JP2008074019A - Liquid ejecting device, image forming device and liquid ejecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejecting device which can stabilize an ejection amount of a droplet with high accuracy. <P>SOLUTION: The liquid ejection device comprises: an ejection port 51 for ejecting a droplet; a heating element 58 arranged at a location opposite to the ejection port; a bubble generating chamber 52 for generating a bubble 66 in the internal liquid by the heating element; a bubble growing chamber 53 opening on the side of the bubble generating chamber, and having the ejection port on the side opposite to the bubble generating chamber; and a driving control means for controlling driving of the heating element. The driving control means generates predetermined heating energy at the heating element at a pulse width of 3 μ s or less, for film-boiling the liquid in the bubble generating chamber. Then the bubble generated by film-boiling in the liquid in the bubble generating chamber, passes a stage in which the bubble almost uniformly makes contact with an opening edge of the bubble growing chamber, close to the bubble generating chamber, grows in the bubble growing chamber, and then communicates with the atmosphere via the ejection port. At the same time the liquid in the bubble growing chamber is ejected from the ejection port as a droplet. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus, an image forming apparatus, and a liquid ejecting method, and in particular, a liquid ejecting apparatus, an image forming apparatus, and the like that eject liquid droplets from nozzles (ejection ports) using thermal energy generated by a heating element. And a liquid discharge method.

  An ink jet recording apparatus ejects ink droplets from each nozzle toward a recording medium while moving a recording head having a plurality of nozzles (ejection ports) relative to the recording medium. These are widely used because they have low noise characteristics during recording operations, low running costs, and can record high-quality images on a wide variety of recording media. The ejection method of the recording head can be broadly classified into a thermal method using a heating element such as a heater and a piezoelectric method using a piezoelectric element such as a piezo. Compared with the piezoelectric method, the thermal method does not require a large space for disposing the ejection elements, can simplify the head structure, and is advantageous in increasing the nozzle pitch due to its structure. Resolution recording is progressing.

  The thermal recording head is a top shooter type in which the heating element and the nozzle (discharge port) are opposed to each other, and the atmosphere communication drive for communicating bubbles generated when the heating element is driven to the atmosphere. There is a type, and it is drawing attention because it can regulate the discharge amount of droplets with a head structure and has a high potential for obtaining a stable discharge amount.

For example, Patent Document 1 describes a recording head of a top shooter type and an atmospheric communication drive type. This recording head employs a two-stage foaming chamber structure composed of first and second foaming chambers in order to stabilize the ejection amount and improve the ejection efficiency.
JP 2004-42395 A

  However, in the recording head described in Patent Document 1, there is a possibility that the ejection amount varies due to variations in bubble growth, and it is difficult to stabilize the ejection amount with high accuracy. In particular, when forming dots with a discharge amount of 1 pl or less, it is difficult to stabilize the discharge amount, which causes a great deterioration in the recorded image.

  In particular, in the case of the structure of Patent Document 1, in the process after the upper surface side of the bubble grows in the second foaming chamber, the liquid in the second foaming chamber is efficiently discharged by the effect of the rectifying action, and the discharge volume varies. Reduction can be expected. However, in the initial stage of bubble growth where the upper surface of the bubble is in the first foaming chamber, the liquid to be discharged escapes from the second foaming chamber toward the first foaming chamber, and is more accurate. There is a problem that the droplet discharge amount cannot be obtained.

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid discharge apparatus, an image forming apparatus, and a liquid discharge method capable of stabilizing the discharge amount with high accuracy.

  In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that a discharge port for discharging a droplet and a heat generation that is arranged at a position facing the discharge port and generates thermal energy for discharging the droplet. An element, a bubble generation chamber for generating bubbles in an internal liquid by the heating element, an opening on the bubble generation chamber side and the discharge port on the opposite side of the bubble generation chamber side, A bubble growth chamber for growing bubbles generated inside, and drive control means for controlling the drive of the heating element, wherein the drive control means has a predetermined heat applied to the heating element with a pulse width of 3 μsec or less. Energy is generated, and the liquid in the bubble generation chamber is film-boiled. Bubbles generated in the liquid in the bubble generation chamber by the film boiling are generated at the bubble generation chamber side opening end of the bubble growth chamber. Abbreviation Through the contact state, the bubble grows in the bubble growth chamber and communicates with the atmosphere from the discharge port, and the liquid in the bubble growth chamber is discharged as a droplet from the discharge port. A liquid ejection device is provided.

  According to the present invention, the liquid in the bubble growth chamber does not flow back to the bubble generation chamber side (that is, the ink supply side), and is not affected by variations in bubble growth. Since the ink is discharged from the discharge port, the discharge amount can be stabilized with high accuracy.

According to a second aspect of the present invention, in the liquid ejection device according to the first aspect, the height of the bubble generation chamber is H1 and the height of the bubble growth chamber is H2 with respect to the ejection direction of the ejection port. The following formula is satisfied.
0.5 ≦ H2 / (H1 + H2) ≦ 0.9

  According to the aspect of the second aspect, not only the discharge amount is stabilized, but also the refill property is improved, and the thermal damage to the liquid can be reduced.

  In order to achieve the above object, a third aspect of the present invention provides an image forming apparatus comprising the liquid ejection device according to the first or second aspect.

  In order to achieve the above object, a discharge port that discharges droplets, a heating element that is disposed at a position facing the discharge port and generates thermal energy for discharging the droplets, and the heating element internally A bubble generating chamber for generating bubbles in the liquid, and an opening formed on the bubble generating chamber side and the discharge port on the opposite side of the bubble generating chamber side to grow bubbles generated inside the bubble generating chamber A liquid ejection method for a liquid ejection apparatus comprising a bubble growth chamber for controlling the drive of the heating element, and generates a predetermined thermal energy in the heating element with a pulse width of 3 μsec or less A step of film boiling the liquid in the bubble generation chamber, and the bubble generated in the liquid in the bubble generation chamber by the film boiling is grown, and is substantially at the bubble generation chamber side opening end of the bubble growth chamber. And a step of further growing bubbles in the bubble growth chamber so as to communicate with the atmosphere from the discharge port, and discharging the liquid in the bubble growth chamber as droplets from the discharge port. A liquid ejection method is provided.

  According to the present invention, the liquid in the bubble growth chamber does not flow back to the bubble generation chamber side (that is, the ink supply side), and is not affected by variations in bubble growth. Since the ink is discharged from the discharge port, the discharge amount can be stabilized with high accuracy.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, an ink jet recording apparatus as an embodiment of an image forming apparatus according to the present invention will be described. FIG. 1 is an overall configuration diagram of an ink jet recording apparatus. As shown in the figure, the ink jet recording apparatus 10 of the present embodiment has a plurality of recording heads provided for each color ink of black (K), cyan (C), magenta (M), and yellow (Y). A printing unit 12; an ink storage / loading unit 14 that stores ink to be supplied to each recording head; a paper feeding unit 18 that supplies recording paper 16; and a decurling unit 20 that removes curl from the recording paper 16. The suction belt conveyance unit 22 that is arranged to face the nozzle surface (ink ejection surface) of the printing unit 12 and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, and the printing result by the printing unit 12 A print detection unit 24 for reading and a paper discharge unit 26 for discharging printed recording paper (printed matter) to the outside are provided.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In the case of an apparatus configuration using roll paper, a cutter 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and is configured such that at least a portion facing the nozzle surface of the printing unit 12 forms a flat surface.

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 12 inside the belt 33 spanned between the rollers 31 and 32, and the suction chamber 34 is connected to the fan 35. The recording paper 16 on the belt 33 is sucked and held by suctioning to negative pressure.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 is conveyed in the paper conveyance direction (sub-scanning direction; right direction in FIG. 1).

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blowing method of spraying clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip transport mechanism instead of the suction belt transport unit 22 is also conceivable, when the print area is transported by a roller / nip, the roller comes into contact with the print surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The ink storage / loading unit 14 has a tank (main tank) that stores ink of a color corresponding to each recording head of the printing unit 12. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. is doing.

  The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than the image recording width of the recording paper 16. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor includes a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads a test pattern printed by the recording head of each color, and detects ejection of each recording head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by blocking the paper holes by pressurization. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined uneven surface shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. ing. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B. Although not shown, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  In this embodiment, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a recording head that discharges light ink such as light cyan and light magenta.

  FIG. 2 is a schematic configuration diagram illustrating a configuration around the printing unit of the inkjet recording apparatus 10. The ink jet recording apparatus 10 includes a carriage 92 that can reciprocate in the paper width direction (main scanning direction) of the recording paper 16 while being guided by the guide rail 90. On the carriage 92, recording heads 12K, 12C, 12M, and 12Y corresponding to the respective color inks of black (K), cyan (C), magenta (M), and yellow (Y) are mounted. Each of the recording heads 12K, 12C, 12M, and 12Y includes a heater as a heating element, and ejects ink droplets from an ink ejection port (nozzle) using thermal energy generated by the heating element. The ink jet recording apparatus 10 transports the recording paper 16 in the sub-scanning direction (paper transport direction), and reciprocally moves the carriage 92 together with the recording heads 12K, 12C, 12M, and 12Y in the main scanning direction. , 12C, 12M, and 12Y, corresponding color ink droplets are ejected from the nozzles. As a result, a desired image is recorded on the recording paper 16.

  Each of the recording heads 12K, 12C, 12M, and 12Y is configured integrally with a sub tank (not shown), and ink stored in the sub tank is sequentially supplied as the recording head consumes ink during the recording operation. . Further, when the ink remaining amount in the sub-tank becomes a predetermined amount or less as the recording operation proceeds, the carriage 92 is moved to a predetermined standby position (maintenance position) as shown in FIG. At the standby position, ink is supplied from the main tank to the sub tank, and after the sub tank is sufficiently filled with ink, the recording operation is resumed. The main tank is equivalent to the ink storage / loading unit 14 shown in FIG.

  In the following, since the recording heads 12K, 12C, 12M, and 12Y corresponding to the respective colors have the same configuration, the recording head is represented by reference numeral 50 as a representative of these.

  FIG. 3 is a cross-sectional view showing the main configuration of the recording head 50. As shown in FIG. 3, the recording head 50 of the present embodiment is a thermal type head that uses a heating element as an ejection element, and in particular, a heater 58 as a heating element and an ejection port (nozzle) 51 face each other. The head shooter type head structure of the air communication drive type that allows bubbles generated when the heater 58 is driven to communicate with the atmosphere is employed. In FIG. 3, the vertical upward direction is shown as the ejection direction of the nozzle 51. Hereinafter, the structure of each part of the recording head 50 will be described in detail.

  As shown in FIG. 3, in the recording head 50, a first substrate 60, a second substrate 62, and a third substrate 64 are sequentially stacked and bonded. As a constituent material of each substrate, for example, the first substrate 60 is silicon (Si), and the second and third substrates 62 and 64 are photosensitive resins. However, the constituent material of each substrate is not limited thereto. Various materials such as metal, glass and ceramics can be used. Further, the constituent materials of the respective substrates may be the same material or different materials. However, it is preferable that they are all made of the same material from the viewpoint of reducing the warpage of each substrate.

  In the first substrate 60, a heater 58 as an ejection element (heat generating element) is formed on the surface on the second substrate 62 side, and a supply port 54 for supplying ink is formed therethrough. Although not shown, electrical wiring for supplying a drive signal to the heater 58 is patterned on the first substrate 60 in a predetermined shape. On the second substrate 62, a space corresponding to a part of the bubble generation chamber 52 and the ink supply path 56 is formed. In the third substrate 64, a space corresponding to part of the bubble growth chamber 53 and the ink supply path 56 is formed, and an ejection port (nozzle) 51 for ejecting ink droplets is formed therethrough. Although not shown, in the recording head 50, a plurality of nozzles 51 are arranged in a zigzag pattern in two rows, and a bubble generation chamber 52, a bubble growth chamber 53, and a heater 58 corresponding to each nozzle 51 are provided. Is provided.

  In a state where the substrates 60 to 64 are laminated and bonded, the heater 58 is disposed on the lower surface side of the bubble generation chamber 52, and the bubble growth chamber 53 communicates with the opposite side (upper surface side). The bubble growth chamber 53 opens to the bubble generation chamber 52 side, and the nozzle 51 communicates with the opposite side (upper surface side). Thus, the bubble generation chamber 52, the bubble growth chamber 53, and the nozzle 51 are arranged and communicated along a direction perpendicular to the surface on which the heater 58 is arranged (that is, parallel to the discharge direction). ing. In the present embodiment, as described above, the top shooter type head structure in which the heater 58 and the nozzle 51 are arranged to face each other is employed, and the bubble generation chamber 52 and the bubble growth chamber 53 are interposed therebetween. Is placed.

  The bubble growth chamber 53 and the nozzle 51 are each formed in a columnar shape (straight section), and these are arranged on the same axis. As shown in FIG. 3, the inner diameter D2 of the bubble growth chamber 53 is configured to be larger than the inner diameter D1 of the nozzle 51 (that is, D2> D1).

  Although not shown in the drawing, the planar shape of the heater 58 is circular, and is similar to the planar shape of the bubble growth chamber 53 and the nozzle 51 (cross-sectional shape perpendicular to the axial direction). It is arranged on the same axis. As will be described later, as a preferred size of the heater 58 in the present embodiment, the length (outer diameter) L of the heater 58 is larger than the inner diameter D2 of the bubble growth chamber and 1.2 times the inner diameter D2 of the bubble growth chamber. Is less than.

  For example, the inner diameter D1 of the nozzle 51 is 13.5 [μm], the inner diameter D2 and the height H2 of the bubble growth chamber 53 are 27 [μm] and 13.5 [μm], respectively. The height H1 of 52 is 9 [μm], and the length (outer diameter) L of the heater 58 is 31.5 [μm].

  An ink supply path 56 formed on the side (the right side in FIG. 3) communicates with the bubble generation chamber 52. A supply port 54 penetratingly formed in the first substrate 60 communicates with the ink supply path 56, and is supplied from a sub tank (not shown) disposed on the back side (lower side in FIG. 3) of the recording head 50. Ink is supplied through the port 54. The bubble generation chamber 52 and the bubble growth chamber 53 are filled with ink supplied from the ink supply path 56.

  With this configuration, when a predetermined drive signal is supplied to the heater 58, bubbles are generated in the ink in the bubble generation chamber 52 on the surface of the heater 58 by the thermal energy generated by the heater 58. In the present embodiment, as will be described later, sufficient thermal energy is input to cause the liquid on the surface of the heater 58 to boil, and flat bubbles are generated. After the bubbles are generated, the bubbles continue to grow in the bubble generation chamber 52 and the bubble growth chamber 53 and communicate with the atmosphere from the nozzle 51, and the ink in the bubble growth chamber 53 is ejected as droplets while being pushed out of the nozzle 51. .

  In the present embodiment, the bubble growth chamber 53 is formed in a columnar shape (straight section), but the present invention is not limited to this. FIG. 4 is a cross-sectional view showing the main configuration of a recording head as a modification of the present embodiment. In FIG. 4, the same reference numerals are given to portions common to FIG. 3. The bubble growth chamber 53 ′ of the recording head 50 ′ in FIG. 4 is configured in a truncated cone shape (tapered section) that tapers in the ejection direction of the nozzle 51 (upper side in FIG. 3). In this case, the taper angle (inclination angle with respect to the ejection direction) θ of the inclined surface 53a of the bubble growth chamber 53 ′ is preferably about 10 to 40 degrees. Similarly, the nozzle 51 is not limited to a cylindrical shape (straight section), and may be configured in a truncated cone shape (tapered section), for example. Further, the planar shape of the heater 58 is not limited to a circular shape, and may be a square shape, for example.

  Next, a discharge control method that is a characteristic part of the present invention will be described. FIG. 5 is an explanatory diagram showing the bubble generation and growth process, and corresponds to an enlarged view of the nozzle periphery in FIG.

  First, predetermined heat energy is generated in the heater 58 with a pulse width of about 0.5 to 3.0 [μsec]. Specifically, sufficient thermal energy is input to boil the ink on the surface of the heater 58. As a result, as shown in FIG. 5A, the ink on the surface of the heater 58 is vaporized, and flat bubbles 66 are generated. Note that if the pulse width exceeds 3.0 [μsec], it is not possible to realize an ejection frequency on the order of several tens [kHz]. Therefore, it is preferable to generate predetermined thermal energy with a pulse width in the above range. .

  When bubbles 66 are generated on the surface of the heater 58 due to film boiling, the energization pulse to the heater 58 is turned off. As a result, the input of thermal energy is stopped, and therefore, there is almost no vaporization (evaporation) of new ink. However, since high thermal energy is input with a short pulse width of about 0.5 to 3.0 [μsec], the generated bubbles 66 start to expand because of high temperature. Since the bubble 66 generated on the surface of the heater 58 expands from a flat shape, as shown in FIG. 5B, the bubble 66 is at the opening end of the bubble growth chamber 53 on the bubble generation chamber 52 side (heater 58 side). It goes through a state of contact in a substantially uniform manner.

  Further, as shown in FIG. 5C, the bubble 66 continues to expand, and a droplet (ink droplet) having a volume substantially equal to the volume of the bubble growth chamber 53 is pushed out from the nozzle 51. Eventually, the bubbles 66 communicate with the atmosphere from the nozzle 51, and the droplets fly away from the nozzle 51.

  Thus, the flat bubbles 66 generated on the surface of the heater 58 due to film boiling are in a state where they are in contact with the opening end of the bubble generation chamber 53 on the bubble generation chamber 52 side (heater 58 side) substantially uniformly (that is, the bubble growth chamber). 53, the opening end of the bubble generating chamber 52 side is closed with the bubble surface), and the ink in the bubble growing chamber 53 grows in such a manner as to be pushed out from the nozzle 51, and communicates from the nozzle 51 to the atmosphere. At the same time, the ink in the bubble growth chamber 53 is ejected from the nozzle 51 as droplets. That is, the ink in the bubble growth chamber 53 does not flow back to the bubble generation chamber 52 side (ink supply path 56 side), and is not affected by the bubble growth variation. Since the nozzle 51 discharges, the discharge amount can be stabilized with high accuracy.

  As described above, the heating condition by the heater 58 as a heating element is sufficient heat to cause the ink on the surface of the heater 58 to boil with a short pulse width of about 0.5 to 3.0 [μsec]. Input energy. Specifically, in the case of water-based ink, an amount of heat for generating bubbles of 300 to 400 [° C.] is given. What is necessary is just to set the thermal energy to input suitably from the relationship of the volume of the ink corresponding to the bubble to generate | occur | produce, latent heat of vaporization, specific heat, etc. In this way, high thermal energy is input in a short period of time at the beginning of the discharge cycle to generate film boiling, to generate flat bubbles on the surface of the heater 58, and only bubble expansion occurs when the bubbles enter the bubble growth chamber 53. Realize the process.

  In realizing such discharge control, as a preferable dimensional condition of each part of the recording head 50, first, the height H1 of the bubble generating chamber 52 is larger than the height of the bubbles when bubbles are generated by film boiling. In consideration of the fact that the ink refill performance can be ensured, it is preferable to determine the lower limit value. In addition, the height H2 and the inner diameter D2 of the bubble growth chamber 53 may be determined according to the discharge amount (volume) of the droplets discharged from the nozzle 51.

  Further, as for the ratio H2 / (H1 + H2) of the height H2 of the bubble growth chamber 53 to the height H1 + H2 of the bubble generation chamber 52 and the bubble growth chamber 53, the one that is as large as possible increases the discharge amount (volume) of the nozzle 51. be able to.

  FIG. 6 shows various characteristics when the ratio H2 / (H1 + H2) of the height H2 of the bubble growth chamber 53 to the height H1 + H2 of the bubble generation chamber 52 and the bubble growth chamber 53 is changed (discharge amount variation, refill properties, This is an evaluation result of thermal damage of ink. As the evaluation criteria for each characteristic, the discharge amount variability is ◎ when the discharge amount variation is ± 3% or less, ◯ when it is ± 3% to ± 7%, and × when it is ± 7% or more. did. In addition, regarding the refill property, the case where the limit frequency at which non-ejection does not occur when the ejection frequency is changed is 30 kHz or more, the case where it is 10 to 30 kHz, and the case where it is 10 kHz or less are x. As for thermal damage of the ink, the ratio of the color density (optical density) of the ink before and after the thermal energy is applied is 0.9 or more, and 0.8 or less than 0.9. ○, the case of less than 0.8 was taken as x. In addition, the thermal damage of the ink was not evaluated as x.

As can be seen from FIG. 6, as a preferable range of H2 / (H1 + H2),
0.5 ≦ H2 / (H1 + H2) ≦ 0.9
It is. That is, by configuring the height H2 of the bubble growth chamber 53 to be in the range of 50 to 90 [%] of the height H1 + H2 of the bubble generation chamber 52 and the bubble growth chamber 53, variation in the discharge amount is reduced. In addition, refilling properties can be improved, and thermal damage of the ink can be suppressed. As a more preferable range of H2 / (H1 + H2),
0.7 ≦ H2 / (H1 + H2) ≦ 0.9
It is. That is, by configuring the height H2 of the bubble growth chamber 53 to be in the range of 70 to 90 [%] of the height H1 + H2 of the bubble generation chamber 52 and the bubble growth chamber 53, the variation in the discharge amount is further reduced. And thermal damage of the ink can be further suppressed. By setting the lower limit value of H2 / (H1 + H2) to 0.7, the ratio of the bubble growth chamber 53 to the whole becomes high, and most of the ink heated to a high temperature by the heater 58 is outside the head in one ejection cycle. This is because the thermal damage of the ink pigment can be reduced.

  Further, in the bubble growth process, as shown in FIG. 5B, as a preferable condition for the bubbles to uniformly contact the opening end of the bubble growth chamber 53 on the bubble generation chamber 52 side (heater 58 side). When the length (outer diameter) of the heater 58 is L (see FIG. 3), the following formula is obtained.

1.2 × D2>L> D2
If the length L of the heater 58 is excessively larger than the inner diameter D2 of the bubble growth chamber 53, particularly 1.2 times or more the inner diameter D2 of the bubble growth chamber 53, the bubble generation chamber 52 side of the heater 58 As a result, the surface area increases and wasteful heat energy that does not contribute to ejection is consumed. Therefore, the length L of the heater 58 is preferably larger than the inner diameter D2 of the bubble growth chamber 53 and less than 1.2 times the inner diameter D2 of the bubble growth chamber 53.

  FIG. 7 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. A serial interface or a parallel interface can be applied to the communication interface 70. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls each unit such as the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, and the like. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heaters 89 of the post-drying unit 42 and other units in accordance with instructions from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (dot data) to the head driver 84. Necessary signal processing is performed in the print control unit 80, and the ejection amount and ejection timing of the ink droplets of the recording head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized. The drive control means of the present invention corresponds to a drive control unit 80 a provided inside the print control unit 80. The above-described discharge control is performed in the drive control unit 80a.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 7, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 generates a drive signal for driving the heater 58 (see FIG. 3) of the recording head 50 for each color based on the dot data supplied from the print control unit 80, and supplies the generated drive signal to the heater 54. To do. The head driver 84 may include a feedback control system for keeping the driving conditions of the recording head 50 constant.

  The print detection unit 24 reads the test pattern recorded by the recording head 50, performs necessary signal processing, etc., and detects the ink ejection status (existence of ejection, dot size, dot position, etc.) of the recording head 50. The detection result is provided to the print control unit 80. The print control unit 80 performs various corrections on the recording head 50 based on information obtained from the print detection unit 24 as necessary.

  As described above, according to the present embodiment, the ink in the bubble growth chamber 53 does not flow back to the bubble generation chamber 52 side (ink supply path 56 side), and is not affected by bubble growth variation. Since ink substantially equal to the volume of the bubble growth chamber 53 is ejected from the nozzle 51, the ejection amount can be stabilized with high accuracy.

  The liquid ejection apparatus, the image forming apparatus, and the liquid ejection method of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements can be made without departing from the gist of the present invention. It goes without saying that or may be modified.

Overall configuration diagram of inkjet recording apparatus Schematic configuration diagram showing the configuration around the printing unit of an inkjet recording apparatus Sectional view showing the main configuration of the recording head Sectional drawing which showed the principal part structure of the recording head as a modification of 1st Embodiment Explanatory diagram showing bubble generation and growth process The figure which showed the evaluation result of each characteristic when changing the ratio of the height of a bubble growth chamber to the height of a bubble generation chamber and a bubble growth chamber Main block diagram showing the system configuration of the inkjet recording apparatus

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 50 ... Recording head 52 ... Bubble generation chamber 53 ... Bubble growth chamber 54 ... Supply port 56 ... Ink supply path 58 ... Heater 60 ... First substrate 62 ... Second Substrate, 64 ... third substrate, 80 ... print controller, 80a ... drive controller

Claims (4)

A discharge port for discharging droplets;
A heating element that is disposed at a position facing the discharge port and generates thermal energy for discharging droplets;
A bubble generation chamber for generating bubbles in the liquid inside by the heating element;
A bubble growth chamber for opening the bubble generation chamber side and forming the discharge port on the opposite side of the bubble generation chamber side to grow bubbles generated inside the bubble generation chamber;
Drive control means for controlling the drive of the heating element,
The drive control means generates predetermined heat energy in the heating element with a pulse width of 3 μsec or less, and causes the liquid in the bubble generation chamber to boil.
Bubbles generated in the liquid in the bubble generation chamber due to the film boiling grow in the bubble growth chamber and pass through the bubble generation chamber through the state where the bubbles grow in the bubble generation chamber side opening end. A liquid ejecting apparatus, wherein the liquid communicates with air from an outlet, and the liquid in the bubble growth chamber is ejected as droplets from the ejection port. 2. The liquid ejection apparatus according to claim 1, wherein the ejection direction of the ejection port satisfies the following expression when the height of the bubble generation chamber is H <b> 1 and the height of the bubble growth chamber is H <b> 2. .
0.5 ≦ H2 / (H1 + H2) ≦ 0.9   An image forming apparatus comprising the liquid ejection device according to claim 1. A discharge port for discharging droplets;
A heating element that is disposed at a position facing the discharge port and generates thermal energy for discharging droplets;
A bubble generation chamber for generating bubbles in the liquid inside by the heating element;
A bubble growth chamber for opening the bubble generation chamber side and forming the discharge port on the opposite side of the bubble generation chamber side to grow bubbles generated inside the bubble generation chamber;
A liquid discharge method for a liquid discharge apparatus comprising: a drive control means for controlling the drive of the heat generating element;
Generating a predetermined thermal energy in the heating element with a pulse width of 3 μsec or less, and boiling the liquid in the bubble generating chamber;
A step of growing bubbles generated in the liquid in the bubble generation chamber by the film boiling and contacting the bubble generation chamber side opening end of the bubble growth chamber substantially uniformly;
A step of further growing bubbles in the bubble growth chamber and communicating with the atmosphere from the discharge port, and discharging the liquid in the bubble growth chamber as droplets from the discharge port;
A liquid discharge method comprising:

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