JP2014144567A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a discharge failure and deterioration of recording image quality due to deviation of ink temperature distribution in a recording head, which is caused by restriction of a heating structure of the recording head itself and heat radiation from members in contact with the recording head and which cannot be solved by temperature control of the recording head single body.SOLUTION: An ink jet recorder comprises: recording heads 3 including plural nozzles which discharge ink that is gel or solid at the normal temperature and becomes liquid by heating at a prescribed temperature, plural pressure generating chambers which correspond to the plural nozzles and generate pressure for discharging ink and an ink manifold forming a common flow channel for introducing the ink to the plural pressure generating chambers; a holding member 4 which holds the recording head 3; head temperature measuring means which measures the temperature of the recording head 3; first heating means which is disposed in the recording head 3 and heats the ink inside; second heating means 42 which heats the holding member 4; and control means which controls heating temperatures of the first heating means and the second heating means respectively, based on the measurement result of the head temperature measuring means.

Description

  The present invention relates to an ink jet recording apparatus, and more particularly, to an ink jet recording apparatus capable of stably ejecting ink that is gel or solid at room temperature and is reduced in viscosity by heating to become liquid.

  In recent years, there has been an increasing demand for recording and forming an inkjet image on a recording medium that does not absorb ink, such as a plastic sheet, using an inkjet recording method that can record and form an image easily and inexpensively. . In this case, instead of the general dye ink or pigment ink, it is gel or solid at normal temperature such as gel ink, hot melt solid ink, wax ink, etc. An image is recorded and formed on a recording medium using an ink (hereinafter, such an ink may be referred to as a phase transition type ink). When such an ink lands on a recording medium, the temperature is lowered and the viscosity rapidly increases. Therefore, there is a merit in that recording can be performed without causing color mixing even on a recording medium having no ink absorbability.

  When ejecting such a phase transition type ink from a recording head, it is important to maintain the viscosity of the ink at a constant viscosity that enables stable ejection. This is because when the viscosity changes, the droplet size and the droplet velocity when ejected from the nozzle change, causing problems such as landing position deviation. For this reason, the recording head is provided with a heater, and the ink in the recording head is heated to a predetermined temperature by energizing the heater, so that the viscosity of the ink can be stably discharged.

  However, when the inside of the recording head that discharges the phase transition type ink as described above is heated by a heater, due to the deviation of the temperature distribution of the ink in the recording head, which does not normally cause problems with other inks, ejection defects and recording image quality This causes the problem of deterioration.

  Particularly in recent years, a recording head capable of discharging at a high frequency has been used due to a demand for higher recording speed, and the amount of ink discharged per unit time has increased. In a situation where a large amount of ink is ejected at such a high frequency, the above-mentioned bias, in which the temperature distribution of the ink in the recording head is eliminated by convection or flow due to ejection in normal ink, is also a problem with temperature-sensitive phase transition inks. Thus, the uniformization of the temperature inside the recording head will not be in time enough for ejection.

  In addition, due to restrictions on the arrangement and holding structure of the recording head incorporated in the printer, it is difficult to evenly arrange the heater in the recording head even if the ink in the recording head is heated, which is far from the heater. There is a temperature difference between the part and the part close to it.

  In particular, the recording head usually has a configuration in which ink is once flown into the ink manifold constituting the common flow path from the outside, and the ink flowing in from the common flow path is introduced into each pressure generating chamber and discharged through the nozzles. However, it is difficult to directly heat the ink with a heater in each pressure generating chamber. For this reason, it is conceivable to heat the ink manifold with a heater, but after flowing out from the common flow path in the ink manifold to the channel which is each pressure generating chamber, it will move away from the heater, so the ink temperature will drop, which This causes a temperature difference in the ink in the recording head.

  This is a full-line head in which a plurality of recording heads are arranged along the nozzle arrangement direction, and the nozzles traverse the entire width in the direction orthogonal to the conveyance direction of the recording medium. This is particularly a problem when the ink manifolds are connected via conduits so that ink flows in and out.

  In other words, in addition to heating the ink manifold, even if the ink in the conduit connecting each recording head is temporarily heated with a heater, the ink temperature cannot be raised sufficiently during the movement from the conduit to each ink manifold. As a result, the temperature is lowered at the connection portion between the recording heads, that is, near the end of each recording head, and the temperature distribution is biased.

  This is a result of the temperature distribution being biased in the vicinity of the connection portion of each print head and the other portions when viewed from the temperature distribution of the nozzle row across the entire print width.

  On the other hand, as a technology for controlling the temperature of the ink in the recording head using a heater, the ink ejection amount is calculated from the print data and the temperature of the recording head is measured with respect to the increase in the ejection amount, and the results are obtained. A technique has been proposed in which the heater temperature is controlled by obtaining the optimum heater temperature (Patent Document 1).

JP 2011-143603 A

  However, the technique described in Patent Document 1 has a control configuration in which the temperature of the heater is increased in accordance with an increase in the amount of ink discharged. No consideration is given to the deterioration of the recording image quality.

  Usually, when the recording head is driven, the head itself generates heat. For this reason, in a situation where a large amount of ink is ejected at a high frequency as described above, the heat generation amount of the recording head increases accordingly. Therefore, in the control configuration in which the temperature is increased in accordance with the discharge amount as in the above technique, the temperature of the ink in the vicinity of the nozzle is excessively heated, resulting in uneven temperature distribution and, of course, the discharge viscosity is desired. There is a possibility that it will fluctuate greatly in comparison with the viscosity of.

  Of course, a heat radiating member such as a heat sink may be provided in contact with the recording head as various members in contact with the recording head, and the heat of the recording head may be actively radiated by the heat radiating member. In this way, even if the heat generation of the recording head increases, it may be possible to prevent the temperature of the internal ink from exceeding a predetermined temperature due to heat dissipation from the heat dissipation member.

  However, the heat dissipating member itself has a configuration that only dissipates heat by contacting the member. Therefore, even if the print head generates a relatively small amount of heat due to a small amount of ink discharged or the discharge stops depending on the print data, the heat of the print head continues to be released through the heat radiating member. The temperature of the ink may be lower than the desired temperature.

  In this case, in the control for detecting the temperature drop of the recording head with restrictions on the heater arrangement as described above and raising the heater temperature, the heat radiation member portion is configured to release the heat of the ink more. In addition to more and more fluctuations from the desired ink viscosity, the temperature difference in the recording head also widens, which may promote the above-described ejection failure and deterioration of recording image quality.

  In view of this, the present invention provides a discharge failure due to a deviation in the temperature distribution of the ink in the recording head, which cannot be eliminated by temperature control of the recording head alone due to restrictions on the heating configuration of the recording head itself or heat radiation from a member in contact with the recording head. It is an object of the present invention to provide an ink jet recording apparatus capable of suppressing deterioration in recording image quality.

  Other problems of the present invention will become apparent from the following description.

In order to solve the above-described problems, the first aspect of the present invention is a method in which an ink that is gel or solid at room temperature and becomes liquid when heated to a predetermined temperature is transferred onto a recording medium that is conveyed based on print data. An inkjet recording apparatus that forms an image by discharging,
A plurality of nozzles for discharging the liquid; a plurality of pressure generating chambers for generating pressure to discharge the ink corresponding to the plurality of nozzles; and a common flow path for introducing the ink into the plurality of pressure generating chambers A recording head having an ink manifold that forms
A holding member for holding the recording head;
Head temperature measuring means for measuring the temperature of the recording head;
A first heating means provided in the recording head for heating the ink in the recording head;
A second heating means provided on the holding member for heating the holding member;
Control means for controlling the heating temperatures of the first heating means and the second heating means based on the measurement result of the head temperature measuring means.

  According to a second aspect of the present invention, the control means in the first aspect is configured so that the temperature of the head is a temperature at which the ink in the head becomes a predetermined temperature based on the measurement result of the head temperature measuring means. When it is determined that the temperature has exceeded, the heating of the second heating means is stopped or the heating temperature is controlled to be lower than the heating temperature so far.

  According to a third aspect of the present invention, there is provided an ink discharge amount calculating means for obtaining an ink discharge amount from the print data in the first aspect, wherein the control means is calculated by the ink discharge amount calculating means. When it is determined that the result has exceeded a preset value, the second heating means is controlled to stop heating or to control the heating temperature to be lower than the previous heating temperature.

  According to a fourth aspect of the present invention, in the first aspect, the holding member is controlled to have a temperature lower than the temperature of the recording head to be measured.

  According to a fifth aspect of the present invention, in the first aspect, the holding member has an ink path through which ink before heating passes.

  According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the first heating means is provided in an ink manifold that forms a common flow path of the recording head. The holding member is configured to hold the recording head in contact with the recording head side surface closer to the nozzle surface than the ink manifold.

  According to a seventh aspect of the present invention, in the sixth aspect, the recording head is orthogonal to the recording medium so that the nozzle traverses the entire width in a direction orthogonal to the conveyance direction of the recording medium. A plurality of the holding members are arranged in a direction, and the holding member has a plurality of openings that are held in contact with the nozzle surface side surfaces of the plurality of recording heads.

  According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the holding member is made of aluminum.

  According to the present invention, it is possible to provide an ink jet recording apparatus that can keep the temperature distribution inside the recording head small, and can suppress the ejection failure and the deterioration of the recording image quality.

The top view which shows the outline | summary of an example of the inkjet recording device which concerns on this invention Perspective view of head unit Front view showing the mounting part of the head in the head unit Plan view showing another aspect of the head unit Head perspective view Sectional drawing which follows the vi-vi line in FIG. Sectional drawing which follows the vii-vii line in FIG. (A) and (b) are diagrams for explaining examples of drive signals. The figure explaining the ink discharge operation of a head chip The graph which shows the example of a change of the viscosity of the ink accompanying the temperature rise and fall of the ink The figure which shows the control structure of the inkjet recording device which concerns on this invention Flowchart for explaining ink heating control in the ink jet recording apparatus according to the present invention. Flowchart for explaining ink heating control in the ink jet recording apparatus according to the present invention. The figure which shows the other control structure of the inkjet recording device which concerns on this invention. Flowchart for explaining ink heating control in the ink jet recording apparatus according to the present invention. The figure which shows an example of the table which prescribed | regulated the relationship between the calculated value of a discharge amount calculation part, and the emitted-heat amount of a head chip. Graph that measures the temperature distribution in the head at each nozzle position when temperature control of the holding plate is not performed and when temperature control is performed at multiple set temperatures Graph showing the transition of temperature distribution in the head when temperature control of the holding plate is not performed based on the discharge amount calculation value Graph showing the transition of temperature distribution in the head when holding plate temperature control is performed based on the discharge amount calculation value

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Outline of inkjet recording apparatus)
FIG. 1 is a plan view showing an outline of an example of an ink jet recording apparatus according to the present invention.

  In the ink jet recording apparatus 1, the recording medium P is transported at a constant speed in a direction indicated by an arrow in the drawing by a transport mechanism (not shown). The specific transport mechanism is not particularly limited. For example, the recording medium P is sandwiched from the front and back by a pair of transport rollers, and the transport roller pair is rotated by driving a main scanning motor to transport the recording medium P at a predetermined speed. Alternatively, an endless belt is stretched over a plurality of rollers installed in parallel at intervals, and the belt is rotated by driving a main scanning motor, and the recording medium P placed on the upper surface of the belt is moved at a predetermined speed. And the like conveyed by

  The recording medium P is not particularly limited, but a recording medium having no ink absorbability such as a plastic sheet can be preferably used. The recording medium P is used in a long shape or a sheet shape cut in advance to a predetermined size.

  On the upper surface of the recording medium P, the head unit 2 is spanned across the width direction orthogonal to the conveyance direction of the recording medium P. The head unit 2 has a plurality of recording heads (hereinafter simply referred to as heads) 3. In the illustrated example, eight heads 3 are arranged in two rows along the orthogonal direction so that a plurality of nozzles cross across the entire width of the recording medium P. By ejecting each ink toward the recording medium P, an inkjet image can be recorded in one pass over the entire width of the recording medium P in the transport process at a predetermined speed.

(Head unit)
FIG. 2 is a perspective view showing details of the head unit 2. FIG. 3 is a front view showing an attachment portion of the head 3 in the head unit 2. FIG. 4 is a plan view showing another aspect of the head unit 2.

  The head unit 2 is formed by fixing and holding a plurality of heads 3 by a common holding plate 4.

  The holding plate 4 is formed longer than the width of the recording medium P. Each head 3 can be inserted through the nozzle surface 3a side of the head 3 so that the head 3 is held in contact with the side surface of the recording head closer to the nozzle surface 3a than the ink manifold that forms a common flow path that will be described later. Two openings 41 are provided. Each head 3 is positioned so that the nozzle surface 3a side is inserted into each opening 41 and the nozzle surface 3a slightly protrudes from the lower surface 4a of the holding plate 4 facing the recording medium P. It is fixed to the holding plate 4 by fixing means (not shown).

  In the head unit 2 shown in FIG. 2, a total of eight heads 3 are arranged and held on the holding plate 4, but in the present invention, the head unit 2 has one head as shown in FIG. On the holding plate 4, for example, an aggregate of a plurality of heads 3 such as a total of eight heads 2 in two rows shown in FIG. A plurality may be arranged and held along one or both of the width direction orthogonal to the transport direction.

  The holding plate 4 is made of a heat-dissipating material, and the head 3 is fixed in the opening 41 by contacting the inner peripheral surface of the opening 41 so as to surround the outer surface of the head 3 on the nozzle surface 3a side. keeping. Thereby, it has the function to discharge | release the heat | fever which each head 3 has to air | atmosphere via the holding | maintenance plate 4. FIG. As a material for the holding plate 4, a metal having a thermal conductivity equal to or higher than that of the portion of the head 3 in contact with the holding plate 4, such as aluminum or copper, is generally used. Aluminum is more preferable from the viewpoint.

  As shown in FIG. 2, a flow path member 5 is provided on the holding plate 4 of the head unit 2 between the plurality of heads 3 arranged in two rows along the length direction of the holding plate 4. It has been. Further above the flow path member 5, there is an ink chamber 6 that is common to each head 3, and the ink supplied from an ink tank (not shown) is temporarily stored in the ink chamber 6. Yes. The ink chamber 6 is disposed above the plurality of heads 3 fixed to the holding plate 4 so as to extend along the length direction of the holding plate 4, and is formed between the flow path member 5 by the two conduits 61A and 61B. Ink can flow in and out.

  As shown in FIG. 3, each head 3 communicates with the flow path member 5 through an ink inflow pipe 34 </ b> A, an ink outflow pipe 34 </ b> B, and a flow path connection member 35. In FIG. 3, reference numeral 351 denotes a flow path formed in the flow path connecting member 35, and 51 denotes a flow path formed in the flow path member 5.

(head)
5 is a perspective view of the head 3, FIG. 6 is a cross-sectional view taken along line vi-vi in FIG. 3, and FIG. 7 is a cross-sectional view taken along line vii-vii in FIG.

  The head 3 accommodates a head chip 30 as an actuator for ejecting ink in a holder 31 made of metal such as aluminum. The holder 31 contacts the periphery of the head chip 30 on the nozzle surface 3a side and supports the head chip 30 inside.

  The head chip 30 shown in the present embodiment has two channel rows formed by arranging a large number of channels 301 as pressure generating chambers and partition walls 302 as pressure applying means in an alternating manner. doing. A nozzle plate 304 is bonded to one end surface of the head chip 30, and a nozzle surface 3 a is formed by the surface of the nozzle plate 304. A nozzle 305 is formed on the nozzle plate 304 at a position corresponding to the channel 301.

  A case 32 made of synthetic resin is connected to the holder 31, and the entire head chip 30 including the FPC 307 is accommodated in the holder 31. The FPC 307 is electrically connected to the control unit 100 (see FIGS. 11 and 14) by a cable (not shown) using the connector 33 provided on the end surface of the housing 32.

  The head chip 30 has a cover substrate 303 provided so as to close all the channels 301 for each channel row. Further, an ink manifold 306 is provided so as to close the opening 303a formed in the cover substrate 303, and a common flow path 306a that is common to each channel row is formed therein. Accordingly, each channel 301 in each channel row communicates with the common flow path 306a through the opening 303a, and ink can flow in and out between the common flow path 306a. The common flow path 306a communicates with the ink inflow pipe 34A and the ink outflow pipe 34B provided so as to penetrate the holder 31, and the ink in the ink chamber 6 flowing in from the ink inflow pipe 34A is in the common flow path. In addition to being introduced into 306a, the ink in the common flow path 306a flows out from the ink outflow pipe 34B to the ink chamber 6.

  The partition wall 302 is formed by a piezoelectric element such as PZT that has been subjected to polarization processing, which is an electrical / mechanical conversion means, and the drive control unit 101 (see FIGS. 11 and 14) is provided on electrodes (not shown) formed on both surfaces thereof. When a drive signal having a predetermined voltage and a predetermined waveform is applied through the FPC 307, the volume of the channel 301 is deformed so as to expand or contract in accordance with the drive signal. As a result, a pressure for ejection is applied to the ink in the channel 301 and the ink is ejected as a droplet from the nozzle 305.

(Head ejection operation)
Here, the ink discharge operation of the head 3 will be described.

  In the head 3, when a drive signal corresponding to print data transmitted from the drive control unit 101 (see FIGS. 11 and 14) is applied to the electrode of the channel 301, the partition wall 302 is shear-deformed and the volume of the channel 301 is increased. And the pressure for ejection is applied to the ink in the channel 301.

  FIG. 8 shows an example of a drive signal given to the head 3 for ejecting ink, and FIG. 9 shows a deformation operation of the partition wall 301 when the drive signal is given. FIG. 9 shows only three adjacent channels 301A to 301C in one channel row.

  In FIG. 8, the horizontal axis represents (AL) time, and the vertical axis represents drive voltage. Further, t1 is the pulse width of the first expansion pulse, t2 is the pulse width of the contraction pulse, and t3 is the pulse width of the second expansion pulse.

(1) In the state shown in FIG. 9A, the head 3 has a first rectangular wave that connects the electrodes d1 and d3 to the ground, rises to the electrode d2 up to the Von voltage value, and holds for a certain time thereafter. When a first expansion pulse (positive voltage) is applied, a voltage Von is first applied by the rising edge (P1) of the first expansion pulse, and in a direction perpendicular to the polarization direction of the piezoelectric materials 302a and 302b constituting the partition walls 302B and 302C. An electric field is generated, and both 302a and 302b are deformed in the joint surface of the partition wall 302. As shown in FIG. 9B, the partition wall 302B and the partition wall 302C are deformed toward each other, and the volume of the channel 301B is expanded. As a result, a negative pressure is generated in the ink in the channel 301B, and the ink flows from the common flow path 306a.

  Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the channel. This AL applied a rectangular wave pulse to the partition wall 302, which is an electrical / mechanical conversion means, measured the speed of the ejected droplet, and changed the rectangular wave pulse width while keeping the rectangular wave voltage value constant. Sometimes it is determined as the pulse width that maximizes the flying speed of the droplet. This value is determined depending on the structure of the head, the density of the ink, and the like.

  A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is the start of rising or falling of the voltage from 0V. Is defined as the time between 10% of 10% and 10% of the start of falling from the peak voltage or 10% of rising. Furthermore, the rectangular wave here refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within 1/10, preferably within 1/20 of AL. .

(2) Since the pressure wave in the channel 301B repeats reversal every 1 AL time, when the potential is returned to 0 after 1 AL time has elapsed from the first application of P1 (P2), the partition walls 302B and 302C are removed from the expanded position. Returning to the neutral position shown in FIG. 9A, high pressure is applied to the ink in the channel 301B.

  Subsequently, a contraction pulse (negative voltage Voff) composed of a rectangular wave is applied. First, as shown in FIG. 9C, the partition walls 302B and 302C are deformed in directions opposite to each other by the fall (P3) of the contraction pulse, and the volume of the channel 301B contracts. By this contraction, a higher pressure is applied to the ink in the channel 301 </ b> B, and the ink column protrudes from the nozzle 305.

(3) When t2 time elapses, the potential is returned to 0 (P4), and subsequently, when the second expansion pulse (voltage Von) is applied (P5), the volume of the channel 301B expands, so that the inside of the channel 301B High negative pressure is applied to the ink. As a result, the meniscus is drawn, the rear end of the ink column protruding from the nozzle 305 is pulled back, the diameter of the ink column is reduced, and the droplet is separated.

  When the voltage returns to 0 after t3 from P5 and the state shown in FIG. 9A is obtained, the pressure wave can be rapidly attenuated.

  The pulse width t1 of the first expansion pulse greatly affects the droplet ejection force. When this pulse width matches 1AL, the ink droplet ejection force (ejection speed) becomes maximum, but 0.8AL to 1.2AL. It is preferable to set it as the range. Moreover, a small droplet can be formed by setting the pulse width t2 of the contraction pulse to a range of 0.1 to 0.5 AL. Furthermore, the pulse width t3 of the second expansion pulse is preferably in the range of 0.2 to 0.6 AL from the viewpoint of the droplet volume and the upper limit of the stable speed.

  8B, the second expansion pulse in the drive signal shown in FIG. 9A is not applied, and the pulse width t2 of the contraction pulse is 1.8 to 2.2 AL. After that, the waveform returns the voltage to zero. This also makes it possible to stably discharge droplets from the nozzle 305.

(ink)
Here, the ink will be described.

  In the present invention, the ink used for image formation has the property of changing phase depending on the temperature of the ink. Specifically, the ink changes in phase from gel or solid to liquid depending on the temperature. As such an ink composition, for example, a composition in which several percent of a gelling agent is added to a composition mainly composed of a polymerization compound and a photopolymerization initiator can be mentioned.

  In the following, an example of a method for producing ink is disclosed.

  First, two kinds of compounds of 5 parts of Solspers 32000 (manufactured by Lubrizol) and 80 parts of HD-N (1,6-hexanediol dimethacrylate, Shin-Nakamura Chemical Co., Ltd.) are placed in a stainless steel beaker and dissolved with heating and stirring. To do. Then, after cooling to room temperature, 15 parts of carbon black (# 56, manufactured by Mitsubishi Chemical Corporation) was added thereto, sealed in a glass bottle with 0.5 mm zirconia beads, and dispersed for 10 hours with a paint shaker A product obtained by removing the zirconia beads is obtained as a pigment dispersion.

  Including the pigment dispersion obtained as described above, the composition is adjusted as shown in Table 1.

  And the composition after filtration which filtered with the Teflon (trademark) 3 [micrometer] membrane filter made from ADVATEC is obtained as an ink as a composition shown in Table 1.

  FIG. 10 shows an example of change in the viscosity of the ink as the temperature of the ink rises and falls. A line L1 shown in FIG. 10 shows an example of change in the viscosity of the ink when the temperature rises, and a line L2 shows an example of the change in the viscosity of the ink when the temperature falls.

  As indicated by the line L1 in FIG. 10, the ink undergoes a phase change in which the viscosity changes remarkably around 60 [° C.] when the temperature rises. Specifically, the ink that was gel or solid at a temperature lower than 60 [° C.] becomes liquid with a markedly reduced viscosity from above 60 [° C.] due to the temperature increase.

  On the other hand, as shown by the line L2 in FIG. 10, the ink undergoes a phase change in which the viscosity changes remarkably as compared with the phase change at the time of temperature rise at about 45 [° C.] when the temperature is lowered. Specifically, an ink that has been kept in a liquid state to a temperature exceeding 45 [° C.] has a very high viscosity and becomes a gel or a solid since the temperature drops below 45 [° C.] due to the temperature drop.

(Ink heating means)
The ink used in the present invention is the above-described phase transition type ink. For this reason, the head unit 2 and each head 3 heat the ink so that the ink reaches a predetermined temperature at which the ink can be stably discharged so that the ink can be stably discharged from the nozzle 305. To do. The predetermined temperature varies depending on the type of ink, physical properties, and the like, but is generally in the range of 35 ° C to 100 ° C.

  Ink is supplied from an ink tank (not shown) to the ink chamber 6, and in the process from the ink chamber 6 to the head unit 2, the ink is heated and kept warm to provide fluidity. The ink is supplied to each head 3 in such a state having fluidity. The temperature range of the ink when ejected from the nozzle 305 is preferably ± 5 ° C. with respect to the set temperature, more preferably ± 2 ° C. with respect to the set temperature, and further preferably ± 1 ° C. with respect to the set temperature. That is.

  The set temperature here refers to a reference temperature set as the temperature of ink when ink is ejected.

  In order to heat the ink in this way, a heating unit is provided in each part of the head unit 2 and the head 3.

  That is, as shown in FIG. 2, a heater 63 is attached to the outer wall surface of the ink chamber 6 of the head unit 2, and the ink stored in the ink chamber 6 is heated by energizing the heater 63. Be able to. In FIG. 2, 62 is a temperature sensor as temperature measuring means for measuring the temperature of ink in the ink chamber 6. The temperature sensor 62 may be disposed inside the ink chamber 6 or may be embedded in the wall of the ink chamber 6.

  Further, as shown in FIG. 6, a heater 308 as a first heating unit is attached to the head 3 on the outer wall surface of the ink manifold 306, and is stored in the common flow path 306 a by energizing the heater 308. The ink to be heated can be heated. The heater 308 may be embedded in the wall of the ink manifold 306.

  In FIG. 6, reference numeral 309 denotes a temperature sensor that is provided so as to be in contact with the outer surface of the head chip 30 and serves as a temperature measuring means for measuring the temperature of the head chip 30. The temperature sensor 309 may be disposed inside the common flow path 306 a or may be embedded in the wall of the ink manifold 306.

  Further, on the upper surface of the holding plate 4 of the head unit 2, as shown in FIGS. 1 to 3, there are second heating means with a length extending over the four heads 3 on the outer sides of the two rows of heads 3. A heater 42 is adhered, and the holding plate 4 itself can be heated by energizing the heater 42. In FIGS. 1 and 2, reference numeral 43 denotes a temperature sensor as temperature measuring means for measuring the temperature of the holding plate 4. The temperature sensor 43 may be disposed on the surface of the holding plate 4 or may be embedded in the holding plate 4.

  These heaters 42, 63, and 308 may be any one as long as they can generate heat by energization to heat the ink, and the amount of heat generation (heating temperature) can be controlled by controlling the energization amount. Preferably, a film heater can be used. These heaters 42, 63, and 308 are electrically connected to and controlled by the control unit 100 (see FIGS. 11 and 14) that performs overall control of the inkjet recording apparatus 1.

  In addition, the heater 42 for heating the holding member 4 can be further subdivided into a plurality of parts and individually controlled in temperature, so that the temperature on the holding plate 4 can be made more uniform.

(Control configuration)
FIG. 11 shows the configuration of the control unit 100 that controls the inkjet recording apparatus 1. The heaters 42, 63, 308 and the temperature sensors 43, 64, 309 are electrically connected to a control unit 100 that performs overall control of the inkjet recording apparatus 1, as shown in FIG. 101 is a drive control unit that generates a drive signal according to print data and controls the ejection operation of each head 3, and 102 is for transmitting and receiving various data such as print data to and from an external device (such as a PC). The interface 103, obtains the optimum energization amount to each heater 42, 63, 308 based on the detection value of each temperature sensor 43, 64, 309, and controls each heater 42, 63, 308 to control the ink heating temperature A temperature control unit 104 serving as a control unit for controlling the recording medium 104 is a transport motor that transports the recording medium P.

(Ink heating control)
Next, an example of ink heating control in the inkjet recording apparatus 1 will be described.

  FIG. 12 is a flowchart showing the operation of the inkjet recording apparatus 1 after the power is turned on.

  When the apparatus power source is turned on (S1), the control unit 100 energizes all the heaters of the inkjet recording apparatus 1 and starts heating the ink. As a result, the heaters 42, 63, and 308 of the head unit 2 and the head 3 are also energized (S2).

  When the heaters 42, 63, and 308 are energized and the heating of the ink is started, the control unit 100 sets each temperature so that the measured values of the temperature sensors 43, 64, and 309 become preset temperature settings. The measured temperature values sent from the sensors 43, 64, and 309 are monitored (S3). When it is detected that the measured value has reached the set temperature, it is determined that the ink in the head 3 has been heated to a predetermined temperature at which stable ejection is possible, and the inkjet recording apparatus 1 is ready for printing ( After that, each head 3 is driven based on the print data, and a predetermined image is recorded on the recording medium P (S4).

  The ink in the head 3 is heated by the heater 308 provided in the ink manifold 306. The direct influence of the heating is on the ink in the common flow path 306a, and the ink flows into the common flow path 306a. The influence of the heating by the heater 308 is small for the ink before starting and for the ink after flowing out from the common flow path 306a to the channel 301. For this reason, the temperature decreases as the distance from the heater 308 increases, and this causes a temperature difference in the ink in the head 3.

  However, according to the present invention, since the holding plate 4 that is fixedly held in contact with the head 3 is also heated by the heater 42, the ambient temperature around the head 3 is also heated to a predetermined temperature. is there. Thereby, heat radiation from the head 3 is suppressed, and the temperature difference of the ink in the head 3 is suppressed to a small value.

  Further, since the temperature difference between the inks in the head 3 is suppressed to be small, the heating temperature of the heaters 308 and 63 for heating the ink to a predetermined temperature can be suppressed to a low level. Normally, the heater set temperature is set to a temperature slightly higher than the ideal ink temperature in consideration of losses such as heat dissipation, so there is a concern that the ink will continue to be exposed to heat, Such a problem does not occur because the heating temperature of the heaters 308 and 63 can be kept low.

  FIG. 13 is a flowchart showing the operation after the start of printing.

  When each head 3 is driven based on the print data and image recording on the recording medium P is started (S10), the control unit 100 causes the temperature sensor 309 provided in the head chip 30 to generate the heat generation temperature of the head chip 30. Is monitored (S11).

  When the head chip 30 continues to drive, the head chip 30 generates heat. However, when the amount of heat generated increases due to the increase in the amount of ink discharged per unit time according to the print data, the temperature of the head chip 30 becomes a predetermined temperature at which ink can be stably discharged. There is a temperature that will exceed. Therefore, the control unit 100 compares the measured value of the temperature sensor 309 with a predetermined constant value that causes the ink to exceed a predetermined temperature, and when the predetermined value is exceeded, the heater provided in the holding plate 4 The energization to 42 is stopped (S12). Thereafter, the printing operation is continued (S13).

  Since the holding plate 4 has a heat dissipation property, when the energization of the heater 42 is stopped, the holding plate 4 functions as a heat sink and starts releasing the heat of the head 3 to the outside air. As a result, the heat of the head chip 30 that has generated heat to such a temperature that the ink exceeds the predetermined temperature is released to the outside air through the holder 31 and the holding plate 4 and cooled. As a result, even if the ink discharge amount increases and the heat generation amount of the head chip 30 increases, the ink inside can be maintained at a predetermined temperature.

  FIG. 14 shows another aspect of the control configuration when the ink heating control is performed. The parts denoted by the same reference numerals as those in FIG. 11 indicate the parts having the same configuration, and the description thereof is omitted.

  In this aspect, the control unit 100 includes the ejection amount calculation unit 105 as an ink ejection amount calculation unit for obtaining the ink ejection amount from the print data. The discharge amount calculation unit 105 calculates the ink discharge amount per unit time by analyzing the print data transmitted via the interface 102.

  FIG. 15 is a flowchart showing the operation after the start of printing when calculating the ink discharge amount.

  When printing is started, print data is transmitted to the control unit 100 via the interface 102 (S20). In the control unit 100, the print data is analyzed by the discharge amount calculation unit 105, and the ink discharge amount per unit time is calculated (S21).

  As the ink discharge amount increases, the amount of heat generated by the head chip 30 also increases. For this reason, the temperature of the head chip 30 may be a temperature that exceeds a predetermined temperature at which ink can be stably ejected. In this aspect, the control unit 100 is prepared in advance with a table that defines the relationship between the calculated value of the discharge amount calculating unit 105 and the heat generation amount of the head chip 30, and the calculated value of the discharge amount calculating unit 105 is prepared from this table. The heat generation amount (heat generation temperature) of the head chip 30 corresponding to is obtained. Then, the control unit 100 compares the heat generation temperature of the head chip 30 obtained from the table with a predetermined constant value that causes the ink to exceed the predetermined temperature (S22), and the calculated value exceeds the predetermined value. The energization to the heater 42 provided on the holding plate 4 is stopped (S23). Thereafter, the printing operation is continued (S24).

  In the case of using the phase transition type ink used in the present invention and having an ink viscosity of 7 to 9 cp at a temperature of 80 ° C., in order to achieve stable ejection and obtain a desired image quality, It is desirable to keep the temperature within 80 ± 5 ° C. in a state where the temperature distribution in the head is uniform. For this purpose, as described above, the relationship between the calculated value (printing rate) of the discharge amount calculating unit 105 and the heat generation amount (head internal temperature) of the head chip 30 according to the value calculated by the discharge amount calculating unit 105. The temperature of the holding plate 4 is controlled based on a table that defines the above.

  An example of such a table is shown in FIG.

  By performing such control, the temperature inside the head can be kept within a certain range. A table defining the relationship between the calculated value of the discharge amount calculation unit 105 and the heat generation amount of the head chip 30 prepared in advance may be set more finely with respect to the printing rate. As a result, the temperature inside the head can be controlled within a narrower range.

  As a result, the holding plate 4 functions as a heat sink in the same manner as described above, and even if the amount of heat generated by the head chip 30 increases due to an increase in the ink discharge amount, the heat is released to the outside air and the ink inside becomes a predetermined temperature. Can be maintained. In addition, since the ink discharge amount is calculated from the print data and the heater 42 of the holding plate 4 is controlled, it is determined in advance that the amount of heat generated by the head chip 30 increases and the heater 42 of the holding plate 4 is controlled. Therefore, more stable discharge becomes possible.

  In the control operation described with reference to FIGS. 13 and 15, the heater 42 of the holding plate 4 is completely energized based on the measured value of the temperature sensor 309 that measures the temperature of the head chip 30 or the calculated value of the ink discharge amount. Although control to stop is performed, depending on the heat generation amount of the head chip 30, instead of the control to stop energization to the heater 42, the energization amount (heating temperature) to the heater 42 is changed to the current energization amount (heating). The temperature of the holding plate 4 may be controlled to be lower than the head temperature by lowering the temperature.

  The graph shown in FIG. 17 shows each nozzle position (head of the head) when the temperature control of the holding plate is not performed and when the temperature control is performed at a plurality of set temperatures using the phase change ink and the recording head having the following specifications. The temperature distribution in the head at each end in the longitudinal direction and the center) is measured and plotted.

  The ink used for the measurement was a phase transition type ink containing a gelling agent, an actinic ray curable composition, a photopolymerization initiator, a radical polymerizable compound, and a coloring material, and was 8.1 mPa · s at a temperature of 80 ° C. It is an ink whose composition is adjusted so that

  The recording head has 1800 nozzles at 600 npi, and each recording head is arranged as a unit by being shifted by two heads and a half pitch. Further, each unitized head is held by a holding plate made of aluminum having good thermal conductivity, and the temperature is controlled by a heater built in the head and a heater of the holding plate.

  In this measurement, the printing with the head is not performed, and the position of the heater and the arrangement of the temperature sensor are the same as those of the heaters 42 and 308 and the temperature sensors 43 and 309 shown in FIGS. It is done with things arranged in places. In the following description, the symbols of the heater and the temperature sensor indicate the heater and the temperature sensor at the same position as the heater and the temperature sensor of the same symbol in the drawing.

  As shown in this graph, when the energization to the heaters 42 and 308 of the holding plate is not controlled based on the measurement value of the temperature sensor 309 that measures the temperature of the head chip (outside the present invention), 60 ° C., 70 ° C., When the temperature is controlled at 80 ° C. (each of the present invention), the temperature distribution in the head is less biased than when the temperature is not controlled, and there is almost no temperature distribution in the head around 80 ° C. at which the stable discharge viscosity is achieved. It shows that.

  Further, the temperature distribution in the head when the holding plate temperature control is not performed based on the discharge amount calculation value in the present invention using the ink and the recording head described above (FIG. 18) and when it is performed (FIG. 19). The difference is shown in a graph.

  As can be seen from FIGS. 18 and 19, when the present invention is not carried out, the head temperature gradually rises due to the heat generation of the head chip itself as the discharge amount increases by continuously printing. When the present invention is implemented, it can be seen that the temperature of the ink in the head is stable regardless of the increase in the ejection amount.

1: Inkjet recording apparatus 2: Head unit 20: Unit 3: Recording head 3a: Nozzle surface 30: Head chip 301: Channel 302: Partition wall 302a, 302b: Piezoelectric material 303: Cover substrate 303a: Opening 304: Nozzle plate 305: Nozzle 306: Ink manifold 306a: Common flow path 307: FPC
308: Heater (first heating means)
309: Temperature sensor 31: Holder 32: Housing 33: Connector 34A: Ink inflow pipe 34B: Ink outflow pipe 35: Flow path connecting member 351: Flow path 4: Holding plate 4a: Lower surface 41: Opening 42: Heater (first) 2 heating means)
43: temperature sensor 5: flow path member 51: flow path 6: ink chamber 61A, 61B: conduit 62: temperature sensor 63: heater 100: control unit 101: drive control unit 102: interface 103: temperature control unit 104: transport motor P: Recording medium

Claims (8)

An ink jet recording apparatus that forms an image by ejecting ink that is a gel or a solid at room temperature and becomes a liquid when heated to a predetermined temperature on a recording medium to be transported based on print data,
A plurality of nozzles for discharging the liquid; a plurality of pressure generating chambers for generating pressure to discharge the ink corresponding to the plurality of nozzles; and a common flow path for introducing the ink into the plurality of pressure generating chambers A recording head having an ink manifold that forms
A holding member for holding the recording head;
Head temperature measuring means for measuring the temperature of the recording head;
A first heating means provided in the recording head for heating the ink in the recording head;
A second heating means provided on the holding member for heating the holding member;
An ink jet recording apparatus comprising: a control unit configured to control heating temperatures of the first heating unit and the second heating unit based on a measurement result of the head temperature measuring unit.   The control unit stops heating the second heating unit when it is determined from the measurement result of the head temperature measuring unit that the temperature of the head exceeds a temperature at which the ink in the head reaches a predetermined temperature. 2. The ink jet recording apparatus according to claim 1, wherein the heating temperature is controlled to be lower than the previous heating temperature. An ink discharge amount calculating means for obtaining an ink discharge amount from the print data;
When the control unit determines that the calculation result by the ink discharge amount calculation unit exceeds a preset set value, the control unit stops heating the second heating unit or sets the heating temperature to be higher than the heating temperature up to that point. 2. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is controlled to be low.   2. The ink jet recording apparatus according to claim 1, wherein the holding member is controlled to have a temperature lower than a temperature of the recording head to be measured.   The ink jet recording apparatus according to claim 1, wherein the holding member has an ink path through which ink before heating passes.   The first heating means is provided in an ink manifold that forms a common flow path of the recording head, and the holding member holds the recording head by contacting the side of the recording head closer to the nozzle surface than the ink manifold. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is configured as described above.   A plurality of the recording heads are arranged in a direction perpendicular to the conveyance direction of the recording medium so that the nozzles traverse the entire width in a direction orthogonal to the conveyance direction of the recording medium, and the holding member is the recording medium The inkjet recording apparatus according to claim 6, further comprising a plurality of openings that are held in contact with the nozzle surface side surface of each head. The inkjet recording apparatus according to claim 1, wherein the holding member is made of aluminum.

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