JP2006239859A - Inkjet head and inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head which can stably exert the intended performance at all times regardless of a degassing level of ink supplied from an ink feeding source or how much a time while the ink is left staying in an apparatus passes before the start of working, by solving the instability due to a decrease of the degassing level when the ink is initially introduced or after the ink is left for a long time, and to provide an inkjet recorder. <P>SOLUTION: Stable ejection of ink is achieved also in the ink which is not degassed or whose degassing level is lowered, by setting a degassing mechanism adjacent to an ink pressure chamber of the inkjet head. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inkjet head, particularly an inkjet head that discharges ink droplets by pressurizing ink filled in a pressure chamber provided in the head with a piezoelectric element, and forms an image on a recording medium using the inkjet head. The present invention relates to an ink jet recording apparatus.

  As shown in FIG. 5, a conventional general ink jet recording apparatus is a replaceable or replenishable ink tank 2 that supplies ink to an ink jet head 1 that ejects ink droplets of a desired volume onto a recording medium. Are connected via an ink supply path 6. In applications such as home inkjet printers where the printing medium is relatively small, printing speed is slow, and printing frequency is low, the ink consumption is small, so the ink capacity of the ink tank does not need to be increased so much. In many cases, it is arranged very close to the inkjet head via a short ink supply path, but in large-scale inkjet recording apparatuses for industrial or printing applications that frequently form large images on relatively large print media, Since a large amount of ink is consumed, a large-capacity ink tank is required as an ink supply source. In particular, in a serial printing type inkjet recording apparatus, an inkjet head is mounted on a carriage that reciprocates in the main scanning direction, and includes a transport unit (not shown) that transports a recording medium in a sub-scanning direction perpendicular to the main scanning direction. By controlling the timing of main scanning, sub-scanning, and ink droplet ejection in synchronization, a desired image is formed on the printing medium. A large-capacity ink tank is mounted on the reciprocating carriage. Since it is difficult to arrange the ink tank, the ink tank is arranged not on the carriage but in a fixed part in the ink jet recording apparatus, and has an extra length sufficient to absorb the reciprocating movement of the carriage between the ink tank and the ink tank. The ink supply path is made of a flexible tube.

  In order to ensure the stable operation when driving the inkjet head, it is necessary to control the water pressure applied to the ejection nozzle surface of the inkjet head within a certain range, and it is not related to the ejection of ink from the nozzle. In order to avoid unintentional outflow and dripping, the ink jet head determines an appropriate range of water pressure that is a negative value and at the same time the negative pressure is below a certain level so as not to prevent ink ejection. In the case of a small-capacity ink dunk, this water pressure control can be performed by arranging the height in the inkjet printing apparatus at a position relative to the height of the inkjet head. In this case, the water pressure applied to the inkjet head varies depending on whether the amount of ink in the ink tank is maximum or near the sky. When the pressure fluctuation range exceeds the appropriate range for stable driving of the ink jet head, as shown in FIG. 5, a sub tank 8 is provided in the middle of the ink supply path connecting the ink tank and the ink jet head. A configuration is adopted in which ink is temporarily stored in the interior and then supplied to the inkjet head. In such a configuration, the water level of the ink in the sub tank is measured by a water level sensor (not shown), and the ink is supplied from the ink tank to the sub tank before the water level drops and the water pressure applied to the inkjet head falls below the lower limit of the appropriate range. The water pressure applied to the ink jet head is controlled within a range that does not exceed the upper limit of the appropriate range. For this purpose, a pump 7 for pumping ink is arranged between the ink cartridge and the sub tank. This pump is a tube pump that can easily control the generated pressure, flow rate, flow velocity, etc., and has a simple configuration. Is often used.

  Also, when ink is first introduced into an empty inkjet head, or when any meniscus of an inkjet head nozzle is broken for some reason and air enters the interior of the inkjet head, etc. It is necessary to inject the ink into the air and push out the air inside. At the same time, the inside needs to be completely filled with the ink. For this purpose, a pressure pump 9 is provided between the ink tank or the sub tank and the ink jet head to provide an ink supply path. The ink inside the ink jet head is transported by pressure, or the ink discharge surface of the ink jet head is sealed with the cap 11, and then the air inside the cap is sucked with the suction pump 12, thereby the air inside the ink jet head via the nozzle of the ink jet head. Any configuration of sucking out and filling with ink is used Furthermore in some cases it has a both mechanisms as shown in FIG. When a pressure pump is provided, ink is supplied through the ink when it is transported under pressure. On the other hand, when printing is performed by the ejection operation of the inkjet head, a sub tank or ink tank is applied to apply an appropriate range of water pressure. As shown in FIG. 5, a three-way valve 10 for switching the ink supply path is disposed so that the ink supply path communicates with the pressure pump.

  Ink used in this type of ink jet printing apparatus is generally deaerated to remove the air dissolved therein. First, air dissolved in the ink reaches a saturated concentration due to fluctuations in pressure, temperature, etc. and precipitates in the ink, which accumulates somewhere between the ink tank and the nozzle of the inkjet head. This is to prevent the stagnant ink flow and disturbing the stable ink supply. Secondly, when the ink from the ink tank is first introduced into the ink jet printing apparatus, Prevents the generation of air bubbles that tend to stay in the pump connector, the pump connector, the sub-tank, the tube connector 13 used in the connection part of the ink jet head, etc., and also the concave and convex parts and the corner part inside the ink jet head, Even if it occurs, it quickly dissolves and removes in the ink in which the degree of dissolved air is not saturated by deaeration, which becomes a bottleneck of ink flow Third, due to pressure fluctuations that occur inside the inkjet head during discharge, air dissolved in the ink is generated as bubbles in the head due to cavitation, and the inkjet head is stably ejected. This is to prevent obstruction. The first and second effects are expected in all ink jet printing apparatuses of this type regardless of the type of ink jet head for the purpose of ensuring a stable supply of ink. In the case of using a so-called piezo-type ink jet head that pressurizes ink filled in a pressure chamber with a piezoelectric element and ejects ink droplets, bubbles in the pressure chamber absorb the pressure applied by the piezoelectric element and eject ink. The second effect is increasingly important to prevent Furthermore, when ink containing dissolved air at a level close to saturation is used with this type of inkjet head, ink cavitation occurs due to pressure fluctuations generated in the pressure chamber by the inkjet head itself, forming bubbles in the pressure chamber itself. The third effect is very important for this type of inkjet head.

  Since the inkjet head has a narrow nozzle as an opening for discharging ink, in order to prevent the nozzle from being clogged with dust or agglomerates generated as a result of deterioration of the ink, the nozzle is prevented. It is common to have a mesh filter that removes particles that cannot pass through the filter. In order to prevent solid particles from entering the interior of the ink jet head, particularly the pressure chamber, such a filter is provided in an opening for introducing ink or in a channel portion adjacent to the pressure chamber inside the ink jet head. In many cases, the aperture ratio of these filters tends to be low because of the use of a closed mesh to prevent the passage of fine particles. As a result, a pressure loss determined by the fluid resistance of the filter with respect to the viscous ink flow and the ink flow velocity occurs. Since the ink flow rate varies depending on the amount of ink discharged per hour from the inkjet head, the pressure loss also varies accordingly, and the water pressure applied to the ejection nozzle surface of the inkjet head is within the appropriate range. It becomes an obstacle to maintain. Therefore, in order to minimize this pressure drop, it is desirable to reduce the fluid resistance of the filter, and the effective opening area as a whole is often increased by increasing the area of the filter. However, in such a design, it is inevitable that the shape of the flow changes in the vicinity of the filter by rapidly expanding the cross-sectional area of the ink flow path in the vicinity of the filter. And because of the fluid resistance of the filter, the flow velocity per unit area there is smaller than before and after that, so if the ink contains bubbles, it will get caught in such a filter mesh, There are many cases where it stops at. In many cases, the bubbles that are retained in this way will gradually grow together to form a bottleneck of ink flow, and the shape, area, aperture ratio, etc. may be carefully designed along with the surrounding shape. is important.

  As described above, in the ink jet recording apparatus using the piezo type ink jet head, the dissolved air is excluded from the ink supply path from the ink tank to the ink jet head and other parts related to the ink supply including the ink jet head itself. It is important to make the structure filled with ink in order to fully exhibit the first, second and third effects. Therefore, specifically, as an ink tank, a cartridge structure in which ink that has been sufficiently deaerated in the manufacturing process is enclosed in an ink bag 3 that suppresses air permeation as much as possible, and the ink bag is stored in a protective container. There are many examples using. In this case, the outlet of the ink bag is sealed with a spout 4 that does not allow air to pass through to prevent dissolution of air from the atmosphere into the ink. For use in an ink jet recording apparatus, the ink tank of this cartridge structure is inserted into the apparatus. In doing so, the ink bag and the ink supply path are connected by piercing the spout with the needle 5 attached to the apparatus, and at the same time, the outer periphery of the needle is tightly sealed with the spout to contact the ink in the ink bag with the atmosphere. prevent. Alternatively, the ink tank may be a simple ink container opened to the atmosphere, and the ink pumped from the ink tank may be supplied to the deaeration device 14 and transported to the sub tank after sufficiently deaerated. Furthermore, when the deaeration level is lowered by arranging the deaeration device between the sub tank and the inkjet head, not between the ink tank and the sub tank, and constantly monitoring the amount of dissolved oxygen in the ink supply path. Is a very complicated structure that keeps the deaeration level of ink in the ink supply path by switching multiple three-way valves and returning the ink in the inkjet head to the sub tank once and returning it to the sub tank. However, this is disclosed in Patent Document 1. The deaeration apparatus used in such an example is generally a vacuum that evacuates the deaeration module via the deaeration module 15 that removes dissolved air from the ink passing through the interior, an exhaust pipe 16 connected thereto, and the exhaust pipe. An exhaust pump 17 is included. As a degassing module, a tube made of a gas-liquid separation type hollow fiber membrane that does not allow liquid to pass through but is permeable to gas is arranged in a vacuum chamber, and ink is allowed to pass through the tube and at the same time, the external vacuum chamber is exhausted. For this reason, Patent Document 2 discloses that air is deaerated from ink through a hollow fiber membrane.

  Patent Document 3 discloses a structure in which a deaeration station is provided in front of an ink vaporization chamber of an ink jet head, and this aims at a first effect among the effects expected by the deaeration. Therefore, the second and third effects are not expected, and the technology disclosed in this document is a piezo-type inkjet head, as can be seen from the front of the ink vaporizing chamber, not the ink pressure chamber. Rather than a thermal inkjet head, a type of inkjet head that discharges ink from the nozzle with that pressure by forming a heating electrode in the vaporizing chamber in the head and instantaneously boiling the ink in contact with it to generate bubbles. Is to be used. The principle of the degassing station is to reduce the solubility of the air by heating the ink, precipitate the supersaturated dissolved air as bubbles and remove it as information by buoyancy, and the effect of degassing is local. Bubbles cannot be removed from the ink supply path. Further, the deaeration level achieved is low, and a sufficient effect cannot be expected for the stable operation of the piezo ink jet head.

  For sub-tanks, it is usually the simplest method to use a container that is normally open to the atmosphere. In that case, the deaerated ink pumped up from the ink tank will be in the atmosphere for a short period of time staying in the sub-tank. The air is dissolved to contain air at a level close to the saturated dissolved amount, and the above-described effect due to the deaerated ink can no longer be expected in the ink supply path downstream of the sub tank, particularly in the ink jet head. In order to prevent this, Patent Document 4 discloses a structure in which the contact area between the ink and the atmosphere is reduced as much as possible by floating on the liquid surface in the sub tank. In addition, by using a structure in which an ink inlet and an outlet are separately provided in an ink bag that suppresses air permeation, similar to the structure of the ink tank described above, the sub-tank reduces the deaeration level of the ink inside. There are also examples to prevent this.

As a pumping pump or pressure pump, a tube pump that has almost no ink flow irregularities or bent portions inside is used to suppress the formation of bubbles during ink introduction and subsequent retention, and at the same time from the ink tank. The contact between the supplied ink and the atmosphere can be cut off. The general structure of the tube pump is such that the liquid or gas in the tube is sent forward by squeezing the elastic tube while squeezing it with a pressing roller as in Patent Document 5.
Japanese Patent Laid-Open No. 11-042795 Japanese Patent Laid-Open No. 11-209670 JP 08207312 JP 2004-174793 A Japanese Patent Laid-Open No. 11-190280

  As described above, in an inkjet recording apparatus using a piezo-type inkjet head, conventionally, all of the interior of the ink supply path from the ink tank to the inkjet head and other parts related to ink supply, including the inkjet head itself, are dissolved air. However, even in such a device, it is always possible to keep the deaeration level of the ink sufficiently high (that is, the amount of dissolved air in the ink is sufficiently low). It's not easy.

  First, when ink is introduced into an empty inkjet recording apparatus in which ink has not yet been introduced, the ink advances while wetting all the inner surfaces of the ink supply path and other parts related to ink supply. However, air and other gases adsorbed on the inner surface at that time come into contact with the ink and melt. In particular, in an apparatus with a large print medium, the total length of the ink supply path is also long, so the area of the inner surface that comes into contact with the ink becomes considerably large, even if ink is supplied from an ink tank filled with degassed ink. When the meniscus at the tip of the ink reaches the ink jet head, the deaerated ink absorbs a lot of air and the deaeration level is significantly reduced.

  As a result, when ink is ejected immediately after the ink is initially filled in the empty ink jet head, the ink supply is insufficient due to the ink bottleneck created by the air bubbles retained inside, and the ink pressure chamber is retained. In many cases, the operation of the inkjet head becomes unstable due to absorption of driving pressure caused by bubbles or bubbles generated by cavitation.

  As described above, bubbles tend to grow around the filter provided in the inkjet head. As a result, an ink bottleneck is formed around the filter, resulting in insufficient supply of ink, or bubbles entering the adjacent pressure chamber. The frequency of occurrence is surely increased when the deaeration level of the ink is lowered. In order to avoid this, the air adsorbed on the inner surface is absorbed by moving forward while wetting the inside of the ink supply path, and all of the ink part where the deaeration level has decreased passes through the head, and the deaeration level decreases. It is necessary to flow the ink until the ink that has not been filled fills the ink jet head. The ink that has passed through the inkjet head until then is discarded, which causes a significant reduction in the economic efficiency of ink use.

Even when the deaeration device is provided in the ink jet recording apparatus as shown in FIG. 5 and thereby maintains the deaeration level of the ink, it is downstream of the deaeration device (portion close to the ink jet head). The deaeration level is inevitably lowered by advancing while wetting the inner surface of the path.
As long as such a deaeration device is outside the ink jet head, the inlet or the filter installed inside the ink jet head is always located downstream of the deaeration device. In order to prevent this, there is a need for a complicated configuration such as that disclosed in Patent Document 1, in which the deaeration level is once lowered and then returned to the deaerator by operating a plurality of three-way valves. It is also essential to install a sensor that constantly monitors the deaeration level. Even if such a configuration is adopted, since the flow velocity per unit area of the ink tends to be slow around the filter as described above, the air bubbles once retained outside the inkjet head must be taken out of the inkjet head. Is very difficult even using a normal reflux mechanism.

  In addition, a problem in maintaining the deaeration level of the ink in the ink supply path is when the ink jet recording apparatus is left for a certain period of time without being operated. Even if the tubes that make up the ink supply path, pumping or pressurizing pumps, sub tanks, tube connectors, etc. are configured so that the ink inside is not exposed to the atmosphere as much as possible, the materials used are not affected. It is difficult to completely stop the penetration of air.

  In order to secure the seal of the connection part such as the connector part, it is common to use packing or O-rings made of elastic rubber or elastomer material, but these elastic polymer materials are made of inorganic materials such as metals, It is difficult to avoid a higher air permeability than inelastic polymer materials such as hard plastics. In particular, such a polymer material having a relatively high air permeability must be used for a portion of the tube constituting the ink supply path where it is indispensable to ensure flexibility in the structure of the ink jet recording apparatus. .

  As described in the “Background Art” section, the serial printing type inkjet recording apparatus is composed of a flexible tube having a sufficient extra length so as not to prevent the carriage from reciprocating in the main scanning direction. It is necessary to use the ink supply path to connect to the inkjet head on the carriage. Air permeates from this part according to the air permeability specific to the tube material, and the deaeration level of the ink inside is reduced for a certain period of time. Inevitable if left unattended.

  In addition, the tube that constitutes the tube pump also needs to use an elastic material because of its operating principle, and in order to ensure durability that can withstand repeated crushing in a state of being crushed by a roller during operation, its elasticity The choice of materials is limited, and suppressing air permeability and ensuring this durability are often trade-offs, making it difficult to achieve these properties simultaneously. Since air permeates into the ink through materials and parts where the air permeability cannot be lowered sufficiently, the ink is generally used during periods when work is suspended, such as at night, weekends, summer holidays, and New Years. It is well known in the industry that uses an inkjet recording apparatus for industrial use that the deaeration level of the inkjet head decreases, and as a result, the operation of the inkjet head becomes unstable when the closed period ends and the operation is resumed. To avoid this, once all of the old ink that has remained in the ink supply path of the inkjet recording device and the deaeration level has fallen is removed when the job is resumed, it is replaced with new deaerated ink. However, through the disposal of the accumulated ink, the economic efficiency of ink use is also reduced.

  The object of the present invention is to solve the instability caused by the decrease in the deaeration level after the initial introduction of the ink and after the ink is left for a long period of time, whether the deaeration level of the ink supplied from the ink supply source, In addition, it is an object of the present invention to provide an ink jet head and an ink jet recording apparatus which can always exhibit their intended performance stably regardless of how long the ink stays in the apparatus.

  An ink jet head according to the present invention includes a piezoelectric element that generates pressure by a voltage applied from outside, a pressure chamber to which pressure generated by the piezoelectric element is directly or indirectly applied through another member, and the pressure At least one nozzle that opens toward the outside adjacent to the chamber; and an opening for introducing ink from the outside; and the pressure communicates with both the opening and the pressure chamber between the opening and the pressure chamber. A degassing means is provided adjacent to the chamber. Thus, the ink introduced from the opening is deaerated by the deaeration means immediately before being supplied into the pressure chamber, and as a result, the ink is always at a deaeration level determined by the capability of the deaeration means. It is introduced into the pressure chamber in a deaerated state. The deaeration means here is means for removing air or other gas dissolved in the liquid ink, and is usually used for this kind of purpose, such as heating of liquid, vibration, direct or Either evacuation through a gas-liquid separation membrane, bubbling with helium gas, or the like can be applied.

  Concomitantly with the above, at the boundary between the deaeration means and the adjacent pressure chamber, there is provided a filter having a maximum dimension of each opening smaller than the minimum dimension of the nozzle opening, which is blocked across the ink flow path. I can do it. In this case, “blocking across the ink flow path” means that the ink introduced into the ink jet head via the opening for introducing the ink from the outside passes through this filter in the ink flow path that is the flow path of the ink. It means a state where the flow passage section is completely covered so that it cannot flow into the pressure chamber from the deaeration means without permeating the gas. Since the filter has fine mesh openings to allow liquid to pass through, the arrangement does not actually block the ink flow even if it is positioned to block the ink flow path. You can pass through the filter. This filter serves to prevent solid particles that can clog the nozzles from entering the pressure chamber mixed with ink, and the filter always degasses to a degassing level determined by the capability of the degassing means. The ink in the state of care will flow.

  Further, as the deaeration means in the present invention, the gas-liquid separation that constitutes at least a part of the space surrounding the space closed except for the opening for introducing the ink and the path communicating with the pressure chamber It is possible to use a structure comprising a membrane, a vacuum chamber adjacent to the outside of the closed space via the gas-liquid separation membrane, and at least one exhaust port that communicates with the vacuum chamber and opens outward. I can do it. The gas-liquid separation membrane here refers to a membrane having a property that the liquid permeability is zero or very low, while the gas permeability is sufficiently large. Due to this property, the liquid, which is the main component, of the ink components introduced from the opening in the closed space communicating with the opening and pressure chamber for introducing the ink, and dissolved or dispersed therein. The solid cannot pass through this gas-liquid separation membrane, or even if it can, the permeation process will be very slow, whereas the gas represented by the air dissolved in the ink is It is possible to permeate this gas-liquid separation membrane. A pressure gradient is created inside and outside the gas-liquid separation membrane by evacuating the vacuum chamber adjacent to the ink through the gas-liquid separation membrane from the outside through an exhaust port that communicates with the vacuum chamber and opens to the outside. Then, air or other gas dissolved in the ink is driven by the pressure gradient, passes through the gas-liquid separation membrane, is discharged into the vacuum chamber, and is quickly exhausted to the outside.

  A closed space except for the opening for introducing the ink and the path communicating with the pressure chamber as described above, and a gas-liquid separation membrane constituting at least a part of the surface around the space, In the deaeration means using a structure comprising a vacuum chamber adjacent to the outside of the space through the gas-liquid separation membrane and at least one exhaust port communicating with the vacuum chamber and opening outward, Within the closed space, a filter can be provided that blocks across the ink flow path and has the maximum size of each opening smaller than the minimum size of the nozzle opening. In this case, the solid particles that may clog the nozzles are formed in the same way as in the case where the filter is provided at the boundary between the deaeration means and the adjacent pressure chamber so as to cross the ink flow path. It plays a role in preventing the pressure chamber from entering the chamber. “Closing across the ink flow path” is an explanation of the arrangement in which the ink must pass through the filter, and the fact that the liquid ink can actually pass through the filter is as described above. It is as follows. In such a configuration, the ink around the filter is always deaerated by the deaeration means.

  Furthermore, as a deaeration means of the present invention, a closed space communicating with the opening for introducing the ink and the pressure chamber, and at least one gas-liquid separation membrane hollow fiber disposed in the space; A structure comprising at least one exhaust port that communicates with the gas-liquid separation membrane hollow fiber and opens outward can be used. The term “gas-liquid separation membrane hollow fiber” as used herein refers to a structure having a thread or tubular structure in which a central portion is hollow and an outer peripheral wall surrounding the hollow portion is composed of the gas-liquid separation membrane. In such a structure, the ink flowing in the closed space communicating with the opening for introducing the ink and the pressure chamber immerses the gas-liquid separation membrane hollow fiber. By evacuating the inside of the gas-liquid separation membrane hollow fiber through an exhaust port opened to the outside, the pressure gradient generated in the gas-liquid separation membrane drives air and other gases dissolved in the ink. The ink is deaerated through the process of moving into the gas-liquid separation membrane hollow fiber and quickly exhausting it to the outside of the inkjet head through the exhaust port.

  In the ink jet recording apparatus according to the present invention, by having the ink jet head as described above, it is possible to always supply a deaeration level ink of a certain level or more to the pressure chamber of the ink jet head. In the case of using a gas-liquid separation membrane or a hollow fiber formed thereby as a main element of the deaeration means, the ink jet is used in order to evacuate the dissolved gas in the ink through them. By having a vacuum exhaust pump inside the ink jet recording apparatus connected to the exhaust port of the head, rather than externally attached, the ink jet recording apparatus alone supplies ink with a deaeration level above a certain level without any additional parts. It can be supplied to the room.

  According to the ink jet head of the present invention configured as described above and the ink jet recording apparatus having the same, even if the ink is initially introduced into the ink jet recording apparatus, or the ink jet recording apparatus does not operate for a certain period of time, Even if the ink left in the air has decreased in the deaeration level due to the permeation of air, by degassing the ink just before the pressure chamber of the inkjet head, the deaeration level always exceeds a certain level in the pressure chamber. Ink can be supplied, and the stability and reliability of the operation are remarkably improved. As a result, it is not necessary to remove and discard the ink whose deaeration level is lowered from the ink supply path, the sub tank, the ink jet head, etc., so that the economical efficiency in using the ink is improved. Even if air bubbles in the ink often stop and grow and become a bottleneck for the flow of ink immediately after the deaeration means or inside the filter, even if the air bubbles stay there Since it is quickly removed by the deaeration means, a plurality of bubbles do not collect and grow, and it does not enter the adjacent pressure chamber and disturb the stable operation of the ink jet head.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a basic configuration relating to ink supply of an ink jet recording apparatus according to an embodiment of the present invention.

  FIG. 2 is a cross-sectional view schematically illustrating an embodiment of the inkjet head of the present invention. The inkjet head of the present invention includes a nozzle 20 that ejects ink, a pressure chamber 21 adjacent to the nozzle 20, an opening 25 that introduces ink from the outside, and an intermediate portion between the opening and the pressure chamber. It has deaeration means 24 arranged. In this embodiment, the main part of the pressure chamber is composed of the piezoelectric element 22, and the pressure generated by the voltage applied from the outside to the piezoelectric element is directly applied to the pressure chamber to discharge the ink inside through the nozzle. Driving force. The ink in the pressure chamber is in contact with the deaeration means via the opening 23, and the ink supplied from the ink supply path 6 outside the inkjet head via the ink introduction opening immediately before entering the pressure chamber. Therefore, the ink in the pressure chamber is always kept at a deaeration level above a certain level. Here, a special structure is not clearly shown as the ink jet deaeration means, but any of ink heating, vibration, evacuation directly or through a gas-liquid separation film, and bubbling with helium gas can be applied. .

  FIG. 3 is a cross-sectional view schematically illustrating a first embodiment of the inkjet head of the present invention. In FIG. 1, the inkjet head 1 serves as a degassing means, as shown in FIG. 3, as shown in FIG. 3, a gas-liquid separation that forms a closed space 26 except for an opening 25 for introducing ink and a path communicating with the pressure chamber 21. A membrane 27, a vacuum chamber 28 adjacent to the outside of the membrane 27, and an exhaust port 29 communicating with the vacuum chamber and opened to the outside are provided. The structure of other parts is the same as that shown in FIG. By providing the evacuation pump 17 connected to the evacuation port via the evacuation pipe 16, the inside of the vacuum chamber can be evacuated by the evacuation pump. As a result, gas such as air dissolved in the ink in the closed space passes through the gas-liquid separation membrane and moves into the vacuum chamber, and then is quickly exhausted. Therefore, the opening for introducing the ink in the ink jet head It is possible to always maintain a deaeration level above a certain level for the ink existing in the closed space except for the path communicating with the section and the pressure chamber. Furthermore, in this embodiment, a filter is provided in which the maximum dimension of each opening is smaller than the minimum dimension of the nozzle opening, which is blocked in the closed space across the ink flow path.

  When such a filter contains bubbles in the ink due to its fluid resistance, it stops, and a plurality of bubbles combine to grow, so that it is easy to form a bottleneck for ink flow. However, in this embodiment, since the ink in the closed space where the filter is installed is always deaerated, even if a bubble enters the closed space for some reason, Since the bubbles pass through the gas-liquid separation membrane and quickly move to the vacuum chamber and are exhausted, a plurality of bubbles do not grow together to form a bottleneck of ink flow. Therefore, it is desirable that this filter should be installed for the purpose of preventing the solid particles in the ink from entering the pressure chamber, but this may prevent the filter from being used at other sites. Such a configuration is not excluded from the present invention.

  As shown in FIG. 1, the evacuation pump is preferably mounted inside the ink jet recording apparatus, but it does not matter if it exists as a separate apparatus outside the ink jet recording apparatus. Other ink supply path configurations outside the ink jet head are similar to those of the conventional ink jet recording apparatus shown in FIG. 5, but since the ink is degassed inside the ink jet head, before reaching that point For parts through which ink passes, the properties of reducing the deaeration level of the ink, such as the sealing performance of the atmosphere, the air permeability, and the amount of air adsorbed on the inner surface with which the ink contacts, are no longer No need to pay attention. As a result, the ink tank 2 may be a container that simply stores ink, and the ink inside may be in contact with air in an ink tank that is open to the atmosphere.

  Further, since it is not necessary to consider the connection between the ink tank and the ink supply path 6 for sealing to the atmosphere, a coupler 18 that is generally used for connecting tubes can be used. For the parts that require flexibility in the ink supply path, there is no need to pay attention to the air permeability and the amount of air adsorbed to the inner wall. You can choose. Tube pumps are used for pumping pump 7 and pressurizing pump 9, but the tubes used there do not need to pay attention to the air permeability, and are the best in terms of quality and reliability such as pump performance and durability. It is possible to select a suitable material.

  The sub-tank 8 is a container including a water level sensor that senses the ink level inside (not shown), and can have a simple structure that is open to the atmosphere like the ink tank. As for the three-way valve 10 and the tube connector 13, it is not necessary to pay attention to the material selection and structure for blocking the contact between the ink and the atmosphere, and the optimum one can be selected from the quality, durability and price. In this embodiment, a general configuration including a pumping pump, a sub-tank, and a pressurizing pump is used. However, these existences are not indispensable, and the ink tank and the inkjet head are directly connected to each other. It does not exclude other embodiments in which the water pressure applied to the ejection nozzle surface of the inkjet is kept within a certain range by controlling the water level within a certain range.

  FIG. 4 is a cross-sectional view schematically illustrating a second embodiment of the present invention. In this embodiment, as a deaeration means, a closed space 26 except for an opening 25 for introducing ink and a path communicating with the pressure chamber 21 is closed, and a single gas-liquid disposed in the space. A separation membrane hollow fiber 31 and two exhaust ports 29 that communicate with the gas-liquid separation membrane hollow fiber and open to the outside are provided. The structure of other parts is the same as that shown in FIG. The ink supplied from the external ink supply path 6 through the ink introduction opening has a large contact area with the gas-liquid separation membrane hollow fiber by filling the closed space. The inside of the membrane hollow fiber is evacuated by an external evacuation pump through two exhaust ports, creating a pressure gradient in the gas-liquid separation membrane, so air or other gas dissolved in the ink inside the closed space Passes through the gas-liquid separation membrane, moves into the hollow fiber, passes through the exhaust port, and is quickly exhausted. As a result, it is possible to always keep the ink inside the closed space at a deaeration level above a certain level. In addition to dissolved air in the ink, even if bubbles enter the closed space for some reason from the ink introduction opening, the bubbles quickly pass through the gas-liquid separation membrane and move into the hollow fiber to be exhausted. Therefore, this structure exerts a great effect on the removal of bubbles.

  In this embodiment, a filter in which the maximum dimension of each opening is smaller than the minimum dimension of the nozzle opening is provided so as to close the opening 23 to the pressure chamber. The air bubbles are removed by the deaeration means using the gas-liquid separation membrane hollow fiber, so that the air bubbles are retained at this part, and a plurality of air bubbles grow and form a bottleneck of ink flow. There is no. In this embodiment, one gas-liquid separation membrane hollow fiber communicates with two exhaust ports, but the structure is such that one end of the gas-liquid separation membrane hollow fiber is closed with one exhaust port. You can also. In addition, the number of gas-liquid separation membrane hollow fibers is increased, and one or two exhaust ports are provided for each, or one or two exhaust ports are arranged in parallel with a plurality of gas-liquid separation membrane hollow fibers. Of course, it is also possible to share and use.

  With the ink jet head shown in the embodiment and the ink jet recording apparatus using the ink jet head, the deaeration level of the ink flowing into the pressure chamber of the ink jet head can always be kept above a certain level, and the ink is introduced at the initial stage. Thus, it is possible to provide an ink jet head and an ink jet recording apparatus that can operate immediately and stably, and that can operate immediately and stably even after the ink is left in the interior for a long period of time.

The figure which shows typically the basic composition which concerns on the ink supply of the inkjet recording device concerning embodiment of this invention. The figure which shows typically the basic composition of the inkjet head of this invention Schematic diagram of the first embodiment of the inkjet head of the present invention Schematic diagram of the second embodiment of the inkjet head of the present invention The figure which shows typically the basic composition of the conventional inkjet recording device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 2 Ink tank 6 Ink supply path 7 Pumping pump 8 Sub tank 9 Pressure pump 10 Three-way valve 12 Tube connector 14 Deaeration device 17 Vacuum exhaust pump 20 Nozzle 21 Pressure chamber 22 Piezoelectric element 24 Deaeration means 25 Ink introduction opening 26 closed space 27 gas-liquid separation membrane 28 vacuum chamber 29 exhaust port 30 filter 31 gas-liquid separation membrane hollow fiber

Claims (7)

A piezoelectric element that generates pressure by a voltage applied from the outside, a pressure chamber to which the pressure generated by the piezoelectric element is directly or indirectly applied through another member, and an outside adjacent to the pressure chamber An ink jet head comprising: at least one or more nozzles opening toward the outside; an opening for introducing ink from the outside; and a deaeration unit adjacent to the pressure chamber between the opening and the pressure chamber. 2. The ink jet head according to claim 1, wherein a filter for closing the ink flow path is provided at a boundary between the deaeration means and the adjacent pressure chamber. The deaeration means includes a closed space that communicates the opening for introducing the ink and the pressure chamber, a gas-liquid separation membrane that forms at least a part of the outer peripheral surface of the space, and an outer side of the closed space. 3. The inkjet according to claim 1, further comprising: a vacuum chamber adjacent through the gas-liquid separation membrane; and at least one exhaust port communicating with the vacuum chamber and opening outward. head. The inkjet head according to claim 3, wherein a filter for closing the ink flow path is provided inside the closed space. The deaeration means includes an opening for introducing the ink and a space communicating with the pressure chamber, at least one gas-liquid separation membrane hollow fiber disposed in the space, and the gas-liquid separation membrane hollow 3. The ink jet head according to claim 1, further comprising at least one exhaust port communicating with the yarn and opening toward the outside. An ink jet recording apparatus for recording ink on a recording material by discharging ink from a recording means, comprising the ink jet head according to any one of claims 1 to 5 as means for recording ink on a recording material. Inkjet recording apparatus. 6. An ink jet recording apparatus that records ink on a recording material by ejecting ink from the recording means. The ink jet head according to any one of claims 3 to 5 and an exhaust port thereof as means for recording ink on the recording material. An ink jet recording apparatus comprising a vacuum exhaust pump connected thereto.

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