state, when the ink in the buffer tank flows out to the nozzle, the liquid level of the ink in the buffer tank is lowered. At this time, the lower end of the first cylindrical member is separated from the liquid level, and the first cylindrical member A meniscus is formed inside the lower end due to the surface tension of the ink. As described above, in a state where the meniscus is stretched inside the first cylindrical member, it is impossible to cause the air to flow out from the air outflow path to the ink cartridge and to cause the ink in the ink cartridge to flow into the buffer tank. However, since the cross-sectional area of the hollow portion of the first cylindrical member is at least lower than that of the atmospheric outflow pipe at the lower end, the meniscus is simple due to a slight drop in the ink liquid level compared to the case where the meniscus is directly formed in the atmospheric outflow pipe. Will be broken.

  Therefore, the meniscus is broken only by the ink level in the buffer tank slightly lowering from the lower end of the first cylindrical member, and the atmosphere flows out from the atmosphere inflow path to the ink cartridge. That is, as soon as the liquid level in the buffer tank decreases, the ink in the ink cartridge is replenished into the buffer tank from the ink inflow path. It is possible to suppress the back pressure fluctuation of the ink acting on the ink.

  In the ink jet printer according to a second aspect, in the first aspect, the lower end surface of the first cylindrical member is formed with a portion having a different separation distance from the liquid surface of the ink in the buffer tank. It is characterized by. As described above, when a portion having a different separation distance from the ink liquid level is formed on the lower end surface of the first cylindrical member, the meniscus formed on the first cylindrical member when the ink liquid level decreases. Since the balance of the surface tension is easily lost, the meniscus can be easily broken.

  An ink jet printer according to a third aspect is characterized in that, in the second aspect, the lower end surface of the first cylindrical member is inclined at a predetermined angle with respect to the ink level in the buffer tank. Is. Since the lower end surface of the first cylinder member is not parallel to the ink liquid level, the balance of the surface tension of the meniscus formed on the first cylinder member is easily lost when the ink liquid level is lowered. Can be easily broken.

  An ink jet printer according to a fourth invention is characterized in that, in the second invention, a protruding portion that protrudes partially downward is formed at one circumferential position of the lower end portion of the first cylindrical member. It is what. Since the balance of the surface tension of the meniscus formed on the first cylindrical member tends to be lost when the ink liquid level decreases in the vicinity of the protruding portion that partially protrudes from the lower end of the first cylindrical member, the meniscus Can be more easily broken. When the meniscus breaks, the ink in the first cylinder member is drawn into the buffer tank along the protruding portion, so that the ink in the first cylinder member is instantaneously replaced with the atmosphere. Therefore, when the ink level is lowered, the air can be quickly discharged to the ink cartridge.

  An ink jet printer according to a fifth aspect of the present invention is the ink jet printer according to any one of the first to fourth aspects, wherein the atmospheric outflow pipe is provided in a vertically penetrating manner in the top plate portion, and the first cylindrical member is the atmospheric air. A portion of the outflow pipe extending from the top plate portion into the tank main body is inserted. Therefore, the atmosphere in the buffer tank enters from the lower end of the first cylinder member, and further flows out to the ink cartridge through the atmosphere outflow pipe inserted in the first cylinder member.

  An ink jet printer according to a sixth aspect of the present invention is the ink jet printer according to any one of the first to fifth aspects, wherein the ink inflow passage includes an ink inflow pipe provided in a vertically penetrating manner on the top plate portion, and the ink inflow pipe. The hollow member has a large cross-sectional area, and a portion of the ink inflow pipe extending from the top plate portion into the tank body is inserted into the cylindrical member, and the ink inflow tube and the first inflow pipe from the top plate portion. It has the 2nd cylinder member extended below rather than a cylinder member, It is characterized by the above-mentioned.

  Since the ink inflow pipe is inserted into the second cylindrical member having a large diameter, and the second cylindrical member extends downward longer than the ink inflow pipe, the buffer tank of the ink inflow pipe having a small cross-sectional area of the hollow portion The inner length can be shortened as much as possible, and the flow resistance of ink when the ink flows from the ink cartridge into the buffer tank can be minimized. In other words, when the liquid level in the buffer tank drops and the air flows out from the air outflow path to the ink cartridge, the ink can be replenished from the ink cartridge to the buffer tank immediately, and the ink liquid level in the buffer tank changes. (In other words, fluctuations in the ink back pressure acting on the nozzles) can be kept small.

  An ink jet printer according to a seventh invention is characterized in that, in any one of the first to sixth inventions, the top plate portion and the first cylindrical member are integrally formed of a synthetic resin. . Thus, by integrally forming the top plate portion and the first cylindrical member with synthetic resin, the number of parts and the number of assembly steps can be reduced.

  An ink jet printer according to an eighth invention is characterized in that, in the seventh invention, the top plate portion, the first cylinder member and the second cylinder member are integrally formed of a synthetic resin. Is. Thus, by integrally forming the top plate portion and the first and second cylindrical members with synthetic resin, the number of parts and the number of assembly steps can be further reduced.

  An ink jet printer according to a ninth invention is characterized in that, in any of the sixth to eighth inventions, the ink inflow pipe and the atmospheric outflow pipe are formed of the same tubular member. The ink inflow pipe and the atmospheric outflow pipe are hollow needle-like tubular members having a thin diameter made of metal, and are relatively expensive. Therefore, they are long for the ink inflow pipe and the atmospheric outflow pipe like the conventional buffer tank. If two types of tubular members having different sizes are used, the cost increases. However, in the present invention, the same tubular member can be used for the ink inflow pipe and the atmospheric outflow pipe, so that the cost of parts can be reduced.

  An ink jet printer according to a tenth aspect of the invention includes a nozzle for ejecting ink, a buffer tank communicating with the nozzle for suppressing fluctuations in back pressure of the ink acting on the nozzle, and a top plate of the tank body of the buffer tank An ink inflow pipe provided in the upper part and extending vertically, and an ink inflow pipe for allowing ink in an ink cartridge mounted on the upper side of the buffer tank to flow into the buffer tank, and also provided in the top plate part An atmospheric outflow pipe that extends, the atmospheric outflow pipe for allowing the air in the buffer tank to flow out to the ink cartridge, and at least the lower end has a larger cross-sectional area than the atmospheric outflow pipe and communicates with the atmospheric outflow pipe A cylindrical member extending from the top plate to a position below the lower end of the air outflow pipe and above the lower end of the ink inflow pipe. It is characterized in that a first cylindrical member.

  In this ink jet printer, the air in the buffer tank flows out to the ink cartridge through the air outflow pipe, and the ink in the ink cartridge flows into the buffer tank through the ink inflow pipe so as to replace the air. Here, the top plate portion of the buffer tank is provided with a first cylindrical member communicating with the atmospheric outflow pipe. The first cylindrical member has a larger sectional area of the hollow portion than the atmospheric outflow pipe, When the ink extends from the buffer tank to the nozzle below the lower end of the ink inflow pipe, and the ink does not flow out from the buffer tank to the nozzle, the liquid level of the ink in the buffer tank is Located near the bottom edge. When the ink flows out from the buffer tank to the nozzle and the ink level is lowered, the ink level is separated from the lower end of the first cylindrical member, and a meniscus is formed inside the lower end of the first cylindrical member. However, since the cross-sectional area of the hollow portion of the first cylindrical member is larger than that of the atmospheric outflow pipe at least at the lower end, the meniscus is slightly decreased due to a slight drop in the ink liquid level as compared with the case where the meniscus is formed in the atmospheric outflow pipe. Can be easily broken.

  Therefore, as soon as the liquid level in the buffer tank decreases, the meniscus formed on the first cylindrical member is broken and the air flows out to the ink cartridge, and the ink in the ink cartridge is replenished into the buffer tank from the ink inflow tube. Will be. For this reason, it is possible to suppress the fluctuation of the ink liquid level in the buffer tank and to reduce the back pressure of the ink acting on the nozzle.

  A buffer tank of an ink jet printer according to an eleventh aspect of the invention is a buffer tank for an ink jet printer that communicates with a nozzle that ejects ink and suppresses fluctuations in the back pressure of the ink that acts on the nozzle. An ink inflow pipe for covering the upper part of the tank main body and allowing the ink in the ink cartridge mounted on the upper side of the tank main body to flow into the tank main body and an air outflow pipe for allowing the air to flow out to the ink cartridge are respectively provided. A top plate portion penetrating vertically, and a cylindrical member in which a cross-sectional area of the hollow portion is larger than the atmospheric outflow pipe at least at the lower end and a portion of the atmospheric outflow tube extending from the top plate portion into the tank body is inserted A cylindrical member extending from the top plate portion to a position below the lower end of the air outflow pipe and above the lower end of the ink inflow pipe; It is characterized in that it comprises.

  According to the eleventh invention, the same operations and effects as those of the tenth invention are achieved. That is, when the ink flows out from the buffer tank to the nozzle and the ink level is lowered, the liquid level is separated from the lower end of the first cylindrical member, and a meniscus is formed inside the lower end of the first cylindrical member. However, since the cross-sectional area of the hollow portion of the first cylindrical member is larger than that of the atmospheric outflow pipe at least at the lower end, the meniscus is easily reduced by a slight drop in the ink liquid level compared to the case where the meniscus is formed in the atmospheric outflow pipe. Can break.

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, an ink jet printer 1 includes an ink jet head 2 having a nozzle 2a for ejecting ink I toward a recording paper P, and is connected to the ink jet head 2 via a supply tube 8 and above it. A buffer tank 4 that holds ink I flowing from the mounted ink cartridge 3, a carriage 5 that linearly moves the inkjet head 2 back and forth in one direction, a transport mechanism 6 that transports the recording paper P, and the inkjet head 2. A purge device 7 for sucking the air inside and the ink I having increased viscosity is provided.

  In this ink jet printer 1, ink I is supplied from the buffer tank 4 in which the ink cartridge 3 is mounted to the nozzle 2a of the ink jet head 2 through the supply tube 8, and the ink jet head 2 is driven by the carriage 5 in the direction perpendicular to the plane of FIG. The ink I is ejected from the nozzles 2a toward the recording paper P conveyed in the left-right direction in FIG. In order to prevent the ink I from leaking from the nozzle 2a when the ink I is not ejected from the nozzle 2a, the nozzle 2a is disposed at a position higher than the liquid level of the ink I in the buffer tank 4. ing.

  The purge device 7 sucks the ink I from the nozzle 2a and the purge cap 10 that can move in a direction approaching / separating from the ink discharge surface and that can be mounted on the inkjet head 2 so as to cover the ink discharge surface. A suction pump 11 is provided. When the ink jet head 2 is outside the printable range of the recording paper P, the suction pump 11 sucks the ink I, which has been mixed into the ink jet head 2 and evaporated to a high viscosity, from the nozzle 2a. Is possible.

  Next, the buffer tank 4 will be described. Before that, the ink cartridge 3 mounted above the buffer tank 4 will be briefly described. As shown in FIG. 1, the ink cartridge 3 includes a synthetic resin cartridge main body 20 that stores the ink I, and a synthetic resin lid member 21 that covers the lower portion of the cartridge main body 20. The cartridge body 20 is formed with two insertion holes 22 through which tips of an ink inflow pipe 36 and an atmospheric outflow pipe 38 described later are inserted. In addition, the cartridge body 20 is also formed with two cylindrical portions 23 that are connected to the upper ends of the two insertion holes 22 and extend into the cartridge body 20. In the two insertion holes 22, plug members 24 having elasticity (for example, made of rubber) for preventing ink leakage are press-fitted.

  The buffer tank 4 is for suppressing the fluctuation of the back pressure acting on the nozzle 2a by keeping the liquid level of the ink I held therein constant. As shown in FIGS. The ink cartridge 3 is mounted above the buffer tank 4, and the ink I in the ink cartridge 3 is configured to flow into the buffer tank 4. The buffer tank 4 includes a tank main body 30 that stores the ink I, and a top plate portion 31 that covers the upper portion of the tank main body 30. The tank main body 30 and the top plate portion 31 are each formed of a synthetic resin. Yes. The buffer tank 4 is formed with an air introduction port 32 for introducing air into the buffer tank 4. An ink outlet 33 is formed at the bottom of the tank body 30 to connect the supply tube 8 and allow the ink I to flow out to the nozzle 2a.

  Further, the buffer tank 4 causes the ink inflow path 34 through which the ink I in the ink cartridge 3 flows into the buffer tank 4 and the air in the buffer tank 4 introduced from the air introduction port 32 to flow out to the ink cartridge 3. And an atmospheric outflow passage 35 for the purpose.

  The ink inflow path 34 has an ink inflow pipe 36 provided in a vertically penetrating manner on the top plate portion 31, a diameter larger than the ink inflow tube 36, and the tank main body 30 from the top plate portion 31 of the ink inflow tube 36. It has the cylindrical member 37 (2nd cylindrical member) by which the part extended inward was inserted. On the other hand, the atmospheric outflow path 35 includes an atmospheric outflow pipe 38 provided in a vertically penetrating manner on the top plate portion 31, and a larger diameter than the atmospheric outflow pipe 38 and from the top plate portion 31 of the atmospheric outflow pipe 38 to the tank. A portion extending into the main body 30 has a cylindrical member 39 (first cylindrical member) inserted therein.

  The ink inflow pipe 36 and the atmospheric outflow pipe 38 are configured by hollow needle-shaped (cylindrical) metal members (for example, an inner diameter of 1.4 mm) having a sharp tip shape. Openings 36 a and 38 a are formed at the tip portions of the ink inflow pipe 36 and the atmospheric outflow pipe 38, respectively. The ink inflow pipe 36 and the atmospheric outflow pipe 38 are attached to the top plate 31 so as to protrude slightly downward from the top plate 31, and the lower ends of the ink inflow pipe 36 and the atmospheric outflow pipe 38 are at substantially the same position. Has been placed. Therefore, the ink inflow pipe 36 and the atmospheric outflow pipe 38 can be configured by the same hollow needle-like member.

  The two cylindrical members 37 and 39 are integrally formed with the top plate portion 31 made of synthetic resin. The cylindrical member 39 is formed in a cylindrical shape having a circular cross section, and has a larger diameter (for example, an inner diameter of about 6 mm) than the atmospheric outflow pipe 38, and the cross-sectional area of the hollow portion is that of the hollow portion of the atmospheric outflow pipe 38. It is larger than the cross-sectional area. A portion of the atmospheric outflow pipe 38 that extends from the top plate portion 31 into the tank body 30 is inserted into the cylindrical member 39 and communicates with the atmospheric outflow pipe 38. Further, the cylindrical member 39 is more than the atmospheric outflow pipe 38. It extends downward. Moreover, as shown in FIGS. 1-3, the protrusion part 39a which protrudes below partially in one place of the circumferential direction of the lower end part of the cylinder member 39 is formed, and in this protrusion part 39a, a cylinder member The separation distance from the lower end surface of 39 to the liquid surface of ink I is configured to be partially different.

  On the other hand, the cylindrical member 37 is formed in a cylindrical shape with a circular cross section, and has a larger diameter (for example, about 6 mm in inner diameter) than the ink inflow pipe 36, and the cross-sectional area of the hollow portion is hollow in the air outflow pipe 38. It is larger than the cross-sectional area of the part. A portion of the ink inflow pipe 36 that extends from the top plate portion 31 into the tank body 30 is inserted into the cylindrical member 37 and communicates with the ink inflow pipe 36. The cylindrical member 37 further includes the ink inflow pipe 36 and the cylinder. It extends below the member 39.

  When the ink cartridge 3 is mounted above the buffer tank 4 by passing the hollow needle-like ink inflow pipe 36 and the atmospheric outflow pipe 38 through the two plug members 24 of the ink cartridge 3, the opening of the atmospheric outflow pipe 38 is opened. The air flows out of the ink cartridge 3 from the air flow path 38a through the air outflow path 35, and the ink I in the ink cartridge 3 flows into the ink inflow pipe 36 from the opening 36a so as to be replaced with the air. Ink I flows into the buffer tank 4 via When the liquid level of the ink I in the buffer tank 4 rises and reaches the vicinity of the lower end of the cylindrical member 39 constituting the atmospheric outflow path 35, the ink I flows into the lower end of the cylindrical member 39 and the atmosphere is generated. Since the air does not enter the cylindrical member 39, the atmosphere does not flow out to the ink cartridge 3, and the ink I does not flow into the buffer tank 4 any more.

As described above, when the ink I is not discharged from the nozzle 2 a and the ink I does not flow out from the buffer tank 4 to the nozzle 2 a, the liquid level of the ink I in the buffer tank 4 is near the lower end of the cylindrical member 39. Has stopped. Here, as shown in FIG. 2, the distance h ₁ between the lower end of the cylindrical member 39 and the lower end of the atmospheric outflow pipe 38 breaks the meniscus formed in the atmospheric outflow pipe 38 due to the surface tension of the ink I. It is set to be larger than the water head difference h ₀ (see FIG. 8) necessary for this. As a specific example, when the surface tension of the ink I is 40 mN / m and the inner diameter of the atmospheric outflow pipe 38 is 1.4 mm, h ₀ is 9 mm. The distance h ₁ between the lower end of 39 and the lower end of the air outflow pipe 38 is 13 mm, which is larger than h ₀ .

Therefore, when the ink I is ejected from the nozzle 2 a and the ink I in the buffer tank 4 flows out to the nozzle 2 a, the liquid level of the ink I in the buffer tank 4 is lowered, but the ink I from the lower end of the atmospheric outflow pipe 38. for the distance to the liquid surface is always larger than h _0, the meniscus is not formed in the small air outlet tube 38 diameter, when the liquid surface of the ink I is separated from the lower end of the tubular member 39 decreases In addition, a meniscus is formed inside the lower end portion of the cylindrical member 39 by the surface tension of the ink I.

  Here, since the inner diameter of the cylindrical member 39 is larger than the inner diameter of the atmospheric outflow pipe 38 (for example, three times or more), the meniscus is formed in the atmospheric outflow pipe 38 like a conventional buffer tank as shown in FIG. Compared with the case where is formed, the water head difference (distance from the lower end surface of the cylindrical member 39 to the liquid surface of the ink I) necessary for breaking the meniscus is very small. For this reason, the meniscus of the cylindrical member 39 breaks and the atmosphere in the buffer tank 4 flows to the atmospheric outflow pipe 38 only when the liquid level of the ink I is slightly lowered.

  Furthermore, a protruding portion 39a that partially protrudes downward is formed at the lower end of the cylindrical member 39, and a portion having a different separation distance to the liquid surface of the ink I is formed by the protruding portion 39a. Become. Therefore, when the liquid level of the ink I is lowered, the balance of the surface tension of the meniscus formed on the cylindrical member 39 is easily lost, and the meniscus can be broken more easily. When the meniscus breaks, the ink I in the cylindrical member 39 is drawn into the buffer tank 4 along the protruding portion 39a by the surface tension of the ink I in the buffer tank 4, while the liquid of the ink I Atmosphere flows into the cylinder member 39 from the position on the left side in FIG. 2 at the lower end of the cylinder member 39 having a large separation distance from the surface, so that the ink I inside the cylinder member 39 instantaneously replaces the atmosphere. Therefore, when the liquid level of the ink I is lowered, the air can be quickly discharged to the ink cartridge 3.

  On the other hand, a portion of the ink inflow pipe 36 extending from the top plate portion 31 into the tank body 30 is inserted into a cylindrical member 37 having a diameter larger than that of the ink inflow pipe 36. The pipe 36 extends downward. Therefore, the ink I flowing into the buffer tank 4 from the ink cartridge 3 through the ink inflow path 34 flows in the large-diameter cylindrical member 37 in the buffer tank 4, and the flow resistance can be extremely reduced. Therefore, the atmosphere in the buffer tank 4 flows out to the ink cartridge 3 and the ink I in the ink cartridge 3 flows into the buffer tank 4 at the same time, so that the ink I is replenished to the buffer tank 4 quickly.

According to the inkjet printer 1 described above, the following effects can be obtained.
The top plate portion 31 of the buffer tank 4 is provided with a cylindrical member 39 having a diameter larger than that of the atmospheric outflow pipe 38 and communicating with the atmospheric outflow pipe 38. The cylindrical member 39 extends downward from the atmospheric outflow pipe 38. Yes. Therefore, when the liquid level of the ink I is lowered, no meniscus is formed in the small-diameter atmospheric outflow pipe 38, and a meniscus is formed in the lower end portion of the large-diameter cylindrical member 39. The formed meniscus is easily broken compared to the small-diameter atmospheric outflow pipe 38. Thereby, since the fluctuation amount of the liquid level of the ink I can be reduced as compared with the conventional buffer tank, the back pressure fluctuation of the ink I acting on the nozzle 2a can be suppressed smaller than that of the conventional one.

  Further, since a protruding portion 39a that protrudes partially downward is formed at the lower end of the cylindrical member 39, the balance of the surface tension of the meniscus formed on the cylindrical member 39 is likely to be lost, and the meniscus can be more easily removed. Can break. Accordingly, when the liquid level of the ink I is slightly lowered, the meniscus of the cylindrical member 39 is quickly broken, so that the atmosphere can be immediately discharged to the ink cartridge 3 through the atmosphere outflow path 35.

  The top plate portion 31 of the buffer tank 4 is also provided with a cylindrical member 37 having a diameter larger than that of the ink inflow pipe 36 and communicating with the ink inflow pipe 36. The cylindrical member 37 is also below the ink inflow pipe 36. It extends to. Therefore, the ink I that has flowed into the buffer tank 4 from the ink cartridge 3 flows in the large-diameter cylindrical member 37 in the buffer tank 4, and thus its flow resistance is reduced. Accordingly, when the atmosphere in the buffer tank 4 flows out to the ink cartridge 3 through the atmosphere outflow path 35, the ink I immediately flows into the buffer tank 4 from the ink inflow path 34, and the ink I enters the buffer tank 4. Since the ink is quickly replenished, fluctuations in the liquid level of the ink I in the buffer tank 4 can be suppressed, and fluctuations in the back pressure of the ink I acting on the nozzle 2a can be minimized.

  Since there is no need to make a difference between the positions of the lower ends of the ink inflow pipe 36 and the atmospheric outflow pipe 38 and the positions of the lower ends can be made the same, the ink inflow pipe 36 and the atmospheric outflow pipe 38 are formed in the same hollow needle shape. Therefore, the component cost can be reduced.

  Since the top plate portion 31 and the cylindrical members 37 and 39 are integrally formed of synthetic resin, the number of parts can be reduced and the number of steps for assembly can be omitted, so that the manufacturing cost can be reduced. .

Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configurations as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted as appropriate.
1] The shape of the lower end of the cylindrical member 39 communicating with the atmospheric outflow pipe 38 is preferably the shape shown in FIG. 3 described above, but is not necessarily limited to that shape. For example, as shown in FIG. 4, the lower end surface of the cylindrical member 39A may be formed in parallel with the liquid surface of the ink I. In this case, the balance of the surface tension of the meniscus is less likely to be lost compared with the shape of FIG. 3 described above, and the liquid level of the ink I is greatly reduced until the meniscus is broken. As compared with the case where the meniscus is formed in the atmospheric outflow pipe 38 having a small inner diameter as in the buffer tank, the meniscus break is remarkably facilitated. Further, the shape processing of the cylindrical member 39A becomes very easy. Furthermore, if the shape has a portion having a different separation distance from the lower end surface of the cylindrical member 39 and the liquid surface of the ink I, the meniscus can be easily broken as compared with the buffer tank of FIG. As shown, the balance of the surface tension of the meniscus may be easily broken by inclining the lower end surface of the cylindrical member 39B with a predetermined angle (for example, about 10 degrees) with respect to the liquid surface of the ink I.

2] It is not always necessary to integrally form the top plate portion 31 and the cylindrical members 37 and 39 with a synthetic resin, and each may be constituted by separate members.
3] In the above embodiment, the ink inflow pipe 36 and the atmospheric outflow pipe 38 penetrate the top plate portion 31 vertically, but as shown in FIG. 6, these ink inflow pipes 36 are provided in the buffer tank 4C. And the air outflow pipe 38 may project only upward without extending downward from the top plate portion 31 and communicate with the cylindrical members 37C and 39C, respectively. In this case, the distance from the lower end of the atmospheric outflow pipe 38 to the liquid level of the ink I can be made longer. Further, since the ink I flows only through the large-diameter cylindrical member 37C in the buffer tank 4C, the flow resistance when the ink I flows into the buffer tank 4C can be further reduced.
4] The cylindrical member 39 into which the atmospheric outflow pipe 38 is inserted has only to have a diameter larger than that of the atmospheric outflow pipe 38 at least at the lower end. For example, the cylindrical member 39 is formed in a so-called trumpet shape whose inner diameter increases toward the lower side. May be.

  5] In the above-described embodiment, the cylindrical members 37 and 39 are formed in a cylindrical shape. However, the cylindrical members 37 and 39 are not limited to these shapes. For example, the cylindrical members 37 and 39 may be formed in a polygonal prism shape. . That is, as long as the cross-sectional area of the hollow portion at least at the lower end of the cylindrical member 37 is configured to be larger than the cross-sectional area of the hollow portion of the ink inflow tube 36, the cylindrical member 37 has any cross-sectional shape compared to the conventional one. Thus, the flow resistance when the ink I flows into the buffer tank 4 can be reduced. In addition, as long as the cross-sectional area of the hollow portion at least at the lower end of the cylindrical member 39 is configured to be larger than the cross-sectional area of the hollow portion of the atmospheric outflow pipe 38, the cylindrical member 39 has any cross-sectional shape compared to the conventional one. The meniscus can be easily broken.

1 is a schematic configuration diagram of an inkjet printer according to an embodiment of the present invention. It is sectional drawing of a buffer tank. It is an enlarged view of the lower end part of a cylinder member. FIG. 4 is a diagram corresponding to FIG. 3 in a modified form. FIG. 6 is a diagram corresponding to FIG. 3 in another modified form. FIG. 6 is a view corresponding to FIG. 2 showing another modification. It is sectional drawing of the conventional ink cartridge and a buffer tank. It is sectional drawing of the conventional buffer tank.

Explanation of symbols

I Ink 1 Inkjet printer 2a Nozzle 3 Ink cartridge 4, 4C Buffer tank 30 Tank body 31 Top plate portion 32 Atmospheric inlet 34 Ink inlet 35 Inlet outlet 35 Ink inlet pipes 37, 37C Tubular member 38 Atmospheric outlet pipes 39, 39A , 39B, 39C Cylinder member 39a Projection

Claims (11)

A nozzle that ejects ink, and a buffer tank that holds ink flowing in from an ink cartridge mounted above and discharges ink toward the nozzle;
The buffer tank is
The ink in the ink cartridge is introduced into the buffer tank, and at least the ink inflow path including a portion extending downward from the top plate portion of the tank body in the buffer tank and the atmosphere is introduced from the outside. An atmosphere introduction port, and an atmosphere outflow passage for causing the atmosphere in the buffer tank to flow out to the ink cartridge,
The air outflow path is
An atmospheric outflow pipe provided on the top plate portion and extending vertically;
A cylindrical member having a hollow cross-sectional area larger than that of the air outflow pipe at least at the lower end and communicating with the air outflow pipe, and is below the lower end of the air outflow pipe from the top plate and below the ink inflow passage. A first tubular member extending to a position above the lower end;
An ink jet printer comprising:   2. The ink jet printer according to claim 1, wherein a portion having a different separation distance from a liquid surface of the ink in the buffer tank is formed on a lower end surface of the first cylindrical member.   The inkjet printer according to claim 2, wherein a lower end surface of the first cylindrical member is inclined at a predetermined angle with respect to a liquid surface of the ink in the buffer tank.   The inkjet printer according to claim 2, wherein a protruding portion that partially protrudes downward is formed at one circumferential position of the lower end portion of the first cylindrical member.   The atmosphere outflow pipe is provided in a vertically penetrating manner in the top plate portion, and the first cylindrical member is inserted into a portion of the atmosphere outflow tube extending from the top plate portion into the tank body. The ink jet printer according to any one of claims 1 to 4, wherein   The ink inflow path includes an ink inflow pipe provided in a vertically penetrating manner on the top plate portion, and a cross-sectional area of a hollow portion larger than that of the ink inflow tube, and the tank main body from the top plate portion of the ink inflow tube. 2. A cylindrical member having an inwardly extending portion inserted therein, wherein the second cylindrical member extends downward from the top plate portion below the ink inflow pipe and the first cylindrical member. The inkjet printer in any one of -5.   The ink jet printer according to claim 1, wherein the top plate portion and the first cylindrical member are integrally formed of a synthetic resin.   The inkjet printer according to claim 7, wherein the top plate portion, the first cylindrical member, and the second cylindrical member are integrally formed of a synthetic resin.   The ink jet printer according to any one of claims 6 to 8, wherein the ink inflow pipe and the atmospheric outflow pipe are formed of the same tubular member. A nozzle for ejecting ink;
A buffer tank that communicates with this nozzle and suppresses fluctuations in the back pressure of the ink acting on the nozzle;
An ink inflow pipe provided on a top plate portion of the tank body of the buffer tank and extending vertically, and an ink inflow pipe for allowing ink in an ink cartridge mounted on the upper side of the buffer tank to flow into the buffer tank;
Similarly, an atmospheric outflow pipe provided on the top plate portion and extending vertically, and an atmospheric outflow pipe for causing the air in the buffer tank to flow out to the ink cartridge,
A cylindrical member having a hollow cross-sectional area larger than that of the atmospheric outflow pipe at least at the lower end and communicating with the atmospheric outflow pipe, the lower end of the ink outflow pipe being lower than the lower end of the atmospheric outflow pipe from the top plate portion A first cylindrical member extending to a position above
An ink jet printer comprising: A buffer tank of an ink jet printer that communicates with a nozzle that ejects ink and suppresses fluctuations in the back pressure of the ink that acts on the nozzle.
The tank body,
An ink inflow pipe for covering the upper part of the tank main body and allowing the ink in the ink cartridge mounted on the upper side of the tank main body to flow into the tank main body and an air outflow pipe for allowing the air to flow out to the ink cartridge are respectively provided. A top plate that penetrates up and down;
At least at the lower end, a cylindrical member in which a cross-sectional area of the hollow portion is larger than that of the atmospheric outflow pipe and a portion of the atmospheric outflow pipe extending from the top plate portion into the tank body is inserted, A cylindrical member extending to a position below the lower end of the outflow pipe and above the lower end of the ink inflow pipe;
A buffer tank for an ink jet printer, comprising:

Images